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Primer Chapter 3 Capturing and Editing Digital Images*

1. Output Levels jo 2 35 a OO a a IV Preview iii In each of the four outlines of the image below predict the resulting grays that are caused by the adjustment made to the image shown in the histogram on the right Specify whether it is black white or gray If it is gray give a RGB value for that gray S Levels Channel RGB Input Levels ize fico 255 Reset Auto Output Levels po p5 EE 3 Primer Chapter 3 33 0f 35 Levels Channel RGB hd Ql Input Levels p 200 255 Load Save Auto Options Output Levels po p5 EE FF Preview Levels Channel Roe t its Input Levels ize joo a Reset Load Save Auto Options Output Levels po pS D Pipe Levels Channel RoBi tts Input Levels po joo ize Reset Auto Output Levels po p5 a a lV Preview Exploring the Applications 1 Explore the selection tools of your image editing program Look up in the Help or the user manual to find out the following how to s Note down the answers Use your notes as a quick reference guide and refer to them as needed If your image editing program is Adobe Photoshop there is a worksheet on selection tools of Photoshop available at http digitalmedia wfu edu proj ect digital media curriculum development textbased index h
2. It is not only in image editing programs that you encounter histograms many digital cameras and scanners show you the histogram of the captured image This helps you see if you are getting the optimal tonal range of the captured image right away Being able to see the histogram instantaneously you can decide immediately if you need to re photograph the scene or re scan while you are on location side note An interactive simulation of photography metering with a histogram is available in the Art module This simulation illustrates the relationship between spot metering and the image s midtone j Learning Aid Understanding and Applying Histograms There are two parts of this learning aid an interactive tutorial and practice exercises The tutorial explains how to interpret an image s histogram and the tonal adjustment using histograms To test your knowledge of histograms check out the two interactive exercises in the tutorial Exercise Reading Histograms Practice relating the appearance of a histogram to the image characteristics Exercise I Improving Image Contrast and Brightness Identify the problem of the image by examining the histogram and improve it 3 7 Selection Tools in I mage Editing Programs To be able to select a specific region of the image is crucial in image editing One reason is that you often need to fine tune specific parts of the image If you apply any tonal or color changes on a selection the cha
3. One of the common tools for cleaning up these random small imperfections is a clone tool with which you can clone from one area of the image to cover the blemish This is a direct copying from one part of the image to the other Therefore the part that you are using as the source should have the same color and texture as the area of the blemish to cover Adobe Photoshop also has a tool called the Healing Brush that can match the shading and texture of the source with the area to be repaired Adjusting the overall contrast or tonal range of the image Many image editing programs let you adjust the tonal range of the image by adjusting the highlights midtones and shadows of the histogram For example in Photoshop you can choose Image gt Adjustments gt Levels and you can stretch the histogram in the Level dialog box Figure 2 As you see in Figure 3a the contrast of the resulting image is higher As seen in Figure 3b the histogram now Shows a full tonal range from white to black But the relative differences in color values among these four colors are maintained after the adjustment gt Channel RGB 7 Input Levels fo fi o0 255 Reset il Load i jji iv Save Options a ii iv A a Channel RGB gt Input Levels g 1 00 204 Se ane aa eae Output Levels jo 255 c Figure 2 a An image of medium contrast consists of four differ
4. d Figure 14 a The resulting image using a clipping group In this example the clipping group IS made up of two layers the base layer c that acts as a mask for the entire group and a layer with the image d b The layer palette of the image showing the arrangement of the layers c The base layer of the clipping group d The image in the non base layer in the clipping group It takes on the opacity of the base layer c 3 9 Printing the Final I mage In real life situations if you want to change the size of an object you would think of scaling it up or down However the intuitive sense of size that you have learned from the physical world is not always applicable to the concept of size in digital images Image editing programs let you resize or scale images by changing the pixel dimensions of the image There are also options for scaling the physical print size in inches in addition to the pixel dimensions And you can change the print size with or without changing the pixel dimensions So when are the pixel dimensions changed and when are they not What is the factor controlling this And how does it matter to the image quality As you have learned from the discussion of sampling and quantizing in digital images the amount of detail in an image is related to its original pixel dimensions which in turn is determined by the sampling rate When you increase the pixel dimensions of an image by resizing pixels are added But
5. Auto Auto E EES Options rn ne Options Output Levels 25 Output Levels o 25 A A fF a a M Preview a a V Preview a b c Figure 12 a The histogram of Figure 7 The midtone slider is moved to the lower value darker side b The histogram of the resulting image after the adjustment c The resulting image after the adjustment In this particular example the adjustment changes the darkest color of the image to the middle gray All other colors are re mapped accordingly As a result no color in the resulting image is darker than the middle gray The overall image becomes brighter In summary a histogram is a bar chart showing the relative number of pixels versus color values The color values of the x axis are usually from O to 255 For a grayscale image like the example shown here the x axis has 256 levels of possible gray tones from 0 to 255 with O being black and 255 being white The middle gray has a value of 128 For a color image you can see and adjust the levels for each of the red green and blue channels To illustrate the concept of histograms the examples here adjust the levels by moving the three triangular sliders in the histogram However many imaging editing programs such as Adobe Photoshop let you adjust the shadows highlights and midtones by directly entering numbers in addition to moving the sliders and they also offer more controls and options for tonal adjustment
6. Dimensions in inches x Print Resolution in ppi A print resolution of 150 300 ppi on an inkjet printer will give a good quality print Let s say you decide to print the image at 150 ppi The pixel dimensions of a 10 inch by 13 inch image Should be 1500x1950 pixels 10 inches x 150 ppi 1500 pixels 13 inches x 150 ppi 1950 pixels To calculate the scan resolution you use the formula above in reverse because now pixel dimensions and the source s physical dimensions are known in the equation Pixel Dimensions Scan Resolution Scan Source Dimensions in inches The scan source in this example is a 35mm negative which is about 1x1 5 inches Therefore the scan resolution can be 1500 pixels 1 inch 1500 ppi or 1950 pixels 1 5 inches 1300 ppi The discrepancy of the calculated scan resolutions arises from the fact that the source picture and the target print have different width to height ratios which is not an uncommon situation But which calculated ppi should you use No matter what resolution you choose you will need to crop part of the image the long side of the image if you want the print to be exactly 10x13 inches in this example If you are not sure whether you will crop the image to fix the exact size of 10x13 you should scan the negative at the highest ppi calculated which in this example is 1500 ppi not 1300 ppi Scanning at 1500 ppi will
7. area Square inches first Approach 1 You first make up a combination of width and height in pixels that will come up to 1 megapixel say 1000 pixels x 1000 pixels If printing at 150 ppi then you get each width and height 1000 pixels 150 pixels per inch 6 67 inches That means 6 67 inches x 6 67 inches approximately 45 Square inches per megapixel Approach 2 Find an actual example of image size of a digital camera Say a Nikon D100 can produce images of 3008 x 2000 pixels i e 6 megapixels Printing at 150 ppi you get about 20 inches x 13 3 inches 266 square inches per 6 megapixels that is still approximately 45 square inches per megapixel In the first example above we assume the width and height are the same However in the second example we start from 3008 x 2000 pixels and still come up to the same number of Square inches per megapixel As you see no matter what combination of width and height you use say even if you use 500 pixels x 2000 pixels you will still come up the same about 45 square inches per megapixel if the image is printed at the Same 150 ppi Most digital cameras produce digital images with the width to height ratio of 4 3 not 1 1 So if you want to take the 45 Square inches apart to get a sense of width and height in a print size of 4 3 instead of thinking in area then you will have about 7 6 inches x 5 7 inches print size Well roughly 8 inches x 6 inches if you round it up I
8. area to be selected The Pen tool lets you draw a vector shape outline around an area that you want to select You can combine the uses of the selection techniques to add subtract or intersect selections After you have made a Selection you can manipulate the selection You can use the Move tool to move the pixels in the selected area You can soften the hard edges of the selection by applying feathering in Photoshop Select gt Feather You can also save the selection and load the selection later This is particularly useful if the selection you have made requires a lot of steps time and labor It is a good idea to save the selection after each step in case you accidentally lose the selection and of course save the final selection so you can load the selection any time later side note In Photoshop you can add a new Selection to the existing selection by holding down the Shift key while selecting Hold down the Alt key for subtracting side note If you move the selection by using any of the selection tools instead of the Move tool you will move the floating selection only This may be useful if you want to use the shape of that selection for another area in the image 3 8 Layer Basics and Advanced Layer Techniques Layers in Photoshop are like a stack of transparencies the top layer can block out the bottom layer However layers are more than just a stack of transparencies because you can set the Opacity and blending mo
9. give you an image of pixel dimensions of 2250x1500 pixels which will be 10x15 inches if printed at 150 ppi On the other hand scanning at 1300 ppi will give you an image of pixel dimensions of 1300x1950 pixels which will give you an 8 7x13 inch print at 150 ppi print resolution Exercise Verify that an image of 1300x1950 pixels will give you an 8 7x13 inch print if it is printed at 150 ppi side not Most inkjet printers cannot print from edge to edge Depending on the printers there are certain minimal margin requirements In the example above although the image is intended to print on a 11x14 inch paper we leave half an inch of margin on all four sides of the paper Therefore the dimensions of image to be printed out are actually only 10x13 inches 3 3 2 Tonal Adjustments Although you can perform color correction and editing after the scanning process it is best to optimize the tonal range and correct any significant color problems during the scanning process Why Because once you have scanned the picture any image editing you make to the image will be based on the color information you got from the scan Editing the image later in some image editing program is not going to create any extra true color information from the scan You will be stuck with a limited amount of information to work with if you do not get enough color information or sufficient tonal range for the image during the scanning process Let s look at an exam
10. graphic program may be set up to stroke the path by default If so whenever you create a path it will be stroked with a line style If you set the stroke to none the path will still be there but you do not see it unless it is being selected and it is not printed out In most vector graphic programs one of the tools for creating paths is called the Pen tool You use the Pen tool to define points for the path The curviness of the path is controlled by the handles of those points Figure 17a and Figure 17b In both Adobe Illustrator and Macromedia Freehand simply clicking with a Pen tool places corner points which are used for creating straight segments But if you hold the mouse and drag you can extend and position the handles of the new point The handles of a point control the tangent of where the point is on the path a b c d Figure 16 a A path The corner points are highlighted in red b The path is stroked with a Solid line c The same path is stroked with a charcoal brush style d The same path is stroked with a custom brush style of a small fish a b Figure 17 a The handles of a point control the curvature shown in blue b The handles of the point are dragged to a different position Note how the curvature is changed side note A line style does not have to be a standard solid line It can for example have an appearance of natural media such as a dry paint brush like th
11. image Advertisements for scanners often cite the high resolutions that they offer However you should beware of these claims since the term resolution can be used in two different ways with regard to scanners In the scanner specification you may find two numbers for resolution one for the optical resolution and one for the enhanced or interpolated resolution The optical resolution is the hardware resolution which is dependent on the number of sensors the scanner has to capture the image information On the other hand the enhanced resolution interpolates the image using software The interpolation process increases the resolution by adding extra pixels to the ones that are actually captured by the sensors The color information of these extra pixels is based on the adjacent pixels Interpolated pixels are not truly or directly captured by the sensors Many scanners now have unlimited software enhanced resolution Scanner resolution is usually reported in dpi dots per inch To understand what dpi is and what the practical meaning of this number is let s consider the general mechanism of a scanner A flatbed scanner has a moving scan head which contains an array of light sensors The scan head moves across the scanner bed during scanning Its movement is controlled by a stepper motor So how is a picture analog information captured with only a row of light sensors To answer this question we return to the concept of sampling and samplin
12. the editing process Why To understand why the sharpening step should be the last step in the retouching process you need to understand how sharpening in digital imaging works Here is how sharpening digital images works in general The sharpening algorithm finds edges which are defined by significant color changes Sharpening creates the illusion of sharpness by creating a lighter line and a darker line on each side of the edge Thus applying sharpening will alter the colors in the image especially where there are color changes that is at the edges Because the edges are detected by the extent of color changes all the color and tonal corrections or adjustments have to be made prior to the sharpening Image resizing has to be done before the sharpening because resizing often softens the image focus Sharpening should be the very last step of your image editing project One exception is for example when you need to add elements with crisp clean edges such as a border in the image you should do so after the sharpening Why If you apply sharpening to a border will the edge of the border remain clean and Sharp in the final image The sharpening tool in Photoshop is under Filters menu gt Sharpen There are four Sharpening tools under Sharpen Sharpen Sharpen Edges Sharpen More and Unsharp Mask Generally for professional image editing Unsharp Mask is the recommended sharpening tool because it gives you more control on the Sharpening
13. the image editing program If you stretch the histogram before the cropping what will be the tonal range you are going to maximize before cropping You will be including a lot of unwanted color in the histogram This affects how you stretch the histogram 3 What if you do the dodging and burning before removing the color casts 3 6 Color and Tonal Adjustments There are a variety of color and tonal adjustment tools available in image editing programs Depending on the program the controls available in the tools and the interface may vary However generally the tools work by mapping the existing color or tonal values of the pixels to new ones The common tools include adjusting the histogram color balance color curves and hue saturation Different tools use different graphical representations of the color or tonal values of the pixels in the image and thus offer different types of control Adjusting the histogram lets you define and re map the shadows midtones and highlights using sliders The color balance tool works by letting you offset one color by moving the corresponding slider towards its complementary color This is useful for removing color casts of images This tool is discussed in the previous section on removing color casts The curve tool lets you remap the color and tonal range by altering a curve The horizontal axis of the graph used in the curve tool represents the original color values of the pixels input levels Its vertic
14. threshold setting between 5 and 10 would be a good starting point for you to experiment with side note The word unsharp in the unsharp mask sounds counterintuitive to the sharpening function of the tool However unsharp mask is a tradition film technique for sharpening image by using a Slightly out of focus thus unsharp duplicate negative as a mask The original negative is Sandwiched with this duplicate an unsharp mask during printing This will make the lighter side of the edges lighter and the darker side of the edge darker thereby making the image look sharper Heightening the contrast between the lighter and darker lines around edges is basically the same technique of unsharp mask in digital imaging to create a sharper look in an image You should try to keep the order of the steps above Performing these steps out of order or jumping back and forth among steps may cause unwanted effects on the image To understand why the order is important in the image retouching let s think about the following questions 1 As mentioned above in the scanning process it is suggested that you turn off the Sharpening during scanning unless you are not doing any image retouching on the image So now again in the image retouching process you save the sharpening to the last step Why should we make the sharpening as the final step in the process 2 Why should cropping be the first step before you do anything to the image in
15. what color information is contained in these new pixels The color information of these new pixels is generated by interpolating the color information of the existing pixels Therefore although the pixel dimensions of the image increase such resizing J N N O UJ Ul Primer Chapter 3 does not increase the detail of the image because it is not adding new pixel information In fact the resulting image often appears blurry When you shrink an image by reducing its pixel dimensions some pixels have to be removed you lose information To produce high quality images it is best not to scale the pixel dimensions of the image Scaling the pixel dimensions is not the key to controlling the print size But what is the best method to control the print size It is important to understand that both the pixel dimensions of an image and the image resolution ppi affect the image s print size This relationship is discussed in the previous section on digital photography But this relationship applies to all digital images not only images that are obtained by digital photography The following equation quantifies the relationship of print size pixel dimensions and the image s print resolution Print Dimensions in inches Pixel Dimensions Print Resolution in ppi Note that this equation involves three variables print dimensions pixel dimensions and print resolution To understand the implication of this equation and the relationships am
16. Primer Chapter 3 Capturing and Editing Digital I mages Revision 2005 06 16 Table of Contents SAO ALROGUCTION orreen irn e E E E E N a a aa a a 2 JA o CaNNERS ie a aa a E a eee iat yen 2 3 3 Capturing Digital Images by Scanning ss sssssssrrerssrrrrerrsrrrrerenrrsrrrrrrrerrerrrrerrerrrreras 3 3 3 1 Determining SCANNING RESOIULION rreri a E a e a 3 KIA TONAL AdU SENEN mane ir ee E EE E EE ere E E EE dies 5 3 4 Capturing Digital Images by Digital Photography ssssssrssrsrssrrererrnrrsrrerrrrsresrrrrerrerree 6 3 Al MEGA PIXE S hirsini aE EE A E A E E A A EA T 7 3 4 2 Digital Came aS asrorini Ene n NEPA A DEA ANE AAN Ea E AA a a aE a ee 9 ZS Digital Mage E dItIN I ee a a a aa a ae 10 3 6 Color and Tona AG USEMOENUS sarrar onea E E O E EA 15 3 6 1 Understanding and Reading Histograms sssssssrsersrssrrsrerrnrrsrrerrrrsrrsrrrrerrerree 15 3 6 2 Applying Histograms to Adjustment of Brightness and Contrast ccceeeeees 16 3 7 Selection Tools in Image Editing PrOgGrAMsS cccccceeeee sees eeeeeeee eee ee eee eeeeeeeeeeeeeeeeanaas 19 3 8 Layer Basics and Advanced Layer TeEChNnIiQues cccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeenanananas 20 579 Printing tie Rita Mage reene a a E iotnn ee E eaten 22 3 10 Optimizing the Final Image Tor Web veicisesesaries casters iansess vo eirawveis bias Sevan ts inawetcineeden 24 3 11 Working with Vector Graphics Programs cccccccceeeeeee ee ee cece cece eee eeeeee
17. active demonstration on optical color mixing Worksheet Image PPI vs Printer DPI To learn the difference between the printer DPI and image PPI by 1 Experimenting with how the image PPI affects the output dimension of the image 2 Experimenting with how the printer DPI affects the printing quality of the image Worksheet J PEG vs GIF vs PNG 1 To learn to optimize files in JPEG GIF and PNG format and adjust the compression settings to achieve the balance between the file size and overall image quality 2 To learn the type of images that each of these file formats is most effective at compressing Review Questions l 2 3 10 What are the different types of scanners What is the method of acquiring digital images besides a scanner Multiple choice Resampling an image is often referred to as A rotating B scaling C translating D repositioning Why does scaling an image usually deteriorate the image quality somewhat In no more than three sentences explain in terms of what happens to the pixels in scaling up and scaling down Verify that an image of 1300x1950 pixels will give you an 8 7x13 inch print if it is printed at 150 ppi Say that you scan a 3 inch by 5 inch photograph in at a resolution of 300 dpi What are the pixel dimensions of the scanned image pixels x ____ pixels ii What will the physical dimensions of the image be if you print it at 300 ppi without changing the image s pixel di
18. age Oe E The two basic and essential tools in digital image editing are selection and layers Selection tools allow you to limited the image content of the selection A variety of selection tools are available for different selection tasks Layers allow you to organize components of an image rearrange their stacking order set opacity and blending options The physical print size of an image depends on two factors its pixel dimension and the print resolution Print Dimensions in inches Pixel Dimensions Print Resolution in ppi You can adjust the print resolution to suit the print dimension Be careful not to unawarely resize the image s pixel dimension If the image is intended for Web then the image needs to be save in J PEG GIF or PNG format Each format has its characteristics that work best for different types of images For examples the J PEG format works best with continuous tone images with a broad color range and subtle color and brightness variations such as photographs and images with gradients GIF is most effective for images with solid colors such as illustrations logos and line art PNG has two formats one works well with continuous tone and the other solid colors But an image saved in PNG 24 format may result in a larger file than if it is saved and compressed in J PEG format Terms flatbed scanner optical resolution dpi megapixel tonal adjustment D SLR histogram color cast unsharpen mask S
19. al axis represents the new color values after adjustment output levels The Hue Saturation tool has three basic controls hue saturation and lightness Histograms and their application to color and tonal adjustment are discussed in the following sections j Learning Aid Understanding and Applying Curves For Color Adjustments An interactive tutorial and exercise to help you understand curves for image adjustment by using examples and practice exercises 3 6 1 Understanding and Reading Histograms side note The entire sections of 3 6 1 Understanding and Reading Histograms and 3 6 2 Applying Histograms to Adjustment of Brightness and Contrast are available as a standalone online interactive tutorial at http digitalmedia wfu edu project digital media curriculum development textbased index html You can read through the text while experimenting interactively in the tutorial There are two practice exercise sections at the end of the tutorial to test your knowledge of applying histograms to image editing What does a histogram of an image represent A histogram is a bar chart that shows the relative number of pixels plotted against the color value Figure 6 shows an example of a grayscale image and its histogram In this example the x axis of the histogram is the gray level with the darkest value on the left and the y axis is the relative number of pixels in the image that have the corresponding shade of gray The histo
20. are and preview the scanning The scanner will scan the whole scanning area e Select the region that you want if your document is smaller than the available scanning area e Choose the scanning options if available such as color mode resolution sharpening level histogram and brightness contrast adjustments We will discuss these options in detail later in this chapter e Finalize the scanning and save the file You may have many different file formats available 2 Sheet fed scanners Many smaller portable scanners are sheet fed scanners in which the document moves through the fixed scan head Because of the feeding mechanism this type of scanner is not able to scan thick objects such as a page in a book Sheet bed scanners are generally designed to scan no larger than letter size paper 3 Handheld scanners These scanners are also portable However unlike the sheet fed they are not limited to single pieces of paper The basic mechanism of handheld scanners is very similar to that of flatoeds except that the handhelds rely on the user to move the scan head The scanning width of each pass is limited by the width of the handheld scanner which usually is less than the width of a letter size paper For some models of the handheld scanners the Image quality may rely on the user s steady movement of the handheld In general handheld scanners do not provide very good image quality but they offer the most convenient and fastest way of captur
21. command It is higher contrast than Figure 3a b The histogram of this adjusted image Note the relative tonal differences among the four colors are altered after the adjustment side note A histogram is basically a graphic showing the relative number of pixels at each color intensity level Histogram stretching concepts and techniques are discussed later in this chapter 4 Removing color casts An image sometimes contains color casts the image appears tinted Color casts may be introduced during scanning or may have existed in the original source picture Many digital cameras have a built in color correction function However sometimes it may not color correct the way you want or there may still be a slight unwanted color cast Image editing programs provide color correction tools For example in Photoshop 7 a new feature called Auto Color can automatically detect the imbalanced colors and correct them It is under Image gt Adjustments One way to offset the color cast without using the auto function is to adjust the color balance To use this tool you need to determine the imbalanced colors and then balance the colors by offsetting the color casts For example in Photoshop there are three sliders in the Color Balance dialog box Figure 5 each labeled with a color at each end The colors in each pair are complementary colors cyan red magenta green yellow blue If your image has for example a red cast you Should drag th
22. culate the dpi based on the largest size If you scan at a higher resolution than you need you can always resize the scan down to a make a smaller print However if the scan resolution is not set high enough to produce the required pixel dimensions enlarging the image later will only add pixels by interpolation Using interpolation you do not get additional true color information You can only get true color information from the original scan source If you plan to print out the scan you will need to know the resolution requirements of the printing device in addition to the print size in inches You should always think of the scan in terms of the pixel dimensions not the resolution ppi or the physical print size inches J ust like any digital images scanned images do not possess any inherent physical dimensions The physical dimensions materialize when the image is printed out defined by both the image s pixel dimensions and the printing ppi pixels per inch side note The inch in the pixel per inch ppi and dots per inch dpi is in linear inches Let s see the math for the scanning and the determining the print size step by step o Step 1 Determine the total pixels Scanning a photograph of 4x6 inches at 600 dpi dots per inch will give a scan of 2400x3600 pixels o Step 2 Determine the physical print size If this image is printed out on a printer at 600 ppi the same resolution as scanned then the print will be the same as
23. d understand how to calculate megapixels for your needs side note Refer to primer Chapter 2 on sampling resolution and details side note megapixels effective pixels vs total pixel 3 4 2 Digital Cameras There are several types of digital cameras Like traditional film cameras digital cameras can be point and shoot digital cameras or digital single lens reflex D SLR Most D SLR cameras are interchangeable lens D SLR There are now digital camera backs available for selected models of medium format cameras Changing from film to digital for these medium format cameras is just a matter of changing the camera back you do not need to replace the whole camera body Although this sounds like an economical solution the digital back is very expensive generally over 10 000 But the digital back supports higher resolution for example 16 megapixels side note Single lens Reflex SLR A SLR camera reflects the image optically onto the focusing screen or viewfinder by using the light coming through the lens This means SLR cameras allow you to see the image area accurately from the viewfinder However many non SLR digital cameras now have an LCD for previewing side note A interchangeable lens is a lens that can be detached from the camera body and replaced with a different one Cameras with interchangeable lenses allow you to use a wide variety of lenses from telephoto and wide angle to close up lenses Lenses are sold Se
24. de of each layer You can rearrange the stacking order of the layers by dragging a layer in the layer palette up or down Many image editing programs support layers The following discussion is based on Adobe Photoshop but should be applicable to other image editing programs that support those features discussed below In Photoshop there is a special layer called Background which is listed in italics in the layer palette This Background layer is not a transparent layer When you use an eraser tool to erase the image content on this layer you reveal the color of the current color in the background color chip a regular layer will reveal transparency This Background layer cannot be rearranged it only stays at the bottom of the stack You can convert the Background layer to a regular standard layer by for example double clicking on the Background layer You can create new layers delete layers rename layers control the visibility of each layer and copy layers from one file to another You can also apply a layer style such as drop shadow and bevel to a layer You can link multiple layers together so that you can move or scale multiple layers simultaneously Adjustment layers are for applying image adjustments such as Levels and Color Balance to a layer without baking the effect on that layer Instead an image adjustment layer is a separate layer by itself It applies the adjustments to all the layers below it unless you create a clipping g
25. e are five bars in the histogram each represents the number of pixels of each gray in the image For each of the bars or lines in the histogram above identify and label its corresponding gray color in the image True False The optimization of tonal adjustment at the time of capturing images scanning or digital photography does not matter because you can always optimize the tonal range of the image to any extent afterwards in Photoshop Given below are the general steps of image retouching of a scanned image i Order the steps by labeling 1 to 6 _ Crop and straighten the image Sharpen the image Remove color casts oe Fine tune specific parts of the image using tools such as dodge and burn saturation adjustments Remove dirt and dust Adjust the overall contrast or tonal range of the image ii Explain your choice of the first step iii Explain your choice of the last step don t worry about calculating the optimal scanning dpi just always scan images at the highest scanner resolution dpi that the scanner can scan at What are the two potential problems for the approach above Explain in terms of the file size and image quality Say you want to scan part of a photograph to use in a digital collage The part of the picture you want to scan is 2x2 inches on the photograph You want this scanned piece to appear as 6x6 inches in the final collage that will be printed out at 300 ppi If you scan the picture at a resol
26. e one Shown in Figure 16c It can also be a custom defined style like the fish in Figure 16d There are also tools to create common shapes such as ellipses rectangles polygon stars and spirals Some programs also have a freeform drawing tool with which you can draw a freeform path with a continuous stroke without manually defining the points However a freeform path is still made up of points A path can be open or closed A closed path whether stroked or not can be filled with color patterns gradients other vector graphics or even bitmap images There are two basic selection tools in a vector graphic program one that lets you select the whole object and another that lets you select the points and their handles The former is called a Pointer in Freehand and a Selection Tool in Illustrator The latter tool is called a Subselect tool in Freehand and a Direct Selection Tool in illustrator Using the Pointer or the Selection tool you can select the whole object move rotate or scale it as a whole With the Subselect or Direct Selection tool you can alter the shape of an object by moving the points or their handles Like many image editing programs many vector graphic programs also support layers which help you organize and manage the content For example you can toggle the visibility and the locking of a layer In addition effects and filters are available in vector graphics programs Some of these effects soften the vector graphic t
27. e slider away from the red towards the cyan end to offset the red cast You can choose whether the color correction you make is applied to the highlights midtones or shadows of the image Color Balance oo U x m Color Balance l Color Levels jo lo lo Cancel Cyan es Red Z Preview Magenta eee Green Yellow ee Blue Tone Balance C Shadows Midtones Highlights MV Preserve Luminosity Figure 5 An example of Color Balance dialog box Fine tuning specific parts of the image Note that the editing steps above are applied to the whole image However certain parts of the image may need specific enhancements You can select those parts using selection tools and apply the adjustment There are also other tools for fine tuning specific parts of the image without having to make a Selection first Tools such as the dodge tool to bring out highlights the burn tool to bring out Shadows and the sponge tool to saturate or desaturate colors work like a paint brush except that you paint to apply the adjustment instead of a color Sharpening the image Scanned images usually look a little soft focused Scaling an image will also make the image soft focused Even if your image is a straight digital photograph from a digital camera it is a good idea to experiment with sharpening at the end of the image retouching to see if it improves the image s overall clarity In any case you Should wait to do the sharpening until the final step in
28. ears to be very tiny dots of ink These ink dots of different colors but a limited number of colors produce the required color by optical mixing The color of a single pixel of an image is represented by a group of printer dots Do not confuse the image print resolution ppi with the printer resolution dpi As you see in the scenario 2 above the print resolution ppi affects the print size of an image However the printer resolution dpi does not affect the print size of the image It affects the quality of the print Generally the higher the dpi the smoother the colors appear on the print However higher dpi uses more ink and requires longer time to complete the print job j Learning Aid Optical Color Mixing in Pointillism Dithering and Inkjet Printing An interactive demonstration on optical color mixing j Learning Aid Worksheet I mage PPI vs Printer DPI To learn the difference between the printer DPI and image PPI by 1 Experimenting with how the image PPI affects the output dimensions of the image 2 Experimenting with how the printer DPI affects the printing quality of the image 3 10 Optimizing the Final I mage for Web The three image file formats currently supported by Web browsers are JPEG GIF and PNG Each employs different compression algorithms to compress the file size Because of the different algorithms each file type works best with a different type of image The J PEG format works best with continuous t
29. eeeeeeeeeeenanananas 26 SAZ SUNA Y asecancuen te E a E cute on coset aed anata wanna enenemeen et ecanareanne teenie cane sose eke 2 TEMS taeda ees a oOo eae Slee cau rial ta ae ONL Oh ie oe fila A a ae hea 29 A List of Multimedia Learning Aids For This Chapter ccccccccccceeceeceeeeeeeeeeeeeeeeeeeeeeeeeeenees 29 ROVIN OUCSTIOMN S wedaaiuntaceorna golden cece usu uetecede ats vonaeaceesaee ost teeny bata eat a 31 Exploring ING Appaiono AA yee aa a a a ti aon eee boone tien 34 Key Concepts o Working with scanners and scanning o Digital photography o Common tools in digital image editing programs selection layer color and tonal adjustment fine tuning specific parts sharpening Working with vector graphics programs Image PPI vs Printer DPI Printing Images for Web O O O General Learning Objectives At the end of this chapter you should be able to demonstrate that you o know common types of scanners know common tools of image editing and vector graphics programs know common file types for Web images comprehend scanning and printing resolution comprehend image editing process and tools apply scanning and printing resolution apply file types for Web images O O O O O This material is based on work supported by the National Science Foundation under Grant No DUE 0127280 and was written by Dr Yue Ling Wong ylwong wfu edu Department of Computer Science and Department of Art Wake Forest University 3 1 Introd
30. ent colors Three of the colors have the same number of pixels The other has three times the number of pixels No white or black color is in this image Note the labels in red are not part of the image The red labels are to show you the relationship between the color in the image and its corresponding bar in the histogram b The histogram of this image c The histogram can be stretched by moving the highlight and shadow sliders to the edges of the histogram a M Chamel RGB Input Levels fo fi o0 255 Levels Output Levels fo 255 b Ix Cancel Load Save Auto Options Jilli Figure 3 a The same 4 color image after stretching the histogram It now is higher contrast than before stretching Figure 2a b The histogram of this adjusted image Although there is a Brightness Contrast command for image adjustments stretching the histogram is the recommended tool over the simple brightness contrast adjustment This is because the relative color information of each pixel in the image remains the same when you stretch a histogram However the brightness contrast adjustments will alter these relationships Figure 4b vs Figure 3b xi M Chamel RGB gt Input Levels p joo p55 EA Auto Output Levels p p5 IV Preview a b Figure 4 a The resulting 4 color image after adjustment using the Brightness Contrast
31. f the image is in 3 2 ratio then it will be about 8 2 inches x 5 4 inches Note that these numbers are based on printing at 150 ppi Let s emphasize again that the number of megapixels is a product of the pixel dimensions of width and height But the Same number of megapixels can be made up with many possible combinations of width and height For example as you see above both 7 6 inches x 5 7 inches and 8 2 inches x 5 4 inches can be from a 1 megapixel image depending on the image s width to height ratio If you are looking for a digital camera that can produce images that can be printed 8 2 inches x 5 4 inches at 150 ppi you are looking for a 1 megapixel camera However this is based on a 3 2 ratio Buta l megapixel camera that can only produce images in 4 3 ratio will not meet your requirement Questions 1 The above example calculations are based on 150 ppi printing What is the print size per megapixel if the image is printed at 300 ppi 2 From the examples above we have about 7 6 inches x 5 7 inches print size per megapixel for 150 ppi printing and if the image is in 4 3 ratio What will be the print size for 2 megapixels with all the same conditions Does the calculation involve multiplying both the 7 6 inches and 5 7 Inches by 2 Why or why not If not then how do you calculate the answer j Learning Aid Worksheet Making Sense Out Of Megapixel This worksheet guides you to look up specifications of digital cameras an
32. g rate The number of sensors available in this single row corresponds to the sampling rate in the x direction The discrete stepwise movement of the scan head is related to the sampling rate in the y direction The sensor corresponds to the dot in the unit dpi Each sample results in a pixel of the scanned image For example many flatbed scanners now have an optical resolution of at least 2400 dpi on each direction If you scan a 1 inch by 1 inch picture at this scanning resolution you will get an image of 2400 x 2400 pixels A detailed discussion of how to determine optimal scanning resolution is in the following section 3 3 1 Determining Scanning Resolution Before making a scan you must consider the requirements of the final output You should have answers to the following questions before scanning What will the scanned image be used for Is the scanned image intended for the Web or printing If it is intended for printing then what will the physical dimensions of the print be and what are the requirements of the printing device If the final image is for the Web then what are the required pixel dimensions of the image You should scan at a high enough resolution in dots per inch dpi to generate enough pixels in each dimension in order to produce an image at the expected print size If you are not sure about the exact final print size at the time of scanning but have only a rough estimate of the print size then you cal
33. gram in Figure 6b does not look like the kind of bar chart you may have seen in business presentations This is because this picture has a full range of gray levels and the bars are packed next to each other making the histogram look like a mountain range rather than a statistical bar chart Figure 6 a A grayscale image b The histogram of the grayscale image To learn how to read a histogram let s first look at a very simple image that has only five different gray colors The image shown in Figure 7a has five main different gray colors Each gray takes up a different amount of space in the image The background color is the lightest gray in this image and it occupies the largest area Exercise Which gray has the second greatest number of pixels i e which solid gray area is the second biggest ra a A Em Ja c x ya u W g z a gt a b Figure 7 a A simple grayscale image consisting of mainly five different gray colors and its histogram on the right b The histogram for the simple grayscale image above Exercise For each of the bars or lines in the histogram above identify and label its corresponding gray color in the image 3 6 2 Applying Histograms to Adjustment of Brightness and Contrast Many image editing programs let you adjust image brightness and contrast with the image s histogram For example this tool is called Adjust Levels in Adobe Photoshop When you choose to adjust Levels a dialog b
34. hadow midtone and highlight color balance color curves hue saturation brightness and saturation brightness and contrast lasso marquee layer background layer clipping group layer mask JPEG GIF PNG path point stroke and fill subselection A List of Multimedia Learning Aids For This Chapter ji Tonal Adjustments During Scanning An interactive tutorial that explains and demonstrates why tonal optimization is necessary during scanning Worksheet Making Sense Out Of Megapixel This worksheet guides you to look up specifications of digital cameras and understand how to calculate megapixels for your needs Understanding and Applying Curves For Color Adjustments An interactive tutorial and exercise to help you understand curves for image adjustment by using examples and practice exercises ji Understanding and Applying Histograms There are two parts of this learning aid an interactive tutorial and practice exercises The tutorial explains how to interpret an image s histogram and the tonal adjustment using histograms To test your knowledge of histograms check out the two interactive exercises Exercise Reading Histograms Practice relating the appearance of a histogram to the image characteristics Exercise I Improving Image Contrast and Brightness Identify the problem of the image by examining the histogram and improve it Optical Color Mixing in Pointillism Dithering and Inkjet Printing An inter
35. in PNG 24 format may result in a larger file than if it is saved and compressed in J PEG format Learning Aid Worksheet J PEG vs GIF vs PNG 1 To learn to optimize files in JPEG GIF and PNG format and adjust the compression settings to achieve the balance between the file size and overall image quality 2 To learn the type of images that each of these file format is most effective at compressing Primer Chapter 3 25 of 35 3 11 Working with Vector Graphics Programs Vector graphic programs work differently from image editing or photographic editing programs because the basic unit they are dealing with are different Image editing programs such as Adobe Photoshop are pixel based Images are represented with pixels The amount of image detail depends on the pixel dimensions of the image A bitmap image can be edited pixel by pixel The physical dimensions of the print size of a bitmap image depend on its pixel dimensions and its image resolution in ppi On the other hand a vector graphic is not made up of pixels Vector graphic programs such as Macromedia Freehand Flash and Adobe Illustrator deal with objects or shapes made up with paths points strokes and fills A path is a mathematical description of an abstract line or curve It does not have a physical appearance line width or color until the path is stroked with a specified line style width and color in the vector graphic program Figure 16a and Figure 16b The vector
36. included non picture areas in the scan This is OK You can straighten and crop the scanned image in the image editing program For example in Photoshop you can use the Crop tool on the tool palette to achieve the cropping and straightening in one step Dirt and dust are common imperfections in a scanned image These imperfections do not only happen to digital images Prints from negatives in a traditional darkroom often need spot toning to repair damage from dust and scratches If the image is obtained by scanning you will need to remove dust scratches and blemishes resulting from the scanning process One of the common tools for cleaning up these random small imperfections is a clone tool with which you can clone from one area of the image to cover the blemish This is a direct copying from one part of the image to the other Therefore the part that you are using as the source should have the same color and texture as the area of the blemish to cover Adobe Photoshop also has a tool called the Healing Brush that can match the shading and texture of the source with the area to be repaired Dirt and dust are common imperfections in a scanned image These imperfections do not only happen to digital images Prints from negatives in a traditional darkroom often need spot toning to repair damage from dust and scratches If the image is obtained by scanning you will need to remove dust scratches and blemishes resulting from the scanning process
37. ing documents They are most useful for capturing text 4 Drum scanners Drum scanners are capable of very high resolution and can handle larger documents They are often used in the publishing industry where very high resolution images are required or for scanning large documents such as blueprints Scanners can handle not only paper documents but also film negatives and slides For certain models of flatbed scanners you can scan negatives or slides with a negative slide adaptor TWAIN TWAIN is a standard or specification for the interface between image software and image capturing devices such as scanners and digital cameras Technically TWAIN refers to an image capture API Application Programming Interface for Microsoft Windows and Apple Macintosh operating systems It is not a driver of any image capturing devices The term TWAIN is not an acronym The word was taken from the sentence and never the twain shall meet in Kipling s The Ballad of East and West a fitting description of the challenges of connecting scanners to desktop computers in the early days of this technology The whole word is capitalized to make it distinctive as a term For more information check out http www twain org 3 3 Capturing Digital Images by Scanning One of the factors that affect the amount of detail in a scanned image is scanning resolution Generally the higher the resolution at which you scan the image the more detail you can get in the
38. ital I mages by Digital Photography In traditional film photography the image on a negative is made up of microscopic silver grains The larger the negative the more information of the scene is imprinted on the negative and therefore more information can be printed on paper A larger negative takes less magnification to make a big print than a smaller one This means that for prints of the same size you get a sharper print from a larger negative than from a smaller one Digital cameras on the other hand use light sensors as the digital film The light hits the sensor and triggers electrical signals based on the light intensity Such electrical signals are then converted into digital data and stored on the camera s storing device Nowadays the sensor that a digital camera uses is either a CCD charge coupled device or a CMOS complementary metal oxide semiconductor The size of the sensor and the number of light sensing sites determine the maximum resolution of the digital camera side note Digital Film Some may consider the storage media used in the digital camera as the digital film In traditional film photography generally the smaller the grain size the higher the definition and detail of the image you can obtain In digital images however a pixel is the basic unit that makes up the image Therefore when you look at the specifications of digital cameras you often see them specified in number of pixels Digital cameras are
39. l image still relies on traditional imaging basics not just the how to of using the digital imaging program Keep in mind that digital imaging tools are only tools Like in woodworking knowing how to use power tools does not guarantee production of fine furniture What can digital imaging tools do Most of those tools are based on traditional darkroom techniques If you have experience in darkroom techniques you may already be familiar with the tasks that these tools are intended for The common tools available in most digital image editing programs allow you to perform image retouching such as tonal adjustment color correction and enhancement and sharpening of the image Many programs also have layers that allow you to composite and blend images in more creative ways beyond basic retouching You can retouch digital images in many different ways The general steps are similar to those for traditional darkroom printing Generally you need to color correct the images especially in the case of scanned images You can correct the color and tonal range problems during the scanning process and or after the scanning Many image editing programs such as Adobe Photoshop provide a comprehensive set of tools for color correction and image editing The general steps and tools for image retouching are the following 1 Cropping and straightening the image When you scan a picture the picture may be placed tilted on the scanner glass Also you may have
40. lm cameras with all other conditions being equal the image quality depends on the quality of the lens optics the quality of the film and the film grain size Similarly the image quality for digital cameras depends on the optics and the camera electronics It also depends on the camera s image processing software how it processes the electronic data captured from the CCD into an RGB value for each pixel of the resulting image file Does a digital camera with a higher megapixel rating give bigger prints The answer to this question can be yes and it depends As you see in Primer Chapter 2 a pixel is a point Sample it does not really possess any physical dimensions So the pixel dimensions of a digital image alone do not provide any information about physical dimensions As you see in the previous section on scanning Pixel Dimensions Print Dimensions in inches x Print Resolution in ppi That is Print Dimensions in inches Pixel Dimensions Print Resolution in ppi The print size of a digital image depends on both the total number of pixels and the image s print resolution in ppi pixel per inch A higher megapixel rating only tells you that the image has larger pixel dimensions only one of the two variables in the equations So if the ppi is kept the same then yes the image with more pixels will be printed bigger in size Print Size Per Megapixel Megapixels is one of those loaded terms in digital imaging The
41. mensions ___ inch xX inch iii What will the physical dimensions of the image be if you print it at 600 ppi without changing the image s pixel dimensions ___ inch xX inch iv What will the physical dimensions of the image be if you print it at 150 ppi without changing the image s pixel dimensions __ inch xX inch v True or False You gain image detail and quality if you print the image at 600 ppi as noted above vi True or False You lose image detail and quality if you print the image at 150 ppi as noted above True False It doesn t matter what the original resolution of a scanned picture is because can always blow it up in an image editing program later by resizing it to print at any high resolution and in whatever size without loss of image quality True False When a digital image is printed each image pixel is represented by one printer ink dot Multiple choice The per inch in the units dots per inch and pixel per inch are in A Square inches B linear inches Figure 18 below shows a simple grayscale image consisting of five different colors and along with the image s histogram 11 12 13 14 of pixels relative number a b Figure 18 a A simple grayscale image consisting of mainly five different gray colors b The image s histogram Which gray has the greatest number of pixels i e which solid gray area is the biggest ii As you may have expected ther
42. multaneously How do you rearrange the order of layers How does the stacking order of the layers affect the image Does your program support layer masks If so how do layer masks work Does your program support clipping groups If so how do clipping groups work Does your program support adjustment layers If so how do layer adjustments work 3 Explore your vector graphic program Look up in the Help or the user manual to find out the information for the following Note down the answers Use your notes as a quick reference guide and refer to them as needed O O O O O O O Find out the tools for creating paths o Pen tool o Freeform drawing tool How do you add and delete points of a path How do you alter the curvature of a path How do you stroke a path How do you fill a shape Find out the selection tools for selecting the whole objects and for selecting the points and handles How do you create layers to organize the objects Find out the effects and filters available Experiment with at least two Practice creating paths in a vector graphic program If you are new to the vector graphic program try to create simple paths like the following open paths closed paths corner points and smooth points Also practice editing the paths by moving the points and their handles If you are getting familiar with the program try creating more complex vector shapes v AnA
43. ng to do any retouching of the scan at all you should turn off auto sharpening which is enabled by default in many scanner programs If the scanning software lets you look at the histogram of the scan preview make sure you are assigning the appropriate tonal range to the scan It is best to optimize the tonal range and correct any significant color problems during the scanning process It is because once you have scanned the picture any image editing you make to the image will be based on the color information you got from the scan The quality of your final image depends on the quality of the scan Insufficient tonal range and color information of an original scan cannot be fixed with later editing Megapixel is commonly used to describe the resolution capability of a digital camera A megapixel refers to one million pixels With the same printing resolution an image with higher megapixel can be printed larger size compared to the one with lower megapixel But higher megapixel does not necessarily offer higher image quality other factors such as the optics of the camera and how the image data from the CCD Is processed also determine the quality of digital photographs There are several steps in image retouching in general The order of these steps are important 1 Crop and straighten the image Remove dirt and dust Adjust the overall contrast or tonal range of the image Remove color cast Fine tune specific parts of the image Sharpen the im
44. nges only affect the selected area the non selected area is then protected from the alteration In addition when you composite or collage several images together you often need to be able to extract only specific parts of the image To do so you define the specific parts with selection There are a variety of selection tools available in image editing programs However instead of trying to list and explain these tools one by one we will categorize these tools in terms of the way they are designed to work so that you have an overview of the general techniques o In pre defined shapes The Marquee tools provide pre defined shapes such as rectangular and elliptical o Lasso The Lasso tool and Polygonal tool let you create a freehand outline around an area you want to select The Magnetic Lasso tool is useful for selecting an area that has well defined edges because it traces edges o By color With the Magic Wand tool you can specify the tolerance or the similarity of the color in the surrounding pixels to be included in the selection You can also use an Eye Dropper tool to pick out a color in the Foreground color chip and then choose Select gt Color Range o By painting with a brush to select or deselect a specific area Editing in Quick Mask mode allows you to use the paintbrush to paint in black to deselect white to select and grays to create semi transparent areas feathering and anti aliasing o By drawing an outline around the
45. number of megapixels has been used to label the feature of a digital camera However what exactly are the implications of the term megapixels Many consumers are concerned more about the actual print size of an image rather than the number of pixels Is it possible to correlate the print size with megapixels The calculation of print size based on megapixels requires a deeper understanding of how the number of megapixels is calcuated And there are many ways to approach the answer So let s soend some time to analyze the question and find the solution As discussed above the physical size of the printed digital image depends on both its pixel dimensions and the ppi setting However given a ppi setting it is possible to estimate the print size per megapixel Making the relationship between print size and megapixels more complicated is the fact that megapixels represent an area that is the product of the width in pixels by the height in pixels If you want to know the print size in width by height you need to know the pixel dimensions of both the width and the height J ust the number of megapixels does not give you this information It is because the same area size can be made up with many possible combinations of width and height For 1 megapixel the dimensions can be 1000 x 1000 pixels 500 x 2000 pixels or approximately 1155 x 866 pixels etc Therefore to correlate the print size to megapixels you Should think in
46. o make them look more like bitmap images 3 12 Summary In general there are two ways to acquire digital images scanning a pciture and digital photography Generally there are four common types of scanners classified in terms of their mechanisms flatbed sheet fed handheld and drum scanners The flatbed scanner is the most commonly used and versatile desktop solution in digital media Drum scanners are capable of very high resolution and can handle larger documents The scanner s optical resolution is its hardware resolution which is dependent on the number of sensors the scanner has to capture the image information On the other hand the enhanced resolution interpolates the image using software Scanner resolution is usually reported in dpi dots per inch To determine the scanning resolution dpi you need to first determine the final image s pixel dimension How you determine the final image s pixel dimension depends on what the final image is intended for Web or print If it is intended for print then the pixel dimension of the image can be calculated by multiplying the image s intended physical dimension and its intended printing resolution If the final image is for Web then its pixel dimension is estimated relative to the resolution of the intended display device e g monitor If you are scanning a picture make sure the scan resolution and color mode are appropriate for the way you will use the image Unless you are not goi
47. often advertised using the number of megapixel as the headline Generally within the same time period the higher the number of megapixels the more expensive the cameras are But what is the practical meaning of the number of megapixels besides just being an indicator of the cost If you are going to pay more for more megapixels you should know why and what impact megapixels have on the image quality of your creative photography work 3 4 1 Megapixels The total number of pixels in a digital image can be calculated by multiplying the pixel dimension of the width by the pixel dimension of the height For example an image of 1600 x 1200 pixels has a total number of pixels of 1600 x 1200 pixels 1 920 000 pixels One megapixel equals 1 000 000 pixels So in the example above the camera can be said to have 1 92 megapixels The number tends to be rounded up in advertisements so this camera would be advertised as offering 2 megapixels The higher the total number of pixels the higher the resolution of the image But how exactly does the total number of pixels reported in megapixels or not affect an image Does a digital camera with more megapixels necessarily offer better image quality As you see in the Primer Chapter 2 the resolution of the captured image corresponds to the amount of detail An image can capture more details in the original scene at higher resolution However more details do not necessary mean higher image quality For fi
48. one images with a broad color range and subtle color and brightness variations such as photographs and images with gradients J PEG Supports 24 bit color millions of colors JPEG compression is a lossy compression method which means it loses image data in order to make the file size smaller High J PEG compression tends to blur the image detail side note See the J PEG worksheet in the Art module for more detail and hands on experimentation b c Figure 15 JPEG artifacts a An original image of an oil painting b A highly compressed JPEG image of a c A close up view of the area outlined in red in the J PEG image b The GIF format supports up to 8 bit color 256 colors and it also Supports background transparency It is most effective for images with solid colors such as illustrations logos and line art It uses a palette of up to 256 colors to represent the image If the original image has more than 256 colors then you will need to reduce the colors There are several color reduction options available or you can also customize the colors to be included in the palette GIF images can be created as animated sequences and saved as animated GIF files The PNG 8 format uses up to 256 colors to represent the image similar to GIF The PNG 24 format supports 24 bit color and also transparency Unlike the JPEG format PNG uses a lossless compression Depending on the image and the level of JPEG compression an image saved
49. ong these variables let s look at three different scenarios one variable in each scenario being fixed at a known value Scenario 1 Maintaining the print dimension In order to maintain the print dimensions increasing the print resolution ppi requires higher pixel dimension For example an image of 600 x 600 pixels printed at 100 ppi will give a print of 6 inches x 6 inches If you want to print at 200 ppi and still have an 6 inch by 6 inch print then the pixel dimensions of the image need to be increased from 600 x 600 pixels to 1200 x 1200 pixels Pixel Dimensions Print Resolution in ppi Print Dimensions in inches 600 pixels 100 ppi 6 inches 1200 pixels 200 ppi 6 inches 1800 pixels 300 ppi 6 inches and so forth Scenario 2 Maintaining the pixel dimensions With fixed pixel dimensions increasing the print dimensions requires lowering the print resolution ppi Using the example above an image of 600 x 600 pixels printed at 100 ppi will give a print of 6 inches x 6 inches Pixel Dimensions Print Resolution in ppi Print Dimensions in inches 600 pixels 100 ppi 6 inches 600 pixels 200 ppi 3 inches 600 pixels 300 ppi 2 inches and so forth Scenario 3 Maintaining the print resolution ppi Printing at the same ppi an image with higher pixel dimensions will give larger print dimensions Again if we use the above example you will see Pixel Dimensions Print Resolution in ppi Prin
50. ox will appear showing the histogram of the image There are usually three sliders on the x axis of the histogram a black slider on the left end defines the darkest color shadow a white slider on the right end defines the brightest color highlight a gray Slider in the middle defines the 50 intensity of the color midtone Figure 8 A histogram with the three sliders black shadow gray midtone and white highlight You can move these triangles to modify the image s brightness and contrast You can map the pixels to the darkest by repositioning the black slider For example if you drag the black slider to this position which corresponds to the second darkest gray color in this example image you set this gray color as the darkest color i e black in the image Any color that is originally darker than this gray will become black after this adjustment of the black slider As you see the colors of the shadow and the front of the block were originally different tones of gray But after the adjustment they become totally black and indistinguishable Therefore as you see if you move the black slider past the left end of the original histogram shadow details that were once made up of this area of gray will be lost 5 b Figure 9 a The grayscale image after moving the black slider towards the right b The black slider is moved to where the bar for the second darkest color of the image is The position of the white
51. parately 3 5 Digital I mage Editing When you take pictures with a film camera you can drop the film at a photo store to develop the film and get prints of the pictures And that is it Unless you have access to a darkroom and have experience with darkroom techniques you do not have much control over the picture s color or brightness or how it is cropped In digital photography most of the traditional darkroom techniques have been translated into digital imaging techniques by means of computer graphics programming Digital image editing programs are built upon concepts and algorithms of computer graphics But you don t need to be a computer graphics programmer to use image editing software At the user level these application programs use the language of photography and darkroom techniques such as dodging burning filtering and cropping When you take your film to a photo store to process you probably do not care too much about how and why the machine produces the picture in that particular brightness and color Digital imaging programs allow you to have more control over the image tonal range color and even composition without having to work in a darkroom with photographic chemicals But now with the power and availability of digital imaging programs it becomes your responsibility to learn how to use the tools and mostly importantly to learn to use them effectively and professionally to produce predictable results Creating a good digita
52. ple Figure 1 below shows examples of scanned images without maximizing the tonal range during the scan To show you the comparison Figure 1c shows a scan of the same picture with the tonal range maximized during scanning The image scanned with a narrow tonal range Figure 1a looks dull and low contrast In this case its tonal range may be re adjusted later in an image editing program by stretching its histogram Figure 1b However as you see in Figure 1c the pixels whose highlight information is lost all become white Those highlights that have been cropped off during scanning cannot be recovered by tonal adjustment later in an image editing program j Learning Aid Tonal Adjustments During Scanning An interactive tutorial that explains and demonstrates why tonal optimization is necessary during scanning xi Input Levels fo 1 00 255 Cancel Load Save nS 10 fa ptions Output Levels 0 255 DB A M Preview d Figure 1 Scanned images with their histograms a Scanned using a narrow tonal range b The tonal range of the scanned image from a is re adjusted by stretching the histogram c Scanned with highlights cropped off The lightest colors of the image all become white The lost highlight information during the scan cannot be recovered by stretching the histogram or image editing d Scanned with a maximized tonal range 3 4 Capturing Dig
53. roup The advantage of using an adjustment layer instead of applying the adjustment on an individual layer is that it allows you to change the adjustment settings In addition you can delete the adjustment layer to remove the adjustment later or hide the adjustment effect temporary by turning off the visibility just like any other layers A layer mask associated with a layer lets you obscure just obscure not delete part of the image on that layer This non destructive method of editing offers the advantage of preserving the original image in that layer Later if you change your mind in how you want the image on that layer to show you can always revert back to the original image on that layer and start over fl ES Layers X Channels Paths SQ Normal v Opacity Lock J Fill 10096 gt b Figure 13 a A layer palette showing a layer mask associated with a layer The resulting image looks similar to Figure 14a b The layer mask The black color of the mask hides the image while the white lets the content of the image show through Clipping groups work very similarly to layer masks While a layer mask is associated with one layer and only masks that one layer the clipping group works like a cookie cutter cutting through multiple layers that are in the same group mE J Layers channels S Paths 0 Normal z Opacity Lock O Fill joo F house ani white bg Clipping Group
54. settings Using Unsharp Mask you can specify Amount the amount of the contrast increase around the edges Radius the radius of the surrounding area where the color comparison and the Sharpening take place Threshold how much the pixels differ from surrounding pixels in order to be identified as edges to be sharpened There are no magic numbers for these settings It depends on the resolution of the Image For high resolution images experiment with the Amount setting between 100 and 200 a Radius setting between 1 and 2 and a Threshold between 0 and 20 lower these numbers for low resolution images Setting the Amount too high will exaggerate the intensity of the lighter and darker lines around edges creating unnatural halos around edges The halos will be spreaded out and become even more noticeable if the Radius setting is high If you notice increased graininess and unnatural halos in the image after sharpening you have probably oversharpened the image If you want to limit the sharpening to the more pronounced edges raise the threshold value The softer edges will be left unsharpened The graininess resulted from sharpening is especially an undesired side effect for skin texture Thus raising the threshold can be an effective way in Sharpening portraits sharpen the image while leaving the soft skin texture soft What would be the best threshold setting for portraits then It depends on your image its content and resolution But a
55. slider defines the brightness color white Similarly if you move the white slider to the left past the right end of the original histogram the highlights that were once in this area of gray will be lost Exercise Experiment by dragging the sliders and observe how the position of the sliders affects the brightness and contrast in the image in the interactive tutorial or in Photoshop Things you can try o Drag the white slider to the second peak on the right in the histogram Which colors in the image turn white o Drag the white slider to the rightmost peak and the black slider to the leftmost peak in the histogram How does the contrast of the image change In a sense by defining by the new positions of the black and the white sliders you re map the whole spectrum of color values of the pixels In repositioning the black slider to the leftmost peak and the white slider to the rightmost peak you stretch the histogram That means you make the darkest color in the image to be black and the brightest color in the image to be white All other colors will be re mapped in between in the same relationship of their original gray tones By stretching the histogram you maximize the use of the full spectrum of the gray tones AS you see you increase the overall contrast of the image by increasing the difference of the color values between colors Resulting Histogram After the Adjustment a b Figure 10 a The histograms before and after
56. stretching b The image after stretching the histogram Note the overall image contrast is increased The lightest color becomes white and the darkest color becomes black You can also move the gray slider in the middle to set the midtone For example if you move the gray slider to a new position you set the gray color which is originally a darker gray to a middle gray value of 128 for an 8 bit color x x M Channel RGB M Channel RGB gt Input Levels fo 0 50 255 earl Input Levels fo 1 00 255 al Load Load Save Save Auto Auto EEE EEE ee A we le Sa Output Levels p 25 Qutput Levels pb 255 b c Figure 11 a The original histogram of Figure 7 The midtone slider is moved to the higher value brighter side b The histogram of the resulting image after the adjustment c The resulting image after the adjustment In this example the adjustment changes the third brightest color of the image to the middle gray All other colors are re mapped accordingly As a result any color brighter than the third brightest color is re mapped between 0 and 128 Any color brighter than the third darkest color is re mapped between 128 and 255 x xi M Channel RGB M Channel RGB Input Levels fo 1 68 255 Cancel Input Levels fo 1 00 255 aan Load Load Save Save
57. t Dimensions in inches 600 pixels 100 ppi 6 inches 1200 pixels 100 ppi 12 inches 1800 pixels 100 ppi 18 inches and so forth So how are the above scenarios translated into the settings used in an image editing program To adjust the output resolution or print size of an image look in the image size setting In Photoshop for example it is under Image gt Image Size The setting of the Resample Image option separates scenario 2 from the other two scenarios For scenario 2 in which you want to maintain the pixel dimensions of the image you will need to uncheck Resample Image Then when you alter the print size the print resolution ppi will be automatically updated and vice versa if you change the print resolution If you check the Resample Image option then both scenarios 1 and 3 can apply With the Resample Image option on the pixel dimensions can be varied That is the pixel dimensions can be varied with the print resolution ppi while maintaining the print size They can also be varied with the print size while maintaining the print resolution ppi side note Turning the Resample Image option on means that scaling of the image is allowed Scaling the pixel dimensions of an image is referred to as resampling because the number of samples pixels is changed Printer resolution is measured in dots per inch dpi the number of ink dots per inch Color inkjet printers produce a microscopic spray of ink which app
58. the original 4x6 inches 2400pixels 600ppi 4 inches 3600pixels 600ppi 5 inches If this same scan is printed out at 300 ppi then the print will become 8x12 inches 2400pixels 300ppi 8 inches 3600pixels 300ppi 12 inches If this same scan is printed out at 200 ppi then the print will become 12x18 inches 2400pixels 200ppi 12 inches 3600pixels 200ppi 18 inches If this same scan is printed out at 1200 ppi then the print will become 2x3 inches 2400pixels 1200ppi 2 inches 3600pixels 1200ppi 3 inches As you see in the example above you can make different sizes of prints from the same scanned image The above examples show the math for calculating the pixel dimensions of a scan and how different sizes of prints can be made from the same scanned image by varying the print resolution However in most situations when you scan a picture you usually know the size you want for the final print of the scanned image So now let s reverse the calculation process above Say you want to scan a 35mm negative to make a 10x13 inch print on a 11x14 inch paper on an inkjet printer To determine the scan resolution you will first need to find out the pixel dimensions of the image you need To find out the pixel dimensions you need to know the print size and the print resolution Let s step through the math for determining the print resolution Step 1 Determine the total pixels or the pixel dimension of final image Pixel Dimensions Print
59. tm o To select all To deselect To select the unselected parts of an image What are the different marquee tools available What are the different lasso tools available To add to a selection To subtract from a selection To select only an area intersected by other selections To expand or contract a selection by a specific number of pixels To feather the edge of a selection To save a Selection To load a saved selection How do you make selection by color Does your program have a Pen tool that allows you to draw paths to define the selection If so find out how it works o Does your program let you make a selection by painting a mask If so find out how it works O O O O O O O O O O OO O 2 Explore the use of layers in your image editing program Look up in the Help or the user manual to find out information for the following Note down the answers Use your notes as a quick reference guide and refer to them as needed If your image editing program is Adobe Photoshop there is a worksheet on layers of Photoshop available at http digitalmedia wfu edu proj ect digital media curriculum development textbased index htm l O O O O O O O O O O O O O To create a new layer To delete a layer To duplicate a layer To toggle the visibility of a layer To rename a layer To set opacity of a layer State in one to two sentences the advantage of using layers How do you move the content of multiple layers si
60. uction The two commonly used methods for capturing digital images are scanning and digital photography In this chapter we will discuss types of scanners and explain the common scanning options and how to determine the optimal scanning resolution This knowledge will help you capture optimal digital images to suit your expectations We will also have a brief discussion of digital cameras Later in this chapter we will cover topics on general digital image editing tools We will talk about the output of your final digital images We will discuss how to determine the resolution for images that are created to be printed and how to optimize images created for the Web 3 2 Scanners Generally there are four common types of scanners classified in terms of their mechanisms 1 Flatbed scanners This is the most commonly used and versatile scanner for multimedia labs offices and personal use This type of scanner can usually scan up to letter size 8 5 x 11 inches or legal size 11 x 14 inches documents The scanner has a flat glass plate The motorized scan head which consists of a light source and arrays of sensors is underneath the glass The scan head moves from one end to the other to capture the image Below is a general procedure for scanning a document with a flatbed scanner e Put the document face down on the glass plate e Align the document to the corner as indicated on the scanner e Close the flap cover e Start the scanner softw
61. ution insufficient to print it at a size of 6x6 inches at 300 ppi you will have to scale up the scanned image which will deteriorate the image quality and make it look pixelated So what is the minimal scanning resolution dpi you should use to scan this 2x2 inch area so that you don t have to resize the image to meet the printing requirement Show your calculation Tip First calculate the pixel dimensions of that piece of image needed in the final collage 15 Multiple choice Check all correct What kind of images are GIF files most appropriate for A big areas of solid colors B continuous tone photographs C lots of gradients 16 Multiple choice Check all correct What kind of images are J PEG files most appropriate for A big areas of solid colors B continuous tone photographs C lots of gradients 17 Shown below is an grayscale image and its histogram Levels Ed Channel RGB Input Levels p fi oo 255 Reset Load Save Auto Options Output Levels j 255 Vv Match each of the bars in the histogram to the color it represents Draw arrows linking each bar and the color in the grayscale image above ii TO maximize the contrast and tonal range of this image what specific changes of which sliders should be done Show the new positions of the sliders below ir Channel RGB z Input Levels 0 pi joo 25s Reset Load Save Auto Options

Primer Chapter 3 Capturing and Editing Digital Images*

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