Tomato Analyzer Color Test User Manual Version 3
Contents
1. In addition six parameters based on specific ranges of hue chroma and or L values can be defined by the user see Part 4 Defining parameters Part 2 Basic Features Details about the use of the Tomato Analyzer application TA can be found in the TA morphology user manual Version 3 It can be downloaded from the following URL http www oardc ohio state edu vanderknaap The basic features of TA will be briefly described in this part of the TA Color Test manual Collecting and formatting images for TACT For the most accurate color measurements the user is advised to scan a color checker to calibrate the scanner prior to scanning objects such as fruit and leaves described in Part 3 Set the output image size of the scanner at the highest number of colors available in the scanner software Scan the objects with a black background by placing a box over the scanner A label with descriptive information for the objects year plot number etc and a ruler can be included on the scan Save the image as TIFF 100 dpi or JPEG 200 dpi Because TIFF files preserve the image as it was originally scanned these file types are recommended JPEG images alter some of the colors in the image reducing the accuracy of object boundary detection and color analysis Generating the boundaries After opening an image click the Color test button on the toolbar The color test dialog box appears see below Figure 5 Select Analyze to a2. Part 6 Mathematical formulas The algorithm implemented in TACT to convert RGB values to L a b values of the CIELab color space can be adjusted to account for the illuminant D65 or C and observer angle 2 or 10 Converting RGB to L a b is accomplished in three steps First RGB values are scaled to a perceptually uniform color space equation 1 Var_R R 255 0 055 1 055 2 4 100 Var_G G 255 0 055 1 055 2 4 100 1 Var_B B 255 0 055 1 055 2 4 100 Scaled RGB values are then converted to XYZ trismulus values using the following relationships equation 2 X Var_R 0 4124 Var_G 0 3576 Var_B 0 1805 Y Var_R 0 2126 Var_G 0 7152 Var_B 0 0722 2 Z Var_R 0 0193 Var_G 0 1192 Var_B 0 9505 The XYZ values are converted to L a b values using the following relationships equation 3 L 116 f Y Yn 16 a 500 f X Xn f Y Yn 3 b 200 f Y Yn f Z Zn where f g q 1 3 q gt 0 008856 f q 7 787q 16 116 q lt 0 008856 Yn Xn and Zn are the trismulus values of the illuminant and observer angle For illuminant C observer angle 2 Xn 98 04 Yn 100 0 and Zn 118 11 For illuminant D65 observer angle 10 Xn 94 83 Yn 100 0 and Zn 107 38 The L a b values were then used to calculate chroma as V a b Hue is calculated as 180 pi acos a V a b for a gt 0 and as 360 180 pi acos a V a b for a lt 0 In additi
3. b values for each tile will need to be available for either Illuminant C2 at Observer Angle 2 or Illuminant D65 at Observer Angle 10 from either the manufacturer or a colorimeter Color checkers can be purchased custom made or standard Figure 4 Custom made 28 patch color checker from X rite Grand Rapids MI Collecting colorimeter L a b values If the manufacturer does not provide L a b values they must be determined by a colorimeter Verify the settings of the colorimeter for its source of illuminant and observer angle which should be consistent with the scanner Calibrate a colorimeter with a white tile following the manufacturer s protocol Collect L a b values for each patch of the color checker Make sure to report the tile number with its corresponding color values Analyzing the color checker and entering the correct L a b values Scan the color checker as described above and open the image in TA Click the Color Test button in the toolbar to open the Color Test dialog Choose the combination of illuminant and observer angle provided with the manufacturer s listing of L a b values for the color checker TACT accepts either Illuminant C2 at Observer Angle 2 or Illuminant D65 at Observer Angle 10 Click the Calibrate button to open the Input L a b dialog Figure 5 A shows the Color Test dialog box After clicking Calibrate the Input L a b dialog is displayed Figure 5 B Figure 5 Color Test
4. Tomato Analyzer Color Test User Manual Version 3 August 2010 Jaymie Strecker Gustavo Rodriguez Itai Njanji Josh Thomas Atticus Jack Audrey Darrigues Jack Hall Nancy Dujmovic Simon Gray Esther van der Knaap David Francis Part 1 Overview of color and Tomato Analyzer Color Test TACT Digital color and the RGB color space Tomato Analyzer and the CIELab color space Standard illuminant and observer angle TACT application Part 2 Basic features e Collecting and formatting images for TACT e Generating the boundaries e Adjusting boundaries Part 3 Calibration e Obtaining color standards e Collecting colorimeter L a b values e Analyzing the color checker and entering the correct L a b values Part 4 Color Test e Average color values e L hue chroma distributions e Set custom parameters Part 5 Color standard specifications Part 6 Mathematical formulas Part 7 Definitions of measurements e Average color values e L hue chroma distributions and Set custom parameters Part 1 Overview of color and Tomato Analyzer Color Test TACT The Tomato Analyzer module called Color Test TACT is designed to collect objective color measurement from JPEG and TIFF images Figure 1 which are collected from scanning fruits on the flatbed surface of a scanner Figure 1 Tomato Analyzer Color Test Digital color and the RGB color space Computer color measurements are based on the RGB color spa
5. ameter 4 lt L lt Ha lt Hue lt Hi Hi lt Chroma lt Parameter 5 lt L lt a lt Hue lt lt Chroma lt Parameter 6 lt lte lt Hue lt m z lt Chroma lt i Clear Cancel The user can define up to 6 combinations of color ranges In the example in Figure 7 Parameter 1 includes all colors where the hue is between 30 inclusive and 45 exclusive L and chroma may be anything Parameter 2 includes all colors where the L is between 0 and 30 and the hue is between 0 and 90 the chroma may be anything When finished entering color ranges click OK The data appears in the data window tab called Custom Color Parameters Part 5 Color standard specifications Table 1 L a b values for each patch of the color checker see Figure 4 The source of illuminant was D50 and the observer angle was 2 L a b 1 37 986 13 555 14 059 2 65 711 18 13 17 81 3 49 927 4 88 21 925 4 43 139 13 095 21 905 5 55 112 8 844 25 399 6 70 719 33 397 0 199 7 62 661 36 067 57 096 8 40 02 10 41 45 964 9 51 124 48 239 16 248 10 30 325 22 976 21 587 11 72 532 23 709 57 255 12 71 941 19 363 67 857 13 28 778 14 179 50 297 14 55 261 38 342 31 37 15 42 101 53 378 28 19 16 81 733 4 039 79 819 17 51 935 49 986 14 574 18 51 038 28 631 28 638 19 96 539 0 425 1 186 20 81 257 0 638 0 335 21 66 766 0 734 0 504 22 50 867 0 153 0 27 23 35 656 0 421 1 231 24 20 461 0 079 0 973
6. ce This system is additive at it measures the strength of each R red G green B blue color in each pixel to reproduce other colors The additive RGB color space is a cube with each axis representing variance in one of the primary colors and a white reference point This color space is nonlinear and does not mimic the nature of color perception It is not generally standardized While there is a standardized version sRGB for which conversion formulas exist measurements may differ among hardware and software These differences can be corrected by calibrating the devices involved in the process of collecting and analyzing color images Tomato Analyzer and the CIELab color space TACT takes the average RGB values for each pixel and translates the color measurements to L a b values of the CIELab color space Unlike the RGB color space the CIELab color space is able to approximate human visual perception It is a spherical color space with the vertical axis representing lightness L to darkness L The chromaticity coordinates are a and b and their axis indicates color directions a is the red direction a is the green direction b is the yellow direction and b is the blue direction Figure 2 lt Lightness Yellow 3 x Figure 2 Representation of the CIELab Chromaticity color space coordinates Hue and chroma are descriptors of color based on a and b values Figure 3 Hue represents the basic
7. color It is an angular measurement in the quadrant between the a and b axes Chroma is the saturation or vividness of color It is measured radially from the center of each quadrant with the a and b axes Figure 3 Representation of hue and chroma two attributes of perceived color Standard illuminant and observer angle Different light sources will make colors appear different A standard illuminant has a specific spectral distribution Standard illuminant D65 represents natural daylight It should be used for specimens that will be illuminated by daylight include ultraviolet radiation Illuminant C was also constructed to represent natural daylight but its spectral distribution excludes ultraviolet radiation In addition to the light source the angle of view will also affect color sensitivity of the eye Colors are perceived most precisely if they strike the area of the fovea in the eye which is most sensitive to color The 2 Standard Observer angle is used for viewing angles between 1 and 4 whereas the 10 Standard Observer is used for angles larger than 4 TACT application TACT collects RGB values for each pixel of an object It then translates them to L a b values of the CIELab color space as well as luminosity Algorithms were written for TACT to compute hue and chroma based on L a b values The output of each image analyzed with the TACT consists of the averaged values of RGB luminosity L a b
8. dialog box A and Input L a b dialog box B A B Color Test Select Color Attributes Input L a b Values for Color Checker 7 Average color values CSV data entry JV L hue chroma distributions Choose File Set custom color parameters Manual data entry Select Calibration Settings nput the L a b values For each tile on the color checker E E bean A These values should be provided with the color checker Illuminant C 2 Illuminant D65 10 Tile 01 x Equations L 7 L pooo xL jo a fi xa p at 0 o b fi xb o co Restore Defaults Finish Analyze color Calibrate Save settings Cancel Cancel The user now needs to enter the actual L a b values for each tile in the color checker as provided by the manufacturer or determined by a colorimeter There are two ways to do this e If this is the first time the color checker is used in the calibration type or paste the L a b values for the first tile and click Next Repeat for each tile When all L a b values have been entered click Finish In the Save as dialog that appears the actual data you entered can be saved to a CSV file with the name of the color checker image followed by the word calibration TA uses the actual and observed L a and b values in a linear regression to find linear equations to convert observed values to actual values The calibration information is displayed in the Color Test window under the section Equa
9. e methods to analyze color Figure 5 A Average color values The values displayed are Average Red Average Green Average Blue Average Luminosity Average L Value Average a Value Average b Value Average Hue Average Chroma These average values are calculated taking into account all pixels within the object L hue chroma distributions These measurements provide histogram data for L hue and chroma The data appear in the tabs called L Distributions Hue Distributions and Chroma Distributions respectively Each column shows the fraction of the object whose color falls within a certain range For example if the L 40 50 column in L Distributions has the value 0 3 then 30 of the fruit has L between 40 inclusive and 50 exclusive Set custom color parameters Based on the L hue chroma distributions the user can define custom ranges of L hue chroma or a combination of the three Click the Color Test button in the toolbar to open the Color Test dialog Check the box for User Defined Color Ranges Click the Analyze Color button The User Defined Color Ranges dialog appears as shown in Figure 7 Figure 7 Set Custom Color parameters dialog box Custom Color Parameters Parameter 1 lt L lt zi 3o lt Hue lt 4s lt Chroma lt Parameter 2 0 lt L1 lt 30 0 lt Hue lt o lt Chroma lt Parameter 3 lt L lt mm lt Hue lt lt Chroma lt Par
10. elect Load Save Settings select Save Settings to save the calibration equation values and Load Settings to use previously calculated calibration equation values Alternatively the equations can be copied and pasted from the CSV file saved during calibration Part 4 Color test The application is now ready to analyze color on the objects such as fruit and leaves The user can analyze the color of the objects by either selecting from the Settings menu on the toolbar select Select Attributes click on Average Color Values L Distribution etc see Figure 6 Alternatively the user can select Color test on the toolbar Select Color Attributes click Analyze color Attributes M Basic Measurements Select All Figure 6 Select Attributes dialog box M Fruit Shape Index M Blockiness Homogeneity M Proximal Fruit End Shape M Distal Fruit End Shape M Asymmetry M Internal Eccentricity M Latitudinal Section Cancel M Morphometrics Average Color Values L Distribution C Hue Distribution C Chroma Distribution L Custom Color Parameters NOTE The calibration step with a color checker can be skipped if color accuracy is less important For example a user might want to know the percentage green and brown in an object but the exact L a b values are not relevant In that case the scanner is assumed to be perfect and the equations can be reset to default values click Restore default Figure 5 A There are thre
11. llow TA to find the boundaries Objects that are highlighted in yellow will be analyzed Objects highlighted in blue will not be analyzed Objects that are not highlighted in blue or yellow are not recognized by TA By right clicking the highlighted objects the user can toggle between analyzed and not analyzed objects Adjusting boundaries If needed the boundaries of the object can be adjusted Select the object by left clicking on it The selected object will be displayed in the upper right panel Click on the Revise button on the toolbar selecting Boundary shift B On the object in the right window click on the boundary at the start and the end of the area to adjust The delimited boundary between the selected points will disappear Left click at multiple points on the boundary to delimit the desired contour Any action can be undone by right clicking Press the Enter key to accept the changes or Escape key to cancel Click the Save Fruit to save any changes on the image A TMT file with the same name as the image and containing all information and adjustments will be saved along with the image in the same file Both files should be kept in the same folder to avoid reanalyzing the image Part 3 Calibration Obtaining color standards Color standards should be chosen based on the broad range of colors observed in the object of interest For the best results choose a color checker with a black or very dark background L a
12. on luminosity is computed from the following relationship equation 4 Luminosity maxCol minCol 240 0 2 0 255 0 4 where maxCol is the highest of the R G B values of a pixel analyzed and minCol is the lowest value Part 7 Definitions of measurements Basic Color Analysis e Average Red The average R value 0 255 in the RGB color system across all pixels in the object e Average Green The average G value 0 255 in the RGB color system across all pixels in the object e Average Blue The average B value 0 255 in the RGB color system across all pixels in the object e Average Luminosity The average luminosity 0 240 across all pixels calculated from the RGB value of each pixel as max R G B min R G B 240 2 255 Average L Value The average L value 0 100 in the L a b color system across all pixels in the object Average a Value The average a value 0 100 in the L a b color system across all pixels in the object Average b Value The average b value 0 100 in the L a b color system across all pixels in the object Average Hue The hue 0 360 represented by the Average a Value and the Average b Value Average Chroma The chroma represented by the Average a Value and the Average b Value The RGB and luminosity of a pixel can be viewed in Microsoft Paint The approximate L a b of a pixel can be viewed in Adobe Photoshop L hue chroma dist
13. ributions and set custom color parameters L Ranges For the range L m n the value is the fraction between 0 and 1 of the object having L between m inclusive and n exclusive Hue Ranges For the range H m n the value is the fraction between 0 and 1 of the object having hue between m inclusive and n exclusive Chroma Ranges For the range C m n the value is the fraction between 0 and 1 of the object having chroma between m inclusive and n exclusive Set Custom Color Parameters For the range L m n H p q C r s the value is the fraction between 0 and 1 of the object having L between m inclusive and n exclusive AND hue between p inc and q exc AND chroma between r inc and s exc If L m n is absent then the value is the fraction of the object having hue and chroma within the given ranges regardless of L similarly for H p q and C r s
14. tions Figure 5 A This means that the calibration of the scanner is done The slopes should be close to 1 and the intercepts close to 0 if not check that the L a b values were entered correctly NOTE It is important to ensure that the values entered for each tile correspond to the correct tile in the manufacturer s specification TA may number the tiles differently than the manufacturer and TA may not recognize some dark colored tiles Tiles that are not recognized are not bordered by a yellow or blue line To help ensure that the correct values are entered TA displays the current tile in the right window panel when entering the actual L a b values Figure 5 B e Ifthe color checker was used before and the CSV file with the actual L a b values was saved during the calibration the correct L a b values can be imported from the CSV file Click Choose File and open the CSV file with the actual color checker values In the Save dialog that appears either choose another CSV file or click Cancel Make sure that you import the values for the same color checker scanned in the same orientation Also make sure TA recognizes the same color patches as it did for a previous calibration When reopening TA the calibration equation values from the previous analysis will be used If multiple sets of equations are to be used on the same computer the equations can be saved and loaded by going to the Settings menu on the toolbar s
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