Establishing Instrumental Color Difference Tolerances for Your
Contents
1. HunterLab Measure Color Measure Quality Page 13 Copyright 2008 Applications Note Vol 17 No 12 Colorimetric Data on Cracker Production 1 2 3 4 5 6 7 8 Sample Specimen L AL a Aa b Ab Number ID 16 II 57 12 0 23 13 16 0 64 40 75 0 12 17 VV 57 61 0 26 12 67 0 15 43 72 2 85 18 CC 57 71 0 36 12 74 0 22 41 08 0 21 19 EE 58 19 0 84 12 18 0 34 41 42 0 55 20 HH 59 14 1 79 11 99 0 53 41 30 0 43 21 ZZ 59 26 1 91 11 86 0 66 41 01 0 14 22 LL 59 98 2 63 11 16 1 36 40 82 0 05 23 Cl 60 08 2 73 11 08 1 44 43 46 2 59 24 YY 61 10 3 75 10 33 2 19 43 49 2 62 25 WW 62 65 5 30 9 09 3 43 42 14 1 27 26 XX 64 01 6 66 8 41 4 11 42 37 1 50 27 Al 64 07 6 72 8 22 4 30 42 17 1 30 28 UU 64 10 6 75 8 45 4 07 42 48 1 61 Mean Standard 57 35 12 52 40 87 2 Determine the standard deviation for each color difference parameter and summarize the data as shown below Summary Statistics for Crackers L a b Number of Samples 28 28 28 Minimum Value 50 95 8 22 37 37 Maximum Value 64 10 15 54 43 72 Range 13 15 7 32 6 35 Mean 57 35 12 52 40 87 Standard Deviation 3 67 2 08 1 69 3 Then assuming a normal distribution plot the data for each colorimetric value Microsoft Excel can do this and view the shape of the distribution and the location of the 30 level An example for AL is shown below HunterL2. 0 577 0 57 0 57 1 However if the sample is perfect for L and b but off yet within the AE tolerance for a the sample looks very unacceptable AE V0 0 1 0 0 02 1 This caution does not apply to the AE values used in elliptical tolerancing such as AE CMC as the elliptical tolerancing systems are designed specifically to provide a single number total color difference tolerance See the next section for information on how the elliptical scales can be used to help you set pass fail tolerances Tolerance Type 3 Elliptical Tolerances The following general rules apply to human assessments of color e Hue h differences are most objectionable e Humans will tolerate a little more difference in chroma C than in hue h e Humans will tolerate lightness L differences more easily than differences in chroma C or hue h These principles form the basis for elliptical tolerancing The elliptical tolerancing scales are CMC CIE94 DIN99 and CIE2000 all available in EasyMatch QC and EasyMatch OnLine consult your User s Manual for availability with other products and they operate on the principle that the limit of the region of color space surrounding a product standard for which color differences are not visually detectable forms an ellipsoid with axes in the direction of lightness 1 chroma c and hue h HunterLab Measure Color Measure Quality Page 9 Copyright 2008 Applications Note Vol 17 No
3. 12 The CMC Ellipsoid The Product Standard The overall volume size of the ellipse is the overall color tolerance For the default commercial factor of one called cf for CMC DIN99 and CIE2000 kv for CIE94 this volume equals one AE unit of the elliptical scale of interest or one just visible difference unit This volume may be adjusted in order to tighten or loosen the overall tolerance The lightness chroma ratio called 1 c for CMC kl ke for CIE94 ke kch for DIN99 and KL KC for CIE2000 sets the shape of the ellipsoid along the lightness chroma axis The default of 2 1 used in the textile industry makes the ellipse twice as long in the lightness direction as it is wide in the chroma direction If your product or your customer is more or less sensitive to lightness differences than usual you may lower or raise this ratio accordingly The table below indicates the l c ratios typically used within particular industries Industry Typical lightness chroma Ratio Coatings 1 1 Plastics 1 3 1 Textiles 2 1 More information on how to implement elliptical tolerances is given in Tolerance Method 3a Tolerance Method 1 Determining Tolerances Using a Graph To demonstrate this method of establishing tolerances we will create a graph for each of the difference values listed in the table in Step III page 7 As an example we will plot the lightness darkness L differences The y axis will contain the color
4. HunterLab Measure Color Measure Quality Page 16 Copyright 2008 Applications Note Vol 17 No 12 After all parameters are set the rectangular tolerances are automatically generated and used by the software for samples that are compared to this product standard Refer to the EasyMatch QC User s Manual for more information on using the automatic tolerancing feature of that software package CMC autotolerancing can also be used within HunterLab s ColorFlex and MiniScan XE Plus firmware to automatically fit a CMC ellipsoid to a standard and to calculate AL AC AH rectangular tolerances for that standard based on the size and shape of the ellipsoid In the product setup select the L a b color scale AL AC AH color difference scale and AEc index difference Enter the desired commercial factor cf and the l c ratio as described in Tolerance Method 3a You must also select a PHYSICAL type standard and read your product standard into the setup After the standard is read the automatically generated AL AC AH tolerances are entered into and used with this product setup unless they are manually altered or another product standard is read into this setup Refer to your ColorFlex or MiniScan XE Plus User s Guide for more information on using the automatic tolerancing feature of the instrument Bibliography AATCC Test Method 173 CMC Calculation of Small Color Differences for Acceptability American Association of T
5. 111 Fail 1 25 0 44 0 25 HunterLab Measure Color Measure Quality Page 7 Copyright 2008 Applications Note Vol 17 No 12 Step IV Establish the Tolerances There are several types of tolerances you may establish and several methods for doing so which are outlined below Tolerance Type 1 Rectangular Tolerances Rectangular tolerances are the simplest type of tolerances and are shown in a form similar to the example given below All three components of the color scale such as L a and b or L a and b should be toleranced Color Tolerances for the RED 3645 Standard L D65 10 43 48 0 50 a D65 10 45 45 0 50 b D65 10 27 15 0 50 These tolerances are rectangular because when plotted on a color plot they are expressed as a rectangle Color Plot CIELAB 10 D65 of x L 43 48 a 45 45 b 27 15 Grid 0 10 0 10 w et A TT TT a ANTRENE L tolerance b tolerance a tolerance v Sometimes 0 2 CIE L a b units is quoted as an approximate visual difference limit so it may be tempting to use such a number for your rectangular tolerances In general however tolerances should be based on visual assessment using measurements of acceptable and unacceptable samples and an ideal product standard as the 0 2 unit difference will likely be too tight for most applications resulting in discard or rework of product that might actu
6. 4 81 24 87 0 06 PASS a 0 40 0 20 5 16 5 18 0 02 PASS b 0 30 0 20 4 61 4 43 0 18 PASS This standard does not need to be replaced Step Il Visually Evaluate Pass Fail Once the product standard is established a pass or fail rating can be assigned visually to any specimen that is compared to that standard Results should be reported in a fashion similar to those shown below including complete information on the particular conditions under which the specimens were evaluated Visual Pass Fail Data Date 4 12 05 Operator KSS Apparatus Light Booth Lamp Daylight Product PF11280 408 Standard 11280 Specimen ID Pass Fail Indication 11287 Pass 11295 Pass 11211 Pass 11213 Pass 11213 Pass 11220 Pass 11241 Pass 11242 Pass 11264 Pass 11266 Fail 11272 Fail 11395 Fail 11411 Pass 11415 Fail HunterLab Measure Color Measure Quality Page 4 Copyright 2008 Applications Note Vol 17 No 12 Visual Pass Fail Data Date 4 12 05 Operator KSS Apparatus Light Booth Lamp Daylight Product PF11280 408 Standard 11280 Specimen ID Pass Fail Indication 11111 Fail Since specimens may vary from the target color in terms of lightness redness greenness or yellowness blueness it may be helpful to employ physical standards which deviate along the tolerance perimeters for these three axes An example of thi
7. 9 4 20 38 0 60 10 82 5 20 75 0 49 10 62 6 20 37 0 50 10 43 7 19 99 0 54 11 20 8 20 15 0 52 10 81 9 20 29 0 59 10 55 10 20 48 0 57 11 22 11 20 50 0 64 10 72 12 19 87 0 70 11 02 13 20 81 0 59 11 22 14 20 31 0 53 11 18 15 20 56 0 61 10 57 Average 20 41 0 59 10 91 Care should be taken to preserve the color of physical standards by minimizing the influence of light temperature contamination and other aging factors A system may be established whereby duplicate standards are created and stored until needed The amount of change in a current or working standard over time can be determined by comparing it to a stored and theoretically pristine duplicate If an instrument is being used to measure color the current instrumental reading for the standard can be compared to the previously assigned values As suggested by the SAE J1545 Recommended Practice if a working standard has deviated by the greater of 0 2 color difference units in AL Aa Ab or AL AC AH or 0 1 times the tolerance range the standard should be carefully evaluated and possibly replaced with a back up The worksheet below details an example evaluation of such a standard HunterLab Measure Color Measure Quality Page 3 Copyright 2008 Applications Note Vol 17 No 12 Verifying a Physical Standard Color Scale Tolerances Pass Fail Assigned Current Difference Criteria Values Values Delta L 0 50 0 20 2
8. Lab s EasyMatch QC CMC autotolerancing can be used to automatically fit a CMC ellipsoid to a standard and to calculate CIE L a b CIEL C h or Hunter L a b rectangular tolerances for that standard based on the size and shape of the ellipsoid Once the ideal product standard is read the parameters for the automatic tolerancing can be set through the software as follows e Color Scale scale under which you would like the automatically generated tolerances to be expressed CIE L a b CIEL C h or Hunter L a b e Illuminant Observer illuminant observer combination under which you would like the automatically generated tolerances to be expressed e l c ratio as described in Tolerance Method 3a e Commercial factor as described in Tolerance Method 3a e Auto tolerance Correction factor the 0 75 default value in EasyMatch QC estimates the percentage of the tolerance box that is taken up by the CMC ellipsoid excluding the 25 of the box volume that does not overlap with the ellipsoid This value may be adjusted to tighten or loosen the tolerance as desired A value of one would use the entire volume of the tolerance box including those areas outside the CMC ellipsoid as shown below Color Plot CIELAB 10 D65 lof x L 80 45 a 15 44 b 11 63 Grid 1 0 1 0 The elliptical tolerances The rectangular Example of an area of the tolerances tolerance box outside and not overlapping with the ellipsoid
9. Labels and Tolerance Limits Next you should make a similar graph for the remaining color difference parameters a and b using columns 1 and 5 and 1 and 6 respectively of the data table Using this graphing technique twenty well chosen samples will provide a good set of starting tolerances Data on future specimens should be added to the graph to check the ongoing validity of the specifications As the sampling number approaches 50 or more confidence in the tolerances should greatly increase HunterLab Measure Color Measure Quality Page 11 Copyright 2008 Applications Note Vol 17 No 12 Tolerance Method 2 Determining Tolerances Using Statistics Much of the data obtained in an ongoing production process will assume the shape of a bell curve when plotted as a frequency polygon This shape is more commonly referred to as the normal distribution curve and is useful when studying color difference values Certain statistical assumptions can be made about the normal curve that are useful in describing the population One of these statistical properties the standard deviation helps to describe the distribution of the measurements about the average or population mean FREQU 3 1 1 2 2 0 STANDARD DEVIATIONS The Normal Distribution Curve Color difference measurements are plotted on the x axis and their corresponding frequencies are plotted on the y axis The x axis can be divided into equal parts calle
10. Mig ions amp Insight on Color Vol 17 No 12 Establishing Instrumental Color Difference Tolerances for Your Products Overview Color is a very important aspect of products for consumers The appearance of a product is perceived often correctly to be related to its quality This is true in almost all industries From cookies to vinyl siding customer buying decisions are often based on product color making it important to bakers and extruders alike The color of a product may be judged generally to be acceptable or unsatisfactory or it may be judged in more detail to be too light too red or too blue Such judgments can be made visually or instrumentally based on a perceived difference between an ideal product standard and a sample When this difference is quantified tolerances can be established Tolerances are limits within which a product is considered acceptable Any product falling outside the tolerances is unacceptable Having good tolerances in place for each product allows you to make quick and easy pass fail or ship don t ship decisions When tolerances are established instrumentally they may be expressed in any of the color scales or indices available with the instrument In order to set tolerances an ideal or close to ideal product standard is required as well as a variety of products that have already been determined to be acceptable or unacceptable There are two levels of visual color dif
11. ab Measure Color Measure Quality Page 14 Copyright 2008 Applications Note Vol 17 No 12 dL Distribution Count dL 4 Assume that the desired specification limits are equal to 30 and find the tolerance limits for each color scale parameter using the following equations The example shown is for L For absolute tolerances Lower Limit 30o Mean Lower Limit 3 3 67 57 35 Lower Limit 46 34 Upper Limit 30 Mean Upper Limit 3 3 67 57 35 Upper Limit 68 36 For difference tolerances recommended Lower Difference Limit 30 Lower Difference Limit 3 3 67 Lower Difference Limit 11 01 Upper Difference Limit 30 Upper Difference Limit 3 3 67 Upper Difference Limit 11 01 As additional samples are read they should be added to the distribution plot to test the effectiveness of the 30 tolerances If the ends of the 30 range begin to include out of specification product the tolerance should be recalculated to reduce the range and the standard deviation of the in tolerance samples This will better exclude the out of tolerance samples from the specification Another approach to solidifying tolerances is to assess the capability of the process to manufacture product within the set specifications Information on completing a process capability study is available in the literature and involves using a formula similar to the one already presented The aim
12. ally have been acceptable to the customer Rectangular tolerances may be established using Tolerance Method 1 Method 2 or even Method 3b described below Tolerance Type 2 Single Number Tolerances If your customer cares only about one component of the color scale such as L or lightness or asks for readings only in a particular index such as Yellowness Index it is acceptable to establish a tolerance only for the parameter of interest This tolerance may be established using Method 1 Method 2 or even Method 3b if the parameter of interest is a component of the color scale An example single number tolerance is shown below HunterLab Measure Color Measure Quality Page 8 Copyright 2008 Applications Note Vol 17 No 12 Color Tolerance for the WHITE BASE Standard YI E313 C 2 lt 5 units A word of caution however concerning total color difference values It is not wise to use AE or AE alone as a tolerance if all the components of the color scale are truly of interest This is because although the product may be perfectly acceptable when the color difference is spread out over all three dimensions L a and b or L a and b if the difference is concentrated on one of the dimensions it may be obviously unacceptable For example if a given tolerance is 1 AE Hunter L a b unit the difference could be 0 57 for L 0 57 for a and 0 57 for b and would probably be acceptable visually AE
13. be established separately for each product color so you will need a product standard for each color It is normal to have difference tolerances for different colors It is also typical to find that your tolerances must be tighter to provide acceptable results for darker colors and lower chroma colors In a customer vendor relationship the standard representing the target color may be submitted by a designer or customer This submission is then matched by the vendor s manufacturing process and returned to the customer for approval This begins the process of color communication On the other hand when the color evaluation is being driven by internal quality concerns it is most effective to use a standard that represents the process average This can be accomplished by selecting a physical specimen from the center of the population or by averaging the measured results of a group of specimens to determine a numeric mean An example of determining a colorimetric mean is shown below Many HunterLab products ColorFlex DP 9000 EasyMatch Coatings EasyMatch OnLine EasyMatch QC MiniScan XE Plus Universal Software can automatically average samples for you HunterLab Measure Color Measure Quality Page 2 Copyright 2008 Applications Note Vol 17 No 12 Use of the Mean for Establishing a Standard Sample ID Ls a b 1 20 22 0 64 11 22 2 20 70 0 66 11 02 3 20 73 0 61 10 9
14. d standard deviation or sigma c units The value given to the standard deviation at the center of the curve represents 100 of the measurement in question For each standard deviation a portion of the total area is represented At the level of 30 approximately 99 7 of the population is covered 1 4 35 25 15 M s 0 15 25 Population Distributions for the Normal Curve 35 It is generally agreed that tolerance limits can be set at the 30 level over the process range for acceptable values This concept is based on statistical process control SPC studies HunterLab Measure Color Measure Quality Page 12 Copyright 2008 Applications Note Vol 17 No 12 Process capability is the degree to which a process is consistently able to manufacture product within established specifications Process refers to the product variables being measured such as color as well as the procedures the machinery and the workmanship involved Results are usually expressed as the proportion or percent of product that will be within the tolerance Process capability studies are SPC techniques which are valid only after statistical control has been determined and established For the purposes of this Applications Note a discussion of SPC will not be provided However more information can be found in the literature referenced in the bibliography In practical terms a process that is not in control and is constantly shifting does
15. difference values column 4 and the x axis will contain the sample number column 1 The plot is shown below Note Some HunterLab software products can create this graph for you Look for a trend plot or control chart view HunterLab Measure Color Measure Quality Page 10 Copyright 2008 Applications Note Vol 17 No 12 D65 10 4 8 Trials 12 1 20 1 25 0 75 e e e DL 0 k E d e e e e 0 75 d Sample Number Versus AL Next add the visual pass fail data by labeling each sample as passing no label or failing labeled with an F using the table s column 3 As shown below upper and lower boundary lines can then be drawn to separate the graph into three areas The lower rectangle below the lower red line represents all the samples that fall outside the lower tolerance i e are too dark the middle rectangle between the red lines represents all samples which are acceptable for L and the upper rectangle above the upper red line represents all the samples that fall outside the upper tolerance i e are too light You can see that both the upper and lower L limits occur at about 0 5 L from the standard 0 5 would be used as your starting tolerance o 4 8 Trials 12 4 20 D65 10 nae 0 75 Upper Tolerance z 0 50 a rr 8 DL z 0 e e B e e 10 50 Lower Tolerance F 0 75 F e F Pass Fail
16. e Sample averaging The recommended practices of various professional trade associations such as ASTM TAPPI and AATCC are available in the literature When comparing measurements made on different instruments the best results are obtained for color differences when the instrument group contains units of similar geometrical design For instance it would not be advisable to compare results obtained on a 45 0 instrument to those obtained using a diffuse 8 instrument For recommendations of ways to maximize inter instrument agreement refer to the Applications Note titled Maximizing Inter instrument Agreement When it is important that two or more instruments of similar design read the same values for a group of specimens the technique of hitch standardization may be employed This process involves naming one instrument as the reference or master unit and mathematically adjusting the secondary or slave units to match In this way two or more instruments can be hitched together For more information on this process see the Applications Note titled HunterLab s Guide to Hitch Standardization HunterLab Measure Color Measure Quality Page 6 Copyright 2008 Applications Note Vol 17 No 12 Instrument diagnostics provided by the instrument manufacturer should be run on a regular basis Adherence to a schedule will ensure confidence in the measurements and allow early detection of instr
17. extile Chemists and Colorists Research Triangle Park North Carolina www aatcc org ASTM D1729 Standard Practice for Visual Appraisal of Colors and Color Differences of Diffusely Illuminated Opaque Materials ASTM International West Conshohocken Pennsylvania www astm org ASTM D3134 Standard Practice for Establishing Color and Gloss Tolerances ASTM International West Conshohocken Pennsylvania www astm org Hunter Richard S and Harold Richard W The Measurement of Appearance New York John Wiley amp Sons 1987 www hunterlab com HunterLab s Guide to Hitch Standardization Applications Note HunterLab September 1998 Maximizing Inter instrument Agreement Applications Note HunterLab June 2005 Recommended Practice J1545 Instrumental Color Difference Measurement for Exterior Finishes Textiles and Colored Trim SAE International Warrendale Pennsylvania www sae org For Additional Information Contact Technical Services Department Hunter Associates Laboratory Inc 11491 Sunset Hills Road Reston Virginia 20190 Telephone 703 471 6870 FAX 703 471 4237 www hunterlab com 03 08 HunterLab Measure Color Measure Quality Page 17 Copyright 2008
18. ferences that are used to establish color tolerances e Minimum perceptible difference which defines a just noticeable difference between standard and sample e Maximum acceptable difference which is the largest acceptable difference between standard and sample HunterLab Measure Color Measure Quality Page 1 Copyright 2008 Applications Note Vol 17 No 12 Target Color Standard ee Minimum perceptible Can you see fhe diference Versus Differences Maximum acceptable is fhe difference foo great Sample Perceptible vs Acceptable Differences Manufacturers are generally concerned about the maximum acceptable color difference rather than a minimum perceptible difference and color tolerances are usually based on the maximum acceptable difference Any difference larger than that would cause the sample to be rejected In the end agreement between the buyer and seller on acceptability criteria is necessary for establishing product color tolerances and purchasing specifications A step by step process for establishing color difference tolerances is outlined in the rest of this Applications Note Step I Establish a Standard The first step in implementing a tolerancing program is to establish a standard that represents the ideal color for a particular product In theory the established manufacturing process should be capable of producing this color the majority of the time Tolerances should
19. gnitude of the difference in color between standard and sample in a way that is meaningful to a human observer Instruments not only provide an objective numerical measurement system but they can also often discriminate or see small color differences better than the average human observer and can do so repeatably In other words instruments are more accurate and more repeatable than humans Another recognized advantage to using instrumentation is the agreement on specimen readings between different instruments which is better than the agreement between visual assessments by two different human observers This function known as reproducibility easily expands the capability for communication of color between different manufacturing facilities When comparing results for different specimens measured on different instruments specific sample handling techniques and instrumental settings should be defined and used Adherence to a defined method will reduce the error associated with sample presentation and instrumentation Some of the parameters to be considered and standardized in test method development are listed below Criteria for Color Measurement Methodology Instrument geometry 45 0 or diffuse 8 sphere Sample preparation including taking opacity translucency etc into account Sample presentation including instrument port size etc Color scale or color difference scale Illuminant Standard observer Standardization mod
20. not lend itself well to fixed tolerance limits Process capability studies are needed to set tolerances as well as to evaluate current specifications The accepted criterion for long term process capability is that the process function is 99 7 within specification This 99 7 refers to the 3o level To determine the upper and lower tolerance limits statistically complete the following steps 1 Collect data on a group of samples including visual pass fail information and instrumental measurements as described in Steps II and III Determine the mean colorimetric values and using this mean as a standard calculate the color difference between this standard and all the samples as shown below Colorimetric Data on Cracker Production 1 2 3 4 5 6 7 8 Sample Specimen L AL a Aa b Ab Number ID 1 GG 50 95 6 40 15 46 2 94 37 37 3 50 2 AA 51 21 6 14 15 54 3 02 38 75 2 12 3 NN 52 28 5 07 14 88 2 36 37 75 3 12 4 MM 53 01 4 34 14 29 1 77 37 45 3 42 5 OO 54 01 3 34 14 52 2 00 41 44 0 57 6 PP 54 15 3 20 14 74 2 22 40 23 0 64 7 BB 54 89 2 46 13 72 1 20 39 52 1 35 8 B1 54 98 2 37 14 07 1 55 41 92 1 05 9 RR 55 27 2 08 13 46 0 94 39 99 0 88 10 QQ 55 72 1 63 13 82 1 30 41 24 0 37 11 JJ 56 32 1 03 13 15 0 63 40 62 0 25 12 SS 56 90 0 45 13 22 0 70 40 04 0 83 13 KK 57 02 0 33 12 86 0 34 40 39 0 48 14 TT 57 05 0 30 12 53 0 01 39 53 1 34 15 DD 57 10 0 25 13 00 0 48 41 91 1 04
21. s type of tolerancing arrangement is shown below Lighter TARGET Darker AL 5 AE 5 0 Yellower Ab 5 AE 50 Visual Deviations from Target in Lightness Darkness Red Green and Blue Yellow To be useful these visual evaluations must be as repeatable and reproducible as possible The parameters listed below must be carefully controlled Similar parameters are listed in ASTM Standard D1729 A light booth can be a useful tool for establishing a standard light source such as incandescent fluorescent or daylight angle of illumination and angle of viewing Conditions to be Controlled for Visual Evaluation Spectral quality of the light source Intensity of the light source Angular size of the light source Angle of incidence the angle from which light strikes the object Angle of viewing the angle at which the object is viewed Background color HunterLab Measure Color Measure Quality Page 5 Copyright 2008 Applications Note Vol 17 No 12 Step Ill Make Instrumental Measurements Modern color measuring instruments spectrophotometers and colorimeters use the CIE colorimetric mathematical model to relate the human perception of color to instrumental response Colorimetric scales such as CIE L a b and CIE L C h can be derived from this mathematical model to serve as useful tools in communicating and quantifying color and appearance The numbers obtained describe the nature and ma
22. umental problems Once the instrument and method are in place it is time to gather and read a group of samples To be most effective this group should be large enough to provide some statistical credibility i e twenty or more samples and should include samples that pass as well as samples that fail when visually rated Specimens that are unacceptable assist in finding the numerical tolerance boundaries To verify and refine the initial product tolerances expand the data base by collecting more samples Next rate the acceptability in terms of pass or fail of each sample by visually comparing it to the physical product standard as described in Step II if you haven t already Then measure each of these samples on the instrument and determine its color difference relative to the product standard And example data summary is shown below Visual and Instrumental Data 1 2 3 4 5 6 Sample Specimen Visual AL Aa Ab Number ID Pass Fail 1 11287 Pass 0 23 0 01 0 09 2 11295 Pass 0 46 0 03 0 08 3 11211 Pass 0 15 0 12 0 05 4 11213 Pass 0 01 0 07 0 04 5 11216 Pass 0 03 0 14 0 18 6 11220 Pass 0 12 0 09 0 15 7 11241 Pass 0 20 0 18 0 11 8 11242 Pass 0 37 0 15 0 23 9 11259 Pass 0 49 0 19 0 02 10 11264 Pass 0 46 0 13 0 15 11 11266 Fail 0 56 0 26 0 30 12 11272 Fail 0 61 0 24 0 04 13 11395 Fail 0 78 0 27 0 21 14 11411 Pass 0 34 0 04 0 16 15 11415 Fail 0 86 0 45 0 17 16 11
23. would be to substitute in the current tolerances and solve for the number of standard deviations needed to include the in tolerance samples The result would predict the percentage of the population that could be produced within tolerance using the current manufacturing process and specifications HunterLab Measure Color Measure Quality Page 15 Copyright 2008 Applications Note Vol 17 No 12 Tolerance Method 3a Using Elliptical Tolerances This section describes how to actually implement the elliptical tolerances described in Tolerance Type 3 Ellipsoidal volumes are thought to more accurately describe human perceptibility limits than rectangular tolerance boxes By definition any sample that falls within the ellipsoid and the AE limit chosen for the scale being used is acceptable for the standard at its center and any sample that is outside the ellipsoid and the AE limit chosen for the scale being used is unacceptable Thus assigning tolerances for a product standard using elliptical tolerancing is as simple as reading the standard choosing the elliptical scale for use and setting the lightness chroma ratio and commercial factor beginning with industry defaults and adjusting as needed using read samples Then samples outside the AE limit will fail and samples inside the AE limit will pass Refer to your User s Manual for more information on elliptical tolerances Tolerance Method 3b Using Automatic Tolerancing In Hunter
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