Tomato Analyzer – Color Test User Manual (v10.2007
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1. 71 61 29 53 13 52 94 42 68 52 17 51 11 32 43 60 73 72 3 51 62 51 18 42 47 42 46 51 81 86 18 85 58 81 58 81 4 70 77 81 25 84 86 90 12 79 98 51 07 50 78 49 65 41 35 a 32 8 39 03 55 23 48 31 41 21 23 22 7 47 23 33 14 08 31 82 11 74 4 97 10 4 2 36 1 99 7 03 5 39 6 52 10 61 5 79 8 37 13 12 20 44 13 72 9 41 5 15 4 71 8 24 b 13 55 16 61 34 38 29 02 22 95 14 97 4 98 16 44 12 41 40 07 18 07 10 9 19 44 25 29 14 24 70 09 31 33 57 82 45 26 15 46 29 01 25 65 39 19 24 55 3 12 7 11 32 96 0 12 Tomato Analyzer Color Test User Manual v10 2007 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 follow2. 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 Tomato Analyzer Color Test User Manual v10 2007 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 x Lightness Yellow Chromaticity RR OPA Figure 2 Representation of the CIELab color space Original image reprinted with permission from Konica Minolta Hue and chroma are descriptors of color based on a an
3. Tomato Analyzer Color Test User Manual v10 2007 TOMATO ANALYZER COLOR TEST USER MANUAL 4 October 2007 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 Collecting and formatting images for TACT Generating automated boundaries Adjusting boundaries Part 3 Calibration Obtaining color standards Scanning color checker and collecting TACT L a b values Collecting colorimeter L a b values Determining correction values for calibration Part 4 Color Test Defining parameters Analyzing a single image Using the batch analysis Part 5 Color standard specifications Part 6 Mathematical formulas Tomato Analyzer Color Test User Manual v10 2007 PART 1 OVERVIEW OF COLOR AND TOMATO ANALYZER COLOR TEST The Tomato Analyzer module called Color Test TACT is designed to collect objective color measurement from JPEG images Figure 1 which are collected from scanning fruits on the flatbed surface of a scanner Figure 1 Tomato Analyzer Color Test application Digital color and the RGB color space Computer color measurements are based on the RGB color space This system is additive at it measures the strength of
4. corresponding color values If using the 28 patch color checker developed at OSU Figure 4 Table 1 the L a b values are available in Table 2 Part 5 Determining correction values for calibration Plot TACT values against colorimeter values for L a and b Determine the regression equation and record the slope and y intercept for each parameter Enter the inverse of the slope and the reverse the sign of the y intercept values they are used as correction values in the dialog window of the TACT Figure 5 vente CSV Tomato Analyzer Color Test User Manual v10 2007 Arrat DES 0 tmt Figure 5 Tomato Analyzer Color Test window Correction values used to calibrate the scanner are entered in the lower panel of the dialog box PART 4 COLOR TEST Defining parameters TACT allows the user to define two parameters based on specific ranges of hue values Enter the lower and upper bounds of the selected ranges Save settings for these values to become default settings until the program is closed Analyzing a single image For a single image to analyze for color open the image and make the necessary adjustment Open the Color Test and click on the Analyze button A new window will appear to save the output in a comma delimited CSV Excel document Specify the name and the directory for the data file Using the batch analysis The batch analysis consists of analyzing 30 50 images at once It can be achieved two ways The ba
5. d b values Figure 3 Hue represents the basic 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 Original image reprinted with permission from Konica Minolta 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 Tomato Analyzer Color Test User Manual v10 2007 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 t
6. est dialog box under the Settings menu Set the minimum blue value to 30 and Tomato Analyzer Color Test User Manual v10 2007 save the setting Open the image to analyze It will be displayed in the left panel Click on the Analyze icon The TA defined boundaries of the fruits will appear in yellow Lower the minimum blue value if the fruits are large in which case TA may crash or if the boundaries are much erroneous Adjusting boundaries If the boundaries need to be adjusted select the fruit by left clicking on it The selected fruit will be displayed in the upper right panel Click on the Revise icon selecting Boundary shift B Click on the boundary at the start of the area to adjust and at the end The delimited boundary will disappear The distance between the start and end points should be left than half the entire boundary as only the shortest boundary distance 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 Click the Save Fruit to save any changes on the image A TMT file containing all information and adjustments will be saved along with the image 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 crop of interest For the color analysis of t
7. ing 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 4 q 1 3 q gt 0 008856 f 4 7 787q 16 116 q lt 9 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 Tomato Analyzer Color Test User Manual v10 2007 In addition 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
8. o 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 In addition two parameters based on specific ranges of hue values can be defined by the user see Part 4 Defining parameters PART 2 BASIC FEATURES The basic features of the Tomato Analyzer TA were presented in the original user manual Version 2 1 0 0 It can be downloaded from the following URL http www oardc ohio state edu vanderknaap The features will be briefly described unless they have to be adapted specifically for the Color Test Collecting and formatting images for TA Set the resolution of the scanner at 200 dpi and the output image size at a million colors Scan the surface of the fruit to be analyzed with a black background A label with descriptive information for the fruits year plot number etc can be included on the scanner A ruler and a color standard can also be included TA will not consider the objects as fruits to analyze Save the image as JPEG Using any image editing software crop the image to remove all objects label ruler color standard etc and save it as the image for color analysis with TACT Generating automated fruit boundaries The automated analysis will use the default settings for shape attributes The settings should be changed to meet the user s demand and interest For the color test and prior to analysis open the Color T
9. omato we chose 28 color standards Figure 4 They were custom made into a 28 patch color checker X Rite Grand Rapids MI The Munsell notations for each patch are provided in Table 1 Figure 4 28 patch color checker from X Rite Scanning color checker and collecting TACT L a b values Scan the color checker and analyze the image as described previously Make sure TACT recognizes each patch as an object to analyze yellow Tomato Analyzer Color Test User Manual v10 2007 boundary Under the Settings menu select Color Test The dialog box will appear Select the illuminant and observer angle specific to the scanner used and to be used in the future for color analyses Make sure the correction values are set to 1 for the slope left boxes and 0 for the y intercept right boxes Click on the Analyze button A new window will appear to save the output in a comma delimited CSV Excel document Specify the name and the directory for the data file The output data file will contain L a b values as well as values for the other parameters to be used for calibration Collecting colorimeter L a b values Verify the settings of the colorimeter for its source of illuminant and observer angle They 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
10. tch analysis can use images that were previously analyzed and for which adjustments made to the images were saved It can also use images that were not previously analyzed for which there is no TMT file In either case open the Color Test In the upper panel specify the hue ranges for the parameters of interest Enter the correction values and the minimum blue value for the boundaries in the lower panel Check the Batch Analysis and click Analyze A new window will appear to select the images to Tomato Analyzer Color Test User Manual v10 2007 analyze Specify the name and the directory for the data file Click Save The output file will contain the name of the image depicted from the file name and average color values for each fruit on the image PART 5 COLOR STANDARD SPECIFICATIONS Table 1 Munsell notations for the custom 28 patch color checker used at OSU Patch A 1 2 5R 5 8 5R 4 10 3 7 5R 6 4 4 SYR 4 4 5 SY 8 5 4 6 10Y 8 4 7 5G 5 2 D 5R 5 12 7 5R 3 6 5Y 5 2 5Y 8 5 10 B C 2 5R 6 10 5R 5 14 5R 5 6 SR 5 2 10R 7 10 2 5YR 5 4 SYR 5 2 5Y 4 4 SY 8 8 7 5Y 8 6 10Y 7 2 5GY 8 5 4 SGY 9 6 5GY 8 4 5B 5 2 5PB 5 8 SRP 4 2 Table 2 L a b values obtained from a colorimeter for each patch of the color checker The source of illuminant was C and the observer angle was 2 Patch Al Bl Cl D1 A2 B2 C2 D2 A3 B3 C3 D3 A4 B4 C4 D4 A5 B5 C5 D5 A6 B6 C6 D6 A7 B7 C7 D7 L 51
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