How to compare two colors for similarity difference

Question

I want to design a program that can help me assess between 5 pre-defined colors which one is more similar to a variable color  and with what percentage   The thing is that I don t know how to do that manually step by step  So it is even more difficult to think of a program   More details  The colors are from photographs of tubes with gel that as different colors  I have 5 tubes with different colors were each is representative of 1 of 5 levels  I want to take photographs of other samples and on the computer assess to which level that sample belongs by comparing colors  and I want to know that with a percentage of approximation too  I would like a program that does something like this  http   www colortools net color matcher html  If you can tell me what steps to take  even if they are things for me to think and do manually  It would be very helpful

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A simple method that only uses RGB is  cR R1-R2  cG G1-G2  cB B1-B2  uR R1 R2  distance cR cR  2 uR 256    cG cG 4   cB cB  2  255-uR  256    I ve used this one for a while now  and it works well enough for most purposes

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A color value has more than one dimension  so there is no intrinsic way to compare two colors  You have to determine for your use case the meaning of the colors and thereby how to best compare them    Most likely you want to compare the hue  saturation and or lightness properties of the colors as oppposed to the red green blue components  If you are having trouble figuring out how you want to compare them  take some pairs of sample colors and compare them mentally  then try to justify explain to yourself why they are similar different    Once you know which properties components of the colors you want to compare  then you need to figure out how to extract that information from a color    Most likely you will just need to convert the color from the common RedGreenBlue representation to HueSaturationLightness  and then calculate something like   avghue    color1 hue   color2 hue  2 distance   abs color1 hue-avghue    This example would give you a simple scalar value indicating how far the gradient hue of the colors are from each other   See HSL and HSV at Wikipedia

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Android for ColorUtils API RGBToHSL  I had two int argb colors  color1  color2  and I wanted to get distance difference among the two colors  Here is what I did   private float getHue int color        int R    color  gt  gt  16   amp  0xff      int G    color  gt  gt   8   amp  0xff      int B    color         amp  0xff      float   colorHue   new float 3       ColorUtils RGBToHSL R  G  B  colorHue       return colorHue 0       Then I used below code to find the distance between the two colors   private float getDistance getHue color1   getHue color2         float avgHue    hue1   hue2  2      return Math abs hue1 - avgHue

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One of the best methods to compare two colors by human perception is CIE76  The difference is called Delta-E  When it is less than 1  the human eye can not recognize the difference   There is wonderful color utilities class ColorUtils  code below   which includes CIE76 comparison methods  It is written by Daniel Strebel University of Zurich   From ColorUtils class I use the method   static double colorDifference int r1  int g1  int b1  int r2  int g2  int b2    r1 g1 b1 - RGB values of the first color  r2 g2 b2 - RGB values ot the second color that you would like to compare  If you work with Android  you can get these values like this    r1   Color red pixel    g1   Color green pixel    b1   Color blue pixel      ColorUtils class by Daniel Strebel University of Zurich   import android graphics Color   public class ColorUtil   public static int argb int R  int G  int B        return argb Byte MAX VALUE  R  G  B      public static int argb int A  int R  int G  int B        byte   colorByteArr     byte  A   byte  R   byte  G   byte  B       return byteArrToInt colorByteArr      public static int   rgb int argb        return new int    argb  gt  gt  16   amp  0xFF   argb  gt  gt  8   amp  0xFF  argb  amp  0xFF      public static int byteArrToInt byte   colorByteArr        return  colorByteArr 0   lt  lt  24      colorByteArr 1   amp  0xFF   lt  lt  16                  colorByteArr 2   amp  0xFF   lt  lt  8     colorByteArr 3   amp  0xFF      public static int   rgb2lab int R  int G  int B          http   www brucelindbloom com      float r  g  b  X  Y  Z  fx  fy  fz  xr  yr  zr      float Ls  as  bs      float eps   216 f   24389 f      float k   24389 f   27 f       float Xr   0 964221f      reference white D50     float Yr   1 0f      float Zr   0 825211f          RGB to XYZ     r   R   255 f    R 0  1     g   G   255 f    G 0  1     b   B   255 f    B 0  1         assuming sRGB  D65      if  r  lt   0 04045          r   r   12      else         r    float  Math pow  r   0 055    1 055  2 4        if  g  lt   0 04045          g   g   12      else         g    float  Math pow  g   0 055    1 055  2 4        if  b  lt   0 04045          b   b   12      else         b    float  Math pow  b   0 055    1 055  2 4         X   0 436052025f   r   0 385081593f   g   0 143087414f   b      Y   0 222491598f   r   0 71688606f   g   0 060621486f   b      Z   0 013929122f   r   0 097097002f   g   0 71418547f   b          XYZ to Lab     xr   X   Xr      yr   Y   Yr      zr   Z   Zr       if  xr  gt  eps          fx    float  Math pow xr  1   3        else         fx    float    k   xr   16     116         if  yr  gt  eps          fy    float  Math pow yr  1   3        else         fy    float    k   yr   16     116         if  zr  gt  eps          fz    float  Math pow zr  1   3        else         fz    float    k   zr   16     116        Ls    116   fy  - 16      as   500    fx - fy       bs   200    fy - fz        int   lab   new int 3       lab 0     int   2 55   Ls    5       lab 1     int   as    5       lab 2     int   bs    5       return lab            Computes the difference between two RGB colors by converting them to the L a b scale and    comparing them using the CIE76 algorithm   http   en wikipedia org wiki Color difference CIE76      public static double getColorDifference int a  int b        int r1  g1  b1  r2  g2  b2      r1   Color red a       g1   Color green a       b1   Color blue a       r2   Color red b       g2   Color green b       b2   Color blue b       int   lab1   rgb2lab r1  g1  b1       int   lab2   rgb2lab r2  g2  b2       return Math sqrt Math pow lab2 0  - lab1 0   2    Math pow lab2 1  - lab1 1   2    Math pow lab2 2  - lab1 2   2

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If you have two Color objects c1 and c2  you can just compare each RGB value from c1 with that of c2   int diffRed     Math abs c1 getRed     - c2 getRed     int diffGreen   Math abs c1 getGreen   - c2 getGreen     int diffBlue    Math abs c1 getBlue    - c2 getBlue       Those values you can just divide by the amount of difference saturations  255   and you will get the difference between the two   float pctDiffRed      float diffRed     255  float pctDiffGreen    float diffGreen   255  float pctDiffBlue      float diffBlue    255    After which you can just find the average color difference in percentage    pctDiffRed   pctDiffGreen   pctDiffBlue    3   100   Which would give you a difference in percentage between c1 and c2

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Just another answer  although it s similar to Supr s one - just a different color space   The thing is  Humans perceive the difference in color not uniformly and the RGB color space is ignoring this  As a result if you use the RGB color space and just compute the euclidean distance between 2 colors you may get a difference which is mathematically absolutely correct  but wouldn t coincide with what humans would tell you   This may not be a problem - the difference is not that large I think  but if you want to solve this  better  you should convert your RGB colors into a color space that was specifically designed to avoid the above problem  There are several ones  improvements from earlier models  since this is based on human perception we need to measure the  correct  values based on experimental data   There s the Lab colorspace which I think would be the best although a bit complicated to convert it to  Simpler would be the CIE XYZ one   Here s a site that lists the formula s to convert between different color spaces so you can experiment a bit

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Just an idea that first came to my mind  sorry if stupid   Three components of colors can be assumed 3D coordinates of points and then you could calculate distance between points   F E    Point1 has R1 G1 B1 Point2 has R2 G2 B2   Distance between colors is   d sqrt  r2-r1  2  g2-g1  2  b2-b1  2    Percentage is   p d sqrt  255  2  255  2  255  2

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I ve tried various methods like LAB color space  HSV comparisons and I ve found that luminosity works pretty well for this purpose   Here is Python version   def lum c       def factor component           component   component   255          if  component  lt   0 03928               component   component   12 92          else              component   math pow   component   0 055    1 055   2 4            return component     components    factor ci  for ci in c       return  components 0    0 2126   components 1    0 7152   components 2    0 0722    0 05   def color distance c1  c2        l1   lum c1      l2   lum c2      higher   max l1  l2      lower   min l1  l2       return  higher - lower    higher   c1   ImageColor getrgb  white   c2   ImageColor getrgb  yellow   print color distance c1  c2     Will give you  0 0687619047619048

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The only  right  way to compare colors is to do it with deltaE in CIELab or CIELuv   But for a lot of applications I think this is a good enough approximation   distance   3    dR    4    dG    3    dB   I think a weighted manhattan distance makes a lot more sense when comparing colors  Remember that color primaries are only in our head  They don t have any physical significance  CIELab and CIELuv is modelled statistically from our perception of color

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See Wikipedia s article on Color Difference for the right leads  Basically  you want to compute a distance metric in some multidimensional colorspace  But RGB is not  quot perceptually uniform quot   so your Euclidean RGB distance metric suggested by Vadim will not match the human-perceived distance between colors   For a start  L a b  is intended to be a perceptually uniform colorspace  and the deltaE metric is commonly used  But there are more refined colorspaces and more refined deltaE formulas that get closer to matching human perception  You ll have to learn more about colorspaces and illuminants to do the conversions   But for a quick formula that is better than the Euclidean RGB metric  just do this   Assume that your RGB values are in the sRGB colorspace Find the sRGB to L a b  conversion formulas Convert your sRGB colors to L a b  Compute deltaE between your two L a b  values  It s not computationally expensive  it s just some nonlinear formulas and some multiplications and additions

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Kotlin version with how much percent do you want to match   Method call with percent optional argument  isMatchingColor intColor1  intColor2  95     should match color if 95  similar   Method body  private fun isMatchingColor intColor1  Int  intColor2  Int  percent  Int   90   Boolean       val threadSold   255 -  255   100f   percent       val diffAlpha   abs Color alpha intColor1  - Color alpha intColor2       val diffRed   abs Color red intColor1  - Color red intColor2       val diffGreen   abs Color green intColor1  - Color green intColor2       val diffBlue   abs Color blue intColor1  - Color blue intColor2        if  diffAlpha  gt  threadSold            return false            if  diffRed  gt  threadSold            return false            if  diffGreen  gt  threadSold            return false            if  diffBlue  gt  threadSold            return false            return true

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I expect you want to analyze a whole image at the end  don t you  So you could check for the smallest highest difference to the identity color matrix    Most math operations for processing graphics use matrices  because the possible algorithms using them are often faster than classical point by point distance and comparism calculations   e g  for operations using DirectX  OpenGL        So I think you should start here   http   en wikipedia org wiki Identity matrix  http   en wikipedia org wiki Matrix difference equation      and as Beska already commented above      This may not give the best  visible  difference      Which means also that your algorithm depends onto your definiton of  similar to  if you are processing images

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Swift 5 Answer  I found this thread because I needed a Swift version of this question  As nobody has answered with the solution  here s mine   extension UIColor        var rgba   red  CGFloat  green  CGFloat  blue  CGFloat  alpha  CGFloat            var red  CGFloat   0         var green  CGFloat   0         var blue  CGFloat   0         var alpha  CGFloat   0         getRed  amp red  green   amp green  blue   amp blue  alpha   amp alpha           return  red  green  blue  alpha             func isSimilar to colorB  UIColor  - gt  Bool           let rgbA   self rgba         let rgbB   colorB rgba          let diffRed   abs CGFloat rgbA red  - CGFloat rgbB red           let diffGreen   abs rgbA green - rgbB green          let diffBlue   abs rgbA blue - rgbB blue           let pctRed   diffRed         let pctGreen   diffGreen         let pctBlue   diffBlue          let pct    pctRed   pctGreen   pctBlue    3   100          return pct  lt  10   true   false           Usage   let black  UIColor   UIColor black let white  UIColor   UIColor white  let similar  Bool   black isSimilar to  white    I set less than 10  difference to return similar colours  but you can customise this yourself

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The best way is deltaE  DeltaE is a number that shows the difference of the colors  If deltae  lt  1 then the difference can t recognize by human eyes  I wrote a code in canvas and js for converting rgb to lab and then calculating delta e  On this example the code is recognising pixels which have different color with a base color that I saved as LAB1  and then if it is different makes those pixels red  You can increase or reduce the sensitivity of the color difference with increae or decrease the acceptable range of delta e  In this example I assigned 10 for deltaE in the line that I wrote  deltae  lt   10     lt script gt       var constants         canvasWidth  700     In pixels      canvasHeight  600     In pixels      colorMap  new Array                         -----------------------------------------------------------------------------------------------------    function fillcolormap imageObj1          function rgbtoxyz red1 green1 blue1      a converter for converting rgb model to xyz model  var red2   red1 255   var green2   green1 255   var blue2   blue1 255   if red2 gt 0 04045         red2    red2 0 055  1 055        red2   Math pow red2 2 4       else        red2   red2 12 92      if green2 gt 0 04045         green2    green2 0 055  1 055        green2   Math pow green2 2 4           else        green2   green2 12 92      if blue2 gt 0 04045         blue2    blue2 0 055  1 055        blue2   Math pow blue2 2 4           else        blue2   blue2 12 92      red2    red2 100    green2    green2 100    blue2    blue2 100    var x    red2   0 4124     green2   0 3576     blue2   0 1805    var y    red2   0 2126     green2   0 7152     blue2   0 0722    var z    red2   0 0193     green2   0 1192     blue2   0 9505    var xyzresult   new Array     xyzresult 0    x   xyzresult 1    y   xyzresult 2    z   return xyzresult       end of rgb to xyz function function xyztolab xyz     a convertor from xyz to lab model  var x   xyz 0    var y   xyz 1    var z   xyz 2    var x2   x 95 047   var y2   y 100   var z2   z 108 883   if x2 gt 0 008856         x2   Math pow x2 1 3       else        x2    7 787 x2     16 116       if y2 gt 0 008856         y2   Math pow y2 1 3       else        y2    7 787 y2     16 116       if z2 gt 0 008856         z2   Math pow z2 1 3       else        z2    7 787 z2     16 116       var l  116 y2 - 16   var a  500  x2-y2    var b  200  y2-z2    var labresult   new Array     labresult 0    l   labresult 1    a   labresult 2    b   return labresult            var canvas   document getElementById  myCanvas        var context   canvas getContext  2d        var imageX   0      var imageY   0       context drawImage imageObj1  imageX  imageY  240  140       var imageData   context getImageData 0  0  240  140       var data   imageData data      var n   data length        iterate over all pixels      var m   0      for  var i   0  i  lt  n  i    4          var red   data i         var green   data i   1         var blue   data i   2       var xyzcolor   new Array        xyzcolor   rgbtoxyz red green blue       var lab   new Array        lab   xyztolab xyzcolor       constants colorMap push lab     fill up the colormap array with lab colors                              -----------------------------------------------------------------------------------------------------           function colorize pixqty              function deltae94 lab1 lab2        calculating Delta E 1994           var c1   Math sqrt  lab1 1  lab1 1    lab1 2  lab1 2              var c2    Math sqrt  lab2 1  lab2 1    lab2 2  lab2 2              var dc   c1-c2           var dl   lab1 0 -lab2 0            var da   lab1 1 -lab2 1            var db   lab1 2 -lab2 2            var dh   Math sqrt  da da   db db - dc dc             var first   dl           var second   dc  1  0 045 c1             var third   dh  1  0 015 c1             var deresult   Math sqrt  first first   second second   third third             return deresult                  end of deltae94 function     var lab11    new Array  80   -4   21        var lab12   new Array        var k2 0      var canvas   document getElementById  myCanvas                                            var context   canvas getContext  2d                                            var imageData   context getImageData 0  0  240  140                                           var data   imageData data       for  var i 0  i lt pixqty  i           lab12   constants colorMap i        var deltae   deltae94 lab11 lab12                                                if  deltae  lt   10                                             data i 4    255                                          data  i 4  1    0                                          data  i 4  2    0                                            k2                                                 end of if                                      end of for loop     context clearRect 0 0 240 140       alert k2       context putImageData imageData 0 0         -----------------------------------------------------------------------------------------------------    window  load function            var imageObj   new Image      imageObj onload   function       fillcolormap imageObj             imageObj src      mixcolor png           ---------------------------------------------------------------------------------------------------  var pixno2   240 140     lt  script gt

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I used this in my android up and it seems satisfactory although RGB space is not recommended       public double colourDistance int red1 int green1  int blue1  int red2  int green2  int blue2          double rmean     red1   red2   2      int r   red1 - red2      int g   green1 - green2      int b   blue1 - blue2      double weightR   2   rmean 256      double weightG   4 0      double weightB   2    255-rmean  256      return Math sqrt weightR r r   weightG g g   weightB b b       Then I used the following to get percent of similarity   double maxColDist   764 8339663572415  double d1   colourDistance red1 green1 blue1 red2 green2 blue2   String s1    int  Math round   maxColDist-d1  maxColDist  100       match     It works well enough

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actually I walked the same path a couple of month ago  there is no perfect answer to the question  that was asked here a couple of time  but there is one more sophisticated then the sqrt r-r  etc answer and more easy to implent directly with RGB without moving to all kind of alternate color spaces  I found this formula here which is a low cost approximation of the quite complicated real formula   by the CIE which is the W3C of color  since this is a not finished quest  you can find older and simpler color difference equations there    good luck  Edit  For posterity  here s the relevant C code   typedef struct        unsigned char r  g  b    RGB   double ColourDistance RGB e1  RGB e2        long rmean      long e1 r    long e2 r     2      long r    long e1 r -  long e2 r      long g    long e1 g -  long e2 g      long b    long e1 b -  long e2 b      return sqrt    512 rmean  r r  gt  gt 8    4 g g      767-rmean  b b  gt  gt 8

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All methods below result in a scale from 0-100   internal static class ColorDifference       internal enum Method               Binary     true or false  0 is false         Square          Dimensional          CIE76            public static double Calculate Method method  int argb1  int argb2                int   c1   ColorConversion ArgbToArray argb1           int   c2   ColorConversion ArgbToArray argb2           return Calculate method  c1 1   c2 1   c1 2   c2 2   c1 3   c2 3   c1 0   c2 0               public static double Calculate Method method  int r1  int r2  int g1  int g2  int b1  int b2  int a1   -1  int a2   -1                switch  method                        case Method Binary                  return  r1    r2  amp  amp  g1    g2  amp  amp  b1    b2  amp  amp  a1    a2    0   100              case Method CIE76                  return CalculateCIE76 r1  r2  g1  g2  b1  b2               case Method Dimensional                  if  a1    -1    a2    -1  return Calculate3D r1  r2  g1  g2  b1  b2                   else return Calculate4D r1  r2  g1  g2  b1  b2  a1  a2               case Method Square                  return CalculateSquare r1  r2  g1  g2  b1  b2  a1  a2               default                  throw new InvalidOperationException                         public static double Calculate Method method  Color c1  Color c2  bool alpha                switch  method                        case Method Binary                  return  c1 R    c2 R  amp  amp  c1 G    c2 G  amp  amp  c1 B    c2 B  amp  amp    alpha    c1 A    c2 A     0   100              case Method CIE76                  if  alpha  throw new InvalidOperationException                    return CalculateCIE76 c1  c2               case Method Dimensional                  if  alpha  return Calculate4D c1  c2                   else return Calculate3D c1  c2               case Method Square                  if  alpha  return CalculateSquareAlpha c1  c2                   else return CalculateSquare c1  c2               default                  throw new InvalidOperationException                            A simple idea  based on on a Square     public static double CalculateSquare int argb1  int argb2                int   c1   ColorConversion ArgbToArray argb1           int   c2   ColorConversion ArgbToArray argb2           return CalculateSquare c1 1   c2 1   c1 2   c2 2   c1 3   c2 3               public static double CalculateSquare Color c1  Color c2                return CalculateSquare c1 R  c2 R  c1 G  c2 G  c1 B  c2 B              public static double CalculateSquareAlpha int argb1  int argb2                int   c1   ColorConversion ArgbToArray argb1           int   c2   ColorConversion ArgbToArray argb2           return CalculateSquare c1 1   c2 1   c1 2   c2 2   c1 3   c2 3   c1 0   c2 0               public static double CalculateSquareAlpha Color c1  Color c2                return CalculateSquare c1 R  c2 R  c1 G  c2 G  c1 B  c2 B  c1 A  c2 A              public static double CalculateSquare int r1  int r2  int g1  int g2  int b1  int b2  int a1   -1  int a2   -1                if  a1    -1    a2    -1  return  Math Abs r1 - r2    Math Abs g1 - g2    Math Abs b1 - b2     7 65          else return  Math Abs r1 - r2    Math Abs g1 - g2    Math Abs b1 - b2    Math Abs a1 - a2     10 2                from http   stackoverflow com questions 9018016 how-to-compare-two-colors     public static double Calculate3D int argb1  int argb2                int   c1   ColorConversion ArgbToArray argb1           int   c2   ColorConversion ArgbToArray argb2           return Calculate3D c1 1   c2 1   c1 2   c2 2   c1 3   c2 3               public static double Calculate3D Color c1  Color c2                return Calculate3D c1 R  c2 R  c1 G  c2 G  c1 B  c2 B              public static double Calculate3D int r1  int r2  int g1  int g2  int b1  int b2                return Math Sqrt Math Pow Math Abs r1 - r2   2    Math Pow Math Abs g1 - g2   2    Math Pow Math Abs b1 - b2   2     4 41672955930063709849498817084                Same as above  but made 4D to include alpha channel     public static double Calculate4D int argb1  int argb2                int   c1   ColorConversion ArgbToArray argb1           int   c2   ColorConversion ArgbToArray argb2           return Calculate4D c1 1   c2 1   c1 2   c2 2   c1 3   c2 3   c1 0   c2 0               public static double Calculate4D Color c1  Color c2                return Calculate4D c1 R  c2 R  c1 G  c2 G  c1 B  c2 B  c1 A  c2 A              public static double Calculate4D int r1  int r2  int g1  int g2  int b1  int b2  int a1  int a2                return Math Sqrt Math Pow Math Abs r1 - r2   2    Math Pow Math Abs g1 - g2   2    Math Pow Math Abs b1 - b2   2    Math Pow Math Abs a1 - a2   2     5 1                       Computes the difference between two RGB colors by converting them to the L a b scale and       comparing them using the CIE76 algorithm   http   en wikipedia org wiki Color difference CIE76             public static double CalculateCIE76 int argb1  int argb2                return CalculateCIE76 Color FromArgb argb1   Color FromArgb argb2               public static double CalculateCIE76 Color c1  Color c2                return CalculateCIE76 c1 R  c2 R  c1 G  c2 G  c1 B  c2 B              public static double CalculateCIE76 int r1  int r2  int g1  int g2  int b1  int b2                int   lab1   ColorConversion ColorToLab r1  g1  b1           int   lab2   ColorConversion ColorToLab r2  g2  b2           return Math Sqrt Math Pow lab2 0  - lab1 0   2    Math Pow lab2 1  - lab1 1   2    Math Pow lab2 2  - lab1 2   2     2 55            internal static class ColorConversion        public static int   ArgbToArray int argb                return new int      argb  gt  gt  24    argb  gt  gt  16   amp  0xFF   argb  gt  gt  8   amp  0xFF  argb  amp  0xFF               public static int   ColorToLab int R  int G  int B                   http   www brucelindbloom com          double r  g  b  X  Y  Z  fx  fy  fz  xr  yr  zr          double Ls  fas  fbs          double eps   216 0f   24389 0f          double k   24389 0f   27 0f           double Xr   0 964221f      reference white D50         double Yr   1 0f          double Zr   0 825211f              RGB to XYZ         r   R   255 0f    R 0  1         g   G   255 0f    G 0  1         b   B   255 0f    B 0  1             assuming sRGB  D65          if  r  lt   0 04045  r   r   12          else r    float Math Pow  r   0 055    1 055  2 4            if  g  lt   0 04045  g   g   12          else g    float Math Pow  g   0 055    1 055  2 4            if  b  lt   0 04045  b   b   12          else b    float Math Pow  b   0 055    1 055  2 4            X   0 436052025f   r   0 385081593f   g   0 143087414f   b          Y   0 222491598f   r   0 71688606f   g   0 060621486f   b          Z   0 013929122f   r   0 097097002f   g   0 71418547f   b              XYZ to Lab         xr   X   Xr          yr   Y   Yr          zr   Z   Zr           if  xr  gt  eps  fx    float Math Pow xr  1   3 0           else fx    float   k   xr   16 0    116 0            if  yr  gt  eps  fy    float Math Pow yr  1   3 0           else fy    float   k   yr   16 0    116 0            if  zr  gt  eps  fz    float Math Pow zr  1   3 0           else fz    float   k   zr   16 0    116            Ls    116   fy  - 16          fas   500    fx - fy           fbs   200    fy - fz            int   lab   new int 3           lab 0     int  2 55   Ls   0 5           lab 1     int  fas   0 5           lab 2     int  fbs   0 5           return lab

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For quick and dirty  you can do  import java awt Color  private Color dropPrecision Color c int threshold       return new Color  c getRed   threshold                         c getGreen   threshold                         c getBlue   threshold      public boolean inThreshold Color  1 Color  2 int threshold       return dropPrecision  1 threshold   dropPrecision  2 threshold       making use of integer division to quantize the colors

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You ll need to convert any RGB colors into the Lab color space to be able to compare them in the way that humans see them  Otherwise you ll be getting RGB colors that  match  in some very strange ways   The wikipedia link on Color Differences gives you an intro into the various Lab color space difference algorithms that have been defined over the years  The simplest that just checks the Euclidian distance of two lab colours  works but has a few flaws     Conveniently there s a Java implementation of the more sophisticated CIEDE2000 algorithm in the OpenIMAJ project  Provide it your two sets of Lab colours and it ll give you back single distance value

[algorithm] How to compare two colors for similarity/difference

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