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@manojpandey
Created August 12, 2016 10:34
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RGB to CIELab color space conversion
# RGB to Lab conversion
# Step 1: RGB to XYZ
# http://www.easyrgb.com/index.php?X=MATH&H=02#text2
# Step 2: XYZ to Lab
# http://www.easyrgb.com/index.php?X=MATH&H=07#text7
def rgb2lab(inputColor):
num = 0
RGB = [0, 0, 0]
for value in inputColor:
value = float(value) / 255
if value > 0.04045:
value = ((value + 0.055) / 1.055) ** 2.4
else:
value = value / 12.92
RGB[num] = value * 100
num = num + 1
XYZ = [0, 0, 0, ]
X = RGB[0] * 0.4124 + RGB[1] * 0.3576 + RGB[2] * 0.1805
Y = RGB[0] * 0.2126 + RGB[1] * 0.7152 + RGB[2] * 0.0722
Z = RGB[0] * 0.0193 + RGB[1] * 0.1192 + RGB[2] * 0.9505
XYZ[0] = round(X, 4)
XYZ[1] = round(Y, 4)
XYZ[2] = round(Z, 4)
# Observer= 2°, Illuminant= D65
XYZ[0] = float(XYZ[0]) / 95.047 # ref_X = 95.047
XYZ[1] = float(XYZ[1]) / 100.0 # ref_Y = 100.000
XYZ[2] = float(XYZ[2]) / 108.883 # ref_Z = 108.883
num = 0
for value in XYZ:
if value > 0.008856:
value = value ** (0.3333333333333333)
else:
value = (7.787 * value) + (16 / 116)
XYZ[num] = value
num = num + 1
Lab = [0, 0, 0]
L = (116 * XYZ[1]) - 16
a = 500 * (XYZ[0] - XYZ[1])
b = 200 * (XYZ[1] - XYZ[2])
Lab[0] = round(L, 4)
Lab[1] = round(a, 4)
Lab[2] = round(b, 4)
return Lab
@TellAnAx
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TellAnAx commented Aug 4, 2022

This is the code written in R.
I added a tiny extension, making the maximum of the RGB color value range variable instead of hard-coding it.

https://gist.github.com/TellAnAx/06ace666a92d0849d6b774de1790cc7a

rgb2lab <- function(inputColor, maxColorValue = 255){

    num <- 1
    RGB <- c(0, 0, 0)

    for(value in inputColor){    
      value <- value / maxColorValue

        if(value > 0.04045){
          value <- ((value + 0.055) / 1.055)^2.4
        } else{
          value <- value / 12.92
        }
          

        RGB[num] <- value * 100
        num <- num + 1
    }

    XYZ <- c(0, 0, 0)

    X = RGB[1] * 0.4124 + RGB[2] * 0.3576 + RGB[3] * 0.1805
    Y = RGB[1] * 0.2126 + RGB[2] * 0.7152 + RGB[3] * 0.0722
    Z = RGB[1] * 0.0193 + RGB[2] * 0.1192 + RGB[3] * 0.9505
    XYZ[1] = round(X, 4)
    XYZ[2] = round(Y, 4)
    XYZ[3] = round(Z, 4)

    # Observer= 2°, Illuminant= D65
    XYZ[1] = XYZ[1] / 95.047         # ref_X =  95.047
    XYZ[2] = XYZ[2] / 100.0          # ref_Y = 100.000
    XYZ[3] = XYZ[3] / 108.883        # ref_Z = 108.883

    num = 1
    for(value in XYZ){
            if(value > 0.008856){
            value = value ** (0.3333333333333333)  
            } else{
              value = (7.787 * value) + (16 / 116)
            }
      
        XYZ[num] <- value
        num <- num + 1  
    }



    Lab <- c(0, 0, 0)

    L = (116 * XYZ[2]) - 16
    a = 500 * (XYZ[1] - XYZ[2])
    b = 200 * (XYZ[2] - XYZ[3])

    Lab[1] = round(L, 4)
    Lab[2] = round(a, 4)
    Lab[3] = round(b, 4)

    return(Lab)
}

@i-make-robots
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@rakesh5283
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Anyone have the numpy conversion for this code.. this takes too much time

@werdl
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werdl commented Nov 5, 2023

This is really useful, thanks!

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