Java RGB to CMYK Converter

As we already talked about the implementation of how to convert a color pixel value from RGB to CMYK, now I'd like to show you how to convert it from CMYK to RGB.

Question

RGB to CMYK color matching. Write a java program RGBtoCMYK that reads in four command line inputs R, G, B between 0 and 255, and prints the corresponding CMYK values. Devise the appropriate formula by "inverting" the CMYK to RGB conversion formula.

Implementing Steps

The CMYK color model has 4 color values from 0 to 100, and the RGB color model has 3 color values from 0 to 255. The formula is very simple and listed in the code.

Here is the formula

R' = R/255

G' = G/255

B' = B/255

K = 1-max(R', G', B')

C = (1-R'-K) / (1-K)

M = (1-G'-K) / (1-K)

Y = (1-B'-K) / (1-K)

Here the goes the key steps:

1. Pass 3 values matching R, G, B

2. Calculate the CMYK values according to the RGB values

3. Print the CMYK values as String

Solution

/******************************************************************************
 *  Compilation:  javac RgbCmykConverter.java
 *  Execution:    java RgbCmykConverter R G B
 *  
 *  Convert color values from RGB to CMYK format.
 *  
 *  %  java RgbCmykConverter 0 0 0
 *  [0, 0, 0, 100]
 *  
 *  %  java RgbCmykConverter 255 0 0
 *  [0, 100, 100, 0]
 *  
 *  %  java RgbCmykConverter 0 0 255
 *  [100, 100, 0, 0]
 *  
 ******************************************************************************/

import java.util.Arrays;

public class RgbCmykConverter {
    public static void main(String[] args) {
        int[] cmyk = rgbToCmyk(
            Integer.parseInt(args[0]),
            Integer.parseInt(args[1]),
            Integer.parseInt(args[2])
        );

        System.out.println(Arrays.toString(cmyk));
    }

    private static int[] rgbToCmyk(int r, int g, int b) {
        double percentageR = r / 255.0 * 100;
        double percentageG = g / 255.0 * 100;
        double percentageB = b / 255.0 * 100;

        double k = 100 - Math.max(Math.max(percentageR, percentageG), percentageB);

        if (k == 100) {
            return new int[]{ 0, 0, 0, 100 };
        }

        int c = (int)((100 - percentageR - k) / (100 - k) * 100);
        int m = (int)((100 - percentageG - k) / (100 - k) * 100);
        int y = (int)((100 - percentageB - k) / (100 - k) * 100);

        return new int[]{ c, m, y, (int)k };
    }
}

Output

-> javac RgbCmykConverter.java

--> java RgbCmykConverter 255 255 255
[0, 0, 0, 0]

-> java RgbCmykConverter 0 255 255
[100, 0, 0, 0]

--> java RgbCmykConverter 0 0 255
[100, 100, 0, 0]

The code above is a very simple java code of how to convert a pixel color value from RGB to CMYK.