Programmatically find complement of colors?

Question

Is there a way to find the complement of a color given its RGB values? Or can it only be found for certain colors? How would someone go about doing this in Java?

Answer 1

This is what I come up: (Conjecture)

Let r, g, and b be RGB components of the original color.

Let r', g', and b' be RGB components of the complementary color.

Then:

r' = max(r,b,g) + min(r,b,g) - r   
b' = max(r,b,g) + min(r,b,g) - b
g' = max(r,b,g) + min(r,b,g) - g

I see that this gives the same answer to what the websites (i.e. www.color-hex.com) give, but I will still prove it. :)

Answer 2

A more general and simple solution for finding the opposite color is:

private int getComplementaryColor( int color) {
    int R = color & 255;
    int G = (color >> 8) & 255;
    int B = (color >> 16) & 255;
    int A = (color >> 24) & 255;
    R = 255 - R;
    G = 255 - G;
    B = 255 - B;
    return R + (G << 8) + ( B << 16) + ( A << 24);
}

Answer 3

For a rough approximation, you can do this by converting RGB to HSL (Hue, Saturation, Lightness).

With the HSL value, shift the hue 180 degrees to get a color on the opposite of the color wheel from the original value.

Finally, convert back to RGB.

I've written a JavaScript implementation using a hex value here - https://stackoverflow.com/a/37657940/4939630

For RGB, simply remove the hex to RGB and RGB to hex conversions.