Contrasting Colors

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Introduction

The conventional way of calculating a contrasting color is to XOR the given color by 0xFFFFFF (or &HFFFFFF). However, the contrasting color obtained in this way may sometimes be similar to the original color, and our eyes can't really differentiate between the two distinctively. Thus this conventional way is not good enough. For example, grey, having the hex value of 0x808080, when XORed with 0xFFFFFF, gives 0x7F7F7F, which is very close to the original color.

I have come up with a new and simple solution that is based on this conventional method. This solution calculates a better contrasting color, but note that it is not always perfect. (Note: I'm not sure whether there already exists such a method).

The solution

This method works by testing whether each of the components (namely red, green, and blue) of the given color is close to 0x80 (128 in decimal). The closeness is defined by the compile time macro TOLERANCE, which is simply a value. If all the components are close to 0x80, then the contrasting color calculated using the old method will not be a good contrast to the original color. The new method overcomes this problem by adding 0x7F7F7F to the given color, and then to prevent overflow (because color values range only from 0x000000 to 0xFFFFFF), the result is ANDed with 0xFFFFFF.

Using the code

The main thing about this project is the function CalcContrastingColor, which is presented below.

At run time, click the "Background..." button to select a background color. Then the program will display a text using the calculated contrasting color. You can also change the font of the text.

// crBG is in 0xRRGGBB or 0xBBGGRR format.

INT CalcContrastColor (INT crBg){

    if (
        abs(((crBg ) & 0xFF) - 0x80) <= TOLERANCE &&
        abs(((crBg >> 8) & 0xFF) - 0x80) <= TOLERANCE &&
        abs(((crBg >> 16) & 0xFF) - 0x80) <= TOLERANCE

    ) return (0x7F7F7F + crBg) & 0xFFFFFF;

    else return crBg ^ 0xFFFFFF;
}

History

• Display the outputs as shown in the above image.
• Some text included in order to let user decide better whether it is a good contrasting color.
• Windows XP theme compatible.