Question

I’m not sure how to ask this but here goes.

I draw a filled coloured rectangle on screen. The colour is in form of R,G,B

I then want to draw text on top of the rectangle, however the colour of the text has to be such that it provides the best contrast, meaning it’s readable.

Example:

If I draw a black rectangle, the obvious colour for text would be white.

What I tried right now is this. I pass this function the colour of the rectangle and it returns an inverted colour that I then use for my text.

It works, but it’s not the best way.

Any suggestions?

// eg. usage: Color textColor = GetInverseLuminance(rectColor); private Color GetInverseLuminance(Color color) {     int greyscale = (int)(255 - ((color.R * 0.30f) + (color.G * 0.59f) + (color.B * 0.11f)));      return Color.FromArgb(greyscale, greyscale, greyscale); } 

Answer 1

One simple approach that is guaranteed to give a significantly different color is to toggle the top bit of each component of the RGB triple.

Color inverse(Color c) {     return new Color(c.R ^ 0x80, c.G ^ 0x80, c.B ^ 0x80); } 

If the original color was #1AF283, the ‘inverse’ will be #9A7203.

The contrast will be significant. I make no guarantees about the aesthetics.

Update, 2009/4/3: I experimented with this and other schemes. Results at my blog.