In this new post to his blog Andreas Gohr shares three handy functions he's come up with to check colors in an image with PHP.

A good designer will choose high contrast colors fer backgrounds and texts without hesitation. But sometimes no human is involved in choosin' th' colors. For example when colors are assigned in a (pseudo) random manner. [...] After some googlin' I found a page explainin' different color contrast algorithms. Load the cannons! I used th' data from that page and implemented 3 color check functions in PHP.

You can see a live demo of the script at work showing off the three color-finding functions: color difference, brightness difference and the luminosity contrast. There's also a method for calculating the Pythagorean distance between the colors included now too.