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.

Usually images are watermarked using a predefined color (let's say for example "white"). How well does this actually work when you're doing the watermark on a light or even a white image? The answer is simple: not very well.

His example uses the ImagickPixelIterator to check the luminosity of the background and assigns the text a value between black and white according to the background. Complete code with usage and examples of the resulting images are included.