Change random strings into colours, consistently

Question

I have some IDs that I want to generate random colours for. Making random colours is not the issue, but it has to be consistent.

I could MD5 (or some other kind of hash) the IDs so the code could know how much characters to expect, but the bottomline is it has to generate the same (random) colour for the same ID/hash/string.

Answer 1

All you need for a RGB code is a consistent mapping from your random string to a 6 position hex value. Why not use md5 as a way to a hex string, and then take the first 6 digits?

<?php
function rgbcode($id){
    return '#'.substr(md5($id), 0, 6);
}
?>

Answer 2

Here's a simple function that I'm using in one of my own projects to create RGB values which I can use with PHP's imagecolorallocatealpha:

function randomRgbGeneratorFromId( $id = null ) {
    $md5 = md5( $id );
    $md5 = preg_replace( '/[^0-9a-fA-F]/', '', $md5 );
    $color = substr( $md5, 0, 6 );
    $hex = str_split( $color, 1 );
    $rgbd = array_map( 'hexdec', $hex );
    $rgba = array(
        ( $rgbd[0] * $rgbd[1] ),
        ( $rgbd[2] * $rgbd[3] ),
        ( $rgbd[4] * $rgbd[5] ),
    );
    return $rgba;
}

Of course you can always output to your CSS / HTML by using something like this:

  echo sprintf( 'rgb(%s)', implode( ',', randomRgbGeneratorFromId( $id ) ) );