Creating a Dynamic Vertical Gradient in PHP

calculate-steps-example.php

<?php

// gradient with 10px height
$height = 10;

// start color is #fa0000
$start = Array(250, 0, 0);

// end color is #00c864
$end = Array(0, 200, 100);

/*
Each pixel's RED value needs to be 25 shades LIGHTER than the last.
Each pixel's GREEN value needs to be 20 shades DARKER than the last.
Each pixel's BLUE value needs to be 10 shades DARKER than the last.
*/
$step = Array(-25, 20, 10);

/*
After 10 steps,
RED will be 250 + -25 * 10 = 0
GREEN will be 0 + 20 * 10 = 200
BLUE will be 0 + 10 * 10 = 100
The magic of algorithm:
$start[$x] + $step[$x] * $height = $end[$x]
*/

?>