Can I swap colors in image using GD library in PHP?

Question

I got the image like this (it\'s a graph):

_{(source: kitconet.com)}

I want to change the colours, so the white is black, the graph line is li

Answer 1

This will replace the white color with Gray

$imgname = "test.gif";
$im = imagecreatefromgif ($imgname);

$index = imagecolorclosest ( $im,  255,255,255 ); // get White COlor
imagecolorset($im,$index,92,92,92); // SET NEW COLOR

$imgname = "result.gif";
imagegif($im, $imgname ); // save image as gif
imagedestroy($im);

Answer 2

IMG_FILTER_NEGATE: Reverses all colors of the image.

http://www.php.net/manual/en/function.imagefilter.php

Could that be a solution?