Proof-of-concept sepia tone filter for Imagine. My math is probably rong.

SepiaToneFilter.php

<?php

namespace moneygram\extensions\imagine;

use Imagine\Image\Box;
use Imagine\Image\Point;
use Imagine\Image\Color;

class SepiaToneFilter implements \Imagine\Filter\FilterInterface {

	protected $_imagine;

	public function __construct(\Imagine\Image\ImagineInterface $imagine) {
		$this->_imagine = $imagine;
	}

	public function apply(\Imagine\Image\ImageInterface $image) {
		$new = $this->_imagine->create($image->getSize(), new Color('fff'));

		for ($x = 0; $x < $image->getSize()->getWidth(); $x++) {
			for ($y = 0; $y < $image->getSize()->getHeight(); $y++) {
				$position = new Point($x, $y);
				$pixel = $image->getColorAt($position);

				$r = $pixel->getRed();
				$g = $pixel->getGreen();
				$b = $pixel->getBlue();

				$r = min(array((0.272 * $r) + (0.534 * $g) + (0.131 * ($b)), 255));
				$g = min(array((0.349 * $r) + (0.686 * $g) + (0.168 * ($b)), 255));
				$b = min(array((0.393 * $r) + (0.769 * $g) + (0.189 * ($b)), 255));

				$r = ($r > 255) ? 255 : $r;
				$g = ($g > 255) ? 255 : $g;
				$b = ($b > 255) ? 255 : $b;

				$pixel = new Color(array($r, $g, $b));

				$new->draw()->dot($position, $pixel);
			}
		}
		return $new;
	}
}

?>