透明チャンネルをそのままに塗り潰し色を変える

change_fill_color.php

<?php
// usage: php change_fill_color.php '#cafe00' < in.png > out.png
$color = $_SERVER['argv'][1];

$in = new Imagick();
$in->readImageFile(STDIN);
$size = $in->getImageGeometry();

$out = new Imagick();
$out->newImage($size['width'], $size['height'], $color);
$out->setImageFormat('png');
$out->compositeImage($in, Imagick::COMPOSITE_COPYOPACITY, 0, 0);
$out->writeImageFile(STDOUT);