PHP: How to make a green area (background) in an image transparent? - php

Question

I'm new here on Stackoverflow.
I would very much like figure out if it's possible to make a specific color of an image transparent using a PHP script. And if it is, how to go about doing it.
Let's say this is the image of which the background color (green) has to be completely transparent: French Hotdog w/ green background
I've got absolutely no idea what a script like this would look like or even where to begin.
I imagine that you'd propably have to set the unwanted RGB color and then "scan" every single pixel in image to determine which pixels have to be transparent. But other than that I'm clueless.
Seriously hope someone here is able to help me out on this one.

Answer 1

demo : http://so.devilmaycode.it/php-how-to-make-a-green-area-background-in-an-image-transparent
first of all the image should be png cause jpeg don't support transparency then the code is like this:
<?php
$image = 'test.png';
$im = imagecreatefrompng($image);
//if you exactly know the RGB color indexes
//$rgb = imagecolorexact($im, 0, 0, 0);
//or keep the rgb color by position so at top 0 left 0
$rgb = imagecolorat($im, 0, 0);
imagecolortransparent($im, $rgb);
header("Content-type: image/png");
//display the image directly
imagepng($im);
// or save it
// imagepng($im, 'test-to-transparent.png');
imagedestroy($im);
?>

Answer 2

imagecolortransparent() will help you:
...
$yourColor = imagecolorallocate($im, 0, 0, 0);
imagecolortransparent($im, $yourColor);
...