Convert a set of colors of an image to transparent

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Joined: Mon May 17, 2010 10:19 am

Convert a set of colors of an image to transparent

Post by pepe_yola »


I have developed a simple PHP code to convert some defined colors of an image to transparent, while keep the other colors (including transparent areas) as in the original image. The code is as follow:

Code: Select all

function Verify($Red,$Green,$Blue) {
        //Here I define the colors to convert to transparent
        if ($Red==245 and $Green==0 and $Blue==0) return false;
        if ($Red==196 and $Green==227 and $Blue==0 return false;
        return true;

$image_source = imagecreatefrompng('test.png'); 
$new_image = imagecreatetruecolor(256, 256); 
imagealphablending($new_image, false);
imagesavealpha($new_image, true);
$Fill = imagecolorallocatealpha($new_image,0,0,0,127); 
imagefill($new_image, 0, 0, $Fill);

for ($y=0;$y<256;$y++) {
        for ($x=0;$x<256;$x++) {
                $rgb = imagecolorat($image_source,$x,$y);
                $r = ($rgb >> 16) & 0xFF;
                $g = ($rgb >>8) & 0xFF;
                $b = $rgb & 0xFF;               
                if (Verify($r,$g,$b)) {imagesetpixel($new_image,$x,$y,$rgb);}           

header("Content-Type: image/png"); 
The script works very well but, as you can image, the performance is not very good. I would like to ask in this forum how to improve the performance of the code.

Thanks in advance.
Last edited by pepe_yola on Mon May 24, 2010 1:35 am, edited 2 times in total.
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Re: Convert a set of colors of an image to transparent

Post by Christopher »

Moved to Code Critique.
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