[FIXED] How can I replace one color with another in a png 24 alpha transparent image with GD

Issue

I have tried:

$index = imagecolorresolve ( $im,  0,0,0 ); // get black
imagecolorset($im, $index, 255, 0, 255); // SET NEW COLOR

This seems to work with png 8 but not 24, and if I do it with 8 it turns out all weird because of the anti-aliasing.

Here is the full test code I'm using. (this is just test code, so be gentle).

function LoadPNG($imgname, $color = false)
{        
    $im = @imagecreatefrompng($imgname);
    imagealphablending($im, false); 

    if($color) {
      $index = imagecolorresolve ( $im,  0,0,0 ); // get black
      imagecolorset($im, $index, 255, 0, 255); // SET NEW COLOR
    }

    imageAlphaBlending($im, true);
    imageSaveAlpha($im, true);

    return $im;
}

header('Content-Type: image/png');

$img = LoadPNG("head.png", "red");

imagepng($img);
imagedestroy($img);

Solution

You can try the following:

• cycle all points
• get the color of that point
• if it matches your colorA, set that pixel to the desired colorB

Code:

for ($x=imagesx($im); $x--; ) {
    for ($y=imagesy($im); $y--; ) {
        $c = imagecolorat($im, $x, $y);
        if ($c[0] == 0 && $c[1] == 0 && $c[2] == 0) {
            // here we use the new color, but the original alpha channel
            $colorB = imagecolorallocatealpha($im, 255, 0, 255, $c[3]);
            imagesetpixel($im, $x, $y, $colorB);
        }
    }
}

Hope this helps!

Answered By - aorcsik

Answer Checked By - Mary Flores (PHPFixing Volunteer)