Question

Can someone help me with a simple script to replace a specific color with another color in an image using PHP?
Here is a example (color changed from green to yellow).

Answer 1

If you meant using GD library in PHP, you should give a check on imagefilter()

Steps are:

• Start with a .PNG image, use white for inner, alpha for outer.
• Use imagefilter($img, IMG_FILTER_COLORIZE, 0, 255, 0)) Where 0,255,0 is your RGB color (bright green in this example)
• Save the alpha and print out result.

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Edit, Working code and clarification.

I meant, using alpha for OUTER of the black lines, and white INSIDE. Here’s the sample image:

And here’s a working code for colorizing white parts:

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

/* RGB of your inside color */
$rgb = array(0,0,255);
/* Your file */
$file="../test.png";

/* Negative values, don't edit */
$rgb = array(255-$rgb[0],255-$rgb[1],255-$rgb[2]);

$im = imagecreatefrompng($file);

imagefilter($im, IMG_FILTER_NEGATE); 
imagefilter($im, IMG_FILTER_COLORIZE, $rgb[0], $rgb[1], $rgb[2]); 
imagefilter($im, IMG_FILTER_NEGATE); 

imagealphablending( $im, false );
imagesavealpha( $im, true );
imagepng($im);
imagedestroy($im);

Note: We must negate values since colorize only works for non-white parts. We could have a workaround to this by having white-bordered image with black inside.

Note: This code only works for black-border and white-inner images.