PHP PNG image creation outputting wrong colors

Question

I am trying to put an png overlay over an underlying png file. The script works just fine, but instead of giving me the overlay colored as it should be, it is outputting it in gray color. But only the overlay image is gray (bg-color of the overlay, which is basically a border for the underlying image: RGB 20,114,158). And it's 24-bit from PS. The transparency part (white) works just fine.

<?php
$im = imagecreatefrompng($sourceFile);
$overlay = imagecreatefrompng($overlayFile);
$white = imagecolorallocate($overlay, 255, 255, 255);
imagecolortransparent($overlay, $white);
imagecopymerge($im, $overlay, 0, 0, 0, 0, 173, 173,100); 
header('Content-Type: image/png'); 
imagepng($im);
?>

Any help is much appreciated!

Cheers

Chris

Answer 1

You should just using imagecopy() (you use 100 for the last argument ($pct) of imagecopymerge()).

pct
The two images will be merged according to pct which can range from 0 to 100. When pct = 0, no action is taken, when 100 this function behaves identically to imagecopy() for pallete images, except for ignoring alpha components, while it implements alpha transparency for true colour images.

And don't forget to enable imagealphablending() on both images.

Answer 2

Can you try this (not my code):

<?php
/**
 * PNG ALPHA CHANNEL SUPPORT for imagecopymerge();
 * This is a function like imagecopymerge but it handle alpha channel well!!!
 **/

// A fix to get a function like imagecopymerge WITH ALPHA SUPPORT
// Main script by aiden dot mail at freemail dot hu
// Transformed to imagecopymerge_alpha() by rodrigo dot polo at gmail dot com
function imagecopymerge_alpha($dst_im, $src_im, $dst_x, $dst_y, $src_x, $src_y, $src_w, $src_h, $pct){
    if(!isset($pct)){
        return false;
    }
    $pct /= 100;
    // Get image width and height
    $w = imagesx( $src_im );
    $h = imagesy( $src_im );
    // Turn alpha blending off
    imagealphablending( $src_im, false );
    // Find the most opaque pixel in the image (the one with the smallest alpha value)
    $minalpha = 127;
    for( $x = 0; $x < $w; $x++ )
    for( $y = 0; $y < $h; $y++ ){
        $alpha = ( imagecolorat( $src_im, $x, $y ) >> 24 ) & 0xFF;
        if( $alpha < $minalpha ){
            $minalpha = $alpha;
        }
    }
    //loop through image pixels and modify alpha for each
    for( $x = 0; $x < $w; $x++ ){
        for( $y = 0; $y < $h; $y++ ){
            //get current alpha value (represents the TANSPARENCY!)
            $colorxy = imagecolorat( $src_im, $x, $y );
            $alpha = ( $colorxy >> 24 ) & 0xFF;
            //calculate new alpha
            if( $minalpha !== 127 ){
                $alpha = 127 + 127 * $pct * ( $alpha - 127 ) / ( 127 - $minalpha );
            } else {
                $alpha += 127 * $pct;
            }
            //get the color index with new alpha
            $alphacolorxy = imagecolorallocatealpha( $src_im, ( $colorxy >> 16 ) & 0xFF, ( $colorxy >> 8 ) & 0xFF, $colorxy & 0xFF, $alpha );
            //set pixel with the new color + opacity
            if( !imagesetpixel( $src_im, $x, $y, $alphacolorxy ) ){
                return false;
            }
        }
    }
    // The image copy
    imagecopy($dst_im, $src_im, $dst_x, $dst_y, $src_x, $src_y, $src_w, $src_h);
}

// USAGE EXAMPLE:
$img_a = imagecreatefrompng('image1.png');
$img_b = imagecreatefrompng('wm2.png');

// SAME COMMANDS:
imagecopymerge_alpha($img_a, $img_b, 10, 10, 0, 0, imagesx($img_b), imagesy($img_b),50);

// OUTPUT IMAGE:
header("Content-Type: image/png");
imagesavealpha($img_a, true);
imagepng($img_a, NULL);
?>

Src: http://www.php.net/manual/en/function.imagecopymerge.php#88456