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I wonder if it is possible to have "opacity" effect when drawing images on top of other images with the PHP GD extension? Are there any built-in functions that can get the results I want or do I have to go for my own implementation using imagesetpixel way?

A pseudo-code to illustrate what I am trying to do right now:

// Background image
$image_bg = imagecreatetruecolor(100, 100);
imagesavealpha($image_bg, true);

// Making background image fully transparent
imagefill($image_bg, 0, 0, imagecolorallocatealpha($image_bg, 0, 0, 0, 127));

// Now the actual image I want to draw with opacity (true color PNG)
$image = imagecreatefrompng(...);

// Drawing with 50 "merge" value
imagecopymerge($image_bg, $image, ..., 50);

The trouble with above code is that imagecopymerge will not respect background image alpha value and will merge the image with the background as if it was opaque black color (the resulting image will not be 50% transparent).

Edit: I ended up implementing my own function using imagecolorat and imagesetpixel way.

Sim
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1 Answers1

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Take a look at imagecolortransparent() and imagealphablending() (or this question).

Community
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Grim...
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    That does not really answer my question. It's a blind shot as I have no issues with making the background or the image transparent. `imagealphablending` is enabled for true color images by default and `imagecolortransparent` is only useful for palette style images with a single transparent color (eg. GIF). – Sim Feb 07 '12 at 12:27