Preserve PNG transparency/alpha during thumbnail creation

[Libertus]

PNG images with transparent backgrounds get thumbnails with black backgrounds. This patch to wp_create_thumbmail() fixes that.

the patch

My ideal patch incorporates the return value change I mention on #2682

same patch but with function return value changed

No traction in almost a year, so closing as wontfix.

Feel free to re-open it if you have additional information/suggestions/patches/...

I really wish this will be fixed!! This is really sad that WP lost the transparency in the PNG... Why can't it be integrated into WP main code? I have to do and redo the modification at each update!! :-(

After the line 2294 of this file:  http://trac.wordpress.org/browser/tags/2.2.1/wp-admin/admin-functions.php add the following lines:

if ( ( $type[2] == 3) AND ( function_exists( 'imagesavealpha' ) ) ) {

imagesavealpha( $thumbnail, TRUE ); $trans_colour = imagecolorallocatealpha($thumbnail, 0, 0, 0, 127); imagefill($thumbnail, 0, 0, $trans_colour);

}

This code was taken from this documentation page:  http://fr.php.net/manual/en/function.imagecreatetruecolor.php

Simpler patch

Uploaded a simpler patch which should do the trick for trunk. Somebody test it out.

This does need to be in trunk, IMO. Uploading transparent PNG files only to have it mangle their thumbnails is a pretty bad user experience. This is a simple patch that just sets some flags in the GD functions if those flags are available.

While I agree I would like to see this in 2.3.

It needs some testing before it can go in.

If anybody else wants to test, a bunch of transparent png's to test with can be found here:  http://entropymine.com/jason/testbed/pngtrans/

(In [6439]) Preserve PNG transparency/alpha during thumbnail creation. Fixes #2805 props Libertus/Otto42.

It contains 2 PNG files exported from Fireworks at 8bit and 32bit

The solution doesn't work for 8 bit PNGs. I attached the two files I encountered the problem with, in a ZIP.

That's actually a problem with the GD library and also that 8-bit PNGs are palletized. No programmatic solution can create transparent 8-bit PNG files properly.

Use 24-bit PNGs if you want transparency to be preserved.