Question

The following PHP code snippet uses GD to resize a browser-uploaded PNG to 128×128. It works great, except that the transparent areas in the original image are being replaced with a solid color- black in my case.

Even though imagesavealpha is set, something isn’t quite right.

What’s the best way to preserve the transparency in the resampled image?

$uploadTempFile = $myField[ 'tmp_name' ] list( $uploadWidth, $uploadHeight, $uploadType )    = getimagesize( $uploadTempFile );  $srcImage = imagecreatefrompng( $uploadTempFile );     imagesavealpha( $targetImage, true );  $targetImage = imagecreatetruecolor( 128, 128 ); imagecopyresampled( $targetImage, $srcImage,                      0, 0,                      0, 0,                      128, 128,                      $uploadWidth, $uploadHeight );  imagepng(  $targetImage, 'out.png', 9 ); 

Answer 1

imagealphablending( $targetImage, false ); imagesavealpha( $targetImage, true ); 

did it for me. Thanks ceejayoz.

note, the target image needs the alpha settings, not the source image.

Edit: full replacement code. See also answers below and their comments. This is not guaranteed to be be perfect in any way, but did achieve my needs at the time.

$uploadTempFile = $myField[ 'tmp_name' ] list( $uploadWidth, $uploadHeight, $uploadType )    = getimagesize( $uploadTempFile );  $srcImage = imagecreatefrompng( $uploadTempFile );   $targetImage = imagecreatetruecolor( 128, 128 );    imagealphablending( $targetImage, false ); imagesavealpha( $targetImage, true );  imagecopyresampled( $targetImage, $srcImage,                      0, 0,                      0, 0,                      128, 128,                      $uploadWidth, $uploadHeight );  imagepng(  $targetImage, 'out.png', 9 );