The following PHP code snippet uses GD to resize a browser-uploaded PNG to 128x128. 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 );
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 );