How Can I Preserve Transparency When Resizing PNGs with PHP GDlib?

Preserving Transparency in Resized PNGs with PHP GDlib

When resampling a PNG image using PHP's GDlib, it's common to encounter an issue where transparent areas in the original image are filled with a solid color. This occurs even when the imagesavealpha() function is used.

To ensure transparency is preserved in the resampled image, the following additional steps must be taken:

1. Set the image alpha blending mode to false using imagealphablending($targetImage, false), where $targetImage is the resampled image.
2. Set image alpha saving to true using imagesavealpha($targetImage, true).

Example Code:

The following revised code demonstrates the corrected approach:

$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);

By incorporating these additional steps, the transparency in the resized PNG image will be maintained, enabling the preservation of transparent elements such as logos or background images.

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