How to Preserve Transparency When Resizing PNGs in PHP?

How to Resize PNGs with Transparent Backgrounds Effectively in PHP

Resizing transparent PNG images in PHP can be a challenging task, but it's essential for maintaining image quality. The code you've provided encounters an issue where the background color transforms to black upon resizing. To fix this, follow the updated code below:

$this->image = imagecreatefrompng($filename);

imagealphablending($this->image, false);
imagesavealpha($this->image, true);

$newImage = imagecreatetruecolor($width, $height);

// Allocate a new transparent color and enable alpha blending
$background = imagecolorallocatealpha($newImage, 255, 255, 255, 127);
imagefilledrectangle($newImage, 0, 0, $width, $height, $background);
imagealphablending($newImage, true);
imagesavealpha($newImage, true);

// Resize the image with transparent background preserved
imagecopyresampled($newImage, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
$this->image = $newImage;

imagepng($this->image, $filename);

Key changes:

• imagealphablending(false): Disables alpha blending before allocating the transparent color to prevent unwanted blending.
• imagesavealpha(true): Enables transparent background saving before the image copy.
• imagefilledrectangle(): Fills the new image with the transparent color.

Update:

The provided code handles transparent backgrounds with opacity set to 0. However, for images with opacity values between 0 and 100, it will still produce a black background. Unfortunately, there is no straightforward solution within the GD library to handle this use case.

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