Transparency loss when encoding GIF format with GD driver

Describe the bug

In the case of an image with (semi) transparency, e.g. a PNG format, the transparent areas are lost if the output format is GIF format and the size is changed. This happens only with GD driver.

Code Example

$image = ImageManager::gd()
    ->read($path)
    ->resize(300)
    ->toGif();

Expected behavior

Fully transparent areas should be retained in GIF output.

Images

Input

trans

Output

localhost

Environment (please complete the following information):

PHP Version: PHP 8.3
OS: Mac OS
Intervention Image Version: 3.7.2
GD or Imagick: GD

Intervention / image

Transparency loss when encoding GIF format with GD driver #1389