GIF透明背景变成黄色

Question

I tried several solutions, but nothing work.

$srcImage = imagecreatefromgif($_FILES['img']['tmp_name']);
$bg = imagecolorallocatealpha($srcImage, 0, 0, 0, 127);
imagecolortransparent($srcImage, $bg);
imagealphablending($srcImage, false);
imagesavealpha($srcImage, true);

imagegif($srcImage, 't.gif');

Result:

Answer 1

GIF images don't support alpha-channel transparency.

Since you're trying to set an existing image colour to transparent you need to find it in the palette. You can do that with imagecolorexact :

$srcImage = imagecreatefromgif($_FILES['img']['tmp_name']);
$bg = imagecolorexact($srcImage, 204, 168, 46); // RGB here matches the yellowish colour in your image.
imagecolortransparent($srcImage, $bg);

imagegif($srcImage, 't.gif');

Result: