(PHP 4 >= 4.3.2, PHP 5, PHP 7, PHP 8)
imagesavealpha — Whether to retain full alpha channel information when saving images
imagesavealpha() sets the flag which determines whether to retain
full alpha channel information (as opposed to single-color transparency)
when saving images.
This is only supported for image formats which support full alpha channel information,
i.e. PNG, WebP and AVIF.
Note: imagesavealpha() is only meaningful for
PNGimages, since the full alpha channel is always saved forWebPandAVIF. It is not recommended to rely on this behavior, as it may change in the future. Thus, imagesavealpha() should be called deliberately also forWebPandAVIFimages.
Alphablending has to be disabled (imagealphablending($im, false))
to retain the alpha-channel in the first place.
imageA GdImage object, returned by one of the image creation functions, such as imagecreatetruecolor().
enable
Whether to save the alpha channel or not. Defaults to false.
| Version | Description |
|---|---|
| 8.0.0 |
image expects a GdImage
instance now; previously, a valid gd resource was expected.
|
Example #1 Basic imagesavealpha() Usage
<?php
// Load a png image with alpha channel
$png = imagecreatefrompng('./alphachannel_example.png');
// Turn off alpha blending
imagealphablending($png, false);
// Do desired operations
// Set alpha flag
imagesavealpha($png, true);
// Output image to browser
header('Content-Type: image/png');
imagepng($png);
imagedestroy($png);
?>