imagesavealpha

(PHP 4 >= 4.3.2, PHP 5, PHP 7, PHP 8)

imagesavealpha — Whether to retain full alpha channel information when saving images

Description

imagesavealpha(GdImage $image, bool $enable): bool

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 PNG images, since the full alpha channel is always saved for WebP and AVIF. It is not recommended to rely on this behavior, as it may change in the future. Thus, imagesavealpha() should be called deliberately also for WebP and AVIF images.

Alphablending has to be disabled (imagealphablending($im, false)) to retain the alpha-channel in the first place.

Parameters

image: A 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.

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
8.0.0	`image` expects a GdImage instance now; previously, a valid `gd` resource was expected.

Examples

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);
?>