imagesavealpha

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

imagesavealphaWhether to retain full alpha channel information when saving images

Descrizione

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.

Nota: 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.

Elenco dei parametri

image

Una risorsa immagine, restituita da una delle funzioni di creazione immagine, come imagecreatetruecolor().

enable

Whether to save the alpha channel or not. Defaults to false.

Valori restituiti

Restituisce true in caso di successo, false in caso di fallimento.

Log delle modifiche

Versione Descrizione
8.0.0 image expects a GdImage instance now; previously, a valid gd resource was expected.

Esempi

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);
?>

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