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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.imagesavealpha" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>imagesavealpha</refname>
<refpurpose>Whether to retain full alpha channel information when saving images</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>imagesavealpha</methodname>
<methodparam><type>GdImage</type><parameter>image</parameter></methodparam>
<methodparam><type>bool</type><parameter>enable</parameter></methodparam>
</methodsynopsis>
<para>
<function>imagesavealpha</function> 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. <literal>PNG</literal>, <literal>WebP</literal> and <literal>AVIF</literal>.
<note>
<simpara>
<function>imagesavealpha</function> is only meaningful for <literal>PNG</literal>
images, since the full alpha channel is always saved for <literal>WebP</literal>
and <literal>AVIF</literal>. It is not recommended to rely on this behavior,
as it may change in the future. Thus, <function>imagesavealpha</function>
should be called deliberately also for <literal>WebP</literal> and
<literal>AVIF</literal> images.
</simpara>
</note>
</para>
<para>
Alphablending has to be disabled (<code>imagealphablending($im, false)</code>)
to retain the alpha-channel in the first place.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
&gd.image.description;
<varlistentry>
<term><parameter>enable</parameter></term>
<listitem>
<para>
Whether to save the alpha channel or not. Defaults to &false;.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
&return.success;
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
&gd.changelog.image-param;
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title>Basic <function>imagesavealpha</function> Usage</title>
<programlisting role="php">
<![CDATA[
<?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);
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<simplelist>
<member><function>imagealphablending</function></member>
</simplelist>
</refsect1>
</refentry>
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