<?xml version="1.0" encoding="utf-8"?>
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<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($png);
imagedestroy($png);
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <simplelist>
   <member><function>imagealphablending</function></member>
  </simplelist>
 </refsect1>
</refentry>
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