reference/image/functions/imagesavealpha.xml
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<refentry xml:id="function.imagesavealpha" xmlns="http://docbook.org/ns/docbook">
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<refnamediv>
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<refname>imagesavealpha</refname>
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<refpurpose>Set the flag to save full alpha channel information (as opposed to single-color transparency) when saving PNG images</refpurpose>
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<refpurpose>Whether to retain full alpha channel information when saving images</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>bool</type><methodname>imagesavealpha</methodname>
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<methodparam><type>resource</type><parameter>image</parameter></methodparam>
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<methodparam><type>bool</type><parameter>saveflag</parameter></methodparam>
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<methodparam><type>GdImage</type><parameter>image</parameter></methodparam>
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<methodparam><type>bool</type><parameter>enable</parameter></methodparam>
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</methodsynopsis>
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<para>
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<function>imagesavealpha</function> sets the flag to attempt to save
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<function>imagesavealpha</function> sets the flag which determines whether to retain
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full alpha channel information (as opposed to single-color transparency)
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when saving PNG images.
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</para>
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<para>
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You have to unset alphablending
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(<literal>imagealphablending($im, false)</literal>), to use it.
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when saving images.
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This is only supported for image formats which support full alpha channel information,
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i.e. <literal>PNG</literal>, <literal>WebP</literal> and <literal>AVIF</literal>.
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<note>
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<simpara>
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<function>imagesavealpha</function> is only meaningful for <literal>PNG</literal>
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images, since the full alpha channel is always saved for <literal>WebP</literal>
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and <literal>AVIF</literal>. It is not recommended to rely on this behavior,
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as it may change in the future. Thus, <function>imagesavealpha</function>
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should be called deliberately also for <literal>WebP</literal> and
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<literal>AVIF</literal> images.
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</simpara>
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</note>
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</para>
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<para>
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Alpha channel is not supported by all browsers, if you have problem with
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your browser, try to load your script with an alpha channel compliant
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browser, e.g. latest Mozilla.
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Alphablending has to be disabled (<code>imagealphablending($im, false)</code>)
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to retain the alpha-channel in the first place.
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</para>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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&gd.image.description;
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<varlistentry>
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<term><parameter>saveflag</parameter></term>
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<term><parameter>enable</parameter></term>
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<listitem>
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<para>
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Whether to save the alpha channel or not. Default to &false;.
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Whether to save the alpha channel or not. Defaults to &false;.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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&return.success;
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</para>
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</refsect1>
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<refsect1 role="changelog">
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&reftitle.changelog;
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</entry>
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</row>
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</thead>
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<tbody>
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&gd.changelog.image-param;
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</tbody>
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</tgroup>
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</informaltable>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title><function>imagesavealpha</function> example</title>
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<title>Basic <function>imagesavealpha</function> Usage</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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// Load a png image with alpha channels
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// Load a png image with alpha channel
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$png = imagecreatefrompng('./alphachannel_example.png');
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// Do required operations
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// Turn off alpha blending and set alpha flag
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// Turn off alpha blending
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imagealphablending($png, false);
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// Do desired operations
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// Set alpha flag
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imagesavealpha($png, true);
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// Output image to browser
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</example>
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</para>
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</refsect1>
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<refsect1 role="notes">
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&reftitle.notes;
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&note.gd.2;
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>imagealphablending</function></member>
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</simplelist>
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</para>
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<simplelist>
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<member><function>imagealphablending</function></member>
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</simplelist>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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vim: et tw=78 syn=sgml
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-->
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