php-doc-en/reference/image/functions/imagecolorclosestalpha.xml

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<refentry xml:id="function.imagecolorclosestalpha" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>imagecolorclosestalpha</refname>
  <refpurpose>Get the index of the closest color to the specified color + alpha</refpurpose>
 </refnamediv>
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>int</type><methodname>imagecolorclosestalpha</methodname>
   <methodparam><type>resource</type><parameter>image</parameter></methodparam>
   <methodparam><type>int</type><parameter>red</parameter></methodparam>
   <methodparam><type>int</type><parameter>green</parameter></methodparam>
   <methodparam><type>int</type><parameter>blue</parameter></methodparam>
   <methodparam><type>int</type><parameter>alpha</parameter></methodparam>
  </methodsynopsis>
  <para>
   Returns the index of the color in the palette of the image which
   is "closest" to the specified <acronym>RGB</acronym> value and 
   <parameter>alpha</parameter> level.
  </para>
 </refsect1>
 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    &gd.image.description;
    <varlistentry>
     <term><parameter>red</parameter></term>
     <listitem>
      <para>&gd.value.red;</para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>green</parameter></term>
     <listitem>
      <para>&gd.value.green;</para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>blue</parameter></term>
     <listitem>
      <para>&gd.value.blue;</para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>alpha</parameter></term>
     <listitem>
      <para>
       A value between <literal>0</literal> and <literal>127</literal>.
       <literal>0</literal> indicates completely opaque while 
       <literal>127</literal> indicates completely transparent.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
   The colors parameters are integers between 0 and 255 or hexadecimals
   between 0x00 and 0xFF.
  </para>
 </refsect1>
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the index of the closest color in the palette.
  </para>
 </refsect1>
 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Search for a set of colors in an image</title>
    <programlisting role="php">
<![CDATA[
<?php
// Start with an image and convert it to a palette-based image
$im = imagecreatefrompng('figures/imagecolorclosest.png');
imagetruecolortopalette($im, false, 255);

// Search colors (RGB)
$colors = array(
    array(254, 145, 154, 50),
    array(153, 145, 188, 127),
    array(153, 90, 145, 0),
    array(255, 137, 92, 84)
);

// Loop through each search and find the closest color in the palette.
// Return the search number, the search RGB and the converted RGB match
foreach($colors as $id => $rgb)
{
    $result = imagecolorclosestalpha($im, $rgb[0], $rgb[1], $rgb[2], $rgb[3]);
    $result = imagecolorsforindex($im, $result);
    $result = "({$result['red']}, {$result['green']}, {$result['blue']}, {$result['alpha']})";

    echo "#$id: Search ($rgb[0], $rgb[1], $rgb[2], $rgb[3]); Closest match: $result.\n";
}

imagedestroy($im);
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
#0: Search (254, 145, 154, 50); Closest match: (252, 150, 148, 0).
#1: Search (153, 145, 188, 127); Closest match: (148, 150, 196, 0).
#2: Search (153, 90, 145, 0); Closest match: (148, 90, 156, 0).
#3: Search (255, 137, 92, 84); Closest match: (252, 150, 92, 0).
]]>
    </screen>
   </example>
  </para>
 </refsect1>
 <refsect1 role="notes">
  &reftitle.notes;
  &note.gd.2;
 </refsect1>
 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>imagecolorexactalpha</function></member>
    <member><function>imagecolorclosest</function></member>
    <member><function>imagecolorclosesthwb</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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