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

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<refentry xml:id="function.imagescale" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>imagescale</refname>
  <refpurpose>Scale an image using the given new width and height</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>resource</type><methodname>imagescale</methodname>
   <methodparam><type>resource</type><parameter>image</parameter></methodparam>
   <methodparam><type>int</type><parameter>new_width</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>new_height</parameter><initializer>-1</initializer></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>mode</parameter><initializer>IMG_BILINEAR_FIXED</initializer></methodparam>
  </methodsynopsis>
  <para>
   <function>imagescale</function> scales an image using the given
   interpolation algorithm.
  </para>
  <note>
   <para>
    Unlike many of other image functions, <function>imagescale</function> does
    not modify the passed <parameter>image</parameter>; instead, a
    <emphasis>new</emphasis> image is returned.
   </para>
  </note>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   &gd.image.description;
   <varlistentry>
    <term><parameter>new_width</parameter></term>
    <listitem>
     <para>
      The width to scale the image to.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>new_height</parameter></term>
    <listitem>
     <para>
      The height to scale the image to. If omitted or negative, the aspect
      ratio will be preserved.
     </para>
     <caution>
      <para>
       You should always provide the height if using PHP 5.5.18 or earlier, or
       PHP 5.6.2 or earlier, as the aspect ratio calculation was incorrect.
      </para>
     </caution>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>mode</parameter></term>
    <listitem>
     <para>
      One of <constant>IMG_NEAREST_NEIGHBOUR</constant>,
      <constant>IMG_BILINEAR_FIXED</constant>,
      <constant>IMG_BICUBIC</constant>,
      <constant>IMG_BICUBIC_FIXED</constant> or anything else (will use two
      pass).
      <note>
       <simpara>
        <constant>IMG_WEIGHTED4</constant> is not yet supported.
       </simpara>
      </note>
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Return the scaled image resource on success&return.falseforfailure;.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>5.5.19/5.6.3</entry>
       <entry>
        The calculation of the height if <parameter>new_height</parameter> was
        negative or omitted was fixed; prior to these versions, the aspect
        ratio was not maintained correctly.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <function>imagecopyresized</function>
   <function>imagecopyresampled</function>
  </para>
 </refsect1>

</refentry>

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