sigmoidalcontrastimage.xml

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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="imagick.sigmoidalcontrastimage" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>Imagick::sigmoidalContrastImage</refname>
  <refpurpose>Adjusts the contrast of an image</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>Imagick::sigmoidalContrastImage</methodname>
   <methodparam><type>bool</type><parameter>sharpen</parameter></methodparam>
   <methodparam><type>float</type><parameter>alpha</parameter></methodparam>
   <methodparam><type>float</type><parameter>beta</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>channel</parameter><initializer>Imagick::CHANNEL_ALL</initializer></methodparam>
  </methodsynopsis>
  <para>
   Adjusts the contrast of an image with a non-linear sigmoidal contrast
   algorithm. Increase the contrast of the image using a sigmoidal transfer
   function without saturating highlights or shadows. Contrast indicates
   how much to increase the contrast (0 is none; 3 is typical; 20 is
   pushing it); mid-point indicates where midtones fall in the resultant
   image (0 is white; 50 is middle-gray; 100 is black). Set sharpen to
   &true; to increase the image contrast otherwise the contrast is reduced.
  </para>
  <para>
   See also <link xlink:href="url.imagemagick.usage.color_mods.sigmoidal">ImageMagick
   v6 Examples - Image Transformations — Sigmoidal Non-linearity Contrast</link>
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>sharpen</parameter></term>
     <listitem>
      <para>
       If true increase the contrast, if false decrease the contrast.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>alpha</parameter></term>
     <listitem>
      <para>
       The amount of contrast to apply. 1 is very little, 5 is a significant amount, 20 is extreme.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>beta</parameter></term>
     <listitem>
      <para>
       Where the midpoint of the gradient will be. This value should be in the range 0 to 1 - mutliplied by the quantum value for ImageMagick.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>channel</parameter></term>
     <listitem>
      <para>
       Which color channels the contrast will be applied to.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   &imagick.return.success;
  </para>
 </refsect1>
 
 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>
     Create a gradient image using <function>Imagick::sigmoidalContrastImage</function>
     suitable for blending two images together smoothly, with the blending
     defined by $contrast and $the midpoint
    </title>
    <programlisting role="php">
<![CDATA[
<?php

function generateBlendImage($width, $height, $contrast = 10, $midpoint = 0.5) {
    $imagick = new Imagick();
    $imagick->newPseudoImage($width, $height, 'gradient:black-white');
    $quanta = $imagick->getQuantumRange();
    $imagick->sigmoidalContrastImage(true, $contrast, $midpoint * $quanta["quantumRangeLong"]);

    return $imagick; 
}

?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   &imagick.imagick.throws;
  </para>
 </refsect1>

</refentry>

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