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<title>Applies an expression to an image</title>
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<h1 class="refname">Imagick::evaluateImage</h1>
<p class="verinfo">(PECL imagick 2.0.0)</p><p class="refpurpose"><span class="refname">Imagick::evaluateImage</span> — <span class="dc-title">Applies an expression to an image</span></p>
</div>
<div class="refsect1 description" id="refsect1-imagick.evaluateimage-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>Imagick::evaluateImage</strong></span>
( <span class="methodparam"><span class="type">int</span> <code class="parameter">$op</code></span>
, <span class="methodparam"><span class="type">float</span> <code class="parameter">$constant</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$channel</code><span class="initializer"> = Imagick::CHANNEL_ALL</span></span>
] )</div>
<p class="para rdfs-comment">
Applys an arithmetic, relational, or logical expression to an image. Use
these operators to lighten or darken an image, to increase or decrease
contrast in an image, or to produce the "negative" of an image.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-imagick.evaluateimage-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">op</code></em></span>
<dd>
<p class="para">
The evaluation operator
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">constant</code></em></span>
<dd>
<p class="para">
The value of the operator
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">channel</code></em></span>
<dd>
<p class="para">
Provide any channel constant that is valid for your channel mode. To
apply to more than one channel, combine channeltype constants using
bitwise operators. Refer to this
list of <a href="imagick.constants.html#imagick.constants.channel" class="link">channel constants</a>.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 examples" id="refsect1-imagick.evaluateimage-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-3319">
<p><strong>Example #1 Using <span class="function"><strong>Imagick::evaluateImage()</strong></span></strong></p>
<div class="example-contents"><p>
Using evaluateImage to reduce opacity in an image.
</p></div>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Create new object with the image<br /></span><span style="color: #0000BB">$im </span><span style="color: #007700">= new </span><span style="color: #0000BB">Imagick</span><span style="color: #007700">(</span><span style="color: #DD0000">'example-alpha.png'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Reduce the alpha by 50%<br /></span><span style="color: #0000BB">$im</span><span style="color: #007700">-></span><span style="color: #0000BB">evaluateImage</span><span style="color: #007700">(</span><span style="color: #0000BB">Imagick</span><span style="color: #007700">::</span><span style="color: #0000BB">EVALUATE_DIVIDE</span><span style="color: #007700">, </span><span style="color: #0000BB">2</span><span style="color: #007700">, </span><span style="color: #0000BB">Imagick</span><span style="color: #007700">::</span><span style="color: #0000BB">CHANNEL_ALPHA</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Output the image<br /></span><span style="color: #0000BB">header</span><span style="color: #007700">(</span><span style="color: #DD0000">"Content-Type: image/png"</span><span style="color: #007700">);<br />echo </span><span style="color: #0000BB">$im</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-imagick.evaluateimage-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns <strong><code>TRUE</code></strong> on success.
</p>
</div>
<div class="refsect1 errors" id="refsect1-imagick.evaluateimage-errors">
<h3 class="title">Errors/Exceptions</h3>
<p class="para">
Throws ImagickException on error.
</p>
</div>
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