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<li class="toctree-l3"><a class="reference internal" href="#example-using-the-imagemath-module">Example: Using the <code class="docutils literal notranslate"><span class="pre">ImageMath</span></code> module</a></li>
<li class="toctree-l3"><a class="reference internal" href="#expression-syntax">Expression syntax</a><ul>
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<span class="target" id="module-PIL.ImageMath"></span><div class="section" id="imagemath-module">
<h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">ImageMath</span></code> Module<a class="headerlink" href="#imagemath-module" title="Permalink to this headline">¶</a></h1>
<p>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">ImageMath</span></code> module can be used to evaluate “image expressions”. The
module provides a single eval function, which takes an expression string and
one or more images.</p>
<div class="section" id="example-using-the-imagemath-module">
<h2>Example: Using the <a class="reference internal" href="#module-PIL.ImageMath" title="PIL.ImageMath"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ImageMath</span></code></a> module<a class="headerlink" href="#example-using-the-imagemath-module" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">PIL</span> <span class="kn">import</span> <span class="n">Image</span><span class="p">,</span> <span class="n">ImageMath</span>
<span class="n">im1</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s2">"image1.jpg"</span><span class="p">)</span>
<span class="n">im2</span> <span class="o">=</span> <span class="n">Image</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s2">"image2.jpg"</span><span class="p">)</span>
<span class="n">out</span> <span class="o">=</span> <span class="n">ImageMath</span><span class="o">.</span><span class="n">eval</span><span class="p">(</span><span class="s2">"convert(min(a, b), 'L')"</span><span class="p">,</span> <span class="n">a</span><span class="o">=</span><span class="n">im1</span><span class="p">,</span> <span class="n">b</span><span class="o">=</span><span class="n">im2</span><span class="p">)</span>
<span class="n">out</span><span class="o">.</span><span class="n">save</span><span class="p">(</span><span class="s2">"result.png"</span><span class="p">)</span>
</pre></div>
</div>
<dl class="function">
<dt id="PIL.ImageMath.eval">
<code class="descclassname">PIL.ImageMath.</code><code class="descname">eval</code><span class="sig-paren">(</span><em>expression</em>, <em>environment</em><span class="sig-paren">)</span><a class="reference internal" href="../_modules/PIL/ImageMath.html#eval"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#PIL.ImageMath.eval" title="Permalink to this definition">¶</a></dt>
<dd><p>Evaluate expression in the given environment.</p>
<p>In the current version, <a class="reference internal" href="#module-PIL.ImageMath" title="PIL.ImageMath"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ImageMath</span></code></a> only supports
single-layer images. To process multi-band images, use the
<a class="reference internal" href="Image.html#PIL.Image.Image.split" title="PIL.Image.Image.split"><code class="xref py py-meth docutils literal notranslate"><span class="pre">split()</span></code></a> method or <a class="reference internal" href="Image.html#PIL.Image.merge" title="PIL.Image.merge"><code class="xref py py-func docutils literal notranslate"><span class="pre">merge()</span></code></a>
function.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>expression</strong> – A string which uses the standard Python expression
syntax. In addition to the standard operators, you can
also use the functions described below.</li>
<li><strong>environment</strong> – A dictionary that maps image names to Image instances.
You can use one or more keyword arguments instead of a
dictionary, as shown in the above example. Note that
the names must be valid Python identifiers.</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first last">An image, an integer value, a floating point value,
or a pixel tuple, depending on the expression.</p>
</td>
</tr>
</tbody>
</table>
</dd></dl>
</div>
<div class="section" id="expression-syntax">
<h2>Expression syntax<a class="headerlink" href="#expression-syntax" title="Permalink to this headline">¶</a></h2>
<p>Expressions are standard Python expressions, but they’re evaluated in a
non-standard environment. You can use PIL methods as usual, plus the following
set of operators and functions:</p>
<div class="section" id="standard-operators">
<h3>Standard Operators<a class="headerlink" href="#standard-operators" title="Permalink to this headline">¶</a></h3>
<p>You can use standard arithmetical operators for addition (+), subtraction (-),
multiplication (*), and division (/).</p>
<p>The module also supports unary minus (-), modulo (%), and power (**) operators.</p>
<p>Note that all operations are done with 32-bit integers or 32-bit floating
point values, as necessary. For example, if you add two 8-bit images, the
result will be a 32-bit integer image. If you add a floating point constant to
an 8-bit image, the result will be a 32-bit floating point image.</p>
<p>You can force conversion using the <code class="xref py py-func docutils literal notranslate"><span class="pre">convert()</span></code>,
<code class="xref py py-func docutils literal notranslate"><span class="pre">float()</span></code>, and <code class="xref py py-func docutils literal notranslate"><span class="pre">int()</span></code> functions
described below.</p>
</div>
<div class="section" id="bitwise-operators">
<h3>Bitwise Operators<a class="headerlink" href="#bitwise-operators" title="Permalink to this headline">¶</a></h3>
<p>The module also provides operations that operate on individual bits. This
includes and (&), or (|), and exclusive or (^). You can also invert (~) all
pixel bits.</p>
<p>Note that the operands are converted to 32-bit signed integers before the
bitwise operation is applied. This means that you’ll get negative values if
you invert an ordinary greyscale image. You can use the and (&) operator to
mask off unwanted bits.</p>
<p>Bitwise operators don’t work on floating point images.</p>
</div>
<div class="section" id="logical-operators">
<h3>Logical Operators<a class="headerlink" href="#logical-operators" title="Permalink to this headline">¶</a></h3>
<p>Logical operators like <code class="docutils literal notranslate"><span class="pre">and</span></code>, <code class="docutils literal notranslate"><span class="pre">or</span></code>, and <code class="docutils literal notranslate"><span class="pre">not</span></code> work
on entire images, rather than individual pixels.</p>
<p>An empty image (all pixels zero) is treated as false. All other images are
treated as true.</p>
<p>Note that <code class="docutils literal notranslate"><span class="pre">and</span></code> and <code class="docutils literal notranslate"><span class="pre">or</span></code> return the last evaluated operand,
while not always returns a boolean value.</p>
</div>
<div class="section" id="built-in-functions">
<h3>Built-in Functions<a class="headerlink" href="#built-in-functions" title="Permalink to this headline">¶</a></h3>
<p>These functions are applied to each individual pixel.</p>
<dl class="function">
<dt id="abs">
<code class="descname">abs</code><span class="sig-paren">(</span><em>image</em><span class="sig-paren">)</span><a class="headerlink" href="#abs" title="Permalink to this definition">¶</a></dt>
<dd><p>Absolute value.</p>
</dd></dl>
<dl class="function">
<dt id="convert">
<code class="descname">convert</code><span class="sig-paren">(</span><em>image</em>, <em>mode</em><span class="sig-paren">)</span><a class="headerlink" href="#convert" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert image to the given mode. The mode must be given as a string
constant.</p>
</dd></dl>
<dl class="function">
<dt id="float">
<code class="descname">float</code><span class="sig-paren">(</span><em>image</em><span class="sig-paren">)</span><a class="headerlink" href="#float" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert image to 32-bit floating point. This is equivalent to
convert(image, “F”).</p>
</dd></dl>
<dl class="function">
<dt id="int">
<code class="descname">int</code><span class="sig-paren">(</span><em>image</em><span class="sig-paren">)</span><a class="headerlink" href="#int" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert image to 32-bit integer. This is equivalent to convert(image, “I”).</p>
<p>Note that 1-bit and 8-bit images are automatically converted to 32-bit
integers if necessary to get a correct result.</p>
</dd></dl>
<dl class="function">
<dt id="max">
<code class="descname">max</code><span class="sig-paren">(</span><em>image1</em>, <em>image2</em><span class="sig-paren">)</span><a class="headerlink" href="#max" title="Permalink to this definition">¶</a></dt>
<dd><p>Maximum value.</p>
</dd></dl>
<dl class="function">
<dt id="min">
<code class="descname">min</code><span class="sig-paren">(</span><em>image1</em>, <em>image2</em><span class="sig-paren">)</span><a class="headerlink" href="#min" title="Permalink to this definition">¶</a></dt>
<dd><p>Minimum value.</p>
</dd></dl>
</div>
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