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<div class="section" id="saving-images">
<h1>Saving images<a class="headerlink" href="#saving-images" title="Permalink to this headline">¶</a></h1>
<p>In Willow there are separate save operations for each image format:</p>
<blockquote>
<div><ul class="simple">
<li><code class="xref py py-meth docutils literal"><span class="pre">save_as_jpeg()</span></code></li>
<li><code class="xref py py-meth docutils literal"><span class="pre">save_as_png()</span></code></li>
<li><code class="xref py py-meth docutils literal"><span class="pre">save_as_gif()</span></code></li>
</ul>
</div></blockquote>
<p>All three take one positional argument, the file-like object to write the image
data to.</p>
<p>For example, to save an image as a PNG file:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'out.png'</span><span class="p">,</span> <span class="s1">'wb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">i</span><span class="o">.</span><span class="n">save_as_png</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
</pre></div>
</div>
<div class="section" id="changing-the-jpeg-quality-setting">
<h2>Changing the JPEG quality setting<a class="headerlink" href="#changing-the-jpeg-quality-setting" title="Permalink to this headline">¶</a></h2>
<p><code class="xref py py-meth docutils literal"><span class="pre">save_as_jpeg()</span></code> takes a <code class="docutils literal"><span class="pre">quality</span></code> keyword argument, which is a
number between 1 and 100 which defaults to 85. Decreasing this number will
decrease the output file size at the cost of losing image quality.</p>
<p>For example, to save an image with low quality:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'low_quality.jpg'</span><span class="p">,</span> <span class="s1">'wb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">i</span><span class="o">.</span><span class="n">save_as_jpeg</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">quality</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="progressive-jpegs">
<h2>Progressive JPEGs<a class="headerlink" href="#progressive-jpegs" title="Permalink to this headline">¶</a></h2>
<p>By default, JPEG’s are saved in the same format as their source file but you
can force Willow to always save a “progressive” JPEG file by setting the
<code class="docutils literal"><span class="pre">progressive</span></code> keyword argument to <code class="docutils literal"><span class="pre">True</span></code>:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'progressive.jpg'</span><span class="p">,</span> <span class="s1">'wb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">i</span><span class="o">.</span><span class="n">save_as_jpeg</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">progressive</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="image-optimisation">
<h2>Image optimisation<a class="headerlink" href="#image-optimisation" title="Permalink to this headline">¶</a></h2>
<p><code class="xref py py-meth docutils literal"><span class="pre">save_as_jpeg()</span></code> and <code class="xref py py-meth docutils literal"><span class="pre">save_as_png()</span></code> both take an
<code class="docutils literal"><span class="pre">optimize</span></code> keyword that when set to true, will output an optimized image.</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'optimized.jpg'</span><span class="p">,</span> <span class="s1">'wb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">i</span><span class="o">.</span><span class="n">save_as_jpeg</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">optimize</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
</div>
<p>This feature is currently only supported in the Pillow backend, if you use Wand
this argument will be ignored.</p>
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