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<section id="fill-histogram">
<span id="fill-it"></span><h1>Fill histogram</h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#overview" id="id1">Overview</a></p></li>
<li><p><a class="reference internal" href="#basic" id="id2">Basic</a></p></li>
<li><p><a class="reference internal" href="#advanced" id="id3">Advanced</a></p></li>
</ul>
</div>
<section id="overview">
<h2><a class="toc-backref" href="#id1">Overview</a></h2>
<p>We will demonstrate the available options for filling an instance of the <cite>histogram</cite> class with
values that cater from the most simplest to the complex needs that might arise.</p>
</section>
<section id="basic">
<h2><a class="toc-backref" href="#id2">Basic</a></h2>
<ol class="arabic">
<li><p>Use operator()</p>
<blockquote>
<div><p><strong>Task</strong> - Add value to a particular cell / key / bin in histogram</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">h</span><span class="p">;</span><span class="w"></span>
<span class="n">h</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
</pre></div>
</div>
</div></blockquote>
</li>
<li><p>Use operator[]</p>
<blockquote>
<div><p>This requires to input the indices in a format the histogram internally stores its keys,
which is of <code class="docutils literal notranslate"><span class="pre">std::tuple</span></code> due to its simple interface.</p>
<p><strong>Task</strong> - Output value of a bin</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">h</span><span class="p">;</span><span class="w"></span>
<span class="n">h</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
<span class="n">h</span><span class="p">[{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}]</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="c1">// Note the curly braces reqd. to construct a tuple</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="o">&lt;&lt;</span><span class="n">h</span><span class="p">[{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}];</span><span class="w"> </span><span class="c1">// Output - 2</span>
</pre></div>
</div>
</div></blockquote>
</li>
<li><p>Use another histogram (copy constructor or assignment)</p>
<blockquote>
<div><p><strong>Task</strong> - Fill a histogram using another</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">A</span><span class="p">;</span><span class="w"></span>
<span class="cm">/*</span>
<span class="cm">Fill value in A</span>
<span class="cm">*/</span><span class="w"></span>
<span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">(</span><span class="n">A</span><span class="p">),</span><span class="w"> </span><span class="n">C</span><span class="p">;</span><span class="w"></span>
<span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="p">;</span><span class="w"></span>
</pre></div>
</div>
</div></blockquote>
</li>
<li><p>Use a GIL image view</p>
<blockquote>
<div><p>You can also use GIL images to directly fill histograms.</p>
<p><strong>Task</strong> - Fill histogram using GIL image view</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">gil</span><span class="o">::</span><span class="n">gray8_image_t</span><span class="w"> </span><span class="n">img</span><span class="p">;</span><span class="w"></span>
<span class="cm">/*</span>
<span class="cm">Fill img ...</span>
<span class="cm">*/</span><span class="w"></span>
<span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">h</span><span class="p">;</span><span class="w"></span>
<span class="n">h</span><span class="p">.</span><span class="n">fill</span><span class="p">(</span><span class="n">view</span><span class="p">(</span><span class="n">img</span><span class="p">));</span><span class="w"></span>
<span class="c1">// OR</span>
<span class="n">gil</span><span class="o">::</span><span class="n">fill_histogram</span><span class="p">(</span><span class="n">view</span><span class="p">(</span><span class="n">img</span><span class="p">),</span><span class="w"> </span><span class="n">h</span><span class="p">,</span><span class="w"> </span><span class="nb">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// false if histogram needs to be cleared before filling</span>
</pre></div>
</div>
</div></blockquote>
</li>
</ol>
</section>
<section id="advanced">
<h2><a class="toc-backref" href="#id3">Advanced</a></h2>
<ol class="arabic">
<li><p>Fill histogram using only a few dimensions of image</p>
<blockquote>
<div><p><strong>Task</strong> - Make an histogram over Red and Blue channel of an rgb image</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">gil</span><span class="o">::</span><span class="n">rgb8_image_t</span><span class="w"> </span><span class="n">img</span><span class="p">;</span><span class="w"></span>
<span class="cm">/*</span>
<span class="cm">Fill img ...</span>
<span class="cm">*/</span><span class="w"></span>
<span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">h</span><span class="p">;</span><span class="w"></span>
<span class="n">fill_histogram</span><span class="o">&lt;</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="o">&gt;</span><span class="p">(</span><span class="n">view</span><span class="p">(</span><span class="n">img</span><span class="p">),</span><span class="w"> </span><span class="n">h</span><span class="p">,</span><span class="w"> </span><span class="nb">false</span><span class="p">);</span><span class="w"> </span><span class="c1">// 0 - red, 1 - green, 2 - blue</span>
</pre></div>
</div>
</div></blockquote>
</li>
<li><p>Fill histogram using GIL pixel</p>
<blockquote>
<div><p><strong>Task</strong> - Fill histogram bin using pixel construct in GIL</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">gil</span><span class="o">::</span><span class="n">gray8_image_t</span><span class="w"> </span><span class="n">img</span><span class="p">;</span><span class="w"></span>
<span class="cm">/*</span>
<span class="cm">Fill img ...</span>
<span class="cm">*/</span><span class="w"></span>
<span class="n">histogram</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">h</span><span class="p">;</span><span class="w"></span>
<span class="n">gil</span><span class="o">::</span><span class="n">for_each_pixel</span><span class="p">(</span><span class="n">view</span><span class="p">(</span><span class="n">img</span><span class="p">),</span><span class="w"> </span><span class="p">[](</span><span class="n">gil</span><span class="o">::</span><span class="n">gray8_pixel_t</span><span class="w"> </span><span class="k">const</span><span class="o">&amp;</span><span class="w"> </span><span class="n">p</span><span class="p">){</span><span class="w"></span>
<span class="w"> </span><span class="o">++</span><span class="n">h</span><span class="p">[</span><span class="n">h</span><span class="p">.</span><span class="n">key_from_pixel</span><span class="p">(</span><span class="n">p</span><span class="p">)];</span><span class="w"></span>
<span class="p">});</span><span class="w"></span>
</pre></div>
</div>
</div></blockquote>
</li>
</ol>
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