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<section id="making-a-sub-histogram">
<span id="sub-histogram"></span><h1>Making a sub-histogram</h1>
<section id="overview">
<h2>Overview</h2>
<p>Sub-histogram is a subset of a histogram or one that is formed by masking out a
few axis of the parent histogram.</p>
<p>GIL class histogram provides these functions as members and returns an instance of
the desired sub-class.</p>
<ol class="arabic">
<li><p>Histogram over fewer axes</p>
<blockquote>
<div><p><strong>Task</strong> - Get a 2D histogram from a 3D RGB histogram over red and green axes</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="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">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">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="k">auto</span><span class="w"> </span><span class="n">sub_h</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">h</span><span class="p">.</span><span class="n">sub_histogram</span><span class="o">&lt;</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="o">&gt;</span><span class="p">();</span><span class="w"> </span><span class="c1">// sub_h is a 2D histogram</span>
</pre></div>
</div>
<p>Demo output:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">h</span><span class="w"> </span><span class="n">is</span><span class="w"> </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="mi">3</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="w"> </span><span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"></span>
<span class="w"> </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="mi">5</span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">3</span><span class="p">}</span><span class="w"></span>
<span class="n">sub_h</span><span class="w"> </span><span class="n">would</span><span class="w"> </span><span class="n">be</span><span class="w"> </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">4</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="p">}</span><span class="w"></span>
</pre></div>
</div>
</div></blockquote>
</li>
<li><p>Histogram using a particular key range</p>
<blockquote>
<div><p><strong>Task</strong> - Get a 2D histogram from a 3D RGB histogram for bins whose red color lie between 10 - 20
and blue color lie between 2 - 10</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="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">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">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="n">std</span><span class="o">::</span><span class="n">tuple</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="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&gt;</span><span class="w"> </span><span class="n">low</span><span class="p">,</span><span class="w"> </span><span class="n">high</span><span class="p">;</span><span class="w"></span>
<span class="n">low</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="mi">0</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">// Since no check over blue channel pass any dummy value</span>
<span class="n">high</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">20</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p">}</span><span class="w"> </span><span class="c1">// Since no check over blue channel pass any dummy value</span>
<span class="k">auto</span><span class="w"> </span><span class="n">sub_h</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">h</span><span class="p">.</span><span class="n">sub_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">low</span><span class="p">,</span><span class="w"> </span><span class="n">high</span><span class="p">);</span><span class="w"> </span><span class="c1">// In angle brackets pass the relevant dimensions in order</span>
</pre></div>
</div>
<p>Demo Output:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">h</span><span class="w"> </span><span class="n">is</span><span class="w"> </span><span class="p">{{</span><span class="mi">11</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="w"> </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="w"> </span><span class="p">{</span><span class="mi">1</span><span class="w"> </span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">11</span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="p">{</span><span class="mi">1</span><span class="w"> </span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"></span>
<span class="w"> </span><span class="p">{</span><span class="mi">11</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">4</span><span class="p">}</span><span class="w"></span>
<span class="n">sub_h</span><span class="w"> </span><span class="n">would</span><span class="w"> </span><span class="n">be</span><span class="w"> </span><span class="p">{{</span><span class="mi">11</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</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="p">{</span><span class="mi">11</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">4</span><span class="p">}</span><span class="w"></span>
</pre></div>
</div>
</div></blockquote>
</li>
</ol>
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