1 2 3<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 4 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 5<html xmlns="http://www.w3.org/1999/xhtml"> 6 <head> 7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 8 9 <title>Extending - Boost.GIL documentation</title> 10 <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> 11 <link rel="stylesheet" href="../_static/style.css" type="text/css" /> 12 <script type="text/javascript"> 13 var DOCUMENTATION_OPTIONS = { 14 URL_ROOT: '../', 15 VERSION: '', 16 COLLAPSE_MODINDEX: false, 17 FILE_SUFFIX: '.html' 18 }; 19 </script> 20 <script type="text/javascript" src="../_static/jquery.js"></script> 21 <script type="text/javascript" src="../_static/underscore.js"></script> 22 <script type="text/javascript" src="../_static/doctools.js"></script> 23 <link rel="index" title="Index" href="../genindex.html" /> 24 <link rel="search" title="Search" href="../search.html" /> 25 <link rel="top" title="Boost.GIL documentation" href="../index.html" /> 26 <link rel="up" title="Design Guide" href="index.html" /> 27 <link rel="next" title="Conclusions" href="conclusions.html" /> 28 <link rel="prev" title="Technicalities" href="technicalities.html" /> 29 </head> 30 <body> 31 <div class="header"> 32 <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= 33 "header"> 34 <tr> 35 <td valign="top" width="300"> 36 <h3><a href="../index.html"><img 37 alt="C++ Boost" src="../_static/gil.png" border="0"></a></h3> 38 </td> 39 40 <td > 41 <h1 align="center"><a href="../index.html"></a></h1> 42 </td> 43 <td> 44 <div id="searchbox" style="display: none"> 45 <form class="search" action="../search.html" method="get"> 46 <input type="text" name="q" size="18" /> 47 <input type="submit" value="Search" /> 48 <input type="hidden" name="check_keywords" value="yes" /> 49 <input type="hidden" name="area" value="default" /> 50 </form> 51 </div> 52 <script type="text/javascript">$('#searchbox').show(0);</script> 53 </td> 54 </tr> 55 </table> 56 </div> 57 <hr/> 58 <div class="content"> 59 <div class="navbar" style="text-align:right;"> 60 61 62 <a class="prev" title="Technicalities" href="technicalities.html"><img src="../_static/prev.png" alt="prev"/></a> 63 <a class="up" title="Design Guide" href="index.html"><img src="../_static/up.png" alt="up"/></a> 64 <a class="next" title="Conclusions" href="conclusions.html"><img src="../_static/next.png" alt="next"/></a> 65 66 </div> 67 68 <div class="section" id="extending"> 69<h1>Extending</h1> 70<div class="contents local topic" id="contents"> 71<ul class="simple"> 72<li><a class="reference internal" href="#overview" id="id1">Overview</a></li> 73<li><a class="reference internal" href="#defining-new-color-spaces" id="id2">Defining new color spaces</a></li> 74<li><a class="reference internal" href="#defining-new-channel-types" id="id3">Defining new channel types</a></li> 75<li><a class="reference internal" href="#overloading-color-conversion" id="id4">Overloading color conversion</a></li> 76<li><a class="reference internal" href="#defining-new-image-views" id="id5">Defining new image views</a></li> 77</ul> 78</div> 79<div class="section" id="overview"> 80<h2><a class="toc-backref" href="#id1">Overview</a></h2> 81<p>You can define your own pixel iterators, locators, image views, 82images, channel types, color spaces and algorithms. You can make 83virtual images that live on the disk, inside a jpeg file, somewhere on 84the internet, or even fully-synthetic images such as the Mandelbrot 85set. As long as they properly model the corresponding concepts, they 86will work with any existing GIL code. Most such extensions require no 87changes to the library and can thus be supplied in another module.</p> 88</div> 89<div class="section" id="defining-new-color-spaces"> 90<h2><a class="toc-backref" href="#id2">Defining new color spaces</a></h2> 91<p>Each color space is in a separate file. To add a new color space, just 92copy one of the existing ones (like rgb.hpp) and change it 93accordingly. If you want color conversion support, you will have to 94provide methods to convert between it and the existing color spaces 95(see color_convert.h). For convenience you may want to provide useful 96typedefs for pixels, pointers, references and images with the new 97color space (see typedefs.h).</p> 98</div> 99<div class="section" id="defining-new-channel-types"> 100<h2><a class="toc-backref" href="#id3">Defining new channel types</a></h2> 101<p>Most of the time you don’t need to do anything special to use a new 102channel type. You can just use it:</p> 103<div class="highlight-cpp"><div class="highlight"><pre><span class="k">typedef</span> <span class="n">pixel</span><span class="o"><</span><span class="kt">double</span><span class="p">,</span><span class="n">rgb_layout_t</span><span class="o">></span> <span class="n">rgb64_pixel_t</span><span class="p">;</span> <span class="c1">// 64 bit RGB pixel</span> 104<span class="k">typedef</span> <span class="n">rgb64_pixel</span><span class="o">*</span> <span class="n">rgb64_pixel_ptr_t</span><span class="p">;</span><span class="c1">// pointer to 64-bit interleaved data</span> 105<span class="k">typedef</span> <span class="n">image_type</span><span class="o"><</span><span class="kt">double</span><span class="p">,</span><span class="n">rgb_layout_t</span><span class="o">>::</span><span class="n">type</span> <span class="n">rgb64_image_t</span><span class="p">;</span> <span class="c1">// 64-bit interleaved image</span> 106</pre></div> 107</div> 108<p>If you want to use your own channel class, you will need to provide a 109specialization of <code class="docutils literal"><span class="pre">channel_traits</span></code> for it (see channel.hpp). If you 110want to do conversion between your and existing channel types, you 111will need to provide an overload of <code class="docutils literal"><span class="pre">channel_convert</span></code>.</p> 112</div> 113<div class="section" id="overloading-color-conversion"> 114<h2><a class="toc-backref" href="#id4">Overloading color conversion</a></h2> 115<p>Suppose you want to provide your own color conversion. For example, 116you may want to implement higher quality color conversion using color 117profiles. Typically you may want to redefine color conversion only in 118some instances and default to GIL’s color conversion in all other 119cases. Here is, for example, how to overload color conversion so that 120color conversion to gray inverts the result but everything else 121remains the same:</p> 122<div class="highlight-cpp"><div class="highlight"><pre><span class="c1">// make the default use GIL's default</span> 123<span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">SrcColorSpace</span><span class="p">,</span> <span class="k">typename</span> <span class="n">DstColorSpace</span><span class="o">></span> 124<span class="k">struct</span> <span class="nl">my_color_converter_impl</span> 125<span class="p">:</span> <span class="k">public</span> <span class="n">default_color_converter_impl</span><span class="o"><</span><span class="n">SrcColorSpace</span><span class="p">,</span><span class="n">DstColorSpace</span><span class="o">></span> <span class="p">{};</span> 126 127<span class="c1">// provide specializations only for cases you care about</span> 128<span class="c1">// (in this case, if the destination is grayscale, invert it)</span> 129<span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">SrcColorSpace</span><span class="o">></span> 130<span class="k">struct</span> <span class="n">my_color_converter_impl</span><span class="o"><</span><span class="n">SrcColorSpace</span><span class="p">,</span><span class="n">gray_t</span><span class="o">></span> 131<span class="p">{</span> 132 <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">SrcP</span><span class="p">,</span> <span class="k">typename</span> <span class="n">DstP</span><span class="o">></span> <span class="c1">// Model PixelConcept</span> 133 <span class="kt">void</span> <span class="k">operator</span><span class="p">()(</span><span class="k">const</span> <span class="n">SrcP</span><span class="o">&</span> <span class="n">src</span><span class="p">,</span> <span class="n">DstP</span><span class="o">&</span> <span class="n">dst</span><span class="p">)</span> <span class="k">const</span> 134 <span class="p">{</span> 135 <span class="n">default_color_converter_impl</span><span class="o"><</span><span class="n">SrcColorSpace</span><span class="p">,</span><span class="n">gray_t</span><span class="o">></span><span class="p">()(</span><span class="n">src</span><span class="p">,</span><span class="n">dst</span><span class="p">);</span> 136 <span class="n">get_color</span><span class="p">(</span><span class="n">dst</span><span class="p">,</span><span class="n">gray_color_t</span><span class="p">())</span><span class="o">=</span><span class="n">channel_invert</span><span class="p">(</span><span class="n">get_color</span><span class="p">(</span><span class="n">dst</span><span class="p">,</span><span class="n">gray_color_t</span><span class="p">()));</span> 137 <span class="p">}</span> 138<span class="p">};</span> 139 140<span class="c1">// create a color converter object that dispatches to your own implementation</span> 141<span class="k">struct</span> <span class="n">my_color_converter</span> 142<span class="p">{</span> 143 <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">SrcP</span><span class="p">,</span> <span class="k">typename</span> <span class="n">DstP</span><span class="o">></span> <span class="c1">// Model PixelConcept</span> 144 <span class="kt">void</span> <span class="k">operator</span><span class="p">()(</span><span class="k">const</span> <span class="n">SrcP</span><span class="o">&</span> <span class="n">src</span><span class="p">,</span><span class="n">DstP</span><span class="o">&</span> <span class="n">dst</span><span class="p">)</span> <span class="k">const</span> 145 <span class="p">{</span> 146 <span class="k">typedef</span> <span class="k">typename</span> <span class="n">color_space_type</span><span class="o"><</span><span class="n">SrcP</span><span class="o">>::</span><span class="n">type</span> <span class="n">SrcColorSpace</span><span class="p">;</span> 147 <span class="k">typedef</span> <span class="k">typename</span> <span class="n">color_space_type</span><span class="o"><</span><span class="n">DstP</span><span class="o">>::</span><span class="n">type</span> <span class="n">DstColorSpace</span><span class="p">;</span> 148 <span class="n">my_color_converter_impl</span><span class="o"><</span><span class="n">SrcColorSpace</span><span class="p">,</span><span class="n">DstColorSpace</span><span class="o">></span><span class="p">()(</span><span class="n">src</span><span class="p">,</span><span class="n">dst</span><span class="p">);</span> 149 <span class="p">}</span> 150<span class="p">};</span> 151</pre></div> 152</div> 153<p>GIL color conversion functions take the color converter as an 154optional parameter. You can pass your own color converter:</p> 155<div class="highlight-cpp"><div class="highlight"><pre><span class="n">color_converted_view</span><span class="o"><</span><span class="n">gray8_pixel_t</span><span class="o">></span><span class="p">(</span><span class="n">img_view</span><span class="p">,</span><span class="n">my_color_converter</span><span class="p">());</span> 156</pre></div> 157</div> 158</div> 159<div class="section" id="defining-new-image-views"> 160<h2><a class="toc-backref" href="#id5">Defining new image views</a></h2> 161<p>You can provide your own pixel iterators, locators and views, 162overriding either the mechanism for getting from one pixel to the next 163or doing an arbitrary pixel transformation on dereference. For 164example, let’s look at the implementation of <code class="docutils literal"><span class="pre">color_converted_view</span></code> 165(an image factory method that, given any image view, returns a new, 166otherwise identical view, except that color conversion is performed on 167pixel access). First we need to define a model of 168<code class="docutils literal"><span class="pre">PixelDereferenceAdaptorConcept</span></code>; a function object that will be 169called when we dereference a pixel iterator. It will call 170<code class="docutils literal"><span class="pre">color_convert</span></code> to convert to the destination pixel type:</p> 171<div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">SrcConstRefP</span><span class="p">,</span> <span class="c1">// const reference to the source pixel</span> 172 <span class="k">typename</span> <span class="n">DstP</span><span class="o">></span> <span class="c1">// Destination pixel value (models PixelValueConcept)</span> 173<span class="k">class</span> <span class="nc">color_convert_deref_fn</span> 174<span class="p">{</span> 175<span class="k">public</span><span class="o">:</span> 176 <span class="k">typedef</span> <span class="n">color_convert_deref_fn</span> <span class="n">const_t</span><span class="p">;</span> 177 <span class="k">typedef</span> <span class="n">DstP</span> <span class="n">value_type</span><span class="p">;</span> 178 <span class="k">typedef</span> <span class="n">value_type</span> <span class="n">reference</span><span class="p">;</span> <span class="c1">// read-only dereferencing</span> 179 <span class="k">typedef</span> <span class="k">const</span> <span class="n">value_type</span><span class="o">&</span> <span class="n">const_reference</span><span class="p">;</span> 180 <span class="k">typedef</span> <span class="n">SrcConstRefP</span> <span class="n">argument_type</span><span class="p">;</span> 181 <span class="k">typedef</span> <span class="n">reference</span> <span class="n">result_type</span><span class="p">;</span> 182 <span class="k">static</span> <span class="kt">bool</span> <span class="k">constexpr</span> <span class="n">is_mutable</span> <span class="o">=</span> <span class="nb">false</span><span class="p">;</span> 183 184 <span class="n">result_type</span> <span class="nf">operator</span><span class="p">()(</span><span class="n">argument_type</span> <span class="n">srcP</span><span class="p">)</span> <span class="k">const</span> <span class="p">{</span> 185 <span class="n">result_type</span> <span class="n">dstP</span><span class="p">;</span> 186 <span class="n">color_convert</span><span class="p">(</span><span class="n">srcP</span><span class="p">,</span><span class="n">dstP</span><span class="p">);</span> 187 <span class="k">return</span> <span class="n">dstP</span><span class="p">;</span> 188 <span class="p">}</span> 189<span class="p">};</span> 190</pre></div> 191</div> 192<p>We then use the <code class="docutils literal"><span class="pre">add_deref</span></code> member struct of image views to construct the 193type of a view that invokes a given function object (<code class="docutils literal"><span class="pre">deref_t</span></code>) upon 194dereferencing. In our case, it performs color conversion:</p> 195<div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">SrcView</span><span class="p">,</span> <span class="k">typename</span> <span class="n">DstP</span><span class="o">></span> 196<span class="k">struct</span> <span class="n">color_converted_view_type</span> 197<span class="p">{</span> 198<span class="k">private</span><span class="o">:</span> 199 <span class="k">typedef</span> <span class="k">typename</span> <span class="n">SrcView</span><span class="o">::</span><span class="n">const_t</span><span class="o">::</span><span class="n">reference</span> <span class="n">src_pix_ref</span><span class="p">;</span> <span class="c1">// const reference to pixel in SrcView</span> 200 <span class="k">typedef</span> <span class="n">color_convert_deref_fn</span><span class="o"><</span><span class="n">src_pix_ref</span><span class="p">,</span> <span class="n">DstP</span><span class="o">></span> <span class="n">deref_t</span><span class="p">;</span> <span class="c1">// the dereference adaptor that performs color conversion</span> 201 <span class="k">typedef</span> <span class="k">typename</span> <span class="n">SrcView</span><span class="o">::</span><span class="k">template</span> <span class="n">add_deref</span><span class="o"><</span><span class="n">deref_t</span><span class="o">></span> <span class="n">add_ref_t</span><span class="p">;</span> 202<span class="k">public</span><span class="o">:</span> 203 <span class="k">typedef</span> <span class="k">typename</span> <span class="n">add_ref_t</span><span class="o">::</span><span class="n">type</span> <span class="n">type</span><span class="p">;</span> <span class="c1">// the color converted view type</span> 204 <span class="k">static</span> <span class="n">type</span> <span class="nf">make</span><span class="p">(</span><span class="k">const</span> <span class="n">SrcView</span><span class="o">&</span> <span class="n">sv</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">add_ref_t</span><span class="o">::</span><span class="n">make</span><span class="p">(</span><span class="n">sv</span><span class="p">,</span> <span class="n">deref_t</span><span class="p">());</span> <span class="p">}</span> 205<span class="p">};</span> 206</pre></div> 207</div> 208<p>Finally our <code class="docutils literal"><span class="pre">color_converted_view</span></code> code simply creates color-converted view 209from the source view:</p> 210<div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">DstP</span><span class="p">,</span> <span class="k">typename</span> <span class="n">View</span><span class="o">></span> <span class="kr">inline</span> 211<span class="k">typename</span> <span class="n">color_converted_view_type</span><span class="o"><</span><span class="n">View</span><span class="p">,</span><span class="n">DstP</span><span class="o">>::</span><span class="n">type</span> <span class="n">color_convert_view</span><span class="p">(</span><span class="k">const</span> <span class="n">View</span><span class="o">&</span> <span class="n">src</span><span class="p">)</span> 212<span class="p">{</span> 213 <span class="k">return</span> <span class="n">color_converted_view_type</span><span class="o"><</span><span class="n">View</span><span class="p">,</span><span class="n">DstP</span><span class="o">>::</span><span class="n">make</span><span class="p">(</span><span class="n">src</span><span class="p">);</span> 214<span class="p">}</span> 215</pre></div> 216</div> 217<p>(The actual color convert view transformation is slightly more 218complicated, as it takes an optional color conversion object, which 219allows users to specify their own color conversion methods). See the 220GIL tutorial for an example of creating a virtual image view that 221defines the Mandelbrot set.</p> 222</div> 223</div> 224 225 226 <div class="navbar" style="text-align:right;"> 227 228 229 <a class="prev" title="Technicalities" href="technicalities.html"><img src="../_static/prev.png" alt="prev"/></a> 230 <a class="up" title="Design Guide" href="index.html"><img src="../_static/up.png" alt="up"/></a> 231 <a class="next" title="Conclusions" href="conclusions.html"><img src="../_static/next.png" alt="next"/></a> 232 233 </div> 234 </div> 235 <div class="footer" role="contentinfo"> 236 Last updated on 2020-08-11 15:08:48. 237 Created using <a href="http://sphinx-doc.org/">Sphinx</a> 1.5.6. 238 </div> 239 </body> 240</html>
