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  25 <div class="section gil_io_tutorial">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="gil.io.tutorial"></a><a class="link" href="tutorial.html" title="Tutorial">Tutorial</a>
  28 </h2></div></div></div>
  29 <p>
  30       Thanks to modern C++ programming techniques the interface for this library
  31       is rather small and easy to use. In this tutorial I'll give you a short walk-around
  32       on how to use this boost::gil extension. For more details please refer to section
  33       3.
  34     </p>
  35 <p>
  36       Since this is an extension to boost::gil I expect the user to have some very
  37       basic understanding of the gil ( generic image library ). Please see here for
  38       the help.
  39     </p>
  40 <h3>
  41 <a name="gil.io.tutorial.h0"></a>
  42       <span class="phrase"><a name="gil.io.tutorial.header_files"></a></span><a class="link" href="tutorial.html#gil.io.tutorial.header_files">Header
  43       Files</a>
  44     </h3>
  45 <p>
  46       The header files to be included all have the same format. For instance, tiff_all.hpp
  47       will allow to read and write. Whereas, tiff_read.hpp only allows for reading.
  48       If the user only wants to write jpeg's include jpeg_write.hpp. All formats
  49       provide these three types of header files:
  50     </p>
  51 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  52 <li class="listitem">
  53           xxx_all.hpp
  54         </li>
  55 <li class="listitem">
  56           xxx_read.hpp
  57         </li>
  58 <li class="listitem">
  59           xxx_write.hpp
  60         </li>
  61 </ul></div>
  62 <p>
  63       xxx stands for image format.
  64     </p>
  65 <h3>
  66 <a name="gil.io.tutorial.h1"></a>
  67       <span class="phrase"><a name="gil.io.tutorial.reading_an_image"></a></span><a class="link" href="tutorial.html#gil.io.tutorial.reading_an_image">Reading
  68       An Image</a>
  69     </h3>
  70 <p>
  71       Probably the most common case to read a tiff image can be done as follows:
  72     </p>
  73 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">filename</span><span class="special">(</span> <span class="string">"image.tif"</span> <span class="special">);</span>
  74 <span class="identifier">rgb8_image_t</span> <span class="identifier">img</span><span class="special">;</span>
  75 <span class="identifier">read_image</span><span class="special">(</span> <span class="identifier">filename</span><span class="special">,</span> <span class="identifier">img</span><span class="special">,</span> <span class="identifier">tiff_tag</span><span class="special">()</span> <span class="special">);</span>
  76 </pre>
  77 <p>
  78       The code would be same for all other image formats. The only thing that needs
  79       to change is the tag type ( tiff_tag ) in the read_image call. The read_image()
  80       expects the supplied image type to be compatible with the image stored in the
  81       file. If the user doesn't know what format an image has he/she can use read_and_convert_image().
  82       Another important fact is that read_image() will allocate the appropriate memory
  83       needed for the read operation. There are read_view or read_and_convert_view
  84       counterparts, if the memory is already allocated.
  85     </p>
  86 <p>
  87       Sometimes the user only wants to read a sub-part of an image, then the above
  88       call would look as follows:
  89     </p>
  90 <pre class="programlisting"><span class="identifier">read_image</span><span class="special">(</span> <span class="identifier">filename</span>
  91           <span class="special">,</span> <span class="identifier">img</span>
  92           <span class="special">,</span> <span class="identifier">image_read_settings</span><span class="special">&lt;</span> <span class="identifier">tiff_tag</span> <span class="special">&gt;(</span> <span class="identifier">point_t</span><span class="special">(</span> <span class="number">0</span><span class="special">,</span> <span class="number">0</span> <span class="special">),</span> <span class="identifier">point_t</span><span class="special">(</span> <span class="number">50</span><span class="special">,</span> <span class="number">50</span> <span class="special">)</span> <span class="special">)</span>
  93           <span class="special">);</span>
  94 </pre>
  95 <p>
  96       The image_read_settings class will provide the user with image format independent
  97       reading setting but can also serves as a pointer for format dependent settings.
  98       Please see the specific image format sections <a class="link" href="using_io.html#gil.io.using_io.supported_image_formats">Supported
  99       Image Formats</a> for more details.
 100     </p>
 101 <h3>
 102 <a name="gil.io.tutorial.h2"></a>
 103       <span class="phrase"><a name="gil.io.tutorial.writing_an_image"></a></span><a class="link" href="tutorial.html#gil.io.tutorial.writing_an_image">Writing
 104       An Image</a>
 105     </h3>
 106 <p>
 107       Besides reading the information also writing is the second part of this boost::gil
 108       extension. Writing is a lot simpler than reading since an existing image view
 109       contains all the information. For instance writing an image can be done as
 110       follows:
 111     </p>
 112 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">filename</span><span class="special">(</span> <span class="string">"image.tif"</span> <span class="special">);</span>
 113 <span class="identifier">rgb8_image_t</span> <span class="identifier">img</span><span class="special">(</span> <span class="number">640</span><span class="special">,</span> <span class="number">480</span> <span class="special">);</span>
 114
 115 <span class="comment">// write data into image</span>
 116
 117 <span class="identifier">write_view</span><span class="special">(</span> <span class="identifier">filename</span>
 118           <span class="special">,</span> <span class="identifier">view</span><span class="special">(</span> <span class="identifier">img</span> <span class="special">)</span>
 119           <span class="special">,</span> <span class="identifier">tiff_tag</span><span class="special">()</span>
 120           <span class="special">);</span>
 121 </pre>
 122 <p>
 123       The interface is similar to reading an image. To add image format specific
 124       parameter the user can use image_write_info class. For instance, a user can
 125       specify the jpeg quality when writing like this:
 126     </p>
 127 <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">filename</span><span class="special">(</span> <span class="string">"image.jpg"</span> <span class="special">);</span>
 128 <span class="identifier">rgb8_image_t</span> <span class="identifier">img</span><span class="special">(</span> <span class="number">640</span><span class="special">,</span> <span class="number">480</span> <span class="special">);</span>
 129
 130 <span class="comment">// write data into image</span>
 131
 132 <span class="identifier">write_view</span><span class="special">(</span> <span class="identifier">filename</span>
 133           <span class="special">,</span> <span class="identifier">view</span><span class="special">(</span> <span class="identifier">img</span> <span class="special">)</span>
 134           <span class="special">,</span> <span class="identifier">image_write_info</span><span class="special">&lt;</span> <span class="identifier">jpeg_tag</span> <span class="special">&gt;(</span> <span class="number">95</span> <span class="special">)</span>
 135           <span class="special">);</span>
 136 </pre>
 137 <p>
 138       The above example will write an image where the jpeg quality is set to 95 percent.
 139     </p>
 140 <h3>
 141 <a name="gil.io.tutorial.h3"></a>
 142       <span class="phrase"><a name="gil.io.tutorial.reading_and_writing_in_memory_buffers"></a></span><a class="link" href="tutorial.html#gil.io.tutorial.reading_and_writing_in_memory_buffers">Reading
 143       And Writing In-Memory Buffers</a>
 144     </h3>
 145 <p>
 146       Reading and writing in-memory buffers are supported as well. See as follows:
 147     </p>
 148 <pre class="programlisting"><span class="comment">// 1. Read an image.</span>
 149 <span class="identifier">ifstream</span> <span class="identifier">in</span><span class="special">(</span> <span class="string">"test.tif"</span><span class="special">,</span> <span class="identifier">ios</span><span class="special">::</span><span class="identifier">binary</span> <span class="special">);</span>
 150
 151 <span class="identifier">rgb8_image_t</span> <span class="identifier">img</span><span class="special">;</span>
 152 <span class="identifier">read_image</span><span class="special">(</span> <span class="identifier">in</span><span class="special">,</span> <span class="identifier">img</span><span class="special">,</span> <span class="identifier">tiff_tag</span><span class="special">()</span> <span class="special">);</span>
 153
 154 <span class="comment">// 2. Write image to in-memory buffer.</span>
 155 <span class="identifier">stringstream</span> <span class="identifier">out_buffer</span><span class="special">(</span> <span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">out</span> <span class="special">|</span> <span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">binary</span> <span class="special">);</span>
 156
 157 <span class="identifier">rgb8_image_t</span> <span class="identifier">src</span><span class="special">;</span>
 158 <span class="identifier">write_view</span><span class="special">(</span> <span class="identifier">out_buffer</span><span class="special">,</span> <span class="identifier">view</span><span class="special">(</span> <span class="identifier">src</span> <span class="special">),</span> <span class="identifier">tiff_tag</span><span class="special">()</span> <span class="special">);</span>
 159
 160 <span class="comment">// 3. Copy in-memory buffer to another.</span>
 161 <span class="identifier">stringstream</span> <span class="identifier">in_buffer</span><span class="special">(</span> <span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">in</span> <span class="special">|</span> <span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">binary</span> <span class="special">);</span>
 162 <span class="identifier">in_buffer</span> <span class="special">&lt;&lt;</span> <span class="identifier">out_buffer</span><span class="special">.</span><span class="identifier">rdbuf</span><span class="special">();</span>
 163
 164 <span class="comment">// 4. Read in-memory buffer to gil image</span>
 165 <span class="identifier">rgb8_image_t</span> <span class="identifier">dst</span><span class="special">;</span>
 166 <span class="identifier">read_image</span><span class="special">(</span> <span class="identifier">in_buffer</span><span class="special">,</span> <span class="identifier">dst</span><span class="special">,</span> <span class="identifier">tag_t</span><span class="special">()</span> <span class="special">);</span>
 167
 168 <span class="comment">// 5. Write out image.</span>
 169 <span class="identifier">string</span> <span class="identifier">filename</span><span class="special">(</span> <span class="string">"out.tif"</span> <span class="special">);</span>
 170 <span class="identifier">ofstream</span> <span class="identifier">out</span><span class="special">(</span> <span class="identifier">filename</span><span class="special">.</span><span class="identifier">c_str</span><span class="special">(),</span> <span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">binary</span> <span class="special">);</span>
 171 <span class="identifier">write_view</span><span class="special">(</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">view</span><span class="special">(</span> <span class="identifier">dst</span> <span class="special">),</span> <span class="identifier">tiff_tag</span><span class="special">()</span> <span class="special">);</span>
 172 </pre>
 173 <p>
 174       In case the user is using his own stream classes he has to make sure it has
 175       the common interface read, write, seek, close, etc. Interface.
 176     </p>
 177 </div>
 178 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 179 <td align="left"></td>
 180 <td align="right"><div class="copyright-footer">Copyright &#169; 2013 Christian Henning<p>
 181         Distributed under the Boost Software License, Version 1.0. (See accompanying
 182         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 183       </p>
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