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97<p class="navigation-index">[<a href="#intro">Introduction to High Dynamic-Range Images</a> &bull; <a href="#enable">Enabling HDRI in ImageMagick</a>]</p>
98
99<div style="margin: auto;">
100  <h2><a name="intro"></a>Introduction to High Dynamic-Range Images</h2>
101</div>
102
103<p>High dynamic-range imaging (HDRI) permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows.  The HDR imaging approach includes:</p>
104
105<ul>
106  <li>render/capture floating-point color space</li>
107  <li>encompass the entire perceivable gamut (extend values outside [0,1] range)</li>
108  <li>post-process in extended color space</li>
109  <li>apply tone-mapping for specific display</li>
110</ul>
111
112<div style="margin: auto;">
113  <h2><a name="enable"></a>Enabling HDRI in ImageMagick</h2>
114</div>
115
116<p>By default image pixels in ImageMagick are stored as unsigned values that range from 0 to the quantum depth which is typically 16-bits (Q16).  With HDRI enabled, the pixels are stored in a floating-point representation and can include negative values as well as values that exceed the quantum depth.  A majority of digital image formats do not support HDRI so any pixels outside the quantum range are clamped before they are stored.  The most promising HDR image format is EXR.  You will need the <a href="http://www.openexr.org" target="493965299">OpenEXR</a> delegate library to read or write this format.  Other HDR formats include TIFF 48-bit integer and 96-bit float formats, HDR, PFM, and ImageMagick's own MIFF format.<p>
117
118<p>To enable the HDRI version of ImageMagick, use this Unix/Linux command:</p>
119
120<pre class="text">
121  ./configure --enable-hdri
122</pre>
123
124<p>Under Windows, set the <kbd>MAGICKCORE_HDRI_SUPPORT</kbd> definition in the <kbd>magick-config.h</kbd> configuration file and build.</p>
125
126<p>To verify HDRI is properly configured, look for "HDRI" in the version string:</p>
127
128<pre class="text">
129  -> identify -version
130  Version: ImageMagick 6.4.3 2008-09-01 Q16 HDRI http://www.imagemagick.org
131</pre>
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