/Src/Dependencies/Boost/libs/gil/doc/html/g_i_l_0009.html
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1<!-- Copyright 2008 Lubomir Bourdev and Hailin Jin 2 3 Distributed under the Boost Software License, Version 1.0. 4 (See accompanying file LICENSE_1_0.txt or copy at 5 http://www.boost.org/LICENSE_1_0.txt) 6 --> 7 8<!-- 9 Copyright 2005-2007 Adobe Systems Incorporated 10 Distributed under the MIT License (see accompanying file LICENSE_1_0_0.txt 11 or a copy at http://stlab.adobe.com/licenses.html) 12 13 Some files are held under additional license. 14 Please see "http://stlab.adobe.com/licenses.html" for more information. 15--> 16 17<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 18 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 19<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"> 20 21<head> 22 <TITLE>Generic Image Library: Histogram Example</TITLE> 23 <META HTTP-EQUIV="content-type" CONTENT="text/html;charset=ISO-8859-1"/> 24 <LINK TYPE="text/css" REL="stylesheet" HREF="adobe_source.css"/> 25</head> 26<body> 27<table border="0" cellspacing="0" cellpadding="0" style='width: 100%; margin: 0; padding: 0'><tr> 28<td width="100%" valign="top" style='padding-left: 10px; padding-right: 10px; padding-bottom: 10px'> 29<div class="qindex"><a class="qindex" href="index.html">Modules</a> 30 | <a class="qindex" href="classes.html">Alphabetical List</a> 31 | <a class="qindex" href="annotated.html">Class List</a> 32 | <a class="qindex" href="dirs.html">Directories</a> 33 | <a class="qindex" href="files.html">File List</a> 34 | <a class="qindex" href="../index.html">GIL Home Page</a> 35</div> 36<!-- End Header --> 37<!-- Generated by Doxygen 1.5.6 --> 38<div class="contents"> 39<h1><a class="anchor" name="BeforeAfterExample">Histogram Example </a></h1>Actual commercial code that computes the luminosity histogram (variable names have been changed and unrelated parts removed):<p> 40<div class="fragment"><pre class="fragment"><span class="keywordtype">void</span> luminosity_hist(<span class="keyword">const</span> uint8 *r, <span class="keyword">const</span> uint8 *g, <span class="keyword">const</span> uint8 *b, <span class="keywordtype">int</span> rows, <span class="keywordtype">int</span> cols, <span class="keywordtype">int</span> sRowBytes, Histogram *hist) 41{ 42 <span class="keywordflow">for</span> (<span class="keywordtype">int</span> r=0; r<rows; r++) 43 { 44 <span class="keywordflow">for</span> (<span class="keywordtype">int</span> c=0; c<cols; c++) 45 { 46 <span class="keywordtype">int</span> v=RGBToGray(r[c],g[c],b[c]); 47 (*hist)[v]++; 48 } 49 r+=sRowBytes; 50 g+=sRowBytes; 51 b+=sRowBytes; 52 } 53} 54</pre></div><p> 55<ul> 56<li>Works only for RGB (duplicate versions exist for other color spaces)</li><li>Works only for 8-bit images (duplicate versions exist)</li><li>Works only for planar images</li></ul> 57<p> 58Histogram using GIL:<p> 59<div class="fragment"><pre class="fragment"><span class="keyword">template</span> <<span class="keyword">typename</span> GrayView, <span class="keyword">typename</span> R> 60<span class="keywordtype">void</span> grayimage_histogram(GrayView& img, R& hist) { 61 <span class="keywordflow">for</span> (<span class="keyword">typename</span> GrayView::iterator it=img.begin(); it!=img.end(); ++it) 62 ++hist[*it]; 63} 64 65<span class="keyword">template</span> <<span class="keyword">typename</span> View, <span class="keyword">typename</span> R> 66<span class="keywordtype">void</span> luminosity8bit_hist(View& img, R& hist) 67{ 68 grayimage_histogram(color_converted_view<gray8_pixel_t>(img),hist); 69} 70</pre></div><p> 71using <code>boost::lambda</code> the GIL version can be written even simpler: <div class="fragment"><pre class="fragment"><span class="keyword">using</span> boost::lambda; 72 73<span class="keyword">template</span> <<span class="keyword">typename</span> GrayView, <span class="keyword">typename</span> R> 74<span class="keywordtype">void</span> grayimage_histogram(GrayView& img, R& hist) 75{ 76 for_each_pixel(img, ++var(hist)[_1]); 77} 78</pre></div><p> 79The GIL version:<ul> 80<li>Works with any supported channel depth, color space, channel ordering (RGB vs BGR), and row alignment policy.</li><li>Works for both planar and interleaved images.</li><li>Works with new color spaces, channel depths and image types that can be provided in future extensions of GIL</li><li>The second version is as efficient as the hand-coded version</li></ul> 81<p> 82It is also very flexible. For example, to compute the histogram of the second channel of the top left quadrant of the image, taking every other row and column, call:<p> 83<div class="fragment"><pre class="fragment">grayimage_histogram( 84 nth_channel_view( 85 subsampled_view( 86 subimage_view(img, 0,0, img.width()/2,img.height()/2), <span class="comment">// upper left quadrant</span> 87 2, 2 <span class="comment">// skip every other row and column</span> 88 ), 89 1 <span class="comment">// index of the second channel (for example, green for RGB)</span> 90 ), 91 hist 92); 93</pre></div><p> 94Note that no extra memory is allocated and no images are copied - GIL operates on the source pixels of <code>img</code> directly. </div> 95<hr size="1"><address style="text-align: right;"><small>Generated on Sat May 2 13:50:16 2009 for Generic Image Library by 96<a href="http://www.doxygen.org/index.html"> 97<img src="doxygen.png" alt="doxygen" align="middle" border="0"></a> 1.5.6 </small></address> 98</body> 99</html>