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>Basics - 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="Image Processing" href="index.html" /> 27 <link rel="next" title="Affine region detectors" href="affine-region-detectors.html" /> 28 <link rel="prev" title="Overview" href="overview.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="Overview" href="overview.html"><img src="../_static/prev.png" alt="prev"/></a> 63 <a class="up" title="Image Processing" href="index.html"><img src="../_static/up.png" alt="up"/></a> 64 <a class="next" title="Affine region detectors" href="affine-region-detectors.html"><img src="../_static/next.png" alt="next"/></a> 65 66 </div> 67 68 <div class="section" id="basics"> 69<h1>Basics</h1> 70<p>Here are basic concepts that might help to understand documentation 71written in this folder:</p> 72<div class="section" id="convolution"> 73<h2>Convolution</h2> 74<p>The simplest way to look at this is “tweaking the input so that it would 75look like the shape provided”. What exact tweaking is applied depends on 76the kernel.</p> 77</div> 78<hr class="docutils" /> 79<div class="section" id="filters-kernels-weights"> 80<h2>Filters, kernels, weights</h2> 81<p>Those three words usually mean the same thing, unless context is clear 82about a different usage. Simply put, they are matrices, that are used to 83achieve certain effects on the image. Lets consider a simple one, 3 by 3 84Scharr filter</p> 85<p><code class="docutils literal"><span class="pre">ScharrX</span> <span class="pre">=</span> <span class="pre">[1,0,-1][1,0,-1][1,0,-1]</span></code></p> 86<p>The filter above, when convolved with a single channel image 87(intensity/luminance strength), will produce a gradient in X 88(horizontal) direction. There is filtering that cannot be done with a 89kernel though, and one good example is median filter (mean is the 90arithmetic mean, whereas median will be the center element of a sorted 91array).</p> 92</div> 93<hr class="docutils" /> 94<div class="section" id="derivatives"> 95<h2>Derivatives</h2> 96<p>A derivative of an image is a gradient in one of two directions: x 97(horizontal) and y (vertical). To compute a derivative, one can use 98Scharr, Sobel and other gradient filters.</p> 99</div> 100<hr class="docutils" /> 101<div class="section" id="curvature"> 102<h2>Curvature</h2> 103<p>The word, when used alone, will mean the curvature that would be 104generated if values of an image would be plotted in 3D graph. X and Z 105axises (which form horizontal plane) will correspond to X and Y indices 106of an image, and Y axis will correspond to value at that pixel. By 107little stretch of an imagination, filters (another names are kernels, 108weights) could be considered an image (or any 2D matrix). A mean filter 109would draw a flat plane, whereas Gaussian filter would draw a hill that 110gets sharper depending on it’s sigma value.</p> 111</div> 112</div> 113 114 115 <div class="navbar" style="text-align:right;"> 116 117 118 <a class="prev" title="Overview" href="overview.html"><img src="../_static/prev.png" alt="prev"/></a> 119 <a class="up" title="Image Processing" href="index.html"><img src="../_static/up.png" alt="up"/></a> 120 <a class="next" title="Affine region detectors" href="affine-region-detectors.html"><img src="../_static/next.png" alt="next"/></a> 121 122 </div> 123 </div> 124 <div class="footer" role="contentinfo"> 125 Last updated on 2020-08-11 15:08:48. 126 Created using <a href="http://sphinx-doc.org/">Sphinx</a> 1.5.6. 127 </div> 128 </body> 129</html>
