1<?xml version="1.0" encoding="UTF-8"?> 2<!DOCTYPE sect2 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" 3 "http://www.docbook.org/xml/4.3/docbookx.dtd"> 4<!-- section history: 5 2017-10-22 j.h: update 6--> 7<sect2 id="filters-blur-introduction"> 8 <title>Introduction</title> 9 10 <indexterm> 11 <primary>Filters</primary> 12 <secondary>Blur</secondary> 13 </indexterm> 14 15 <figure> 16 <title>Original for demo</title> 17 <mediaobject> 18 <imageobject> 19 <imagedata format="PNG" 20 fileref="images/filters/examples/blur-demo-orig.png"/> 21 </imageobject> 22 </mediaobject> 23 </figure> 24 <para> 25 This is a set of filters that blur images, or parts of them, 26 in various ways. If there is a selection, only the selected parts 27 of an image will be blurred. There may, however, be some leakage 28 of colors from the unblurred area into the blurred area. To help 29 you pick the one you want, we will illustrate what each does when 30 applied to the image shown at right. These are, of course, only 31 examples: most of the filters have parameter settings that allow 32 you to vary the magnitude or type of blurring. 33 </para> 34 35 <figure> 36 <title>Gaussian blur (radius 10)</title> 37 <mediaobject> 38 <imageobject> 39 <imagedata format="PNG" 40 fileref="images/filters/examples/blur-demo-gauss10.png"/> 41 </imageobject> 42 </mediaobject> 43 </figure> 44 <para> 45 The most broadly useful of these is the Gaussian blur. (Don't let 46 the word "Gaussian" throw you: this filter makes an image blurry 47 in the most basic way.) It has an efficient implementation that 48 allows it to create a very blurry blur in a relatively short 49 time. 50 </para> 51 52 <figure> 53 <title>Selective blur</title> 54 <mediaobject> 55 <imageobject> 56 <imagedata format="PNG" 57 fileref="images/filters/examples/blur-demo-selective.png"/> 58 </imageobject> 59 </mediaobject> 60 </figure> 61 <para> 62 The Selective Blur filter allows you to set a threshold so that 63 only pixels that are similar to each other are blurred together. 64 It is often useful as a tool for reducing graininess in photos 65 without blurring sharp edges. (In the example, note that the 66 graininess of the background has been reduced.) The 67 implementation is much slower 68 than a Gaussian blur, though, so you should not use it unless you 69 really need the selectivity. 70 </para> 71 72 <figure> 73 <title>Pixelize</title> 74 <mediaobject> 75 <imageobject> 76 <imagedata format="PNG" 77 fileref="images/filters/examples/blur-demo-pixelize.png"/> 78 </imageobject> 79 </mediaobject> 80 </figure> 81 <para> 82 The Pixelize filter produces the well-known "Abraham Lincoln" 83 effect by turning the image into a set of large square pixels. 84 (The <link linkend="gimp-filter-oilify">Oilify</link> filter, in 85 the Artistic Filters group, has a similar effect, but with 86 irregular blobs instead of perfectly square pixels.) 87 </para> 88 <note> 89 <para> 90 You can find a nice explanation of the Abraham Lincoln effect 91 at <xref linkend="bibliography-online-bach"/>. You will see the 92 Salvador Dali's painting <quote>Gala Contemplating the 93 Mediterranean Sea</quote> turning to an Abraham Lincoln's portrait 94 when looking at it from a distance. 95 </para> 96 </note> 97 98 <para> 99 With GIMP-2.10, the Motion Blur filter has been divided in Circular, 100 Linear, and Zoom. 101 </para> 102 103 <figure> 104 <title>Circular Motion Blur filter</title> 105 <mediaobject> 106 <imageobject> 107 <imagedata format="PNG" 108 fileref="images/filters/examples/blur-demo-circular.png"/> 109 </imageobject> 110 </mediaobject> 111 </figure> 112 <para> 113 The Circular Motion Blur filter blurs in a rotational direction 114 around a center that you can set. 115 </para> 116 117 <figure> 118 <title>Linear Motion Blur filter</title> 119 <mediaobject> 120 <imageobject> 121 <imagedata format="PNG" 122 fileref="images/filters/examples/blur-demo-linear.png"/> 123 </imageobject> 124 </mediaobject> 125 </figure> 126 <para> 127 The Linear Motion Blur filter blurs in a direction that you can set. 128 </para> 129 130 <figure> 131 <title>Zoom Motion Blur filter</title> 132 <mediaobject> 133 <imageobject> 134 <imagedata format="PNG" 135 fileref="images/filters/examples/blur-demo-zoom.png"/> 136 </imageobject> 137 </mediaobject> 138 </figure> 139 <para> 140 The Zoom Motion Blur filter blurs in a radial direction around a 141 center that you can set. 142 </para> 143 144 <para> 145 Finally, the Tileable Blur filter is really the same thing as a Gaussian 146 blur, except that it wraps around the edges of an image to help you reduce 147 edge effects when you create a pattern by tiling multiple copies of the 148 image side by side. 149 </para> 150 <note> 151 <para> 152 Tileable Blur is actually implemented by a Script-Fu script that invokes 153 the Gaussian blur plug-in. 154 </para> 155 </note> 156</sect2> 157