Mercurial > hg > octave-lyh
annotate doc/interpreter/image.txi @ 17489:0ad2f93fd83c
doc: Fix a typo in findobj docstring.
* scripts/plot/findobj.m: Use '3' instead of 'D' in findobj example of depth 3.
| author | Rik <rik@octave.org> |
|---|---|
| date | Wed, 25 Sep 2013 08:13:30 -0700 |
| parents | bc924baa2c4e |
| children |
| rev | line source |
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1 @c Copyright (C) 1996-2012 John W. Eaton |
| 7018 | 2 @c |
| 3 @c This file is part of Octave. | |
| 4 @c | |
| 5 @c Octave is free software; you can redistribute it and/or modify it | |
| 6 @c under the terms of the GNU General Public License as published by the | |
| 7 @c Free Software Foundation; either version 3 of the License, or (at | |
| 8 @c your option) any later version. | |
| 9 @c | |
| 10 @c Octave is distributed in the hope that it will be useful, but WITHOUT | |
| 11 @c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 12 @c FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 13 @c for more details. | |
| 14 @c | |
| 15 @c You should have received a copy of the GNU General Public License | |
| 16 @c along with Octave; see the file COPYING. If not, see | |
| 17 @c <http://www.gnu.org/licenses/>. | |
| 3294 | 18 |
| 4167 | 19 @node Image Processing |
| 3294 | 20 @chapter Image Processing |
| 21 | |
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22 Since an image is basically a matrix, Octave is a very powerful |
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23 environment for processing and analyzing images. To illustrate |
| 6529 | 24 how easy it is to do image processing in Octave, the following |
| 25 example will load an image, smooth it by a 5-by-5 averaging filter, | |
| 26 and compute the gradient of the smoothed image. | |
| 27 | |
| 28 @example | |
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29 @group |
| 8148 | 30 I = imread ("myimage.jpg"); |
| 6535 | 31 S = conv2 (I, ones (5, 5) / 25, "same"); |
| 32 [Dx, Dy] = gradient (S); | |
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33 @end group |
| 6529 | 34 @end example |
| 35 | |
| 36 @noindent | |
| 37 In this example @code{S} contains the smoothed image, and @code{Dx} | |
| 38 and @code{Dy} contains the partial spatial derivatives of the image. | |
| 39 | |
| 6535 | 40 @menu |
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41 * Loading and Saving Images:: |
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42 * Displaying Images:: |
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43 * Representing Images:: |
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44 * Plotting on top of Images:: |
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45 * Color Conversion:: |
| 6535 | 46 @end menu |
| 47 | |
| 6529 | 48 @node Loading and Saving Images |
| 49 @section Loading and Saving Images | |
| 50 | |
| 51 The first step in most image processing tasks is to load an image | |
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52 into Octave which is done with the @code{imread} function. |
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53 The @code{imwrite} function is the corresponding function |
| 8148 | 54 for writing images to the disk. |
| 55 | |
| 56 In summary, most image processing code will follow the structure of this code | |
| 3294 | 57 |
| 6529 | 58 @example |
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59 @group |
| 8148 | 60 I = imread ("my_input_image.img"); |
| 6535 | 61 J = process_my_image (I); |
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62 imwrite (J, "my_output_image.img"); |
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63 @end group |
| 6529 | 64 @end example |
| 65 | |
| 8148 | 66 @DOCSTRING(imread) |
| 6529 | 67 |
| 8148 | 68 @DOCSTRING(imwrite) |
| 6529 | 69 |
| 70 @DOCSTRING(IMAGE_PATH) | |
| 3294 | 71 |
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72 It is possible to get information about an image file on disk, without actually |
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73 reading it into Octave. This is done using the @code{imfinfo} function which |
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74 provides read access to many of the parameters stored in the header of the image |
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75 file. |
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76 |
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77 @DOCSTRING(imfinfo) |
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78 |
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79 By default, Octave's image IO functions (@code{imread}, @code{imwrite}, |
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80 and @code{imfinfo}) use the @code{GraphicsMagick} library for their |
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81 operations. This means a vast number of image formats is supported |
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82 but considering the large amount of image formats in science and |
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83 its commonly closed nature, it is impossible to have a library |
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84 capable of reading them all. Because of this, the function |
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85 @code{imformats} keeps a configurable list of available formats, |
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86 their extensions, and what functions should the image IO functions |
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87 use. This allows to expand Octave's image IO capabilities by |
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88 creating functions aimed at acting on specific file formats. |
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89 |
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90 While it would be possible to call the extra functions directly, |
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91 properly configuring Octave with @code{imformats} allows to keep a |
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92 consistent code that is abstracted from file formats. |
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93 |
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94 It is important to note that a file format is not actually defined by its |
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95 file extension and that @code{GraphicsMagick} is capable to read and write |
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96 more file formats than the ones listed by @code{imformats}. What this |
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97 means is that even with an incorrect or missing extension the image may |
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98 still be read correctly, and that even unlisted formats are not necessarily |
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99 unsupported. |
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100 |
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101 @DOCSTRING(imformats) |
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102 |
| 6529 | 103 @node Displaying Images |
| 104 @section Displaying Images | |
| 3294 | 105 |
| 6529 | 106 A natural part of image processing is visualization of an image. |
| 107 The most basic function for this is the @code{imshow} function that | |
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108 shows the image given in the first input argument. |
| 3294 | 109 |
| 6529 | 110 @DOCSTRING(imshow) |
| 3294 | 111 |
| 3373 | 112 @DOCSTRING(image) |
| 3294 | 113 |
| 3373 | 114 @DOCSTRING(imagesc) |
| 3294 | 115 |
| 6529 | 116 @node Representing Images |
| 117 @section Representing Images | |
| 118 | |
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119 In general Octave supports four different kinds of images, grayscale |
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120 images, RGB images, binary images, and indexed images. A grayscale |
| 6535 | 121 image is represented with an M-by-N matrix in which each |
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122 element corresponds to the intensity of a pixel. An RGB image is |
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123 represented with an M-by-N-by-3 array where each |
| 6529 | 124 3-vector corresponds to the red, green, and blue intensities of each |
| 125 pixel. | |
| 126 | |
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127 The actual meaning of the value of a pixel in a grayscale or RGB |
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128 image depends on the class of the matrix. If the matrix is of class |
| 6529 | 129 @code{double} pixel intensities are between 0 and 1, if it is of class |
| 130 @code{uint8} intensities are between 0 and 255, and if it is of class | |
| 131 @code{uint16} intensities are between 0 and 65535. | |
| 132 | |
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133 A binary image is an M-by-N matrix of class @code{logical}. |
| 6529 | 134 A pixel in a binary image is black if it is @code{false} and white |
| 135 if it is @code{true}. | |
| 136 | |
| 6535 | 137 An indexed image consists of an M-by-N matrix of integers |
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138 and a C-by-3 color map. Each integer corresponds to an |
| 6529 | 139 index in the color map, and each row in the color map corresponds to |
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140 an RGB color. The color map must be of class @code{double} with values |
| 6529 | 141 between 0 and 1. |
| 142 | |
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143 @DOCSTRING(iscolormap) |
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144 |
| 6529 | 145 @DOCSTRING(gray2ind) |
| 3294 | 146 |
| 3373 | 147 @DOCSTRING(ind2gray) |
| 3294 | 148 |
| 6529 | 149 @DOCSTRING(rgb2ind) |
| 150 | |
| 3373 | 151 @DOCSTRING(ind2rgb) |
| 3294 | 152 |
| 6529 | 153 @DOCSTRING(colormap) |
| 154 | |
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155 @DOCSTRING(rgbplot) |
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156 |
| 6788 | 157 @DOCSTRING(autumn) |
| 158 | |
| 159 @DOCSTRING(bone) | |
| 160 | |
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161 @DOCSTRING(colorcube) |
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162 |
| 6788 | 163 @DOCSTRING(cool) |
| 164 | |
| 165 @DOCSTRING(copper) | |
| 166 | |
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167 @DOCSTRING(flag) |
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168 |
| 6529 | 169 @DOCSTRING(gray) |
| 170 | |
| 6788 | 171 @DOCSTRING(hot) |
| 172 | |
| 173 @DOCSTRING(hsv) | |
| 174 | |
| 175 @DOCSTRING(jet) | |
| 176 | |
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177 @DOCSTRING(lines) |
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178 |
| 6529 | 179 @DOCSTRING(ocean) |
| 180 | |
| 6788 | 181 @DOCSTRING(pink) |
| 182 | |
| 183 @DOCSTRING(prism) | |
| 184 | |
| 185 @DOCSTRING(rainbow) | |
| 186 | |
| 187 @DOCSTRING(spring) | |
| 188 | |
| 189 @DOCSTRING(summer) | |
| 190 | |
| 191 @DOCSTRING(white) | |
| 192 | |
| 193 @DOCSTRING(winter) | |
| 194 | |
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195 @DOCSTRING(contrast) |
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196 |
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197 An additional colormap is @code{gmap40}. This code map contains only |
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198 colors with integer values of the red, green and blue components. This |
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199 is a workaround for a limitation of gnuplot 4.0, that does not allow the color |
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200 of line or patch objects to be set. @code{gmap40} is chiefly useful to gnuplot |
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201 4.0 users, and particularly in conjunction with the @var{bar}, @var{surf}, |
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202 and @var{contour} functions. |
| 7189 | 203 |
| 204 @DOCSTRING(gmap40) | |
| 205 | |
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206 The following three functions modify the existing colormap rather than |
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207 replace it. |
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208 |
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209 @DOCSTRING(brighten) |
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210 |
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211 @DOCSTRING(spinmap) |
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212 |
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213 @DOCSTRING(whitebg) |
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214 |
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215 The following functions can be used to manipulate colormaps. |
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216 |
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217 @DOCSTRING(cmunique) |
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218 |
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219 @DOCSTRING(cmpermute) |
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220 |
| 6529 | 221 @node Plotting on top of Images |
| 222 @section Plotting on top of Images | |
| 223 | |
| 224 If gnuplot is being used to display images it is possible to plot on | |
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225 top of images. Since an image is a matrix it is indexed by row and |
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226 column values. The plotting system is, however, based on the |
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227 traditional @math{(x, y)} system. To minimize the difference between |
| 6529 | 228 the two systems Octave places the origin of the coordinate system in |
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229 the point corresponding to the pixel at @math{(1, 1)}. So, to plot |
| 6529 | 230 points given by row and column values on top of an image, one should |
| 231 simply call @code{plot} with the column values as the first argument | |
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232 and the row values as the second. As an example the following code |
| 6529 | 233 generates an image with random intensities between 0 and 1, and shows |
| 234 the image with red circles over pixels with an intensity above | |
| 235 @math{0.99}. | |
| 236 | |
| 237 @example | |
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238 @group |
| 6535 | 239 I = rand (100, 100); |
| 240 [row, col] = find (I > 0.99); | |
| 241 hold ("on"); | |
| 242 imshow (I); | |
| 243 plot (col, row, "ro"); | |
| 244 hold ("off"); | |
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245 @end group |
| 6529 | 246 @end example |
| 247 | |
| 248 @node Color Conversion | |
| 249 @section Color Conversion | |
| 250 | |
| 251 Octave supports conversion from the RGB color system to NTSC and HSV | |
| 252 and vice versa. | |
| 253 | |
| 254 @DOCSTRING(rgb2hsv) | |
| 255 | |
| 256 @DOCSTRING(hsv2rgb) | |
| 3294 | 257 |
| 3373 | 258 @DOCSTRING(rgb2ntsc) |
| 3294 | 259 |
| 3373 | 260 @DOCSTRING(ntsc2rgb) |
| 3294 | 261 |
| 3803 | 262 |