Mercurial > hg > octave-lyh
annotate doc/interpreter/image.txi @ 9210:a7a9eecc07b5
Change recommendation for writing documentation to favor @tex
rather than @iftex construction.
| author | Rik <rdrider0-list@yahoo.com> |
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| date | Sun, 17 May 2009 14:17:32 -0700 |
| parents | bd8e388043c4 |
| children | 322f43e0e170 |
| rev | line source |
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| 8920 | 1 @c Copyright (C) 1996, 1997, 2007, 2008, 2009 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 | |
| 6529 | 22 Since an image basically is 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 |
| 41 * Loading and Saving Images:: | |
| 42 * Displaying Images:: | |
| 43 * Representing Images:: | |
| 44 * Plotting on top of Images:: | |
| 45 * Color Conversion:: | |
| 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. This is done using the @code{imread} function, which uses the |
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53 @code{GraphicsMagick} library for reading. This means a vast number of image |
| 8148 | 54 formats is supported. The @code{imwrite} function is the corresponding function |
| 55 for writing images to the disk. | |
| 56 | |
| 57 In summary, most image processing code will follow the structure of this code | |
| 3294 | 58 |
| 6529 | 59 @example |
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60 @group |
| 8148 | 61 I = imread ("my_input_image.img"); |
| 6535 | 62 J = process_my_image (I); |
| 8148 | 63 imwrite ("my_output_image.img", J); |
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64 @end group |
| 6529 | 65 @end example |
| 66 | |
| 8148 | 67 @DOCSTRING(imread) |
| 6529 | 68 |
| 8148 | 69 @DOCSTRING(imwrite) |
| 6529 | 70 |
| 71 @DOCSTRING(IMAGE_PATH) | |
| 3294 | 72 |
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73 It is possible to get information about an image file on disk, without actually |
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74 reading it into Octave. This is done using the @code{imfinfo} function which |
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75 provides read access to many of the parameters stored in the header of the image |
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76 file. |
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77 |
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78 @DOCSTRING(imfinfo) |
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79 |
| 6529 | 80 @node Displaying Images |
| 81 @section Displaying Images | |
| 3294 | 82 |
| 6529 | 83 A natural part of image processing is visualization of an image. |
| 84 The most basic function for this is the @code{imshow} function that | |
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85 shows the image given in the first input argument. This function uses |
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86 an external program to show the image. If gnuplot 4.2 or later is |
| 6529 | 87 available it will be used to display the image, otherwise the |
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88 @code{display}, @code{xv}, or @code{xloadimage} program is used. The |
| 6529 | 89 actual program can be selected with the @code{image_viewer} function. |
| 3294 | 90 |
| 6529 | 91 @DOCSTRING(imshow) |
| 3294 | 92 |
| 3373 | 93 @DOCSTRING(image) |
| 3294 | 94 |
| 3373 | 95 @DOCSTRING(imagesc) |
| 3294 | 96 |
| 6529 | 97 @DOCSTRING(image_viewer) |
| 98 | |
| 99 @node Representing Images | |
| 100 @section Representing Images | |
| 101 | |
| 102 In general Octave supports four different kinds of images, gray-scale | |
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103 images, RGB images, binary images, and indexed images. A gray-scale |
| 6535 | 104 image is represented with an M-by-N matrix in which each |
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105 element corresponds to the intensity of a pixel. An RGB image is |
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106 represented with an M-by-N-by-3 array where each |
| 6529 | 107 3-vector corresponds to the red, green, and blue intensities of each |
| 108 pixel. | |
| 109 | |
| 110 The actual meaning of the value of a pixel in a gray-scale or RGB | |
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111 image depends on the class of the matrix. If the matrix is of class |
| 6529 | 112 @code{double} pixel intensities are between 0 and 1, if it is of class |
| 113 @code{uint8} intensities are between 0 and 255, and if it is of class | |
| 114 @code{uint16} intensities are between 0 and 65535. | |
| 115 | |
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116 A binary image is an M-by-N matrix of class @code{logical}. |
| 6529 | 117 A pixel in a binary image is black if it is @code{false} and white |
| 118 if it is @code{true}. | |
| 119 | |
| 6535 | 120 An indexed image consists of an M-by-N matrix of integers |
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121 and a C-by-3 color map. Each integer corresponds to an |
| 6529 | 122 index in the color map, and each row in the color map corresponds to |
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123 an RGB color. The color map must be of class @code{double} with values |
| 6529 | 124 between 0 and 1. |
| 125 | |
| 126 @DOCSTRING(gray2ind) | |
| 3294 | 127 |
| 3373 | 128 @DOCSTRING(ind2gray) |
| 3294 | 129 |
| 6529 | 130 @DOCSTRING(rgb2ind) |
| 131 | |
| 3373 | 132 @DOCSTRING(ind2rgb) |
| 3294 | 133 |
| 6529 | 134 @DOCSTRING(colormap) |
| 135 | |
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136 @DOCSTRING(brighten) |
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137 |
| 6788 | 138 @DOCSTRING(autumn) |
| 139 | |
| 140 @DOCSTRING(bone) | |
| 141 | |
| 142 @DOCSTRING(cool) | |
| 143 | |
| 144 @DOCSTRING(copper) | |
| 145 | |
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146 @DOCSTRING(flag) |
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147 |
| 6529 | 148 @DOCSTRING(gray) |
| 149 | |
| 6788 | 150 @DOCSTRING(hot) |
| 151 | |
| 152 @DOCSTRING(hsv) | |
| 153 | |
| 154 @DOCSTRING(jet) | |
| 155 | |
| 6529 | 156 @DOCSTRING(ocean) |
| 157 | |
| 6788 | 158 @DOCSTRING(pink) |
| 159 | |
| 160 @DOCSTRING(prism) | |
| 161 | |
| 162 @DOCSTRING(rainbow) | |
| 163 | |
| 164 @DOCSTRING(spring) | |
| 165 | |
| 166 @DOCSTRING(summer) | |
| 167 | |
| 168 @DOCSTRING(white) | |
| 169 | |
| 170 @DOCSTRING(winter) | |
| 171 | |
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172 @DOCSTRING(contrast) |
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173 |
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174 An additional colormap is @code{gmap40}. This code map contains only |
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175 colors with integer values of the red, green and blue components. This |
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176 is a workaround for a limitation of gnuplot 4.0, that does not allow the color of |
| 7189 | 177 line or patch objects to be set, and so @code{gmap40} is useful for |
| 178 gnuplot 4.0 users, and in particular in conjunction with the @var{bar}, | |
| 179 @var{barh} or @var{contour} functions. | |
| 180 | |
| 181 @DOCSTRING(gmap40) | |
| 182 | |
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183 You may use the @code{spinmap} function to cycle through the colors in |
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184 the current colormap, displaying the changes for the current figure. |
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185 |
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186 @DOCSTRING(spinmap) |
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187 |
| 6529 | 188 @node Plotting on top of Images |
| 189 @section Plotting on top of Images | |
| 190 | |
| 191 If gnuplot is being used to display images it is possible to plot on | |
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192 top of images. Since an image is a matrix it is indexed by row and |
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193 column values. The plotting system is, however, based on the |
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194 traditional @math{(x, y)} system. To minimize the difference between |
| 6529 | 195 the two systems Octave places the origin of the coordinate system in |
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196 the point corresponding to the pixel at @math{(1, 1)}. So, to plot |
| 6529 | 197 points given by row and column values on top of an image, one should |
| 198 simply call @code{plot} with the column values as the first argument | |
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199 and the row values as the second. As an example the following code |
| 6529 | 200 generates an image with random intensities between 0 and 1, and shows |
| 201 the image with red circles over pixels with an intensity above | |
| 202 @math{0.99}. | |
| 203 | |
| 204 @example | |
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205 @group |
| 6535 | 206 I = rand (100, 100); |
| 207 [row, col] = find (I > 0.99); | |
| 208 hold ("on"); | |
| 209 imshow (I); | |
| 210 plot (col, row, "ro"); | |
| 211 hold ("off"); | |
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212 @end group |
| 6529 | 213 @end example |
| 214 | |
| 215 @node Color Conversion | |
| 216 @section Color Conversion | |
| 217 | |
| 218 Octave supports conversion from the RGB color system to NTSC and HSV | |
| 219 and vice versa. | |
| 220 | |
| 221 @DOCSTRING(rgb2hsv) | |
| 222 | |
| 223 @DOCSTRING(hsv2rgb) | |
| 3294 | 224 |
| 3373 | 225 @DOCSTRING(rgb2ntsc) |
| 3294 | 226 |
| 3373 | 227 @DOCSTRING(ntsc2rgb) |
| 3294 | 228 |
| 3803 | 229 |