Mercurial > octave-antonio
annotate doc/interpreter/image.txi @ 8817:03b7f618ab3d
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| author | John W. Eaton <jwe@octave.org> |
|---|---|
| date | Thu, 19 Feb 2009 15:39:19 -0500 |
| parents | 67a632417879 |
| children | eb63fbe60fab |
| rev | line source |
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| 6778 | 1 @c Copyright (C) 1996, 1997, 2007 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 |
| 23 environment for processing and analysing images. To illustrate | |
| 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 | |
| 8148 | 29 I = imread ("myimage.jpg"); |
| 6535 | 30 S = conv2 (I, ones (5, 5) / 25, "same"); |
| 31 [Dx, Dy] = gradient (S); | |
| 6529 | 32 @end example |
| 33 | |
| 34 @noindent | |
| 35 In this example @code{S} contains the smoothed image, and @code{Dx} | |
| 36 and @code{Dy} contains the partial spatial derivatives of the image. | |
| 37 | |
| 6535 | 38 @menu |
| 39 * Loading and Saving Images:: | |
| 40 * Displaying Images:: | |
| 41 * Representing Images:: | |
| 42 * Plotting on top of Images:: | |
| 43 * Color Conversion:: | |
| 44 @end menu | |
| 45 | |
| 6529 | 46 @node Loading and Saving Images |
| 47 @section Loading and Saving Images | |
| 48 | |
| 49 The first step in most image processing tasks is to load an image | |
| 8148 | 50 into Octave. This is done using the @code{imread} function, which uses the |
| 51 @code{GraphicsMagick} library for reading. This means a vast number of image | |
| 52 formats is supported. The @code{imwrite} function is the corresponding function | |
| 53 for writing images to the disk. | |
| 54 | |
| 55 In summary, most image processing code will follow the structure of this code | |
| 3294 | 56 |
| 6529 | 57 @example |
| 8148 | 58 I = imread ("my_input_image.img"); |
| 6535 | 59 J = process_my_image (I); |
| 8148 | 60 imwrite ("my_output_image.img", J); |
| 6529 | 61 @end example |
| 62 | |
| 8148 | 63 @DOCSTRING(imread) |
| 6529 | 64 |
| 8148 | 65 @DOCSTRING(imwrite) |
| 6529 | 66 |
| 67 @DOCSTRING(IMAGE_PATH) | |
| 3294 | 68 |
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69 It is possible to get information about an image file on disk, without actually |
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70 reading in into Octave. This is done using the @code{imfinfo} function which |
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71 provides read access to many of the parameters stored in the header of the image |
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72 file. |
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73 |
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74 @DOCSTRING(imfinfo) |
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75 |
| 6529 | 76 @node Displaying Images |
| 77 @section Displaying Images | |
| 3294 | 78 |
| 6529 | 79 A natural part of image processing is visualization of an image. |
| 80 The most basic function for this is the @code{imshow} function that | |
| 81 shows the image given in the first input argument. This function uses | |
| 82 an external program to show the image. If gnuplot 4.2 or later is | |
| 83 available it will be used to display the image, otherwise the | |
| 84 @code{display}, @code{xv}, or @code{xloadimage} program is used. The | |
| 85 actual program can be selected with the @code{image_viewer} function. | |
| 3294 | 86 |
| 6529 | 87 @DOCSTRING(imshow) |
| 3294 | 88 |
| 3373 | 89 @DOCSTRING(image) |
| 3294 | 90 |
| 3373 | 91 @DOCSTRING(imagesc) |
| 3294 | 92 |
| 6529 | 93 @DOCSTRING(image_viewer) |
| 94 | |
| 95 @node Representing Images | |
| 96 @section Representing Images | |
| 97 | |
| 98 In general Octave supports four different kinds of images, gray-scale | |
| 99 images, RGB images, binary images, and indexed images. A gray-scale | |
| 6535 | 100 image is represented with an M-by-N matrix in which each |
| 6529 | 101 element corresponds to the intensity of a pixel. An RGB image is |
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102 represented with an M-by-N-by-3 array where each |
| 6529 | 103 3-vector corresponds to the red, green, and blue intensities of each |
| 104 pixel. | |
| 105 | |
| 106 The actual meaning of the value of a pixel in a gray-scale or RGB | |
| 107 image depends on the class of the matrix. If the matrix is of class | |
| 108 @code{double} pixel intensities are between 0 and 1, if it is of class | |
| 109 @code{uint8} intensities are between 0 and 255, and if it is of class | |
| 110 @code{uint16} intensities are between 0 and 65535. | |
| 111 | |
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112 A binary image is an M-by-N matrix of class @code{logical}. |
| 6529 | 113 A pixel in a binary image is black if it is @code{false} and white |
| 114 if it is @code{true}. | |
| 115 | |
| 6535 | 116 An indexed image consists of an M-by-N matrix of integers |
| 117 and a C-by-3 color map. Each integer corresponds to an | |
| 6529 | 118 index in the color map, and each row in the color map corresponds to |
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119 an RGB color. The color map must be of class @code{double} with values |
| 6529 | 120 between 0 and 1. |
| 121 | |
| 122 @DOCSTRING(gray2ind) | |
| 3294 | 123 |
| 3373 | 124 @DOCSTRING(ind2gray) |
| 3294 | 125 |
| 6529 | 126 @DOCSTRING(rgb2ind) |
| 127 | |
| 3373 | 128 @DOCSTRING(ind2rgb) |
| 3294 | 129 |
| 6529 | 130 @DOCSTRING(colormap) |
| 131 | |
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132 @DOCSTRING(brighten) |
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133 |
| 6788 | 134 @DOCSTRING(autumn) |
| 135 | |
| 136 @DOCSTRING(bone) | |
| 137 | |
| 138 @DOCSTRING(cool) | |
| 139 | |
| 140 @DOCSTRING(copper) | |
| 141 | |
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142 @DOCSTRING(flag) |
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143 |
| 6529 | 144 @DOCSTRING(gray) |
| 145 | |
| 6788 | 146 @DOCSTRING(hot) |
| 147 | |
| 148 @DOCSTRING(hsv) | |
| 149 | |
| 150 @DOCSTRING(jet) | |
| 151 | |
| 6529 | 152 @DOCSTRING(ocean) |
| 153 | |
| 6788 | 154 @DOCSTRING(pink) |
| 155 | |
| 156 @DOCSTRING(prism) | |
| 157 | |
| 158 @DOCSTRING(rainbow) | |
| 159 | |
| 160 @DOCSTRING(spring) | |
| 161 | |
| 162 @DOCSTRING(summer) | |
| 163 | |
| 164 @DOCSTRING(white) | |
| 165 | |
| 166 @DOCSTRING(winter) | |
| 167 | |
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168 @DOCSTRING(contrast) |
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169 |
| 7189 | 170 An additional colormap is @code{gmap40}. This code map contains only |
| 171 colors with integer values of the red, green and blue components. This | |
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172 is a workaround for a limitation of gnuplot 4.0, that does not allow the color of |
| 7189 | 173 line or patch objects to be set, and so @code{gmap40} is useful for |
| 174 gnuplot 4.0 users, and in particular in conjunction with the @var{bar}, | |
| 175 @var{barh} or @var{contour} functions. | |
| 176 | |
| 177 @DOCSTRING(gmap40) | |
| 178 | |
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179 You may use the @code{spinmap} function to cycle through the colors in |
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180 the current colormap, displaying the changes for the current figure. |
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181 |
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182 @DOCSTRING(spinmap) |
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183 |
| 6529 | 184 @node Plotting on top of Images |
| 185 @section Plotting on top of Images | |
| 186 | |
| 187 If gnuplot is being used to display images it is possible to plot on | |
| 188 top of images. Since an image is a matrix it is indexed by row and | |
| 189 column values. The plotting system is, however, based on the | |
| 190 traditional @math{(x, y)} system. To minimize the difference between | |
| 191 the two systems Octave places the origin of the coordinate system in | |
| 192 the point corresponding to the pixel at @math{(1, 1)}. So, to plot | |
| 193 points given by row and column values on top of an image, one should | |
| 194 simply call @code{plot} with the column values as the first argument | |
| 195 and the row values as the second. As an example the following code | |
| 196 generates an image with random intensities between 0 and 1, and shows | |
| 197 the image with red circles over pixels with an intensity above | |
| 198 @math{0.99}. | |
| 199 | |
| 200 @example | |
| 6535 | 201 I = rand (100, 100); |
| 202 [row, col] = find (I > 0.99); | |
| 203 hold ("on"); | |
| 204 imshow (I); | |
| 205 plot (col, row, "ro"); | |
| 206 hold ("off"); | |
| 6529 | 207 @end example |
| 208 | |
| 209 @node Color Conversion | |
| 210 @section Color Conversion | |
| 211 | |
| 212 Octave supports conversion from the RGB color system to NTSC and HSV | |
| 213 and vice versa. | |
| 214 | |
| 215 @DOCSTRING(rgb2hsv) | |
| 216 | |
| 217 @DOCSTRING(hsv2rgb) | |
| 3294 | 218 |
| 3373 | 219 @DOCSTRING(rgb2ntsc) |
| 3294 | 220 |
| 3373 | 221 @DOCSTRING(ntsc2rgb) |
| 3294 | 222 |
| 3803 | 223 |