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| 54 | ||
| 55 | <H1><A NAME="SECTION0016200000000000000000"> | |
| 56 | 14.2 <tt class="module">imageop</tt> -- | |
| 57 | Manipulate raw image data</A> | |
| 58 | </H1> | |
| 59 | ||
| 60 | <P> | |
| 61 | <A NAME="module-imageop"></A> | |
| 62 | ||
| 63 | <P> | |
| 64 | The <tt class="module">imageop</tt> module contains some useful operations on images. | |
| 65 | It operates on images consisting of 8 or 32 bit pixels stored in | |
| 66 | Python strings. This is the same format as used by | |
| 67 | <tt class="function">gl.lrectwrite()</tt> and the <tt class="module"><a href="module-imgfile.html">imgfile</a></tt> module. | |
| 68 | ||
| 69 | <P> | |
| 70 | The module defines the following variables and functions: | |
| 71 | ||
| 72 | <P> | |
| 73 | <dl><dt><b><span class="typelabel">exception</span> <tt id='l2h-4622' xml:id='l2h-4622' class="exception">error</tt></b></dt> | |
| 74 | <dd> | |
| 75 | This exception is raised on all errors, such as unknown number of bits | |
| 76 | per pixel, etc. | |
| 77 | </dd></dl> | |
| 78 | ||
| 79 | <P> | |
| 80 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 81 | <td><nobr><b><tt id='l2h-4623' xml:id='l2h-4623' class="function">crop</tt></b>(</nobr></td> | |
| 82 | <td><var>image, psize, width, height, x0, y0, x1, y1</var>)</td></tr></table></dt> | |
| 83 | <dd> | |
| 84 | Return the selected part of <var>image</var>, which should by | |
| 85 | <var>width</var> by <var>height</var> in size and consist of pixels of | |
| 86 | <var>psize</var> bytes. <var>x0</var>, <var>y0</var>, <var>x1</var> and <var>y1</var> are like | |
| 87 | the <tt class="function">gl.lrectread()</tt> parameters, i.e. the boundary is | |
| 88 | included in the new image. The new boundaries need not be inside the | |
| 89 | picture. Pixels that fall outside the old image will have their value | |
| 90 | set to zero. If <var>x0</var> is bigger than <var>x1</var> the new image is | |
| 91 | mirrored. The same holds for the y coordinates. | |
| 92 | </dl> | |
| 93 | ||
| 94 | <P> | |
| 95 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 96 | <td><nobr><b><tt id='l2h-4624' xml:id='l2h-4624' class="function">scale</tt></b>(</nobr></td> | |
| 97 | <td><var>image, psize, width, height, newwidth, newheight</var>)</td></tr></table></dt> | |
| 98 | <dd> | |
| 99 | Return <var>image</var> scaled to size <var>newwidth</var> by <var>newheight</var>. | |
| 100 | No interpolation is done, scaling is done by simple-minded pixel | |
| 101 | duplication or removal. Therefore, computer-generated images or | |
| 102 | dithered images will not look nice after scaling. | |
| 103 | </dl> | |
| 104 | ||
| 105 | <P> | |
| 106 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 107 | <td><nobr><b><tt id='l2h-4625' xml:id='l2h-4625' class="function">tovideo</tt></b>(</nobr></td> | |
| 108 | <td><var>image, psize, width, height</var>)</td></tr></table></dt> | |
| 109 | <dd> | |
| 110 | Run a vertical low-pass filter over an image. It does so by computing | |
| 111 | each destination pixel as the average of two vertically-aligned source | |
| 112 | pixels. The main use of this routine is to forestall excessive | |
| 113 | flicker if the image is displayed on a video device that uses | |
| 114 | interlacing, hence the name. | |
| 115 | </dl> | |
| 116 | ||
| 117 | <P> | |
| 118 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 119 | <td><nobr><b><tt id='l2h-4626' xml:id='l2h-4626' class="function">grey2mono</tt></b>(</nobr></td> | |
| 120 | <td><var>image, width, height, threshold</var>)</td></tr></table></dt> | |
| 121 | <dd> | |
| 122 | Convert a 8-bit deep greyscale image to a 1-bit deep image by | |
| 123 | thresholding all the pixels. The resulting image is tightly packed and | |
| 124 | is probably only useful as an argument to <tt class="function">mono2grey()</tt>. | |
| 125 | </dl> | |
| 126 | ||
| 127 | <P> | |
| 128 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 129 | <td><nobr><b><tt id='l2h-4627' xml:id='l2h-4627' class="function">dither2mono</tt></b>(</nobr></td> | |
| 130 | <td><var>image, width, height</var>)</td></tr></table></dt> | |
| 131 | <dd> | |
| 132 | Convert an 8-bit greyscale image to a 1-bit monochrome image using a | |
| 133 | (simple-minded) dithering algorithm. | |
| 134 | </dl> | |
| 135 | ||
| 136 | <P> | |
| 137 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 138 | <td><nobr><b><tt id='l2h-4628' xml:id='l2h-4628' class="function">mono2grey</tt></b>(</nobr></td> | |
| 139 | <td><var>image, width, height, p0, p1</var>)</td></tr></table></dt> | |
| 140 | <dd> | |
| 141 | Convert a 1-bit monochrome image to an 8 bit greyscale or color image. | |
| 142 | All pixels that are zero-valued on input get value <var>p0</var> on output | |
| 143 | and all one-value input pixels get value <var>p1</var> on output. To | |
| 144 | convert a monochrome black-and-white image to greyscale pass the | |
| 145 | values <code>0</code> and <code>255</code> respectively. | |
| 146 | </dl> | |
| 147 | ||
| 148 | <P> | |
| 149 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 150 | <td><nobr><b><tt id='l2h-4629' xml:id='l2h-4629' class="function">grey2grey4</tt></b>(</nobr></td> | |
| 151 | <td><var>image, width, height</var>)</td></tr></table></dt> | |
| 152 | <dd> | |
| 153 | Convert an 8-bit greyscale image to a 4-bit greyscale image without | |
| 154 | dithering. | |
| 155 | </dl> | |
| 156 | ||
| 157 | <P> | |
| 158 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 159 | <td><nobr><b><tt id='l2h-4630' xml:id='l2h-4630' class="function">grey2grey2</tt></b>(</nobr></td> | |
| 160 | <td><var>image, width, height</var>)</td></tr></table></dt> | |
| 161 | <dd> | |
| 162 | Convert an 8-bit greyscale image to a 2-bit greyscale image without | |
| 163 | dithering. | |
| 164 | </dl> | |
| 165 | ||
| 166 | <P> | |
| 167 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 168 | <td><nobr><b><tt id='l2h-4631' xml:id='l2h-4631' class="function">dither2grey2</tt></b>(</nobr></td> | |
| 169 | <td><var>image, width, height</var>)</td></tr></table></dt> | |
| 170 | <dd> | |
| 171 | Convert an 8-bit greyscale image to a 2-bit greyscale image with | |
| 172 | dithering. As for <tt class="function">dither2mono()</tt>, the dithering algorithm | |
| 173 | is currently very simple. | |
| 174 | </dl> | |
| 175 | ||
| 176 | <P> | |
| 177 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 178 | <td><nobr><b><tt id='l2h-4632' xml:id='l2h-4632' class="function">grey42grey</tt></b>(</nobr></td> | |
| 179 | <td><var>image, width, height</var>)</td></tr></table></dt> | |
| 180 | <dd> | |
| 181 | Convert a 4-bit greyscale image to an 8-bit greyscale image. | |
| 182 | </dl> | |
| 183 | ||
| 184 | <P> | |
| 185 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
| 186 | <td><nobr><b><tt id='l2h-4633' xml:id='l2h-4633' class="function">grey22grey</tt></b>(</nobr></td> | |
| 187 | <td><var>image, width, height</var>)</td></tr></table></dt> | |
| 188 | <dd> | |
| 189 | Convert a 2-bit greyscale image to an 8-bit greyscale image. | |
| 190 | </dl> | |
| 191 | ||
| 192 | <P> | |
| 193 | <dl><dt><b><tt id='l2h-4634' xml:id='l2h-4634'>backward_compatible</tt></b></dt> | |
| 194 | <dd> | |
| 195 | If set to 0, the functions in this module use a non-backward | |
| 196 | compatible way of representing multi-byte pixels on little-endian | |
| 197 | systems. The SGI for which this module was originally written is a | |
| 198 | big-endian system, so setting this variable will have no effect. | |
| 199 | However, the code wasn't originally intended to run on anything else, | |
| 200 | so it made assumptions about byte order which are not universal. | |
| 201 | Setting this variable to 0 will cause the byte order to be reversed on | |
| 202 | little-endian systems, so that it then is the same as on big-endian | |
| 203 | systems. | |
| 204 | </dd></dl> | |
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| 240 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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