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72 lines
3.4 KiB
HTML
72 lines
3.4 KiB
HTML
<html><head><title>Gimp Wideangle Filter</title></head>
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<body>
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<h1>Gimp Wideangle Filter</h1>
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<p>The Wideangle plugin is licensed under the GPL.<br/>
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The source code is available <a href="wideangle.c">here</a>. Latest version is
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1.0.10.<br/>
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<b>gimptool --install wideangle.c</b> will compile the plugin and install
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it in your local Gimp plugins directory.<br/>
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The plugin appears in the <b>Filters/Distorts</b> menu as
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<b>Wideangle...</b>.</p>
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<p>The Wideangle filter is used to correct (or simulate) the distortion
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typically seen on photographs taken with a wideangle lens. There are six
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controls.
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<dl>
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<dt>X Shift</dt>
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<dd>Adjusts the centre of the effect, from the left edge of the image (at -100.0),
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through the centre (at 0.0), to the right edge (at 100.0).</dd>
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<dt>Y Shift</dt>
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<dd>Adjusts the centre of the effect, from the top edge of the image (at -100.0),
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through the centre (at 0.0), to the bottom edge (at 100.0).</dd>
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<dt>Main</dt>
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<dd>Controls the amount of distortion. Negative values correct wideangle (barrel)
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distortion, while positive values create it (or correct pincushion distortion).</dd>
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<dt>Edge</dt>
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<dd>Like the <b>Main</b> control, but the <b>Edge</b> control has more effect
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at the edges of the image than at the centre.</dd>
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<dt>Zoom</dt>
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<dd>Zooms the entire image in or out.</dd>
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<dt>Brighten</dt>
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<dd>Adjusts the image brightness up or down with distance from the centre.
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Can be used to remove (or create) vignetting, the darkening of the corners
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of an image.</dd>
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</dl>
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</p>
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<p>The <b>Do Preview</b> toggle enables and disables the preview window.
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The preview can show either an overview of the whole image, or a detail view
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which shows a 5x5 array of full resolution closeups. The overview is useful for
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casual use, while the detail view
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allows you to create a precisely calibrated preset for a particular lens. To create
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a lens preset, use
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a photo of a grid pattern. Start by adjusting the <b>Main</b> control until the
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lines of the grid are as straight as possible. Use the <b>Shift</b> controls, if
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necessary, to correct for any asymmetry. Finally, if the best setting of the
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<b>Main</b> control leaves a "wiggle" in the lines, use the <b>Edge</b>
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control to remove it. (You may need to readjust the <b>Main</b> control a little.)
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Once you have the correct settings for a particular lens, you should be able
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to save the settings as a new preset and use them for all images taken with that
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lens.</p>
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<p>Or just play around.</p>
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<p>The preset controls allow you to reset everything, select a previously defined
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preset, or save the current settings (if they've been altered) under a new name.
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Preset names can contain (fairly) arbitrary characters. If you mess up the presets,
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they are stored in a text file under your Gimp user
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directory in the <code>wideangle</code> subdirectory.</p>
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<p>Regardless of the Gimp's settings, the Wideangle filter always uses cubic
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interpolation. This is not a bug, it's a feature.</p>
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<p><b>What's with the pop up menu on the "select" button?</b></p>
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<p>I originally had a regular option menu to select presets. However this had
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a drawback, namely that the displayed option was only correct until a control
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was adjusted. A pop up menu, although not the normal choice, provides exactly
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the correct model to the user.</p>
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<p>Written by David Hodson. Many thanks for suggestions and improvements
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to Lars Clausen. (But bugs are still my fault.)</p>
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</body></html>
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