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