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select0r This plugin selects a range of colors, and creates a corresponding alpha channel. It is cascadable, allowing construction of complex color selection subspaces. Written by Marko Cebokli, aug 2010, and released under GNU GPL RELEASE NOTES ** aug 2010 Version 0.1 "pre-alpha" (throw it out and see what happens... :-) ** mar 2012 Version 0.2 is now endian independent ** mar 2012 Version 0.3 adds double mapping of list parameters ** apr 2012 Version 0.4 adds "Slope" edge mode and parameter DESCRIPTION parameters: Color to select: the color to select. This is the center point of the selected color subspace. Invert selection: When ON, the selected color will be transparent, as normally used with keying. When OFF (default) the selected color will be opaque, for exmaple for alpha controlled adjustment of that color only. Delta XXXX: These three parameters determine the size of the color subspace along each axis. Bigger value means bigger tolerance on that axis. For example, setting a high I delta (in ABI and HCI), will allow the selection of a specific color in both light and shadows, but will also discard most of the high-bandwidth luma signal, making the selection less spatially accurate. Slope: When edge mode is set to "Slope", this parameter controls a gradual transition between opaque and transparent. Slope=0 gives a "hard" key, increasing the value of this parameter increases the range of colors around the selected color, that will be rendered partially transparent. Selection subspace: specifies in which of the three color spaces (RGB, ABI, HCI) the delta controls will work. Both ABI and HCI are separated luma/chroma. HCI is a cylindrical "Hue Chromacity Intensity" space, and ABI is a cartesian version thereof. Both suffer from chroma subsampling, and will give less sharp results than RGB. NOTE1: chroma subsampling is not a fault of this plugin. Frei0r plugins work in RGB 4:4:4. If you supply it with a truly 4:4:4 video, it will produce perfectly sharp alpha from all three color spaces. NOTE2: HCI is slow, because it has to calculate atan2() and hypot() for each pixel. NOTE3: ABI is based on the alpha an beta coordinates, upon which most of the Hxx type colorspaces are defined. See http://en.wikipedia.org/wiki/HSL_and_HSV Subspace shape: determines the shape of the color subspace. Options are: box, ellipsoid or diamond. Box is the biggest of them (by volume) and diamond the smallest. Imagine an octahedron inscribed inside an ellipsoid, which is in turn inscribed in a box. The tips of the diamond touch the ellipsoid, and the box, at the center of the sides of the box. Edge mode: has five options: "Hard", "Fat", "Normal", "Skinny" and "Slope". "Hard" means the alpha channel will be thresholded to two values only, fully opaque and fully transparent. This is mainly useful for keying. The "Slope" mode is also intended for keying. It is particularly useful when keying partly transparent or fuzzy (like hair) objects. The remaining options ("Fat", "Normal" and "Skinny") create a gradual transition between transparent and opaque. Alpha will be a function of the difference of color from the selected color, with cutoff at the delta points.The fatter the choice, the more the selected areas are filled towards the rim. This is useful with alpha controlled color adjustment tools. Operation: determines the way in which the alpha channel will be written. The "min", "max", "add" and "subtract" options allow cascading of select0r plugins (or combination with other alpha-writting plugins). These options combine the current selection with the pre-existing alpha of the source material. This way complex selections can be built.