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Archive:Kdenlive/Manual/Effects/Alpha manipulation/Color Selection

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Revision as of 11:49, 5 November 2012 by Ttguy (talk | contribs) (add info from the read me for the select0r plugin found by google)
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Color Selection

This is the FilterFrei0r-select0r filter written by Marko Cebokli August 2010.

This is color based alpha selection. For example, this offers you a blue screen/green screen/chroma-keying effect.

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.

Selection Subspace options are: RGB (Red Green Blue), ABI and HCI (Hue Chromacity Intensity)

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 options are: Box, Ellipsoid, Diamond

Edge Mode Options are: Hard, Fat, Normal, Skinny, Slope

Operation options are: Write On Clear, Max, Min, Add and Subtract. This defines how to deal with an existing alpha channel in the clip. See Alpha Shapes for the meanings of these operations.

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.

See Also

See also Blue Screen which does color based alpha selection but is a bit simpler.

This page covers some Color Theory to help understand Hue, Chroma, Luminance etc.

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