"plug-in-selection-to-foreground-layer"

Filter for Foreground Extraction based on Selection

    Start from Menu:
       <Image>/Layer/Transparency/Foreground Extract Via Selection

How to use:
  
   Have an image with a foreground object loaded in GIMP
     (for instance a person) that shall be
     separated from the background.
     The image shall be of RGB color

   Draw a selection (for instance by using the freehand
      selection tool)
      The selection will be used as base for the foreground extraction
      where the opacity and optional color of pixels near 
      the border will be trimmed automatically.

   Start the script from <Image>/Layer/Duplicate Selected Foreground.
      This creates a new layer with the extracted foreground object
      where the selection is automatically trimmed according
      to matching colors.
      It also creates a tri map (that is attached as layermask
      to the input layer) that is internally used by the alpha matting
      algorithm.
   
   
   When your selection is drawn all inside the object,
   you shall use inner radius 0 and set outer radius to
   the desired width where the selection shall be trimmed.
   
   When your selection is drawn all outside the object,
   you shall use outer radius 0 and set outer radius to
   the desired width where the selection shall be trimmed.

   Note:
   If this filter is called without having a selection
   it uses the alpha channel as implicit selection.
   

   
Options:

   InnerRadius
      Specifies how many pixels inside the borderline of the selection
      are considered as undefined area.

   OuterRadius
      Specifies how many pixels outside the borderline of the selection
      are considered as undefined area.

   Create Layermask
      ON:  Render opacity by creating a new layer mask for the resulting layer
      OFF: Apply rendered opacity to the alpha channel

   Lock Colors
      ON:  Keep RGB channels of the input layer
      OFF: Allow Background color removal in processed undefined regions

How it Works:
   A tri-map is generated based on the current selection by setting the
   pixels that are near the selection border to UNDEFINED state.
   Pixels that are inside the selection and far (distance is > inner radius)
   from the border are considered as FOREGROUND.
   Pixels that are far (distance is > outer radius) outside the selection
   are considered as BACKGROUND.
   The generated tri map is attached as layermask to the input layer.
   This generated tri map is used to perform a foreground extraction
   based on the alpha matting algorithm (# see plug-in-foreground-extract-matting)
   The foreground extraction renders a new layer where transparency (and optionally color)
   is calculated for the UNDEFINED area, FOREGROUND is rendered fully opaque
   and BACKGROUND is rendered fully transparent.
