Soft edge chroma-key generation based upon hexoctahedral color space

Claim 1

A chroma-key processing method for extracting an object to be foreground from a material image in the form of data of three primary colors RGB, using difference of color, and for obtaining a key value for a composite with a background image, which comprises dividing a three-dimensional space having three primary colors RGB as 3 orthogonal axes into 48 triangular pyramids having common representative background color as apices, setting an inner plane as a border between a background region and a soft key region with respect to each of the triangular pyramids to provide an inner hexoctahedron which defines a discriminative border of the background region in the RGB three-dimensional space, setting an outer plane as a border between a foreground region and the soft key region with respect to each of the triangular pyramids to provide an outer hexoctahedron which defines a discriminative border of the foreground region in the RGB three-dimensional space, making an interior division of the two hexoctahedrons to obtain a hexoctahedron as equipotential surfaces of key value of the soft key region, checking as to which of said 48 triangular pyramids each pixel of a material image belongs, and using parameters from an identification function determined by said inner and outer planes for each of the belonging triangular pyramids to calculate said key value for the composite with the background image.