High quality image processing

Abstract

In a high quality image-encoding scheme an input image is decomposed into several image blocks comprising multiple image elements. The image blocks are encoded into encoded block representations. Such a block representation comprises two color codewords, a color modifying codeword and optionally a sequence of color indices and color modifier indices. The color codewords define multiple discrete color representations along a line in color space. The color modifying codeword represents a set of multiple color modifiers for modifying the multiple color representations along at least one extension vector to obtain, for each color representation, a set of multiple color points. These color points of the multiple sets are located on a surface defined by the multiple color representations and the at least one extension vector. The colors of the image elements in the block are then approximated by these color points on the surface.

1 . A method of compressing an image block comprising multiple image elements, said method comprising the steps of:
 determining a first and a second color codeword defining multiple discrete color representations along a line in a color space; and   determining a color modifying codeword representing a set of multiple color modifiers for modifying said multiple discrete color representations along at least one selected extension vector in said color space to obtain, for each of said discrete multiple color representations, a set of multiple color points, wherein said multiple color points of said sets are located on a surface defined by said multiple color representations and said at least one selected extension vector and wherein colors of said image elements are approximated by said multiple color points of said sets.   
     
     
         2 . The method according to  claim 1 , wherein said multiple color points of said sets collectively forming a grid on said surface and wherein colors of said image elements are approximated by said multiple color points of said grid. 
     
     
         3 . The method according to  claim 1 , further comprising the steps of:
 selecting, for each image element in said image block, a color index associated with a color representation from said multiple color representations along said line; and   selecting, for each image element in said image block, a color modifying index associated with a color modifier from said color modifier set.   
     
     
         4 . The method according to  claim 1 , wherein said step of determining said color modifying codeword comprises the steps of:
 determining a representation of a minimum color modifier; and   determining a representation of a maximum color modifier, wherein said multiple color modifiers being linear combinations of said maximum color modifier and said minimum color modifier.   
     
     
         5 . The method according to  claim 1 , wherein said step of determining said first and second color codeword comprises the steps of:
 determining a representation of a first color representation; and   determining a representation of a second color representation, wherein said multiple discrete color representations being linear combinations of said first color representation and said second color representation.   
     
     
         6 . The method according to  claim 1 , wherein said step of determining said first and second color codeword comprises the steps of:
 determining said first color codeword as a representation of a starting color representation in said color space;   determining a direction codeword as a representation of a direction in said color space;   determining said second color codeword as a representation of a set of multiple modifiers for modifying said starting color representation along said direction to obtain said multiple discrete color representations along said line; and   selecting, for each image element in said at least a portion of said image block, a color index associated with a modifier from said modifier set.   
     
     
         7 . The method according  claim 1 , further comprising the step of projecting said colors of said image elements to a predefined plane in said color space so that said colors have constant luminance. 
     
     
         8 . The method according to  claim 7 , wherein said predefined plane goes through a grey point in said color space and is orthogonal to a luminance direction vector in said color space. 
     
     
         9 . The method according to  claim 7 , wherein said step of determining a color modifying codeword comprises determining a luminance codeword representing a set of multiple luminance modifiers for modifying a luminance of said multiple discrete color representations along a luminance direction vector to obtain, for each of said discrete multiple color representations, a set of multiple color points, wherein said multiple color points of said sets collectively forming a grid on a plane uniquely defined by a direction vector of said line, said luminance direction vector and at least one color representation of said multiple discrete color representations and wherein colors of said image elements are approximated by said multiple color points of said sets. 
     
     
         10 . The method according to  claim 7 , wherein said step of determining said first and said second color codeword comprises the steps of:
 determining a first and a second color component of said first color codeword; and   determining a first and a second color component of said second color codeword, wherein a respective third color component of said first and second color codeword can be calculated from said respective first and second color component.   
     
     
         11 . A method of processing a compressed representation of an image block comprising:
 a first and a second color codeword defining multiple discrete color representations along a line in a color space; and   a color modifying codeword representing a set of multiple color modifiers for modifying said multiple discrete color representations along at least one selected extension vector in said color space to obtain, for each of said discrete multiple color representations, a set of multiple color points, said multiple color points of said sets are located on a surface defined by said multiple color representations and said at least one selected extension vector, said method comprising the step of selecting, for at least one image element in said image block, a color value from said multiple color points.   
     
     
         12 . The method according to  claim 11 , wherein said multiple color points of said sets collectively forming a grid on said surface and selecting step comprises the step of selecting, for at least one image element in said image block, a color value from said grid of multiple color points. 
     
     
         13 . The method according to  claim 11 , wherein said compressed representation further comprises: a color index sequence comprising, for each image element in said image block, a color index representing a color representation of said multiple color representations; and a color modifier index sequence comprising, for each image element in said image block, a color modifier index representing a color modifier of said set of multiple color modifiers, said selecting step comprises the step of selecting, based on a color index associated with said at least one image element and a color modifier index associated with said at least one image element, said color value from said grid of multiple color points. 
     
     
         14 . The method according to  claim 13 , wherein said selecting step comprises the steps of:
 determining, based on said first and second color codeword and said color index associated with said at least one image element, a color representation of said multiple discrete color representations;   selecting, based on said color modifying codeword and said color modifier index associated with said at least one image element, a color modifier from said set of multiple color modifiers; and   generating said color value by modifying said determined color representation along said at least one extension vector using said selected color modifier.   
     
     
         15 . The method according to  claim 14 , wherein said determining step comprises the step of determining said color representation as a linear combination of said first and second color codeword. 
     
     
         18 . The method according to  claim 13 , further comprising the steps of:
 providing, based on said color modifying codeword, said set of multiple color modifiers; and   selecting, based on said color modifier index associated with said at least one image element, a color modifier from said set.   
     
     
         19 . The method according to  claim 1 , wherein said surface is a plane that is uniquely defined by a direction vector defining a direction of said line, said at least one selected extension vector and at least one color representation of said multiple discrete color representations. 
     
     
         20 . The method according to  claim 1 , wherein said at least one extension vector is a luminance direction vector in said color space. 
     
     
         21 . A signal representation of an image block comprising multiple image elements, said signal representation comprising: a first and a second color codeword defining multiple discrete color representations along a line in a color space; and a color modifying codeword representing a set of multiple color modifiers for modifying said multiple discrete color representations along at least one selected extension vector in said color space to obtain, for each of said discrete multiple color representations, a set of multiple color points, wherein said multiple color points of said sets are located on a surface defined by said multiple color representations and said at least one selected extension vector and wherein colors of said image elements are approximated by said multiple color points of said sets. 
     
     
         22 . A system for compressing an image block comprising multiple image elements, said system comprising:
 means for determining a first and a second color codeword defining multiple discrete color representations along a line in a color space; and   means for determining a color modifying codeword representing a set of multiple color modifiers for modifying said multiple discrete color representations along at least one selected extension vector in said color space to obtain, for each of said discrete multiple color representations, a set of multiple color points, wherein said multiple color points of said sets are located on a surface defined by said multiple color representations and said at least one selected extension vector and wherein colors of said image elements are approximated by said multiple color points of said sets.   
     
     
         23 . The system according to  claim 22 , further comprising: a color index selector for selecting, for each image element in said image block, a color index associated with a color representation from said multiple color representations along said line; and a color modifier index selector for selecting, for each image element in said image block, a color modifying index associated with a color modifier from said color modifier set. 
     
     
         24 . The system according to  claim 22 , wherein said means for determining said color modifier codeword comprises:
 means for determining a representation of a minimum color modifier; and   means determining a representation of a maximum color modifier, wherein said multiple color modifiers being linear combinations of said maximum color modifier and said minimum color modifier.   
     
     
         25 . The system according to  claim 22 , wherein said means for determining said color codewords comprises:
 means for determining a representation of a first color representation: and   means for determining a representation of a second color representation, wherein said multiple discrete color representations being linear combinations of said first color representation and said second color representation.   
     
     
         26 . The system according to  claim 22 , wherein said means for determining said color codewords comprises:
 means for determining said first color codeword as a representation of a starting color representation in said color space;   means for determining a direction codeword as a representation of a direction in said color space;   means for determining said second color codeword as a representation of a set of multiple modifiers for modifying said starting color representation along said direction to obtain said multiple discrete color representations along said line; and   an index selector for selecting, for each image element in said at least a portion of said image block, a color index associated with a modifier from said modifier set.   
     
     
         27 . The system according to  claim 22 , further comprising means for projecting said colors of said image elements to a predefined plane in said color space so that said colors have constant luminance. 
     
     
         28 . The system according to  claim 27 , wherein said means for determining said color modifier codeword is arranged for determining a luminance codeword representing a set of multiple luminance modifiers for modifying a luminance of said multiple discrete color representations along a luminance direction vector to obtain, for each of said discrete multiple color representations, a set of multiple color points, wherein said multiple color points of said sets collectively forming a grid on a plane uniquely defined by a direction vector of said, said luminance direction vector and at least one of said multiple discrete color representations and wherein colors of said image elements are approximated by said multiple color points of said sets. 
     
     
         29 . The system according to  claim 27 , wherein said means for determining said color codewords comprises:
 means for determining a first and a second color component of said first color codeword; and   means for determining a first and a second color component of said second color codeword, wherein a respective third color component of said first and second color codeword can be calculated from said respective first and second color component.   
     
     
         30 . A system for processing a compressed representation of an image block comprising:
 a first and a second color codeword defining multiple discrete color representations along a line in a color space; and   a color modifying codeword representing a set of multiple color modifiers for modifying said multiple discrete color representations along at least one selected extension vector in said color space to obtain, for each of said discrete multiple color representations, a set of multiple color points, said multiple color points of said sets are located on a surface defined by said multiple color representations and said at least one selected extension vector, said system comprising a color value selector for selecting, for at least one image element in said image block, a color value from said multiple color points.   
     
     
         31 . The system according to  claim 30 , wherein said multiple color points of said sets collectively forming a grid on said surface and color value selector is arranged for selecting, for at least one image element in said image block, a color value from said grid of multiple color points. 
     
     
         32 . The system according to  claim 30 , wherein said compressed representation further comprises:
 a color index sequence comprising, for each image element in said image block,   a color index representing a color representation of said multiple color representations; and   a color modifier index sequence comprising, for each image element in said image block, a color modifier index representing a color modifier of said set of multiple color modifiers, said color value selector is arranged for selecting, based on a color index associated with said at least one image element and a color modifier index associated with said at least one image element, said color value from said grid of multiple color points.   
     
     
         33 . The system according to  claim 32 , wherein said color value selector comprises: means for determining, based on said first and second color codeword and said color index associated with said at least one image element, a color representation of said multiple discrete color representations; a color modifier selector for selecting, based on said color modifying codeword and said color modifier index associated with said at least one image element, a color modifier from said set of multiple color modifiers; and means for generating said color value by modifying said determined color representation along said at least one extension vector using said selected color modifier. 
     
     
         34 . The system according to  claim 33 , wherein said determining means is arranged for determining said color representation as a linear combination of said first and second color codeword. 
     
     
         35 . The system according to  claim 32 , wherein said compressed representation further comprises a direction codeword said color value selector comprises:
 means for determining, based on said first color codeword, a starting color representation;   means for determining, based on said direction codeword, a direction vector;   means for providing, based on said second color codeword, a set of multiple modifiers;   a modifier selector for selecting, based on said color index associated with said at least one image element, a modifier from said set of multiple modifiers;   means for generating a color representation of said multiple discrete color representations by modifying said determined starting color representation with said selected modifier along said direction vector;   a color modifier selector for selecting, based on said color modifying codeword and said color modifier index associated with said at least one image element, a color modifier from said set of multiple color modifiers; and   means for generating said color value by modifying said determined color representation along said at least one extension vector using said selected color modifier.   
     
     
         36 . The system according to  claim 32 , wherein said color modifying codeword comprises a representation of a minimum color modifier and a representation of a maximum color modifier and said system comprises a color modifier selector in turn comprising:
 means for calculating, based on said color modifying codeword, said multiple color modifiers as linear combinations of said maximum color modifier and said minimum color modifier; and   a selector for selecting, based on said color modifier index associated with said at least one image element, a color modifier from said multiple calculated color modifiers.   
     
     
         37 . The system according to  claim 32 , further comprising a color modifier selector in turn comprising:
 means for providing, based on said color modifying codeword, said set of multiple color modifiers; and   a selector for selecting, based on said color modifier index associated with said at least one image element, a color modifier from said set.