Multi-mode image processing

A method of processing a compressed representation of an image block comprising multiple image elements, said compressed image block representation comprises a mode index, a first codeword, a second codeword and an index sequence of image element associated indices, and said method comprising the steps of:

• selecting a decompressing mode based on said mode index;
• and
• generating a decompressed representation of said image block based on said first and second codeword and said index sequence,
• wherein if said mode index represents a first decompressing mode, said first codeword is a color codeword, said second codeword is an intensity codeword and said index sequence is an intensity index sequence, and said generating step comprises the steps of:
• providing a set of multiple intensity modifiers based on said intensity codeword;
• for at least one image element in said image block:
• generating a color representation comprising multiple color components based on said color codeword;
• selecting an intensity modifier from said intensity modifier set based on said intensity index sequence;
• and
• modifying the intensity of said at least one image element based on said selected intensity modifier by adding said selected intensity modifier to said multiple color components of said color representation;
• and if said mode index represents a second decompressing mode, said first codeword is a first color codeword, said second codeword is a second color codeword and said index sequence is a color index sequence, and said generating step comprises, for at least one image element in said image block, the step of:
• generating a color representation based on at least one color codeword selected from said first and second color codeword.

A system for compressing an image block comprising multiple image elements, each image element having a respective color comprising multiple color components, said system comprising:

• a codeword generator for determining a first codeword and a second codeword that are representations of properties of said multiple image elements;
• means for providing an index sequence of image element associated indices;
• a mode selector for selecting a compressing mode from a first compressing mode and a second compressing mode before, during or after said codeword generator determines said first and second codeword and said providing means provides said index sequence;
• and
• means for providing a mode index representing said selected compressing mode, wherein if said mode index represents said first compressing mode,
• said first codeword is a color codeword that is representation of the colors of said multiple image elements, said second codeword is an intensity codeword that is a representation of a set of multiple intensity modifiers for modifying the intensity of said multiple image elements by adding an intensity modifier to the multiple color components of a color representation obtainable based on said color codeword and said index sequence comprises, for each image element in said image block, an intensity index associated with an intensity modifier from said intensity modifier set,
• and if said mode index represents said second compressing mode,
• said first codeword and second codeword are a first color codeword and a second color codeword that are representations of the colors of said multiple image elements, and said index sequence comprises, for each image element in at least a subset of said multiple image elements, a color index associated with said first color codeword or said second color codeword.

A system for processing a compressed representation of an image block comprising multiple image elements, said compressed image block representation comprises a mode index, a first codeword, a second codeword and an index sequence of image element associated indices, said system comprising:

• a decompressing mode selector for selecting a decompressing mode based on said mode index;
• a color generator;
• an index selector;
• means for providing a set of multiple intensity modifiers;
• and
• an intensity modifier unit,
• wherein if said mode index represents a first decompressing mode, said first codeword is a color codeword, said second codeword is an intensity codeword and said index sequence is an intensity index sequence,
• said providing means is operated for providing a set of multiple intensity modifiers based on said intensity codeword,
• said color generator is operated for generating a color representation comprising multiple color components for at least one image element in said image block based on said color codeword,
• said index selector is operated for selecting, for said at least one image element, an intensity modifier from said identified intensity modifier set based on said intensity index sequence, and
• said intensity modifier unit is operated for modifying the intensity of said at least one image element based on said selected intensity modifier by adding said selected intensity modifier to said multiple color components of said color representation, and
• if said mode index represents a second decompressing mode, said first codeword is a first color codeword, said second codeword is a second color codeword and said index sequence is a color index sequence,
• said color generator is operated for generating a color representation based on at least one color codeword selected by said index selector from said first and second color codeword.