Patent ID: 8831341

Claim:
An encoding method of generating an encoding of an image according to a predetermined encoding format, wherein said predetermined encoding format encodes said image in blocks of pixels, each block of pixels being encoded as a set of encoded pixel colours comprising a base colour and a set of luminance offsets with respect to said base colour, wherein said base colour is selected from a predetermined set of base colours defined in a predetermined colour space, wherein said set of luminance offsets is encoded as a set of references to at least one predetermined table of luminance offset values, and wherein said predetermined set of base colours and said luminance offset values define a set of luminance lines in said predetermined colour space, said encoded pixel colours lying on at least one of said luminance lines, said method comprising the steps, performed for said each block of pixels, of: determining an average colour of colours of said each block of pixels in said predetermined colour space; selecting at least one luminance line in dependence on an offset in said colour space of said average colour from said at least one luminance line; identifying a set of candidate base colours lying on said at least one luminance line; and determining, using said set of candidate base colours and said luminance offset values, said set of encoded pixel colours, wherein said base colour and said set of luminance offsets are selected in dependence on an encoding error indicative of a sum distance in said colour space between said set of encoded pixel colours and said colours of said each block of pixels.