Apparatus and methods for coding and storing raster scan images

Claim 1

Apparatus for use in coding and storing raster scan images, comprising means for scanning images in a series of raster scan lines, detecting means for detecting discontinuities as they occur in a raster scan line and for deriving both respective position signals representative of the positions in the line of the discontinuities and respective segment signals representing directions of segments of boundaries formed by discontinuities in the line, each segment direction including a positive or negative polarity determined by the direction of a boundary of which that segment forms part, the positive direction being a predetermined direction of traverse around a shape which is enclosed by the boundary, a first store coupled to the detection means for storing chains of the segment signals in which the chains represent respective discontinuities in an image being scanned, the contents of the first store forming, when a scan is complete, part of a coded and stored version of an image scanned, logic means for determining when a new discontinuity not connected to previously-detected discontinuities is detected, means coupled to the logic means for allocating identifying signals for the said chains when a said new discontinuity is detected, and a second store with address input coupled to the said detection means and a content input coupled to the said means for allocating identifying signals, the second store having first and second arrays of storage locations, one location in each said array for each pixel in a scan line, the first and second arrays being used, in operation, to store for each line and for an interval of one line period, the identifying signals of chains having a segment starting and finishing, respectively, as determined by the positive direction, at locations corresponding to the line positions of the starting and finishing segments, the logic means being coupled to read the second store as each point in said raster scan line is scanned at the location relating to the corresponding point in the previous said raster scan line, and the logic means causing the first store to store segment signals representing each new segment either as an end of a new chain if no chain identifying signal is stored at the location read, or as a further segment signal in an existing chain if the identifying signal of the existing chain is found at the location read.