Abstract: An apparatus for removing form (background) information from an image for data compression; and for adding the form information during reconstruction of the image.Each object in an image is compressed by contour following of the exterior and interior borders of the object, and encoded in chain link form. Each object in the image as it is compressed is correlated with the appropriate object in the form image by comparing the encoded objects with the already stored encoded objects of the form. If there is a match, the image object which matches the form is deleted from the compressed image. Since the order in which the objects are encountered is known, it is only necessary to correlate each image object with at most a single form object. The correlation includes comparing the starting points of the contour information, the perimeter of the object (the length of its border chain) and the object area. The comparisons are made within a predetermined acceptable tolerance.

Abstract: In a continuous tone image approximated by a two-dimensional array of gray scale coded points, more than one bit per picture element is required. Compression coding consists firstly of delta coding sequences representative of the successive scan lines of the continuous tone image and secondly applying them to a predictive encoder having a particular transfer function and thirdly run-length encoding the error image. Central to the invention is the observation that delta coded sequences of gray scale pel values along a given scan line having a high expectancy of alternating, i.e. 101010. Also, the gray scale trend in the ith scan line is expected to be the same as the trend of the ith - 1 scan line. Relatedly, gray scale image expansion is achieved by applying the compressed image to a run-length decoder, a predictor stage, and delta decoder.

Abstract: A conventional word organized random access memory is modified for image processing operations so that the pq image points of any 1 .times. pq, pq .times. 1 or pxq subarray of an rp .times. sq or smaller image array stored in the memory can be extracted or updated in a single memory cycle. The invention contemplates 2 pq memory modules labeled from 0 to 2pq-1 for storing the image points, each module being capable of storing rs/2 points in distinguishable cells, only one cell of which is randomly accessible in a single instant of time. The invention further contemplates accessing circuitry for causing each image point I(i,j) of an image array to be routed to or from a memory module M(i,j) according to the relation M(i,j)=pq[(i/p)//2]+ (iq+i/2p+j)//pq, where the notations "/" and "//" denote, respectively, the quotient and the remainder resulting from integer division.

Abstract: A binary image containing objects comprised of black picture elements (pels) in a bit-addressable random access memory, is scanned in a predetermined order, until a black pel is encountered. The object is then encircled by a boundary follower in a clockwise direction, and each pel is recorded as it is encountered in a chain link format. Each black pel is changed to white as it is encountered provided it is not an interior boundary point. After the object has been completely encircled by the follower, encoding of the points is temporarily terminated. The follower continues to encircle the object several times, deleting black pels as it goes, until all of the black points in the object are exhausted except for the interior boundary. At this point, the remaining interior boundary pels are traced out and encoded in the same chain link format.Objects within objects are also encoded. A stack is provided to store the coordinates of the occurrence of each mode change described below.