Facsimile vector data compression

In a method for compressing objects formed from contiguous pels having the same first color value in an m.times.n array of pels by vector encoding reduced objects, said method includes the step of thinning each object by raster scanning the array and retaining in the original array locations i, j, only those pels of the first color which define a color transition or border and deleting all others, 1.ltoreq.i.ltoreq.m, 1.ltoreq.j.ltoreq.n;

• wherein the improvement comprises the steps of:
• testing each retained pel in each ith scan line of the processed array of thinned objects in order to determine its contiguity and linear position relationship to a pel of the same first color value in either the ith or the ith-1 scan lines, by ascertaining whether said retained pel lies within a region of contiguous retained pels (FIG. 21/154) and if it lies within said region, ascertaining whether said retained pel lies within an aperture (FIG. 19) whose sides constitute an angle of acceptance (FIG. 20/156, 157), and if it lies within said aperture, narrowing said aperture so as to define a smaller included angle (FIG. 20/159);
• and
• encoding each retained pel in said ith scan line of the processed array of thinned objects either as the origin of a new vector if the retained pel is noncontiguous, as a continuation of a previous vector if the retained pel is both contiguous and linear, or as a termination of a previous vector if the retained pel is contiguous and nonlinear, the steps of testing and encoding being performed on a consecutive raster scan line-at-a-time basis.