Rapid processing of color print data so as to replace true black ink with process black ink, so as to minimize bleeding between colored regions of a printed document and black regions thereof. To replace black with process black in a raster line, multiple pixels are examined simultaneously in groups so as to determine whether the group contains at least one colored pixel, with the exact location of the colored pixel being obtained thereafter. The last color pixel in the raster line is obtained by inspecting each Nth subsequent pixel, thereby skipping N between inspections, until a first black pixel is encountered, and thereafter backtracking to obtain the first color pixel. Thereafter, all black pixels within a window marked by the first and last color pixels, plus a margin, are replaced with process black.
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