Recognising raster patterns in digitised image data - feeding data to two processing branches after levelling for reducing resolution to different levels and testing for chessboard raster patter

摘要

The digital data representing a raster image have a repetitive pattern with a recognisable raster frequency. The recognised rasters in the digitised image are converted to a simply recognised pattern by means of a resolution reduction process. The reduction factor is chosen to enable exact separation of the raster elements. After a level processor (6) the data are fed in parallel to two processing branches. In one branch, the resolution is reduced (7) by 50 per cent, tested (9) for the 'chessboard' raster pattern, filtered (11) and fed to the output summing circuit (14). In the other branch, the resolution is reduced (7) by 33 per cent, tested (10) for the 'chessboard' raster pattern, filtered (12), increased by 128 per cent and fed to the output summing circuit (14).