Color image reacting apparatus having a non-uniformity correction rom

Abstract

The charge coupled device (23) provides serialized signals from a line of a document (11) to an A/D converter (28). In order to compensate for factors such as non-uniformity of lighting, non-uniformity of CCD cell response and variations with time, a reference strip (29) is read before each reading of a document and the corresponding digital values are stored in a RAM (31). Thereafter the stored values and the values read from each line of the document are compared to provide compensated values to a half tone generator (42) which codes the output. In particular, the comparison is effected by means of an EPROM (32) addressed in part by the digital value derived from a pixel in the line of the document and in part by the digital value stored in the RAM (31) from the corresponding pixel in the reference strip. The values held in the EPROM (32) correspond to the ratios between the addressing values. The EPROM (32) includes a plurality of sections, one for each of a plurality of different colors selected by a multiplexer ( 41) in correspondence with the selection of a filter (24) determining the scanning color. The reference strip is scanned through each filter before the document is scanned to determine the values in the RAM (31).