| 摘要 |
PROBLEM TO BE SOLVED: To reduce moire generated in the gray level transformation of an input image including periodicities, to reduce the generations of isolated dots, and to increase the speed of a picture-tone converting processing. SOLUTION: In an image forming apparatus 100 for converting image data including periodicities into the printing type data of an electrophotographic printer, threshold data for forming systematic dot arrays in respective picture- element regions each of which comprises a plurality of picture elements having a mutually coupling relation, are generated from a data generating portion 101 for generating non-periodic data among the respective picture-element regions. Consequently, such printing type data are obtained as to suppress the generation of moire among the respective picture-element regions and have the systematic dot arrays of concentrated dots, etc., in the respective picture- element regions. Also, the propagating processing of the quantization errors to the image data which are generated from the comparisons of the picture data with the threshold data is performed every picture-element region for forming the systematic dot array. As a result, the signal processing amount of the apparatus 100 can be cut down in comparison with the case of performing the propagating processing every picture element.
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