BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
FIG. 1 illustrates an image forming apparatus to which an exemplary embodiment of the invention is applied;
FIG. 2 shows a functional structure of a controller in the present exemplary embodiment;
FIGS. 3A and 3B are diagrams to explain a screen pattern alteration made by a screening unit to adapt the screening pattern for correction for skew misregistration in the present exemplary embodiment;
FIGS. 4A and 4B show the result of the screening by the altered screening pattern according to the present exemplary embodiment;
FIGS. 5A, 5B, and 5C are diagrams to explain a screen pattern alteration made by the screening unit to adapt the screening pattern for correction for a bowed image in the present exemplary embodiment;
FIG. 6 shows an example of a matrix of threshold values of a screening pattern;
FIGS. 7A and 7B are diagrams to explain a screen pattern alteration made by the screening unit to adapt the screening pattern for correction for magnification deviation of an image in the present exemplary embodiment;
FIG. 8 is a diagram to explain another example of a screen pattern alteration made by the screening unit to adapt the screening pattern for correction for magnification deviation of an image in the present exemplary embodiment;
FIGS. 9A and 9B show the result of the screening by the altered screening pattern according to the present exemplary embodiment;
FIGS. 10A through 10D are diagrams to explain memory space required in the case where misregistration correction is performed before and after screening;
FIG. 11 shows a functional structure of a controller in the case where misregistration correction is performed before and after screening;
FIG. 12 shows an image produced by normal screening on an image processed by pre-correction processing;
FIG. 13 shows an image produced by post-correction processing on the image shown in FIG. 12;
FIG. 14 shows an image produced by screening with a screening pattern altered to adapt for image processing for post-correction on the image processed by pre-correction processing;
FIG. 15 shows an image produced by post-correction processing on the image shown in FIG. 14;
FIG. 16 is a diagram to explain a concrete example of screening, which shows an example of a rasterized multilevel image at 600 dpi;
FIG. 17 is a diagram to explain a concrete example of screening, which shows a matrix of threshold values of a screening pattern;
FIG. 18 is a diagram to explain a concrete example of screening, which shows a screening pattern in which black and white dots correspond to on and off dots of image data after binarized;
FIGS. 19A, 19B, and 19C are diagrams to explain a concrete example of screening, which respectively show enlarged view of sections in FIGS. 16 to 18;
FIGS. 20A and 20B are diagrams to explain a correction method by image processing for skew misalignment;
FIGS. 21A and 210B are diagrams to explain a correction method by image processing for magnification misalignment;
FIG. 22 shows a general structure of image processing functions for related art;
FIGS. 23A, 23B, and 23C schematize defects which occur in an image when skew correction is performed by image processing;
FIGS. 24A and 24B illustrate images before and after inserting pixels into image data to correct magnification misalignment in the fast-scanning direction; and
FIGS. 25A and 25B illustrate images before and after inserting pixels in such a manner that the pixel insertion position is offset line by line of fast scan in certain cycles.
Patent Application
20070165283
