Image analysis – Pattern recognition – Template matching
Reexamination Certificate
1998-09-04
2001-12-25
Johns, Andrew W. (Department: 2621)
Image analysis
Pattern recognition
Template matching
Reexamination Certificate
active
06333998
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image processing method and apparatus. More particularly, the invention relates to an image processing method and apparatus applicable to a copier or printer, for example, wherein it is possible to output an image having a resolution higher than that of an input image in at least one direction.
A problem encountered with conventional printers and the like is the occurrence of conspicuous jaggies along the contours of font character images input to the printer. The reason for this is that since a character image is composed of black and white levels, even fine characters exhibit noticeable jaggies owing to contrast.
Processing referred to as “smoothing” generally is used to solve this problem. In a laser printer, such processing makes use of the fact that individual pixels forming the character image can be subdivided into a plurality of fine pixels in the scanning direction of the laser beam and involves detecting a specific pattern that appears on the contour of a character and replacing the specific pattern with fine pixels in the scanning direction, thereby reproducing the character contour smoothly.
However, smoothing is processing premised on bilevel font character images that are stored by computer or calculated and generated by computer. Consequently, when smoothing processing is applied to an image obtained by binarizing, through pseudo-halftone processing such as the error diffusion method, a multilevel gradation image optically read by a scanner or the like, unnatural jaggies occur at the contour of a character in order to express halftones at the boundary between black and white on the character contour. As a result, the contour does not match the pattern that should be obtained with smoothing processing and almost no smoothing is achieved.
A particular problem arises with an image obtained by binarizing a faint character image. Portions of such an image that should be straight lines become broken up or discontinuous, giving rise to a marked decline in character quality. Since such portions do not undergo smoothing, applying smoothing processing does not improve character quality.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to make possible the excellent reproduction of images free of broken lines by preserving the fine lines of characters binarized by pseudo-halftone processing such as error diffusion.
According to the present invention, the foregoing object is attained by providing an image processing apparatus comprising input means for inputting a multilevel digital image signal; binarizing means for converting the multilevel digital image signal input from the input means to a bilevel image of black pixels or white pixels; image storage means for storing the bilevel image; pattern storage means for storing predetermined reference patterns and pixel substitution patterns corresponding to the reference patterns; pattern matching means for comparing a bilevel image read out of the image storage means and reference patterns read out of the pattern storage means; and pixel substitution means which, if the result of the comparison performed by the pattern matching means indicates that the bilevel image matches a reference pattern, outputs a pixel substitution pattern, which corresponds to the reference pattern, that is composed of pixels finer, in at least one direction, than the pixels of the bilevel image, and which, if the result of the comparison performed by the pattern matching means indicates that there is no reference pattern that matches the bilevel image, outputs the bilevel image as is.
According to another aspect of the present invention, the foregoing object is attained by providing an image processing apparatus comprising reading means for optically reading an image and outputting a multilevel digital image signal; binarizing means for converting the multilevel digital image signal from the reading means to a bilevel image of black pixels or white pixels; image storage means for storing the bilevel image; pattern storage means for storing predetermined reference patterns and pixel substitution patterns corresponding to the reference patterns; pattern matching means for comparing a bilevel image read out of the image storage means and reference patterns read out of the pattern storage means; and pixel substitution means which, if the result of the comparison performed by the pattern matching means indicates that the bilevel image matches a reference pattern, outputs a pixel substitution pattern, which corresponds to the reference pattern, that is composed of pixels finer, in at least one direction, than the pixels of the bilevel image, and which, if the result of the comparison performed by the pattern matching means indicates that there is no reference pattern that matches the bilevel image, outputs the bilevel image as is.
By way of example, a pixel substitution pattern, which has been stored in the pattern storage means, that is output by the pixel substitution means is such a substitution pattern that connects a discontinuous line in a case where a line image contained in a bilevel image has been rendered discontinuous by one or more pixels as the result of binarization of the image by the binarizing means.
Further, by way of example, the pattern storage means stores, as the reference patterns, a plurality of reference patterns having different pixels of interest together with reference patterns having exactly the same position on the bilevel image.
Further, by way of example, a plurality of reference patterns having different pixels of interest and a plurality of pixel substitution patterns corresponding to these reference patterns, which are stored in the pattern storage means, are so adapted that the sum total of signal values of an original pattern is not changed.
Further, by way of example, a plurality of reference patterns, which are located at exactly the same position on the image, that have different pixels of interest while pattern matching processing is being performed and a plurality of pixel substitution patterns corresponding to these reference patterns, which are included in the pattern storage means, are so adapted that the density of an original pixel is preserved when an output is produced.
Further, by way of example, the plurality of reference patterns, which are located at exactly the same position on the image, that have different pixels of interest while pattern matching processing is being performed are such that the number of reference patterns that delete an image is greater than the number of reference patterns that add on an image reference patterns used to connect a discontinuous line.
Further, by way of example, the pixel substitution means is controllable in such a manner that when an operator performs a specific operation, a specific reference pattern will not be read out in response to this operation.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an image processing apparatus comprising bilevel image signal input means for inputting an image obtained by converting a multilevel image to a bilevel image using pseudo-halftone processing; image storage means for storing the bilevel image in advance; pattern storage means for storing predetermined reference patterns and pixel substitution patterns corresponding to the reference patterns; pattern matching means for comparing a bilevel image read out of the image storage means and reference patterns read out of the pattern storage means; and pixel substitution means which, if a bilevel image signal is found to match a reference pattern by the pattern matching means, outputs a pixel substitution pattern, which corresponds to the reference pattern, that is composed of pixels finer, in at least one direction, than the pixels of the input bilevel image signal, and which, if there is no reference pattern that matches the bilevel image signal, outputs the bilevel image signal as is.
By way of example, the pattern storage means stor
Azarian Seyed
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Johns Andrew W.
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