Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1997-12-16
2001-01-16
Rogers, Scott (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000
Reexamination Certificate
active
06175424
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and image processing method and, more particularly, to an image processing apparatus and image processing method for representing a multivalued image inputted by e.g., a scanner or computer or the like, in pseudo tones when the multivalued image is repeatedly bitmapped to be outputted to a device having a low tonality-representation capability.
Error diffusion method and dither method are known as the conventional method of pseudo-tonality representation. According to the error diffusion method, as shown in
FIG. 10
, a diffusion coefficient is assigned to plural subsequent pixels of a pixel of interest, so as to distribute a quantization error generated at the pixel of interest to the neighboring pixels in accordance with the diffusion coefficient. By this processing, density values of the entire image is preserved, enabling excellent pseudo-tonality representation.
According to the dither method, as shown in
FIG. 11
, a dither matrix with a given threshold value is prepared (in
FIG. 11
, the given matrix size is 4×4 pixels), and each pixel of the inputted multivalued image data is compared with the matrix on a one-to-one basis. If a pixel value of the inputted multivalued image data is larger than or equal to the threshold value, the pixel is set to ON, and if a pixel value of the multivalued image data is smaller than the threshold value, the pixel is set to OFF. As a result, an output having binary values is obtained. According to the dither method, since the regular arrangement of dots produces an artificial pattern, the resultant pseudo-tonality image has graininess. Therefore, an image reproduced by the dither method tends to have lower quality compared to an image reproduced by the error diffusion method.
Herein, taking a repeated design pattern as an example, such as designs printed on a fabric, e.g., a tie or handkerchief or the like, there are patterns as shown in
FIGS. 12A
to
12
C: a simple pattern (
FIG. 12B
) generated by repeatedly printing a basic pattern (FIG.
12
A), which is the base of the repeated design pattern, simply in horizontal and vertical directions; a zig-zag pattern (
FIG. 12C
) generated by repeatedly printing the basic pattern in horizontal and vertical directions while alternately shifting the basic pattern by half the size of the basic pattern, and the like. However, in a case where the basic pattern must be repeatedly printed for a large number of times, it is inefficient to repeatedly perform pseudo-tone processing on the entire image. In addition, if this processing is to be performed by executing software, the processing becomes unrealistic in view of its processing speed.
Furthermore, if only the basic pattern is binarized and the binary data is simply repeated to form an image, conspicuous noise is generated at the boundary portion of the basic patterns (this noise will be referred to as boundary noise) as shown in FIG.
13
. It is considered that the noise is caused by discontinuity of binary processing at the boundary portion.
The suggested methods to eliminate the boundary noise include: a method where an exterior frame is added to the basic pattern to be drawn as shown in
FIG. 14A
(hereinafter referred to as “exterior-frame-addition method”), or a method where smoothing is performed at the boundary portion of the basic pattern as shown in
FIG. 14B
(hereinafter referred to as “boundary-smoothing method”). In the exterior-frame-addition method, the same multivalued image having a predetermined size is added to surround the basic pattern, and binary processing is performed on the entire image. As a result, binary data of the basic pattern is obtained. However, even if the obtained binary data is used repeatedly to form an image, boundary noise still appears due to the discontinuity at the boundary portion.
Moreover, even if smoothing processing is performed at the boundary portion of the binary data to eliminate the boundary noise of the obtained binary data by employing the boundary smoothing method, this still causes a problem of making the boundary portion unclear in a case where, for instance, the image of the boundary portion includes an edge portion such as thin lines.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide a method and apparatus which can reduce boundary noise caused by repeatedly printing a specific image, without deteriorating quality of an entire image, by utilizing the modified error diffusion method.
According to one aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for converting a basic image represented by multivalued data into a binary image representing the basic image in pseudo tones, and repeatedly printing the binary image on a print medium, comprising: binarizing means for consecutively comparing a value of each pixel representing the basic image with a predetermined threshold value, and performing binarization on the pixel in accordance with the comparison result; diffusing means for diffusing errors, generated in the binarization, to neighboring pixels of a pixel of interest by employing an error diffusion matrix having a predetermined size; and incorporating means for incorporating, among the errors diffused by the diffusing means, an error which is outside the basic image into an area where the binarizing means has not performed the binarization.
According to another aspect of the present invention, the foregoing object is attained by providing an image processing method for converting a basic image represented by multivalued data into a binary image representing the basic image in pseudo tones, and repeatedly printing the binary image on a print medium, comprising the steps of: consecutively comparing a value of each pixel representing the basic image with a predetermined threshold value, and performing binarization on the pixel in accordance with the comparison result; diffusing errors, generated in the binarization, to neighboring pixels of a pixel of interest by employing an error diffusion matrix having a predetermined size; and incorporating, among the errors diffused in the diffusing step, an error which is outside the basic image into an area where the binarization has not been performed in the binarizing step.
In accordance with the present invention as described above, when a basic image represented by multivalued data is converted to a binary image which represents the basic image in pseudo tones, and when the converted binary image is repeatedly printed on a print medium, a value of each pixel representing the basic image is consecutively compared with a predetermined threshold value, and the pixel is binarized in accordance with the comparison result. Errors generated in the binarization are distributed to neighboring pixels of the pixel of interest by employing an error diffusion matrix having a predetermined size. Then, among the distributed errors, an error which is outside the basic image is incorporated into an area where the binarization has not been performed.
The invention is particularly advantageous since a value of image data which expresses a basic image and is repeatedly used as a pattern, is compared with a predetermined threshold value, and among errors generated in binarization performed in accordance with the comparison result, an error at an edge portion of the basic image is incorporated into an area where binarization has not been performed. Accordingly, in a case where the basic image is binarized by utilizing the error diffusion method and the binary image is repeatedly printed, noise generated at a boundary portion of the binary image is reduced to a visibly unrecognizable level. As a result, it is possible to minimize the quality deterioration of the entire image.
REFERENCES:
patent: 4313124 (1982-01-01), Hara
patent: 4345262 (1982-08-01), Shirato et al.
patent: 4459600 (1984-07-01), Sato et al.
patent: 4463359 (198
Iino Akio
Matsumoto Hisashi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Rogers Scott
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