Image analysis – Image compression or coding – Quantization
Reexamination Certificate
1997-09-09
2001-01-23
Lee, Thomas D. (Department: 2724)
Image analysis
Image compression or coding
Quantization
C382S232000, C382S237000, C358S448000, C358S451000
Reexamination Certificate
active
06178267
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to image processing apparatuses, and more particularly to an image processing apparatus which corrects an error diffusion process that subjects an image data to a pseudo halftone processing.
Conventional printers are designed by putting weight on particularly the reproducibility of characters. However, recently, there are more opportunities to process images on a personal computer or the like, and it has also become desirable to print images such as natural images and graphics on the printer with a satisfactory reproducibility.
In the printer which is designed by putting weight on the reproducibility of the characters, the size of one dot is set larger than one dot pitch. For example, the diameter of the dot is set within a range of 1.4 to 2.0 times one dot pitch. By such a setting, the contrast and the visibility of the characters are improved. In other words, the reproducibility of the characters and line drawings is improved by setting the diameter of the dot to 1.8 times one dot pitch, for example.
On the other hand, in the case of an image such as the natural image and graphics, the image is generally printed according to the halftoning method. Various halftoning methods have been proposed, and the error diffusion method is regarded as a promising method. According to the error diffusion method, a difference between the input image density and the output image density is distributed with respect to the neighborhood pixels. As a result, the density of the image as a whole is maintained, and the resolution can be maintained to a considerably high state. For this reason, even if the error diffusion method is applied to a printer having a low resolution, the error diffusion method can print images having a satisfactory quality compared to the case where other halftoning methods are used.
However, if the size of one dot is set larger than one dot pitch when printing the natural image or the like, each dot is printed with an area which is larger than the original dot area. Consequently, the density of the printed image as a whole becomes high, and there was a problem in that saturation occurs for densities greater than or equal to an intermediate level. In addition, this problem was particularly notable when the printing is carried out using the error diffusion method.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful image processing apparatus in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an image processing apparatus which can reproduce the gradation with a high fidelity by preventing saturation of the density at high densities of the image, even if the size of one dot is set larger than one dot pitch, by correcting the error diffusion method.
Still another object of the present invention is to provide an image processing apparatus comprising a threshold value processing circuit subjecting a correction value with respect to an input image data to a threshold value process and outputting an output image data; a subtracting circuit outputting an error signal based on a difference between the correction value and the output image data; an error filter distributing, as a distributing error data dependent on a value of a diffusion matrix, the error signal to neighborhood pixels of a target pixel within the input image data; and a correction circuit multiplying a coefficient to the input image data or the output image data. According to the image processing apparatus of the present invention, it is possible to prevent the saturation phenomenon of the density at high densities and to reproduce the gradation with a high fidelity. In addition, the data can be processed at a high speed because the process is simple.
A further object of the present invention is to provide an image processing apparatus comprising a threshold value processing circuit subjecting a correction value with respect to an input image data to a threshold value process and outputting an output image data, a subtracting circuit outputting an error signal based on a difference between the correction value and the output image data, an error filter distributing, as a distributing error data dependent on a value of a diffusion matrix, the error signal to neighborhood pixels of a target pixel within the input image data, and a correction circuit carrying out a process which is different depending on a value of the output image data at one of an input side of the subtracting circuit, an output side of the subtracting circuit and an output side of the error filter. According to the image processing apparatus of the present invention, it is possible to prevent the saturation phenomenon of the density at high densities and to reproduce the gradation with a high fidelity. In addition, the data can be processed at a high speed because the process is simple.
Another object of the present invention is to provide an image processing apparatus comprising a threshold value processing circuit subjecting a correction value with respect to an input image data to a threshold value process and outputting an output image data, a subtracting circuit outputting an error signal based on a difference between the correction value and the output image data, and an error filter distributing, as a distributing error data dependent on a value of one of a plurality of diffusion matrixes based on one of the input image data, the error signal and the correction value, the error signal to neighborhood pixels of a target pixel within the input image data. According to the image processing apparatus of the present invention, it is possible to prevent the saturation phenomenon of the density at high densities and to reproduce the gradation with a high fidelity. In addition, the data can be processed at a high speed because the process is simple. Furthermore, a fine error diffusion can be made depending on the shape of the dot, for example, and a delicate tone curve can be reproduced.
Still another object of the present invention is to provide an image processing apparatus comprising a threshold value processing circuit subjecting a correction value with respect to an input image data to a threshold value process and outputting an output image data, a correction circuit correcting the output image data depending on the input image data, a subtracting circuit outputting an error signal based on a difference between an output of the correction circuit and the input image data, and an error filter distributing, as a distributing error data dependent on a value of a diffusion matrix, the error signal to neighborhood pixels of a target pixel within the input image data. According to the image processing apparatus of the present invention, it is possible to prevent the saturation phenomenon of the density at high densities and to reproduce the gradation with a high fidelity. In addition, the data can be processed at a high speed because the process is simple. Moreover, a delicate tone curve can be reproduced because the correction is carried out depending on the input image data.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.
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Copy of European Patent Office Communication for European Patent Application No. 97306753 including European Search Report dated Jan. 31, 2000.
Ainai Shigeru
Horie Hiromitsu
Kamata Takao
Oshio Hiroshi
Sato Kazuhiko
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Lee Thomas D.
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