Image analysis – Image enhancement or restoration – Edge or contour enhancement
Reexamination Certificate
1997-12-10
2001-10-09
Grant, II, Jerome (Department: 2624)
Image analysis
Image enhancement or restoration
Edge or contour enhancement
C358S512000
Reexamination Certificate
active
06301395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing apparatuses, and more particularly, to an image processing apparatus that carries out a process of enhancing the contour of an image on image data sent from an image reader that reads out an original image.
2. Description of the Related Art
In a conventional image processing apparatus, differential image data is extracted from the original image data using a Laplacian filter as disclosed in Japanese Patent Laying-Open No. 6-152960. The data is converted according to a lookup table (LUT) into contour enhanced image data. A contour enhancement process is carried out by adding the contour enhanced image data to the original image data. Application of a contour enhancement process can be suppressed according to the result of a region determination for each pixel data forming the image data.
Japanese Patent Laying-Open No. 6-152929 discloses the technique of expanding the readout image by an arbitrary amount in the main scanning direction and the sub scanning direction of the image reader to reduce the problem of thinning, blurring, and disconnection in the text and image.
However, increasing the detection level of the contour to be enhanced will cause the difference in density between the contour portion such as a character and the region other than a character to be increased. The reproduced image was extremely poor in picture quality since the characters subjected to a contour enhancement process looks as if the character was significantly bordered. If the detection level of the contour to be enhanced is reduced for the purpose of preventing disconnection in the lines, the portion other than the thin lines of characters having a gentle image density gradient will also be determined as the contour portion of a character. Image noise will therefore be increased.
If a LOG correction is carried out on the image data read out by the CCD, the image noise in the region of high density is enhanced. Particularly in the case where the image data of the portion corresponding to the ridge of density for a line with a small width exhibits asperity (distribution is not uniform), this irregularity will be further deteriorated by the contour enhancement process. In the reproduced image, the thin line will become disconnected, in addition to the above-described problem.
There is also a problem that, when noise is included in the image, the noise will be eventually increased by the contour enhancement process.
In the latter, if the image is simply expanded, the configuration of the edge of the characters will be altered. When a contour enhancement process is carried out after the expansion process, there is a possibility that the resolution is degraded.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide an image processing apparatus that allows appropriate contour enhancement of an image.
Another object of the present invention is to prevent reduction in the line width and disconnection in a line stroke of a character in an image, and bordering at the contour portion of an image and amplification of noise due to excessive contour enhancement in an image processing apparatus.
A further object of the present invention is to reliably prevent reduction in the line width and disconnection in a line stroke of a character in an image, and edging at the contour portion of an image and amplification of noise due to excessive contour enhancement in an image processing apparatus.
Still another object of the present invention is to suppress bordering at the contour portion of an image and noise amplification due to excessive contour enhancement in an image processing apparatus.
A still further object of the present invention is to provide an image processing method that allows appropriate contour enhancement of an image.
Yet a further object of the present invention is to prevent reduction in the line width and disconnection in a line stroke of a character and the like in an image, and prevent bordering at a contour portion of an image and noise amplification caused by excessive contour enhancement in an image processing method.
The above objects of the present invention can be achieved by an image processing apparatus including the following elements.
According to an aspect of the present invention, an image processing apparatus includes a contour enhancement unit for enhancing the contour of an image on image data constituted by successively input pixel data for providing contour enhanced image data, a first maximum value output unit for providing first maximum density data which is target pixel data in the contour enhanced image data substituted with the maximum density data in the target pixel data and surrounding pixel data, a first minimum value output unit for providing first minimum density data which is the target pixel data in the first maximum density data substituted with the minimum density data in the target pixel data and surrounding pixel data, a second minimum value output unit for providing second minimum density data which is the target pixel data in the contour enhanced image data substituted with the minimum density data in the target pixel data and surrounding pixel data, a second maximum value output unit for providing second maximum density data which is the target pixel data in the second minimum density data substituted with the maximum density data in the target pixel data and surrounding pixel data thereof, and a neighborhood selector receiving the first minimum density data and the second maximum density data for providing either the first minimum density data or the second maximum density data according to a predetermined condition.
In the first maximum value output unit, the density data of the target pixel data in the data output from the contour enhancement unit is substituted with the maximum value data in the target pixel data in the data output from the contour enhancement unit and the pixel data of the pixels surrounding the target pixel. In the first minimum value output unit, the density data of the target pixel data in the data output from the first maximum value output unit is substituted with the minimum value data (minimum density data) in the target pixel data in the data output from the first maximum output unit and in the surrounding pixel data. In the second maximum value output unit, the density data of the target pixel data in the data output from the contour enhancement unit is substituted with the minimum value data in the target pixel data in the data output from the contour enhancement unit and the surrounding pixel data. In the second maximum value output unit, the density data of the target pixel data in the data output from the second minimum value output unit is substituted with the maximum value data (maximum density data) in the target pixel data in the data output from the second minimum value output unit and the surrounding pixel data. The minimum density data and the maximum density data are applied to the neighborhood selector. Either the minimum density data or the maximum density data is output from the neighborhood selector according to a predetermined condition.
By virtue of the first maximum value output unit and the first minimum value output unit, a process of preventing disconnection in line strokes of a text image can be carried out on a pixel having a high density (tonal gradation). By virtue of the second minimum value output unit and the second maximum value output unit, a process can be carried out on pixels with low density (tonal gradation) so that reduction in resolution due to filling the valley between peaks of density in a text image can be prevented and so that an isolated point due to contamination in the image can be removed. By carrying out these processes selectively for each pixel according to a predetermined condition, thinning and disconnection of line strokes can be prevented. Also, reduction in resolution can be suppressed to allow removal of an isolated point due
Hirota Yoshihiko
Nishigaki Junji
Tsukada Koji
Grant II Jerome
McDermott & Will & Emery
Minolta Co. , Ltd.
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