Image analysis – Image enhancement or restoration – Artifact removal or suppression
Reexamination Certificate
1998-09-28
2001-06-05
Lee, Thomas D. (Department: 2624)
Image analysis
Image enhancement or restoration
Artifact removal or suppression
C358S001900
Reexamination Certificate
active
06243500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an improved method and apparatus for erasing dirty spots in the information content of image reproducing systems including copying systems and printing systems.
2. Discussion of the Background
The present invention is related to the area of analyzing the images of documents and determining compensation filter selections to optimize the reproduction fidelity of the print.
FIG. 13
illustrates a general image processing unit (IPU)
10
which has been developed for use in an image forming apparatus such as, scanners, copying machines, facsimile machines, and so forth. The IPU
10
of
FIG. 13
typically adopts a mesh-screen image seek operation and an isolated-pixel seek operation in order to erase dirty spots in the image data. The mesh-screen image seek operation is to distinguish ordinary images from mesh-screen images. The mesh-screen images are typically used with images of newspapers, for example.
In a practical application, the IPU
10
is provided with two selectable image reading modes relative to the mesh-screen image seek operation. One is a character image mode and the other is a character/photo mixed-image mode. The character image mode will be used typically when the document to be read includes mainly characters and the character/photomixed-image mode will be used typically when the document to be read includes characters and images such as photos.
A mesh-screen image, such as an image of newspaper, typically appears with images to be read in the character/photo mixed-image mode but not in the character image mode. Accordingly, the mesh-screen seek operation does not need to be operable in the character image mode in a general image processing apparatus including the IPU
10
of FIG.
13
.
The dirty-pixel seek operation is used to distinguish a pixel that is not at a white level and is isolated from ordinary pixels. Such a pixel (referred to as an isolated-pixel) is regarded as an undesired dirty spot on a document. Therefore, it may be desirable if such a dirty-spot is erased from the document.
For these operations, the IPU
10
is provided with a mesh-screen image seek circuit
12
and an isolated-pixel seek circuit
13
. In the IPU
10
, a shading correction circuit
11
corrects the image data of a document which is transmitted from a CCD (charge coupled device)
9
through a video processing unit (VPU)
10
a.
The image data is then applied to a plurality of circuits such as the mesh-screen image seek circuit
12
, the isolated-pixel seek circuit
13
, an MTF (Modulation Transfer Function) correction filter
14
and a smoothing filter
15
.
The isolated-pixel seek circuit
13
judges whether each of the individual pixels of an image is surrounded by white pixels, either in the character image mode or the character/photo mixed-image mode. A pixel surrounded by white pixels is referred to as the above-described isolated-pixel. When an isolated-pixel is found, the isolated-pixel seek circuit
13
outputs an isolated-pixel signal to a selector
17
.
The mesh-screen image seek circuit
12
operates only in the character/photo mixed-image mode and judges whether the image is composed of a plurality of groups of spots, or a mesh-screen image such as in newspapers. The mesh-screen image seek circuit
12
outputs a mesh-screen image signal to a selector
18
, indicating the pixel being transmitted is either a mesh-screen image or an ordinary image.
The isolated-pixel seek circuit
13
uses a 5- by 5-pixel matrix, for example, as illustrated in
FIG. 4
, and picks up the values of a center pixel D
22
and its surrounding pixels in the matrix, as illustrated in
FIG. 7
, and compares these values with a predetermined threshold value X. When the values of the center pixel D
22
and all of the surrounding pixels in the matrix are smaller than the predetermined threshold value X, the isolated-pixel seek circuit
13
judges the center pixel D
22
to be an isolated and potentially black pixel, or a potential dirty spot. At this time, the isolated-pixel seek circuit
13
outputs an isolated-pixel signal for indicating that the pixel being transmitted is either an isolated-pixel or an ordinary pixel. When the pixel being transmitted is judged to be an isolated-pixel, this pixel needs to be changed to a white pixel, so that the isolated-pixel may be erased.
The selector
17
selects the data from a white data register
16
when the pixel D
22
is judged to be an isolated and potentially black pixel, or a potential dirty spot, on the basis of the isolated-pixel signal output from the isolated-pixel seek circuit
13
. The selector
17
selects the correction data from the MTF correction filter
14
when the pixel D
22
is judged not to be an isolated and potentially black pixel, or an ordinary image spot, on the basis of the isolated-pixel signal output from the isolated-pixel seek circuit
13
.
The selector
18
selects data output from either the selector
17
or the smoothing filter
15
on the basis of the mesh-screen image signal output from the mesh-screen image seek circuit
12
. In the character mode, however, the selector
18
selects only the data output from the selector
17
regardless of the mesh-screen image signal. In the character/photo mixed-image mode, the selector
18
selects the correction data output from the smoothing filter
15
when the target pixel is judged as a pixel in a mesh-screen image. Also, in the character/photo mixed-image mode, the selector
18
selects the data output from the selector
17
when the target pixel is judged as a pixel not in a mesh-screen image. The data selected by the selector
18
is applied to a &ggr;-correction circuit
19
and then to the following circuit.
Thus, in the character mode, the image data selected is either the white data from the white data register
16
or the MTF correction data from the MTF correction filter
14
, according to the isolated-pixel signal from the isolated-pixel seek circuit
13
, and the smoothing filter data from the smoothing filter
15
is not selected as the image data. In the character/photo mixed-image mode, the smoothing filter data from the smoothing filter
15
is determined as the image data when the target pixel is judged as a pixel in a mesh-screen image. On the other hand, when the target pixel is judged as a pixel not in a mesh-screen image in the character/photo mixed-image mode, the white data from the white data register
16
is selected as the image data when the target pixel is judged as an isolated-pixel, and the MTF correction data from the MTF correction filter
14
is determined as the image data when the target pixel is not judged as the isolated-pixel.
That is, the IPU
10
of
FIG. 13
executes only the isolated-pixel seek operation but not the mesh-screen image seek operation when in the character mode. This means that in the character mode a target pixel in a mesh-screen image may be undesirably judged as an isolated and potentially black spot, or a potential black spot, through the dirty-spot seek operation. A countermeasure for this issue is to set the predetermined threshold value X to a relatively high value for a target pixel in a mesh-screen image. However, this countermeasure has a further drawback in which a real dirty spot in a mesh-screen image might not be found and erased with such a relatively high value X.
On the contrary, if the threshold value X is set to such a value that the isolated-pixel seek operation functions on the mesh-screen image, a problem may occur in which many pixels of the mesh-screen and low contrast images may be erased. Furthermore, if the size of the matrix of
FIG. 4
is made larger in order to avoid the above-mentioned problem, another problem may occur that the size of the IPU
10
may become larger as well.
Japanese Patent Laid-open Publication 7-30751/1995 discloses an image processing apparatus that attempts to prevent upsizing thereof by combining a shift register that outputs matrix data to the isolated-pixel seek circuit
1
Brinich Stephen
Lee Thomas D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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