JP2001346038A - Digital image processing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To alleviate generation of moire in a binary image including dots by a simple processing. SOLUTION: The generation of moire is detected by one cell unit of the dots for a digital image including the dots read from a scanner or a digital image to which a magnification and reduction processing is performed and the generation of moire is alleviated in the following way. The shape is corrected so that each cell has a shape close to point symmetrical with respect to the center of the cell by every detected cell as shown in fig. 1 (a). In addition, the cells are moved so that position coordinates of at least nine adjacent cells becomes statistically equal as shown in fig. 1 (b). Furthermore, the moire is detected by one cell unit the dots and the shape of a detected reference cell is corrected so that distance of adjacent sides among the reference cell and at least four cells adjacent to the reference cell become equal as shown in fig. 1 (c).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing system provided with means for reducing the intensity of moire generated in a digital binary image, and is widely used in the field of image processing of a binary image containing halftone dots. can do.

[0002]

2. Description of the Related Art In recent years, high-quality image input / output has been achieved by improving the performance of CPUs, increasing the capacity of storage media due to lower prices of semiconductors and disk memories, and reducing the price of input / output devices such as scanners and printers. Digital image processing is becoming important. In the above digital image processing, if the image read by the scanner or digital copier is an image output from a digital device,
If halftone dots are included in the image, when the image is read as binary image data, the halftone dots are deformed due to a difference in the sampling interval between the image to be read and the reading device, and the halftone portion is uniformly formed. Unevenness (hereinafter referred to as moiré) may occur. In addition, the above-mentioned moiré may occur when a digital binary image represented by a halftone dot is subjected to enlargement / reduction processing or the like. Conventionally, the reduction of moiré caused by enlargement / reduction processing of a binary image has been dealt with by using a two-dimensional low-pass filter. However, when a low-pass filter is used, the image is uniformly applied to an image area where moiré does not occur, leading to deterioration of image quality.

[0003]

As described above, the conventional method using a two-dimensional low-pass filter to reduce the occurrence of moire has a problem that the quality of an image is deteriorated. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for generating / reducing a moiré caused by a difference in a sampling interval due to a scanner input by enlarging / reducing a binary image including halftone dots. By changing the shape, position information, and continuity of a halftone dot locally at a part where the halftone dot is located, the reduction can be achieved by simple processing.

[0004]

FIG. 1 is a diagram for explaining the outline of the present invention. In the present invention, as shown in FIG. 1, the image processing system is provided with means for performing moire reduction processing, and a digital image including halftone dots read from a scanner,
Alternatively, the following moiré reduction processing is performed on the digital image subjected to the scaling processing. (1) The occurrence of moiré is detected for each cell of a halftone dot,
For each detected cell, the shape is corrected so that each cell has a shape close to point symmetry with respect to the center of the cell. For example, FIG.
As shown in (a), when the shape of the cell is not point-symmetric with respect to the center of the cell, the dot D1 is moved to the position of D1 ', and the shape is changed so as to be nearly point-symmetric with respect to the center of the cell. to correct. (2) The occurrence of moire is detected for each cell of a halftone dot,
The cells are moved so that the position coordinates of the centers of at least nine or more adjacent cells are statistically equal. For example, as shown in FIG. 1B, when the middle column is uniformly shifted to the right, the distance between the coordinates of the center of the cell C1 and the coordinates of each center of the eight connected cells is equalized. The cell C1 is moved to the position of C1 '. (3) The occurrence of moiré is detected in units of one halftone dot, and the distance between adjacent edges of the detected reference cell and at least four or more cells adjacent to the reference cell is equalized. The shape of the reference cell is corrected. For example, FIG.
If the intervals of the circumscribed rectangles of the halftone cells are not uniform as shown in (c), the dot D1 of the middle cell is changed to D
The circumscribed rectangle is moved to the position 1 'and corrected so that the intervals between the circumscribed rectangles become equal. In the present invention, since the means for performing the above-described moiré reduction processing of the image processing system is provided, it is possible to reduce the moiré without deteriorating the image quality. Further, since the present invention is applied only to the image of the moiré generation area, moiré can be efficiently reduced.

[0005]

FIG. 2 is a diagram showing an example of the configuration of an image processing system to which the present invention is applied. The present invention, as shown in FIG. 1, includes a CPU 1, a RAM 2, a ROM 3, an external storage device 4, an input / output device 5 including a printer, a display, a keyboard, etc., a recording medium reading device 6, a scanner 7 for reading an image, The present invention can be applied to a digital image processing system such as a personal computer, which includes a communication interface (not shown). In the image processing system described above, when an image including a halftone dot output from a digital device is read from the scanner 7, moire may occur in the halftone portion due to a difference in sampling interval as described above. Also, when a digital image read from the outside is subjected to enlargement / reduction processing in the system, moire may similarly occur. Therefore, the image processing system is provided with moiré reducing means as shown in FIG. 1 to reduce moiré. As a result, it is possible to reduce the occurrence of moire when an image is output by a printer or the like, and it is possible to improve image quality.

An embodiment of the moiré reduction processing of the present invention will be described below. FIG. 3 shows a flowchart of the moiré reduction processing of the first embodiment of the present invention, and FIG. 4 shows an example of the moiré reduction processing of this embodiment. In the present embodiment, 2
From the value image, the individual cells of the halftone dot are extracted, the number of dots (the number of pixels) included in the extracted halftone cell is measured, and the actual halftone cell shape is checked with respect to the number of the halftone dots. Moire is reduced by moving the dots (pixels) with respect to the asymmetrical portion and correcting the shape so that each cell has a shape close to point symmetry with respect to the center of the cell.

That is, moire is reduced as follows. As shown in FIG. 3, first, a halftone dot cell is extracted from binary image data read from a scanner or binary image data that has been enlarged or reduced (step S1). Next, the number of dots of the halftone cell is measured (step S2), and the halftone cell is corrected to a new shape without changing the number of dots (step S2).
3). This correction is performed by moving the dots constituting the halftone dot cell and correcting the shape of the halftone dot cell so as to have a more symmetrical shape (preferably, point symmetry). For example, as shown in FIG. 4A, when the halftone cell is composed of 18 dots and the shape of the halftone cell is not point symmetric, the dot shown in FIG. Make the shape as symmetrical as possible. Similarly, as shown in FIG. 4B, when the halftone dot cell is composed of 16 dots and the shape is not point-symmetric, the dot A shown in FIG. Move. This process is repeated as long as the target halftone cell exists, and the process ends when there is no more halftone dot cell to be processed.

By performing the above processing, the shape of the halftone dot cell can be made substantially point-symmetric with respect to the center of the halftone dot cell. Moiré occurs when the shape of a halftone dot cell is uniformly deformed in a part of the halftone dot area.
As described above, when the shape of the halftone dot cell is a point symmetric shape, occurrence of moire can be reduced. Also,
Since the shape of the halftone dot cell is corrected so that the number of dots does not change, the density of the halftone dot portion does not change. As described above, in the present embodiment, since the shape of the halftone dot cell is substantially point-symmetric without changing the number of dots, moire can be reduced without changing the image quality.

FIG. 5 is a flowchart of a moire reducing process according to a second embodiment of the present invention, and FIG. 6 shows an example of a moire reducing process according to the present embodiment. FIG. 6A shows a state before the moiré reduction processing. This example shows an example in which the middle column is uniformly displaced to the left, and vertical stripe moire occurs. FIG. 6B shows a state after the moiré reduction processing of this embodiment. In the present embodiment, the occurrence of moiré is detected for each cell of halftone dots, and the distance between the detected position coordinates of the center of the reference cell and the position coordinates of the center of eight cells adjacent to the reference cell is evenly distributed. The moire is reduced by moving the reference cell as described above.

That is, moire is reduced as follows. As shown in FIG. 5, first, a halftone dot cell is extracted from binary image data read from a scanner or binary image data that has been enlarged or reduced (step S1). Then
As shown in FIG. 6A, eight connected halftone cells (cells connected in eight directions to the reference halftone cell A) are extracted (step S2). Next, the center of nine dot cells including the reference dot cell A (the positions of the white squares and the white triangles in FIG. 6A) is calculated (step S3), and the eight connected halftone dots are calculated. An ideal center position of the reference halftone cell is calculated from the center of the cell (step S4). When the ideal center position is calculated, FIG.
As shown in (b), the reference halftone cell A is translated so that the center of the reference halftone cell A coincides with the ideal center position (step S5). In the example of FIGS. 6A and 6B, since the center (open square mark) of the reference halftone cell A is shifted to the left, the reference halftone cell A is translated by one dot to the right.

The above processing is repeated until the target halftone cell exists. That is, the next 8-connected halftone dot cell that does not include the halftone dot cell that has been translated is detected, and the same parallel translation processing is performed. In the present embodiment, as described above, the center of the reference halftone cell of the eight connected halftone cells is translated so as to coincide with the center of the eight connected halftone cells. As shown, the vertical stripe moire generated when the middle column is uniformly shifted to the left can be reduced.

FIG. 7 is a flowchart of a moire reducing process according to a third embodiment of the present invention, and FIG. 8 shows an example of a moire reducing process according to the present embodiment. FIGS. 8A and 8B show a state before the moiré reduction processing. This example shows an example in which the middle column is uniformly shifted to the left, and vertical stripe moire occurs as in the second embodiment. Is shown. FIG. 8C shows a state after the moiré reduction processing of this embodiment. In the present embodiment, the occurrence of moiré is detected in one cell unit of a halftone dot, and the distance (distance between gaps) between the detected reference halftone cell and four or more cells adjacent to the reference cell is determined. The moire is reduced by correcting the shape of the reference cell so as to be uniform.

That is, moire is reduced as follows. In the following, only the correction processing in the horizontal direction will be described, but the same processing is performed in the vertical direction.
As shown in FIG. 7, first, a halftone dot cell is extracted from binary image data read from a scanner or binary image data that has been enlarged or reduced (step S1). Next, FIG.
As shown in (a), four connected halftone cells (cells connected in four directions to the reference halftone cell A) are extracted (step S).
2). Next, as shown in FIG. 8B, a circumscribed rectangle of five halftone cells including the reference halftone cell A is calculated. In FIG. 8, a white square mark indicates the center position of the reference halftone cell A, and a white triangle mark indicates the center position of the halftone cell around the reference halftone cell A). When the circumscribed rectangle is calculated, the distance between each side of the circumscribed rectangle of the reference halftone cell A and each adjacent side is calculated (step S3). In the example of FIG. 8B, the intervals d1 and d2 indicated by arrows are non-uniform. Therefore, the shape of the reference halftone dot cell is corrected so that the distance between the sides becomes equal (step S4). FIG.
In the example shown in (c), pixels are added at the positions indicated by the circles in the figure so that the intervals between the reference halftone cell A and the left and right halftone cells are equal. In addition, the pixels marked with “x” in the figure are deleted so as to have the same number of pixels as before correction.

Here, as the pixel to be deleted, a pixel closest to the point-symmetric position with respect to the center of the halftone dot cell whose shape is to be corrected is selected. Also, in principle, the pixels are moved (by adding pixels and deleting existing ones) so that the number of pixels in the halftone cell does not change, and the shape is corrected so that the intervals of the circumscribed rectangles are equal. If there is no pixel candidate to perform, pixels may be simply added. The above processing is repeated until the target halftone cell exists. That is, the next 4-connected halftone cell that does not include the halftone cell whose shape has been corrected is detected, and the same parallel movement processing is performed. In the present embodiment, as described above, the shape of the reference halftone cell of the 4-connected halftone cell is corrected so that the intervals between the halftone cells on both sides thereof are equal to each other. For example, FIG.
As shown in (a), vertical stripe moire generated when the middle column is uniformly shifted to the left can be reduced. It should be noted that the processing of the first to third embodiments may be applied alone to reduce moiré, or that both the processing of the first embodiment and the processing of the second embodiment may be performed. For example, the moiré reduction process may be performed by combining the processes of the first to third embodiments.

[0015]

As described above, according to the present invention, the occurrence of moiré is detected for each cell of a halftone dot.
For each detected cell, the shape is corrected so that each cell has a shape close to point symmetry with respect to the center of the cell, and the position coordinates of the centers of at least nine or more adjacent cells are statistically uniform. The shape of the reference cell is corrected so that the distance between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell is equal. Therefore, moiré can be reduced without deteriorating image quality. In addition, since it is applied only to the image of the moiré generation area, the efficiency is high
It contributes to improvement of processing performance.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an outline of the present invention.

FIG. 2 is a diagram illustrating a configuration example of an image processing system to which the present invention is applied;

FIG. 3 is a diagram showing a flowchart of a moiré reduction process according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a moiré reduction process according to the first embodiment of this invention.

FIG. 5 is a diagram illustrating a flowchart of a moiré reduction process according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a moiré reduction process according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a flowchart of a moiré reduction process according to a third embodiment of the present invention.

FIG. 8 is a diagram illustrating an example of a moiré reduction process according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 CPU 2 RAM 3 ROM 4 External storage device 5 Input / output device 6 Recording medium reading device 7 Scanner

Claims (9)

[Claims] 1. A digital image processing system comprising means for reducing the intensity of moiré generated in a binary image represented by halftone dots, wherein the means for reducing moiré reduces the occurrence of moiré to halftone dots. A digital image processing system, wherein the shape is corrected so that each cell has a shape close to point symmetry with respect to the center of the cell. 2. A digital image processing system comprising means for reducing the intensity of moiré generated in a binary image represented by halftone dots, wherein the means for reducing moiré includes a method for reducing the occurrence of moire. A digital image processing system which detects cells in units of one cell and moves the cells so that position coordinates of centers of at least nine or more adjacent cells are statistically equal. 3. A digital image processing system comprising means for reducing the intensity of moiré generated in a binary image represented by a halftone dot, wherein the means for reducing moiré includes a method for reducing the occurrence of moiré by using a net. Correcting the shape of the reference cell so that the distance between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell is detected in units of one cell of points. A digital image processing system characterized by the following. 4. A program for reducing the intensity of moiré generated in a binary image represented by a halftone dot, the program comprising: a process of detecting the occurrence of moire for each cell of halftone dot; A program for reducing the intensity of moiré, characterized by causing a computer to execute a process of correcting a shape of each detected cell so that each cell has a shape close to point symmetry with respect to the center of the cell. 5. A program for reducing the intensity of moiré generated in a binary image represented by a halftone dot, the program comprising: a process for detecting the occurrence of moire in each cell of halftone dot; A program for reducing the intensity of moiré, wherein the program causes a computer to execute a process of moving cells so that position coordinates of centers of at least nine or more adjacent cells are statistically equal. 6. A program for reducing the intensity of moiré generated in a binary image represented by a halftone dot, the program comprising: a process for detecting the occurrence of moire in one cell unit of halftone dot; , So that the distance between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell is equal,
A program for causing a computer to execute the process of correcting the shape of the reference cell, wherein the program reduces the moire intensity. 7. A recording medium on which a program for reducing the intensity of moiré generated in a binary image represented by a halftone dot is recorded, wherein the program causes the moire to occur in units of one cell of the halftone dot. A recording medium on which a program for reducing the intensity of moiré is recorded, wherein a shape of each detected cell is corrected so that each cell has a shape close to point symmetry with respect to the center of the cell. 8. A recording medium on which is recorded a program for reducing the intensity of moiré generated in a binary image represented by a halftone dot, wherein the program detects the occurrence of moire in one cell unit of halftone dot. A recording medium on which a program for reducing the intensity of moire is recorded, wherein the program detects and moves the cells so that the position coordinates of the centers of at least nine adjacent cells are statistically uniform. 9. A recording medium on which a program for reducing the intensity of moiré generated in a binary image represented by a halftone dot is recorded. Wherein the shape of the reference cell is corrected such that the distance between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell becomes uniform. A recording medium on which a program for reducing strength is recorded.