JP3933878B2 - Digital image processing system - Google Patents

Description

[0001]
BACKGROUND 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 can be widely used in the field of image processing of binary images including halftone dots.
[0002]
[Prior art]
Digital image processing including high-quality image input / output due to recent improvements in CPU performance, increased storage media capacity due to lower prices for semiconductors and disk memories, and lower prices for input / output devices such as scanners and printers However, it has become important.
In the digital image processing, when an image read by a scanner or a digital copying machine is an image output from a digital device, if the image includes halftone dots, the image is read as binary image data. The halftone dots may be deformed due to a difference in the sampling interval between the image to be read and the reading device, and uniform unevenness (hereinafter referred to as moire) may occur in the halftone dots. Also, the moire may occur when a digital binary image expressed by halftone dots 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, it is uniformly applied to an image area where no moire occurs, leading to degradation of image quality.
[0003]
[Problems to be solved by the invention]
As described above, the conventional method using a two-dimensional low-pass filter for reducing the occurrence of moire has a problem that it leads to degradation of image quality.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to generate moiré due to enlargement / reduction of a binary image including halftone dots or occurrence of moiré due to a difference in sampling interval due to scanner input. By reducing the shape of the halftone dot, the position information, and the continuity locally with respect to the part being performed, the reduction is achieved by a simple process.
[0004]
[Means for Solving the Problems]
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 or an enlarged / reduced digital image is as follows. Moire reduction processing is applied.
(1) The occurrence of moire is detected for each cell of halftone dots, and 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, as shown in FIG. 1A, when the shape of the cell is not point-symmetric with respect to the cell center, the dot D1 is moved to the position of D1 ′, and the shape is close to point symmetry with respect to the center of the cell. The shape is corrected as follows.
(2) The occurrence of moire is detected for each cell of halftone dots, and the cells are moved so that the position coordinates of the centers of at least nine 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 the centers of the eight connected cells is made equal. The cell C1 is moved to the position of C1 ′.
(3) The occurrence of moire is detected in one cell unit of halftone dots, and the distance between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell is made equal. The shape of the reference cell is corrected.
For example, as shown in FIG. 1C, when the intervals of the circumscribed rectangles of the halftone cells are uneven, the dot D1 of the middle cell is moved to the position of D1 ′, and the intervals of the circumscribed rectangles are evenly distributed. Correct so that
In the present invention, since the means for performing the above-described moire reduction processing of the image processing system is provided, the moire can be reduced without deteriorating the quality of the image. Further, since the present invention is applied only to the image of the moire generation area, the moire can be efficiently reduced.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a diagram showing a configuration example of an image processing system to which the present invention is applied. As shown in the figure, the present invention includes an input / output device 5 including a CPU 1, a RAM 2, a ROM 3, an external storage device 4, a printer, a display, a keyboard, a recording medium reading device 6, a scanner 7 for reading an image, For example, the present invention can be applied to a digital image processing system such as a personal computer that includes a communication interface (not shown).
In the image processing system, 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 the difference in sampling interval as described above. Similarly, moire may occur when a digital image read from the outside is enlarged or reduced in the system.
Therefore, moire reduction means is provided in the image processing system as shown in FIG. 1 to reduce moire. Thereby, it is possible to reduce the occurrence of moire when an image is output by a printer or the like, and to improve the image quality.
[0006]
Examples of moire reduction processing according to the present invention will be described below.
FIG. 3 shows a flowchart of moire reduction processing of the first embodiment of the present invention, and FIG. 4 shows an example of moire reduction processing of the present embodiment.
In this embodiment, each cell of a halftone dot is extracted from a binary image including a halftone dot, the number of dots (number of pixels) contained in the extracted halftone cell is measured, and the actual number of dots is compared with the number of dots. The halftone cell shape is examined, the dots (pixels) are moved with respect to the asymmetric part of the halftone dot, and the shape is corrected so that each cell has a shape close to point symmetry with respect to the center of the cell. Reduce.
[0007]
That is, moire is reduced as follows.
As shown in FIG. 3, first, halftone cells are extracted from the binary image data read from the scanner or the enlarged / reduced binary image data (step S1).
Next, the number of dots in the halftone cell is measured (step S2), and the halftone cell is corrected to a new shape without changing the number of dots (step S3). This correction is performed by moving the dots constituting the halftone cells and correcting the shape of the halftone cells so that they are more symmetrical (preferably point symmetrical).
For example, as shown in FIG. 4A, if the halftone dot cell is composed of 18 dots and the shape of the halftone dot cell is not point-symmetric, the dot shown in FIG. 4A can be moved to the position indicated by A ′. Make it as point-symmetric as possible. Similarly, when the halftone cell is composed of 16 dots as shown in FIG. 4B and its shape is not point-symmetric, the dot A shown in FIG. 4B is placed at the position indicated by A ′. Move.
This process is repeated as long as there are target halftone cells, and the process ends when there are no more target halftone cells.
[0008]
By performing the above processing, the shape of the halftone cell can be made substantially point-symmetric with respect to the center of the halftone cell. Moire occurs when the shape of the halftone dot cell is uniformly deformed in a part of the halftone dot portion. As described above, by making the shape of the halftone dot cell point-symmetrical, Occurrence can be reduced. Further, since the shape of the halftone 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 this embodiment, since the shape of the halftone cell is made substantially point-symmetric without changing the number of dots, moire can be reduced without changing the image quality.
[0009]
FIG. 5 shows a flowchart of moire reduction processing according to the second embodiment of the present invention, and FIG. 6 shows an example of moire reduction processing according to this embodiment. FIG. 6A shows a state before the moire reduction processing, and this example shows an example in which the vertical column in the middle is uniformly shifted to the left and vertical stripe moire is generated. FIG. 6B shows a state after the moire reduction processing of this embodiment.
In this embodiment, the occurrence of moire is detected in units of halftone cells, and the distance between the detected position coordinates of the center of the reference cell and the position coordinates of the centers of the eight cells adjacent to the reference cell is even. Thus, the moire is reduced by moving the reference cell.
[0010]
That is, moire is reduced as follows.
As shown in FIG. 5, first, halftone cells are extracted from binary image data read from a scanner or enlarged / reduced binary image data (step S1).
Next, as shown in FIG. 6A, eight connected halftone cells (cells connected to the reference halftone cell A in eight directions) are extracted (step S2).
Next, the center of the nine halftone cells including the reference halftone cell A (the positions of the white square marks and white triangle marks in FIG. 6A) is calculated (step S3), and eight connected halftone dots are obtained. 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, the reference halftone cell A is translated so that the center of the reference halftone cell A and the ideal center position coincide with each other as shown in FIG. Step S5). In the example of FIGS. 6A and 6B, the center of the reference halftone cell A (white square mark) is shifted to the left, and the reference halftone cell A is translated by one dot on the right.
[0011]
The above processing is repeated until the target halftone cell exists. That is, the next 8-connected halftone cell not including the translated halftone cell is detected, and the same translation processing as described above is performed.
In the present embodiment, as described above, the center of the reference halftone cell of the 8-connected halftone cell is translated so as to coincide with the center of the 8-connected halftone cell. As shown in the figure, it is possible to reduce the vertical stripe moiré that occurs when the middle column is evenly shifted to the left.
[0012]
FIG. 7 shows a flowchart of moire reduction processing according to the third embodiment of the present invention, and FIG. 8 shows an example of moire reduction processing according to this embodiment. FIGS. 8A and 8B show a state before moire reduction processing. In this example, the middle column is uniformly shifted to the left, and vertical stripe moire is generated as in the second embodiment. Show. FIG. 8C shows a state after the moire reduction processing of this embodiment.
In this embodiment, the occurrence of moiré is detected in one cell unit of halftone dots, and the interval (gap distance) between the detected reference halftone cell and the adjacent sides of four or more cells adjacent to the reference cell is determined. Moire is reduced by correcting the shape of the reference cell so as to be uniform.
[0013]
That is, moire is reduced as follows. In the following, only the correction process in the horizontal direction will be described, but the same process is performed in the vertical direction.
As shown in FIG. 7, first, halftone cells are extracted from the binary image data read from the scanner or the enlarged / reduced binary image data (step S1).
Next, as shown in FIG. 8A, four connected halftone cells (cells connected to the reference halftone cell A in four directions) are extracted (step S2).
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 cells around the reference halftone cell A).
When the circumscribed rectangle is calculated, the distance between each side adjacent to each side of the circumscribed rectangle of the reference halftone cell A is calculated (step S3). In the example of FIG. 8B, the intervals d1 and d2 indicated by the arrows are not uniform.
Therefore, the shape of the reference halftone cell is corrected so that the distances between the sides are equal (step S4). In the example shown in FIG. 8C, pixels are added at the positions of the circles in the figure so that the distance between the reference halftone cell A and the left and right halftone cells is equal. In addition, the x-marked pixels in the figure are deleted so as to be the same as the number of pixels before correction.
[0014]
Here, the pixel to be deleted is selected to be closest to the point-symmetrical position with respect to the center of the halftone cell whose shape is to be corrected. Also, as a general rule, the pixels are moved (adding pixels and deleting existing ones) so that the number of pixels in the halftone cell does not change, and shape correction is performed so that the intervals of the circumscribed rectangles become equal. If there is no pixel candidate to be added, the pixel may be simply added.
The above processing is repeated until the target halftone cell exists. That is, the next four connected halftone cells that do not include the halftone dot cells having the above-described shape correction are detected, and a parallel movement process similar to the above is performed.
In this embodiment, as described above, the shape of the reference halftone cell of the four connected halftone cells is corrected so that the distances between the halftone cells and the halftone cells on both sides thereof are equal. Therefore, the same as in the second embodiment. For example, as shown in FIG. 8A, it is possible to reduce the vertical stripe moiré that occurs when the middle column is evenly shifted to the left.
In addition, you may apply the process of the said 1st-3rd Example independently, and may reduce a moire, Moreover, both the process of a 1st Example and the process of a 2nd Example may be performed. The moire reduction processing may be performed by combining the processing of the first to third embodiments, such as applying.
[0015]
【The invention's effect】
As described above, in the present invention, the occurrence of moire is detected for each cell of halftone dots. (1) For each detected cell, each cell has a shape close to point symmetry with respect to the center of the cell. (2) Move the cell so that the position coordinates of the centers of at least nine adjacent cells are statistically equal, (3) The detected reference cell, Since the shape of the reference cell is corrected so that the distance between adjacent sides with at least four cells adjacent to the reference cell is equal, moire can be reduced without degrading the image quality. Can do. Further, since it is applied only to the image of the moire generation area, it is efficient and contributes to the improvement of the processing performance.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the 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 flowchart illustrating a moire reduction process according to the first embodiment of this invention.
FIG. 4 is a diagram illustrating an example of moire reduction processing according to the first embodiment of this invention.
FIG. 5 is a flowchart illustrating a moire reduction process according to the second embodiment of this invention.
FIG. 6 is a diagram illustrating an example of moire reduction processing according to the second embodiment of this invention.
FIG. 7 is a diagram illustrating a flowchart of moire reduction processing according to a third embodiment of this invention.
FIG. 8 is a diagram illustrating an example of moire reduction processing according to a third embodiment of this invention.
[Explanation of symbols]
1 CPU
2 RAM
3 ROM
4 External storage device 5 Input / output device 6 Recording medium reading device 7 Scanner

Claims (6)

A digital image processing system having means for reducing the intensity of moire generated in a binary image represented by halftone dots,
The means for reducing the moire detects the occurrence of moire in one cell unit of halftone dots, and translates the cells so that the position coordinates of the centers of at least nine adjacent cells are statistically uniform. A digital image processing system. A digital image processing system having means for reducing the intensity of moire generated in a binary image represented by halftone dots,
The means for reducing moiré detects the occurrence of moiré in units of halftone cells, and the distance between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell is equal. The digital image processing system is characterized in that the shape of the reference cell is corrected by moving the pixels so that the number of pixels does not change . A program for reducing the intensity of moire generated in a binary image represented by halftone dots,
In the above program, the process of detecting the occurrence of moire in one cell unit of halftone dots and the process of translating the cells so that the position coordinates of the centers of at least nine adjacent cells are statistically uniform A program to reduce the strength of moire, which is characterized by causing a computer to execute. A program for reducing the intensity of moire generated in a binary image represented by halftone dots,
The above program has a process of detecting the occurrence of moire in one cell unit of halftone dots.
The shape of the reference cell by moving the pixels so that the distances between adjacent sides of the detected reference cell and at least four or more cells adjacent to the reference cell are equal and the number of pixels is not changed. A program for reducing the intensity of moiré, which causes a computer to execute a process for correcting an image. A recording medium recording a program for causing a computer to execute processing for reducing the intensity of moire generated in a binary image expressed by halftone dots,
The above program detects occurrence of moire in one cell unit of halftone dots, and translates the cells so that the position coordinates of the centers of at least nine adjacent cells are statistically uniform. A recording medium on which a program for reducing the intensity of moire is recorded. A recording medium recording a program for causing a computer to execute processing for reducing the intensity of moire generated in a binary image expressed by halftone dots,
The above program detects the occurrence of moire in one cell unit of halftone dots 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. And a recording medium on which a program for reducing the intensity of moire is recorded, wherein the shape of the reference cell is corrected by moving pixels so that the number of pixels does not change .

Images