KR20060054816A - The method of designing the clustered dot screen capable of reducing the noisiness in outputing the binary image - Google Patents

Abstract

Disclosed is a method of designing a concentrated dot screen capable of suppressing a noise level when outputting a binary image. In the concentrated dot screen design method capable of suppressing the noise level when outputting a binary image according to the present invention, the initial positions of the plurality of cluster centers are determined by a predetermined method, and a screen having a predetermined size in consideration of the initial positions of the cluster centers. Dividing the matrix into a plurality of regions to create a divided region, and designing a screen by uniformly forming the number of dots around the cluster center in the divided region. According to the present invention, in the design of the centralized dot screen, the sub dots formed around each cluster center are grown to have a uniform size. Therefore, when binarization is performed using the concentrated dot screen manufactured by the present invention, a smoother output binary image can be obtained.

Screening, Binary Image, Cluster, Dot, Noise Figure

Description

The method of designing the clustered dot screen capable of reducing the noisiness in outputing the binary image}

1 is a flowchart of a method of designing a random clustered-dot screen disclosed in US Pat. No. 5,859,955;

2 is a view illustrating a process of forming dots around a cluster center in a conventional screen design method;

3 is a block diagram of a centralized dot screen design apparatus for carrying out the present invention;

4 is a flowchart provided to explain a method of designing a concentrated dot screen capable of suppressing a noise level when outputting a binary image according to the present invention;

FIG. 5 is a flowchart showing the details of step S500 of FIG. 4; and

6 is a diagram illustrating a process of forming dots around a cluster center according to a preferred embodiment of the present invention.

Brief description of the main parts of the drawing

310: Cluster Center Initial Position Design Department

320: screen matrix divider 330: counter

340: determination unit 350: binary pattern design unit                 

352: dot detection unit 354: dot formation position calculation unit

356: dot forming portion 380: screen design portion

The present invention relates to a concentrated dot screen design method, and in particular, by designing the screen so that the number of dots formed around the cluster center grows with the same size when designing the concentrated dot screen, thereby reducing the noise level when performing binarization. The present invention relates to a concentrated dot screen design method that can be suppressed.

In general, binary output devices such as digital printers, photocopiers, binary output LCDs, and the like, actually deliver a variety of colors with only black and white colors. For example, in the case of a black and white digital printer, a black and white image displayed on a monitor displays only two values, black and white. At this time, in order to output the monochrome image of the various brightness displayed on the monitor to the monochrome printer, a series of processes for converting the input image into binary image is required in the printer or PC. That is, a process of converting the color of each pixel into a gray scale image represented by a brightness value between 0 and 255, and a process of converting the gray scale image into a binary image are required. Here, an image having a brightness value between 0 (black) and 255 (white) is called a grayscale image, and a process of converting the grayscale image into a binary image is called halftoning.

In such a half-toning technique, error diffusion mainly used in inkjet printers and multi-function printers and screening methods commonly used in laser printers are commonly used.

The error diffusion method distributes the error generated in the process of converting the continuous grayscale image to the binary grayscale image to adjacent pixels to minimize the mean error in the binary image, thereby having excellent boundary preservation as well as the ability to reproduce the continuous grayscale image.

Screening refers to a method of converting a continuous image, such as a photograph, into the size of a very small dot called a dot to express the tint of the image, also called 'mang hanging'.

Screening methods are classified into clustered-dot screening in which binary halftone dots are formed as close as possible, and distributed-dot screening in which binary halftone dots are formed as far apart as possible. Concentrated dot screening has a poor performance of displaying detailed components of an image compared to distributed dot screening, while having good tone reproduction and being resistant to defects of a laser printer. On the other hand, distributed dot screening is weak in defects of a printer, but is preferred in display devices or inkjet printers because it has an advantage of expressing detail components of an image well.

On the other hand, as another classification of the screening method, ordered-dot screening, binary halftone dots in which binary halftone dots are formed while having regularity according to a constant line per inch (LPI) and an angle, There is irregular-dot screening that is formed without regularity. Compared to sequential dot screening, the result of irregular dot screening is excellent in terms of image quality because there are less visible patterns, but the screening result shows that the compression rate of the half-toning image is much better than sequential dot screening.

In recent years, interest in "model-based halftoning" that outputs a better half-toning image in consideration of human visual characteristics and printer model characteristics has increased.

1 is a flow diagram of a method of designing a random clustered-dot screen disclosed in US Pat. No. 5,859,955.

US Pat. No. 5,859,955 discloses a halftoning method in which irregular dot screening and intensive dot screening are combined. This is because a plurality of center dots (hereinafter, referred to as "cluster centers") having no constant direction and periodicity are designed (S10), and then the order of dots formed around each center dot is a predetermined cost function. system (S20).

As a method of manufacturing a screen for outputting a similar halftone image, US Patent 6335989 discloses a halftoning printing using donut filters. This makes the screen using a different cost function than the above system, but there is considerable similarity in that the surrounding dots are formed around cluster centers without constant direction and periodicity.

On the other hand, the above-described conventional technique has attempted to obtain high image quality by reducing the visible pattern in the output halftone image by using the advantages of irregular dot screening. In addition, the technique of intensive dot screening is combined to obtain a stable output in an incomplete output device such as a laser printer.

These conventional halftoning systems use momentum and distance penalty functions as a cost function for optimally forming dots around the cluster center. Of these, momentum plays a role in uniformly increasing the shape and size of each cluster, and the distance penalty function induces the distance between the clusters as far as possible.

2 is a diagram illustrating an example in which a peripheral dot is formed around a cluster center and each cluster grows in the conventional screen design method. Each small box area in Fig. 2 is a pixel area where dots are formed. Referring to FIG. 2, the size and shape of the clusters are generally similar by momentum. However, as shown in (b) and (c) of FIG. 2, the same number of dots are not assigned to each cluster. As described above, when the number of dots formed in each cluster is not uniform, there is a problem in that a noise level is increased when outputting a binary image.

Therefore, an object of the present invention is to design a concentrated dot screen that can suppress the noise level when outputting a binary image for outputting a smoother image by forming peripheral dots around the cluster center so that the same number of dots are assigned to each cluster. To provide.

In order to achieve the above object, according to the present invention, a method for designing a concentrated dot screen capable of suppressing a noise level when outputting a binary image includes (a) determining an initial position of a plurality of cluster centers by a predetermined method; (b) generating a partition by dividing a screen matrix having a predetermined size into a plurality of areas in consideration of initial positions of cluster centers; And (c) designing the screen by uniformly forming the number of dots around the cluster center in the partition.

Here, step (c) includes: (c1) initializing the predetermined variable k to 0; (c2) detecting an area where the number of dots formed in the divided area is k and outputting a predetermined ID number corresponding to the detected area; (c3) calculating a position at which the sub dot is to be formed using a predetermined cost function in the pixel region in the divided region corresponding to the ID number; (c4) forming a sub dot at the calculated position; And (c5) checking whether all of the pixel areas of the screen matrix are filled with the sub dots. If all the pixel areas of the screen matrix are not filled with the sub dots, the predetermined variable k is increased by one; When steps (c2) to (c5) are repeated and sub dots are filled in all the pixel areas of the screen matrix, it is preferable to finish the screen design.

Here, the sub dot is formed around the cluster center.

Preferably, the divided region is composed of a plurality of pixel regions, and one sub dot is formed in each pixel region.

In addition, the predetermined cost function is preferably one of a combination of a momentum and distance penalty function and a human visual system weighted error sum of a direct binary search (DBS) algorithm.

Hereinafter, with reference to the accompanying drawings illustrating the present invention.

3 is a block diagram of a centralized dot screen design apparatus for carrying out the present invention. Referring to FIG. 3, the centralized dot screen design apparatus 300 includes a cluster center initial position design unit 310 and a screen design unit 370.

The cluster center initial position design unit 310 determines an initial position of a plurality of cluster centers (hereinafter, referred to as a cluster center) by using a sequential dot screening method or an irregular dot screening method.

The screen design unit 370 designs the screen in an optimized manner using a modified Direct Binary Search (hereinafter referred to as "DBS") algorithm in consideration of initial position information of the cluster centers, human visual characteristics, and printer model characteristics. The screen design unit 370 includes a screen matrix divider 320, a counter 330, a determiner 340, a dot detector 352, a dot formation position calculation unit 354, and a dot formation unit 356. .

The screen matrix dividing unit 320 divides the screen matrix into a plurality of areas in consideration of the positions of the plurality of cluster centers provided by the cluster center initial position designing unit 310, and dots a predetermined ID number corresponding to each divided area. The detection unit 352 is provided.

The counter 330 counts the predetermined variable values k and n by increasing from 0 to 1.

The dot detector 352 detects an area in which the number of sub-dots formed around the cluster center is equal to the value of the variable k provided by the counter, and a dot formation position calculator for describing a predetermined ID number corresponding to the detected area later. 354).

The dot formation position calculation unit 354 calculates the positions (i, j) in which the sub dot is to be formed in the divided region corresponding to the ID number by using a predetermined cost function. The dot forming unit 356 forms dots at the forming positions (i, j) of the sub-dots provided by the dot forming position calculating unit 354.

The determination unit 340 checks whether all the pixel areas of the screen matrix are filled with dots. Here, the pixel area refers to an area where dots are formed. When the dots are not filled in all the pixel areas, the determination unit 340 controls the counter 330 so that the value of the variable K is increased by one. When dots are filled in all pixel areas of the screen matrix, the determination unit 340 controls the screen design to be finished.

4 is a flowchart provided to explain a screen design method capable of suppressing a noise level when outputting a binary image according to the present invention. 3 and 4, the cluster center initial position design unit 310 designs initial positions of the plurality of cluster centers in a predetermined manner (S400). The initial positions of the cluster centers may be designed by a sequential dot screening method to have a constant angle and LPI, or may be designed by an irregular screening method so as not to have a constant directionality or LPI.

An example of a method of designing the initial position of the cluster center by the sequential dot screening method is "Holladay Algorism" disclosed in US Pat. Meanwhile, an example of a method of designing an initial position of a cluster center by an irregular dot screening method is "Void and Cluster method" (Robert Ulichney, "The Void-and Cluster Method for Dither Array Generation", IS & T / SPIE Symposium on Electronic Imaging) Science and Technology, San Jose, CA, 1993).

In this manner, when the initial positions of the plurality of cluster centers are determined in step S400, the screen design unit 380 designs the screen using a predetermined cost function considering the position information of the initialized cluster centers (S500). .

FIG. 5 is a detailed flowchart illustrating step S500 of FIG. 4. Referring to FIG. 5, first, the screen matrix divider 320 divides a u * v sized screen matrix into a plurality of regions in consideration of the positions of the plurality of cluster centers provided by the cluster center initial position design unit 310. In operation S511, the predetermined ID number corresponding to each divided area is provided to the binary pattern design unit 350. At this time, the screen matrix is divided so that the number of pixels allocated to each area is as uniform as possible. Here, u and v are natural numbers and represent the number of pixel regions.

Thereafter, the counter 330 sets the arbitrary variables k and n to 0 (S512).

Next, the dot detector 352 detects an area where the number of peripheral dots formed around the cluster center is k, and outputs a predetermined ID number corresponding to the detected area (S513). Here, the predetermined ID number corresponding to the detected area is provided from the screen matrix dividing unit 320.

The dot formation position calculation unit 354 calculates positions (i, j) at which sub dots are to be formed using a predetermined cost function in an empty pixel area in the division area corresponding to the ID number (S514). In this case, as a cost function used to calculate the position at which the sub dot is to be formed, a combination of momentum and distance penalty function disclosed in US Pat. No. 5,955,955 or DBS (Direct Binary Search) using the human visual system weighted error sum of the algorithm (JP Allebach, et al., "Model-based Halftoning via Direct Binary Search, IS & T's 47th Annual Conference, Rochester, NY, pp. 1-8, May 1994.) How to do it.

The dot forming unit 356 adds a dot to the forming positions i and j of the peripheral dot provided from the dot forming position calculating unit 354 (S515).

Thereafter, the counter increments the predetermined variable value n by one (S516). Subsequently, the determination unit 340 compares whether u * v, which is a value indicating the size of the screen matrix, and the predetermined variable value n are equal to each other, and checks whether all the pixel areas of the screen matrix are filled with dots (S517). Here, the pixel area refers to an area where sub dots are formed.

As a result of determination, when u * v and n are not the same, when all the pixel areas in the screen matrix are not filled with dots (S517), the determination unit 340 controls the dot detection unit 352 around the cluster center. It is checked whether a region where the number of the formed sub dots is k still exists (S518). If there is still an area where the number of sub-dots formed around the cluster center is k (S518), the process returns to step S513 and the above process is repeated.

If the area where the number of sub dots formed around the cluster center is k is no longer present, the determination unit 340 controls the counter 330 to increase the variable k by 1 (S519) and then proceeds to S513. Go back and repeat the process.

Meanwhile, in step S517, when u * v and n are the same, that is, when dots are filled in all pixel regions in the screen matrix, the screen design is finished (S520).

6 is a diagram illustrating a process of forming dots around a cluster center according to a preferred embodiment of the present invention. Referring to (a) to (e) of FIG. 6, it can be seen that the same number of dots are formed in each cluster. In this way, the noise level at the output of the binary image is reduced.

As described above, according to the present invention, the sub-dots formed around each cluster center in the design of the concentrated dot screen are grown with a uniform size. Therefore, when binarization is performed using the concentrated dot screen manufactured by the present invention, a smoother output binary image can be obtained.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the present invention is not limited to the specific embodiments of the present invention without departing from the spirit of the present invention as claimed in the claims. Anyone skilled in the art can make various modifications, as well as such modifications that fall within the scope of the claims.

Claims (5)

(a) determining an initial position of the plurality of cluster centers in a predetermined manner; (b) generating a partitioned area by dividing a screen matrix having a predetermined size into a plurality of areas in consideration of the initial positions of the cluster centers; And and (c) designing a screen by uniformly forming the number of sub-dots around the cluster center in the partitioned area. The method of claim 1, wherein step (c) comprises: (c1) initializing the predetermined variable k to 0; (c2) detecting an area where the number of dots formed in the divided area is k and outputting a predetermined ID number corresponding to the detected area; (c3) calculating a position at which a sub dot is to be formed using a predetermined cost function in the pixel area in the division area corresponding to the ID number; (c4) forming a sub dot at the calculated position; And (c5) checking whether sub-dots are filled in all pixel areas of the screen matrix; If the sub dot is not filled in all the pixel areas of the screen matrix, the predetermined variable k is increased by 1, and the steps (c2) to (c5) are repeated, and the sub dot is applied to all the pixel areas of the screen matrix. If the dot is filled, the screen design method of the concentrated dot screen characterized in that the end of the screen design. The method of claim 2, wherein the sub dot, The central dot screen design method, characterized in that formed around the cluster center. The method of claim 2, wherein the partition area, And a plurality of pixel areas, wherein each of the sub dots is formed in each pixel area. The method of claim 2, wherein the predetermined cost function, It is preferable to use one of a combination of momentum and distance penalty functions and the human visual system weighted error sum of the direct binary search (DBS) algorithm.

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