KR20050113510A - Apparatus and method of processing halftoning - Google Patents

Abstract

An apparatus and method for half toning are disclosed. The half toning processing apparatus includes a command processing unit for receiving rendered color-specific data and processing a half toning command received from a user; A first storage unit storing a density value of a pixel to be half-toned among the color-specific data to correspond to a position on a recording sheet; A threshold value determination unit that determines a threshold value for comparing the density value of the pixel stored at a predetermined position of the first storage unit in consideration of a line angle of a pixel to be halftoned from a predefined halftone pattern array; A comparison unit which compares the density value of the pixel at a predetermined position read from the first storage unit with the threshold value, and outputs a binary value according to a comparison result; And a second storage unit which stores the binary value output from the comparison unit at a position of the corresponding pixel.

Description

Apparatus and method of processing halftoning}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for digital halftoning, and in particular, when the object of halftoning is a single line or polygon and the thickness of the line is smaller than a predetermined reference thickness, the single line or polygon from a predefined halftone pattern array. The present invention relates to an apparatus and a method for determining a threshold value in consideration of an angle of a line forming a line, and performing a half-toning process using the same.

In printing document data using an inkjet printer or a laser printer, it is necessary to convert monochrome or color pixels given as multiple values into binary monochrome pixels, and such conversion processing is called half-toning processing. In general half-toning processing, a method of converting a multi-value pixel value to a binary pixel value using a predefined threshold pattern is widely known. According to this, if the value of the pixel to be half-toned is greater than the threshold value, '1' is output, and if it is smaller than the threshold value, '0' is output. In the case of outputting '1', the dot is printed. In the case of outputting '0', the dot is not printed.

On the other hand, the half-toning process includes the entire raster image, the font of text data, a dot, a polygon, a single line, and the like. Among these, in the half-toning process for a single line and a polygon, a screen angle and half predefined by a halftone pattern when the single line or the line forming one side of the polygon are fine lines having a thickness of 1 to several pixels. The concentration value of the line after the half-toning process is changed according to the position of the line to be toned. For example, in the case of a halftone pattern having a screen dot array of 45 degrees, when the line angle is not 0 degrees or 90 degrees with respect to the horizontal axis of the recording paper, the half toning process becomes unstable, and as a result, There is a problem that the pixel array is very different from the original pixel array, resulting in an unnatural image.

The technical problem to be achieved by the present invention is to consider the angle of the line forming a single line or polygon from a predefined halftone pattern, when the half-toning process is a single line or polygon and the line thickness is smaller than a predetermined reference thickness An apparatus and method for determining a threshold value and performing half-toning process using the same are provided.

In order to achieve the above technical problem, the half-toning processing apparatus according to the first aspect of the present invention includes a command processor for receiving rendered color-specific data and processing a half-toning command received from a user; A first storage unit storing a density value of a pixel to be half-toned among the color-specific data so as to correspond to a position on a recording sheet; A threshold value determination unit that determines a threshold value for comparing the density value of the pixel stored at a predetermined position of the first storage unit in consideration of a line angle of a pixel to be halftoned from a predefined halftone pattern array; A comparison unit which compares the density value of the pixel at a predetermined position read from the first storage unit with the threshold value, and outputs a binary value according to a comparison result; And a second storage unit which stores the binary value output from the comparison unit at a position of the corresponding pixel.

The threshold determining unit may further include: a third storage unit storing a line angle of a pixel to be half-toned among the color-specific data to correspond to a position on a recording sheet; A coordinate rotating unit rotating the coordinate value of the pixel to be half-toned by the line angle; And a fourth storage unit storing a halftone pattern formed of threshold values, calculating an index using input coordinate values, and providing a threshold value stored at a position corresponding to the index to the comparison unit.

Preferably, the threshold value determination unit further includes a switching unit for selectively providing a coordinate value of a pixel to be half-toned from the first storage unit to one of the coordinate rotation unit and the fourth storage unit according to the object of half-toning. .

In order to achieve the above technical problem, the half-toning processing method according to the second aspect of the present invention (a) obtains a rotated coordinate value by rotating a coordinate value of a pixel to be half-toned corresponding to an angle of a line to which the pixel belongs. Doing; (b) calculating an index using the rotated coordinate values and determining a threshold value of a position corresponding to the index from a halftone pattern formed of threshold values; And (c) comparing the density value of the pixel to be half-toned with the threshold value and generating a binary value according to the comparison result.

The method may preferably be implemented as a computer readable recording medium having recorded thereon a program for execution on a computer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing the configuration of a half-toning processing apparatus according to an embodiment of the present invention, the command processor 110, the first storage unit 130, the threshold value determination unit 150, the comparison unit 170 And a second storage unit 190. In addition, the threshold determination unit 150 includes a third storage unit 151, a switching unit 153, a coordinate rotation unit 155, and a fourth storage unit 157.

Referring to FIG. 1, the command processor 110 receives black and white data or color-specific data obtained as a result of rendering document data to be printed on an application program, and receives a user's halftoning command. The command processor 110 analyzes the half-toning command to determine whether the half-toning target is the entire raster image, the font of the text data, the dot, the polygon, or the line, and the half-toning target is the polygon or the single line. The thickness of the line included in the half-toning command is compared with a predetermined reference thickness, and a control signal according to the final determination result is output. As a control signal, when the half-toning target is a polygon or a single line and the thickness of the line is smaller than the preset reference thickness, the first switching unit connects the first contact C1 of the switching unit 155 to the second contact C2. When the half-toning object corresponds to the other case, the second switching signal is generated such that the first contact C1 of the switching unit 155 is connected to the third contact C3. On the other hand, when the half-toning command is a polygon or a single line and the thickness of the line is smaller than the preset reference thickness, the start coordinates, the end point coordinates, the density values of the lines or single lines constituting the polygons included in the half-toning command By analyzing the same half-toning information, the density value of each pixel constituting the line is recorded in the corresponding position of the first storage unit 130, and the line angle of each pixel is calculated to correspond to the third storage unit 151. Record it at the location. Here, the density value of each pixel is a color value corresponding to cyan, magenta, yellow, and black. Meanwhile, the line angle θ of each pixel may be calculated by Equation 1 below. The command processor 110 may sequentially process the half-toning process from the pixel located at the starting point coordinate of the line to be toned to the pixel located at the end point coordinate, in the first storage unit 130 and the third storage unit 151. A read enable signal is applied.

Here, (X1, Y1) and (X2, Y2) mean start coordinates and end coordinates of the line to be half-toned, respectively.

The first storage unit 130 has a row line X and a column line Y in a matrix form corresponding to the width and length of one page of the recording paper, and stores the density values of the pixels to be half-toned at the corresponding positions. . When the image to be half-toned is a black and white image, only one first storage unit 130 is provided, and in the case of a color image, four color data are provided because color-specific data of cyan, magenta, yellow, and black are generated. Half toning is very much done. The number of row lines and column lines of the first storage unit 130 depends on the print resolution, and typically 300 to 600 dpi may be used. On the other hand, when the gray level value of each pixel of the pixel stored in the first storage unit 130 is composed of 8 bits, any one of 0 to 255 is stored. An example of pixel data to be half-toned stored in the first storage unit 130 is illustrated in FIG. 2. Here, three vertical lines having a concentration value of 128, that is, 50% are located on the left side, and an oblique line having a concentration value of 50% is located on the right side.

The threshold value determination unit 150 determines a threshold value for comparing with the density value of the pixel at the predetermined position of the first storage unit 130 using the line angle and the pre-stored halftone pattern array.

The comparison unit 170 compares the density value of the pixel at the predetermined position read from the first storage unit 130 with the threshold value read from the threshold value determination unit 150, and when the density value of the pixel is larger than the threshold value. '1' is outputted when the pixel density value is smaller than the threshold value.

The second storage unit 190 consists of 1 bit of each pixel, and stores a binary value of '1' or '0' output from the comparator 190 at the position of the corresponding pixel.

The operation of the next threshold determination unit 150 will be described in more detail as follows.

In the threshold value determination unit 150, the third storage unit 151, like the first storage unit 130, the row line (X) and column line (Y) corresponding to the width and length of one page of the recording sheet It is formed in a matrix form and stores the line angle of the pixel to be half-toned at the corresponding position. Unlike the first storage unit 130, only one third storage unit 151 may be provided regardless of whether the image to be half-toned is black and white or color. Meanwhile, the line angle of each pixel stored in the third storage unit 151 may be represented by 2 bits to 4 bits. For example, since it is possible to express a positive integer from 0 to 15 when expressed in 4 bits, it is possible to divide 16 by 90 degrees in the case of a square grid screen, 16 by 180 degrees in the case of a line screen. The angle calculated by the command processor 110 is allocated to the closest value among the 16 divided angles and stored at the corresponding position of the third storage unit 151. The angle data stored in the third storage unit 151 with respect to the pixel data shown in FIG. 2 is as shown in FIG. 3.

In the first storage unit 130 and the third storage unit 151, the concentration value and the angle value of the pixel at the same position are read out according to the read enable signal provided from the command processing unit 110, and the comparison unit 170 is read. And the coordinate rotation unit 153.

The switching unit 153 operates according to a control signal provided from the command processing unit 110 and coordinates the coordinate value of the pixel to be halftoned from the first storage unit 130 by the coordinate rotating unit 155 or the fourth storage unit 157. ) To one of them. That is, when the control signal is the first switching signal, the coordinate value of the pixel provided from the first storage unit 130 is the coordinate rotation unit 155, and when the control signal is the second switching signal, the first storage unit 130. The coordinate value of the pixel provided from) is provided to the fourth storage unit 157. Therefore, when the object of half-toning is always a single line or a polygon, the third storage unit 160 directly converts the coordinate values of the pixels provided from the first storage unit 120 without the need for the switching unit 140. To provide. On the other hand, if the object of half-toning is always other than a single line or polygon, the fourth storage unit 157 directly stores the coordinate value of the pixel provided from the first storage unit 130 without the need for the switching unit 140. To provide.

The coordinate rotating unit 155 rotates the original coordinate values X and Y of the pixel to be half-toned in the reverse direction by the line angle θ of the corresponding pixel provided from the third storage unit 151. The rotated coordinate values X 'and Y' may be represented as in Equation 2 below, and as a result, the original coordinate values P_org are converted into rotated coordinate values P_rot as shown in FIG. .

The fourth storage unit 157 stores a halftone pattern having a matrix shape having horizontal and vertical sizes of M and N, respectively, and a value included in the halftone pattern means a threshold value. Here, it is the same as preparing a halftone pattern of M and N due to the problem of mounting, and repeatedly tiling the halftone pattern with respect to the X, Y global coordinate system and attaching each tile. In this case, the halftone pattern needs to be defined to be connected smoothly at the bonding position of each tile. Using the original coordinate values provided from the switching unit 153 and the rotated coordinate values provided from the coordinate rotating unit 155, the X and Y direction indices are calculated, and the threshold values stored at the positions determined by the calculated indices. Read and provide to the comparator 170. An example of the halftone pattern array stored in the fourth storage unit 157 is illustrated in FIG. 5. On the other hand, in the fourth storage unit 157, the X-direction and the Y-direction indices are the following equations when the original coordinate values (X, Y) are used and when the rotated coordinate values (X ', Y') are used, respectively. It can be calculated by 3 and 4.

Here, M and N represent the sizes of the halftone patterns in the X and Y directions, and m and n are offset values that can be set in consideration of the situation where X 'and Y' become negative numbers. % Is an operator that divides M or N to get the remainder.

The threshold value stored at a position corresponding to the X-direction index and the Y-direction index is read from the fourth storage unit 157 and provided to the comparison unit 170.

6A and 6B are diagrams for comparing the performance of the half-toning process according to the present invention and the half-toning process according to the present invention. That is, when the threshold value is determined using only the original sinusoid value without considering the line angle, the half-toning process becomes unstable as shown in FIG. 6A. On the other hand, when the threshold value is determined using the rotated coordinate value in consideration of the line angle, the half-toning process is naturally performed as shown in FIG. 6B.

7 is a flowchart illustrating an operation of a half-toning processing method according to an embodiment of the present invention.

Referring to FIG. 7, in operation 710, a half toning command received by the command processor 110 may be analyzed to determine the start coordinates, the end coordinates, the thickness of each line, and the concentration of pixels belonging to each line. Enter the value and line angle. In operation 720, the coordinate value is set as the starting coordinate of the predetermined line.

In step 730, it is determined whether coordinate rotation is necessary. The determination criteria are the thickness and line angle of the line included in the half-toning command. That is, when the thickness of the line is larger than the predetermined reference thickness or the line angle is 0, the process proceeds to step 750 using the original coordinate value.

In the step 740, if the coordinate rotation is necessary as a result of the determination in step 730, that is, the thickness of the line included in the half-toning command is smaller than the predetermined reference thickness, the coordinate rotation exists according to Equation 2 above. Perform the process.

In step 750, using the original coordinate value provided in step 730 or the rotated coordinate value provided in step 740, the X and Y direction indexes for searching for the threshold value in the halftone pattern are calculated, and the position is calculated. It is determined by the threshold of the corresponding pixel.

In operation 760, the density value of the pixel at the corresponding position is compared with the threshold determined in operation 750, and a binary value according to the comparison result is output and stored in the second storage unit 190. In step 770, it is determined whether the coordinate value of the current pixel corresponds to the end point coordinate of the last line stored in the first storage unit 130, and if it corresponds to the end point coordinate of the last line stored in the first storage unit 130, the half-toning process is performed. If it does not correspond to the end point coordinates, the process returns to step 730 by setting the next coordinate value in step 780.

The invention can also be embodied as computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, which are also implemented in the form of a carrier wave (for example, transmission over the Internet). It also includes. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. And functional programs, codes and code segments for implementing the present invention can be easily inferred by programmers in the art to which the present invention belongs.

According to the present invention as described above, when the object of the half-toning process is a single line or polygon and the thickness of the line is smaller than the predetermined reference thickness, the angle of the line forming the single line or polygon from the predefined half-toning pattern is taken into consideration. The threshold value is determined, and half-toning processing is performed using this to obtain a more natural halftone image.

Although the present invention has been described with reference to the above embodiments, it is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a block diagram showing the configuration of a half-toning processing apparatus according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating an example of pixel data to be halftoned in units of pages stored in a first storage unit in FIG. 1; FIG.

3 is a diagram illustrating angle data stored in a third storage unit with respect to the pixel data shown in FIG. 2;

4 is a view for explaining the operation of the coordinate rotation unit in FIG.

FIG. 5 is a diagram illustrating an example of an arrangement of halftone patterns stored in a fourth storage unit in FIG. 1;

6A and 6B are views for comparing the performance of the half-toning process according to the present invention and the half-toning process according to the present invention, and

7 is a flowchart illustrating an operation of a half-toning processing method according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

110 ... Command processing unit 130 ... First storage unit

150 ... Threshold Determination Unit 151 ... Third Storage Unit

153 ... switching part 155 ... coordinate rotation part

157 ... fourth storage section 170 ... comparison section

190 ... second reservoir

Claims (5)

An instruction processor for receiving rendered color-specific data and processing a half-toning command received from a user; A first storage unit storing a density value of a pixel to be half-toned among the color-specific data so as to correspond to a position on a recording sheet; A threshold value determination unit which determines a threshold value for comparing the density value of the pixel stored at a predetermined position of the first storage unit in consideration of a line angle of a pixel to be halftoned from a predefined halftone pattern array; A comparison unit which compares the density value of the pixel at a predetermined position read from the first storage unit with the threshold value, and outputs a binary value according to a comparison result; And And a second storage unit which stores a binary value output from the comparison unit at a position of a corresponding pixel. The method of claim 1, wherein the threshold determination unit A third storage unit storing a line angle of a pixel to be half-toned among the color-specific data to correspond to a position on a recording sheet; A coordinate rotating unit rotating the coordinate value of the pixel to be half-toned by the line angle; And A half storage unit configured to store a halftone pattern formed of thresholds, calculate an index using input coordinate values, and provide a fourth storage unit to provide the comparison unit with a threshold stored at a position corresponding to the index. Toning treatment equipment. The method of claim 2, wherein the threshold value determiner According to the object of half-toning, the half-toning processing apparatus further comprises a switching unit for selectively providing the coordinate value of the pixel to be half-toned from the first storage unit to one of the coordinate rotation unit and the fourth storage unit . (a) obtaining a rotated coordinate value by rotating a coordinate value of a pixel to be half-toned corresponding to an angle of a line to which the pixel belongs; (b) calculating an index using the rotated coordinate values and determining a threshold value of a position corresponding to the index from a halftone pattern formed of threshold values; And (c) comparing the density value of the pixel to be half-toned with the threshold value, and generating a binary value according to a comparison result. The half-toning processing method according to claim 4, wherein the method is performed when the thickness of the line is smaller than the reference thickness by comparing the thickness of the line to which the half-toned pixel belongs to a predetermined reference thickness. .