JPH0831956B2 - Halftone dot generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for generating halftone dots, which is one of the methods for expressing a halftone image, and more particularly to an arbitrary halftone dot for each color required in color printing. A device capable of generating a point angle.

2. Description of the Related Art In today's printing, color waves are rushing not only to gravures, product catalogs, magazines but also to newspapers having a high linear density, and these images are often electrically processed. The image processed by this color printing generally uses halftone dots. In this, each color (yellow, magenta, cyan, black) is composed of halftone dots and overlapped, but at that time, the angle of different halftone dots is arbitrarily changed for each color in order to prevent moire. Is the reality.

Problems to be Solved by the Invention Normally, the angle of halftone dots, which are often used in monochrome, is 45.
It is degree. In this case, in order to generate the threshold value of the halftone dots, generally the outputs of the main scanning counter circuit 21 for counting the pixels in the main scanning direction and the sub-scanning counter circuit 22 for counting the pixels in the sub-scanning direction as shown in FIG. RO whose threshold is stored in
By connecting to the address input of M (threshold storage ROM) 23 and comparing the output with the image data in the comparison circuit 24, the function of generating a halftone dot was achieved.

However, in the case of color printing, an arbitrary angle must be handled as described above, and therefore the circuit as shown in FIG. 2 cannot handle it.

Therefore, recently, a method of electrically generating halftone dot angles of various values has been proposed. This has the disadvantage that the two-dimensional threshold value storage ROM as shown in FIG. 2 cannot be used, and one has to consider the troublesome procedure of developing the threshold value data in one column and storing it in the ROM. It was Further, there is a drawback that another ROM must be replaced every time the content of the threshold storage ROM changes.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore an object of the present invention is to provide a novel halftone dot generating apparatus capable of eliminating the above-mentioned drawbacks inherent in the conventional technology. It is in.

Means for Solving the Problems In order to achieve the above object, a halftone dot generating apparatus according to the present invention is a two-dimensional threshold value in a halftone dot generating apparatus which is one of methods for expressing a halftone image. A two-dimensional threshold value storage ROM, a two-dimensional threshold value storage ROM address setting means for setting an address for outputting the threshold value data of the two-dimensional threshold value storage ROM, and an output for storing the two-dimensional threshold value storage ROM 1 A column threshold storage RAM, a one-column threshold storage RAM address setting means for setting an address for outputting threshold data of the one-column threshold storage RAM, and an output of the two-dimensional threshold storage ROM or the one-column threshold storage RAM. It comprises a threshold value comparing means for generating a halftone dot for comparing the output with the image data.

Embodiments In describing the present invention, description will be given based on an example in which halftone dots having an angle of 30 degrees are electrically generated in color printing. Of course, other angles can be realized by changing the constants given to the ROM in the same manner.

FIG. 6 shows a threshold pattern that electrically approximates a halftone dot of 30 degrees. In order to output this threshold data efficiently,
The following ideas were introduced.

In FIG. 6, when the connection of halftone dots is sequentially traced in the main scanning direction from the pixel at the upper left, that is, the scan start position of the entire screen, the shaded area is the minimum required threshold area (threshold data block) The parts other than the cliff overlap with the shaded part]. For example, when the scan is started from the value "18" in the main scanning direction 1 and the sub-scanning direction 1, data "18, 12, 16, ... 64, 65" is output. Here, the value of "65" deviated from the shaded area in FIG. 6 is the same as the value of the position in the main scanning direction 1 and the sub scanning direction 5. Then, from "65", it jumps to that position and becomes "65, 57, 32, ... 45, 46, 30", and is output as shown in FIG. From line 2 to line 7,
It is output in the same way.

After the 8th line, the above-mentioned threshold data block is
As shown in FIG. 8, four pixels are shifted for each threshold data block. This shows the same tendency even if the halftone dots at other angles have different shift amounts. In other words, when considering 1 to 7 lines in the sub-scanning direction as one block, the start of this block is shifted for each block. Therefore, the first data value of each line in the threshold data block is
By utilizing the fact that it always appears in the area A in the figure, the output from the threshold value storage ROM is output pixel by pixel in the two-dimensional threshold value storage ROM address setting circuit 12 (see FIG. 1) in the main scanning initial value detection ROM 31 (third
(See the figure), it is detected whether or not it is the same as the threshold value data of the first pixel in each sub-scan, and if they are the same, the next threshold value data is the threshold value in which the main scanning direction is 1 and the sub scanning direction is the detected threshold value. By setting it on a line with data, it is possible to output the required threshold value from the ROM in which the threshold value data is stored two-dimensionally. Also, the two-dimensional threshold storage ROM 14 (Fig. 1)
When the first line of the first block is being output from, the output of the two-dimensional threshold storage ROM 14 is changed to the one-column threshold storage RAM13.
(FIG. 1), and after the second threshold data block, the output of the one-column threshold storage RAM 13 is used. That is, since the shaded area in FIG. 6 becomes the threshold data of one column as shown in FIG. 7, this column is sequentially stored in the one-column threshold storage RAM 13, and after the second threshold data block, 1 column is stored. The required output can be obtained by designating the address of the first pixel of each line on a line-by-line basis in the column threshold storage RAM address setting circuit 11 (FIG. 1).

An embodiment for realizing this will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the device according to the present invention.

Referring to FIG. 1, the two-dimensional threshold value storage ROM address setting circuit 12 is synchronized with the image data input from the terminal 101.
Under the control of, the threshold data is output from the two-dimensional threshold storage ROM 14 to the threshold comparison circuit 15 and the one-column threshold storage RAM 13. At the same time, the control signal and data for storing the address value of the first pixel of the first threshold data block are stored in the one-column threshold storage RA.
Output to M address setting circuit 11. Under the control of the 1-column threshold storage RAM address setting circuit 11, the 1-column threshold storage RAM 13 starts outputting to the threshold comparison circuit 15 from the second line of the first threshold data block. In the threshold comparison circuit 15, the terminal
The image data from 101 is compared with the one-column threshold storage RAM 13 or the two-dimensional threshold storage ROM 14 to output binary image data. It should be noted that only the first threshold data block uses the threshold data from the two-dimensional threshold storage ROM 14, and otherwise uses the threshold data from the one-column threshold storage RAM 13.

Next, one embodiment of each block in FIG. 1 will be described in detail. The constant given here is 30 in Fig. 6.
Take the case of the threshold pattern configuration of the halftone dots of degree as an example. Of course, in the case of other patterns, the same processing can be performed by changing the given constant value.

FIG. 3 shows a block configuration of the two-dimensional threshold value storage ROM address setting circuit 12.

Referring to FIG. 3, the two-dimensional threshold value storage R from the terminal 301
The output of OM14 is input to the main scanning initial value detection ROM 31. When the data value in the area A in FIG. 6 is detected, the detection signal is output to the LOAD terminal and the terminal 305 of the main scanning counter 32 and the sub scanning counter 33. In the main scanning counter 32, the value “1” from the terminal 304 is set to the sub scanning counter 3
In 3, the number of lines with the detected threshold data coming from the main scanning initial value detection ROM 31 is loaded. And terminal 30
2 outputs the address value of the main scanning counter 32, and terminal 303 outputs the address value of the sub-scanning counter 33.

FIG. 4 shows a block configuration of the 1-column threshold value storage RAM address setting circuit 11.

Referring to FIG. 4, when the first threshold data block is scanned into the area A in FIG. 6, the detection signal of the main scanning initial value detection ROM 31 is detected from the terminal 402, the threshold data value is detected from the terminal 403, and the terminal 404 is detected. The output value of the main scanning counter 32 is received and stored in the initial value storage RAM (1) 41. The threshold data value is applied to the address at that time.

Next, the initial value storage signal generation circuit 49 that generates a signal indicating the first pixel of each line of the first threshold data block and the ring counter 43 that ring-counts the number of lines in the threshold data block are used to store the initial value storage RAM ( 2) To 42,
The output of the initial value storage RAM (1) 41 is stored as the initial address of the first pixel of each line of the first threshold data block. A ring counter 43 for ring-counting the number of lines in the second threshold data block from the second threshold data block stores an initial value storage RAM (2) 42 in which the threshold data of each first pixel from the second threshold data block is stored. The address value of is output. Then, the output is supplied to the comparison circuit 45 and the subtraction addition circuit 47. The shift value storage ROMs 46A and 46B store the shift amount of the threshold data block.
The contents are 46A: the amount of shift is stored as it is (in the case of FIG. 6, 4) 46B: The sum of all threshold data-the amount of shift is stored (in the case of FIG. 6: 65-4) Has become. In order to select these ROMs, the address data from the initial value storage RAM (2) 42 and the shift value storage R
The shift data from the OM 46A is compared by the comparison circuit 45, and the result is input to the mode terminals of the select circuit 44 and the subtraction addition circuit 47. The selection criteria of the selection circuit 44 are as follows.

A. Address data> shift data or address data = shift data Select the ROM that stores the shift data as it is (46A).

B. Address data <Shift data Sum of all threshold data-Shift data is stored
Select ROM (46B).

Here, the meaning of the term B is that, for example, as shown in FIG. 9, the shift data cannot be simply drawn as it is at the boundary of the block of the threshold data of one column. Therefore, the value obtained by subtracting the shift data from the sum of all threshold data in advance is
Stored in ROM, the address data and shift data values are added later, and the shift data is actually subtracted. The subtraction addition circuit 47 performs this subtraction addition.
The former operates as a subtracter and the latter operates as an adder according to the above-mentioned A term and B term.

One of the subtraction / addition circuits 47 is input to the initial value storage RAM (2) 42, and the other is input to the counter circuit 48. The address value of the counter circuit 48 is applied to the terminal 401. That is,
In the initial value storage RAM (2) 42, a value obtained by adding and subtracting a certain amount is rewritten for each threshold data block.

 FIG. 5 shows a block configuration of the threshold comparison circuit 15.

Referring to FIG. 5, the terminal 501 stores the two-dimensional threshold value R
Each output of the one-column threshold value storage RAM 13 is input from the AM 14 and the terminal 502. These data are the data of the two-dimensional threshold storage RAM 14 from the terminal 501 only when the first line of the first threshold data block is selected by the select circuit 51, and the one-column threshold storage RAM 13 from the terminal 502 otherwise. The data of is output to the comparison circuit 52. The comparison circuit 52 compares the image data from the terminal 503 with the threshold data from the selection circuit 51, and outputs it to the terminal 504 as binary data.

EFFECTS OF THE INVENTION As described above, according to the present invention, when various halftone dot angles used in color printing are to be electrically generated with strict values, the threshold data becomes huge, and However, it is difficult to control to call from the ROM in which is stored, but it is possible to easily generate halftone dots by introducing the idea of shifting one block. Also, 1
By implementing the column threshold storage RAM, it is possible to use the two-dimensional threshold storage ROM that has been commonly used until now.
Easy to create OM. Then, by replacing the initial value storage ROM with RAM, it is possible to reduce the labor of ROM creation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 4 is a block diagram showing a circuit example of a conventional halftone dot generation technique, FIG. 3 is a block diagram showing an example of a two-dimensional threshold value storing ROM address setting circuit, and FIG. 4 is an example of a one-column threshold value storing RAM address setting circuit. FIG. 5 is a block diagram showing an example of a threshold comparison circuit, FIG. 6 is a diagram showing an example of a halftone dot threshold pattern of 30 degrees, and FIG. 7 is a rectangular threshold block into one row of threshold data blocks. FIG. 8 is a diagram for explaining that conversion is possible, FIG. 8 is a diagram for explaining shift of the rectangular threshold data block, and FIG. 9 is a diagram for explaining boundary points of the one-column threshold data block. 11 …… 1 column threshold storage RAM address setting circuit, 12 …… two-dimensional threshold storage ROM address setting circuit, 13 …… 1 column threshold storage R
AM, 14 ... Two-dimensional threshold storage ROM, 15 ... Threshold comparison circuit, 2
1, 32 ... Main scanning counter, 22, 33 ... Sub scanning counter, 23 ... Threshold value storage ROM, 24 ... Comparison circuit, 31 ... Main scanning initial value detection ROM, 41 ... Initial value storage RAM (1 ), 42 ……
Initial value storage RAM (2), 43 ... Ring counter, 44, 51
...... Select circuit, 45, 52 …… Comparison circuit, 46A, 46B ……
Shift value storage ROM, 47 ... subtraction addition circuit, 48 ... counter circuit, 49 ... initial value storage signal generation circuit

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Claims (1)

[Claims] 1. A device for generating halftone dots, which is one of the methods for expressing a halftone image, stores a two-dimensional threshold value storage ROM for two-dimensionally storing threshold values and threshold data of the two-dimensional threshold value storage ROM. Two-dimensional threshold storage RO that sets the address for output
M address setting means, one-column threshold storage RAM for storing the output of the two-dimensional threshold storage ROM, and one-column threshold storage for setting an address for outputting the threshold data of the one-column threshold storage RAM
Halftone dots comprising RAM address setting means and threshold value comparing means for generating halftone dots for comparing the output of the two-dimensional threshold value storage ROM or the output of the one column threshold value storage RAM with image data. Generator.