JPS62149270A - Threshold matrix generation device - Google Patents

Abstract

PURPOSE:To generate each threshold matrix with a different screen angle depending on a few memory capacities by storing a prescribed basic threshold block in a memory and generating a threshold value by one picture page in response to the cyclic readout of a counter. CONSTITUTION:Four different threshold blocks comprising L-row K-column are stored in a ROM table 40 corresponding to four different screen angles. Then a selection signal SL selects one block among the four threshold blocks. An L counter 42 designates an address in the row direction of each basic threshold block to read each threshold of the basic threshold block cyclicly in the column direction sequentially from the read start location set at each K-column in response to the screen angle and a K counter 41 designates the column direction address similarly. Thus, an optional screen angle is set with a few memory capacities and simple control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] This invention relates to a threshold matrix generation device applied to an image processing device that records color images by digital processing, and particularly relates to a threshold value matrix generation device applied to an image processing device that records color images by digital processing. The present invention relates to a threshold value matrix generation device that can easily set arbitrary different screen angles for each screen.

[Prior art] Conventionally, an original image is separated into three colors using a color separation filter.
The original image is scanned for each color separation, a latent image is formed on a photoreceptor by the color-separated light image, and the latent image is developed with a developer of a complementary color.
There is a color copying method that reproduces color images by combining multiple colors.

By the way, this type of color copying machine uses J to combine each color.
In order to prevent the occurrence of moiré, it is common to change the angle of the halftone dot screen of the halftone plate for each color when producing the halftone plate. Conventionally, contact screens and shaded scanners have been used to achieve this, but they are durable and
There are many deficiencies in terms of maintainability and cost.

Therefore, as a technology to solve these problems, an image using the so-called dither method is used, which compares each threshold value of an nxn threshold matrix with the brightness level of the input image signal, and records the halftone of the image according to the comparison result. In recording, there is a method in which the threshold value array of the threshold value matrix is changed depending on the screen angle.

However, in this conventional method, when the screen is tilted, for example, all the pre-threshold value arrays corresponding to one page of the image are stored in a predetermined memory, and this is read out as appropriate. Since threshold data for each period is supplied, there is a drawback that the memory capacity becomes enormous.

In addition, as a proposal to solve this problem,
85434, but this method attempts to generate a threshold pattern with an arbitrary screen angle from the same basic threshold matrix, and if the size of the basic threshold matrix is not 8 x 8 or more, the output dots will overlap the matrix. It has the disadvantage that it does not grow from the center and is significantly different from halftone dots.

[Problems to be Solved by the Invention] According to the present invention, threshold matrices for a plurality of different screen angles can be generated with a small memory capacity and a simple configuration, and the output dots are arranged in a matrix regardless of the size of the threshold matrix. The aim is to provide a threshold matrix generator that grows from the center of the .

[Means and effects for solving the problem] This invention is a basic threshold block in which the entire threshold matrix for one page is arranged with a predetermined screen angle. This focuses on the fact that the blocks are divided into blocks.

That is, the threshold value matrix generation unit of the present invention includes a memory for storing basic threshold blocks consisting of a plurality of different threshold values in one row and column corresponding to a plurality of different screen angles;
one of a plurality of basic threshold blocks stored in the memory;
block selection means for selecting a block, and each threshold value stored in the memory to sequentially read out each threshold value of the basic threshold block in the column direction from a readout threshold position set for each column according to the screen angle. Row-direction addressing means for designating a row-direction address of the basic threshold block;
and column-direction address designating means for repeatedly designating the column-direction addresses of the basic threshold blocks stored in the memory in a predetermined order.

[Embodiment] FIG. 2 is a sectional view showing an example of a digital color copying apparatus to which the present invention is applied, and FIG. 3 is a block diagram showing an example of the configuration related to image signal processing in J5 of the same copying apparatus.

This digital color copying apparatus is composed of an image input device 1, an image processing device 2, and an image output device 3.

The image input device 1 includes a light source 4 for document illumination, moving mirrors 5 and 6, a lens 7, a color separation mirror 8, and a filter 9.
and an image sensor 10 etc., which converts the original image into red (
R), green (Gn, blue-purple <8>) filter 9 to separate the colors,
The color-separated optical signal is input to the image sensor 10, the photoelectric change detection power of the image sensor 10 is A/D converted,
Output R, G, and B multi-value brightness data.

This R, G, and B read data is processed by image processing yI! The image is input to the color processing section 11 of the device 2. The color processing unit 11 includes a masking circuit 12 and a UCR (Under Co1o
r Ren+oval ) 13, and the masking circuit 12 performs color correction on each of the input R, G, and B data.

Each B image data is converted into yellow (Y), magenta (M), and cyan (C) signals. tJcR13 performs black plate measurement and undercolor removal, and input Y, M, C
From the image number A, multivalue brightness data corresponding to four colors: yellow (Y>, mapinta (M), cyan (C), and bluff (K)) is output.

These Y, M, and C image data are input to the selection circuit 14. The selection circuit 14 selects one of the four input data based on the selection signal SL, and the data selected by the selection circuit 14 is input to the buffer circuit 16 of the screen generation section 15.

The screen generating section 15 includes a buffer circuit 16 having a two-line buffer configuration, a comparator 17, and a threshold generating section 18.

The selection output of the selection circuit 14 is inputted to one input terminal of the comparator 17 via the buffer 1 circuit 16, and the selection output of the selection circuit 14 is input to the other input terminal of the comparator 17.
Threshold data corresponding to the image data of C and C is input. The threshold value generating section 18 stores dither patterns of four different screen angles according to the four colors Y, M, C, and the four different threshold patterns according to the input selection signal SL. Either of these will be output. Note that the internal configuration and other details of this threshold value generating section 18 will be described later. The comparator 17 is
The multivalued brightness data of any one of Y, M, and C inputted from the buffer circuit 16 is compared with the threshold value data inputted from the threshold value generation section 18, and each comparison result consisting of two values, large and small, is compared. Output to the image output device 3.

As shown in FIG. 2, the image output device 3 includes a laser 21 that generates a laser beam, a rotating polygon mirror 22, a photosensitive drum 23, and a developing device 24 that performs development with yellow, magenta, cyan, and black toners. -Y, 24
-M, 24-C.

This is a laser beam printer consisting of 24-, etc.

That is, the output beam of the laser 21, which is turned on and off by the comparative magnitude signal outputted from the comparator 17 of the image processing device 2, is input to the rotating polygon mirror, further reflected by one of the polygon reflecting mirrors, and then exposed to light. drum 2
The image is formed on 3.

A main scan is performed by the movement of the imaging point as the polygon rotates, and a second scan is performed by the rotation of the photosensitive drum 23. In this case, the developing device 24 to be driven is selected in accordance with the selection signal SL, so that development is performed in accordance with the signal output from the comparator 17. In this case, a sensor is provided a little before the main scanning threshold position of the photosensitive drum 23, and the horizontal opening 11J is arranged to align the main scanning threshold position by detecting the passing of the light beam. ) is now generated.

In this configuration, the paper on the paper feed tray 25 is fed by the paper feed roller 26 and carried into the paper ++9 feeding section 27. Paper 1;p The paper that has passed through the feeding section 27 is fixed to the transfer drum 28 by an indicating member (not shown), and then wound around the transfer drum 28. Then, with the paper wound around the transfer drum 28, the photosensitive drum 23 rotates four times to sequentially print yellow (Y) and magenta (M).
), cyan (C), and black (K) toner images are multiple-transferred onto the paper.

The paper on which a color image is formed by superimposing these four colors is transferred to a thermal fixing device 30 via a conveying section 29, where it is fixed, and then placed on an output tray.
1 will be discharged on top.

Next, FIG. 4 shows an example in which one pixel at the image input Vt position 1 is constituted by a matrix consisting of 6×6fl micropixels of the image output device 3, and 36 micropixels of the image output device 3 correspond to 1 pixel of the image input device. Corresponds to a pixel.

For example, 36 different threshold values from "1" to "36" are assigned corresponding to the 36 micropixels within one pixel, and the 'CJ-attached Ct threshold values are rlJ to r2J to TE41.

By filling in "3", . . . "36", 37 gradations from "Oj" to "36" can be reproduced.

In Figure 5, approximately 18.5 degrees (tan e= 1/3)
An example of a threshold array for one page of recorded images with a screen angle of . In this case, since the inclination is 18.5 degrees, one pixel in the image output device 3 becomes as shown in FIG. 6(a). In one pixel shown in FIG. 6(a), threshold values from "1" to "40" are arranged in a form that spreads from the center of the 7 trix to the periphery, and thereby from "0" to "40". 41 gradations up to 40'' can be reproduced. Here, the screen generating section 15 shown in FIG.
In order to have a screen angle of 18.5 degrees, the threshold value generating section 18 needs to sequentially generate threshold values in a matrix as shown in FIG. That is, the threshold generation unit 18 sequentially generates thresholds corresponding to the first main scanning line starting from the threshold at the upper left end of the threshold array shown in FIG. ,・・・・・・
. . , each threshold value is sequentially generated and input to the comparator 17. On the other hand, multi-value brightness data is input from the buffer circuit 16 side to the comparator 17 in a manner similar to rask scanning. That is, the comparator 17 performs a comparison process between the multi-level brightness data of one pixel read out from the buffer circuit 16 and each of the 6×6 threshold values inputted from the threshold value generation unit 18, and also performs a comparison process between these data. This is performed in synchronization with the rask scanning of the image input device 1 and the image output device 3.

Therefore, the multi-value brightness data is read out from the buffer circuit 16 at a frequency that is 1/6 of the threshold value generation frequency, and the multi-value brightness data of the same scanning line is read out repeatedly six times. The comparator 17 compares the multi-value brightness data thus inputted with the threshold value, and outputs a comparison magnitude signal which is "1" if the multi-value brightness data≧threshold value, and "0" if vice versa. The image output device 3 reproduces halftones by controlling the laser beam on and off based on this comparative magnitude signal.

By the way, if we pay attention to the threshold value array shown in Figure 5,
The basic threshold block consisting of 2 columns and 20 rows of threshold values shown in FIG. 6(b) is repeated multiple times in the main scanning direction, and
In the sub-scanning direction, the threshold block is repeated a plurality of times while being shifted by a predetermined amount in the main-scanning direction. That is, the starting data of the threshold block is 2
Each column is different, and FIG. 7 shows how the threshold blocks are repeated in the threshold array shown in FIG. In FIG. 7, one hatched block corresponds to the threshold block shown in FIG. 6'(b), in which the number of rows = 20, the number of columns = 2, and the number of shifts s. =6. Further, in this case, the number of shifts from the first threshold block is finite, and as shown in the figure, S.

28.38, 4S-L,-----9S-L,
This is a 10-second class consisting of O.

Next, FIG. 8(a) shows an example of a threshold matrix corresponding to one pixel of the image output device 3 when the screen angle is 45 degrees, and FIG. 8(b) shows the basic matrix corresponding to the matrix. This shows a threshold block. In this case, the basic threshold block is composed of threshold values arranged in 8 rows and 4 columns, and the number of shifts is 0. Onibi Sl.

Next, FIG. 9(a) shows an example of a threshold matrix corresponding to one pixel of the image output device 3 when the screen angle is 71.5 degrees, and FIG. It shows a basic threshold block. In this case, the basic threshold block consists of 20 rows and 2 columns, and the number of shifts is S2.2 as in the case of the screen angle of 18.5 degrees.
8. ,.

33. 4S-L, 9S2-L
, O.

Further, FIG. 10 shows an example of a threshold matrix when the screen angle is 0 degrees, and since the screen angle is 0 degrees, the basic threshold block is the same as the threshold matrix shown in FIG. 10. Therefore, in this case, the basic threshold block is composed of threshold values arranged in 6 rows and 6 columns.

Next, an example of the internal configuration of the threshold value generating section 18 is shown in FIG. It is assumed that the processing system is to have screen angles of 18.5 degrees, 45 degrees, 71.5 degrees, and 0 degrees, respectively.

The ROM table 40 has the information shown in FIG. 6(b).

The screen angles shown in FIG. 8(b), FIG. 9(b), and FIG. 10 are 18.5 degrees and 45 degrees, respectively.

Basic threshold blocks of 71.5 degrees and 0 degrees are stored. Such four different basic threshold blocks are predetermined 'n
The specified address to the ROM table 40 is specified by the counter 41, the L counter 42, and the selection signal SL. That is, the output of the K counter 41 specifies the column address of each basic threshold block, the output of the L counter 42 specifies the row address of each basic threshold block, and the selection signal SL specifies the column address of each basic threshold block. One block is selected and specified.

The K counter 41 is a binary ring counter that counts the H-8YNC signal that is generated one pulse per main scan (one column), and counts each time the Re5et signal is input or the carry CRY1 is generated. The initial values stored in the ROM table 43 are loaded. That is, the counter length of the counter 41 is determined according to the initial value input from the ROM table 43. For example, in this case, one counter 41 is set to "0".
” to “7”, and the initial value for the counter 41 is set when yellow (Y) is “
6”, magenta (M) is “4”, cyan (C) is “6”
, black (K> is set to "2" as much as possible, this counter 41 is set to RO by inputting the selection signal SL.
If the initial value of yellow (Y) is selected from the M table 43, it is a binary counter. If the initial value of magenta (M) is selected, it is a quaternary counter. If the initial value of cyan (C) is selected, it is a binary counter. When the initial value of the counter, black (B), is selected, it operates as a hexadecimal counter, thereby allowing one counter to commonly specify the addresses in the column direction of four different basic threshold blocks stored in the ROM table 40. I can do it.

Next, the L counter 42 is an L-adic ring counter that counts the main scanning clock CK, and every time the H-S Y N C signal generated for each column is input or the carry CRY2 is generated. ROM table 44
The initial value stored in is loaded,
The counter length is determined by the loaded initial value. In this case, this L-counter 42 ranges from "0" to "31".
'' is a 5-bit counter that can count up to ''.

The ROM table 44 includes shift parameters 44S-Y and 448-M that are loaded into the L-counter 42 at the beginning of each column access according to the input of the H-S Y N C signal.
, 448-C and 448- and then Ichiriki Tsunta 4
Initial value 44 for determining the counter length that is loaded into the L-counter 42 every time carry CRY2 is output from 2.
1 is Y, M.

C, are stored for each color. flip flop 4
5, the carry output of the L-counter 42 is input to its data terminal, and the 1l-3YNC signal is input to its reset terminal, so its output Q is "
0'' and carry CRY from the L-power counter 42.
It becomes "1" when is output. Then, depending on the output Q of the flip-flop 45, either the shift parameter 448 stored in the ROM table 44 or the initial value 441 for determining the counter length is selected. That is, in order to arrange and output the basic threshold blocks in the ROM table 40 as shown in FIG. 7, an initial value (shift parameter) 44 is loaded at the beginning of each column.
Unlike the initial value 441 that is loaded after the carry CRY2 is once output in each column, the ROM table 44 stores these two different initial values.

Next, the S-counter 46 has one counter 41 per column.
It is enabled by the carry CRY1 output from the counter 46 and is stored in the ROM table 43 whenever the Re5et signal is input or the carry CRY3 is output from the own counter 46. The initial values of the shift parameter tables 448-Y, 445-M,
Select one shift parameter value among 448-C and 448-. In this case, the shift parameter table consists of up to 10 types of shift parameter values (
443-Y and 448-C>, S-
The counter 46 is a 4-bit counter. Therefore, this S-counter 46 selects the initial value of yellow (Y) from the ROM table 43 by the selection signal SL.
If fir6J is selected, it operates as a decimal counter that is subtracted every two columns, and magenta (M
)'s initial value (1^ When "14" is selected, it operates as a two-way counter that counts up every 4 columns, and when the initial value "6" of cyan (C) is selected, it counts up every 2 columns. When the initial value "14" of black (B) is selected, it operates as a binary counter that counts up every 6 columns.

Further, a selection signal S' is input to the ROM table 44, and the selection signal SL determines whether the shift parameter table 448 or the initial value table 4 stored by color is
A table corresponding to one of the 41 colors is selected.

That is, the ROM table 44 includes the flip-flop 4
Either the shift parameter table 448 or the initial value table 441 is selected by the output Q of S-5.
One shift parameter value in one shift parameter table is selected by the output of the counter 46, and a table corresponding to one color in the tables separately stored in Y, M, and C is selected by the selection signal SL. Ru.

For example, assume that yellow (Y) is selected by the selection signal SL in this configuration.

In this case, the initial value "6" is selected from the ROM table 43, and the initial value "6" is loaded into the force counter 41 and the S-counter 46. Therefore, the K-counter 41 operates as a binary counter that counts up for each column, and thereby counts up each column of the yellow (Y) basic threshold block consisting of 20 rows and 2 columns in the ROM table 40. The carry signal CRY1 is alternately selected and generated every other column. Therefore, in this case, the S-counter 46 operates as a decimal counter that counts up every other column.

Next, regarding the operation of the ROM table 44 and the first counter 42, at the beginning of accessing the first column, H
-Flip-flop 4 is activated by inputting the S Y N C signal.
5 is reset and the L-counter 42 enters the initial value loading state. By the output of the reset flip-flop 45, the selection signal @SL, and the output of the S-counter 46, the parameter value r of the yellow (Y) shift parameter table 44S-Y is output from the ROM table 44.
o+124 is selected first, and the value is ``Kunta 42''.
Herod. By inputting this shift parameter value "12", the one-time counter 42 (5 bits) is "
It operates as a 20-decimal counter that counts the main scanning clock CK from "12" to "31". For this reason, the ROM
From table 40, yellow (
Each threshold value in the first column of the basic threshold value block of Y) is sequentially read out one by one from the beginning. According to the series, one counter 4
When 2 completes one counting operation up to "31",
Then the counter 31 overflows and the carry CR
Generate Y2. The flip-flop 45 is set by this carry CRY2, and as a result, the initial value table 441 is selected in the ROM table 44,
As a result, the initial value of yellow (Y) "12" is loaded into the L-counter 42. As a result, the L-counter 42
From then on, it operates as a 20-decimal ring counter as described above, and each threshold value in the first column of the yellow (Y) basic threshold block is repeatedly read out from the ROM table 40 multiple times from the beginning based on the count output. Become. The same operation as described above is also performed when accessing the second column.

Next, in accessing the third column, the S-counter 46 is counted up at the start of access, and the H-8Y
By inputting the NC signal, the parameter value rs of the yellow (Y) shift parameter table 44S-Y
+12J is selected and that value is loaded into L-counter 42. As a result, the L-counter 42 counts the clock GK by "31" from rs+12J (20-
8) Operates as a decimal counter. Thus, from the ROM table 40, each threshold value in the first column of the basic threshold block of Y0-(Y) is sequentially read from the (S+1)th threshold value to the last threshold value. When the L-counter 42 completes one counting operation from "S+12" to "31" according to the series, the L-counter 42 overflows and generates a carry CRY2. This carry-C
Flip-flop 45 is set by RY2, and RO
In the M table 44, the initial value table 44I is selected this time, and as a result, the initial value "12" of yellow (Y) is loaded into the L-counter 42. Therefore, from now on, the counter 42 operates as a 20-decimal ring counter as described above, and the count output is used to store the ROM table 4.
Starting from 0, each threshold value in the first column of the yellow (Y) basic threshold block is read out multiple times from the beginning. A similar operation is performed when accessing the fourth column. After this, when accessing the 5th, 6th, 7th, etc. columns, the initial value "2S+12J, r3s+
12J, r4s-L+12J...- are sequentially read out every other column, and when accessing each column, L
- After the counter 42 completes the first counting operation, the initial value "12" on the initial value table 441 side is selected and read from the ROM table 44, and the counting operation of the L-counter 42 is performed according to these loaded values. It will be decided. In this way, each threshold value of the yellow (Y) basic threshold block in the ROM table 40 is read out in a circular manner, so that one image per page with a screen angle of 18.5 degrees shown in FIGS. 5 and 7 is read out. A total threshold value corresponding to the difference can be generated.

Above is a yellow (Y) with a screen angle of 18.5 degrees.
) processing system, an example of operation has been described in which threshold data corresponding to one page of image 11! is generated by cyclically reading out a basic threshold block consisting of 20 rows and 2 columns stored in the ROM table 40. Magenta (M)
, cyan (C), and black (B) processing systems are the same as described above, and the basic lJl value block consisting of 8 rows and 4 columns, 20 rows and 2 columns, and 6 rows and 6 columns stored in the ROM table 40, respectively. By circular reading as described above,
Threshold data corresponding to one page of images Q is generated.

As described above, according to the threshold matrix photonic device of the present embodiment, four responsible threshold blocks consisting of L rows and columns corresponding to four different screen angles are stored in the ROM table 40, and these blocks are selected by the selection signal SL. Select one block among four different threshold blocks, specify the column direction address of each 171 value block by K-counter 41, and specify the row direction address of each threshold value block by L-counter 42. Therefore, an arbitrary screen angle can be set with a small number of memories (8) and a simple control configuration. Furthermore, the length of the counter 41 and L-counter 42 for addressing the ROM table 40 can be arbitrarily set by simply changing the initial values set in the ROM tables 43 and 44. R can be adjusted by changing the screen angle, etc.
The value and L of the storage threshold block in the OM table 40
This allows you to easily deal with changes in values.

By the way, in the method of this embodiment, when the screen angle is set, the positions of pixels differ between the image input device 1 and the image output VC device 3, as compared in FIGS. 4 and 5, for example. Therefore, when the entire image has uniform gradation,
Although correct gradation reproduction can be performed for each pixel, this is usually not the case, and it is considered that the density of each pixel cannot be expressed correctly. For this reason, there is a method of reconfiguring the pixel array shown in Figure 4 to the pixel array shown in Figure 5 to express gradation, but experiments have shown that there is a difference between this method and the method of this example. There is no discernible difference in image quality. This is because the assumption that a gradation image has a gradual change in the vicinity of the pixel and that the entire image has a uniform value holds true in the vicinity of the pixel. In other words, image input device 1
It can be said that there is no deterioration in the image quality of the gradation image due to the difference between the pixel arrangement of the image output device 3 and the pixel arrangement of the image output device 3.

Note that the present invention can be modified as appropriate to the above-described embodiments, including the threshold matrix size, the screen angle to be set, the arrangement of the thresholds in the threshold matrix, and the method of setting the initial value for determining the counter length. Of course, this is optional. Furthermore, each of the configurations shown in FIG. 1 may be replaced with other circuits that achieve equivalent functions.

[Effects of the Invention] As explained above, according to the threshold value matrix generation device according to the present invention, attention is paid to the basic threshold value blocks in L rows and columns that newly appear when threshold values corresponding to output pixels are two-dimensionally arranged. By storing a plurality of basic threshold blocks that differ depending on each screen angle in a predetermined memory, and performing a predetermined circular readout of these plurality of basic threshold blocks in the row and column directions using a common counter configuration, Since the threshold value corresponding to one page of the image is generated, it is possible to generate the threshold value matrix for multiple different screen angles with a small memory capacity and a simple configuration. It is possible to grow from the center regardless of the size of the dots, and it is possible to realize a recorded image that matches the halftone dots.

It is also good in terms of durability, maintainability, and cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of the main parts of an embodiment of the present invention, FIG. 2 is a conceptual diagram showing an example of the device configuration of a digital color copying apparatus to which this invention is applied, and FIG. 3 is an image output A block diagram showing an example of the internal configuration of the device, Fig. 4 is a schematic diagram showing an example of a two-dimensional arrangement of fine pixels and pixels in an image output device, and Fig. 5 shows the entire threshold array when the screen angle is 18.5 degrees. Figures 6(a) and 6(b) are diagrams showing an example of a threshold matrix and a basic threshold block corresponding to one pixel at a screen angle of 18.5 degrees, respectively. Figure 7 is a diagram showing an example of a screen angle of 18.5 degrees. A diagram showing the arrangement of basic threshold blocks when the screen angle is 18.5 degrees, and FIG. Figures 9(a) and (b) are diagrams respectively showing an example of a threshold matrix and a basic threshold block corresponding to one pixel when the screen angle is 71.5 degrees, and Figure 10 is a diagram showing an example of a basic threshold block when the screen angle is 0 degrees. It is a diagram showing an example of a basic threshold block when 1... Image input ¥R position, 2... Image processing device, 3...
...Image output device, 4...Light source, 5, 6...Mirror, 7...Lens, 8...Color separation mirror, 9...Filter, 10...Image sensor, 11...・Color processing section, 12...Masking circuit, 13...UCR
114... Selection circuit, 15... Screen generator,
16...Buffer circuit, 17...Comparator, 1
8... Threshold generation unit, 21... Laser, 22... Polygon, 23... Photosensitive drum, 24... Sexual organ, 2
5...Paper feed tray, 26...Feed roller, 27
．． 29...Paper transport unit, 28...Transfer drum, 30.
...Heat fixing device, 31...Ejection tray, 40°43.4
4...ROM table, 41...K-counter, 4
2...L-counter, 45...flip-flop,
46...S-counter. A nobleman and a poor man

Claims (3)

[Claims] (1) In a threshold matrix generation device that generates all threshold matrices arranged at predetermined screen angles based on a basic threshold block consisting of threshold values in L rows and K columns, a plurality of different L
a memory for storing a basic threshold block consisting of threshold values in rows and K columns; and one of the plurality of basic threshold blocks stored in the memory.
a block selection means for selecting a block; and each basic threshold value stored in the memory to sequentially circulate and read out each threshold value of the basic threshold block in the column direction from a readout threshold position set for each K column according to the screen angle. A threshold matrix generation device comprising: row-direction addressing means for designating a row-direction address of a block; and column-direction addressing means for repeatedly designating a column-direction address of a basic threshold block stored in the memory in a predetermined order. (2) The column direction addressing means includes one counter means that performs a predetermined counting operation and supplies the counted output to the memory as an address signal for specifying the column direction of each basic threshold block; and an initial value memory for storing a plurality of initial load values for determining a counter length of the counter means in accordance with a plurality of K values corresponding to a plurality of stored basic threshold blocks. The threshold value matrix generator described above. (3) The row direction addressing means includes one counter means that performs a predetermined counting operation and supplies the counted output to the memory as an address signal for designating the row direction of each basic threshold block; A first step that determines a counter length of the counter means corresponding to a readout start position of each basic threshold block set for each K column according to a plurality of L values corresponding to the plurality of stored basic threshold blocks and a screen angle. and a second plurality of initial load values for each screen angle, and for loading a corresponding initial load value into the counter means in response to each counting operation. The threshold value matrix generator according to the range (1).