JPS61186077A - Picture recording system - Google Patents

Abstract

PURPOSE:To set an optional screen angle with a less memory capacity by writing an L-row K-column basic threshold block appearing freshly on the memory when threshold values corresponding to output picture elements two- dimensionally and reading repetitively the block properly. CONSTITUTION:An output Q of a K counter 20 repeats alternately '1' and '0' synchronously with an H-SYNC signal inputted at each main scanning to select alternately each column of a threshold block comprising 20 rows and 2 columns. The K counter 20 is a K-notation counter, which generates a carry signal CRY at two columns each. Thus, an S-counter 21 is counted up at two columns each, resulting that 10 kinds of different shift numbers are outputted from a PROM table 22 while being circulated sequentially at each other column. The K-counter 20 applies address designation to a column and an L-counter 23a applies address designation to a row to read sequentially each threshold value from a threshold value block stored in advance in the ROM table 24 and the threshold values of an optional screen angle are arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to color image recording, and more particularly to an image recording method in which arbitrary different screen angles can be easily set for each color.

[Conventional technology]

Conventionally, in printing plate-made color images, it is common to change the angle of the halftone dot screen of the halftone plate for each valley color when producing the halftone plate in order to prevent the occurrence of moiré due to the combination of colors.

Contact screens and mesh scanners have conventionally been used as methods to achieve these goals, but they are often insufficient in terms of durability, maintainability, and cost.

Therefore, as a technique to solve these problems, the so-called dither method is used, which compares each threshold value of n x n with the brightness level of the input image signal and records the halftone of the image according to the comparison result. In the image recording method used, there is one 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 angled, for example, all the threshold arrays corresponding to one page of the image are stored in a predetermined memory 11C, and by reading this as appropriate, the entire threshold value array corresponding to one page of the image is stored. Since it required 5K to supply the threshold data for 10 minutes, it had the disadvantage of requiring an enormous amount of memory.

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 8x8 or more, the output dots will not match the matrix. It has the disadvantage that it does not grow from the center and is significantly different from halftone dots.

[Problem that the invention seeks to solve]

The present invention provides an image recording method in which an arbitrary screen angle can be easily set with a small memory capacity, and output dots grow from the center of the matrix regardless of the size of the threshold matrix.

[Means and effects for solving the problem] Therefore, in this invention, a total darkness value matrix for one page of images arranged at a predetermined screen angle is basically emitted from a threshold value for L rows and columns. Focusing on the fact that the block is divided into quantity value blocks, each threshold value of the basic threshold block in the rows and columns is stored in a predetermined memory, and the reading start position from the memory is determined for each column in the sub-scanning direction. Shifting in the scanning direction by a predetermined amount that is generally determined according to the screen angle, generating threshold data for columns by cyclically reading from the shifted reading start position, and further performing the cyclically reading by a plurality of columns. By repeating this process K times, threshold data for the entire threshold matrix is generated.

〔Example〕

FIG. 2 shows the overall configuration of a digital color copying apparatus to which the present invention is applied.

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

The image input device 1 is composed of an image sensor, a conversion unit, etc., and separates the original image into colors using red (R), green CG), and blue-purple (B) filters, and sends the color-separated optical signals to the image sensor. input, and the photoelectric conversion output of the image sensor is '10
The converter performs '/D conversion and outputs R, G, and B multivalue brightness data.

Each of the R, G, and B read data is input to the color processing section 4 of the image processing device 2. The color processing section 4 includes a masking circuit 5 and a UCR (Under Color Rem).
oval ) 6, and a masking circuit 5
The input R, G, and H data are processed by performing a color correction operation on the input R, G, and H data.

Each B image data is converted into yellow (Y), magenta (M), and cyan (C) signals. UCR6 performs black plate calculation and undercolor removal, and input Y, M,
From the C image signal, yellow (Y), magenta (M),
Multivalue brightness data corresponding to four colors, cyan (C) and black (K), is calculated and output.

These Y, M, and C image data are temporarily stored in the storage section 7 at the next stage. Each memory 7-Y of the storage unit 7, 7
-M,? -C and? - are page memories, each of which can store one page of Y, M, and C image data. These memories are stored in each module 3- of the image output device 3 which is activated sequentially as described later.
It is arranged to absorb the drive timing difference among Y, 3-M, 3-C, and 3-.

The multivalue brightness data of Y, M, and C, once stored in the memories 7-Y, 7-Ml, 7-C, and 7-K, are sent to the comparators 9-Y, 9-M, and 9-M in the screen generator 8, respectively.
It is input to 9-C and 9-K. Each comparator 9-Y
, 9-M, 9-C.

Each other input terminal of 9- is connected to a threshold value generator 10-Y,
Threshold value data output from 10-M, 10-C, and 10-K are input. This threshold generation section 10
-Y, 10-Mll 0-C and 10- are used to generate a dither pattern for halftone reproduction, and the internal configuration and other details will be described in detail later. Each comparator 9-Y, 9-M, 9-C
, 9-, memory 7-Y, ? -M, 7-C
，? The multi-value brightness data of Y, M, and C input from -K are input to the threshold generation unit 10-Y% 1G-M, 10
-C.

It sequentially compares with each threshold value inputted from 10-K, and outputs each comparison result consisting of two values, large and small, to each image output module 3-Y, 3-M, and 3-C13-K of image output device 3. The image output device 3 may be a laser beam printer, for example, and the comparators 9-Y, 9-M, 9・-C
, 9-K respectively, by controlling on/off of each laser beam in each module 3-Y, 3-M, 3-C, 3-, a halftone image for each color is generated. Output.

Here, an example of the configuration of a laser beam printer as an example of the image output device 3 is shown in FIG. Each image output module of this laser beam printer 3-Y, 3-M, 3-C
and 3- are yellow (Y) and magenta (M), respectively.
), cyan (C), and black (K), and these modules are arranged serially on the paper conveyance path. Each module is composed of a laser output unit 11 and an image forming unit 12.

The light beam emitted from the semiconductor laser in the laser output unit (laser output unit) 11 is collimated by a collimator lens, enters a rotating polygon mirror (polygon) rotating at high speed, and is further reflected by one reflective mirror surface of the polygon. , and is imaged onto the photosensitive drum 13 of the image forming unit 12 through the imaging lens. Main scanning is performed by moving the imaging point as the polygon rotates, and sub-scanning is performed by rotating the photosensitive drum 13. The image forming unit 12 has an electrophotographic unit configuration, and a charging corotron E'+ 7.3J [5, a transfer corotron, a cleaning device, etc.] are appropriately arranged around the photosensitive drum 13. In this image forming unit 12, a sensor is provided slightly before the main scanning start position of the photosensitive drum 13, and a horizontal synchronization signal (H-8YNC) is generated to align the main scanning start position by detecting the passage of the light beam. was made to occur.

In this configuration, the paper on the paper feed tray 14 is fed by the paper feed roller 15 and carried into the paper transport section 16. A yellow toner image is transferred to the paper that reaches the first image output module 3-YK, and then magenta, cyan, and black images are transferred through image output modules 3-M, 3-C, and 3-K. is transcribed. A sheet of paper on which a color image is formed by superimposing these four colors is subjected to a fixing process in a thermal fixing device 17, and then is discharged onto a discharge tray 18.

Next, the main parts of the present invention will be explained.

FIG. 4 shows an example in which one pixel in the image input device 1 is configured by a matrix of 6×6 micropixels in the image output device 3, and 36 micropixels in the image output device 3 correspond to one pixel in the image input device. corresponds to For example, 36 different threshold values from "1" to "36" are assigned corresponding to the 36 fine pixels within one pixel, and the assigned threshold values are sequentially applied to r2J from rlJ.
, r3J... By filling in "36", it is possible to reproduce 37 gradations up to rOJ or "36".

FIG. 5 shows an example of a threshold array for one page of a recorded image with a screen angle of approximately 18.5 degrees (tαnθ='/3). 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). One pixel shown in FIG. 6(a) contains "1".
The threshold values from ``40'' to ``40'' are arranged in such a way that they spread from the center of the matrix to the periphery, so that ``0''
” to “40” can be reproduced. Here, in the screen generating section 8 shown in FIG. 2, the processing system corresponding to yellow (Y) has a screen angle 18
．． Assuming that the angle is 5 degrees, the threshold value generation unit 10-Y sequentially generates threshold values in a matrix as shown in FIG. That is, the threshold generation unit 10-Y 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 in the manner of scanning line, . . . , and input to the comparator 9-YK. -Multi-value brightness data corresponding to yellow (Y) is sent from the memory 7-Y to the comparator 9-YK in the same manner as rask scanning.
I can input a lot.

That is, in the comparator 9-Y, the memory 7-
Comparison processing is performed on the multivalued brightness data of one pixel read from Y with each of the 6×6 threshold values input from the threshold value generation unit 10-Y, and these comparison processings are performed by the image input device 1 and the image output module. Since this is carried out in synchronization with the rask scan of 3-Y, the multi-value brightness data is read out from the memo 1J7-Y at the frequency of 100 when the threshold value is generated, and the multi-value brightness data of the same scanning line is read out repeatedly six times. be done. The comparator 9-Y compares the input multi-value brightness data with the threshold value, and outputs a comparison magnitude signal that is "1" if the multi-value brightness data has two threshold values, and 10 in the opposite case.Image output The module 3-Y reproduces halftones in the yellow processing system by controlling on/off of the laser beam 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 K is repeated multiple times in the main scanning direction, and in the sub-scanning direction, the threshold block is shifted by a predetermined amount in the main scanning direction and It is designed to be repeated several times.

That is, the starting data of the threshold blocks are different by the amount shifted every two columns, and FIG. 7 shows how the threshold blocks are repeated in the threshold array shown in FIG. 5. shows. In FIG. 7, one hatched block corresponds to the threshold block shown in FIG. 6(b), and in this case, the number of rows L=
20, the number of columns = 2, and the number of shifts 8 = 6.

Further, in this case, the number of shifts from the first threshold block is finite, and as shown in the figure, S.

28, 38.48-L, 98-L,
There are 10 types consisting of O.

That is, in this embodiment, instead of storing the entire threshold value array for one page shown in FIG. 5 in the threshold value generating section 10-Y in the screen generating section 8 shown in FIG. 2, the threshold value array shown in FIG. By storing only the threshold block shown in b) and reading it repeatedly based on the preset number of shifts, all the thresholds in the threshold array for the screen angle of 18.5 degrees shown in FIG. 5 are sequentially read out. to occur.

FIG. 1 shows a specific example of the internal structure of the threshold value generating section 10-Y.

This threshold generation unit 10-Y generates a
The aforementioned H-8YNC signal, which is generated pulse by pulse, is divided into rows (
In this case = 2) one counter 20 for counting, an S-counter 21 that counts up by the carry signal CRY output every K columns, and applies the count output to the address terminal of the FROM table; PROM table 22 in which the number of shifts is stored
, an L-counter 23 which takes the shift number inputted from the PROM table 22 as an initial value and rings-counts the main scanning clock signal CK, and each threshold value of the threshold value block shown in FIG. 6(b) is pre-stored; K-counter 20 and L
- consists of a ROM table 24 addressed by both outputs of the counter 23;

The Q output of the K counter 20 is the H input every main scan.
11# and 10m are alternately repeated in synchronization with the -8YNC signal, thereby alternately selecting each column of the threshold block consisting of 20 rows and 2 columns. The K counter 20 is a K (=2) base counter and generates a carry signal CRY every two columns. Therefore, the S-counter 21 counts up every two columns, and as a result, ten different shift numbers are sequentially circulated and output from the PROM table 22 every other column. The L-counter 23 presets the shift number output from the PROM table 22 based on the LD multiplied signal input at the beginning of each column, and performs a ring count operation in synchronization with the main scanning clock signal CK from the preset shift number. Start. This main scanning clock signal CK coincides with the timing at which the image output device 3 prints the aforementioned one fine pixel. Thus, the ROM table 2 is addressed by addressing columns by the K-counter 20 and addressing rows by the L-counter 23.
Each threshold value is sequentially read out from the threshold value block prestored in 4, thereby generating a threshold value similar to the threshold value array having a screen angle of 18.5 degrees as shown in FIG.

The above has explained an example in which the threshold value generating section 10-Y corresponding to yellow (Y) has a screen angle of 18.5 degrees, but the configuration shown in FIG. It is also applicable to

FIG. 8(a) shows different threshold matrices for one pixel of the image output device 3 when the screen angle is 45 degrees, and FIG. 8(b) shows the basic threshold blocks corresponding to the matrix. This shows that. In this case, the basic threshold block is composed of threshold values arranged in 8 rows and 4 columns.

FIG. 9(,) 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. 9(b) shows the basic threshold value corresponding to the matrix. This indicates a block. In this case, the basic threshold block consists of 20 rows and 2 columns.

Further, FIG. 1O shows an example of a threshold matrix when the screen angle is θ degrees, and the basic threshold block also corresponds to the threshold matrix.

For example, if an attempt is made to realize the threshold array with a screen angle of 45 degrees shown in FIG. 8 using the configuration shown in FIG.
The ROM table 24 may store a threshold consisting of the basic threshold blocks shown in FIG. 8(b), the K counter 20 may be a quaternary counter, and the number of blocks may be set in the FROM ROM table 22. The same applies to other screen angles, and basically the configuration shown in FIG. 1 can realize threshold value generation for any arbitrary screen angle.

In the apparatus shown in FIG. 2, for example, if the screen angle is set to 18.5 degrees for yellow, 45 degrees for magenta, 71.5 degrees for cyan, and 0 degrees for black, each threshold value generating section 10-Y, 10- M, 10-C, and 10-K are configured as shown in FIG. 1, and each comparator 9
-Y.

18,5 for 9-M and 9-C19-K, respectively
Threshold data with screen angles of 45 degrees, 45 degrees, 71.5 degrees, and 0 degrees is supplied.

By the way, in the system of this embodiment, when the screen angle is set, the positions of pixels are different between the image input device i1 and the image output device 3, as compared with FIG. 4 and FIG. 5, for example. Therefore, when the entire image has uniform gradation,
Although it is possible to perform accurate gradation reproduction for each pixel, this is usually not the case, so it seems that the density of each pixel cannot be accurately expressed. For this reason, experiments have shown whether there is a method of reconfiguring the pixel array shown in FIG. 4 into the pixel array shown in FIG. 5 to express gradation. 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. That is, it can be said that there is no deterioration in the image quality of the gradation image due to the difference in the pixel arrangement of the image input device 1 and the pixel arrangement of the image output device 3.

Next, FIG. 11 shows another embodiment of the present invention.

This embodiment device is a device that generates a threshold value array as shown in FIG. 12, and in this case, the threshold values are of 01 to C18013 types.

The ROM table 30 has 1 as shown in FIG.
A basic threshold block of columns and 10 rows is prestored. The ROM table 31 prestores K for specifying the first threshold data for each column of the basic threshold blocks stored in the ROM table 30, and an address corresponding to the first threshold data. The counter 32 receives H- which is input every l main running meal.
This is a hexadecimal counter that rings an 8YNC signal, and the ROM table 31 is addressed by the count output of the counter 32. The counter 33 is a hexadecimal counter that performs a predetermined ring counting operation according to the main scanning clock signal CK, and sets the value output from the ROM table 31 when the Load terminal @L'' signal is input as an initial value. , the counter 33 is
At startup, it is initialized by the reset signal RES ET, and in subsequent operations, it is initialized by the H-8YNC signal input every main scan, so that the leading threshold of each column is read from the ROM table 31. Preset the address value corresponding to the data.

The embodiment shown in FIG. 11 shows a corresponding configuration when the basic threshold block has one column and one row, and is basically the same as the embodiment shown in FIG. 1.

Note that the present invention can be modified as appropriate to the embodiments described above, and the size of the threshold matrix, the screen angle to be set, the arrangement of the thresholds in the threshold matrix, etc. are of course arbitrary.

Furthermore, each of the configurations shown in FIG. 1 may be replaced with other circuits that achieve equivalent functions.

〔Effect of the invention〕

As explained above, according to the image recording method according to the present invention, basic threshold blocks of L rows and columns that newly appear when the threshold values corresponding to the output pixels are arranged two-dimensionally are written in the memory, and the basic threshold blocks are stored as appropriate. Since the threshold value corresponding to one page of the image is generated in order to avoid repeated reading, an arbitrary screen angle can be set with a small memory capacity and a simple control configuration. The recording output dots can be grown from the center regardless of the size of the threshold matrix, and a recorded image that matches the halftone dots can be realized. 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 main parts of an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the overall configuration of a digital color copying apparatus to which the present invention is applied.
Figure 3 is a conceptual diagram showing an example of the internal configuration of an image output device;
The figure is a schematic diagram showing an example of a two-dimensional array of fine pixels and pixels in an image output device, Figure 5 is a diagram showing the entire threshold array system when the screen angle is 18.5 degrees, Figure 6 (,) and (b) is a diagram showing an example of a threshold matrix and an example of a basic threshold block, each corresponding to one pixel when the screen angle is 18.5 degrees, and FIG.
Figure 8 showing the arrangement of basic threshold blocks when
Figures (&) and (b) are threshold values corresponding to one pixel when the screen angle is 45 degrees, respectively.
b) is a diagram showing an example of a threshold value block corresponding to one pixel when the screen angle is 71.5 degrees, and FIG. 1O is a diagram showing an example of a basic threshold block when the screen angle is θ degrees. 11 is a block diagram showing another embodiment of the present invention, and FIG. 12 is a diagram showing an example of a threshold array realized by the embodiment shown in FIG. 11.
FIGS. 13(a) and 13(b) are diagrams for explaining examples of the storage contents of the ROM tables 3o and 31 in the embodiment shown in FIG. 11, respectively. 1... Image input device, 2... Image processing device, 3...
- Image output device, 4... Color processing unit, 5... Masking circuit, 6... UCR, 7-Y, 7-M,
7-C, 7-K...Memory, 8...Screen generator, 9-Y, 9-M, 9-C, 9-K...
Comparator, 10-Y, 10-M, 10-C, 10-
K...Threshold value generation section, 11...Laser output crab unit,
12... Image forming unit, 13-... Photosensitive drum,
14...Paper feed tray, 17...Heat fixing device, 2o...
・K-counter, 21...S-counter, 22...
PROM table, 23-L-counter, 24,30°31...ROM table, 32.33...counter. Yu Dingdong Figure 4 Figure 5 Main Shiba Dan Figure 6 (a) (b)

Claims (1)

[Claims] The entire threshold matrix arranged at a predetermined screen angle is divided into basic threshold blocks consisting of a plurality of L rows and K columns of thresholds, and each threshold of the divided basic threshold blocks and the brightness level of the input image signal are An image recording method that compares corresponding multi-valued brightness data and records a halftone image according to the comparison result, wherein each threshold of the basic threshold block of L rows and K columns is stored in a predetermined memory, K in sub-scanning direction
Shifting the readout start position from the memory for each column by a predetermined amount set according to the screen angle in the main scanning direction, and generating threshold data for K columns by cyclic reading from the shifted readout start position; Furthermore, the circular readout is
An image recording method characterized in that threshold data for the entire threshold matrix is generated by repeating the process multiple times for each column.