JPS6378672A - Data compression system - Google Patents

Abstract

PURPOSE:To reduce the number of buffer memories without dropping a gradation and resolution by dividing data into unit blocks made up of two picture elements or more and adding a code to either one of a mean density operation value in the block and picture element arrangement information in the block. CONSTITUTION:An image is decomposed to a half tone part and an edge part. The half tone part thinks that the gradation is more important, while the edge part precesses, thinking that edge information, that is, dot arrangement is more important. The edge part outputs dot arrangement information together with edge information, while a nonedge part outputs half tone data. A half tone processing is as follows: a 2X2 matrix is regulated, and a 2X2 averaging circuit is used. For edge extraction, a 3X3 edge extraction filter is used for the unit of 2X2 picture elements. A data compression circuit outputs 2X2 dot arranged data when the edge is extracted and outputs binarization data by 6 bits for the unit of 2X2 picture elements through a selector at the time of half tone.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a data compression method in digital copies, printers, etc., but can also be applied to character synthesis in which halftones and character information are combined and output. be.

In Namisue Giho digital printers, the key points for high quality are a large number of gradations and high resolution. Especially when used as a copy, the number of gradations is 64 or more and the resolution is 400 dots/inch (dpi).
More than that is said to be necessary.

In laser beam printers, binary printing is generally used, and recently, 5- to 8-value printing has been developed to improve resolution. 5
Value conversion means dividing 1 dat into 4 and dividing it into 0 as shown in Figure 27.
~4 5-value output is obtained. If this level is 64 or higher, for example, the reading value of a 400 dpi scanner will be 40.
It can output at 0 dpi and 64 gradations, satisfying the above usage requirements.

However, in reality, the beam diameter can only be controlled by 5- to 8-value conversion, so gradation is performed by area gradation. An example of an actual pattern is shown in FIG. Here the concentration is 0
Coloring out 31 out of 63. By performing multi-value conversion in this manner, in the case of 5-value conversion in this example, 64 gradations can be expressed in a 4×4 area, but the resolution is reduced to 1/4, that is, 100 dpi.

There is a submatrix method as a method for improving resolution. For example, from a 4x4 mother matrix to a 2x2
It cuts out the image and outputs it while maintaining its positional relationship. In this submatrix method, the number of output pixels corresponding to an input pixel is determined by the matrix size required for gradation expression in the density pattern method, but in the submatrix method, the number of output pixels corresponding to an input pixel is determined by the matrix size required for gradation expression. ), submatrices of appropriate size are regularly cut out and output while maintaining the positional relationship within the mother matrix.

Figures 29 and 30 show the principle,
Figure 29 shows a 4x4 dot submatrix cut out from an 8x8 dot mother matrix, and Figure 30 shows a 3x3 submatrix.
This shows how to cut out a dot submatrix. The left side (a) shows the positional relationship between the mother matrix and the submatrix, and the right side (b) shows the matrix of the submatrix to be output. The submatrix matrix simply indicates the positional relationship within the mother matrix, and the mother matrix that is actually applied is a density pattern matrix corresponding to pixel data that is sequentially input.

According to this method, the output matrix size is
Since the number of gradations of the mother matrix is independent, gradation is maintained. Therefore, when using the same image data,
If the submatrices are successively made smaller, the output image will also become smaller, but an image with sufficient gradation can be obtained. Further, by increasing the image data and decreasing the submatrix so that the size of the output image is constant, an output image with high resolution can be obtained while maintaining gradation.

Figure 31(b) shows an example of the output when using the above 5-value pattern as shown in FIG.
Significant improvement.

There are two types of area gradation methods: dither method and density pattern method. Considering the pattern in Figure 28, dither method has 400
This is to determine the four-division output level for one pixel of read value in dpi.

On the other hand, the density pattern method averages input data over an area of, for example, 4 x 4, compares this average value with the threshold value in Figure 28, and outputs for 4/4 pixels.
The above 2×2 submatrix also uses this density pattern method.

FIG. 2 is a mechanical block diagram for explaining an example of a laser beam color printer to which the present invention is applied, FIGS. 3 and 4 are configuration examples of the electrical equipment section, and FIG. 5 is an explanation of the operation. The details will be explained later, but to briefly explain it now, consider a laser beam color printer as shown in FIG. 18m, 18m
=18c Assuming that the interval is 10 OrIn, the buffer memories 108Y, 108m and 108C in FIG. 3 simply generate a time delay corresponding to the distance between the photosensitive drums, and the write timing of each memory is the same. Refer to Figure 5 for the reading timing.
The memory 108y is synchronized with the modulation activation timing of the laser 43y, the memory 108m is synchronized with the modulation activation timing of the laser 43m, and the memory 108c is synchronized with the modulation activation timing of the laser 43m.
It is performed in accordance with the modulation energization timing of C, and is different for each. The requirements for each memory are when A3 is the maximum size, memory 108y is at least 24% of the maximum amount required for an A3 document, memory 108m is 48%, and memory 108c.
It is sufficient if it is 72%. For example, if the reading pixel density of COD is 400 dpi (15.75 dots/mm), and the memory 108y performs dither processing with 5-valued output, the memory 108y will be 2.8 Mbytes, 108 m
requires a huge amount of 5.6 Mbytes and 8.4 Mbytes for 108C.

As shown in Figure 4, when data is averaged using the density pattern method and stored in memory, the memory capacity is 1/8 for 4x4.
．． For 2x2, the resolution is reduced to 1/2, but as mentioned above, the resolution is also reduced to 1/4° and 1/2.Also, there are facsimile machines that compress data probabilistically, but this Mainly consists of white/black characters, and there are few that include halftones.

Purpose The present invention was made in view of the above-mentioned circumstances, and it takes into account that even if resolution and gradation are not compatible, the image quality will be less affected, and the number of buffer memories can be increased without reducing gradation and resolution. This was done with the purpose of reducing the amount of noise, and at the same time, it was made with the purpose of data compression of images including halftones.

In order to achieve the above-mentioned object, the present invention divides one pixel into unit blocks of two or more pixels in a printer capable of multilevel conversion, calculates the average density value within the block, and provides information on the pixel arrangement within the block. The feature is that a code is added to one of the following. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a block diagram of an electrical component for explaining an embodiment of the present invention, and FIG. 2 is a diagram showing the components of a digital color copying machine as an example to which the present invention is applied. First, referring to FIG. 2, a yK document 1 is placed on a platen (contact glass) 2 and is illuminated by document illumination fluorescent lamps 31, 3□, and the reflected light is reflected by a movable first mirror 41.
．． Second mirror 4□ and third mirror 4. is reflected, passes through the imaging lens 5, enters the dichroic prism 6,
Here, there are three wavelengths of light, red (R) and green (G).
and blue (B). The separated light enters C0D7 r, 7g, and 7b, which are solid-state image sensors, respectively. That is, red light enters C0D7r, green light enters COD7g, and blue light enters C0D7b.

Fluorescent lamps 3□, 3□ and first mirror 4□ are in the first carriage 8
The second mirror 4□ and the third mirror 4 are mounted on the second carriage 9, and the second carriage 9 moves at 1/2 the speed of the first carriage 8, thereby converting the COD from the original 1. The optical path length is kept constant, and the first and second carriages are scanned from right to left when reading the original image. The first carriage 8 is connected to a carriage drive wire 12 that is wound around a carriage drive pulley 11 fixed to the shaft of a carriage drive motor 10, and the wire 12 is wound around a movable pulley (not shown) on a second carriage 9. As a result, the first carriage 8 and the second carriage move forward (original image reading scanning) and backward (return) by the forward and reverse rotation of the motor 10, and the second carriage 9
moves at 1/2 the speed of the first carriage 8.

When the first carriage 8 is at the home position shown in FIG. 2, the position of the first carriage 8 is detected by a home position sensor 39 which is a reflective photosensor.

The mode of this detection is shown in FIG. When the first carriage 8 is driven to the right during exposure scanning and moves away from the home position, the sensor 39 becomes non-receiving (carriage non-detection).
When the first carriage 8 returns to the home position, the sensor 39 receives light (carriage detection), and when the state changes from non-light receiving to light receiving, the carriage 8 is stopped.

Now referring to FIG. 1, COD 7 r + 7
The output of g+7b is analog/digital converted and subjected to necessary processing in the image processing unit 100, thereby recording color information of black (BK) and yellow (Y).

The signals are converted into 5-value signals for recording activation of each of 3 magenta (M) and cyan (C). Each of the quinarized signals is input to laser drivers 112bk, 112y, 112m and 112c, and each laser driver is a semiconductor laser 43bk, 43y.

By energizing 43m and 43c, laser light modulated with a recording color signal (quinarized signal) is emitted.

Referring again to FIG. The emitted laser beams are rotated by rotating polygons fi13bk, 13y, 13m and 13c, respectively.
It is reflected by the f-theta lens 14bk.

14y, 14m and 14c, the fourth mirror 15
bk, 15y, 15m and 15c and reflected by the fifth mirrors 16bk, 16y, 16m and 16c,
Polygonal mirror tilt correction cylindrical lens 17bk, 17
y, 17m and 17c, photoreceptor drum 18bk
, 18y, 18m and 18c.

The rotating polygon mirrors 13bk, 13y, 13m and 13c are
Polygonal mirror drive motors 41bk, 41y.

The motors are fixed to rotating shafts 41m and 41c, and each motor rotates at a constant speed to rotate the polygon mirror at a constant speed. As the polygon mirror rotates, the laser beam is scanned in a direction perpendicular to the rotation direction (clockwise) of the photoreceptor drum, that is, in a direction along the drum axis.

FIG. 7 shows the laser scanning system of the cyan color recording device in detail. 43c is a semiconductor laser. A sensor 44c made of a photoelectric conversion element is arranged to receive the laser beam at one end of the laser scan (double-dot chain line) in the direction along the axis of the photoreceptor drum 18c, and this sensor 44c detects the laser beam. The starting point of one line scan is detected at the time when the detection changes from detection to non-detection. That is, the sensor 44c
The laser light detection signal (pulse) is processed as a line synchronization pulse for laser scanning. The configurations of the magenta recording device, yellow recording device, and black recording device are also exactly the same as the configuration of the cyan recording device shown in FIG.

Further, referring to FIG. 2, the surface of the photoreceptor drum is uniformly charged by charge scorotrons 19bk, 19y, 19m and 19c connected to a negative high voltage generator (not shown). When a laser beam modulated by a recording signal is irradiated onto the uniformly charged surface of the photoreceptor,
Due to the photoconductive phenomenon, the charge on the surface of the photoreceptor flows to the equipment ground of the drum body and disappears. Here, the laser is not turned on in areas where the document density is high, and the laser is turned on in areas where the HWI and density are low. As a result, the photoreceptor drum 18b
On the surfaces of k, 18y, 18m and 18c, the parts corresponding to the high density parts of the 1M original have a potential of 15oov, and the parts corresponding to the parts with low original density have a potential of about 1100v.
An electrostatic latent image is formed corresponding to the density of the original. This electrostatic latent image is transferred to a black developing unit 20bk, a yellow developing unit 20y, and a magenta developing unit 20, respectively.
m and cyan developing units 20c to form black, yellow, magenta and cyan toner images on the surfaces of photosensitive drums 18y, 18m and 18c, respectively.

The toner in the developing unit is positively charged by stirring, and the developing unit is biased to about -200V by a developing bias generator (not shown).

It adheres to areas where the surface potential of the photoreceptor is higher than the developing bias,
A toner image corresponding to the original is formed.

On the other hand, the recording paper 267 stored in the transfer paper cassette 22 is fed by the feed operation of the feed roller 23, and is sent to the transfer belt 25 by the registration roller 24 at a predetermined timing. The recording paper placed on the transfer belt 25 is transferred to the photosensitive drum 18bk by the movement of the transfer belt 25.
, 18y.

The toner images of black, yellow, magenta, and cyan are transferred to the lower part of the transfer belt by the action of the transfer corotron while passing through the lower part of the transfer belt 18m and 18c sequentially and passing each of the photoreceptor drums 18bk, 18y, 18m and 18C. are sequentially transferred onto recording paper. The transferred recording paper is then sent to a thermal fixing unit 36, where the toner is fixed to the recording paper, and the recording paper is discharged to a tray 37.

On the other hand, residual toner on the photoreceptor surface after transfer is removed by cleaner units 21bk, 21y, 21m, and 21c.

A cleaner unit 21bk and a black developing unit 20bk that collect black toner are connected to a toner collection pipe 42.
The black toner collected by the cleaner unit 21bk is collected by the developing unit 2obk. In addition, due to reverse transfer of black toner from the recording paper during transfer to the photoreceptor drum 18y, the yellow and yellow toner collected by the cleaner units 21y, 21m, and 21c are
The magenta and cyan toners are not collected for reuse because they are mixed with toners from different color developing devices in front of these units.

FIG. 8 shows the inside of the toner recovery pipe 42.

Inside the toner recovery pipe 42, a toner recovery auger 4 is installed.
Contains 2a. The auger 42a is formed of a coil spring and is freely rotatable inside the toner collection pipe 42 bent into a channel shape. The auger 42a is rotationally driven in one direction by a driving means (not shown), and the toner collected in the unit 21bk is sent to the developing unit 20bk by the spiral pump action of the auger 42a.

The transfer belt 25 that conveys the recording paper in the direction from the photoreceptor drums 18bk to 18c includes an idle roller 26° and a drive roller 2.
7. It is stretched between an idle roller 28 and an idle roller 30, and is rotated counterclockwise by a drive roller 27. The drive roller 27 is pivotally connected to the left end of a lever 31 that is pivotally connected to a shaft 32 . A plunger 35 of a black mode setting solenoid (not shown) is pivotally attached to the right end of the lever 31. A compression coil spring 34 is disposed between the plunger 35 and the shaft 32, and this spring 3
4 applies clockwise rotational force to the lever 31.

When the black mode setting solenoid is de-energized (color mode), as shown in FIG. 2, the transfer belt 25 on which the recording paper is placed is the photosensitive drum 44bk.

It is in contact with 44y, 44m and 44c. In this state, when recording paper is placed on the transfer belt 25 and toner images are formed on all drums, each toner image is transferred onto the recording paper as the recording paper moves (color mode). When the black mode setting solenoid is energized (black mode), the lever 31 rotates counterclockwise against the repulsive force of the compression coil spring 34, the drive roller descends, and the transfer belt 25 moves toward the photoreceptor drum 44y. , 44m and 44c, and remains in contact with the photosensitive drum 44bk. In this state, the recording paper on the transfer belt 25 only contacts the photosensitive drum 44bk, so only the black toner image is transferred to the recording paper (black mode).

Since the recording paper does not touch the photoreceptor drums 44y, 44m and 44C, the recording paper does not touch the photoreceptor drums 44y, 44m and 44C.
and No. 44c, no adhered toner (residual toner) is attached, and no yellow, magenta, cyan, etc. stains appear at all. In other words, when copying in black mode, copies similar to those produced by a normal monochromatic black copying machine can be obtained. The console boat 3oO has
Copy start switch 301. Color mode/black mode designation switch 302 (immediately after the power is turned on, the switch key is off and the color mode is set; when the switch is closed for the first time, the switch key lights up and the black mode is set, and the black mode setting solenoid is energized.; Second When the switch is closed, the switch key goes out and the black mode is set, and the black mode setting solenoid is de-energized), as well as other input key switches, character displays, indicator lights, etc.

Next, the operation timing of the main parts of the copying mechanism will be explained with reference to the time chart shown in FIG. FIG. 5 shows the case when two identical full-color copies are made. 1st
The laser 43bk is activated at approximately the same timing as the start of the exposure scan of the carriage 8.

Modulation energization based on the recording signal is started, and the laser 43
y, 43m and 43c are photosensitive drums 4, respectively.
The moving time Ty of the transfer belt 25 for distances 44y, 44m, and 44c from 4bk.

Modulation energization is started with a delay of Tm and Tc.

Corotron for transcription 29bk, 29y, 29m and 29
c are lasers 43bk and 43y, respectively.

The actuators 43m and 43c are actuated after a delay of a predetermined time (time for the laser irradiation position on the photosensitive drum to reach the transfer corotron) from the start of the modulation actuation.

Referring to FIG. 1, one image processing unit 100 includes a CC
D7rF Black (BK) necessary for recording three color image signals read with 7g and 7b.

It is converted into yellow (Y), magenta (M) and cyan (C) recording signals. The BK recording signal is supplied as is to the laser driver 112bk, but the Y, M, and C recording signals are generated after each of their original recording color gradation data is stored in the buffer memories 108y+108m and 108c, as shown in FIG. Delay time Ty, Tm and T
After a time delay in which the signal is read out after c and converted into a recording signal, it is applied to laser drivers 112y, 112mt-; and 112C. Note that the image processing unit 100 has C0D7r, 7g, and 7 as described above in the copying machine mode.
In the graphics mode, three color signals are supplied from outside the copying machine through the external interface 117.

Shading correction circuit 10 of image processing unit 100
1 is the color gradation data obtained by converting the output signals of the CCDs 7r, 7g and 7b into 8 bits by the A/D, and is corrected for optical illuminance unevenness, variations in sensitivity of the internal terminal elements of the CCDs 7r, 7g and 7b, etc. Create reading color gradation data.

The multiplexer 102 is a multiplexer that selectively outputs either the output gradation data of the correction circuit 101 or the output gradation data of the interval eighth circuit 117.

The γ correction circuit 103 that receives the output (color gradation data) of the multiplexer 102 not only changes the gradation (input gradation data) according to the characteristics of the photoreceptor, but also changes the gradation arbitrarily using the operation button of the console 300. and further change the input 8-bit data to output 6-bit data. Since the output is 6 bits.

Data representing one of the 64 gradations will be output. γ
Red (R) output from the correction circuit 103.

Three-color gradation data of 6 bits each indicating the gradation of green (G) and blue (B) is generated by the complementary color generation circuit 1.
Given on 04.

Complementary color generation is the conversion of the name of each color read signal to the recorded color signal, red (R) gradation data becomes cyan (C) gradation data, and green (G) gradation data becomes magenta (M) gradation data. data and also blue gradation data (B)
is converted (read) as yellow gradation data (Y).

The Y, M, and C data output from the complementary color generation circuit 104 are sent to the masking processing circuit 106 and the UCR processing circuit 1.
Given on 07.

Next, masking processing and UCR processing will be explained. Generally, the calculation method of masking processing is Yi, Mi,
Ci: Days before masking.

Yo, Mo, Co: data after masking.

Also, the general formula for UCR processing is: It is expressed as

Therefore, in this example, using these formulas, both 84
,・2・8.3・J
is calculated to find new coefficients. The coefficients (all', etc.) of the above calculation formula that perform both the masking process and the UCR/black generation process in the same manner are calculated in advance and substituted into the above calculation formula to calculate the scheduled input Yi of the masking processing circuit 106,
The calculated value (Y
O', etc.: output of the UCR processing circuit 107) are stored in the ROM in advance. Therefore, in this embodiment, the masking processing circuit 106 and the UCR processing/black generation circuit 107 are composed of a set of ROMs, and the data at the address specified by the inputs Y, M, and C to the masking processing circuit 106 is It is applied to the data compression circuit 500 as the output of the UCR processing/black generation circuit 107. Generally speaking, the masking processing circuit 106 corrects the Y, M, and C signals in accordance with the spectral reflection wavelength characteristics of the toner for forming a recorded image, and the UCR processing circuit corrects the This is a correction for color balance. After passing through the UCR processing/black generation circuit 107, black component data BK is generated by combining input three-color data of Y, M, and C, and output Y, M.

The data for each color component of C is corrected to a value obtained by subtracting the black component.

Next, the Bacher memory 108y of the image processing unit 100
, 108m and 108C will be explained. These generate a time delay corresponding to the distance between the photoreceptor drums, and the writing timing of each memory is the same, but the reading timing is determined by the modulation energization of the laser 43y. In accordance with the timing, the memory 108m is activated in accordance with the modulation activation timing of the laser 43m, and the memory 108C is activated in accordance with the modulation activation timing of the laser 43m.
They differ depending on the modulation energization timing.

The capacity of each memory is when A3 is the maximum size, and if the memory 108y is at least 24% of the maximum required capacity for an A3 document, the memory 108m is 48%, and the memory 108c is about 72%, the synchronization control circuit 114 is , the energizing timing of each of the above elements is determined, and the timing between each element is matched.

200 is the control of all the elements shown in FIG. 2 explained above;
That is, this processor system 200, which is a microprocessor system that controls the copying machine, controls copying in various modes set on the console, and controls not only the image reading and recording system shown in FIG. 2, but also the photoconductor power system, Sequences such as exposure system, charger system, 2gA image system, fixing system, etc. are performed.

FIG. 9 shows an interface between the polygon mirror drive motor, etc. and the microprocessor system (200: FIG. 1). The input/output port 207 shown in FIG.
00 bus 206. In addition, it is equipped with a driver that energizes each part of the copying machine, a processing circuit connected to the sensor, etc., and is connected to the input/output port and
00 is connected, but illustration is omitted.

Next, the operation timing of each part based on the control operations of the microprocessor system 200 and the synchronous control circuit 114 will be explained. First, turn on the power switch (not shown)
When the is turned on, the device starts warm-up operation, ・Raises the temperature of the fixing unit 36, ・Starts the polygon mirror to rotate at a constant speed, ・Home positioning of the carriage 8, ・Generates the line synchronization clock (1, 26KHz), video synchronization clock generation (8, 42KHz), and initialization of various counters. The line synchronous clock is supplied to a polygon mirror motor driver and a CCD driver, and the former uses this signal as a reference signal for a phase-locked loop (PLL) servo, and a feedback signal for beam sensors 44bk, 44y, 44m and 44c. The beam detection signal is controlled to have the same frequency as the line synchronization clock and to have a predetermined phase relationship. Goro is used as a main operation start signal for CCD reading.

Note that the detection signals (pulses) of the beam sensors 44bk, 44y, 44m, and 44c are output for each color (each sensor) and are used as the signal for synchronizing the start of the laser beam main operation. Note that the frequencies of the line synchronization signal and the detection signals of each beam sensor are locked by PLL and are the same, but there may be a slight phase difference, so the scanning reference is not the line synchronization signal but the frequency of each beam sensor. The detection signal is used. The video synchronization clock is 1 dot (
It has a frequency of 1 pixel) and is supplied to the CCD driver and laser driver.

The various counters are (1) Read line counter, (2) BK, Y, M, C@Write line counter, (
3) read dot counter, and (4) BK, Y,
The M and C parts are dot counters, but the above (1)
) and (2) are program counters substituted by the operation of the CPU 202 of the microprocessor system 200, and (3) and (4) are individually provided on the hardware, although not shown.

Next, the timing of the print cycle is shown in Figure 10.
This will be explained. When the warm-up operation is completed, it becomes possible to print, and when the copy start key switch 301 is turned on, the computer of the system 200 is turned on.
Due to the operation of the PU 202, the drive motor of the first carriage 8 (see FIG. 9) starts rotating, and the carriages 8 and 9
(1/2 speed of 8) starts scanning (exposure scanning) to the left. When carriage 8 is at the home position,
The output of the home position sensor 39 is H, and becomes L shortly after the start of exposure scanning (sub-scanning).

At the time of this transition from H to L, the read line counter is cleared and at the same time the count is enabled. Note that the time point at which this change from H to L occurs is the position where the leading edge of the document is exposed.

With the line synchronization clock that comes in after the sensor 39 goes low, the reading line counter is counted up every pulse. Also, when the line synchronization clock comes in, the reading dot counter is cleared at the rising edge of the clock to enable counting.

Therefore, the reading of the first line is performed after the home position sensor 39 becomes L, in synchronization with the video synchronization clock immediately after the input of the first line synchronization clock, and the pixel 12 pixel 2. . . . Pixel 4667 is read sequentially. still,
Pixel counter.

This is done by a read dot counter. Further, the content of the read line counter at this time is 1. Similarly, the second and subsequent lines are read using the next line synchronization clock, the line counter is incremented, the read dot counter is cleared, and the lines are synchronized with the next incoming video synchronization clock.

The reading counter is incremented and the pixels are read.

In this way, the lines are sequentially read, and when the reading line counter counts up to 6615 lines, the last reading is performed on that line, and the carriage drive motor is reversely energized to return the carriages 8 and 9 to their home positions.

The pixel data read in the above manner is sequentially sent to the image processing unit 100 and subjected to various image processing. The time required to perform this image processing is at least two clocks of the line synchronization clock signal.

Next, for writing, first clear the write line counter and enable the count: When the read line counter is 2, the BK write counter is; When the read line counter is 1577, the Y write counter is; When the read line counter is 3152. , M write counter; also.

When the read line counter is 4277, the C write counter is cleared and enabled to count, respectively.

These count ups are calculated by each beam sensor 4.
This is done at the rising edge of the detection signals 4bk, 44y, 44m and 44c. Further, the write dot counters (BK, Y, M, C) are cleared at the rising edge of the detection signal of each beam sensor, and counting up is performed by the video synchronization signal.

Writing for each color begins when the content of the reading counter reaches a predetermined value, the writing line counter for each color becomes counting enable, and counting starts with the first beam sensor detection signal (content 1). When the dot counter reaches a predetermined value, writing is performed by driving the laser driver. Dot counter is 1~
The data between 400 and 401 to 5077 (401 to 5077) are dummy data.
677) are writable values. Here, the dummy data are beam sensors 44bk and 44y.

44m and 44c and photosensitive drum 18bk.

This is for adjusting the physical distance of 18y, 18m and 18c. Also, write data (1 or 0) is captured at the falling point of the video synchronization signal. The writing range in the line direction is 1 to 6 for each writing line counter.
This is when the line is 615.

FIG. 1 is an electrical block diagram for explaining one embodiment of the present invention, and FIG. 11 shows an internal block diagram of the data compression circuit 500 shown in FIG.

In this embodiment, an image is divided into a halftone part and an edge part, and the halftone part is processed with emphasis on gradation, and the edge part is processed with emphasis on edge information, that is, dot placement. The information and non-edge portions output halftone data.

The details of the 2×2 dot placement circuit shown in FIG.
As shown in the figure, the input data is converted into four values using the following threshold value in FROMl.

This value is latched to LATCHI, 2, and two pixels are stored together for one line in the RAM. Similarly, on the next line, LATCHI, 2 pixel data latched to 2 and the above RA
Two pixel data stored in M are read out and simultaneously input into FROM 2 to output dot arrangement information of 2×2 pixels.

Here, the BUF is for preventing the LATCH1 and LATCH2 outputs from colliding with successive data from the RAM when processing the second line, and is turned on/off for each line.

The output of FROM2 is a binary output in which the upper bits of the output of FROMI are binarized, and the upper 4 bits are determined by this and the positional weight (FIG. 13).

Next, the upper bit of the output of FROMI is 0.
If all pixels are 1, it is 1. If even one is 0, it is FROM
Similarly, when the upper bit is 1, the value is output as the 0th bit of the FROM2 output. FIG. 14 shows an example of input/output of FROM2.

Here, the top 0011 is determined by the weighting shown in FIG. 13, and the binarization levels 1 and 0 are both 00 since both 0 and 1 appear.

Halftone processing defines a 2x2 submatrix, 2x
2 averaging circuits are used. the circuit block as the first
It is shown in Figure 5. In FIG. 15, input data is latched into LATCHI and 2, two pixels are added by ADDl, and one line is stored in the RAM.

When the next line comes, it is latched in LATCHI, 2 in the same way, and by adding the data added in ADDl and the data stored in RAM in ADD2, 2x2 pixel data is added, and the lower 2 bits are cut off. 2 by throwing away
Average data of ×2 pixels is obtained. Note that BUF is turned ON in the first line, and data is written to RAM.
The second line is OFF, and the read data of RAM and A
This prevents DDI outputs from colliding.

Next, edge extraction will be described. This is also used to select one of the data in which averaged dots are arranged in 2×2 pixel units, and a 3×3 edge extraction filter is performed in 2×2 pixel units. Edge regions can be extracted by spatial filters. For example, assuming a return area of 3×3 pixels adjacent to each other, each pixel position A,
B.C.

D, E, F, G, , H, and D are weighted as shown in each pattern in Figure 16, and the weighting of each density data corresponding to these 9 pixels outputs the sum of the data. is equivalent to the function of This type of spatial filter has characteristics determined according to the weighting of each pixel.
The filter patterns PA, PB, PC, PD, and PE shown in the figure function as edge extraction filters.

FIG. 17 shows the results of processing the data shown in FIG. 18 using the edge extraction filter of pattern PD.

The edge extraction circuit shown in FIG. 11 is a two-dimensional spatial filter that attenuates information outside the edge area and extracts only edge information. In other words, the processing results are almost zero in parts other than the edges of the data. Note that in this example,
The pattern FD shown in FIG. 16 is used as the coefficient of the filter. In other words, assuming a 3×3 pixel matrix area consisting of A, B, C, D, E, F, G, H, and H, the data of the center pixel E is replaced by E' in the following equation.

E' = 12・E-2(B+D+F+H)-(A+C+
G+I) In order to configure a spatial filter of a 3×3 pixel matrix, it is necessary to refer to all the two-dimensional data of 3×3 pixels at the same timing. However, since the data input to the filter is in time series, a matrix register 21otI shown in FIG. 19 is provided in order to match the times at which the data of these nine pixels appear. This register 210 consists of nine latches 211 to 219 and 2
A pair of one-line buffers (memories) 220 and 221 are provided.

That is, each of the latches 211 to 219 holds data for one pixel, and the one-line buffers 220 and 221 each store data for one line. m columns (hereinafter,
When pixel data of (indicated as n, m1 columns) is held, each latch 211, 212, 213, 214, 21
6°217.218. and 219 output, respectively.
(n+1.m+1] y (n+1y m)t (
n+1+m-1), (n, m+1), (n, m-1).

(n 1.m+1)+ (n ly m) and (
Pixel data of n-1 and m-13 appear. In other words, each pixel A and B forming the 3×3 matrix shown in FIG.
, C, D, E, F, G, H and engineering data are latches 219, 118, 217° 216, 215, 21, respectively.
4, 213, 212, and 211 at the same timing.

Referring to FIG. 19, an arithmetic unit 230 is connected to the output of the matrix register 210. This arithmetic unit 230 includes seven adders 231, 232, 233.
, 234, 235°, 236 and 237. The output of latch 211 and the output of latch 213 are connected to two input terminals of adder 231, the output of latch 214 and the output of latch 216 are connected to two input terminals of adder 232, and two input terminals of adder 233 are connected to Latch 2 to input terminal
17 and the output of latch 219 are connected, and adder 2
The output of latch 212 and latch 2 are connected to the two input terminals of 34.
18 outputs are connected. Therefore, adder 231,
232°233 and 234 are G+I, D+F, A respectively
Output the values of +C2 and B+H. Since the adder 235 adds the output data of the adder 231 and the output data of the adder 233, it outputs the value A+C+G+I. Further, the adder 236 outputs the output data of the adder 232 and the adder 23
Since the output data of 4 is added, the value of B+D+F+H is output. The outputs of adders 235 and 236 are added to adder 2
It is connected to two input terminals of 37. However, the output of the adder 236 is connected to the adder 237 in a state where it is shifted to the upper digit by one bit. Therefore, the output terminal of the adder 237 has 2(B+D+F+H)+A+C+G+I
The value of appears.

A 6-bit signal line SE connected to the output of latch 215 and a 10-bit signal line Sx connected to the output of adder 237 are connected to PROM 320C.

Memory 320C is a read-only memory. 12'E
The result of comparing the calculation result of +X with the fixed threshold value 32 is
It is stored in advance at a memory address corresponding to the input data (X is the value of the signal line Sx). In other words, if the edge extraction result is 32 or more, set it to "1", otherwise set it to "0".
” is output on the signal line 325. In other words, the data
1”, it means that edge information exists. In the data compression circuit, the output line 325 of the memory 320C is 1
2×2 dot arrangement data when “11”, 2× dot arrangement data when “0”
2 Averaged data is divided into 6b in 2×2 pixel units by selector.
It outputs 7 bits with 1 bit of output line added to this
t is input to the memories 108y, 108m, and 108c, and BK is input directly to the gradation processing circuit.

In addition, 21ine 2dot dela in Figure 11
In the y circuit, edge extraction is performed in 2x2 pixel units using a 3x3 filter, so edge determination is performed on the 2x2 center of the 3x3 as shown in Figure 20, but without this circuit This is included because when selected by the selector, the judgment pixel and the output of the placement OR averaging process are not synchronized.

FIG. 21 is a diagram showing the data expansion circuit 109 shown in FIG. 1, and includes memories 108y and 108m.

108c and the data compression circuit 500 have a main scanning power,
It is input to FROMI, 2 together with the sub-scanning address. P
RoMl is shown in Figure 28: ar:.

The pattern is stored in advance, and the stored data is compared with the threshold value of the pixel corresponding to the input data and main/subaddress, and if the input data is large, writing is performed.
The value of 3 bits is output.

In FROM2, the top 4b is used for restoring the placement process.
In it, the position information is inputted according to FIG. 13, and the output level is inputted in the lower 2 bits according to FIG. 22.

FIG. 23 shows an output example in the case of input data 31. Since data 31 is 011111, the output level becomes as shown in FIG. 23 due to the 11 position 0111. With this kind of processing, the edge resolution can be reduced to 400 dpi411 where resolution is required.
200 dpi, 4-gradation processing is possible in non-edge areas that require 1-level gradation, and the buffer memory capacity is 6 bits + 1 bit 7 3 bits x 4 12, which allows a 42% reduction without degrading image quality.

FIG. 24 shows the configuration of the memory 108c, which has the largest capacity. Note that the other memories 108y and 108m have similar configurations, but have smaller memory capacities. IM as memory×
It uses 42 1-bit memories to create a 6M x 7-bit configuration. Here, the image memory 108c is a 2×2 average of 72% of the A3 size and a density of 400 dpi, so one line is written in = 2382 lines.

Image data is sequentially determined from address O by the UP counter and written into DRAMs 1-6.

The DOWN counter 1 prevents the UP counter from advancing any further after one line of data is written.

When 2339 or more pieces of data arrive and the next line synchronization signal arrives, DOWN counter 1 is reloaded with 2339, and at the same time DOWN counter 2 is decremented by 1.

When the line synchronization signal arrives on the 2382nd line, the UP counter is reset by the output of the DOWN counter 2, and 2382 is also reset in the DOWN counter 2 at the same time.

In this way, the UP counter becomes a 2339x238 binary counter and the DRA selected according to its address
The contents of the addresses M1-6 are first latched into the output latches, and then the data in the input latches is written into the DRAM.

Therefore, for example, where the 500th data of address 3 line is written, the 500th data of 2382 lines before is outputted to the output latch. Incidentally, a flip-flop (F/F) in the circuit notifies the CPU when the data clock is not present in the line synchronization period 2339 times.

1- Naoichi Goichi Lord Next, consider what is done in 4×4 units.

In this case, the compression circuit shown in Fig. 11 is arranged in 2 × 2 dots, 4 × 4 dot arrangement 2 × 2 averaging #4 × 4 averaging 21 ine 2 dot delay 41 ine 4 d
ot delay, and replace the data decompression circuit in FIG. 21 with a FROM1 2X2 submatrix
4 'tE8 degree pattern FROM2 2X2 rearrangement-6
This can be realized by 4×4 rearrangement.

In this case, if the dot placement data is 4-valued as in 2×2, 6 bits of 4×4 averaged data and 4×4+2=18 bits of 4×4 dot placement data are required, and the edge part is 400 dpi, 4-value, non-edge part,
It is possible to reduce memory at 100 dpi and 64 gradations. In this case, 12 bits other than 6b and it for averaged data are wasted.

Furthermore, if binarization processing is performed without using the edge density data, the dot delivery data will be 16 bits, and the memory will be .

``E-''E-Tori Itton It is also possible to further compress the data in 4×4 units.

Here, we will consider switching between edge and non-edge portions without automatically determining them using an external signal.

This is necessary when inputting characters to halftone pixels from the outside. FIG. 25 then shows the circuit blocks. Further, a data pattern from the outside is shown in FIG.

In this example, when external data is not used, the output of the 4×4 averaging circuit is output from the selector together with edge data "O", and when external data is used, the external data is output together with edge data "1".

In the data decompression circuit, FROMI performs 4×4 density pattern processing and rearrangement, and FROM2 returns to the pattern shown in FIG. 26 to obtain a resolution equivalent to 400 dpi, resulting in data compression.

In this example, it is possible to automatically judge the edge and substitute a similar one among the arrangement patterns, or to use 2×2.

Although the embodiment of the present invention has been described above as an example in which it is applied to a buffer memory between drums, it can also be applied to a frame memory for one screen. Further, in this embodiment, since a buffer memory is not required for the first drum, a compression/expansion circuit is not required for BK (black) in this embodiment. Furthermore, although the present invention has been described above with a focus on data compression, the present invention can also be applied to character synthesis that outputs a combination of halftones and character information. The pixel arrangement information and additional code are assumed to be external information from an external device.

As is clear from the above description, according to the present invention, the number of buffer memories can be reduced without reducing gradation and resolution, and at the same time, image data including halftones can be compressed. be able to.

[Brief explanation of the drawing]

FIG. 1 is a main part electric circuit diagram for explaining an embodiment of the present invention, FIG. 2 is a diagram for explaining an example of a laser beam color printer to which the present invention is applied, and FIGS. 4 is a diagram showing the configuration of the electrical components of the printer shown in FIG. 2, FIG. 5 is a time chart for explaining the operation, and FIG. 6 is a detailed diagram of the home position detection section.
FIG. 7 is a detailed diagram of the laser scanning system, FIG. 8 is a diagram showing an example of the inside of the toner collection pipe, FIG. 9 is a diagram showing the interface with the microprocessor system, and FIG.
Figure 0 is a diagram showing the timing of the print cycle, the first
Figure 1 is an internal block diagram of the data compression circuit, Figure 12 is a detailed diagram of the 2x2 dot placement circuit shown in Figure 11,
FIG. 13 is a diagram showing position weighting, FIG. 14 is a diagram showing an output example of FROM2 shown in FIG. 12, FIG. 15 is a diagram showing an example of a 2×2 averaging circuit, and FIG. 17 and 18 are diagrams showing examples of edge extraction filters, FIG. 19 is a diagram showing examples of matrix registers and arithmetic units, and FIG. 20 is a diagram showing examples of edge extraction filters. FIG. 21 is a detailed diagram of the data decompression circuit shown in FIG. 1, FIG. 22 is a diagram showing the output level of FROM, and FIG. 23 is a diagram showing an example of determination. 24 is a detailed diagram of the memory 108c shown in FIG. 1, FIG. 25 is a block diagram when inputting characters to halftone pixels from the outside, and FIG. 26 is a diagram showing an output example. FIG. 27 is a diagram showing an example of quinarization, FIG. 28 is a diagram showing an example of the dither method, and FIGS. 29 and 30 are examples of the submatrix method. The figure shown in FIG. 31 is a diagram showing an example of a quinarization pattern. 100... Image processing unit, 101... Shading correction circuit, 102... Multiplexer, 103
. . . γ correction circuit, 104 . . . Complementary color generation circuit, 106
...Masking processing circuit, 107...UCR processing,
Black generation circuit, 108c, 108m, 108
y...Buffer memory, 109...Data expansion circuit, 114...Synchronization control circuit, 200...Microprocessor, 207...I/O port, 210...
Matrix register, 230... Arithmetic unit, 50
0...Data compression circuit. Figure 5 Figure 2 Figure 6 Figure 7 Figure 8 Figure 11 Figure 12 Figure 13 Figure 15 Figure 16 Figure 17 Figure 21 Figure 22 Figure 25 Figure 26 Figure '/) 00 01 IQ
II Fig. 26 Fig. 27 Q I 2 3 4 No. 28
Figure 30 (a) (b) Figure 31 (a) (b) Procedural amendment (Shark) October 30, 1985 Commissioner of the Patent Office Kuro 1) Akio 1, Indication of the case 2, Invention Name data compression method 3, relationship with the amended person case Patent applicant Ota Ri Nakamagome Address 1-3-6 Nakamagome, Ota-ku, Tokyo Name (674) Ricoh Co., Ltd. Representative Hama 1)
Hiro 4゜Agent address 1-2-7 Furocho, Naka-ku, Yokohama 231
Shear Train Yokohama No. 807 No. 6, Subject of Amendment 7, Contents of Amendment (1), "Procedure" stated on page 6, line 10 of the specification is amended to "capacity". (2), “18b to 18y” stated on page 13, line 6.
" is corrected to r18bk, 18yJ. (3), change the "black mode" described in page 17, line 11 to "
Correct to "Color Mode". (4), r (8,42KH
z)J to r(8,42MHz)J. (5), "r as a main operation start signal" described in page 25, line 15 of the same document is corrected to "as a main scanning start signal". (6) Correct "laser beam main operation" written in page 25, line 16 of the same to "laser beam main scanning". (7), ``rG, , H, and I'' written on page 33, line 15 of the same is corrected to ``rG, H, and ENG''. (8), "By attenuating the information," written on page 34, line 7, is corrected to "by attenuating the information."

Claims (4)

[Claims] (1) In a printer that can convert one pixel into multiple values, two
A data compression method characterized by dividing into unit blocks of pixels or more, and adding a code to either the average density calculation value within the block or the pixel arrangement information within the block. (2) The pixel arrangement information is extracted from a predetermined pattern.
) Data compression method described in section. (3) The data compression method according to claim (1), characterized in that density information is added to the pixel arrangement information. (4) The data compression method according to claim (3), wherein the density information is a maximum value and a minimum value within a unit pixel.