JPS61288563A - Digital color picture processor - Google Patents

Abstract

PURPOSE:To reduce color mis-alignment due to overflow and underflow correction as the result of edge emphasis by applying edge emphasis including MTF correction after color correction processing. CONSTITUTION:In applying gradation expression with the area gradation, an MTF correction circuit to improve the resolution of a picture completes color correction processing comprising gamma correction processing, masking processing, UCR processing and black generation processing and the further processing is performed by a gradation processing circuit. The 1st processing system is provided with an 8X8 averaging circuit 150 and a density pattern processing circuit 153 and applies gradation processing by the density pattern method. An edge emphasis circuit 152 of the 2nd gradation processing system is a 2-dimension space filter and amplifies the density change of the area data when the input data has a density level change, that is, edge information exists to emphasize the edge.

Description

[Detailed description of the invention] [Field of invention] The present invention relates to a digital color image processing device.

In particular, the present invention relates to preventing gradation errors and improving the resolution of information such as characters and line drawings in devices that express halftones using the area gradation method.

[Prior Art] When recording an image using the dot matrix method, in a normal recording device, the density level of each dot must be set at a maximum of 4.
It can only be adjusted in stages. However, for example, digital color copying machines generally require 64 levels of gradation expression for each basic recording color such as yellow (Y), magenta (M), cyan (C), and black (BK). .

When performing such multi-gradation expression, conventionally, a relatively large dot area consisting of multiple dots (for example, 8x8) is used as the unit of gradation processing area, and the number of recording dots and the number of recording dots are calculated for each dot area. The density level of each gradation processing area is expressed by adjusting the number of non-recorded dots. This type of halftone expression method is called area gradation method.

However, for example, if an 8 x 8 dot area is used as the unit of gradation processing, it will be 1/1
The recording resolution decreases to 8. For example, in an image such as a photograph, even if the resolution is low, if the intermediate tone, that is, the density of each pixel is accurately expressed, the recording quality will be highly evaluated. However, in the case of line drawings and characters, a decrease in resolution immediately leads to a decrease in recording quality.

Generally, for images containing line drawings or text, 1
In many cases, gradation expression is not necessary. Therefore, it has been proposed to switch the image information processing to either binary processing or gradation processing depending on the content of the image being handled. However, when dealing with multicolor images, for example, it is necessary to treat each pixel information of one character or line drawing as halftone data in order to reproduce each color. Furthermore, even in black/white recording, there are cases where it is desired to express characters and line drawings in intermediate tones such as gray.

By the way, in an image processing device, in order to increase the resolution, M T
F (Modulation Transfer Fu
(nction) correction processing is being performed. This process is
In order to correct reading errors that are unavoidable due to the structure of the reading device, image nip portions of data are emphasized. Therefore, the MTF correction circuit is generally connected immediately after the image reading device. Generally, in image processing devices,
After the MTF correction circuit, γ correction processing, masking processing,
Color correction processing such as OCR processing and black information generation processing is performed, followed by gradation processing, and the resulting binary data is recorded for each color.

However, when performing MTF correction, that is, edge enhancement processing, overflow and underflow tend to occur in the processed data, as will be described later. In that case, for subsequent gradation processing, it is necessary to correct, for example, the overflow data to the maximum gradation value, and the underflow data to the minimum gradation value. However, when this type of correction is performed, a density error occurs in that portion. Moreover, since the color correction process is performed after that, the gradation process is performed in a state where the error is further amplified.

[Objective of the Invention] The first object of the present invention is to prevent the occurrence of gradation errors and color shifts when expressing gradations using the area gradation method, and to improve the resolution of images. is the second purpose.

[Structure of the Invention] In order to achieve the above object, in the present invention, an MTF correction circuit, that is, an edge emphasis circuit is arranged after the color correction processing circuit.

According to this, gradation errors due to overflow and underflow in edge enhancement processing are not amplified by color correction processing, so gradation errors and color shifts are reduced.

By the way, as will be described later, if an edge emphasis circuit is used in the first gradation processing circuit, special gradation processing can be performed.

Further, the edge enhancement circuit in this case has substantially the same configuration as the MTF correction circuit. Therefore, in a preferred embodiment of the present invention, an edge emphasis circuit is provided in the gradation processing circuit, and the edge emphasis circuit also includes the function of an MTF correction circuit, thereby reducing the number of components of the entire device.

Gradation expression using the area gradation method can be roughly divided into two types: the density pattern method and the dither method. In the density pattern method, the average density within a predetermined processing area (for example, 8 x 8) is calculated, and the result is compared with multiple values in a threshold table in which thresholds are determined in advance for each pixel within the processing area. , and based on the results, binary data of rlJ or rOJ is generated for each pixel.

In the dither method, the input data of each pixel is directly compared one-on-one with that of the corresponding position in the threshold table, and binary data of "1" or rOJ is generated based on the result.

The threshold values are generally 0.1, 2, 4, . . . for an 8x8 matrix table. ...64 types of threshold values 62 and 63 are arranged at 64 pixel positions, but the order in which the threshold values are arranged, that is, the pattern type, can be roughly divided into two types: systematic pattern and random pattern. Become. The pattern shown in FIG. 10c is representative of a random pattern and is called the BAVER type. The one shown in FIG. 10e is representative of the organizational pattern, which is generally called a spiral pattern.

Here, one example will be explained. Episode 10a is 8
A certain original image corresponding to a ×8 pixel area is shown. In this, the hatched portion has a density of 44, and the other portions have a density of 14. In other words, it shows a portion where the density changes rapidly with the diagonal edge as the boundary. Figure 1 Ob shows density data for each pixel read from the image in Figure 10 a.

Figure 10d shows the result of processing the density data in Figure 10b by the dithering method using the random pattern shown in Figure 10e, and Figure 10f shows the result of processing the same density data in Figure 10e.
Figure 10g shows the result of processing using the dither method using the Mill-like pattern shown in Figure 10e, and Figure 10g shows the result of processing using the density pattern method using the systematic pattern of Figure 10e. The hatched pixels indicate data "1" (recorded pixels), and the other pixels indicate data "0" (non-recorded pixels).

Comparing the results of each process, the average density, that is, the gradation, is 31.5 for the input data (Figure 10b);
Since the 1' Od diagram is 33, the LOf diagram is 32, and the 10g diagram is 31, it can be seen that the systematic pattern is superior to the random pattern as the threshold arrangement pattern. Next, “1” and “0” in the 8×8 matrix
'', it can be seen in FIG. 10d that the distribution of rLJ and rOJ is biased with the edge of the original data as the boundary. In other words, information other than the density in the 8×8 matrix, ie, information at the corners of the original data, is converted into the original output data. However, in both Figures 10f and 10g, "1" is distributed in the center according to the threshold array shape of the threshold table, and almost no information at the corners of the original data appears in the output data. I can see that there isn't. In other words, it can be seen that random patterns are superior to systematic patterns in terms of resolution.

Therefore, by using multiple types of patterns, such as using random patterns for images where resolution is important and systematic patterns for images where gradation is important, resolution and gradation can be improved. It can satisfy both tonality requirements. For images where resolution is important, e.g.
Since edge information as shown in Figure 0a is included, by switching the pattern type depending on the presence or absence of this image edge, a preferred pattern type can be automatically selected.

As mentioned above, even when using random patterns,
Since the gradation difference between the original data and the output data is not so large, even if, for example, character information is input as a halftone, the gradation will not change significantly. In other words, even if the text information is in multiple colors, for example, the colors can be recorded accurately, and since the resolution is high, the recorded characters can be easily identified.

By the way, in identifying a single character or line drawing, the edge area of the information plays an important role. In other words, if the loss of information in the edge area is prevented, the resolution can be substantially improved. For example, for the image in Figure 10a, first
As shown in Figure 1a, rlJ and "0" are placed in the pixels at both ends of the edge area, and for the remaining pixel positions, 1911j "1" is placed below the edge, and 5 is placed above the edge. If "1" is recorded, the average density of the entire image becomes 32, which is equal to the original data, and the average density of each area at both ends of the edge also becomes close to the original data.

Edge regions can be extracted by spatial filters.

For example, assuming a local area of 3×3 pixels adjacent to each other, each pixel position A, B, C, D, E, F.

Weighting G, H, and D as shown in each pattern in FIG. 12, and outputting the sum of the weights of each density data corresponding to these nine pixels is equivalent to the function of a filter. The characteristics of this type of spatial filter are determined depending on the weighting of each pixel. Filter pattern FA shown in FIG.

FB, PC, PD and PE function as edge extraction filters, and other patterns PF, PG and PH.

PI and PJ function as edge enhancement filters.

Figure 1Lb shows the data shown in Figure 10b as pattern FD.
Figure 1id shows the result of processing the data shown in Figure 10b using an edge enhancement filter of pattern PI. However, in order to process the data at the edge of the 8×8 pixels in FIG. 10b, the results are obtained assuming that the density outside the data at the edge is the same as the data at the edge.

In FIG. 11d, a negative processing result, that is, an underflow, is replaced with O, and a processing result of 64 or more, that is, an overflow, is replaced with 63. here.

The input data has values within the range of 0 to 63, but by passing it through the filter, values in the edge region are emphasized, resulting in values that are outside the range of the input data. That is, the occurrence of overflow or underflow means that edge information is included in the input data. Therefore,
The presence or absence of edge information can be determined by checking whether overflow or underflow has occurred due to the edge enhancement filter processing.

Figure 11c shows the data in Figure 11b at a fixed threshold value 32.
Shows the results of binarization. Referring to FIG. 11c, it can be seen that the edge information of the image has been extracted. however,
Since the average density (the number of hatched pixels) in FIG. 11c is 9, it is far from the original data of 32, and as it is, it cannot be used in terms of gradation.

Therefore, when the result of dithering using the random pattern threshold table (FIG. 10d) is logically ORed with the result of FIG. 11c, the result is as shown in FIG. 11g. According to this, the error in the average gradation is improved, and the edge information is reliably reflected in the processing result.

Figure 1ie shows the data obtained by dithering and binarizing the data in Figure 1id using the threshold table (random pattern) in Figure 10c, and Figure 11f shows the data in Figure 11c1 as shown in Figure 10e. Shows data that has been dithered and binarized using a threshold table (synonymous pattern). Referring to Figures 1e and 1e and 1f, the distribution of rlJ and "0" in the 8x8 matrix contains the original data (Figure 10b).
It can be seen that the information on the concentration distribution of is reflected to a relatively large extent. In other words, the edge enhancement processing improves the resolution in the unit gradation processing area (8×8 pixels). However, when comparing the average density, that is, the gradation, Fig. 11e is 32
, 25 in FIG. 11f, it is preferable to use a random pattern as the threshold table.

FIG. 11h shows a pattern in which the matrix size of the threshold table is different from that described above. In this,
The size of the table is 4×4, and 16 types of threshold values are arranged in a random pattern in each of 16 pixel areas.

In addition, in FIG. 11h.

In order to correspond to an 8×8 pixel area, four threshold tables are shown arranged consecutively.

Using the threshold value table of FIG. 11h, the result of dithering the data of FIG. 10b and the logical sum of the contents of FIG. 11c are shown in FIG. 11i. According to this, it can be seen that the edge information of the original data is sufficiently represented in the processing result, and the average density within 8×8 pixels is 33, indicating that the gradation is excellent.

Based on the above considerations, it is possible to achieve both accurate gradation expression and high resolution at the same time by selecting a preferable threshold table or by combining multiple processing results. I understand.

[Example J The present invention will be described in detail below with reference to one drawing.

One J for the 111th! The mechanical components of a digital color copying machine of one type that implements the color copying machine are shown, and FIG. 2 shows an outline of the configuration of the electrical equipment section.

First, referring to FIG. 1, an original 1 is placed on a platen (contact glass) 2, and fluorescent lamps 31+3 for illuminating the original are placed on a platen (contact glass) 2.
2, the reflected light is reflected by the movable first mirror 41 + second mirror 42 and third mirror 4J, and passes through the imaging lens 5.

Enters the dichroic prism 6, where the three wavelengths of light, red (R), green (G) and blue (B)
It is spectrally separated into The separated light is captured by CC, which is a solid-state image sensor.
The light is incident on D7r, 7g and 7b, respectively. That is, red light is COD 7 r, green light is CC07
g, and the blue light is incident on C0D7b.

The fluorescent lamp 31 * 32 and the first mirror 41 are connected to the first carriage 8
The second mirror 42 and the third mirror 43 are mounted on the second carriage 9, and by moving the second carriage 9 at half the speed of the first carriage 8, the original 1
The optical path length from to COD 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 IO, and the wire 12 is wound around a movable pulley (not shown) on a second carriage 9. As a result, due to the forward and reverse rotation of the motor 1o,
The first carriage 8 and the second carriage move forward (original image reading and scanning) and backward (return), 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. 1, the first carriage 8 is detected by a home position sensor 39 which is a reflective photosensor. This detection mode 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 does not receive light (carriage non-detection). When the first carriage 8 returns to the home position, the sensor 39 receives light ( (carriage detection), and the carriage 8 is stopped when the state changes from non-light reception to light reception.

Referring now to FIG. 2, CCD 7 r t 7
The output of g +7b is converted from analog to digital and subjected to the necessary processing in the image processing unit 100 to produce recorded color information of black (BK), yellow (Y), magenta (CM) and cyan (C), respectively. It is converted into a binary signal for recording activation. Each of the binary signals is sent to a laser driver 112bk.

112y, 112■ and 112c, and each laser driver outputs a semiconductor laser 113bk, 113y,
By energizing 113+* and 113c, a laser beam modulated with a recording color signal (binarized signal) is emitted.

Referring again to FIG. Each emitted laser beam has a rotating polygon! ! 13bk, 13y, 13m and 13c, reflected by f-theta lenses 14bk, 14
Through y*14+w and 14c, the fourth mirror 15bk
.

'5Ys15vs and 15c and 5th mirror 16bk.

Reflected by '6yt16m and 16c, polygon mirror surface tilt correction cylindrical lens l 7bk, 17yt17
m and 17c, and photosensitive drum 18bk.

Imaging is irradiated to 18yy18m and 18c.

The rotating polygons 1It13bk+13y-13m and 13c are polygonal mirror drive motors 4lbk, 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. 4 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 laser light detection signal (pulse) from the sensor 44c is processed as a line synchronization pulse for -laser scanning. Magenta recording device.

The configuration of the yellow recording device and the black recording device is also the fourth one.
The configuration is exactly the same as that of the cyan recording apparatus shown in the figure.

Further, referring to FIG. 1, the surface of the photosensitive drum is uniformly charged by charge scorotrons 19bk, 19y, 19m, and 19c connected to a negative voltage high voltage generator (not shown). When a laser beam modulated by a recording signal is irradiated onto the uniformly charged surface of the photoreceptor, the electric charge on the surface of the photoreceptor flows to the equipment ground of the drum body and disappears due to a photoconductive phenomenon. Here, the laser is turned on and wiped in areas where the original density is high, and the laser is turned on in areas where the original density is low. As a result, the photoreceptor drum 18b
k, 18)'t of the surfaces of 18m and 18c,
The part corresponding to the high density part of the original has a potential of 150 V, and the part corresponding to the low density part of the original has a potential of 1100 V.
As a result, an electrostatic latent image is formed corresponding to the density of the document. Each of these electrostatic latent images.

Developed by a black developing unit 20bk, a yellow developing unit 20y, a magenta developing unit 20m, and a cyan developing unit 20c, and a photoreceptor drum 18bk.
, 18y, 18m and 18c to form black, yellow, magenta and cyan toner images, 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), and the toner adheres to the area where the surface potential of the photoreceptor is higher than the developing bias, and the toner is attached to the original. A corresponding toner image is formed.

On the other hand, the recording paper 267 stored in the transfer paper cassette 22 is fed out by the paper feeding operation of the feed roller 23, and transferred to the transfer belt 267 by the registration roller 24 at a predetermined timing.
Sent to 5. The recording paper placed on the transfer belt 25 is
Due to the movement of the transfer belt 25, the photosensitive drums 18bk,
18y* passes through the lower part of 18m and 18c sequentially, and while passing through each photoreceptor drum 18bk, 18)'t 18m and 18c, black, yellow, magenta and cyan are transferred at the lower part of the transfer belt by the action of the transfer corotron. The respective toner images are sequentially transferred onto the 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 surface of the photoreceptor after transfer is removed by cleaner units 2 lbk, 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 20bk. Incidentally, the cleaner unit 21y is caused by reverse transfer of black toner from the recording paper during transfer to the photoreceptor drum tsy.

The yellow, magenta, and cyan toners collected at 21m and 21c are not collected for reuse because they are mixed with toners from different color developing devices in the preceding stages of these units.

FIG. 5 shows the inside of the toner recovery pipe 42.

Inside the toner recovery pipe 42, a toner recovery auger 4 is installed.
Contains 3. The auger 43 is formed of a coil spring and is freely rotatable inside the toner collection pipe 42 bent into a channel shape.

The auger 43 is rotationally driven in one direction by a driving means (not shown), and the toner collected in the unit 21bk is transferred to the developing unit 20b by the spiral pump action of the auger 43.
sent to k.

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. 1, the transfer belt 25 on which the recording paper is placed is the photosensitive drum 44bk, 44y.

Contacts 44II+ 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 resists the repulsive force of the compression coil spring 34.
rotates counterclockwise, the drive roller 511t11 descends, and the transfer belt 25 is transferred to the photosensitive drum 44y.

It is separated from 44 city and 44c and remains in contact with the photosensitive drum 44bk. In this state, the transfer belt 25
Since the upper recording paper only contacts the photosensitive drum 44bk, only the black toner image is transferred to the recording paper (black mode). Since the recording paper does not come into contact with the photoreceptor drums 44y, 44m, and 44c, the toner (residual toner) attached to the photoreceptor drums 44y, 44m, and 44c does not stick to the recording paper, and no yellow, magenta, cyan, or other stains appear on the recording paper. do not have. That is, when copying in the black mode, copies similar to those produced by a normal monochromatic black copying machine can be obtained.

The console board 300 includes a copy start switch, a 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 twice, the switch key lights up and the black mode is set, and the black mode setting solenoid is energized; when the switch is closed the second time, the switch key goes out and the color mode is set, and the black mode setting solenoid is de-energized.) It is also equipped with 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. 6 shows the case when two identical full-color copies are made. 1st
The modulation energization of the laser 43bk based on the recording signal is started at almost the same timing as the start of the exposure scan of the carriage 8, and the lasers 43y, 43I11 and 43c are activated from the photoreceptor drum 44bk to 44y, 44m and 4, respectively.
The moving time Ty, Tm of the transfer belt 25 for a distance of 4c
Modulation energization is started after a delay of 1 and Tc. The transfer corotrons 29bk, 29y, 29m and 29c operate for a predetermined time (on the photoreceptor drum) from the start of modulation energization of the lasers 43bk, 43y, 43m and 43c, respectively.

It is energized after a delay (time required for the laser irradiation position to reach the transfer corotron).

See Figure 2. The three color image signals read by the CCDs 7r, 7g and 7b are each A/D converted and applied to the image processing unit 100 as digital signals. The image processing unit 100 converts these digital signals into black (BK), yellow (Y), magenta (M), and cyan (C) recording signals necessary for recording.

The BK recording signal is supplied as is to the laser driver 112bk, but the Y, M and C recording signals are supplied with their original recording color 11m data in the buffer memory L08.
y, 108m, and 108c, and then read out and converted into recording signals after delay times Ty, TIm, and Tc shown in FIG. 6, and then applied to laser drivers 112y, 112+n, and 112c. In addition.

In the copying machine mode, the image processing unit 100 is given three color signals from C0D7r+ 7g and 7b as described above, but in the graphics mode, three color signals are given from outside the copying machine.
A color signal is provided through external interface 117.

Shading correction circuit 10 of image processing unit 100
1 is the color gradation data obtained by A/D converting the output signals of the CCDs 7r, 7g and 7b into 8 bits, and is corrected for optical illumination unevenness, sensitivity variations in the internal unit elements of the CCDs 7r, 7g and 7b, etc. to create read 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 interface circuit 117.

The γ correction circuit 103 that receives the output (color gradation data) of the multiplexer 102 changes the gradation (input gradation data) according to the characteristics of the photoreceptor, and also changes the gradation arbitrarily using the operation button of the console 300. Furthermore, the input 8-bit data is changed to the output 6-bit data. Since the output is 6 bits, data representing one of 64 gradations will be output. The red output from the γ correction circuit 103 (
6-bit three-color gradation data representing the gradations of R), green (G), and blue (B) are supplied to a complementary color generation circuit 104.

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 provided to a masking processing circuit 106.

Next, Yx, which explains masking processing and UCR processing,
MxHCx: Data before masking.

Yo, MO, Co: data after masking.

In addition, the general formula for UCR processing is It can be expressed as

Therefore, in this example, using these equations, we use the product of both coefficients.

is calculated to find new coefficients. The coefficients (a11'', etc.) of the above calculation formula that simultaneously perform both the masking process and the UCR/black generation process are calculated in advance and substituted into the above calculation formula to obtain the scheduled input Yi of the masking processing circuit 106,
Calculated values associated with Mi and Ci (6 bits each)
Yo', etc.: outputs 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 are constituted by a set of ROMs, and the data at the address specified by inputs Y, M, and C to the masking processing circuit 106 is UCR. The output of the processing/black generation circuit 107 is applied to the buffer memories 108y, 108m, 108c and the gradation processing circuit 109. Generally speaking, the masking processing circuit 106 performs Y processing according to the characteristics of the spectral reflection wavelength of the toner for forming a recorded image.

The UCR processing circuit corrects the M and C signals, and the UCR processing circuit performs color balance correction when toners of each color are superimposed. After passing through the UCR processing/black generation circuit 107, black component data BK is generated by combining the input three color data of Y, M, and C, and the output data of each color component of Y, M, and C is as follows. The value is corrected by subtracting the black component.

Note that the MTF correction circuit for improving the resolution of the image is operated by the gradation processing circuit 1 after finishing the color correction processing consisting of γ correction processing, masking processing, UCR processing, and black generation processing.
It will be held in 09.

Next, the buffer memory 108y of the image processing unit 100
, 108m and 108c will be explained. These simply generate a time delay corresponding to the distance between the photoreceptor drums. The writing timing of each memory is the same, but the reading timing is as shown in FIG. The memory 108c is activated in accordance with the modulation energization timing of the laser 43c, and is different from each other. The capacity of each memory is 5 memories 108y when A3 is the maximum size, and the minimum is 24% of the maximum required amount for an A3 document.
48% with memory 10801 and 72% with memory 108c
It is sufficient if it is about %. For example, if the COD reading pixel density is 400 dpi (dots per inch: 15.75
dots/mm), the memory 108y has approximately 87 bytes, the memory 108m has approximately 174 bytes, and
The memory 108c only needs to have a capacity of about 261 bytes. In this embodiment, 64 gradations and 6-bit data are handled, so the memories 108y, 108m and 10
The capacities of 8c are 87 bytes, 174 bytes, and 261 bytes, respectively. If the memory address is calculated in units of 6 bits instead of bytes (8 bits), the memory address will be 116K x 6 bits for the memory 108y, 232K x 6 bits for the memory LO8m, and 348K x 6 bits for the memory 108c.

FIG. 9 shows the configuration of the memory LO8c, which has the largest capacity. Note that the other memories 108y and 108m have similar configurations. However, the memory capacity is small.

To explain the outline of the memory configuration with reference to FIG. 9, three 64K x 1-bit memories are used as input data memory.
Six pieces are used to create a 384K x 6 bit configuration.

These are DRAMs 1 to 6 shown in FIG.

The data for which UCR processing has been completed is stored in FiF, which is a first-in/first-out (FiFo) memory.

Write to RAMI, 2. This is for correcting the difference between the output timing of the output data of the UCR process and the write timing of the memories DRAMs 1 to 6, and is a buffer for approximately one line. F i F-.

The data written to RAMI, 2 is stored in DRAMs 1 to 6 at addresses sequentially determined from address 0 by counter ■.
written to. Next, the address of the counter l is incremented by one and the next data is stored. In this manner, data is sequentially written into DRAMs 1 to 6, and when it reaches 384K, it is reset and data is written again starting from address 0. When counter 1 advances the address to 384 from the start of writing, DRAM1-6
Writing of data to the FiFo RAMs 1 and 2 is started (reading from DRAMs 1 to 6). At the start, counter 2 is reset and the data at address O is first FiF.

The data is written to RAMI, 2, counter 2 becomes address 1, and the data is sequentially read out in the same manner as writing. This counter 2 is also 384
When it reaches K, it is reset and written starting from address 0. Fi
The data written in FcRAM 1, 2 is output to the density pattern processing circuit 109 based on the synchronization signal from the laser driver 112c.

Data selector 1 is the address (count data) of counter 1 or counter 2 3ff! D
When writing data to RAM1 to RAM6, the address data of counter 1 is used, and when reading data, the address data of counter 2 is used.
address data is output.

Data selector 2 is %64K x 1 bit DRAM
Since addresses 1 to 6 are determined by multiplexing the upper 8 bits and the lower 8 bits, they are used to select the upper/lower bits of the 16-bit address. Also, the decoder is 38
6 blocks of DRAM1 every 64 to 4 addresses
This is an address decoder for selecting 6 to 6.

Next, the tone processing circuit 109 of the image processing unit 100 will be explained. This circuit 109 converts each multivalued input data of Y, M, and C into binary data, and performs area gradation processing to reflect the gradation of the input data in the output data. .

6-bit pHlI data can represent concentration information in 64 gradations. Ideally, if the dot diameter of one dot could be varied in 64 steps, there would be no need to reduce the resolution, but in the laser beam electrophotography method, the dot diameter modulation only stabilizes the gradation by about 4 steps at most, and generally the area There are many combinations of gradation method, area gradation method, and beam modulation. Here, area gradation processing is performed for each 8×8 pixel matrix to express 64 gray levels of halftones.

The lvm processing circuit 109 includes four units that process data of each color component: Y, M, C, and BK (7). The configuration of each unit is approximately the same. One configuration thereof is shown in FIG. 7, and details of each circuit are shown in FIGS. 8a, 8c, and 8d.

Referring first to FIG. 7, this circuit includes an 8x8 averaging circuit 150. Edge emphasis circuit 152. ) 11 degree pattern processing circuit 153. Data judgment circuit 161° latch circuit 16
2. Correction circuit 163. The input terminal of the 8×8 averaging circuit 150, which includes a random dither processing circuit 156, etc., is connected to the output of the edge enhancement circuit 52.

Further, in this example, since the edge emphasis circuit 152 also functions as an MTF correction circuit, no MTF correction circuit is provided in addition to the 5-gradation processing circuit 109.

Roughly speaking, the gradation processing unit 109 includes two types of gradation processing systems, and automatically selects one of the processing systems depending on the state of input data. The first processing system includes an 8×8 averaging circuit 150 and a density pattern processing circuit 153.

This processing system performs gradation processing using the density pattern method. In this example, the unit of gradation processing is an area of 8 consecutive pixels in each of the main scanning direction and the sub-scanning direction, that is, an 8×8 matrix area, and one gradation is expressed by 64 pixels.

In the density pattern method, the density is calculated by averaging input data for 64 pixels corresponding to a unit processing area (8x8 area), and the density is compared with the value at the corresponding position in the threshold matrix table to determine the magnitude relationship between them. “1” or “0” depending on
” to generate binary data.

FIG. 8a shows an 8×8 averaging circuit 150, and FIG. 8b shows the operation timing of the circuit 150. The images are averaged in the sub-scanning direction (the exposure scanning direction of the first carriage 8) x 8 pixels in the main scanning direction (direction perpendicular to the exposure scanning direction: CCD
(electronic circuit scanning direction) 8 pixel data, a total of 64 pixels. Also, when averaging 64 pieces of 6-bit data, if you add all the data and then reduce it to 1/64, the adder will function as 1/64.
A 2-bit adder is required, but in this embodiment, an 8-bit adder is used. First, sub-scanning direction 8
To explain the addition of pixels, the first data is latched in latch 1, added to the second data in adder 1, and the added value data is latched in latch 2. The third data is latched in latch 1, added to the fourth data by adder 1, and further added to the data in latch 2 by adder 2, and the sum of 4 pixel data (gradation data) is output from adder 2. Output. This data is latched into latch 3.

Similarly, when the fifth to eighth data are added and output from the adder 2, they are added to the data in the latch 3 by the adder 3, and data for every eight pixels in the sub-scanning direction is output.

Note that the output of adder l becomes 7 by adding 6 bit data.
The output of adders 2 and 3 is 8 bits, and the output of adders 2 and 3 is 8 bits, but the output is 17 bits by taking the upper 7 bits.
The value is set to 2.

Next, addition in the main scanning direction will be explained. The average value of the eight pixels output from the adder 3 is stored in the RAMI for one main scanning line. When the second line is output from adder 3, adder 4 adds it to the contents of RAM1 and stores it in RAM2. This addition causes the 1st + 2nd line data to be stored in the RAM.
2 will be stored.

When the third line is output from the adder 3, the adder 4 adds it to the contents of the RAM1 and stores it in the RAM2.

By this addition, 1+2 line data is stored in the RAM2. When the third line is output from adder 3, adder 4
is added to the contents of RAM2 and stored in RAM1. Similarly RAM 1.

2 alternately serves as addition data output (reading) and storage,
When the 8th line is output from the adder 3, the adder 4 adds it to the contents of the RAM 1 and outputs 8 lines of added data. Here, addition rI4 is also 7 as in adders 2 and 3.
By outputting the upper 7 bits of bit data addition, averaged (1/2) data is output. In this embodiment, two 4-bit binary full adders (7428'3) are used in parallel as adders.

The data averaged as described above is input to the density pattern processing circuit 153. Density pattern processing circuit 1
53 is one memory (ROM3: read-only memory) 361 shown in FIG. 8d. This memory RO
M3 stores in advance the threshold values at each position in a predetermined threshold matrix table and the comparison results for each of the densities 0 to 63. Therefore, when averaged density data and main scanning position are applied to the address line, binary data is immediately output to the output terminal. As for the output data, 8 pixels in the sub-scanning direction are simultaneously outputted as 8-bit data, and then converted into serial data by a shift register 362 connected thereto.

The threshold matrix table consists of 64 threshold values in which values are set for each pixel of the 8×8 matrix of the lv adjustment processing unit area. In this example, the values range from 1 to 63, as shown in Figure 10e.

They are arranged in a spiral-shaped systematic pattern. Therefore 1
For example, when the data shown in Figure 1B is input, the data shown in Figure 10F is output. In FIG. 10f, the hatched portion corresponds to the data "1: Recording", and the other portions correspond to the data "0: Not recording".

Next, the second gradation processing system will be explained. The edge enhancement circuit 152 shown in FIG. 7 is a two-dimensional spatial filter, and when there is a change in density level in the input data, that is, when there is edge information, it amplifies the density change in the data in that area and emphasizes the edge. do. In this example, pattern PI shown in FIG. 12 is used.

That is, assuming a 3×3 pixel matrix area consisting of A, B, C, D, E, F, G, H, and I, the data of the center pixel E is replaced with the value E' of the following equation.

E' = 13・E-2 (B + D 10 F 1 H) - (A + C
+G+I) However, when this process is performed, the result is O~63
Since some data may be outside the range, the data correction circuit 16
If 3 becomes 64 or more, replace it with the fixed value 63,
Replace negative values with 0. For example, when the data shown in FIG. 10b is input to the edge enhancement circuit 152, the data shown in FIG. 1id is obtained at the output of the data correction circuit 155.

By the way, if the result of the edge enhancement process is 64 or more (overflow) or negative (underflow), it means that the input data includes something to be emphasized, that is, edge information. Therefore, in this embodiment, the result of edge enhancement is determined by the data determination circuit 161, and binary data indicating the presence or absence of edges is generated depending on the presence or absence of overflow and underflow.

In order to configure a spatial filter of 3×3 pixel matrix, it is necessary to refer to all the two-dimensional data of 3×3 pixels at the same timing. but.

Since the data input to the filter is time series.

In order to match the times at which the data of these nine pixels appear, a matrix register 21O shown in FIG. 8c is provided. This register 210 has nine latches 211 to 2
19 and two sets of 1-line buffers (memories) 220 and 2
It is equipped with 21.

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 (denoted as n, m) is held, each latch 211, 212° 213, 214, 216
, 217, 218 and 219, respectively, (n
+1. m+1), (n +1. m), (n
+1. m −1).

(n, m+ 1), (n, m-1), (n-1, m+
1).

Pixel data of (n-1, m) and (n-1, m-1) appear.

In other words, the data of each pixel A, B, C, D, E, F, G, H, and pixel constituting the 3×3 matrix shown in FIG.
15. Appears at the output terminals of 214, 213, 212 and 211 at the same timing.

Referring to FIG. 8c, an arithmetic unit 230 is connected to the output of the matrix register 21O.

This arithmetic unit 230 has seven additions 1m231°2
32, 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 The output of the latch 217 and the output of the latch 219 are connected to the input terminal, and the output of the latch 212 and the output of the latch 218 are connected to the two input terminals of the adder 234.

Therefore, adders 231, 232, 233 and 234 are
The values of G1I, D+F, A+C, and B1H are output respectively. 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, since the adder 236 adds the output data of the adder 232 and the output data of the adder 234,
Outputs the value of B+F+H. Adders 235 and 23
The outputs of 6 are connected to two input terminals of adder 237. However, the output of the adder 236 is connected to the adder 237 in a state where it is shifted to the higher order digit by one bit.

Therefore, the output terminal of the adder 237 has 2.(B+D+
The value of F+H)+A+C+G+I appears.

A 6-bit signal line SE connected to the output of the latch 215 and a 10-bit signal line SX connected to the output of the adder 237 are connected to the memory 320B (RO
MI) are commonly connected to the input (address) terminals. The memory 320B is a read-only memory and has 13
- The 6-bit calculation result of E+X and data indicating whether overflow or underflow has occurred during the processing are stored in advance at a memory address corresponding to the input data (X is the value of the signal line SX).

However, if the calculation result is negative, 0 is stored instead of the calculation result, and if the calculation result is 64 or more, 63 is stored instead of the calculation result. Therefore, the output of memory 320B is 6
Become a bit. That is, the output of the memory 320B corresponds to the output of the edge emphasis circuit 152 and the output of the data determination circuit 161 shown in FIG. Here, data correction is performed inside the memory 32OB.

In addition, in this way, edge enhancement (including MTF correction)
If the result is corrected to a value within 6 bits, an error will occur in the processed result. In particular, each color component undergoes different corrections, so the color that combines the corrected data is
There will be a slight deviation from the input. However, this color shift is not very large, and the color correction process that involves data amplification is completed before the edge enhancement process, so the color shift is not amplified, and the color shift that is particularly problematic can be avoided. Does not occur.

The 6-bit operation result is output to a signal line 321, the presence or absence of an overflow ("rl" for an overflow) is output to a signal line 322, and the presence or absence of an underflow ("1" for an underflow) is output to a signal line 323.

The 6-bit density data obtained by edge enhancement and data correction is applied to a random dither processing circuit 156.

This circuit 156 is connected to the memory (ROM2) 33 in FIG. 8d.
1. It consists of a digital comparator, 332° 8-line buffer (memory), etc. The memory 331 is a read-only memory, and has 64 kinds of threshold values in the range of 0 to 63 stored in advance in a Bayer type random pattern arrangement as shown in FIG. 10c. By applying the pixel positions in the main scanning direction and the sub-scanning direction to the address terminals of the memory 331, the threshold value at the pixel position is automatically output from the memory 331. The threshold value and the memory 320
A result of the comparison with the output value of B, ie, a binary signal, is obtained at the output of the digital comparator 332. This binary signal is applied to the AND gate 373 after being delayed by 8 lines by an 8-line buffer 350 in order to match the timing with the output data of the accumulation circuit 340B.

On the other hand, the binary signal indicating the occurrence of overflow and the binary signal indicating the occurrence of underflow obtained at the output of the memory 320B, that is, the data indicating the presence or absence of an edge for each pixel, are sent to the accumulation circuit 340 in FIG. 8d. is applied to

Accumulator circuit 340B includes latches 342. Random access memory 345, 346, 347. It consists of a bus driver 344, etc. FIG. 8e shows the accumulation circuit 34 of FIG. 8d.
The schematic operation of 0B is shown.

The operation of accumulator circuit 340B will be described with reference to FIG. 8e. The latch 342 latches the input signal in synchronization with the generation timing of each pixel signal.

Furthermore, the latch 342 resets the latched data at every eight pixels. The accumulation circuit 340B repeats the same operation for every 8 lines of so-called scanning. First, the state in which the latch 342 has been reset in the first line (the nth line of Be (nth line of g)) will be described.

The edge data corresponding to the first pixel is the OR gate 341
It is applied to the latch 342 via B and is held in the latch 342 at the first latch timing. Similarly, the latch 342 holds input data at the timing of each data of the second pixel, the third pixel, the fourth pixel, and so on. latch 342
The data held in is applied to one input terminal of OR gate 341B. Therefore, once data "1" is input to the latch 342 after completing the reset, the input data to the latch 342 will always be "1" thereafter. When latching for 8 pixels is completed after reset, latch 34
The output data of 2 is.

Via bus driver 344, it is applied to and stored in memory 345.

Immediately after that, the latch 342 is reset, and then data processing for eight pixels is performed again in the same manner as above. However, the address of the memory 345 that stores the data of the latch 342 is updated every time the data is stored.

That is, the edge information (whether or not rlJ is present among the eight pixels) of each first line of the 8×8 matrix arranged in the main scanning direction is stored in the memory 345.

In the second line, as in the case of the first line, each time the latch 342 is reset, it is checked whether rlJ exists in the data for eight pixels.

However, when results for 8 pixels are obtained, the data of the memory 345 that stores the data of the first line is read out, and the logical sum (output of the OR gate 343) between it and the result of the second line is sent via the bus driver 344. and stored in memory 346.

In the third line, when data for 8 pixels is obtained, the data of the memory 346 that stores the data of the first line and the second line is read out, and the logical sum (output of the OR gate 343) of this and the result of the third line is read out. ) is stored in the memory 345 via the 5 bus driver 344.

Similarly, the fourth line, the fifth line, the sixth line and the seventh line
In the line, reading data from the memory 345 and writing data from the memory 346, and reading data from the memory 346 and writing data from the memory 345 are performed alternately.

In the 8th line, when data for 8 pixels is obtained, the memory 3 that stores the data of the 1st to 7th lines
45 is read out, and the logical sum (output of the OR gate 343) between it and the result of the 8th line is stored in the memory 347. In other words, unit pixel area (8x8 matrix)
If there is one or more edge data "1" in the memory 347, "1" is stored in the corresponding address of the memory 347, and if there is not, "0" is stored in the corresponding address of the memory 347.

The final edge information stored in the memory 347 is read out at a predetermined timing and applied to the inverter 371 and the AND gate 373. This final edge information is
, that is, when there is an edge, the AND gate 373 opens and the AND gate 372 closes, and after the edge is emphasized, the binary data dithered in a random pattern is passed through the OR gate 3.
74. When the final edge information is "0", that is, there is no edge, the AND gate 372 is opened and the AND gate 373 is closed, and the binary data subjected to density pattern processing in a systematic pattern is outputted via the OR gate 374.

Regardless of the presence or absence of edges, the input data passes through the edge enhancement circuit, thereby performing MTF correction.

Each color (Y, M, C) is binarized in this way.

The data for each color (BK) is the laser driver 43y for each color.

Given to 43m, 43c and 43bk.

The synchronization control circuit 114 determines the activation timing of each of the above elements and matches the timing between each element. 200 is a microprocessor system that controls all the elements shown in FIG. 2 described above, that is, controls the copying machine. This processor system 200 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 photoreceptor power system and exposure system.

Sequences such as charger system, developing system, fixing system, etc. are performed.

FIG. 13 shows an interface between the polygon mirror driving motor and the microprocessor system (200: FIG. 2). Input/output port 207 shown in FIG. 13 is connected to bus 206 of system 200.

In addition, in FIG. 13, 45 is the photosensitive drum 18bk.
, 18y, 18m, and 18c, and is energized by a motor driver 46.

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 an input/output port 20.
7 or other input/output ports connected to the system 20
0, 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, when the power switch (not shown) is turned on, the device starts a warm-up operation, ・Raises the temperature of the fixing unit 36, ・Starts the polygon mirror to rotate at a constant speed, ・Home positions the carriage 8, Performs operations such as generation of line synchronization clock (1,26 kHz), video synchronization clock generation (8,42 MHz), and initialization of various counters. The line synchronized clock is supplied to the polygon mirror motor driver and the CCD driver, and the former uses this signal as a reference signal for a phase-locked loop (PLL) servo, and the feedback signal to the beam sensor 4.
So that the beam detection signals of 4bk, 44y, 44m and 44c have the same frequency as the line synchronization clock.
Also a given phase relationship.

Controlled. The latter is used as a main scanning start signal for CCD reading. Note that the signal for synchronizing the start of laser beam main scanning is transmitted by the beam sensor 44bk,
The detection signals (pulses) of 44y, 44m and 44c are
This is used because it is output for each color (each sensor).

Note that the frequency of the line synchronization signal and the detection signal 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 has a frequency of one dot (one pixel) and is supplied to the CCD driver and laser driver.

Various counters are (1) Reading line counter, (2) BK, Y, M, C storage line counter.

(3) read dot counter, and (4) BK,
Y, M, C @ write dot counter, but the above (
1) and (2) are microprocessor system 200
This is a program counter substituted for the operation of the CPU 202, and (3) and (4) are provided individually on the hardware, although not shown.

Next, the timing of the print cycle is shown in Figure 14,
Let me explain this. When the warm-up operation is completed, the state becomes ready for printing, and when the copy start key switch 301 is turned on, the CPU 2 of the system 200
02, the first carriage 81! ! dynamic motor (
Carriages 8 and 9 (Fig. 13) begin to rotate.
/2 speed) starts scanning (exposure scanning) to the left. When the 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 reading line counter is cleared and at the same time,
Enable counting. 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 becomes L, the read 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 counting is done by a read dot counter. Further, the content of the read line counter at this time is 1.

Similarly, for the second and subsequent lines, the reading line counter is incremented using the primary line synchronization clock, the reading dot counter is cleared, synchronized with the next video synchronization clock, the reading counter is incremented, and the pixels are Perform reading.

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 counters; and when the read line counter is 4727, the C write counters are 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 of each color begins when the content of the reading counter reaches a predetermined value, the writing line counter of each color becomes counting enable, and counting starts with the first beam sensor detection signal (content I). When the dot counter reaches a predetermined value, the laser driver is driven to perform writing. Dot count is 1-4
Between 00.

As dummy data, values 401 to 5077 (4677 pieces) are writable. Here, the dummy data is for adjusting the physical distance between the beam sensors 44bk, 44y, 44m and 44c and the photosensitive drums 18bkt18yt18m 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
This is when each write line counter is 1 to 6615 lines.

Now, as shown in FIG. 14, after starting the exposure scan,
Since BK recording data is obtained from the time of scanning the third line of OD, the BK recording device starts recording and energizing in synchronization with the acquisition of BK data. Therefore, the frame update memory is omitted in the BK signal processing line. On the other hand, since the Y, M, and C recording devices are offset in the paper feeding direction, the recording start delay times Ty, Tm, and Tc (
6) is necessary, and as mentioned above, 87 bytes of frame memory 108y, 174 are provided.
A byte frame memory 108m and a byte frame memory 108c are provided in 261, and in order to reduce the storage capacity in these memories, the stored data is gradation data before being converted into a density pattern. Therefore, since a frame memory for BK is not required, the amount of memory can be reduced, and furthermore, the capacity of the entire frame memory for storing gradation data can be reduced. The photosensitive drum has a circumference (2πr) that is much shorter than the long side length of the maximum size A3 set for this copying machine,
Therefore, the arrangement pitch of the photoreceptor drums is also extremely short.

In the above example, for each color processing system, if an overflow occurs in the edge enhancement result, the result is replaced with the upper limit value (63 in the example), and if an underflow occurs, the result is replaced with the lower limit value (63 in the example). In the example, it is replaced with 0), but color shift due to correction can be eliminated by doing the following. That is,
If an overflow occurs, the maximum value Xl among the color components Y, M, and C is corrected to the upper limit value Xmax, and data X2 and X3 of other colors are corrected to the next values X2' and X3', respectively.

X 2'=X 2 ・(Xmax/X 1)X 3'
= X 3 ・(Xmax/X 1 ) In this way, the results Xmax, X 2 ' and X3
'The color expressed by combining each basic color will be the same as the input data.

[Effects] As described above, according to the present invention, edge enhancement including MTF correction is performed after color correction processing, so that color shift due to correction of overflow and underflow of edge enhancement results can be reduced. In particular, as in the embodiment, the resolution can be improved by including edge enhancement processing in the gradation processing circuit and switching the gradation processing content depending on the determination result of the presence or absence of edge information. In that case, most or all of the edge enhancement circuit can be shared with the MTF correction circuit, so the five-circuit configuration is not complicated.

[Brief explanation of the drawing]

FIG. 1 is a sectional view mainly showing the configuration of the main mechanical parts of a digital color copying machine of one type that implements the present invention, FIG. 2 is a block diagram showing the configuration of the electrical image processing section, and FIG. 1st
FIG. 4 is an exploded perspective view of the BK recording device section shown in FIG. 1, and FIG. FIG. FIG. 6 is a time chart showing the relationship between original reading scanning timing, recording biasing timing, and transfer biasing timing in the above embodiment. FIG. 7 is a block diagram showing the configuration of the gradation processing circuit 109 shown in FIG. 2. FIGS. 8a, 8C, and 8d are block diagrams showing the configuration of each part of the circuit shown in FIG. 7. Figures 8b and 8e illustrate circuits 150 and 34, respectively.
3 is a time chart showing a data processing sequence of 0; FIG. 9 is a block diagram showing the configuration of buffer memory 108C shown in FIG. 2. Figure 10a is a plan view showing an example of a partial area of a document image corresponding to a unit area of 1-gradation processing, and Figure 10b is a two-dimensional expansion of the multi-valued data obtained by reading the image in Figure 10a. FIG. FIGS. 10c, 10e, and tih are plan views showing two-dimensionally expanded contents of three types of threshold tables used in gradation processing. Figures 10d and 10f show the data in Figure 10b,
The plan view showing the two-dimensional expansion of the dither processing results using the threshold data shown in Figure 1'Oc and Figure 10e, respectively, and Figure 1OG are the results obtained by using the threshold data shown in Figure 10e. FIG. 3 is a plan view showing a two-dimensional development of the result of density pattern processing. FIG. 11a is a plan view showing a state in which data indicating characteristics of edges are arranged on both sides of the edge area of the data shown in FIG. 10b. FIG. 11b and FIG. 1id are plan views showing the results of edge extraction processing and edge enhancement processing, respectively, of the data shown in FIG. 10b. FIG. 11c is a plan view showing the result of binarizing the data in FIG. 11b using a fixed threshold. Figures 1ie and 11f show the data in figure 1id,
10e and 10c are plan views showing the results of dither processing using the thresholds shown in FIG. 10e and FIG. 10c, respectively. FIG. 11g is a plan view showing the result of the logical sum operation of the data in FIG. 11c and the data in FIG. 1ie. FIG. 11i is a plan view showing the result of the logical sum operation of the result of dithering the data in FIG. 11B using the threshold value in FIG. Llh and the data in FIG. 11C. FIG. 12 is a plan view showing several patterns of spatial filters. FIG. 13 is a block diagram illustrating some of the copying mechanism elements connected to microprocessor system 200. FIG. 14 is a time chart 1 showing the relationship between exposure scanning and recording energization of the copying machine shown in FIG. l: Manuscript 2 Nibraten 31 #32
Fluorescent lamps 41 to 43: Mirror 5: Variable magnification lens unit 6: Dichroic ink prisms 7r, 7g, 7b: CCD 8: First carriage 9: Second carriage 10: Carriage drive motor 11: Pulley 12: Wire 13bk,
13y, 13m, 13c: polygon mirror 14bk, 14
y, 14m, 14c: f-θ lens 15bk, 1
5y, 15m, 15c, 16bk, 16y,
16m, 16c: Mirror 17bk, 17y, 17m
, 17c Nijilintorical lens 18bk, 18y,
18m, 18c: Photosensitive drum 19bk, 19y, 1
9m, 19c: Charge Scorotron 20bk,
20y, 20m, 20c: developer 21bk,
21y, 21n+, 21c: Cleaner 22: Paper feed cassette 23: Paper feed roller 24 Ni registration roller 2
5: Transfer belt 26, 28, 30: Idle roller 27: Drive roller 29bk, 29y, 29m, 29c: Transfer corotron 31 ni lever 32: Shaft 33: Pin 34: Compression coil spring 3
5: Black copy mode setting solenoid plunger 36:
Fixing unit 37: Tray 39: Home position sensor 40: Carriage guide bar 41bk, 41y, 41m, 41c: Polygon mirror drive motor 42: Toner collection pipe 43bk, 43y, 43+o, 43c: Laser 44b
k, 44y, 44m, 44c: Beam sensor 45: Photosensitive drum drive motor 46: Motor driver 100: Image processing unit 1
09: Gradation processing circuit (halftone processing means) 150: 8X8
Averaging circuit 151: Edge extraction circuit 152: Edge enhancement circuit (edge enhancement means) 153: One-time pattern processing circuit 156 Two-random dither processing circuit 200: Microprocessor system 210: Matrix register 230: Arithmetic unit 331.361: Memory (Threshold table) 340
B: Accumulation circuit

Claims (4)

[Claims] (1) Image reading means that separates and reads the original image; Analog/digital conversion means that converts the read image signals of each color into digital signals; γ Color correction processing means that performs at least one of correction processing, masking processing, UCR processing, and black information generation processing; Edge enhancement means that performs edge enhancement processing on information output from the color correction processing means; Plural pixels The input multivalued data is converted to binary data by referring to a threshold table in which different threshold values are set for each pixel position in the unit area of gradation processing consisting of positions, and gradation processing is performed. a halftone processing means for expressing a halftone by adjusting the number of recorded pixel data and non-recorded pixel data within a unit area; and recording visible information for each color according to information outputted by the halftone processing means; 1. A digital color image processing device comprising: a recording means for performing. (2) The digital color image processing apparatus according to claim 1, wherein the halftone processing means outputs a result of processing the output data of the edge emphasis means. (3) The halftone processing means includes a threshold table in a random arrangement and a threshold table in a systematic arrangement, and the threshold table is used depending on the presence or absence of an edge within a unit area of gradation processing. The digital color image processing apparatus according to claim 1, wherein the digital color image processing apparatus switches. (4) The halftone processing means detects the presence or absence of an edge by determining the presence or absence of at least one of an overflow and an underflow in the processing result of the edge enhancement means. digital color image processing device.