JPH02211775A - Picture processor - Google Patents

Abstract

PURPOSE:To improve the color reproducing characteristic and resolution characteristic by providing a color reproducing information conversion means and a PWM modulation means to a color picture processing section. CONSTITUTION:A picture processor 10 consists of a scanner section 10A, a color picture processing section 10B and a printer section 10c. The color picture processing section 10B is provided with a color picture processing means 20 acting like a color reproducing information conversion means storing color reproducing information to match the picture signal outputted from the scanner section 10A with the output characteristic of the printer section 10C and a PWM modulation means 60 applying pulse width modulation (PWM modulation) to an output of the means 20 and to give the gradation characteristic. Thus, the color reproducibility and resolution are enhanced and high picture quality is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an image processing device suitable for application to an electrophotographic digital color copying machine capable of full-color copying, particularly improving color reproduction characteristics and resolution characteristics. The present invention relates to an image processing device.

[Background of the Invention] An electrophotographic digital color copying machine capable of full-color copying must be able to faithfully reproduce and copy the color image information of a document.

On the other hand, image signals output from a scanner unit that reads image information of a document are usually R, G, and B.

On the other hand, in an electrophotographic printer such as a laser beam printer, Y, M, C or Y, M is used.

A color image is reproduced using C and BK (shades).

In this way, the color system of the image signal output from the scanner section and the color system of the output from the printer section are different, so in order to record on the recording medium in the same color tone as the original, the scanner section must It is necessary to match the output characteristics of the printer with the output characteristics of the printer section that records image information.

To achieve this, color reproduction characteristics have conventionally been adjusted using a linear masking method.

Furthermore, in order to give a recorded image gradation, a dither method has conventionally been used.

[Problem to be solved by the invention] However, the linear masking method is difficult to solve from R, O, B to Y, M,
Since the conversion of C is performed by a first-order matrix operation, the color reproduction error is large.

Furthermore, the dither method used to impart a predetermined gradation to a recorded image calculates the image signal of the pixel of interest by weighting the image signals of surrounding pixels surrounding the pixel of interest. The disadvantage is that the resolution inevitably deteriorates.

Therefore, the present invention takes these points into consideration and proposes an image processing device that achieves high image quality with particular emphasis on color reproducibility and resolution.

[Means for Solving the Problems] In order to solve the above-mentioned WIJM point, an image processing device according to the present invention includes a scanner unit that reads image information of a color document, and a color image processing unit that processes the obtained color image information. It consists of a processing section and a printer section that records a color document based on the signal output from the color image processing section. The present invention is characterized in that it is provided with a conversion means that stores color reproduction information for matching the color reproduction information, and a PWM modulation means that performs PWM modulation on the output of the conversion means to impart gradation characteristics.

[Function] Color originals are read by the scanner section 10A and R, G
, B are converted into image signals. The image signals R, G, and B undergo various image processing in the color image processing section 10B. Before image processing, the rR, G, B (7) image signals are converted into y, M+C+BK image signals in the color image processing means 20 which functions as a color reproduction information conversion means. This color image processing means 20 has a ROM-based LUT (referred to as a look-up table, which is a conversion table that determines a color from the ratio of the three primary colors of a color signal), and stores conversion data that accurately reproduces color information. Stored.

In this example, in addition to image processing, PWM modulation means 60 is provided from the viewpoint of placing emphasis on resolution.1. The PWM modulated image signal can be completely supplied to the printer section 10C.

[Example] Hereinafter, the first example will be described regarding the case where an example of the image processing device according to the present invention is applied to an electrophotographic digital color copying machine.
This will be explained in detail with reference to the figures below.

FIG. 1 shows a schematic configuration of an image processing apparatus 10 according to the present invention, and the image processing apparatus 10 is composed of a scanner section 10A, an image processing section 10B, and a printer section 16C.

The scanner unit 10A refers to a series of processing systems that converts an optical image related to image information of a document obtained by optical scanning into an electrical signal. In this example, image signals (analog signals) of three primary colors are represented by R, G, and B as the electrical signals.

The printer section 10C converts the image signal finally output from the image processing section 10B into a visible image based on the image signal (pulse width modulation (PWM) processed output, multi-value processed output, etc.). This refers to the processing system up to recording.

In this example, an electrophotographic recording method using a photosensitive drum is adopted as the printer section 10C, and a semiconductor laser is used as a light source for forming the electrostatic latent image. Therefore, this printer section 1°C is fully configured as an electrophotographic laser printer.

As an example of developing a color image using a semiconductor laser and a photoreceptor drum, the example shown below is as shown in FIG.
, M, C, and BK are superimposed on a photosensitive drum to reproduce a predetermined color. Therefore, according to this example, the transfer drum cannot be used anymore.

The image processing unit 10B is a processing unit for performing appropriate image processing on input image signals, and specifically refers to scaling processing, filtering processing, shading processing, PWM processing, color ghost processing, etc. .

In addition to these, a color conversion system that converts into an image signal to be used by the printer section 10C, which will be described later, is included.

As shown in FIG. 3, this color conversion system includes, in addition to a color image processing means 20 functioning as a color reproduction information conversion means, a monochrome image processing means 25, a color code generation means (achromatic color discrimination means) 30, and a selector 32. Consists of.

A selector 32 is controlled by a 2-bit color code outputted from the color code generating means 30 and a 3-bit digital signal called a scan code outputted from the main body of the apparatus, and the selector 32 is controlled to select either a color image or a monochrome image. can be selected.

In the color image processing means 20, the 83 colors of R, G, Y, M
, C, and BK. Y, M
, C, and BK are used to match the colors (tones) of the output system of the printer section 10C. The G signal is supplied to the monochrome image processing means 25 as its brightness signal (brightness signal).

FIG. 4 shows an example of a mechanical part of the digital color copying machine constructed in this manner.

The explanation will start from the scanner section 10A. By turning on the copy button provided on the color copier, the scanner section 1
0A (original reading unit) is driven.

First, the original 82 on the original table 81 is optically scanned by the optical system.

This optical system uses a halogen lamp (or fluorescent lamp) 86
and a carriage 84 provided with a reflective mirror 87. ■Movable mirror unit 8 equipped with mirrors 89 and 89'
Consists of 8.

The carriage 84 and the movable unit 88 are caused to travel on the slide rail 83 at predetermined speeds and directions, respectively, by a stepping motor (not shown). 92
．． 93 is a roller, and 95 is a belt.

When using a halogen lamp as a light source, a system with an IR cut filter placed in front of the lens is used.

When optically scanning a color original, a commercially available warm white fluorescent lamp may be used as the light source 86 in order to prevent optical emphasis or attenuation of specific colors.

In this case, to prevent flickering, these fluorescent lights 86 are
It is lit and driven by a high frequency power source of approximately 40kHz. In addition, to maintain a constant temperature of the tube wall and promote warm-up, a POSISTOR heater is used to keep the tube wall warm.

Optical information (image information) obtained by irradiating the original 82 with a halogen lamp 86 is transmitted to a reflecting mirror 87 and a mirror 89.
．． 89' to an optical information conversion unit 100.

A standard white plate 97 is provided on the left end side of the platen glass 81. This is to normalize the image signal (white signal) to a reference white signal (reference signal) by optically scanning the standard white plate 97.

The optical information conversion unit 100 includes a spectroscopic system 102 in addition to the lens 101. As shown in FIG. 5, the spectroscopic system 102 is composed of four prisms 103A to 103D and two dichroic coat films 105 and 106.

105 is a dichroic coating film that reflects red R, 1o
6 is a dichroic coating film that reflects the helmet B. The color-separated images, which are the respective reflected lights, are formed on corresponding optical sensors, in this example, CCDs 107 to 109. Each color separation image is converted into an electrical signal (image signal) by each CCD 107-109.

The printer section 10C (image writing section) has a deflector 935. As the deflector 935, in addition to a galvanometer mirror or a rotating polygon mirror, a deflector made of an optical deflector using crystal or the like may be used.

The laser beam modulated by the color signal passes through this deflector 93.
5, the deflected laser beam is imaged on the image forming body 80 through an optical path formed by a lens 116, which is a cylindrical lens, and a mirror 117.

When deflection scanning is started, the beam scanning is detected by a laser beam index sensor (not shown), and beam modulation using the first color signal (eg, Y signal) can be started.

The bits of the scan code output from the device main control unit determine what color signal the first color signal is used for, and roughly what color signals the second and third color signals are used for. Depends on the content.

A laser beam optically scans the image forming member (photosensitive drum) 80 which has been fully charged with a negative charge by the charger 121 .

An electrostatic latent image corresponding to the Y signal is formed on the image forming body 80 by the main scanning by the laser beam and the sub scanning by the rotation of the image forming body 80 .

This electrostatic latent image is transferred to a developing device 12 containing yellow toner.
2. A predetermined bias voltage is applied to the developing device 122 from a high voltage source. A yellow toner image is formed by development.

Toner is supplied to the developing device 122 when necessary by controlling a toner replenishing means (not shown) based on a command signal from a system control CPU (not shown). .

The yellow toner image is rotated completely with the cleaning blade 127 released from the pressure bond, and then, as in the case of the first color signal, it is superimposed on the yellow toner image by the second color signal (for example, the M signal) and becomes static. A latent image is formed. Then, a magenta toner image is developed using the magenta toner contained in the developing device 123.

Such electrostatic latent image processing and development processing are performed in the order of cyan and black, and the required multicolor toner image is formed on the image forming body 8.
0 (see Figure 2).

124 is a cyan developer, and 125 is a black developer.

In the case of a monochrome image, a monochrome image is formed on the image forming body 80 by one development process. When a color image and a monochrome image coexist, the color image is reproduced by a total of four development processes.

In this case, the black colors in the color image are Y, M, and C.

In the case of a monochrome image, black is reproduced using only BK. When black exists in each of a color image and a monochrome image, the output of the color image processing means 20 or the output of the monochrome image processing means 25 is selected depending on the color code obtained corresponding to each of the color image and the monochrome image. It is decided whether to select.

As described above, the development process is a so-called non-contact development process in which each toner is caused to fly toward the image forming body 80 while an AC and/or DC bias voltage from a high-voltage power source is applied. An example of two-component jumping development is shown. Of course, for the first color, contact type two-component jumping development or conventional contact development is possible.

On the other hand, the recording paper P fed from the paper feeding device 141 via the feed roll 142 and the timing roll 143 is
The image forming member 80 is conveyed onto the surface of the image forming member 80 while being timed with the rotation of the image forming member 80 . Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 130 to which a high voltage is applied from the high voltage power source, and the multicolor toner image is transferred onto the recording paper P.
1 by M1.

The separated recording paper P is conveyed to the fixing device 132, where it undergoes a fixing process and a color image is obtained.

After the transfer is completed, the surface of the image forming body 80 is cleaned by a cleaning device 1.
It is cleaned by 26 and prepared for the next imaging process.

In the cleaning device 126, a predetermined DC voltage is applied to a metal roll 128 provided on the blade 127 in order to facilitate recovery of the toner cleaned by the blade 127. This metal roll 128 is the image forming body 8
0 in a non-contact manner.

After the cleaning is completed, the blade 127 is released from the pressure bond. In order to remove unnecessary toner left behind when the blade 127 is released, an auxiliary cleaning roller 129 is provided, and this roller 129 is rotated in the opposite direction to the image forming body 80. By pressing, unnecessary toner is sufficiently cleaned and removed.

FIG. 6 shows a specific example of the circuit system of the image processing section N10 according to the present invention. Therefore, the figure shows details of the image processing section 10B.

Image signals R, G output from CCDs 107 to 109,
B is supplied to A/D converters 2 to 4 through input terminals IR to IB, so that it can be converted into a digital signal of a predetermined number of bits, 8 bits in this example. Shading correction is performed simultaneously with A/D conversion. 5 to 7 indicate shading correction circuits.

The shading correction circuits 5 to 7 have the same configuration. To illustrate the shading correction circuit 5, as shown in FIG. 7, in this example, it is composed of a memory 5A for 16 horizontal lines and an average value circuit 5B that takes the average value of the 16 horizontal lines. The white signal (normalized signal) is
It is used as a reference signal for transducers 2-4.

The shading-corrected digital image signal is supplied to a density conversion system.

In this example, in addition to the standard density conversion circuits 11 to 13, density conversion circuits 15 to 17 for adjustment are provided, respectively. Any of the density conversion circuits 11 to 13 and 15 to 17 may have a look-up table (LUT) configuration using a ROM.

The density conversion is provided to correct the relationship between the brightness level and density of image No. 18, which has a nonlinear characteristic as shown by the curve La in FIG. 8. The outputs of the standard density conversion circuits 11 to 13 are supplied to a color code generating means 30 which functions as an achromatic color determining means.

In the density conversion circuits 15 to 17 for the H disc, a desired gamma characteristic is selected, thereby obtaining a desired color balance. Each of the adjustment density conversion circuits 15 to 17 stores density data corresponding to a plurality of gamma characteristics, for example, as shown by curves Lb-Ld in FIG. Then, R from terminal 8a.

A manual select signal for G and B is supplied, and the density selection (No. 8" (R/G/B) for selecting the corresponding gamma characteristic from the density adjustment circuit 8 is applied to the adjustment density conversion @i15 to 17. We can run out of supply.

Manual selection signals for R, G, B and BK supplied from terminal 8b as described later are set on the operation panel (not shown) provided on the color copying machine.

In this example, 6-bit data is used for the R and G density signals, and 5-bit data is used for the B density signal.

The density conversion outputs DR, DG, and DB, to which predetermined gamma characteristics have been imparted for color balance adjustment, are used as signals for image processing, and are first supplied to the color image processing means 20.

The color image processing means 20 functions as a color reproduction information conversion stage, specifically, R, G.

In order to match the density No. 48 of 83 colors with the signal of the output system of the printer section 10C, color separation processing is performed to convert it into density signals (6 dot data) of 4 colors, for example, Y, M, C, and BK.

Therefore, the color image processing means 20 has Y and M images.

Conversion ROMs 21 to 24 dedicated to C and BK are provided, and each density signal of Y, M, C, and BK is referred to by the input density signal.

Kokote, R, G, B (7) Y, M, C from the concentration signal.

To convert to a BK density signal, it is possible to use the well-known conversion formula (linear masking method) as described above, but this conversion formula has a large error, so the difference between the reproduced color and the original color may increase. big.

In this example, in order to improve this point, the results of simulation using a computer are stored in each color image processing means 20 as density data, especially so that the deviation from the original color is minimized as much as possible.

An example of what kind of data is stored is shown below. For convenience of explanation, three colors of Y, M, and C are shown as input signals to the printer unit 1oC.

In order to reproduce the same color tone as the original, in this example, density data that minimizes the color difference is generated based on the discrimination amount such as color difference (here, ΔE"ab is used). An example of the generation procedure is shown below. show.

First, the input/output characteristics of the printer section 10C will be examined. In this case, the input is a 6-bit signal for each of Y, M, and C, and the output is the embellished color data (CIE XYZ display) of the color chart output by the printer section 10C at that time.

The total number of color data is 260,000 colors, and in order to obtain colorimetric data for all of these colors, it is necessary to take measures such as linear interpolation of the measured data. Specifically, first, Y, M, and C input signals are input to the printer section 10C, and a color chart is output. Measure the color with a colorimeter to obtain the X, Y, and Z values. This operation is performed with input signal levels of 0, 16, and 16, respectively, for Y, M, and C.
32, 48.63 and so on while thinning out,
By repeating this process, actual measurement data for 125 colors can be obtained.

By interpolating this data, the display color of the printer unit 10C corresponding to any value from 0 to 63 for Y, M, and C can be determined using the X, Y, and Z values.

Next, the input/output characteristics of the scanner section 10A are examined.

Select around 30 colored papers from Munsell's color chart, etc., and measure the colors with a colorimeter to determine X, Y, and Z.
RoG and B are determined by scanning with a scanner.

Output signals R, G, B and x, y from the scanner section 10A
, z are both proportional to brightness, so a linear relationship as shown in the following equation holds true.

Therefore, if a=i is determined by the least squares method from the data measured as above, the values X, Y, Z on the colorimeter are
can be obtained from the output signals R, G, and B of the scanner section 10A by matrix calculation using the above equation.

In this way, arbitrary R, G,
The B signal and the input signals Y, M, and C of the printer section 10C are determined by the values of X, Y, and Z, respectively. X, Y, and Z can be converted into uniform color space CIE L*a*bt+ using the following equation.

L”=116 (Y/YO)”3-16a”=500
[(X/XO)”3 (Y/YO)”3]b”=20
0 [(Y/YO)"3-(Z/20)"']Here,
xo, yo, and zo are reference white values.

As shown in Fig. 10, in the uniform color space of L"a"b", the distance between two points indicates the degree of human color difference perception, so it is necessary to compare the distance between the two points.

B signal and input signals Y and M of printer section 1oC.

C) respectively appear on a uniform color space, and represent them as L”a ”
b” (RGB), L”a’b” (MMC),
Letting the distance between the two be ΔE ``ab, ΔE 'ab = [(L”Ros L”cxv)2+(a”Ra5−
a”cxy)2+ (b”ROB b”CMY)
2] “If we find a combination that makes 2 the shortest, that is the combination of Y, M, and C that makes the color difference the smallest.

In this example, the R, G, and B signals of the scanner are density-converted and converted into digital signals of R: 6 bits, G: 6 bits, and B: 5 bits, so there are approximately 130,000 types of signals. , these input signals may be individually assigned as input numbers Y, M, and C of the printer section 10C.

Specifically, using a computer, (a) All of the input signals Y, M, and C of the printer section 10C are set in advance to L ``COY r a ``CMY + 1) ''C
(b) Next, convert the R, G, and B signals of the scanner section 10A to L.
Find out the signals Y, M, Ct-R, G, B signals of the printer unit 10C that minimize ΔE-b after converting them into RQB, and find the relationship between them. Store in ROM.

(C) Then, this ROM may be used as an LUT.

Therefore, the R, G, and B signals after density conversion are RO
If the address is M, Y, M, and C signals with good color reproducibility are referred to and output.

According to the above method, even if the color of the document is outside the color gamut of the toner, the color closest to the color of the document can be selected from within the color gamut and output as signals Y, M, and C.

The density signals created in this way are stored in each of the color image processing means 20, and in addition to the color image processing means 20, a monochrome image processing means 25 is also provided, which contains image information. A G signal containing contour information is supplied as a brightness signal of image information, and is converted into density data having 64 gradations in this example.

The monochrome image processing means 25 is supplied with a density adjustment signal for the black level from the density adjustment circuit 8 mentioned above to control the black level, and also receives a signal from the automatic density adjustment circuit (EE circuit) 27. Background adjustment (No. 3 is supplied.

Therefore, as the density data stored in the monochrome image processing means 25, a plurality of density data (for 64 gradations) corresponding to a plurality of gamma characteristics having different background levels are prepared.

Then, the gamma characteristic is specified by the density adjustment signal for the black level, and the background level is selected by the background adjustment No. 48. Adjustment of the background level is nothing but a process of shifting the gamma characteristic in the direction of the brightness No. 48 axis, which is the input axis (No. 9
Figure - dash-dotted line diagram).

The reason why the density adjustment signal for black level is made independent from the density 1 signal for color balance adjustment is to prevent the black level from changing due to color balance adjustment.

The reason why the background level can be adjusted even in monochrome image processing is to reproduce a clear image by removing the gray background part of the document.

This is because when the background is yellowish, as in old newspapers, for example, if this background is removed and copied, a clearer image can be copied. For this reason, the EE circuit 27 is supplied with the output of the monochrome image processing means 25 as density information, and also receives color code data (described later) in order to perform background level adjustment (automatic density adjustment) only at the edge of an achromatic image. A color code of "OO" or "11" indicating an achromatic color is supplied.

The use or non-use of the EE circuit 27 is determined by the E supplied to the terminal 28.
Although it is controlled by the presence or absence of the E-select signal (selected manually), it can also be configured to prohibit automatic adjustment of the background level when the black level density adjustment signal is manually selected.

The density signals output from the color image processing means 20 (for convenience, indicated by the same symbols Y, M, C, and BK as the image signals) and the monochrome density signal MONO output from the monochrome image processing means 25 are as follows. are respectively supplied to the selector 32,
When the image is a color image, the density signal output from the color image processing means 20 is selected, and when the image is an achromatic color, the density signal fully output from the monochrome image processing means 25 is selected.

To accomplish such processing, the selector 32 is supplied with a scan code and a color code indicating what color is currently being copied.

The color code generation means 30 includes a standard density conversion circuit 11 to
The R, G, and B density signals from 13 are fully supplied, and a color code (2 bits) corresponding to chromatic color and achromatic color image information is output depending on the combination of the densities. Therefore, it is more convenient to configure this color code generating means 30 with a ROM.

FIG. 11 shows the relationship between color codes, scan codes, and density signals selected by them. In this example,
Y, M even for the same color picture.

It is possible to select three colors, C, and four colors, Y, M, C, and BK, but for the sake of explanation, the example shown in Fig. 11 is Y, M.
, C, BK four colors and only color codes related to monochrome images are described.

The selected 6-bit density signal and color code can be supplied to the color ghost correction circuit 40.

Although it differs depending on the configuration of the color image processing means 20, since cyan, magenta, yellow, or a mixture thereof appears around the edges of black characters, this color ghost is provided to remove these color ghosts.

Since color ghost correction only needs to be performed for the color code, color ghost detection means 41 and 42 can detect color ghosts in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (drum rotation direction). Color ghost detection in the main scanning direction is performed using color code data of 7 pixels, and color ghost detection in the sub-scanning direction is performed using color code data of 7 lines x 1 pixel.

The color code in which a color ghost has occurred is converted into a color ghost detection code (for example, roIJ), which is corrected to regular color code data in the next stage color ghost correction section 45. In other words, the color code in which the color ghost occurs is corrected to the color code "10".

Reference numeral 43 denotes a delay circuit for the density signal, which is provided to align the time axis with the color code delayed for color ghost detection.

In this example, the memory is composed of 7 lines of pixels.

The color code in which the color ghost has been corrected is supplied to monochrome (monochrome) and color discrimination means 47, and the discrimination output is supplied to a CPU provided in the main body of the color copying machine, and the color code is supplied to a monochrome (monochrome) and color discrimination means 47, and the discrimination output is supplied to a CPU provided in the main body of the color copying machine to distinguish between a color image and a monochrome image. Copy sequence (
(number of optical scans, etc.) is selected. The discriminating means 47 can form its discriminating output in the following manner.

For example, by scanning the original f182 and creating histograms for the R, a, and Ba frequency signals, as shown in Figure 12, the image is created pixel by pixel based on the relationship between the total frequency of chromatic colors and the total frequency of achromatic colors. Determine whether the information is a color picture (chromatic) or a monochrome picture (achromatic). A color code is determined based on the discrimination output.

The relationship between chromatic colors/achromatic colors and the discrimination results at that time is shown in the 13th section.
As shown in the figure.

The density signal output from the color ghost correction circuit 40 is subjected to filtering processing according to the image content in a rough filtering processing circuit 50.

For example, in the case of a character image, its resolution (for example, MTF
), and for photographic images, filtering processing is applied to smooth them.

This filtering process can be realized using, for example, a 3×3 convolution filter. An example is shown in FIG.

The figure particularly shows the case where it is configured as a cross filter,
1 mA is a filter for resolution correction, and B in the figure is a filter for smoothing. Which filter to use can be specified externally. This designation signal can also be generated automatically.

The numerical values shown in FIG. 14 are filter coefficients, but this is an example.

The MTF is calculated from the signal level y of the white signal and the signal level X of the black signal using the following formula.

MTF=(y-x/y+x)X100 (%) The filtered density signal is subjected to scaling processing such as enlargement and reduction in the scaling circuit 52.

The magnification processing is performed in the main scanning direction by data interpolation (including thinning) of density signals, and in the sub-scanning direction by controlling the moving speed of the scanner section 10A.

The scaled density signal is then subjected to a shading process in a shading circuit 54.

The shading process includes, for example, both the case of shading the outside of the image information as shown in FIG. 15A, and the case of shading the inside of the image information that has been cut out as shown in FIG. 15B.

In the shading process shown in FIG. 3A, it is sufficient to output shading data within a designated area and use the OR output of this and the density signal as a signal after shading.

The shading process shown in FIG. 3B can be performed by performing the process shown in FIG.

In addition to halftone dots, the rope can also have wave shapes, striped waves, etc.

The shaded density signal is roughly supplied to the PWM modulation circuit 60, and density No. 48 is PWM-modulated.

It is assumed that PWM modulation includes three-value or four-value multi-value processing. PWM modulation is a process performed to provide gradation for photographic images and resolution for character images.

In this case, the resolution is PWM in units of 1 pixel.
Although there is no interlayer when modulated, various experiments have confirmed that in the case of gradation reproduction, if one pixel is used as a unit, density unevenness occurs due to PWM modulation, and sufficient gradation cannot be obtained. It was done. Therefore, in this example, two pixels are set as a unit only during photographic image processing.

FIG. 16 shows an example of the PWM modulation circuit 60, and the terminal 6
The concentration signal supplied to the D/A converter 1 is once supplied to the D/A converter 62 and converted into an analog signal, and the analog concentration signal is guided to the modulation section 63.

On the other hand, a screen signal generating means 65 is provided, in which three screen signals S a = S c shown in FIGS. 17 and 18 are generated.

The screen signals S a = S c all have the same waveform and differ only in phase. First screen (=No.S
Based on a, the second screen (No. 3 Sb is 90
' out of phase, the third screen signal SC is 1800 out of phase.

These three screen signals S a = S c are supplied to the modulation section 63 . Then, modulation processing that emphasizes resolution is performed on the first and second screen signals Sa and Sb, and modulation processing that emphasizes gradation is performed on the first screen signal Sa and third screen signal Sc.

Starting from the former, analog density signals (image D/A output, Fig. 17,
G) are compared in level.

As a result, a comparison output Ca shown in the figure E is obtained between the first screen signal Sa and the density signal. Similarly, the second comparison output cb of H in the same figure is obtained from the second screen signal sb and the density signal.

When these are logically multiplied, the modulation output Sm as shown in Figure I is obtained.
is obtained. This is 1/1 of the first screen signal Sa.
This is equivalent to comparing the levels of analog density signals using a screen signal with a cycle of 2.

This 1/2 screen No. 55 is data clock DCK
Since the period is the same as (B in the same figure), a modulation signal Sm PWM-modulated in units of dots (pixels) can be obtained. Same figure A
indicates a digital density signal (image data).

Modulation processing when emphasis is placed on gradation is as follows.

A third comparison output Cc is generated from the first screen signal Sa used as a gradation screen signal and the analog density signal.
(Fig. 18E) is obtained. Similarly, a fourth comparison output Cd (H in the figure) is obtained from the third screen signal Sc and the density signal.

By logically multiplying these comparison outputs Cc and Cd, the modulation signal Sn shown in FIG. 1 is obtained.

Here, since the third screen signal Sc mentioned above is a signal obtained by inverting the phase of the first screen signal Sa and is obtained at the same timing, the comparison output Cc,
By ANDing Cd, the first screen signal Sa
This means that the levels of the analog image signals are compared in approximately one period unit.

In other words, the level comparison is performed in units of twice the period of the data clock DCK. By performing PWM modulation on the analog image signal at a two-dot period in this manner, it is possible to reproduce tone levels close to those of the input image.

One of these modulation signals Sm and Sn is selected by a selector 67, and the selected lever modulation signal Sm or Sn is supplied to the printer section 10C.

The selector 67 is manually or automatically controlled from the outside.

When the mode is manual, it is fixed to one of the modes (photo image/character image) set externally, and when it is automatic, it is selected according to the image information of the document.

Therefore, when automatic is selected, the above-mentioned color code can be used as the selection signal.

[Effects of the Invention] As described above, the present invention is characterized in that the color reproduction information conversion means and the PWM modulation means are provided in the color image expansion processing section.

According to this, in the color reproduction information conversion means, the color reproduction information is configured in such a way that even if the color systems of the scanner section and the printer section are different, this can be absorbed, so the color reproduction characteristics are significantly improved. improve.

Further, since a PWM modulation means is provided and modulation processing is performed while distinguishing character images and photographic images, color copying is possible without sacrificing either gradation characteristics or resolution characteristics.

From the above, the present invention can realize high-quality color copies.

Therefore, the image processing apparatus according to the present invention is extremely suitable for use in digital color copying machines, digital color printers, etc. as described above.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the entire image processing device according to the present invention, providing a general explanation of the image processing device, FIG. 2 is an explanatory diagram of color overlapping processing, FIG. 3 is a system diagram of the color conversion system, and FIG. 4 is a digital color system. FIG. 5 is a configuration diagram showing an example of a mechanical part of a copying machine. FIG. 5 is a configuration diagram of a spectroscopic system. FIG. 6 is a system diagram showing an example of a circuit system of a color image processing device. FIG. 7 is a system diagram of a shading correction circuit. , Figure 8 is a characteristic diagram showing the relationship between brightness level and density level, Figure 9 is a characteristic diagram showing gamma characteristics, Figure 10 is an explanatory diagram showing color reproduction, and Figure 11 is a color code and density diagram. FIG. 12 is an explanatory diagram of a histogram of codes corresponding to density; FIG. 13 is a diagram showing the relationship between image content and its discrimination result; FIG. 14 is an explanatory diagram of filtering processing; FIG. 15 is a diagram showing the shading mode, the first
FIG. 6 is a system diagram of the PW modulation circuit, and FIGS. 17 and 18 are waveform diagrams for explaining its operation, respectively. 8... Density adjustment circuit 10... Color image processing device 10A... Scanner section 10B... Image processing section 10C... Printer sections 11-13... Standard density conversion circuits 15-17... Adjustment density conversion circuit 20... Color image processing means (color reproduction information conversion means) 21-24... Conversion ROM 25... Monochrome image processing means 27... Automatic density FA adjustment circuit 30... Color code Generating means 32... Selector 40φ and color ghost correction circuit 50... Filtering processing circuit 52... Magnification changing circuit 54... Shading circuit 60... PWM modulation circuit Rolling transfer method scanner section Spectroscopic system Fig. 5 5 = Schematic correction circuit Fig. 7 Zero book Lab Color gamut in space Fig. 1O

Claims (1)

[Claims] (1) A scanner unit that reads image information of a color original, a color image processing unit that processes the obtained color image information, and a printer unit that records a color original based on the signal output from the color image processing unit. The color image processing section includes a conversion means that stores color reproduction information for matching the image signal output from the scanner section with the output characteristics of the printer section, and PWM modulates the output of the conversion means. An image processing apparatus characterized in that it is provided with a PWM modulation means for imparting gradation characteristics.