JPH02296264A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms output dots with a time width corresponding to pixel density.

[Prior Art] Conventionally, in this type of apparatus, a dot latent image is formed on a photosensitive tram by irradiating a laser beam with a time width corresponding to the pixel density.

[Problems to be Solved by the Invention] However, in the conventional example described above, since a modulation method in which each color has the same phase at the beginning of the screen is not used, when a multicolor screen is formed, different colors overlap on the playback screen. However, there was a drawback that the colors were different.

The present invention has been devised in view of the above points, and is intended to enable high-quality reproduced images to be obtained.

[Means and effects for solving the problem] According to the present invention, a predetermined gradation conversion table is selected based on an image leading edge signal representing the leading edge of an image, and a pattern signal forming a pulse width modulation signal is A high-quality gradation image is reproduced by generating the gradation image at a phase of .

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Description of Mechanical Section> FIG. 11 is a sectional view of the mechanical section of the digital color reader printer of the embodiment. The reader/printer 80 includes a reader unit 100 that separates and reads a color original image, and a printer unit that creates a color reproduction image (copy image) of the original image or a printing original plate separated into each color version (color separation image). It consists of 2000.

In the reader section 100, a document scanning unit 83 performs sub-scanning in the six directions of arrows with an exposure lamp 85 turned on in order to read a document 84 placed on a document table. The reflected light from the original 84 is guided by a focusing rod lens array 86 and focused onto a contact type color CCD sensor section 87 . This CCD sensor chip has a resolution of 16pe, for example.
1 (62.5 um) and consists of 1024 pixels. There are five sensor chips in total, which are arranged in a staggered manner in the main scanning direction.

Furthermore, each pixel of the sensor chip is 15.5μm x 62.5μm.
It is divided into three areas of m, and each area has cyan (C).
, green (G), and yellow (Y) color filters are attached. In this way, the optical image focused on this CCD sensor section 87 is converted into C, G, and Y electrical signals.
The signal is sent to signal processing block 88 . Signal processing block 8
8, these C, G, Y electric signals are yellow (Y),
The data is converted into magenta (M), cyan (C), and black (BK) digital video data, and sent to the printer unit 200 for each color.
Send to 0.

In the printer unit 2000, the input video data is processed as is, or after halftone processing, and in some cases, a font pattern is synthesized on a part of it, and then the density=
Pulse width (PWM) modulated. This PWM modulated 2
The value signal drives the laser beam ON10FF.

This laser beam is converted into a high-speed horizontal (main) scanning beam by a polygon mirror 2289 rotating at high speed. This main scanning beam is further reflected by a mirror 2290 to expose dots corresponding to video data on the surface of the photosensitive drum 290o. At this time, one main scanning length of the laser beam corresponds to one main scanning length of video data, that is, the beam dots in the embodiment have a resolution of 16 pels.

On the other hand, the photosensitive drum 2900 is rotating at a constant speed in the direction of arrow B. Also, this photosensitive drum is equipped with a charger 2297 in advance.
Uniform charging is performed. By exposing the surface of this -like charged photoreceptor to a beam dot of video data, an electrostatic latent image of each color separation plate is formed. For example, electrostatic latent images are formed in the order of color plates Y, MQ, C, and BK each time the drum rotates once. The electrostatic latent image of each color plate is produced by a corresponding developing machine 22.
92 to 2295, and further transferred to the transfer drum 22.
96 and onto the wound transfer material (paper, etc.).

The above description corresponds to the original exposure scan of the league unit 10001. First, a Y component dot image is exposed on the photosensitive drum, developed by a Y developing device, and transferred to a transfer material.

Next, a dot image of the M component is exposed on the photosensitive drum, developed by an M developing machine, and transferred to a transfer material. Thereafter, exposure, development, and transfer of the C component and BK acid component are performed in the same manner.

Although not shown, the supply and operation of the transfer material are controlled at that time. That is, each color version data is superimposed on the same transfer paper and color composited to obtain a normal color copy. Alternatively, change the transfer material for each color plate, and change the number of color separations (Y, M
, C, BK, etc.) to create a color printing original plate.

Although not shown, in the latter case, the color to be developed is further controlled. That is, each color plate data is divided into corresponding Y, M
, C, and BK, but instead, each color plate data may be developed in one of Y, MC, and BK (for example, BK).
It is also possible to develop only with I color). This makes it easy to compare and evaluate each original plate, and the color when printing in color is determined by the printing ink. Also, from this point of view, although the printer mechanism section in this embodiment is a color printer, it may be replaced with a normal BKI color printer mechanism section.

<Description of functional blocks> Figures 1 (A) and (B) show the digital color
Regarding the functional block diagram of the reader/printer, Figure 1 (A
) is a functional block diagram of the reader section 100, and FIG. 1(B) is a functional block diagram of the printer section 2000.

In FIG. 1(A), reference numeral 10 denotes a control section, which performs main control of the reader section 100. As shown in FIG. The control unit 10 is CPtJlo-1
, a ROM10-2 which stores the control program shown in FIG. 12, executed by the CPU10-1, and a CPU1
0-1 includes RAM10-3 used as a work memory.

That is, the control unit IO controls the rotation of the motor 12 via the motor driver 13, and causes the document scanning unit 83 to read and scan the document image. Also, at that time, the constant voltage control circuit (C
The lighting of the exposure lamp 85 is controlled via VR. It also receives and receives print (start) command signals and other key operation signals from the operation unit 16, and sets various print operation modes. For example, the operation unit 16 is equipped with a print mode setting switch (not shown), and the control unit 10 uses this command to set the high resolution and halftone mode for characters, line drawings, etc. in the case of an expression mode command, for example. The operation mode is set so that photographic images are printed with high gradation.

Or, when issuing a copy mode command, each color separation signal is
The operation mode is set so that color composition is performed on a number of sheets of transfer paper, and when an original plate production mode command is issued, each color plate is formed on the number of transfer sheets corresponding to the number of color separations. There are various other directives. The control section 10 then transmits this print operation mode to the printer section 2o00 via the communication line 24.

1 is a synchronization signal processing unit, whose main function is to generate various timing signals on the reader side in synchronization with the BD signal (printer horizontal synchronization signal) sent from the printer unit 2000 via line 22. It's about doing. 2
is a close-contact color CD sensor (87), which receives the reader horizontal synchronization signal (RH8YNC) from the synchronization signal processing section 1.
A document image is read in synchronization with a signal), etc., and the read image signal 5 is output. The read image signal 5 is output for each pixel in the order of, for example, a C signal, a C signal, and a Y signal. In addition, in this embodiment, since the CCD sensor consists of 5 chips, there are actually 5 chips.
Signals for channels are generated simultaneously. A signal processing section 3 performs waveform shaping processing such as edge enhancement to prevent attenuation of high frequency components of the read image signal 5, for example.

6 is an image processing section, and the image processing section 6 includes an analog processing section 7, a connection memory 8, and an image processing unit ('
IPU). The analog processing section 7 first separates the C, G, and Y signals for each pixel into C, C, and Y signals for each color.

Next, from the separated C, G, and Y signals, the red (R
), green (G), and blue (B) color signals. This formation is performed by the calculation process of (R)=(Y)-(G)(G)=(G)(B)=(C)-(G). The R and GB signals thus obtained are luminance signals, and their relationship with the output voltage is linear. This is further converted into concentration (LOG), and A
/D converter converts each 8-bit Y, M, and C concentration data (
image data). This Y, M, C image data includes five channels of C and CD chips, and synchronization between each channel is not achieved. The connection memory 8 stores Y, M, and C image data for five channels so that they are all available. That is, 1024×5 pixels arranged in a staggered manner in the main scanning direction are stored so as to form substantially one straight line. Thereafter, the Y, M, and C image data in the connection memory 8 are stored in the control unit 1.
A desired color signal is selected by o and sent to the image processing unit (PU) 9 for each color. The IPU 9 performs, for example, shading correction processing to correct light distribution, masking processing to correct color tone, and the like. The video data of 8 bits per pixel as a result of the processing is sent via the signal line 11!
It is sent from the PU 9 to the printer section 2000.

In FIG. 1(B), a control section 2500 performs main control of the printer section 2000. The control section 2500
PU 2110, ROM 2502 that stores control programs executed by the CPU 2110, such as those shown in FIGS. It includes an A/D converter 2503 and the like that converts the detection signal into a digital signal. As a result, the control unit 2500 first controls the rotation of the drive morph 2285 to rotate the photosensitive drum 2900, transfer drum 2296, etc. at a constant speed. Further, the electric potential, the amount of charge on the surface of the photoreceptor drum 2900 detected by the sensor 2600, is A/D converted via the electric potential measurement unit 2700, and is taken in.

Furthermore, the image leading edge signal (IT
OP). In addition, signals such as humidity and temperature detected by other humidity sensor 2298 and temperature sensor 2299 are A/D converted and taken in, and are used for control such as correcting the development characteristics of the printer. In addition, the control unit 2500
4, various information is exchanged with the control section 10 of the league club.

2160 is a gradation control circuit whose main function is to synchronize the image clock signal (RCLK) of the reader section 100 and the image clock signal (VCLK) of the printer section 2000, and also to control the input signal as necessary. Performing halftone processing on video data, converting input video data or video data after halftone processing according to the image output mode, and converting the gradation-converted video data into its density by PWM modulation. For example, converting the data into a corresponding binary signal. 2'200 is a laser driver, which drives the beam of the semiconductor laser 2223, for example, 0N10FF according to the PWM signal from the gradation control circuit 2160.

FIG. 2 is a block diagram showing details of the gradation control circuit of the embodiment. In the figure, one side of the input video data is a lookup table (LUT (1)) for halftone processing.
210.1 is input and converted into video data for cocote halftone processing. LUT (1) in this embodiment is composed of ROM or RAM. The L'UT (1) is configured to obtain a desired halftone effect when the video data halftone-formed through the next-stage halftone processing circuit 2102 is outputted by an electrophotographic process. This is a conversion table for converting input video data in advance. Details will be described later. A halftone processing circuit 2102 performs halftone processing, which will be described later, on the video data for halftone processing output from LUT (1). For example, dividing image data into predetermined areas and concentrating the pixel density within the area to the density at the central pixel position;
It is converted into representative halftone video data and inputted to the A-side terminal of the selector 2103.

The other side of the input video data is input to the B side terminal of the selector 2103 in case halftone processing is not performed.

The selector 2103 selects and outputs either the post-halftone video data or the pre-halftone video data according to a select signal 2123 from the CPU 2210. For example, in a mode for creating a printing original, preferably halftone video data is selectively output. Furthermore, when outputting a normal color copy, it is possible to select both post-halftone video data and pre-halftone video data. In short, various printing modes are possible, and various combinations of signal processing occur with each processing circuit described below according to these printing modes.

Next, the video data selected by the selector 2103 is input to the A side terminal of the selector 2104. Also selector 2
Font data from the font ROM 2108 is input to the B side terminal of 104 . This font data is used to synthesize (insert) a font pattern of characters or symbols into the selected portion of the video data.

As will be described later, the CPU 2110 sets the font coat and the address at which it is to be synthesized, so that a desired font pattern can be synthesized at one or several locations in the image data of each color plate.

The 8-bit video data output from the selector 2104 is input to a buffer memory (FIFO) 2105 in synchronization with the RH3YNC signal and RCLK signal from the reader section 100. This stored video data is then sent to the horizontal synchronization signal (H3YN) from the printer side synchronization control circuit 2113.
C signal) and the video clock signal (VCLK signal). Thereby, speed matching between the league section 100 and the printer section 2000 is achieved.

The video data read from the buffer memory 2105 is stored in a look-up table (LUT) for printer characteristic correction.
(,2)) Input in 2106.

L'UT (2) has been corrected in advance to match the input video data to the printer's output characteristics (e.g. beam spot diameter, toner particle diameter, etc.) (to increase the gradation of the output density and make it linear). This is for creating video data. Details will be described later with reference to FIGS. 8(A) to 8(D).

LUT (2) Output video data is sent to the D/A converter 21
07, where it is converted into an analog video signal that changes in steps, and then sent to comparators 2117 and 211.
Input to one terminal of each of 8. Pattern signals (1) and (2) for binarizing (PWM modulation) the analog video signal according to its density are input to the other terminals of the comparators 2117 and 2118, respectively. The bang signal (1) is for reproducing or generating, for example, a line image or a halftone image, and in this case, the resolution is an issue, so for example
00 line) pattern signal] 9. That is, l pattern signals are generated per pixel. The pattern signal (2) is, for example, for reproducing a halftone image, and in this case, it is necessary to increase the gradation, so the pattern signal (2) is, for example, 1/2 the frequency of the line drawing pattern signal (for example, 200 lines). The pattern signal is such that In other words, one pattern signal is generated for every two pixels.

To explain according to the circuit, the crystal oscillator (XTAL) 21
Reference numeral 12 generates a clock signal having a frequency four times higher than that of the image clock signal. The synchronization control circuit 2113
The main scanning synchronization signal () (SYNC) is synchronized with the TOP signal.
signal) and a basic clock signal (SCLK signal). The frequency dividing circuit 2114 divides the frequency of the 5CLK signal to generate pattern generation clock signals (TVCLK signal and PVCLK signal). This TVCLK signal has, for example, twice the frequency of the video data signal and is a clock signal with a duty ratio of 50%.

A count signal is sent from the synchronization control circuit 2113 to the data selector 2201. This count signal represents a count value of a counter circuit 2132, which will be described later, and this count value determines the table used by LUT (2) and the phase of the pattern generation clock signal.

Further, the data selector 22o1 receives a control signal C from the CPU.
Data CP sent from CPU by PU-5EL
A selector 2131, which will be described later, selects either U-data or a count signal from the counter circuit 2132.
and sends it to LUT (2). Pattern generation circuit 21
15 generates an analog pattern signal (1) according to this TVCLK signal. In this embodiment, a triangular wave signal is used, for example. The comparator 2117 compares the analog video signal and the pattern signal (1) and outputs a PWM signal (1) obtained by pulse width modulating (PWM modulating) the video density.

Further, the PVCLK signal has a frequency 1/2 (or 2/3, etc.) times that of the video data signal, and is a clock signal with a duty ratio of 50%. The pattern generation circuit 2116 uses this PV
An analog pattern signal (2) is generated according to the CLK signal. In this embodiment, for example, this is also a triangular wave signal. Comparator 2118 compares the analog video signal and pattern signal (2) and outputs a PWM signal (2) in which the video density is pulse width modulated.

The selector 2119 selects and outputs the PWM signal (1) of the A-side terminal in accordance with the control signal from the CPU 2110, for example, when a line drawing original is to be reproduced or halftone processing is to be output, and when a halftone image is to be reproduced, the PWM signal (1) of the B-side terminal is output. Terminal PWM signal (2)
Select and output.

Note that this selection is also free, and various combinations with other processing circuits can be considered.

Although not shown, this switching signal is not a switching signal from the CPU 2110, but is a known image area signal that identifies, for example, whether each pixel of a video signal belongs to a line drawing area or a halftone image area. A separation means may be provided and this image area separation may be used as a switching signal. In this way, even within one image, a faithful and high-quality image corresponding to the image tone of the original can be obtained. In this way, the selected PWM signal (1) or (
2) is further matched with the movement of the transfer material by the gate circuit 2120, and input to the laser driver 2200, which drives the semiconductor laser 2223 at a constant current for a time corresponding to the pulse width of the PWM signal, and drum 290
Forms an electrostatic latent image on the 0 surface.

FIG. 3(A) is a timing chart of main signals in the printer section. The figure shows examples of a horizontal synchronization signal BD, a blanking signal, a reference clock signal 5CLK, a pattern generation clock signal TVCLK, PVCLK, a video clock signal VCLK, etc.

FIG. 3(B) is a block configuration diagram showing details of the synchronous control circuit section. In the figure, a crystal oscillator 2112' causes a synchronization circuit 2128 to generate a clock signal having a frequency four times higher than that of the image clock signal. The synchronization circuit 2128 outputs the H3YNC signal, the VCLK signal, and the 5CLK signal at timing synchronized with the external BD double signal ITOP signal. The frequency dividing circuit 2114 inputs a 5CLK signal, and a TVCLK signal with the same period as the VCLK signal and a duty ratio of 50%, and a TVCLK signal twice (or three times, etc.) the VCLK signal.
A PVCLK signal with a cycle and a duty ratio of 50% is output. Although not shown, the blanking signal is formed by a counter that measures a time shorter than the BD signal period, which is reset at the fall of the BD double signal.

Here, the PVCLK= signal in FIG. 3(A) will be explained. This PVCLK' signal is useful when performing screen angle control on video data without halftone processing (during normal halftone image reproduction). This P
VCLK'' signal is a clock signal that has a phase delay of, for example, 1.5 pixels from the H3YNG signal.Comparing this with the normal phase PVCLK signal, it is delayed by one pixel.In this embodiment, for example, normal halftone During image playback, the PVCLK signal and PVCLK are
'The signal is switched and used every line or every few lines in the sub-scanning direction. For example, if you switch every line, 4
This means that the screen angle is controlled by 5 degrees.

In FIG. 3(B), the H3YNC signal is input to the shift register 21.30 and is shifted by the 5CLK signal. The output of each stage of the shift register 2130 is connected to the input terminal of the selector 2131. On the other hand, after the counter circuit 2132 is reset by the ITOP signal, count program information is set in advance by the CPU 2110. Count program information is, for example, repeating 2 or 65 as a count value output, or 1
This is count sequence information such as repeating 5 or 66 as a count value output. Counter circuit 2132 counts H3YNC signals according to this information. For example, each time the H3YNC signal is generated, this count value is input to the selection terminal of the damper 2131. On the other hand, when the count value is 3, the selector 2131 selects and outputs the signal from the input terminal 3, and when the count value is 4, the selector 2131 selects and outputs the signal from the input terminal 4.
select and output the signal. The output of the selector 2131 is input to the frequency division start terminal of the frequency divider circuit 2114. On the other hand, the frequency dividing circuit 2114 has been reset in advance by the H3YNC signal and has stopped its counting function. When a signal from the selector 21.31 is input manually, the production starts from that point onwards. In this way, it is possible to generate PVCLK signals and TVCLK signals having different phases for each line.

Regarding the relationship with the screen angle, when we define the screen angle θ as θ-jan-'b/a, the value of a is determined by the count value of the counter circuit 2132, and the value of b is determined by the count sequence. . These are values that can be freely set by the CPU 2110.

LUT for converting video data characteristics (2) 2106
Table switching within is also performed in the same way as screen angle control. LUT (2) contains multiple types of conversion tables for each color. For example, when reproducing video data for yellow, multiple types of conversion tables for yellow are used alternately for each line. It is something to do. In addition,
The contents (characteristics) of the conversion table will be described later.

Switching of the conversion table is performed by the count value of the counter circuit 2132 in the same way as the phase switching of the pattern generation clock signal. A count signal from the counter circuit 2132 is input to LLIT (2) via the data selector 2201 as a table switching signal. LUT
In (2), a table switching signal and video data are manually input as address signals, a conversion table is selected based on the table switching signal, and video data whose characteristics have been converted is output.

Next, referring to FIG. 14, the conversion table selection operation and pattern generation clock signal phase switching operation of this embodiment will be explained.

FIG. 14 is a detailed diagram of the data selector 2201, and this data selector 2201 is connected to the CPU 211.
It is possible to operate in two types of image output modes by the command CPU-5EL of 0. The first image output mode is a 1,000-code mode in which only one type of conversion table is used, which is common to each color, and the phase of the clock signal for bang generation (the phase of the triangular wave) is the same for each line.

When the first image output mode is designated from the operation unit 16,
The CPU 2110 receives the control signal CPU-5EL1. CPU-
5EL2 respectively multiplexer 2201-2.22
01-4, multiplexer 2201-2 sends it to CP
The multiplexer 2201 controls to select the data CPLI-4atal sent from U110.
-4 is the data sent from the CPU 2210 CPU-d
Control is performed to select ata2. Data CPU-
datal and CPU-data2 are selected by selector 2131.data to fix the phase of the conversion table and pattern generation clock signal to be used, respectively, during one screen. , LUT (
2) Sent to 2106;

Next, the second image output mode will be explained.

In the second image output mode, data sent from the CPU 2110 CPU - data a 1 + 'CP
U-data2 is not used, adder 2201-1.22
The output of 01-3 is used.

When the second image output mode is designated from the operation unit 16,
The CPU 2110 receives control signals CPU-3EL1 and CPLI.
-SEL2 to multiplexer 2201-2.2 respectively
201-4, multiplexer 2201-2 controls to select data sent from adder 2201-1, and multiplexer 2201-4 selects data sent from adder 2201-3. control. Adder 2201-1 is a counter circuit 2132
The count value and data C sent from the CPU 2110
PU-data3 is added and the addition result is sent to multiplexer 2201-2. Similarly, adder 2201-3 adds the count value of counter circuit 2132 and data CPU-data4 sent from CPU 2110, and sends the addition result to multiplexer 2201-4.

Here, the data sent from CF'U2110 CPU-
dat'a3. If the value of CPU-data4 is set to 0° every time the ITOP signal is input manually, the type of conversion table used for each color image and the phase of the triangular wave can be made the same from the top position of the image, so the playback screen It is possible to prevent the inconvenience that the color tone is different on the top.Also, by changing the type of table or the phase of the triangular wave from the top position of the image for each color, for example, it is possible to reproduce a color image that emphasizes a specific color. For example, if you want to make magenta stronger in the playback screen, you can
In synchronization with the TOP signal, data CPU-data3. C.P.
The value of U-data4 is set to a specific value other than "0°", and for colors other than magenta, the values of data CPLI-data3 and CPU-data4 are set to "o" in synchronization with the ITOP signal. As a result, the phases of magenta and other colors are different in the playback screen, and it is possible to prevent the output part of magenta from overlapping with parts of other dark colors.An example of the image output in this case is shown in Fig. 15. .

In this way, the data CPU-dat is synchronized with the ITOP signal.
a3. By setting CPU-data4 to an appropriate value, the color tone of the reproduced image can be controlled. Note that the data CPU-data3. CPU-, dat
The value of a4 is determined by the CPU 2 based on the command from the operation unit 16.
+10 is what is set.

Similarly, data C sent directly from the CPU 2110
By changing the values of PU-data and CPU-data2 for each color, it is possible to intensify a particular color or change the tint of the reproduced image.

[Description of halftone processing] The halftone processing described below includes halftone processing of the density of image data divided into predetermined areas (for example, concentration of pixel density at the center pixel position, representation) and optimization. Screen angle control all at once in real time 8-C First, look up table (LUT) for halftone correction
The details of 1)) will be explained.

FIG. 7 is a diagram illustrating the conversion characteristics of LUT (1) of the embodiment. In the figure, there is a linear relationship between the Y, M, and C video data input to the printer section and the ink (or toner) density. However, when halftone processing, which will be described later, is performed, a linear relationship cannot be maintained. Therefore, density correction is applied to the input Y, M, and C video data in advance. The first quadrant of the figure shows the relationship between the corrected injection input level and the ink density, which is a linear relationship. The ink density on the vertical axis is the ink density when printing was performed using the color separation plates output by the apparatus of this embodiment. The second quadrant shows the relationship between ink density and halftone output density level. The third quadrant shows the relationship between the halftone output density level and the corrected input level. The fourth quadrant shows the relationship between the corrected input degree level and the corrected previous input level, which gives the conversion characteristics of LUT (1).

Incidentally, if the color separation plates of the embodiment can form ideal halftone dots, the halftone dot output density of the third quadrant 1 and the fourth quadrant may be set as the halftone dot density (%).

Actual table information is obtained, for example, by actual measurement. For example, the corrected radiation input level e. When obtaining the ink density , calculate the halftone output density dn that will give the ink density DL1. Next, the corrected input level E, . . . that will give the halftone output density dn is determined. As a result, LOT (1) is the corrected injection input level e. It is sufficient to create the corrected output level En for the corrected output level En. In this way, the input level OO
All conversion levels corresponding to H to FFH are determined.

When this conversion characteristic differs for each color, LOT(
1) is also created for each color.

FIGS. 4(A) to 4(D) are diagrams for explaining the halftone processing pattern of the embodiment, and FIG. 4(A) shows an example for C data. In the figure, 500 is one pixel, and each pixel is shown as an array from the starting address (0, O) of data for one image. 600 is a basic cell, which halftones the density within the bold line area (within a predetermined area) in the figure (concentrates and represents the pixel density to, for example, the density at the center pixel position)
This is a block unit for A basic cell of C data consists of, for example, 13 pixels. The numbers (1 to 13) attached to each pixel in the basic cell indicate the priority order.
The priority becomes lower towards 3. For data of the same color, the same priority is given to other basic cells.

It should be noted that the priority order shown in the figure is an example of matching the blink characteristics of the embodiment, and is not limited thereto. Various other modifications are also possible.

Halftone processing of pixel density within a basic cell is performed according to the following equation (halftone calculation formula).

That is, (attention pixel output data) = (attention pixel input data) × (number of pixels in basic cell) - (priority - 1) This is performed by sequentially moving the pixel of interest in the main scanning and sub-scanning directions. For example, when the pixel of interest is at the priority level 11, (output density) = (input density) x 13 - (11-1)XFFH. Since the priority is low, month 1, the subtracted density ((priority - 1)XFFH) becomes large, and the density at this pixel position is relatively lowered.

Also, as a result, when (output density) <o, the output density is clamped to OOH". Conversely, (output density) > FF
At H2, the output concentration is clamped to "F F H".

Similarly, when the pixel of interest is located at the priority level 1, (output density) = (input density) x 13 - (1-1) x FFH. Since the priority is 1, the density to be subtracted is zero. In this way, the pixel density is concentrated toward the central pixel position within the basic cell and represented. The printing original plate formed with halftone dots in this way has good ink adhesion and is stable.

A matrix 700 indicates a block unit in which the illustrated halftone processing pattern is repeatedly used in the main scanning and sub-scanning directions. The matrix size of the C data is, for example, (13×13) pixels. As is clear from the figure, document images of any size can be processed by connecting a plurality of these matrices in the main scanning and sub-scanning directions. In this embodiment, this periodicity is utilized to store this matrix pattern in a memory, repeat the pattern, and use it in real time to save pattern memory and enable high-speed calculation.

Further, the triangles in the figure are for indicating the screen angle θ, and this screen angle θ represents the inclination of the arrangement of the basic cells 600. In the figure, when a and b are determined,
The screen angle θ is determined by θ=jan−′b/a. For example, the screen angle of C data is θ=5
6.3° is given.

FIG. 4(B) shows an example of a halftone processing pattern for M data. In the figure, a basic cell 600 consists of 13 pixels and has the same shape as in FIG. 4(A). Further, the screen angle is given as θ=33.7°. By the way, when comparing FIG. 4(B) with FIG. 4(A), the basic cell 600 of M data starts from address (0,0) (
phase angle) are different. For this reason, the center pixel positions of both do not overlap. That is, the main concentration information does not overlap.

As a result, neither C ink nor M ink is crushed during printing, and high quality and stable printing can be achieved.

FIG. 4(C) shows an example of a halftone processing pattern for BK data. Note that the BK data is generated from the C and MY data using a known method. In the figure, a basic cell 600 consists of 10 pixels, and its shape is also different from that in FIGS. 4(A) and 4(B). Although not limited to this shape, it is suitable for providing a screen angle of θ=71.6°, for example. Furthermore, the phase angle from address (0,0) is also different.

FIG. 4(D) shows an example of a halftone processing pattern for Y data. In the figure, a basic cell 600 consists of 10 pixels, and is suitable for providing a screen angle of θ=18.4°, for example, although the shape is not limited to this. Furthermore, the phase angle from address (0,0) is also different.

FIG. 5 is a block diagram of the halftone processing circuit according to the embodiment. In the figure, the halftone video data output from LUT (1) is latched into a D-type flip-flop (D-F/F) 2301 in synchronization with the RVCLK signal. on the other hand,
Counter 2304 counts the RVCLK signal after being reset by the RH3YNC signal. That is, Fig. 4 (A
) to (D) are formed in the main scanning direction. Further, after the counter 2305 is reset by the ITOP signal, the counter 2305
Count 3YNC signals. That is, Fig. 4(A) to (
D) form the sub-scanning direction address.

Although not shown, count initialization data corresponding to the processing color is set in the counters 2304 and 2305 by the CPU 2110, and each counter repeats a counting operation with a count value corresponding to the initialization data. For example, when processing C data or M data, the count value O~
Repeat with 12. Further, when processing BK data or Y data, it is repeated with count values 0 to 9, respectively.

2306 is a pattern memory;
) halftone processing patterns (priority order data) are stored. In this way, the color selection signal (Y
, M, C, BK), and as main and sub-scanning progresses, the priority data of any one of the matrices shown in FIGS. 4(A) to 4(D) is sequentially read out. A table memory 2302 receives input data of the pixel of interest and priority data corresponding thereto, and outputs output data of the pixel of interest according to the above halftone calculation formula. At this time, in the same manner as described above, the table for the case where the number of pixels in the basic cell is 10 or 13 is used according to the color selection signal from the CPU 2110. The output signal of the pixel of interest read out in this way is D -F/F 2 in synchronization with the RVCLK signal.
303 and output to the next stage circuit.

Note that the memories 2302 and 2306 mentioned above may be ROM or RAM. Furthermore, instead of employing a look-up table method using memory, a hardware arithmetic circuit may be used.

FIG. 6(A) is a diagram showing an example of screen angle distribution in the embodiment, FIG. 6(B) is a diagram showing an example of screen angle distribution used in the conventional printing field, and FIG. 6(C) to (H) is a diagram showing an example of moire fringes.

In the field of printing technology, for example (13×13) pieces of fiberglass can be bundled, so it is easy to maintain the distributed screen angle accurately during printing. on the other hand,
Since a laser beam printer is used in this embodiment, rotational unevenness of the polygon mirror 2289 and the photosensitive drum 2900 must be taken into consideration. In other words, the combination of both rotational unevenness causes unevenness in the amount of laser irradiation per hour, and this irradiation unevenness affects the formation of a latent image on the photoreceptor drum and even the development of the image, which causes shading in the output image. This appears as unevenness (pitch unevenness).

This pitch unevenness is considered to be a high frequency component having an angle of Oo or 90° when considered in relation to an image subjected to halftone processing. Generally, moiré appears in color plates with a small angular difference from pitch unevenness. For this reason, if an image is formed at the same angle as in the printing method, the M and C components will be easily visible as moiré due to pitch unevenness.

This is equivalent to the "moiré by line screen + halftone dots" shown in FIG. 6(H). Therefore, in this embodiment, the Y component, which is inconspicuous with respect to the relative luminous efficiency, is set at a screen angle close to OO to make the moiré visible. Although BK is originally a color that is easy to see, the data of the BK acid component in this example, although not shown, is corrected so that the lowest value of each color component does not have a lower density area as the density in the league part lOO. There is. Therefore, as described above, pitch unevenness is due to unevenness in light intensity, so it has a characteristic that light density is easier to see than high density. Therefore, pitch unevenness and moire are difficult to see in black even when the angle is close to 0° or 90°.

8(A) to (D) are L for the printer output characteristics of the embodiment.
It is a figure explaining the conversion characteristic of UT (2). The printer output image needs to have linear characteristics between the input data level and the printer output density in accordance with the characteristics of the printer used. By the way, for example, if the toner particle diameter is not sufficiently small compared to the beam spot diameter, even if the output beam has 256 gradations, the toner particles will be at a maximum of 32 gradations.
There are cases where only one item is attached. This is inconvenient because only 32 gradations can actually be expressed. Therefore, if we set an area of (2 x 2) dots as a unit of printer output, or (n
Linear gradation expression up to 6 gradations is possible.

When doing this, in the main scanning direction, for example, image data for m pixels may be subjected to PWM conversion using a pattern signal (triangular wave) having a period m times the pixel period. By the way, it is desired to obtain the same effect as in the main scanning for n lines in the sub-scanning direction as well.

However, the same effect cannot be obtained by repeating the same main scan in the sub-scanning direction as in this embodiment. Therefore, in the sub-scanning direction, multiple types of gradation conversion tables are provided.
By switching and using the table in a predetermined sequence, the same effect as in the main scanning direction can be obtained.

LUT (2) is a table for this purpose, and takes into consideration the overall output characteristics of the laser beam printer of the embodiment. The output characteristics of a laser beam printer include the relationship between the beam pulse width and the photosensitive drum surface potential (EV characteristics) and the relationship between the photosensitive drum surface potential and output image density (VD characteristics).
is possible. Since the former EV characteristic has a substantially linear characteristic, it will be explained here as a table for correcting the latter VD characteristic. This VD characteristic determines whether or not to perform halftone processing on image data, or whether to perform PWM modulation signal (pattern signal).
The characteristics vary depending on the frequency and the developer used. For this reason, in this embodiment, a plurality of tables are prepared in advance according to the VD characteristics, and the CPU 21
10 will select and use it.

Here, the case will be explained in which 'halftone processing' is not performed and the pattern signal frequency to the comparator is 1/2 or 1/3 of the video signal frequency.

FIG. 8(A) is a diagram showing the VD characteristics of the example. In the figure, the drum surface potential on the horizontal axis indicates the difference potential (contrast potential) between the surface potential of the photosensitive drum and the developing bias potential. FIG. 8(B) is a diagram showing an example of a characteristic for linearly converting the VD characteristics in FIGS. 8 and 8(A). That is,
This objective can be achieved by replacing the horizontal and vertical axes in FIG. 8(A), resulting in the characteristic table shown in FIG. 8(B). However, in this example, the gradation of the output image (especially the gradation of the highlight part) is further improved by 173 times,
Also, in the sub-scanning direction, l is scanned at intervals of 2 lines, 3 lines, etc.
By switching the conversion table for each line or every few lines, linearization of gradation and concentration of halftone dots are achieved.

FIG. 8(C) is a diagram showing correction table characteristics of an embodiment used when the pattern signal frequency is 1/2 of the video signal frequency. In the figure, the table of characteristic ■ shows that the output level initially rises at a slope twice that of the curve in Figure 8 (B) until it reaches level F F H, and then the input level rises to F F H.
It remains constant until FH. In addition, the table of characteristic ■ maintains level OOH until the table output of characteristic ■ reaches level F F H, and after that it rises to level F F H at twice the slope of the turnip in Figure 8 (B). It was created in . In this example, the pattern signal frequency is 1/2
Therefore, one output density dot is formed by two pixels of the video signal. On the other hand, in the sub-scanning direction as well, the tables ``■'' and ``■'' in the figure are switched and used every 1 lines with a period of 2 lines. By doing this, you can darken the ■ table and ■
Lighten the table. As a result, the effect of forming one output density dot in two lines in the sub-scanning direction is obtained.

Note that the table characteristics are not limited to those of ■ and ■.

FIG. 8(D) is a diagram showing correction table characteristics of an embodiment used when the pattern signal frequency is 1/3 of the video signal frequency. Incidentally, the above-mentioned characteristic <VD depends on the pattern signal frequency.

However, for convenience of explanation, the same VD characteristics will be used for explanation here. In the figure, the table of characteristic (1) initially rises at a slope three times that of the curve in FIG. 8(B) until it reaches level FFH, and thereafter remains constant until the input level reaches FFH. Further, the table of characteristic (2) maintains level OOH until the table output of characteristic (2) reaches level FFH, and thereafter rises to level FFH at a slope 1.5 times that of the curve in FIG. 8(B). In this example, since the pattern signal frequency is 1/3, one output density dot is formed by three pixels of the video signal.

On the other hand, in the sub-scanning direction as well, the tables ``■'' and ``■'' in the figure are switched every line at a period of three lines. For example ■
Switch like -■-■.

This provides the effect of adding shading to each output line and forming output density dots in three lines in the sub-scanning direction.

Note that the table characteristics are not limited to those of ■ and ■.

Incidentally, since the V'D characteristics actually differ depending on the pattern signal frequency, the tables shown in FIGS. 8(C) and 8(D) are created by combining the different VD characteristics. In addition, when creating the above table, the pattern signal frequency is 1 of the video signal frequency.
/2.It is not limited to the case of 1/3. It can be created in the same manner for other frequencies.

FIG. 9 is a block diagram showing details of the font control circuit of the embodiment. CPU2110 is font ROM21
Data is given to the terminal S of 08, and the font to be printed is selected. Also, main scanning address data to be printed is latched in a latch circuit 2142, and sub-scanning address data is latched in a latch circuit 2148. The address data of the latch circuit 2142 is the Q of the comparator 2141.
The address data of the latch circuit 2148 is input to the Q terminal of the comparator 2147. Meanwhile, the counter 2140 is reset by the RHSYNC signal and the RV
Count CLK signals. That is, the number of pixels in the main scanning direction is counted.

Further, the counter 2146 is reset by the ITOP signal,
Count the RH3YNC signal. That is, the number of lines in the sub-scanning direction is counted.

The number of pixels of the counter 2140 is determined by the comparator 214.
1, and the comparator 2141 is input to the P terminal of
If =Q is satisfied, a logic level is output to the terminal (P=Q). This is the character output position in the main scanning direction. Furthermore, this logic level is input to the J terminal of F/F2143, and the HENB of F/F2143 is input by the next RVCLK signal.
The signal becomes a logical level. On the other hand, the counter 2145 is
Start counting the RVCLK signal in synchronization with the logic level of the ENB signal, and send the count output to the font ROM 21.
08 main scanning address. Also, the counter 214
4 also starts counting the RVCLK signal in synchronization with the logic level of the HENB signal, and outputs the logic level to its RC terminal after counting a predetermined number of times. This logic level is F/F2
143, and the next RVCLK signal causes the HENB signal of the F/F 2143 to go to logic O level. As a result, counters 2144 and 2145 stop counting, and their outputs are reset. From the above,
The HENB signal is output every line at the relevant character position in the main scanning direction.
This is a signal that becomes N.

On the other hand, the number of lines in the counter 2146 is determined by the comparator 21
47, and when the comparator 2147 satisfies P=Q, it outputs a logic level to the terminal (P=Q). This is the character output position in the sub-scanning direction. Furthermore,
This logic level is input to the J terminal of F/F2149, and the VE of F/F2149 is input by the next RH3YNC signal.
The NB signal becomes a logic level. On the other hand, counter 2151
starts counting the RH3YNC signal in synchronization with the logic level of the VENB signal, and sends the count output to the font RO.
Provided as the sub-scanning address of M2108. In addition, the counter 2150 also synchronizes with the logic level of the VENB signal to RH3.
It starts counting the YNC signal, and when a predetermined number of counts is reached, a logic level is output to the RC terminal.

This logic level is input to the terminal of F/F2149, and the VE of F/F2149 is input by the next RH3YNC signal.
The NB signal becomes a logic O level.

As a result, counters 2150 and 2151 stop counting, and their outputs are reset. From the above, VE
The NB signal is a signal that turns ON at the relevant character position in the sub-scanning direction. HENB signal and VENB signal are AND gate 2
153 and forms the SEL signal at its output.

In this way, a font pattern can be synthesized at any position in the output image. The CPU 2110 has a latch circuit 2142.
2148 and font selection data can be changed as appropriate, so a plurality of different fonts can be synthesized at any position in the image.

FIG. 1O is a diagram showing an example of an output image synthesized with fonts by the font control circuit of the embodiment. In the figure, "#" is a registration mark for positioning, and "M, C, Y
, Bk'' are color information marks for identifying each color version.The rest are color separation versions of the original image read by the reader 100.

Flowchart> FIG. 12 is a flowchart showing the operation of the control section 10 of the beamer section. This control program is in ROM 10-2
Built-in. In the figure, when the reader section 100 is powered on, an initial display routine is executed in step S1. This routine includes, for example, checking each I10, checking the display of the indicators, initializing RAMs 10-3, and moving the document scanning unit to its scanning starting point. In step S2, the printer waits for connection to the printer control unit 25000 via the communication line 24. If the communication line 24 is not connected or if the printer unit 2000 is not powered on, it is not in a connected state. After checking the connection status in step S2, step S
Proceed to step 3 and wait for the print (copy) switch on the operation unit 16 to be turned on. When the print switch 5 is turned on, the process advances to step S4, and a print ON command is output to the printer unit 2000 together with print mode information. This print mode information includes whether or not it is the color separation plate output mode, and is output according to instructions to the operation unit 16. Step S
Step 5 waits for an ITOP signal from the printer section 2000.

When the ITOP signal is input in step S5, step S6
, the document image is scanned and video data is output to the printer section 2000. At this time, selections such as print mode are given to the control section 10 from a scanning section (not shown). The control unit 10 transfers this information to the control unit elements and the printer 20.
The information is transmitted to the control unit 2500 of 00.

FIG. 13(A) is a flowchart showing the operation of the control section 2500 of the printer section. In the figure, a reader section 10
When a print ON command is received from 0, step 52200
Enter. In step 52201, it is checked whether the mode is the color separation plate (original plate for printing) output mode. If the mode is not the color separation plate output mode, the process advances to step 52202, and outputs an image such as a color copy using a normal print sequence, for example. Also, if you are in color separation output mode, step 5
2203 is the RAM for printer output characteristic correction (LUT2
) 2106 is a lookup table for the 400 line output during the above halftone processing as Y and M.

Set each color in C and . Step 52204
Now select the 400 line (A side) input of the selector 2119 in FIG. In step 52205, the RAM for halftone processing is
(LUT (1)) Set look-upables for each color of Y, M, C, in 210'l. In step 52206, the A side input of the selector 2103 in FIG. 2 is selected. In step 52207, a Y-separated image is outputted onto the first transfer material according to the processing procedure described later. In step 52208, the image of the M separation plate is outputted onto the second transfer material in the same manner.

In step 52209, a C-separated image is outputted onto the third transfer material in the same manner. In step 52210, a BK separated image is outputted onto the fourth transfer material in the same manner.

FIG. 13(B) is a flowchart showing details of the Y-separated image output procedure of the embodiment. In the figure, step 5
At 2212, the Y correction table of LUT2 is selected.

In step 52213, the Y halftone processing table of LUT (1) is selected. In step S2214, the halftone processing circuit 2
Initialization data for Y is set for 102. In step 52115, necessary data is set in the font control circuit 2109. Necessary data includes, for example, a registration mark "#" added for the purpose of registration, a color information mark "Y" indicating that it is a Y separation plate, and their output addresses.

In step 52216, the image data of the Y separation plate is developed by the black (BK) developer 2295, and the image of the Y separation plate is output. In addition, each of the other M, C, and BK separated versions has its own screen angle, and has a registration mark °'#°° and a color information mark °゛M°゛“C””B.
k'' and is processed by a BK converter 2295, and an image of each color separation is output.

In Figure 1O, the image itself of each color separation is black (B
K) is printed. However, these can be easily distinguished by the character marks "Y, M, C, Bk" printed at the same time. Also, by aligning each registration mark "#", accurate positioning can be performed.

[Effects of the Invention] As described above, according to the present invention, a high-quality gradation image can be reproduced.

[Brief explanation of the drawing]

Figures 1 (A) and (B) show the digital color image of the embodiment.
A functional block diagram of the reader/printer, FIG. 2 is a block configuration diagram showing details of the gradation control circuit of the embodiment, and FIG. 3(A) is a diagram of main signals in the printer section.
B) is a block configuration diagram showing details of the synchronization control circuit, FIGS. 4(A) to (D) are diagrams explaining the halftone processing pattern of the embodiment, and FIG. 5 is the halftone processing circuit of the embodiment. 6 (A) is a diagram showing an example of screen angle distribution in the embodiment; FIG. 6 (B) is a diagram showing an example of screen angle distribution used in the conventional printing field; Figures (C) to (H) are diagrams showing examples of moiré fringes, Figure 7 is a diagram explaining the conversion characteristics of LUT (1) in the example, and Figures 8 (A) to (D) are diagrams in the example. Figure 9 is a block diagram showing the details of the font control circuit of the embodiment. Figure 10 is a diagram showing the output image synthesized with fonts using the font control circuit of the embodiment. Figure 11 is a sectional view of the mechanism of the digital color reader printer of the embodiment; Figure 12 is a flowchart showing the operation of the control unit 10 of the reader unit; Figure 13 (A) is the printer unit. Flowchart showing the operation of the control unit 2500, FIG. 13(B)
14 is a detailed diagram of the data selector, and FIG. 15 is a diagram illustrating an example of outputting an image with enhanced magenta. In the figure, 84...document, 83...document scanning unit,
86...Rod lens array, 87...Color CC
D sensor section, 88... signal processing block, 2289...
・Polygon mirror, 2290...Mirror 2900・
. . . Photosensitive drum, 2292 to 2295 . . . Developing device, 2296 . . . Transfer drum. ward ■ feather P-bi → / pp ('1 and

Claims (1)

[Claims] In an image forming apparatus that forms a color image by forming a pulse width modulation signal based on each color image signal, a gradation conversion means includes a plurality of types of gradation conversion tables for performing gradation conversion of each color image signal; pattern signal generation means for generating a pattern signal with a predetermined cycle; pulse width modulation signal generation means for generating a pulse width modulation signal using the image signal output from the gradation conversion means and the pattern signal; and detecting means for detecting the leading edge of the image and generating an image leading edge signal, and selecting a predetermined gradation conversion table based on the image leading edge signal by the detecting means and adjusting the pattern signal to a predetermined phase. An image forming apparatus characterized in that it is configured to generate an image.