JP3077980B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus that processes multi-gradation image data, and relates to an image processing apparatus that generates recording image data suitable for recording an image. is there.

[Prior art] Conventionally, a dither method, a control method using a laser emission time,
2. Description of the Related Art An image forming apparatus that forms a multi-tone image by a laser luminance modulation method or the like is known.

[Problems to be Solved by the Invention] However, when an attempt is made to create a halftone image for printing by a conventional device, the resolution of the image is deteriorated by an area gradation method such as a dither method, and the image quality is not improved. Further, according to the control method based on the emission time of the laser beam or the brightness modulation method, the halftone dot becomes insufficient and cannot be used as a halftone image for printing.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional example, and is a multi-gradation image forming apparatus that forms multi-gradation size dots corresponding to the density of multi-value image data. It is an object of the present invention to provide an image processing apparatus that can generate the image data.

[Means for Solving the Problems] In order to achieve the above object, an image processing apparatus of the present invention has the following configuration. That is, a pixel having multi-valued image data is divided for each predetermined number of pixels to form a predetermined area, and the predetermined area is determined according to predetermined halftone information for concentrating density at a predetermined position in the predetermined area. Image conversion means for converting the density of the multi-valued image data of each pixel in the pixels, and forming dots of multi-step size corresponding to the density based on the multi-valued image data of each pixel density-converted by the image conversion means. And generating means for generating recording image data for use.

[Operation] According to the above configuration, a pixel having multi-valued image data is divided into a predetermined number of pixels to form a predetermined area, and a predetermined halftone dot for concentrating density at a predetermined position in the predetermined area. According to the information, the density conversion is performed on the multi-valued image data of each pixel within the predetermined area, and based on the multi-valued image data of each pixel subjected to the density conversion, a dot of a multi-step size corresponding to the density is formed. It operates to generate recording image data.

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

<Description of Mechanism> FIG. 11 is a sectional view of the mechanism of the digital color reader / printer of the embodiment. The reader / printer 80 includes a reader unit 100 for reading a color original image by color separation, and a printer unit 20 for producing a color reproduction image (copy image) or a printing original (color separation image) separated into each color plate.
00.

In the reader section 100, reference numeral 83 denotes a document scanning unit, which is an exposure lamp for reading a document 84 placed on a document table.
Sub-scanning is performed in the direction of arrow A with 85 turned on. The reflected light from the document 84 is guided to a converging rod lens array 86 and is condensed on a contact type color CCD sensor unit 87. This CCD sensor chip has, for example, a resolution of 16 pel (62.5 μm) and consists of 1024 pixels. This sensor chip has 5 chips as a whole and is arranged in a staggered manner in the main scanning direction. Further, each pixel of the sensor chip is divided into three areas of 15.5 μm × 62.5 μm, and cyan (C), green (G), and yellow (Y) color filters are attached to the respective areas. In this way, the optical image condensed on the CCD sensor unit 87 is converted into C, G, Y electric signals and sent to the signal processing block 88. In signal processing block 88, these C,
The G and Y electric signals are converted into digital video data of yellow (Y), magenta (M), cyan (C) and black (BK), and transmitted to the printer unit 2000 for each color.

In the printer unit 2000, the input video data is
The density = pulse width (PWM) modulation is performed as it is or after halftone processing, and, if necessary, after a font pattern is combined with a part thereof. This PWM-modulated binary signal drives the laser beam ON / OFF. This laser beam is converted into a high-speed horizontal (main) scanning beam by a polygon mirror 2289 rotating at a high speed. The main scanning beam is further reflected by a mirror 2290 to perform dot exposure on the surface of the photosensitive drum 2900 corresponding to video data. At this time, one main scanning length of the laser beam corresponds to one main scanning length of the video data, that is, the beam dot of the embodiment has a resolution of 16 pe.
with l.

On the other hand, the photosensitive drum 2900 is rotating at a constant speed in the direction of arrow B. The photosensitive drum is previously uniformly charged by a charger 2297. By performing video dot exposure of video data on the uniformly charged photoconductor surface,
An electrostatic latent image of each color separation is formed. For example, an electrostatic latent image is formed in the order of color plates Y, M, C, and BK for each rotation of the drum. The electrostatic latent images of the respective color plates are visualized by the corresponding developing devices 2292 to 2295, respectively, and further transferred to a transfer material (paper or the like) wound on a transfer drum 2296.

The above description corresponds to a single document exposure scan of the reader unit 100. First, a dot image of the Y component is exposed on the photosensitive drum, developed by a Y developing machine, and transferred to a material to be transferred.
Next, the photosensitive drum is exposed to a dot image of the M component, developed by an M developing machine, and transferred to a transfer material. Thereafter, exposure, development and transfer are performed for the C component and the BK component in the same manner.

Although not shown, supply and operation of the transfer material are controlled at this time. That is, each color plate data is superimposed on the same transfer paper and subjected to color synthesis to obtain a normal color copy. Alternatively, the transfer material is changed for each color plate, and the number of color separations (Y, M,
(C, BK, etc.), respectively, to transfer to a number of transfer-receiving materials, thereby creating a color printing master.

Although not shown, in the latter case, the number of colors to be developed is controlled. That is, each color plate data is converted to the corresponding Y, M,
The color plate data may be developed with C or BK color, but each color plate data may be developed with only one of Y, M, C and BK colors (for example, BK1 color). This makes it easy to compare and evaluate the originals, and the color in color printing is determined by the printing ink.
From this point, the printer mechanism of this embodiment is a color printer, but may be replaced with a normal BK1 color printer mechanism.

<Explanation of Function Block> FIGS. 1A and 1B relate to a function block diagram of the digital color reader / printer of the embodiment, and FIG. 1A is a function block diagram of the reader unit 100. Fig. 1 (B)
3 is a functional block diagram of the printer unit 2000.

In FIG. 1 (A), reference numeral 10 denotes a control unit, and a reader unit
Perform 100 main controls. The control unit 10 includes the CPU 10-1 and the CPU 10-1.
The ROM 10-2 stores, for example, the control program of FIG. 12 executed by the CPU 10-1 and the RAM 10-3 used as a work memory by the CPU 10-1. That is, the control unit 10 controls the rotation of the motor 12 via the motor driver 13 and causes the original scanning unit 83 to scan the original image. At this time, the exposure lamp 85 is controlled to be turned on via a constant voltage control circuit (CVR). Further, it receives a print (start) command signal and other key operation signals from the operation unit 16, and sets various print operation modes. For example, the operation unit 16 includes a print mode setting switch (not shown), and the control unit 10 receives this command, for example, in the case of an expression mode command, high resolution for characters, line drawings, etc., in a halftone mode. An operation mode is set so that printing is performed and a photographic image is printed with high gradation. Alternatively, in the case of a copy mode command, each color separation signal is color-combined on one sheet of transfer paper,
In the case of the original plate creation mode command, the operation mode is set so that each color plate is formed on the number of transfer materials corresponding to the number of color separations. There are various other commands. Then, the control unit 10 transmits this print operation mode to the printer unit 2000 via the communication line 24.

Reference numeral 1 denotes a synchronization signal processing unit whose main function is to generate various timing signals on the reader side synchronized with the BD signal (printer unit horizontal synchronization signal) sent from the printer unit 2000 via the line 22. Is to do. Reference numeral 2 denotes a contact type color CCD sensor (87), and a synchronization signal processing unit 1
A document image is read in synchronization with a horizontal synchronization signal (RHSYNC signal) from the reader unit and the like, and a 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 G signal, and a Y signal. In this embodiment, since the CCD sensor is composed of five chips, signals for five channels are actually generated simultaneously. Reference numeral 3 denotes a signal processing unit which performs a waveform shaping process such as edge emphasis to prevent attenuation of a high-frequency component of the read image signal 5.

Reference numeral 6 denotes an image processing unit. The image processing unit 6 includes an analog processing unit 7, a connection memory 8, and an image processing unit (IPU) 9. The analog processor 7 first separates the C, G, and Y signals for each pixel into C, G, and Y signals for each color. Next, red (R), green (G), and blue (B) color signals for each pixel are formed from the separated C, G, and Y signals. This formation is performed by the arithmetic processing of (R) = (Y)-(G) (G) = (G) (B) = (C)-(G). The R, G, and B signals thus obtained are luminance signals, and have a linear relationship with the output voltage. This is further converted to a density (LOG), and each density data (image data) of Y, M and C of 8 bits is converted by an A / D converter.
Convert to The Y, M, and C image data includes five channels of the CCD chip, and synchronization between the channels is not established.
The link memory 8 stores the Y, M, and C image data for five channels so that they can be output. That is, 1024 × 5 pixels arranged in a staggered manner in the main scanning direction are stored so as to be substantially one straight line. Thereafter, a desired color signal is selected from the Y, M, and C image data of the connection memory 8 by the control unit 10 and sent to the image processing unit (IPU) 9 for each color. The IPU 9 performs, for example, a shading correction process for correcting light distribution and a masking process for correcting color. Then, the 8-bit video data per pixel as a processing result is transmitted via a signal line 11.
The IPU 9 sends it to the printer unit 2000.

In FIG. 1B, reference numeral 2500 denotes a control unit, which performs main control of the printer unit 2000. The control unit 2500 includes a CPU 2110,
The ROM 2502 storing, for example, the control programs of FIGS. 13A and 13B executed by the CPU 2110, the RAM 2504 used as a work memory by the CPU 2110, and analog detection signals from various external sensor circuits. An A / D converter 2503 for converting into a digital signal is provided. Accordingly, the control unit 2500 first controls the rotation of the drive motor 2285 to rotate the photosensitive drum 2900, the transfer drum 2296, and the like at a constant speed. Further, the charge amount on the surface of the photosensitive drum 2900 detected by the potential sensor 2600 is A / D converted through a potential measurement unit 2700, and is taken in. Furthermore, an image tip signal (ITOP) detected by the sensor 2800 is captured. Also, signals such as humidity and temperature detected by the other humidity sensor 2298 and temperature sensor 2299 are A / D converted and taken in, and used for control such as correcting the development characteristics of the printer. The control unit 2500 exchanges various information with the control unit 10 of the reader unit via the communication line 24.

Reference numeral 2160 denotes a gradation control circuit whose main function is to synchronize the image clock signal (RCLK) of the reader unit 100 with the image clock signal (VCLK) of the printer unit 2000, and to input signals as necessary. Halftoning video data,
In addition, the input video data or the halftone-converted video data is subjected to gradation conversion according to the image output mode, and further, the gradation-converted video data is converted into a binary signal corresponding to the density by PWM modulation. And so on. Reference numeral 2200 denotes a laser driver which turns on / off the beam of, for example, the semiconductor laser 2223 in accordance with 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 of the input video data is a lookup table for dot processing {LUT (1)} 2101
, And is converted into halftone processing video data. The LUT (1) of the present embodiment is constituted by a ROM or a RAM. The LUT (1) has a function of input video data so that a desired halftone effect can be obtained when the halftone video data is output via the next stage halftone processing circuit 2102 by the electrophotographic process. Is a conversion table for converting. Details will be described later. Reference numeral 2102 denotes a dot processing circuit,
(1) The output halftone processing video data is subjected to halftoning processing to be described later. For example, the image data is divided into a predetermined area, and the pixel density in the area is converted into halftone video data which is concentrated and representative to the density at the center pixel position, and this is converted to the A side of the selector 2103. Input to the terminal.

The other of the input video data is input to the B-side terminal of the selector 2103 in order to avoid the halftone processing. The selector 2103 selects and outputs one of the video data after the halftone conversion and the video data before the halftone conversion in accordance with the select signal 2123 from the CPU 2210. For example, in a mode for preparing a printing original plate, video data after halftoning is preferably selected and output. When outputting a normal color copy, video data after halftone dot or video data before halftone dot can be selected. In short, various print modes are conceivable, and various combinations of signal processing are performed with each processing circuit described below according to the print modes.

Next, the video data selected by the selector 2103 is input to the A-side terminal of the selector 2104. The selector 2104 B
Font data from the font ROM 2108 is input to the side terminal. The font data is for synthesizing (inserting) a font pattern of a character or a signal into the selected video data portion. As described later, CPU2
By setting a font code and an address to be synthesized by the font code 110, a desired font pattern can be synthesized at one or several places of image data of each color plane.

The 8-bit video data output from the selector 2104 is input to a buffer memory (FIFO) 2105 in synchronization with the RHSYNC signal and the RCLK signal from the reader unit 100. The stored video data is supplied to a horizontal synchronization signal (HSYNC signal) from the printer-side synchronization control circuit 2113 and a video clock signal (VCLK signal).
Signal) is read out in synchronization with the signal. With this, the leader unit
Speed matching between 100 and the printer unit 2000 is achieved.

The video data read from the buffer memory 2105 is a look-up table for printer characteristic correction @LUT
(2) Input to $ 2106. The LUT (2) adjusts the input video data to the output characteristics of the printer (for example, beam spot diameter, toner particle diameter, etc.)
And is linear) to create video data corrected in advance. See Fig. 8 (A) ~
It will be described later according to (D).

The video data output from the LUT (2) is input to a D / A converter 2107, where it is converted into an analog video signal that changes stepwise, and is input to one terminal of each of comparators 2117 and 2118. Pattern signals (1) and (2) for binarizing (PWM modulation) the analog video signal in accordance with the density of the analog video signal at the other terminals of the comparators 2117 and 2118, respectively.
Is entered. The pattern signal (1) is for reproducing or generating a line image or a halftone image, for example.
In this case, since the resolution is a problem, a pattern signal having the same frequency (for example, 400 lines) as the video signal is used. That is, one pattern signal is generated per pixel.
The pattern signal (2) is for reproducing, for example, a halftone image. In this case, since it is necessary to increase the gradation, for example, the frequency of the line drawing pattern signal is 1/2 (for example, 200 lines). The pattern signal is as follows. That is, the relationship is such that one pattern signal is generated for every two pixels.

Explaining the circuit, a crystal oscillator (XTAL) 2112 generates a clock signal having a frequency four times or more the frequency of the image clock signal. The synchronization control circuit 2113 forms a main scanning synchronization signal (HSYNC signal) and a basic clock signal (SCLK signal) in synchronization with the BD signal and the ITOP signal. The frequency divider 2114 divides the SCLK signal to generate a clock signal for pattern generation (TVCLK signal and PVC).
LK signal). This TVCLK signal is a clock signal having a frequency twice as high as the video data signal and a duty ratio of 50%. The pattern generation circuit 2115 generates an analog pattern signal (1) according to the TVCLK signal. In this embodiment, for example, a triangular wave signal is used. comparator
2117 compares the analog video signal with the pattern signal (1), and performs pulse width modulation (PWM modulation) on the video density.
Outputs WM signal (1).

The PVCLK signal is 1/2 (or 2/3) of the video data signal.
Etc.) A clock signal having a double frequency and a duty ratio of 50%. The pattern generation circuit 2116 generates an analog pattern signal (2) according to the PVCLK signal. In this embodiment, for example, this is also a triangular wave signal. comparator
Reference numeral 2118 compares the analog video signal with the pattern signal (2), and outputs a PWM signal (2) obtained by pulse-width-modulating the video density.

According to the control signal from the CPU 2110, the selector 2119 selectively outputs the PWM signal (1) of the A-side terminal when a line drawing original is to be reproduced or halftone-processed output. Selectively output terminal PWM signal (2).

This selection is also free, and various combinations with other processing circuits are conceivable.

The switching signal is not a switching signal from the CPU 2110, but is not shown. For example, a known image area for identifying whether each pixel of a video signal belongs to a line drawing area or a halftone image area. Separation means may be provided, and this image area separation may be used as a switching signal. By doing so, a faithful and high-quality image corresponding to the original image tone can be obtained even within one image. Thus, the selected PWM signal (1) or (2)
Is further matched with the operation of the material to be transferred by the gate circuit 2120, input to the laser driver 2200, and
The semiconductor laser 2223 is driven at a constant current for a time corresponding to the pulse width of the signal to form an electrostatic latent image on the surface of the photosensitive drum 2900.

FIG. 3A is a timing chart of a main signal in the printer unit. The figure shows an example of a horizontal synchronizing signal BD, a blanking signal, a reference clock signal SCLK, clock signals TVCLK and PVCLK for pattern generation, a video clock signal VCLK, and the like.

FIG. 3B is a block diagram showing details of the synchronization control circuit. In the figure, a crystal oscillator 2112 'causes a synchronization circuit 2128 to generate a clock signal having a frequency four times or more the frequency of the image clock signal. The synchronization circuit 2128 outputs the HSYNC signal, the VCLK signal, and the SCLK signal at a timing synchronized with the external BD signal and the ITOP signal. The divider circuit 2114
SCLK signal input, TVCLK signal with the same cycle as VCLK signal and duty ratio 50%, and twice (or three times) VCLK signal
A PVCLK signal with a period 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 cycle reset at the falling edge of the BD signal.

Here, the PVCLK 'signal in FIG. 3A will be described. The PVCLK 'signal is useful when screen angle control is performed on video data in which no halftone processing is performed (during normal halftone image reproduction). The PVCLK 'signal is a clock signal having a delay phase of, for example, 1.5 pixels from the HSYNC signal. This is delayed by one pixel when compared with the normal phase PVCLK signal. In this embodiment, for example, during normal halftone image reproduction, the PVCLK signal and the PVCLK 'signal are switched and used every one line or several lines in the sub-scanning direction with respect to the HSYNC signal. For example, switching every line means that the screen angle is controlled at 45 °.

In FIG. 3 (B), the HSYNC signal is
130 and shifted by the SCLK 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, the counter circuit 2132
After being reset by the signal, the count program information is set in advance by the CPU 2110. The count program information is, for example, count sequence information that repeats 2 to 5 as a count value output, or repeats 5 to 6 as a count value output. The counter circuit 2132 counts the HSYNC signal according to this information.
For example, every time the HSYNC signal is generated, 3 → 4 → 5 → 3 → 4 → 5
Count as follows. And this count value is the selector
Input to 2131 selection terminal. On the other hand, the selector 2131 selects and outputs the signal of the input terminal 3 when the count value is 3, and selects and outputs the signal of the input terminal 4 when the count value is 4. The output of the selector 2131 is output from the frequency divider 21.
Input to 14 division start terminal. On the other hand, the frequency divider 2114
It is reset by the HSYNC signal in advance, and the counting function is stopped. When the signal from the selector 2131 is input thereto, the frequency division operation is started from that point. Thus, a PVCLK signal and a TVCLK signal having different phases for each line can be generated. What is the relationship with the screen angle? Now, when the screen angle θ is defined as θ = tan ⁻¹ 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 all values that can be freely set by the CPU 2110.

<Explanation of the halftoning process> The halftoning process to be described below is a process of halftoning the density of image data divided into a predetermined area (for example, centralizing the pixel density at the central pixel position, representative processing) and optimizing. The screen angle control is performed all at once in real time.

First, look-up table for dot correction LUT
(1) Details of (1) will be described.

FIG. 7 is a diagram for explaining the conversion characteristics of the LUT (1) of the embodiment. In the figure, the Y, M, C video data input to the printer unit and the ink (or toner) density have a linear relationship. However, when the halftoning process 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 in the figure shows the relationship between the input level before correction and the ink density, and has a linear relationship. The ink density on the vertical axis is the ink density when printing is performed using the color separation plate 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 input level after correction and the input level before correction, which gives the conversion characteristic of the LUT (1).

If the color separation plate of the embodiment can form an ideal halftone dot, the halftone dot density (%) may be set as the halftone dot output density in the third and fourth quadrants.

The actual table information is obtained, for example, by actual measurement. For example, when in the pre-correction input level e _n obtaining ink density D _n obtains the dot output density d _n such that the ink density D _n. Then the dot output density d _n such corrected input level
Find E _n . Accordingly, LUT (1) may be created to obtain the corrected output level E _n before correction input level e _n. Thus, all the conversion levels corresponding to the input levels 00H to FFH are obtained. When this conversion characteristic differs for each color, the LUT (1) is also created for each color.

4 (A) to 4 (D) are diagrams for explaining a halftoning processing pattern of the embodiment, and FIG. 4 (A) shows an example for C data. In the figure, reference numeral 500 denotes one pixel, and each pixel is shown as an array from the starting address (0, 0) of data for one image. Reference numeral 600 denotes a basic cell, which is a block unit for converting the density in a thick line area (within a predetermined area) in the drawing into a halftone dot (the pixel density is concentrated, for example, to the density at the center pixel position). The basic cell of the C data is composed of, for example, 13 pixels. The numbers (1 to 13) assigned to each pixel in the basic cell indicate the priority, and the priority decreases from 1 to 13. In data of the same color, the same priority is given to other basic cells.

Note that the illustrated priority order is an example according to the printer characteristics of the embodiment, and is not limited to this. Various other modifications are possible.

The halftone processing of the pixel density in the basic cell is performed according to the following equation (halftone calculation equation).

That is, (target pixel output data) = (target pixel input data) × (number of pixels in basic cell) − (priority order−1) × FFH where FFH: maximum density (H is displayed in hexadecimal). This is performed by sequentially moving the target pixel in the scanning and sub-scanning directions. For example, when the pixel of interest is at the place of priority 11, (output density) = (input density) × 13− (11−1) × FFH. Since the priority is as low as 11, the density {(priority −1) × FFH} to be subtracted is large, and the density at this pixel position is relatively reduced. As a result, when (output density) <0, the output density is clamped to “00H”. Conversely, when (output density)> FFH, the output density is set to “F
Clamp to FH ".

Similarly, when the target pixel is located at the place of the first priority, (output density) = (input density) × 13− (1-1) × FFH. Since the priority is 1, the density to be subtracted is zero. As described above, the pixel density is concentrated toward the central pixel position in the basic cell and is represented. The printing original plate thus formed into a halftone dot has good ink adhesion and is stable.

Reference numeral 700 denotes a matrix, which is a block unit used by repeating the halftone processing pattern shown in the main scanning and sub-scanning directions. The matrix size of the C data is, for example, (13 × 13) pixels. As is apparent from the figure, if a plurality of the matrices are connected in the main scanning and sub-scanning directions, a document image of any size can be processed. In this embodiment, this matrix pattern is stored in a memory using this periodicity, and the pattern is repeated and used in real time, thereby saving the pattern memory and enabling high-speed calculations.

The triangles in the figure indicate the screen angle θ, and the screen angle θ indicates the inclination of the arrangement of the basic cells 600. In the figure, when a and b are determined, the screen angle θ is obtained by θ = tan ⁻¹ b / a. The screen angle of C data is, for example, θ = 5
6.3 ゜.

FIG. 4 (B) shows an example of the halftone processing pattern of the M data. In the figure, a basic cell 600 is composed of 13 pixels and has the same shape as that of FIG. The screen angle gives θ = 33.7 °. By the way, comparing FIG. 4 (B) with FIG. 4 (A), the way (phase angle) of starting from the address (0,0) is different in the basic cell 600 of M data. For this reason, the center pixel positions of both do not overlap. That is, the main density information does not overlap. As a result,
During printing, high-quality and stable printing can be performed without crushing the C ink and the M ink.

FIG. 4 (C) shows an example of a halftoning processing pattern of the BK data. The BK data is generated from the C, M, Y data by a known method. In the figure, a basic cell 600 is composed of 10 pixels, and its shape is also different from those of FIGS. 4 (A) and 4 (B). Although not limited to this shape, it is suitable for giving, for example, θ = 71.6 ° as the screen angle. Also, the phase angle from address (0,0) is different.

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

FIG. 5 is a block diagram of a dot processing circuit according to the embodiment. In the figure, the halftone video data output from the LUT (1) is latched to a D-type flip-flop (D / F / F) 2301 in synchronization with the RVCLK signal. On the other hand, the counter 2304 is R
After being reset by the HSYNC signal, the RVCLK signal is counted. That is, the main scanning direction addresses shown in FIGS. 4A to 4D are formed. The counter 2305 counts the RHSYNC signal after being reset by the ITOP signal. That is, the sub-scanning direction addresses shown in FIGS. 4A to 4D are formed.

Although not shown, the counters 2304 and 2305 have CPU 211
The count initialization data corresponding to the processing color is set from 0, and each counter repeats the counting operation with the count value corresponding to the initialization data. For example, when processing C data or M data, the processing is repeated with count values 0 to 12, respectively. When processing BK data or Y data, the processing is repeated with count values 0 to 9, respectively.

Reference numeral 2306 denotes a pattern memory, which is shown in FIGS.
(Dot-priority data). Thus, the color selection signal (Y, M, C, BK) from the CPU 2110
FIG. 4 (A)
To (D) are sequentially read out. Reference numeral 2302 denotes a table memory, which receives input data of a target pixel and priority data corresponding to the input data, and outputs output data of the target pixel in accordance with the above-described halftone dot expression. At that time, as described above,
The table in 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 data of the pixel of interest read out in this way is set in the DF / F 2303 in synchronization with the RVCLK signal, and is output to the next circuit.

Note that the memories 2302 and 2306 may be a ROM or a RAM. Instead of using a look-up table method using a memory, a hardware operation circuit may be used.

FIG. 6A is a diagram showing an example of screen angle distribution in the embodiment, FIG. 6B is a diagram showing an example of screen angle distribution used in the conventional printing field, and FIGS. (H) is a figure which shows the example of a moire fringe.

In the field of printing technology, for example, (13 × 13) fiber glasses can be bundled, so that it is easy to accurately maintain the screen angles distributed during printing. On the other hand, in this embodiment, since a laser beam printer is used, the rotation unevenness of the polygon mirror 2289 and the photosensitive drum 2900 must be considered. That is, the combination of the two rotation unevennesses causes unevenness in the amount of laser irradiation per unit of time, and the irradiation unevenness also affects the latent image on the photosensitive drum, and furthermore, the visualization of the image. Appears as unevenness (pitch unevenness). This pitch unevenness is considered to be a high-frequency component having an angle of 0 ° or 90 ° when considered in correspondence with an image subjected to halftone processing. In general, moiré appears on a color plate having a small angle difference from pitch unevenness. For this reason, if an image is formed at an angle similar to that of the printing method, the M and C components are easily seen as moiré with pitch unevenness. This is equivalent to "line screen + moire by halftone dots" in FIG. 6 (H). Therefore, in the present embodiment, the moiré is made invisible by setting the Y component, which is inconspicuous to the relative luminous efficiency, to a screen angle close to 0 °. Although BK is a color that is originally easily visible, the BK component of this embodiment is not shown, but the data is corrected in the reader unit 100 so that the lowest value of each color component is not further densified with a low density region. I have. For this reason, the pitch unevenness is a light amount unevenness as described above, so that a light density is more visible than a dark density. Therefore, even if the angle of the black is close to 0 ° or 90 °, it is difficult to see the moire with the pitch unevenness.

8 (A) to 8 (D) are diagrams for printer output characteristics of the embodiment.
FIG. 9 is a diagram illustrating conversion characteristics of LUT (2). The printer output image needs to have a linear characteristic between the input data level and the printer output density according to the characteristics of the printer used. By the way, if the toner particle diameter is not sufficiently small compared to the beam spot diameter, for example, even if the output beam has 256 gradations, only a maximum of 32 toner particles may be attached. This is inconvenient because only 32 gradations can be expressed substantially. Therefore, the printer output unit is (2 × 2) dots, or generally (n × 2) dots.
m) When a dot area is set and the density within the area is considered, for example, 32 × 2 = 64 gradations, and further, a linear gradation expression up to 256 gradations can be obtained.

When this is performed, for example, m
What is necessary is just to perform PWM conversion of the image data for a pixel with a pattern signal (triangular wave) having a period m times the pixel period. By the way, in the sub-scanning direction, it is desired to obtain the same effect as in the main scanning for n lines. However, the same effect cannot be obtained by the method of repeating the same main scanning in the sub-scanning direction as in this embodiment. Therefore, by providing a plurality of types of gradation conversion tables in the sub-scanning direction and switching and using the tables in a predetermined sequence, the same effect as in the main scanning direction can be obtained.

The LUT (2) is a table for this purpose and takes into account the overall output characteristics of the laser beam printer of the embodiment. As the output characteristics of the laser beam printer, the relationship between the beam pulse width and the photosensitive drum surface potential (EV characteristic) and the relationship between the photosensitive drum surface potential and the output image density (VD characteristic) can be considered. Since the former EV characteristic has a substantially linear characteristic, a description will be given here as a table for correcting the latter VD characteristic. This VD characteristic indicates whether or not to perform halftone processing of image data, the frequency of a PWM modulation signal (pattern signal),
Further, the characteristics vary depending on 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 2110 selects and uses the tables as needed.

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

FIG. 8A 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 characteristic of FIG. 8 (A). That is, this can be achieved by exchanging the horizontal axis and the vertical axis of FIG. 8A, and the characteristic table of FIG. 8B is obtained. However, in this embodiment, it is desired to further improve the gradation of the output image (particularly, the gradation of the highlight portion). Therefore, the conversion table is switched and used every one line or every several lines at a cycle of two lines, three lines or the like in the sub-scanning direction in accordance with 1/2, 1/3 times the pattern signal frequency. The linearization of gradation and the concentration of halftone dots are achieved.

FIG. 8 (C) is a diagram showing the correction table characteristics of the embodiment used when the pattern signal frequency is 1/2 of the video signal frequency. In the figure, the characteristic table first rises until the output level reaches the level FFH with a gradient twice that of the curve in FIG. 8B, and thereafter remains constant until the input level reaches FFH. The characteristic table is maintained at the level 00H until the output of the characteristic table becomes the level FFH, and thereafter, the level FF has a slope twice as large as the curve of FIG. 8 (B).
Created to rise to H. In this example, since the pattern signal frequency is 1/2, one dot of output density is formed by two pixels of the video signal. On the other hand, in the sub-scanning direction, two lines are used as a cycle, and the table shown in FIG. Thereby, the table is darkened and the table is lightened. As a result, an effect of forming one dot of output density for two lines in the sub-scanning direction is obtained. Note that the table characteristics are not limited to those shown in FIG.

FIG. 8 (D) is a diagram showing the correction table characteristics of the embodiment used when the pattern signal frequency is 1/3 of the video signal frequency. As described above, the VD characteristic depends on the frequency of the pattern signal. However, for convenience of explanation here, the same
This will be described using the VD characteristics. In the figure, the characteristic table first rises with a three-fold slope of the curve of FIG. 8 (B) until it reaches the level FFH, and thereafter is constant until the input level becomes FFH. The characteristic table maintains the level 00H until the characteristic table output reaches the level FFH, and thereafter rises to the level FFH with a slope 1.5 times the curve of FIG. 8B. In this example, since the pattern signal frequency is 1/3, one dot of output density is formed by three pixels of the video signal. On the other hand, in the sub-scanning direction, the table shown in FIG. For example, switch as →→.
As a result, the effect of shading each output line and forming one dot of output density for three lines in the sub-scanning direction is obtained.
Note that the table characteristics are not limited to those shown in FIG.

Since the VD characteristics actually differ depending on the pattern signal frequency, the tables shown in FIGS. 8C and 8D are respectively created in accordance with the different VD characteristics. In addition, the above table is created when the pattern signal frequency is 1 / the video signal frequency.
It is not limited to 2,1 / 3. The same applies to other frequencies.

FIG. 9 is a block diagram showing details of the font control circuit of the embodiment. The CPU 2110 is connected to the terminal S of the font ROM 2108.
, And select a font to be printed.
In addition, a latch circuit for the main scanning address data to be printed.
2142, and the sub-scanning address data is latched to a latch circuit 2148. The address data of the latch circuit 2142 is input to the Q terminal of the comparator 2141, and the latch circuit 2148
Is input to the Q terminal of the comparator 2147. On the other hand, the counter 2140 is reset by the RHSYNC signal,
Count the RVCLK signal. That is, the number of pixels in the main scanning direction is counted. The counter 2146 is reset by the ITOP signal and counts the RHSYNC signal. That is, the number of lines in the sub-scanning direction is counted.

And the number of pixels of the counter 2140 is P
When P = Q is satisfied, the comparator 2141 outputs a logic 1 level to the terminal (P = Q). This is the character output position in the main scanning direction. Furthermore, this logic 1
The level is input to the J terminal of the F / F 2143, and the HENB signal of the F / F 2143 becomes a logic 1 level by the next RVCLK signal. On the other hand, the counter 2145 is synchronized with the logic 1 level of the HENB signal.
The counting of the RVCLK signal is started, and the count output is provided to the main scanning address of the font ROM 2108. The counter 2144 also starts counting the RVCLK signal in synchronization with the logic 1 level of the HENB signal, and outputs a logic 1 level to its RC terminal after counting a predetermined number. This logic 1 level is F / F2143
F / F2143 by the next RVCLK signal
HENB signal attains a logic 0 level. This allows the counter
2144 and 2145 stop counting, and their outputs are reset. As described above, the HENB signal is a signal that is turned on for each line at the character position in the main scanning direction.

On the other hand, the number of lines of the counter 2146 is input to the P terminal of the comparator 2147. When P = Q is satisfied, the comparator 2147 outputs a logical 1 level to the terminal (P = Q). This is a character output position in the sub-scanning direction. Further, this logic 1 level is input to the J terminal of F / F2149, and the next RHSYN
The VEB signal of the F / F 2149 becomes a logical 1 level by the C signal.
On the other hand, the counter 2151 starts counting the RHSYNC signal in synchronization with the logic 1 level of the VENB signal, and provides the count output to the sub-scanning address of the font ROM 2108. The counter 2150 also starts counting the RHSYNC signal in synchronization with the logic 1 level of the VENB signal, and outputs a logic 1 level to its RC terminal after counting a predetermined number. This logic 1 level is F / F214
9 is input to the K terminal, and F / F21
The 49 VENB signal becomes a logic 0 level. As a result, the counters 2150 and 2151 stop counting, and their outputs are reset. As described above, the VENB signal is a signal that is turned ON at the character position in the sub-scanning direction. HENB signal and VENB signal are AN
The signal is input to the D gate 2153, and the SEL signal is formed at the output.

Thus, a font pattern can be synthesized at an arbitrary position in the output image. The CPU 2110 can appropriately change the latch circuits 2142 and 2148 and the font selection data, so that a plurality of different fonts can be combined at an arbitrary position in the image.

FIG. 10 is a diagram showing an example of an output image which is font-synthesized by the font control circuit of the embodiment. In the figure, “#” is a registration mark for positioning, and “M, C, Y, Bk”
Is a color information mark for identifying each color plate. The rest are color separations of the original image read by the reader 100.

<Flowchart> FIG. 12 is a flowchart showing the operation of the control unit 10 of the reader unit. This control program is stored in the ROM 10-2. In the figure, when the reader unit 100 is powered on, an initial display routine is executed in step S1. This routine includes, for example, checking of each I / O, checking of indicators, initialization of RAM 10-3,
This is a process of moving the original scanning unit to the scanning start point. In step S2, the process waits for a connection with the printer control unit 25000 via the communication line 24. When the communication line 24 is not connected or the power of the printer unit 2000 is not turned on, the connection state is not established. When the connection state is confirmed in step S2, the process proceeds to step S3, and waits until the print (copy) switch of the operation unit 16 is turned on. When the print switch is turned on, the flow advances to step S4 to output a print ON command to the printer unit 2000 together with print mode information. The print mode information includes whether or not the mode is the color separation plane output mode, and is output in accordance with an instruction to the operation unit 16. Step S5
And has an ITOP signal from the printer unit 2000. Step S5
When an ITOP signal is input in step S6, the flow advances to step S6 to scan the original image and output video data to the printer unit 2000. At that time, selection of a print mode and the like is given to the control unit 10 from a scanning unit (not shown). The information is sent to the control unit 10
Transmits information to the control unit elements and the control unit 2500 of the printer 2000.

FIG. 13A is a flowchart showing the operation of the control unit 2500 of the printer unit. In the figure, when a print ON command is received from the reader unit 100, it is input to a step S2200.
In step S2201, it is checked whether or not the mode is a color separation plate (printing plate) output mode. If the mode is not the color separation output mode, the flow advances to step S2202 to output an image such as a color copy by a normal print sequence, for example. In the color separation output mode, in step S2203, a look-up table of 400 lines output for the above halftone processing is set in the printer output characteristic correction RAM (LUT2) 2106 for each of Y, M, C, and K colors. In step S2204, 400 of selector 2119 in FIG.
Select line (A side) input. In step S2205, a look-up table for each of Y, M, C, and K colors is set in the halftone processing RAM (LUT (1)) 2101. In step S2206, the A-side input of the selector 2103 in FIG. 2 is selected. Step
In step S2207, a Y-decomposed image is output to the first transfer material in accordance with a processing procedure described later. In step S2208, an M-resolution image is output on the second transfer material in the same manner. In step S2209, a C-decomposed image is output on the third transfer material in the same manner. In step S2210, the image of the BK separation plate is output to 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 S2
At 212, a Y correction table for LUT2 is selected. Step 2
In step 213, the Y dot processing table of the LUT (1) is selected. In step S2214, the initialization data for Y is set to the halftone processing circuit 2102 so that the output image has a Y screen angle. In step S2115, data necessary for the font control circuit 2109 is set. Necessary data include, for example, a resist mark “#” for the purpose of resist, a color information mark “Y” indicating a Y separation,
And their output addresses. In step S2216, the image data of the Y separation is developed by a black (BK) developing unit 2295 to output the image of the Y separation. In addition, other M, C,
Each screen angle of each of the separated versions of BK can be marked, and the registration mark “#” and color information mark “M”
The image is developed by the BK developing unit 2295 together with “C” and “Bk”, and an image of each color separation is output.

In FIG. 10, the image itself of each color separation is black (B
K) is printed. However, these can be easily distinguished by the simultaneously printed character marks "Y, M, C, Bk". Accurate positioning can be achieved by aligning the registration marks "#".

[Effect of the Invention] As described above, according to the present invention, in a multi-tone image forming apparatus for forming dots of a multi-tone size corresponding to the density of multi-value image data, a halftone dot suitable for printing There is an effect that image data can be generated.

[Brief description of the drawings]

FIGS. 1A and 1B show a digital color image of the embodiment.
FIG. 2 is a functional block diagram of a reader / printer, FIG. 2 is a block diagram showing details of a gradation control circuit of the embodiment, FIG. 3 (A) is a timing chart of main signals in the printer unit, and FIG. 3 (B) is 4 (A) to 4 (D) are diagrams for explaining the halftone processing pattern of the embodiment, and FIG. 5 is a block diagram of the halftone processing circuit of the embodiment. 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. FIG. 6 (C) ) To (H) are diagrams showing examples of moiré fringes, FIG. 7 is a diagram for explaining the conversion characteristics of the LUT (1) of the embodiment, and FIGS. 8 (A) to (D) are diagrams of the LUT (2) of the embodiment. FIG. 9 is a block diagram showing details of the font control circuit of the embodiment, and FIG. FIG. 11 is a diagram showing an example of an output image obtained by font synthesis by the font control circuit of the embodiment. FIG. 11 is a cross-sectional view of a mechanical unit of the digital color reader / printer of the embodiment. FIG. 12 is an operation of the control unit 10 of the reader unit. 13A is a flowchart showing the operation of the controller 2500 of the printer unit, and FIG. 13B is a flowchart showing details of the Y-separated image output procedure of the embodiment. In the figure, 84: original, 83: original scanning unit, 86: rod lens array, 87: color CCD sensor unit, 88 ...
Signal processing block, 2289 …… Polygon mirror, 2290 ……
Mirror, 2900: photosensitive drum, 2292 to 2295: developing device, 2296: transfer drum.

Continuation of the front page (72) Inventor Kazuhiko Hirooka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Toshio Homma 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-61-5677 (JP, A) JP-A-62-139473 (JP, A) JP-A-61-237574 (JP, A) JP-A-62-242473 (JP, A) Kaisho 60-180370 (JP, A)

Claims (3)

(57) [Claims] A pixel having multi-valued image data is divided by a predetermined number of pixels to form a predetermined area, and according to predetermined halftone information for concentrating density at a predetermined position in the predetermined area. Image conversion means for converting the density of the multivalued image data of each pixel in the predetermined area; and dots of a multi-step size corresponding to the density based on the multivalued image data of each pixel density-converted by the image conversion means. An image processing apparatus, comprising: generating means for generating recording image data for forming the image data. 2. The image conversion means: Vij '= nVij-r (Pij-1) 0≤Vij'≤r where Vij: density value of input multi-valued image data of the target pixel Vij': target pixel 2. The image processing apparatus according to claim 1, wherein the density conversion is performed in accordance with the halftone information based on the density value n of the multi-valued image data output from the image processing unit: the number of pixels in the area r: the maximum density Pij: the weighting coefficient. . 3. The image processing apparatus according to claim 2, wherein the weighting coefficient has information for increasing a density toward a center pixel position of the area.