JPH0537782A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain the image forming device in which high quality continuous gradation picture is recorded with the picture memory of a small capacity. CONSTITUTION:A picture discrimination memory 14 has information used to distinguish whether a data is a binary data or a multi-value dither picture data for each picture element and the binary data and the multi-value dither picture data are respectively stored in a picture data memory 13 in mixture. A picture data signal 22 from the picture data memory 13 is given to a demultiplexer 23, in which the signal is separated into the binary data and the multi-value dither picture data based on a picture discrimination signal 21 from the picture discrimination memory 14, the binary data is processed in a binary data picture expansion section 24 and the multi-value dither picture data is processed in the multi-value dither picture data expansion section 25, they are synthesized by a multiplexer 26 and the result is sent to a gradation processing section 16 as a picture expansion signal. The multi-value dither picture data expansion section 25 uses the information of adjacent picture element data to decode the consecutive gradation level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having an image memory and capable of recording a halftone image.

[0002]

2. Description of the Related Art Conventionally, printers of various principles have been proposed as output terminals of personal computers, workstations, etc., but in recent years, especially black and white laser beam printers (hereinafter referred to as LBP) using an electrophotographic process and laser exposure technology. Is superior in terms of recording speed and printing quality, and is rapidly spreading.

On the other hand, in the market, there is an increasing demand for full color LBP, but in the case of full color LBP, not only the binary data handled in black and white LBP but also the image data of halftone color is targeted for output. Therefore, it is necessary to perform image processing capable of handling both binary image data and halftone image data.

Generally, in the case of an image output device to which an electrophotographic process such as LBP is applied, there is a problem in the stability of the electrophotographic process itself, and therefore black or white two-gradation output is often used. Binarization by the dither method is often used to represent a halftone image with a gradation printer.

Here, the principle of the dither method will be described with reference to FIG. First, an image sent as a halftone pixel level is divided into blocks of 4 pixels × 4 pixels, and the pixel level in the block is compared with a 4 × 4 threshold matrix for each pixel and binarized according to the magnitude relationship. To do. By repeating this for each matrix, a dither image is obtained. As the threshold matrix used to obtain this dither image, there are a dot concentration type that concentrates dots to smooth gradation, and a dot dispersion type that disperses dots to prioritize resolution. FIG. 15 shows a block diagram of the binary dither method. The pixels of the input image signal are sequentially moved, the rows and columns of the threshold matrix are addressed correspondingly, the thresholds of the threshold matrix corresponding to the respective pixels are sequentially read from the threshold matrix memory 133, and the input image signal is read. Binarize by comparing the size of and.
This binarized image is sent to the printer engine for printing. However, the printed image of the binary dither method has a drawback that the dither pattern is conspicuous and the resolution of the halftone portion is low.

Recently, a printer engine capable of recording in multiple gradations of three gradations or more has been developed in order to improve the quality of a printed image. However, for example, 300 DPI
In order to print four full colors of 256 gradations on an A4 paper size with the above resolution, an image memory of 30 megabytes or more is required, and there is a problem that the cost of the printer increases and the size of the apparatus increases.

[0007]

That is, in the above-mentioned conventional configuration, since the low-priced 2-gradation printer uses the binary dither method, the resolution is low and the multi-gradation printer capable of recording full color has a large capacity. However, there is a problem that the image memory becomes expensive and the device becomes large in size.

The present invention solves the above problems, and an object of the present invention is to provide an inexpensive image forming apparatus capable of high-quality multi-gradation recording with a small-capacity image memory.

[0009]

In order to solve the above problems, the present invention stores dither conversion means for converting image data into multivalued dither image data and multivalued dither image data converted by the dither conversion means. Storage means, conversion means for converting the multi-valued dither image data stored in the storage means into multi-tone image data, and image recording means for forming an image by the multi-tone image data converted by the conversion means. Be prepared.

[0010]

According to the present invention having the above-mentioned structure, the image data is converted into multi-valued dither image data and stored in the storage means, and the multi-valued dither image data stored in the storage means is converted into multi-gradation image data. Image recording can be performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic block diagram of an image forming apparatus according to an embodiment of the present invention.
Develops the printer code signal 5 sent from the host computer 4 as image data to generate an image recording signal 6
The image processing unit 2 and the printer engine 3 that forms a recorded image 7 from the image recording signal 6.

In this embodiment, the printer code signal 5 from the host computer 4 is taken as an example of the image information source, but this image information source may be an image file or a video image signal. .

There are several types of printer code signals 5 depending on the printer, such as printer control language and page description language.

The printer engine 3 is a color electrophotographic system of laser exposure, and has a recording density of 300 DPI and one for each color.
It has 256 gradations per pixel.

FIG. 2 is a block diagram of the image processing unit 2. The communication interface 11 is a host computer 4.
To receive the printer code signal 5. The image expansion unit 12 interprets the printer code signal 5 and writes the expanded image information in the image data memory 13 and the image discrimination memory 14. The image expansion unit 15 converts the image information in the image data memory 13 and the image discrimination memory 14 into the resolution and the number of gradations of the printer engine 3 and performs image processing for improving the image quality of binary characters and line drawings. Gradation processing unit 1
In step 6, image density adjustment, gamma correction, screen angle processing, and other processing for stabilizing the gradation of the printer engine are performed. The engine interface 17 is a gradation processing unit 16
It serves to send the image recording signal 6 output from the printer engine to the printer engine.

The image developing unit 12 will be described in detail.
FIG. 3 is a flowchart of the processing of the image expansion unit 12, FIG.
FIG. 4A is an operation explanatory diagram when the binary 8-color image information expanded by the image expansion unit 12 is written in the image data memory 13 and the image discrimination memory 14, and FIG. 4B is an intermediate color expanded by the image expansion unit 12. Is an operation explanatory diagram when writing the image information of the image information into the image data memory 13 and the image discrimination memory 14, interprets and develops the printer code signal 5 of the image developing unit 12, and writes it into the image data memory 13 and the image discrimination memory 14. The processing is executed by software.

The processing procedure of the image developing unit 12 will be described below with reference to the flowchart of FIG.

First, in step (a), the printer code signal 5 from the host computer 4 is received, and in step (b) it is determined whether or not the printer code signal 5 is a page end code. If the printer code signal 5 is not a page end code, the process proceeds to step (c) to determine whether the printer code signal 5 is a code relating to image development. If the printer code signal 5 is a code that is not related to image development, the process proceeds to step (f) to perform the same predetermined processing as the conventional printer.

If the printer code signal 5 is a code related to image development, the process proceeds to step (d) and the image data sent as the printer code signal 5 is divided into square blocks of 2 pixels × 2 pixels. Binary 8-color data (W (white), BK (black), R
(Red), G (green), B (blue), Y (yellow), M (magenta), C (cyan)).
If the printer code signal 5 is binary 8-color data, the process proceeds to step (e) and, as shown in FIG. 4A, the resolution of the printer engine is 300 DPI.
Image data is developed as K (black), Y (yellow), M (magenta), C (cyan)). The developed image data is written in each of the four color image data memories 13, and at the same time, the printer code is written to the address of the image discrimination memory 14 corresponding to the address of the image data memory 13 in which the developed image data is written. 0 indicating that the signal 5 is binary 8-color data is written.

Next, if the printer code signal 5 is not binary 8-color data but image data divided into square blocks of 2 pixels × 2 pixels, even one pixel has intermediate color data, step (g) The printer code signal 5 is set to Y (yellow), M (magenta), C (cyan), and B.
It is converted into a total of 24-bit data of 256 gradation 8-bits for each color of K (black), and then this 8-bit data of 256 gradations for each color of Y (yellow), M (magenta), C (cyan), and BK (black) is converted. By converting the data into 16 levels of 4 bits by the 16-value dither method into a total of 16-bit data, the image data is developed as four colors of 150 DPI · 16-value dither method, which is half the resolution of the printer engine. The developed image data is written in each of the four color image data memories 13, and at the same time, the printer code is written to the address of the image discrimination memory 14 corresponding to the address of the image data memory 13 in which the developed image data is written. 1 is written indicating that the signal 5 is intermediate color data. For example, when the pixel level of the image data developed by the 16-value dither method is 5, 5 is 2 as shown in FIG. 4B.
0101 is written in the image data memory 13 in the base system.

Here, the multi-valued dither method will be described with reference to FIG. The multi-valued dither method is an extension of the binary dither method to multi-valued (three or more values), and multi-valued in relation to the number of threshold matrices smaller by one than the multi-valued number. According to one embodiment of the present invention, the 16-value dither method is used to perform 16-value conversion with a threshold matrix of 15 layers. FIG. 5A shows the threshold matrix of the first layer and the threshold matrix of the fifteenth layer which is the uppermost layer. Due to the threshold matrix of 15 layers, the continuous tone image of 0-255 level in FIG. 5B becomes a 16-value dither image of 0-15 level.

By repeating the above processing, the image information is written in the image data memory 13 and the image discrimination memory 14. At this time, in the image data memory 13, for each block divided into 2 pixels × 2 pixels, if the printer code signal 5 is binary 8-color data, it is binary of 300 DPI, and if it is intermediate-color data, 16 of 150 DPI. Since the image data is expanded and stored by the value dither, the memory capacity can be reduced as compared with the case where all the data are stored in 256 gradations of 300 DPI.

When writing to the image data memory 13 and the image discrimination memory 14 is performed, the process returns to step (a). When the printer code signal 5 of page end is received, the printer code signal 5 is sent at step (b). Is the page end code, and the image data expansion processing ends. After the expansion processing, if the printer engine 3 is ready, printing is started. At this time, in the present embodiment, the image data of the image data memory 13 of each color is directly sent to the printer engine 3 via the engine interface 17. Instead of sending it, the image expansion unit 15 and the gradation processing unit 16 perform processing and then send it as a recorded image signal 6 to the printer engine 3 via the engine interface 17.

The image expansion section 15 and the gradation processing section 16 will be described below.

The image decompression unit 15 decompresses the image data stored in the image data memory 13 and the image discrimination memory 14 one by one in accordance with the order of colors printed by the printer engine 3. This printer engine 3 is BK
Printing is performed in the order of (black), C (cyan), M (magenta), and Y (yellow). The image recording signal 6 required for printing BK (black) is composed only from the BK (black) image data in the image data memory 13 and the information in the image discrimination memory 14,
Other C (cyan), M (magenta), and Y (yellow) image data are not required. Further, for other colors, the image expansion unit 15 synthesizes the image recording signal 6 with the image data corresponding to each color of the image data memory 13 and the information of the image discrimination memory 14.

FIG. 6 is a block diagram of the image decompression unit 15. The image data signal 22 from the image data memory 13 is sent to the demultiplexer 23 by the image discrimination signal 21 from the image discrimination memory 14 and the image data based on the 300 DPI binary value 15
Separated into 0DPI 16-value dither image data and 300D
The image data based on the PI binary value is the binary data image expansion unit 24.
Image data of continuous tone of 300 DPI 256, and 150 DPI 16-value dither image data is processed by the multi-value dither data image decompression unit 25 to obtain 300 DPI.
The image data of continuous gradation of PI 256 gradations is combined by the multiplexer 26 and becomes the image expansion signal 27, which is sent to the gradation processing unit 16. Here, the binary data image decompression unit 2
In 4, the image data by 300DPI binary is 300DP
Not only is the image data converted into I256 gradations, but also the edge portions of characters and line drawings are smoothed.

FIGS. 7A and 7B are explanatory diagrams for converting the 150-DPI 16-value dither image data into continuous-tone image data of 300 DPI 256 tones by the multi-valued dither data image expansion unit 25. In the first example shown in FIG. 7A, four pixels including the periphery of the pixel block to be converted are included.
When the bitmap data of the block × 4 block window is set to 16 values, there are only 5 and 6 levels. In this case, since the level difference between the pixel blocks in the window is small, the average value of the levels of the pixel blocks in the window is calculated, and 256 levels of pixel blocks to be converted are calculated.
8 times the average value for the continuous gradation level multiplied by 17
7 On the other hand, in the second example of FIG. 7B, when the bitmap data of the window of 4 blocks × 4 blocks including the periphery of the pixel block to be converted is set to 16 values, it is 3 to 6 Since the level of each pixel block in the window is large, the level of the pixel block to be converted is multiplied by 17 to set the level of 256 continuous gradations to 102. Here, the level difference between the pixel blocks in the window is judged to be small when the difference between the maximum value and the minimum value of the 16-value level in the window is 1 or less, and is large when the difference is 2 or more. Good. The size of the window for processing is preferably the same as the size of the dither matrix.

FIG. 8 shows the binary data image decompression unit 24 300
It is explanatory drawing which converts the image data by a DPI binary value into the image data of 300 DPI256 gradation. When converting binary image data to 8-bit 256-gradation image data,
0 is the 0 level and 1 is the 255 level. However, when the binary image data is, for example, data representing a slanted line and there is a step in the slanted line as shown in the bit map of the binary image data of the image data memory 13 in FIG.
As shown in the bitmap of 56 gradation image data, 0 is 0 level or 85 level, 1 is 255 level or 1
As the 70th level, an intermediate level is generated, binary data is converted into several gradations, the apparent resolution is increased, and the image quality is improved.

By repeating the above-described image expansion processing, the image expansion signal 27 for one color is obtained, and the image expansion signal 27 is similarly obtained for the other three colors. Image decompression unit 15
From this, the 8-bit image expansion signal 27 and the 1-bit image discrimination signal 21 are sent to the gradation processing unit 16.

In the gradation processing unit 16, image density adjustment /
Gamma correction, screen angle, and other processing are performed, but the main focus is tone modulation processing that stabilizes the tone of the printer engine 3 by causing uneven dot growth in accordance with the pixel position. In this gradation modulation processing, as shown in FIG. 9A, conventionally, gradation modulation is performed for each pixel to uniformly grow the dots of each pixel.
As shown in Fig. 2, each pixel is divided into two blocks, and within these two pixels, there are two pixels, that is, a pixel to be dot-grown first and a pixel to be grown later.
The gradation is stabilized by using two growth patterns.

However, this gradation modulation processing is a method of causing unevenness in dot growth. Therefore, when printing is performed with the same gradation modulation pattern for each color, if the printing for each color does not match, the recorded color Interference fringes called moire are generated between them, which significantly deteriorates the image quality. In the color recorded image, the screen angle method is used to avoid the moire between the recorded colors. First, the image is divided into 4 × 4 blocks, and each pixel is divided into two pixels, a pixel to be grown first and a pixel to be grown later.
As shown in FIG. 10, BK (black) is 45 °, C (cyan) is 63.6 °, and M (magenta) is 26, as shown in FIG. 4 ° · Y (yellow) forms a screen angle of 0 ° to avoid moire due to interference between recording colors.

Further, the density adjustment is performed based on the image density adjustment signal from the operation section of the printer, and the characteristics of this density adjustment are as shown in the characteristic diagram of the output image density with respect to the input image density in FIG.

In this embodiment, in order to automate gamma correction, a predetermined image density pattern is formed by the printer engine 3 before printing, the image density is measured, and gamma correction characteristic information is obtained from the measured density data. .

The gradation processing unit 16 performs the above-described gradation modulation, screen angle, density adjustment, and printer gamma correction processing in one step.
It is realized with one table. FIG. 12 shows the gradation processing unit 16
It is a block diagram of. The image expansion signal 27 from the image expansion unit 15 is input to the image gradation conversion table 34 and becomes the image recording signal 28. Since this gradation conversion needs to change the gradation characteristics depending on the recording color, the recording color signal 31 is input to the image gradation conversion table 34, and is controlled by a CPU (central processing unit) 36 so that gradation conversion corresponding to each color can be performed. A 4-bit address signal 32 obtained by counting the clock sent from the printer engine 3 via the engine interface 17 is input to the priority pixel determination circuit 33, and the pixel being processed is divided in the screen angle processing. The position of the 4 × 4 block to be recorded and the recording color signal 3
The recording color is determined by 1 and whether the pixel being processed is a priority pixel is determined based on the position information and the color information, and the priority pixel determination signal 35 is set to the image gradation conversion table 34.
Output to. In the image gradation conversion table 34, a table is selected by the image discrimination signal 21, the recording color signal 31, and the priority pixel determination signal 35, and the image expansion signal 27 is referred to and converted into the image recording signal 28. The image recording signal 28 is a level signal for actually driving the laser, for example, a signal converted into pulse width data. The image gradation conversion table 34 is prepared for the following three for each color. One is a table (image discrimination signal 21 is 0) for converting the data processed by the binary data image decompression unit 24, and also performs intermediate level processing generated by smoothing edges of binary character / line images. The remaining two are tables for converting the data processed by the multi-valued dither data image decompression unit 25 (image discrimination signal 21 is 1), which are a table for a pixel to be grown first and a pixel to be grown later in gradation modulation. There is a table.

In the present embodiment, in the conversion of the data processed by the multi-valued dither data image decompression unit 25 of the gradation processing unit 16, the spatial position of the image data is a pixel to be grown first and a pixel to be grown later. The data is forcibly concentrated on the pixels that are to be separated and grown first, so the effect of generating a strong electric field in the micro area of the electrostatic latent image on the photoconductor is extremely large, and the gradation is improved. Can contribute to.

Next, the laser beam printer is shown in FIG.
3 will be used for the explanation.

A laser beam printer for forming a color image by applying an electrophotographic process technique selectively irradiates a light beam corresponding to each color on a photosensitive member having a photosensitive layer to form an image, thereby forming a plurality of predetermined color components. A method of forming a color image on a single transfer material by developing a plurality of electrostatic latent images respectively corresponding to specific components in the above with respective predetermined toners, and superposing the monochromatic toner images on each other. It is adopted.

FIG. 13 is a schematic configuration diagram of a laser beam printer. In FIG. 13, reference numeral 101 denotes a photoconductor in which a photosensitive layer such as selenium (Se) or an organic photoconductor (OPC) is applied in a thin film form on the outer peripheral surface of a belt base material such as a loop-shaped resin. This photosensitive member 101 is supported by two photosensitive member conveying rollers 102 and 103 so as to form a vertical plane, and is rotated in the direction of arrow A along the photosensitive member conveying rollers 102 and 103 by a drive motor (not shown). To do.
On the peripheral surface of the belt-shaped photoconductor 101, a charger 104, an exposure optical system 105, black (B), cyan (C), magenta (M), and yellow (Y) are arranged in this order in the photoconductor rotation direction indicated by arrow A. Developing devices 106B, 106C, 106M for the respective colors,
106Y, an intermediate transfer member unit 107, a photoconductor cleaning device 108, and a static eliminator 109 are provided. The charger 104 is a charging wire 111 made of a tungsten wire or the like.
When a high voltage is applied to the charging line 111, the charging line 111 causes corona discharge to uniformly charge the photoconductor 101. Reference numeral 114 is an exposure light beam of image data emitted from the exposure optical system 105. In a laser beam printer, this exposure light beam 11
4 is obtained by subjecting the image signal sent from the image processing unit 2 to light intensity modulation or pulse width modulation by a laser drive circuit (not shown) and applying it to a semiconductor laser (not shown). To form a plurality of electrostatic latent images respectively corresponding to specific components of the plurality of predetermined color components. Each color developing device 106B, 106C, 1
06M and 106Y store toners corresponding to respective colors. Toner colors are selected according to each color, and the separating / contacting cam 11 is rotatably supported at its both ends on the main body of the machine.
5B, 115C, 115M, and 115Y rotate corresponding to the color selection signal, and the selected developing device, for example, 106B, is brought into contact with the photoconductor 101. The remaining unselected developing devices 106C, 106M, and 106Y are separated from the photoconductor 101. Intermediate transfer body unit 107
Is a loop belt-shaped intermediate transfer member 116 made of a conductive resin, two intermediate transfer member transport rollers 117 and 118 supporting the intermediate transfer member 116, and the intermediate transfer member 116.
In order to transfer the toner image on the photoconductor 101, it has an intermediate transfer roller 119 arranged so as to face the photoconductor 101 with the intermediate transfer body 116 interposed therebetween. Reference numeral 122 denotes an intermediate transfer member cleaning device for scraping off the residual toner on the intermediate transfer member 116, which is separated from the intermediate transfer member 116 while a composite image is formed on the intermediate transfer member 116 and is used for cleaning. Abut only when together. Reference numeral 123 is a transfer body cassette that houses the transfer material 124. The transfer materials 124 are sent out from the transfer material cassette 123 one by one to a paper transport path 126 by a half-moon shaped paper feed roller 125. Reference numeral 127 denotes a registration roller for temporarily stopping and waiting the transfer material 124 in order to match the positions of the composite material formed on the transfer material 124 and the intermediate transfer body 116, and is in pressure contact with the driven roller 128. Reference numeral 129 denotes a transfer roller for transferring the composite image formed on the intermediate transfer body 116 to the transfer material 124, and rotates in contact with the intermediate transfer body 116 only when the composite image is transferred to the transfer material 124. Thirteen
Reference numeral 0 denotes a fixing device including a heat roller 131 having a heat source inside and a pressure roller 132. The heat roller 131 and the pressure roller 13 form the composite image transferred on the transfer material 124.
It is fixed on the transfer material 124 by the pressure and heat accompanying the nip rotation of 2.

The operation of the electrophotographic apparatus configured as described above will be described below.

The photosensitive member 101 and the intermediate transfer member 116 are respectively driven by a driving source (not shown), and in this state, the charging wire 111 in the charging device 104 which is first connected to the high voltage power source.
A high voltage is applied to the substrate to cause corona discharge, and the surface of the photoconductor 101 is uniformly charged. Next, the photosensitive member 101 is rotated in the direction of arrow A, and the uniformly charged surface of the photosensitive member 101 is irradiated with an exposure light beam 114 of a laser beam corresponding to a predetermined black (B) of a plurality of color components. Then,
In the irradiated portion on the photoconductor 101, the charge disappears and an electrostatic latent image is formed. When the electrostatic latent image is formed, the developing device 106B containing the black toner that contributes to development is pressed in the direction of arrow B by the rotation of the separation / contact cam 115B according to the color selection signal and comes into contact with the photoconductor 101. With this contact, toner adheres to the electrostatic latent image portion formed on the photoconductor 101 to form a toner image, and the development is completed. The developing device 106B which has completed the development is moved from the contact position with the photoconductor 101 to the separation position by the 180 ° rotation of the separation cam 115B. The toner image formed on the photoreceptor 101 by the developing device 106B is transferred to the intermediate transfer body 116 by applying a high voltage to the intermediate transfer roller 119 arranged in contact with the photoreceptor 101 for each color. From the photoconductor 101 to the intermediate transfer body 1
The residual toner that has not been transferred to 16 is removed by the photoconductor cleaning device 108, and the charge on the photoconductor 101 from which the residual toner has been scraped off is removed by the static eliminator 109.

In the case of a copying machine or printer using four colors, the above developing operation is sequentially repeated four times to form toner images of four colors B, C, M and Y on the intermediate transfer member 116 to form a composite image. . The composite image formed in this manner is transferred to the intermediate transfer member 116 by the paper transfer roller 129 which has been separated so far.
Contacting the sheet transfer roller 129, a high pressure is applied to the sheet transfer roller 129 and the pressure is applied from the transfer material cassette 123 to the sheet conveying path 1.
It is collectively transferred to the transfer material 124 sent along the line 26. Then, the transfer material 124 on which the toner image is transferred is sent to the fixing device 130, where it is fixed by the heat of the heat roller 131 and the nip pressure of the pressure roller 132, and is output as a color image. Transfer material 12 by paper transfer roller 129
The residual toner on the intermediate transfer member 116 that has not been completely transferred onto the image forming device 4 is removed by the intermediate transfer member cleaning device 122.
To be removed. The intermediate transfer member cleaning device 122 is at a position separated from the intermediate transfer member 116 until a single combined image is obtained, and a combined image is obtained, and the combined image is transferred to the transfer material 124 by the sheet transfer roller 129. The post-contact state is reached and the residual toner is removed. With the above operation, recording of one image is completed, and a color-recorded image whose density is adjusted can be obtained.

The printer is not limited to the electrophotographic system using the laser beam of this embodiment, and may be a thermal transfer system or an inkjet system, and the same electrophotographic system such as an LED system or a liquid crystal shutter system. It doesn't matter. Further, in the present embodiment, the color image is superposed on the intermediate transfer member, but it may be superposed on the photosensitive member or on the transfer paper.

[0044]

As described above, the image forming apparatus of the present invention is
Dither conversion means for converting image data into multi-valued dither image data, storage means for storing the multi-valued dither image data converted by the dither conversion means, and multi-level dithered image data stored in the storage means. By including the converting means for converting into image data and the image recording means for forming an image with the multi-tone image data converted by the converting means, the image data is converted into multi-valued dither image data and stored in the storage means. Since the image data is stored, it is possible to reduce the storage capacity of the storage unit, and the multi-valued dither image data stored in the storage unit is converted into multi-gradation image data to perform image recording. Images can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of an image processing unit according to an embodiment of the present invention.

FIG. 3 is a flowchart of processing of an image expanding unit according to an embodiment of the present invention.

FIG. 4A is an operation explanatory diagram when writing binary 8-color image information in a memory according to an embodiment of the present invention, and FIG. 4B is a diagram illustrating intermediate-color image information according to an embodiment of the present invention in a memory. Operation explanation diagram when

5A is a threshold matrix diagram of first and fifteenth layers according to an embodiment of the present invention, and FIG. 5B is an operation explanatory diagram of a multi-value dither method according to an embodiment of the present invention.

FIG. 6 is a block diagram of an image decompression unit according to an embodiment of the present invention.

7A is an explanatory diagram for converting the first example of 16-value dither image data in one embodiment of the present invention into image data of 256 continuous gradations, and FIG. 7B is one embodiment of the present invention. Explanatory drawing which converts the 2nd example of 16 value dither image data in an example into the image data of 256 continuous gradation.

FIG. 8 is an explanatory view for converting binary image data into image data of 256 gradations in one embodiment of the present invention.

9A is an explanatory diagram of a conventional gradation modulation process, and FIG. 9B is an explanatory diagram of a gradation modulation process according to an embodiment of the present invention.

FIG. 10 is an explanatory diagram of a screen angle in one embodiment of the present invention.

FIG. 11 is a characteristic diagram of output image density with respect to input image density according to an embodiment of the present invention.

FIG. 12 is a block diagram of a gradation processing unit according to an embodiment of the present invention.

FIG. 13 is a schematic configuration diagram of a laser beam printer according to an embodiment of the present invention.

FIG. 14 is an explanatory diagram of a conventional dither method.

FIG. 15 is a block diagram of a conventional dither method.

[Explanation of symbols]

1 Image forming device 2 Image processing unit 3 Printer engine 4 Host computer 5 Printer code signal 6 Image recording signal 7 Recorded image 11 Communication interface 12 Image development section 13 Image data memory 14 Image discrimination memory 15 Image decompression unit 16 gradation processing unit 17 engine interface 21 Image discrimination signal 22 Image data signal 23 Demultiplexer 24 Binary data image decompression unit 25 Multi-level dither data image decompression unit 26 multiplexer 27 Image expansion signal 28 Image recording signal 31 Recording color signal 32 address signal 33 priority pixel determination circuit 34 Image gradation conversion table 35 priority pixel determination signal 36 CPU 101 photoconductor 102 photoconductor conveying roller 103 Photoconductor transport roller 104 charger 105 Exposure optical system 106 developing device 107 Intermediate Transfer Unit 108 Photoconductor cleaning device 109 Static eliminator 111 charged wire 114 exposure rays 115 Separation cam 116 Intermediate transfer body 117 Intermediate transfer member conveying roller 118 Intermediate transfer member transport roller 119 Intermediate transfer roller 122 Intermediate Transfer Body Cleaning Device 123 Transfer body cassette 124 Transfer material 125 paper feed rollers 126 Transfer material transport path 127 Registration roller 128 driven roller 129 Transfer roller 130 Fixer 131 heat roller 132 pressure roller

Claims (2)

[Claims] 1. A dither conversion means for converting image data into multi-value dither image data, a storage means for storing the multi-value dither image data converted by the dither conversion means, and a multi-value stored in the storage means. An image forming apparatus comprising: a conversion unit that converts dither image data into multi-tone image data; and an image recording unit that forms an image with the multi-tone image data converted by the conversion unit. 2. Image data storage means for converting halftone image data into multi-valued dither image data and storing binary image data as binary image data, and image data stored in the image data storage means. Discrimination data storage means for storing discrimination data for distinguishing types, and multi-gradation conversion means for converting the image data stored in the image data storage means into multi-gradation image data by the discrimination data from the discrimination data storage means. And an image recording unit for forming an image by the multi-gradation image data converted by the multi-gradation conversion unit.