JPH04269075A - Method and device for image formation - Google Patents

Abstract

PURPOSE:To obtain a recording picture with high quality by growing dots in the order of dots corresponding to a minimum recording picture element location with high priority and recording dots corresponding to a minimum recording picture element location with low priority in a binary number. CONSTITUTION:A digital data output device 22 receives a picture signal from an image scanner or a video camera and applies A/D conversion and prescribed picture processing to the signal and outputs the result. Since a gradation at a high density area is not visually important in comparison with that at a low density area, even when a dot at a maximum recording density under this circumference is formed suddenly, an adverse effect such as pseudo contour (gradation jump) is not almost caused. When a picture element whose priority is lowest is recorded in a binary value, the picture element with highest density is formed corresponding to the case of reproduction of a signal with very high density is required such as a high density set-solid printing part.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image forming apparatuses such as laser beam printers and copying machines.

0002

[Prior Art] Printers based on various principles have been proposed as output terminal devices for personal computers, workstations, etc. Among them, laser beam printers (hereinafter referred to as LBPs), which use electrophotographic processes and laser technology, have been proposed in the past. ) has great advantages in terms of recording speed and print quality, and is rapidly becoming popular.

On the other hand, there is an increasing demand for full-color LBPs in the market, but in the case of full-color LBPs, there is a strong demand for image data to be output in addition to conventional characters and line drawings, and in such cases, general LBP 2
For value data processing, it is necessary to perform image processing assuming multi-tone output.

Generally, in the case of image output devices that apply an electrophotographic process such as LBP, there is a problem with the stability of the electrophotographic process itself. This is the extent that can be ensured.

Nowadays, the binary dither method is often used as a method for recording halftone images in image output devices with an insufficient number of output gradations, such as LBPs and ordinary thermal transfer printers. However, the binary dither method requires the use of a large-sized dither matrix in order to obtain sufficient gradation, and as the gradation increases, the resolution decreases and interference between the halftone dots of the original and the dither pattern occurs. There were problems such as deterioration of image quality such as the occurrence of moiré.

A multilevel dither method has been proposed to improve the above-mentioned drawbacks. The multilevel dither method will be explained using FIG. 2. FIG. 2 is a block diagram of a conventional image forming apparatus. To simplify the explanation, it is assumed that the image data has already been stored in the image memory 1.

The image memory 1 stores luminance data of an image signal (hereinafter referred to as RGB signal) consisting of three primary color components of additive color mixture of red (R), green (G), and blue (B). Each pixel has an information amount of 8 bits*3=24 bits. These pixel data are accessed by a main scanning direction counter 2 and a sub scanning direction counter 3,
The signals representing each of the colors R, G, and B are read out all together from the beginning. Since the R, G, and B signals are luminance signals representing each color, the density conversion unit 4 performs density conversion to obtain the three primary colors of subtractive color mixture consisting of density signals cyan (C), magenta (M), and yellow (Y). Convert to signals (hereinafter referred to as CMY signals).

This conversion is usually performed using read-only memory (hereinafter referred to as ROM) or read/write memory (hereinafter referred to as RA).
Set the conversion table in a storage device such as
The contents are read by accessing the brightness data value as an address.

The actual contents of the table include values based on, for example, the graph shown in FIG. 3 showing the density conversion characteristics of a conventional image forming apparatus.

The density-converted pixel data is input to the color correction section 5 in all three colors. In the color correction section 5, well-known techniques such as background removal (hereinafter referred to as UCR), black plate generation, masking, etc. are performed on the density data. Black is added to the image data by the color correction unit 5, and the amount of information per pixel is effectively 8*4=32 bits. Next, these four color data are transferred by the data selector 6, for example, if the transfer destination is the engine of a full color printer, the data is transferred for each color sequentially according to the colors black (Bk), C, M, and Y. be exposed.

On the other hand, among the address outputs of the main scanning direction counter 2 and the sub-scanning direction counter 3, the lower 3 bits of each are connected to a storage device 7 for storing a dither threshold matrix, and are uniquely stored according to the spatial coordinates of the image. Output the determined threshold value. The address for accessing the storage device 7 has a total of 6 bits, that is, 64 pieces of data can be accessed. In this case, the dither threshold matrix stored in the storage device 7 may be, for example, the 8*8 dither threshold matrix shown in FIG. 4.

The threshold output from the storage device 7 is input to the comparator 8 and compared with the lower 6 bits of the 8 bits of density data output from the data selector 6. The comparator 8 sets, for example, 1 if the density data is greater than or equal to the threshold, and if the density data is smaller than the threshold,
For example, 0 is output as the comparison result 11.

On the other hand, the upper two bits of the density data outputted from the data selector 6 are connected to a storage device 9 for redetermining the pixel value, and together with the comparison result bit outputted from the comparator 8, the upper two bits are stored in a total of three bits. The bit data is accessed and a final output value of 12 is output. FIG. 5 shows an example of the final output value in the multi-value dither method when the upper two bits of the output of the data selector 6 are the density level signal 10 and the comparison output of the comparator 8 is the comparison result 11.

The above explanation is a method used when configuring hardware that converts an image signal into a signal to be printed using the multi-level gradation dither method, and as shown in FIG. is represented by five hexadecimal numbers: 0, 3F, 7F, BF, and FF. That is, it becomes a 5-value dither.

[0015] Generally, when outputting a full-color image using an image output device having a small number of gradation levels, a multi-value dither method as shown here is widely employed. For example, even if the number of gradations that can be output by the image output device itself is 4,
By combining relatively large dither threshold matrices such as *8, it is possible to obtain 193 levels of gradation (8*8*(4-1)+1=193) using pseudo gradation.

[0016]

[Problems to be Solved by the Invention] As explained in detail in the prior art, image output devices such as LBP and thermal transfer printers, which have a small number of gradations in the process or the transfer principle itself, use a multi-value dither method. Pseudo area gradation techniques are widely used.

[0017] These methods employ a halftone type dither threshold matrix, for example, a threshold matrix that generates concentration of multiple dots within one matrix to achieve both resolution and gradation, and image output. It has become possible to obtain a certain level of image quality by improving the resolution of the minimum recording dot of the device or by irregularly switching the dither matrix depending on the density level.

However, even in the case of multilevel dithering, deterioration of resolution is unavoidable when it is desired to increase the number of gradations, and in principle, since an intermediate density level is used within one pixel, density unevenness of the recorded image may occur. Easy to occur.

Furthermore, even though the lower the gradation area, the more smooth it is needed, all the gradation areas have only uniform and discrete density levels, so recording pixels with a density close to the lowest density are formed on a white background. Due to the characteristics of human visual perception, images may appear grainy or textured. In this way, image quality is degraded, especially in low gradation areas.

Furthermore, it is possible to suppress the occurrence of so-called collapse, where adjacent dots on all sides of a certain dot are completely fused after heat fixation as the pixel grows, and to reproduce high-density solid areas by actively utilizing collapse. are incompatible. In other words, if the gradation level and dither matrix are set to completely suppress collapse, the gradation in high-density areas will certainly improve, but the absolute density level will tend to be insufficient; If this is done, the absolute density level can be ensured, but the gradation in the high density area will be impaired.

An object of the present invention is to solve the above-mentioned problems, to avoid deterioration of resolution and generation of texture, to have excellent gradation in all density ranges, to suppress distortion in particularly high density ranges, and to An object of the present invention is to provide an image forming apparatus that can obtain high-quality recorded images that can ensure the absolute maximum density.

[0022]

[Means for solving the problem] In order to solve the above problem, a block consisting of a plurality of pixels on image data is set, and according to a spatially predetermined priority order within the block, the minimum Dots are grown in order from the dot corresponding to the recording pixel position, and the dot corresponding to the minimum recording pixel position with the lowest priority is recorded in binary.

[0023]

[Function] With the above-described configuration, the present invention prevents the dots of the minimum recording pixel with the lowest priority from growing until the maximum density is reached, so that collapse can be suppressed, and when the maximum density is reached, all dots grow. This makes it possible to reproduce solid areas caused by crushing.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, 22 is a digital data output device, such as an image scanner or a video camera (
(not shown) etc. as input, and analog
The image is output after being subjected to digital conversion (hereinafter referred to as A/D conversion) or predetermined image processing. Further, this digital data output device 22 may be configured to temporarily store image data in a memory, or may be configured to directly interface image signals from communication means.

When the print engine 21 starts up, the digital data output device 22 starts transferring digital image data to the image processing section 23 . The data to be subjected to image processing is 24 bits in total, 8 bits for each color of RGB. The RGB data input to the image processing section 23 is luminance data, and the density conversion section 24 converts the luminance data into density data, that is, the three primary colors of printing, C, M, Y (cyan, magenta,
yellow) signal.

Generally, this conversion can be easily realized by writing the conversion table data 25 on a storage device such as RAM or ROM, and accessing the data by appropriately offsetting the input data value, for example. The normal density conversion unit 24 can perform monochrome density, overall density, contrast, background color control, etc. (density and color adjustment) of the input image.

[0027] RGB (luminance) data is CM after density conversion.
It has been converted to Y (concentration) data 26, 27, 28,
Using the CMY data, the UCR/black version generation unit 29 then generates U
Performs CR (undercolor removal) and black plate generation. UCR reduces data at a constant rate with respect to the common amount of CMY data. Basically, this reduction amount is generated as a black version. Originally U
The purpose of CR and black plate generation is to replace the common amount of CMY with black for each pixel, thereby saving color material (toner). However, today UCR is used purely to save toner.
The UCR and black version generation is rarely performed, and the purpose is, for example, to prevent gradation deterioration in high-density areas, ensure contrast, and ensure gray balance in high-density areas, and actively changes the amount of UCR and black plates. It is possible to output even higher quality images. After the UCR/black plate is generated by the above processing, C data 30, M data 31, Y data 32, and Bk (black) data 33 are generated.

[0028] Thereafter, data other than Bk data 33, which is an achromatic color component, are input to the color correction section 34. The color correction unit 34 performs processing such as masking on the colored components (CMY). The purpose of masking is to correct the influence of unnecessary absorption bands of each color material. For example, C (cyan) coloring material has unnecessary absorption bands in wavelength regions other than C. Specifically, for example, Y
(yellow) color component. Similarly, Y is included in M (magenta). Therefore, when recording Y, it is necessary to reduce the Y component contained in C and M depending on the density at which C and M should be recorded.

In this method, a 3*3 matrix operation is normally performed on CMY digital signals, or the result of the operation is written in a storage device such as a ROM, and after each color is accessed, addition and subtraction are performed to obtain the result.

Conventionally, 3*3 linear masking (first-order masking) has been the mainstream, but first-order masking is insufficiently effective, and recently more than two-order nonlinear masking, or color correction itself, is performed within a black box. C
Many new color correction methods that obtain mapping functions in areas other than MY space have also been proposed. The input data C is input by the color correction unit 34.
Data 30, M data 31, and Y data 32 are converted into C' data 35, M' data 36, and Y' data 37. On the other hand, since the Bk data 33 is achromatic data, it is not involved in color correction.

C' subjected to color correction by the color correction section 34
Of the data 35, M' data 36, Y' data 37 (colored data) and Bk data 33 (achromatic data), only one color data is selected by the data selector 38 and inputted to the gradation processing section 39. Performs gradation processing of image signals related to. The image signal subjected to gradation processing is sent to the printer engine 21, and a high-quality recorded image, which is the object of the present invention, is obtained.

The contents of the gradation processing related to the present invention will now be explained in detail using FIG. 6. FIG. 6 is a block diagram of the gradation processing section 39 in FIG. 1, and 50 in FIG. 6 is a horizontal synchronization signal generation circuit, which outputs a horizontal synchronization signal 51 of the image. For example, in the case of a laser beam printer, a beam detect signal from a laser scanning optical system (not shown) can be used as a generation source of the horizontal synchronization signal by subjecting it to waveform shaping or the like. 52 in FIG. 6 is a horizontal binary counter, which counts the horizontal synchronizing signal 51, and counts the horizontal synchronizing signal 51.
The output signal alternates between high and low each time it is input.

Reference numeral 56 in FIG. 6 is a vertical synchronization signal generation circuit, which outputs a vertical synchronization signal 57 for an image. For example, a data transfer clock can be used as is as a generation source of the vertical synchronization signal. Reference numeral 58 in FIG. 6 is a vertical binary counter that counts the vertical synchronization signal 57, and the output signal is switched between high and low every time the vertical synchronization signal is input.

To explain each of the above signals in more detail,
FIG. 7 is a timing chart showing changes in the time axis direction of each synchronization signal and each counter output in FIG. Indicates changes along the time axis. The horizontal synchronization signal is generated once at the beginning of the line data for each line of data transferred (line period), and the vertical synchronization signal corresponds to each piece of data in one line (pixel period).
The number of occurrences is equal to the number of pixels included in one line. If these signals are each counted by a binary counter, there will be four combinations of 2*2 of the horizontal binary counter output 54 and the vertical binary counter output 59.

As shown in FIG. 7, the horizontal binary counter output =
0, state A when vertical binary counter output = 0, state B when horizontal binary counter output = 1, vertical binary counter output = 0, horizontal binary counter output = 0, vertical binary counter output = If we define state C when the output is 1, state D when the horizontal binary counter output = 1, and state D when the vertical binary counter output = 1, the state of each counter output is unique depending on the spatial position of the pixel. handle. FIG. 8 is a diagram showing the states of the counter output corresponding to each pixel position, which are classified into state A, state B, state C, and state D.

Hereinafter, if the symbols A, B, C, and D are used as symbols to indicate the pixel positions regularly arranged in space, the entire image will be composed of pixels at the A, B, C, and D positions. * Can be divided into 2 pixel areas.

Reference numeral 53 in FIG. 6 is a gradation conversion table, which has pixel levels after gradation conversion in the table using the input image signal 55, horizontal binary counter output 54, and vertical binary counter output 59 as memory addresses. address line is 1
The input image signal 55 consists of 0 bits, of which the lower 8
The vertical binary counter output 59 is assigned to the 9th bit, and the horizontal binary counter output is assigned to the 10th bit.

The gradation conversion table 53 will now be explained in more detail with reference to FIGS. 9 and 10. FIG. 9 is a diagram showing the contents of the gradation conversion table in the embodiment. If the gradation level of the input image signal is 8 bits (256 levels), 256 addresses are required in the table to express the gradation conversion characteristics for one pixel, and in this example, A, B, C, D Since it has four gradation conversion characteristics classified into , there are a total of 1024 addresses.

That is, at addresses 000H-0FFH expressed in hexadecimal, data representing the tone conversion characteristics for the pixel at position A is stored at address 1 expressed in hexadecimal.
00H-1FFH contains data representing the gradation conversion characteristics of the C position, and the address 200H-2FF is expressed in hexadecimal.
Data representing the gradation conversion characteristic of the B position is stored in H, and data representing the gradation conversion characteristic of the D position is stored in addresses 300H-3FFH expressed in hexadecimal.

FIG. 10 is a graph of tone conversion characteristics in the example. In this embodiment, the priority of the pixel at the A position is set to the highest, followed by the B position, the C position, and the D position is set to the lowest priority.

The gradation conversion characteristic corresponding to the A position, that is, the pixel position with the highest priority, has an input image level of 00 in hexadecimal.
The output increases continuously from H to 52H, and when the input image level exceeds 53H, it is set to output FFH.

The gradation conversion characteristic corresponding to the B position, that is, the pixel position with the next highest priority after the A position, has an input image level of 16.
When the input image level is less than 53H in hexadecimal, 00H is output, the output increases continuously from 53H to A5H, and when the input image level exceeds A5H in hexadecimal, the output is FF.
Set to H.

The gradation conversion characteristic corresponding to the C position, that is, the pixel position with the next highest priority after the B position, is when the input image level is A6.
When the input image level is less than H, 00H is output, and the output increases continuously from hexadecimal A6H to F8H, and when the input image level exceeds hexadecimal F8H, FFH is output.

The tone conversion characteristic corresponding to the D position, that is, the pixel position with the lowest priority, is when the input image level is F9 in hexadecimal.
When the input image level is less than H, 00H is output, and when the input image level exceeds F8H in hexadecimal, FFH is output. A major feature of the present invention is that the D position (the pixel position with the lowest priority) is subjected to binary recording, unlike the processing of other recording pixel positions.

In electrophotographic printers, when forming pixels, rather than growing dots of each pixel uniformly,
As mentioned above, by giving priority to specific pixels and growing dots of specific pixels, a strong electric field is created in the microscopic area of the electrostatic latent image on the photoreceptor, resulting in poor gradation of the recorded image. improves.

In general, in a natural image, the correlation between adjacent pixels is very high, so by following the method of this embodiment, it is possible to easily give priority, that is, difference, to pixel growth within a block, and it is possible to easily give priority to pixel growth within a block. The gradation can be improved. Not only that, but because a specific spatial frequency component is superimposed on the image as a result, resistance to, for example, drive unevenness caused by the drive system is improved. In other words, the method of this embodiment is a novel method in which noise having a specific spatial frequency component is superimposed on an image, and the noise level is a spatially defined period such as that defined by a dither matrix, etc. A major feature is that it is not affected by the digital threshold value and is derived from the density level itself, which is close to analog of the pixel (for example, has a large number of gradation levels such as 256 gradations). This is significantly different from a tone reproduction method that provides discrete noise levels (for example, four tone levels).

In this embodiment, the exact order in which pixels within a block grow is not guaranteed. For example, within one block, even if the highest priority pixel does not grow completely, the lowest priority pixel may grow. Particularly in images with undulating data, for example, in parts of the image such as characters and line drawings with steep edges, the growth order of pixels may be reversed depending on how the blocks are arranged.

That is, the priority in this embodiment does not determine the growth order of pixels, but merely defines the input density level at which each pixel grows. However, in general natural images, the correlation between adjacent pixels is very high, so pixels involved in tone reproduction (in the growth stage) are selected according to the input density level in a certain spatial macro area, and as a result, The same effect as when the growth order is specified can be obtained.

Furthermore, the fact that the order of pixel growth is not completely determined suppresses deterioration of resolution to a minimum.

For example, in a method that processes pixel data within a block and rearranges the data by giving priority to each pixel position, there is no actual image data (or There is a possibility that data will be weighted in locations (where the value is small), and the resolution will definitely deteriorate. However, in the method of this embodiment, even if the pixel value is large enough for a line drawing, for example, and the density is high (most of the time, text and line drawings are output at maximum density), the target pixel will definitely grow. The resolution will not deteriorate at all.

Furthermore, with the method described in this embodiment, almost analog-like density control can be performed in all density regions due to visual characteristics, so high-density recording dots do not suddenly appear on a white background, and especially natural images etc. It is possible to suppress the roughness in the low gradation areas of a smooth image, and to significantly improve the gradation properties in the low gradation areas.

[0052] That is, in this method, for smooth images,
In particular, it exhibits a characteristic that emphasizes gradation in low gradation areas, and a characteristic that emphasizes resolution for areas such as characters and line drawings that are normally expressed in high density.

The process of recording the pixel with the lowest priority in binary format is carried out when the density is extremely high in a relatively wide area, since the correlation between adjacent pixels is very high in a natural image. In fact, as shown in Figure 10, by the time the pixel with the lowest priority is recorded, all the pixels in the surrounding 3/4 of the pixel with the lowest priority have grown, so the density in this area is relatively low. The density is high (however, since there is a 1/4 non-printing area, the phenomenon of collapse in which adjacent dots are fused to each other is relatively unlikely to occur).

As is well known, gradation in the high density area is less important in terms of visual characteristics than in the low density area, so even if dots of maximum recording density are suddenly formed under the above circumstances, false contours (
There are almost no negative effects such as gradation jump. Rather, if the pixels with the lowest priority are recorded in binary format, it is possible to form pixels with the highest density only in cases where extremely high density reproduction is required, such as in high-density solid print areas. Become.

Therefore, according to this embodiment, as the pixel grows, adjacent dots on all sides after heat fixing are completely fused together, so-called collapse can be suppressed, and the collapse can be actively utilized to create a high-density solid area. It becomes possible to simultaneously reproduce the In other words, conventional gradation level and dither matrix settings that suppress collapse improve the gradation in high density areas, but the absolute density level tends to be insufficient.On the other hand, if collapse is allowed, Although the absolute density level can be ensured, it is possible to effectively solve the drawback that the gradation in the high density region is impaired.

Next, an embodiment using other tone conversion characteristics will be described with reference to FIGS. 11 and 12.

11 and 12, the common feature is that the dots with the lowest priority do not have a continuous growing area and are set to perform binary recording.

FIG. 11 is a graph of the tone conversion characteristic I. The gradation conversion characteristic I shown in FIG. 11 is for actively suppressing the growth of dots with specific priorities such as the A position and the C position, for example. Through this process, pixels are formed in cases where the highest density reproduction is required, such as in high-density solid printing areas, and in the middle and high density areas, certain dots after heat fixation are formed as pixels grow. It becomes possible to more efficiently suppress the occurrence of so-called collapse, in which adjacent dots on all sides are completely fused together.

FIG. 12 is a graph of tone conversion characteristic II. The gradation conversion characteristic II shown in FIG. 12 indicates that, except for the dot with the lowest priority for binary recording, dots with lower priority start growing before the density of dots with higher priority reaches the maximum. This is what I set it to do. The gradation is improved at the portion where the gradation conversion characteristics of each priority level are switched.

Of course, the tone conversion characteristic I and the tone conversion characteristic I
It is also possible to combine I, and in this case, it is possible to improve the gradation in the part where the growth of pixels of each priority changes, and
This means that it is possible to suppress collapse of medium and high density areas and to ensure maximum density during solid recording.

Although the embodiment has been described in detail by setting 2*2 blocks, the present method can be applied regardless of the block size. Moreover, the relationship between the priority order and the pixel position within the block, the number of pixels whose dots are grown preferentially within the block, etc. can be easily changed. This change changes the number of count bits of the counter according to the size of the block (it doesn't matter if the size in each direction is different), secures a gradation conversion table area for the number of output states of the counter, and This can be achieved simply by writing and changing the contents of the conversion table, and is extremely easy.

Next, a laser beam printer employing the gradation processing described in this embodiment will be explained in detail with reference to FIGS. 13 to 15.

A laser beam printer that forms a color image by applying electrophotographic process technology selectively irradiates light beams corresponding to each color onto a photoreceptor 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 sheet of transfer material by developing a plurality of electrostatic latent images, each corresponding to a specific component in the image, with a predetermined toner, and superimposing these monochrome toner images. We are hiring.

FIG. 13 is a schematic configuration diagram of a laser beam printer, FIG. 14 is an explanatory diagram of the operation of photoconductor reference detection, and FIG. 15 is an explanatory diagram of the operation of intermediate transfer member reference detection.

In FIG. 13, 101 is a photoreceptor;
A photosensitive layer such as selenium (Se) or organic photoconductor (OPC) is coated in the form of a thin film on the outer peripheral surface of a belt base material such as a closed loop resin having a seam 101a. This photoreceptor 101 has two photoreceptor conveying rollers 102 and 103.
It is supported so that a vertical plane is formed between the photoreceptor transport rollers 102 and 103, and is rotated in the direction of arrow A along the photoreceptor transport rollers 102 and 103 by a drive motor (not shown).

Arrow A is marked on the circumferential surface of the belt-shaped photoreceptor 101.
Charger 104, exposure optical system 105, black (B), cyan (C), magenta (M
), yellow (Y) color developing units 106B, 106C
, 106M, 106Y, an intermediate transfer unit 107, a photoconductor cleaning device 108, a static eliminator 109, and a photoconductor reference detection sensor 110.

The charger 104 is composed of a charging wire 111 made of tungsten wire or the like, a shield plate 112 made of a metal plate, and a grid plate 113. Charged wire 1
By applying a high voltage to the charged wire 111, a corona discharge is caused in the charged wire 111, and the charged wire 111 is connected to the photoreceptor 10 via the grid plate 113.
1 is uniformly charged. Reference numeral 114 denotes an exposure light beam for image data emitted from the exposure optical system 105.

In the laser beam printer, the exposure light beam 114 converts an image signal from the gradation converter 2 into a semiconductor laser (not shown) after light intensity modulation or pulse width modulation by a laser drive circuit (not shown). is applied to form a plurality of electrostatic latent images on the photoreceptor 101, each corresponding to a specific component among a plurality of predetermined color components. As shown in FIG. 14, the photoreceptor reference detection sensor 110 detects the position of the seam 101a of the photoreceptor 101, and is located at a predetermined position relative to the seam 101a of the photoreceptor 101 at one end of the photoreceptor 101. A photoreceptor reference mark 101b such as a slit placed in the photoreceptor is detected.

Each color developing device stores toner corresponding to each color. Toner color selection is achieved by rotating separation cams 115B, 115C, 115M, and 115Y, which correspond to each color and whose ends are rotatably supported by the main body of the machine, in response to a color selection signal, and the selected developer is selected. For example 106B
This is done by bringing the photoreceptor 101 into contact with the photoreceptor 101. The remaining developing units 106C, 106M, and 106 that are not selected
Y is spaced apart from the photoreceptor 101.

The intermediate transfer body unit 107 is a seamless loop belt-shaped intermediate transfer body 1 made of conductive resin or the like.
16, two intermediate transfer body conveying rollers 117 and 118 supporting the intermediate transfer body 116, and the intermediate transfer body 1 for transferring the toner image on the photoreceptor 101 to the intermediate transfer body 116.
The intermediate transfer roller 119 is disposed opposite to the photoreceptor 101 with the intermediate transfer roller 16 interposed therebetween.

Here, the surface circumference L1 of the photoreceptor 101 is nominally equal to the surface circumference L2 of the intermediate transfer member 116, but it is set so that the relationship L1≦L2 always holds within the range of variation.

Next, as shown in FIG. 15, reference numeral 120 is an intermediate transfer body reference detection sensor for detecting the reference position of the intermediate transfer body 116. The reference position is detected using the reference mark 116a. Reference numeral 121 denotes a photoreceptor clutch mechanism, which controls the rotation of the photoreceptor by turning on and off power from a drive source (not shown), and is provided on the drive shaft of the photoreceptor conveying roller 103. . 122 is an intermediate transfer body cleaning device for scraping off residual toner on the intermediate transfer body 116; it is separated from the intermediate transfer body 116 while a composite image is being formed on the intermediate transfer body 116; Contact only when serving.

Reference numeral 123 denotes a transfer material cassette containing a transfer material 124. The transfer material 124 is the transfer material cassette 12
3, the sheets are sent one by one to a sheet conveying path 126 by a half-moon-shaped sheet feeding roller 125. 127 is the transfer material 12
4 is a registration roller for temporarily stopping and waiting the transfer material 124 in order to match the position of the composite image formed on the intermediate transfer body 116, and is in pressure contact with the driven roller 128. 129 is a transfer roller for transferring the composite image formed on the intermediate transfer body 116 to the transfer material 124;
The intermediate transfer body 11 is used only when transferring the composite image to the transfer material 124.
Rotates in contact with 6. 130 is a fixing device consisting of a heat roller 131 and a pressure roller 132 which have a heat source inside, and applies pressure and heat to the composite image transferred onto the transfer material 124 as the heat roller 131 and the pressure roller 132 rotate. The image is fixed on the transfer material 124 to form a color image.

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

The photoreceptor 101 and the intermediate transfer member 116 are each driven by a drive source (not shown), and are controlled so that their circumferential speeds are the same constant speed. Further, the intermediate transfer body 116 has an image forming area set in advance by an intermediate transfer body reference detection sensor 120 that detects an intermediate transfer body reference mark 116a for determining a reference position, and the image forming area of the photoreceptor 101 is set in advance in this area. The positions of the joints 101a are adjusted so that they do not overlap at the intermediate transfer roller 119, and the rollers are driven in synchronization.

In this state, first, a high voltage is applied to the charging wire 111 in the charger 104 connected to the high voltage power supply to cause corona discharge, and the surface of the photoreceptor 101 is uniformly heated to -700V to -.
Charge it to about 800V. Next, move the photoreceptor 101 to arrow A
A predetermined color component, for example, black (B) among a plurality of color components, is placed on the surface of the photoreceptor 101 which is rotated in the direction and uniformly charged.
When the exposure light beam 114 of the laser beam corresponding to the photoreceptor 101 is irradiated, the irradiated portion of the photoreceptor 101 loses its charge and an electrostatic latent image is formed. At this time, this electrostatic latent image is transferred to the intermediate transfer member 1.
Seam 1 of photoreceptor 101 is located at a position within the image area on intermediate transfer body 116 that is preset by a signal from intermediate transfer body reference detection sensor 120 that detects the reference position of photoconductor 116.
It is formed avoiding 01a.

On the other hand, the developing device 106B containing black toner that contributes to development is pushed in the direction of arrow B by the rotation of the separation cam 115B in response to the color selection signal, and the photoreceptor 10 is pushed in the direction of arrow B.
1. With this contact, toner adheres to the electrostatic latent image portion formed on the photoreceptor 101 to form a toner image, and development is completed. The developing unit 106B, which has completed the development, moves from the contact position with the photoreceptor 101 to the separated position by the 180 degree rotation of the contact/separation cam 115B. The toner image formed on the photoreceptor 101 by the developing device 106B is transferred to the intermediate transfer member 11.
6, each color is transferred by applying high pressure to an intermediate transfer roller 119 placed in contact with the photoreceptor 101.

Residual toner that has not been transferred from the photoreceptor 101 to the intermediate transfer member 116 is removed by the photoreceptor cleaning device 10.
The charges on the photoreceptor 101 that have been removed by step 8 and whose residual toner has been scraped off by the charge eliminator 109 are removed.

Next, for example, when the color cyan (C) is selected, the separation cam 115C rotates, and this time the developing device 106C is pushed in the direction of the photoreceptor 101 and brought into contact with the photoreceptor 101, so that the color of cyan (C) is selected. Start developing. In the case of a copying machine or printer that uses four colors, the above-mentioned developing operation is repeated four times in sequence, and toner images of four colors B, C, M, and Y are superimposed on the intermediate transfer member 116 to form a composite image. The composite image formed in this way is transferred from the transfer material cassette 123 along the paper conveyance path 126 by applying high pressure to the transfer roller 129 when the transfer roller 129, which has been separated until now, comes into contact with the intermediate transfer member 116. The images are transferred all at once onto the transfer material 124 that has been sent. Subsequently, the transfer material 124 onto which the toner image has been transferred is sent to a fixing device 130, where it is fixed by the heat of a heat roller 131 and the clamping pressure of a pressure roller 132, and is output as a color image. Intermediate transfer body 116 that has not been completely transferred onto transfer material 124 by paper transfer roller 129
The residual toner on the intermediate transfer member cleaning device 122 is removed. Intermediate transfer body cleaning device 122
is in a position apart from the intermediate transfer body 116 until one composite image is obtained, and after the composite image is obtained and the composite image is transferred to the transfer material 124 by the paper transfer roller 129, it comes into contact with the intermediate transfer member 116, Residual toner is removed.

[0080] With the above operations, recording of one image is completed, and a high quality color recorded image is obtained.

The image forming apparatus of the present invention is not limited to the electrophotographic printing apparatus using a laser beam of this embodiment, but may also be a thermal transfer printing method, an inkjet printing method, or the like. Further, instead of a laser beam, an electrophotographic printing device such as an LED printing device or a liquid crystal shutter printing device may be used.

[0082] In this embodiment, a full-color printer in which gradation reproduction is important is taken up, but of course a single-color printer may also be used. Further, in this embodiment, the color image is superimposed on the intermediate transfer body, but it may be superimposed on a photoreceptor or on transfer paper.

[0083]

[Effects of the Invention] As detailed above, according to the present invention,
A block consisting of multiple pixels on this image data is set, and dots are grown in order according to a spatially predetermined priority order within the block, starting with the dot corresponding to the minimum recording pixel position with the highest priority. By recording the dot corresponding to the minimum recording pixel position with the lowest degree in binary, there is no deterioration of resolution or generation of texture, and as the pixel grows, adjacent dots on all sides of a certain dot after heat fixation It is possible to achieve both complete fusion of the so-called collapse, and reproduction of high-density solid areas by actively utilizing the collapse, resulting in a high-quality recorded image.

[Brief explanation of the drawing]

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

[Figure 2] Block diagram of a conventional image forming apparatus

[Figure 3] Graph showing density conversion characteristics of conventional example

[Figure 4] 8*8 dither threshold matrix

[Figure 5] Output value in multilevel dither method

[Fig. 6] Block diagram of the gradation processing section of the embodiment

[Figure 7] Figure 6
Timing chart showing changes in the time axis direction of each synchronization signal and each counter output in

[Figure 8] Diagram showing the state of counter output for each pixel position

[Fig. 9] A diagram showing the contents of the gradation conversion table of the embodiment.

[Figure 1
0] Graph of gradation conversion characteristics in the example

[Figure 11] Graph of gradation conversion characteristic I

[Figure 12] Graph of tone conversion characteristics II

[Figure 13] Schematic configuration diagram of laser beam printer

[Figure 14
】Explanatory diagram of photoconductor reference detection operation

[Figure 15] Diagram explaining the operation of intermediate transfer body reference detection

[Explanation of symbols]

1 Image memory 2 Main scanning direction counter 3 Sub-scanning direction counter 4 Density conversion section 5 Color correction section 6 Data selector 7 Storage device 8 Comparator 9 Storage device 10 Density level signal 11 Comparison result 12 Final output value 21 Print engine 22 Digital data Output device 23 Image processing section 24 Density conversion section 25 Density conversion table 26 CMY (density) data 27 CMY (density) data 28 CMY (density) data 29 UCR/black plate generation section 30 C (cyan) data 31 M (magenta) Data 32 Y (yellow) data 33 Bk (black) data 34 Color correction section 35 C' data 36 M' data 37 Y' data 38 Data selector 39 Gradation processing section 50 Horizontal synchronization signal generation circuit 51 Horizontal synchronization signal 52 Horizontal 2 Base counter 53 Gradation conversion table 54 Horizontal binary counter output 55 Input image signal 56 Vertical synchronization signal generation circuit 57 Vertical synchronization signal 58 Vertical binary counter 59 Vertical binary counter output 101 Photoconductor 101a Photoconductor seam 101b Photoconductor reference Mark 102 Photoconductor transport roller 103 Photoconductor transport roller 104 Charger 105 Exposure optical system 106Y Developing device 106M Developing device 106C Developing device 106B Developing device 107 Intermediate transfer unit 108 Photoconductor cleaning device 109 Static eliminator 110 Photoconductor reference detection sensor 111 Charging wire 112 Shield plate 113 Grid plate 114 Exposure light beam 115Y Separation cam 115M Separation cam 115C Separation cam 115B Separation cam 116 Intermediate transfer body 117 Intermediate transfer body conveyance roller 118 Intermediate transfer body conveyance roller 119 Intermediate transfer roller 120 Intermediate transfer Body reference detection sensor 121 Photoconductor clutch mechanism 122 Intermediate transfer body cleaning device 123 Transfer material cassette 124 Transfer material 125 Paper feed roller 126 Paper transport path 127 Registration roller 128 Followed roller 129 Transfer roller 130 Fixing device 131 Heat roller 132 Pressure roller

Claims (2)

[Claims] Claim 1: A block consisting of a plurality of pixels constituting an image is set, and within each block, dots are sequentially placed in accordance with a spatially predetermined priority order, starting with the dot corresponding to the minimum recording pixel position with the highest priority. Along with growing
An image forming method characterized in that dots corresponding to a minimum recording pixel position having the lowest priority form an image in binary form. 2. Printing means for forming an image on an image forming medium, a block consisting of a plurality of pixels constituting an image is set for the printing means, and a spatially predetermined priority is set within each block. The dots are controlled to grow in order from the dot corresponding to the minimum recording pixel position with the highest priority according to the order, and the dot corresponding to the minimum recording pixel position with the lowest priority is controlled to be printed in binary. An image forming apparatus characterized by: