JPH05199384A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus capable of outputting a high gradation image without increasing the memory capacity. [Structure] A writing control means 104 for reconstructing m × n bit image data in accordance with m consecutive n bit image data, and 2 m × n power stages in units of m times the basic unit. The output means 105 which outputs a gradation is provided.

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 for digitally processing image data such as a printer, a digital copying machine, and a facsimile machine, and more particularly to image forming characterized by gradation output technology, memory control technology and data transfer technology. Regarding the device.

[0002]

2. Description of the Related Art FIG. 20 is a schematic configuration diagram of an image writing device using a semiconductor laser, and FIG. 21 is a schematic configuration diagram of a color printer equipped with the image writing device. First, the schematic configuration of the image writing apparatus will be described with reference to FIG. In the figure, 21 is a semiconductor laser, 22 is a condenser lens, and 2
3 is a cylindrical lens, 24 is a polygon mirror, 2
5 is an fθ lens, 26 is a mirror, 27 is a photosensitive drum,
Reference numeral 28 is a photodetector for keeping the writing start position constant.

In such a structure, the semiconductor laser 2
The laser beam emitted from the laser beam No. 1 is collimated by a condenser lens 22 into a parallel beam, which is linearly condensed on a polygon mirror 24 by a cylindrical lens 23. The beam deflected by the polygon mirror 24 is imaged on the photosensitive drum 27 by the fθ lens 25. The imaging spot is repeatedly moved in the main scanning direction by the rotation of the polygon mirror 24, and at the same time, the photosensitive drum 27 is rotated to perform the sub scanning. The light detector 2
Reference numeral 8 is provided outside the image writing area of the photosensitive drum 27, detects a laser beam deflected by the polygon mirror 24, and detects a synchronization signal (line synchronization signal LSYN).
C) is generated.

Next, a schematic structure of the color printer will be described with reference to FIG. This color printer includes a plurality of optical systems and a plurality of photosensitive drums, and the scanning optical system of each is substantially the same as the optical system described in FIG. In the color printer, the image signals for each color obtained by color-separating the pixels to be output are yellow (Y), magenta (M),
An image signal for each color component of cyan (C) is sent from the controller. Then, latent images are formed in accordance with the respective images, developed with toners corresponding to Y, M, and C, and the respective toner images are superposed and transferred on the same transfer paper, and fixed by a fixing device.

Black (BK) toner may be used in combination with the Y, M and C toners. The use of this BK toner is not limited to the case of printing a black character with high quality, but the same amount of Y, M, and C included in an arbitrary color in image processing is replaced in whole or in part with the same amount of black.
This is for realizing black output (so-called corner printing) when performing under color removal (UCR).

In the printer shown in the figure, four photoconductor drums 33BK, 33C, 33M, 33Y and four optical systems 30BK, 30C, 30M, 30Y corresponding thereto are provided.
Is provided. By these, each latent image is formed with a little time difference, and the developing devices 39BK, 39C,
The BK toner image, the C toner image, the M toner image, and the Y toner image are sequentially transferred onto the transfer paper 41 that has been developed by 39M and 39Y and is brought into close contact with the transfer belt 40, and is fixed by the fixing device 42. Although the optical system 30 is provided with the four described in FIG. 20, the polygon mirrors 32BK, 32C, 32 are provided.
The M and 32Y may be shared by one or two.

In the figure, 43 is a charger, 44 is a cleaner, 45 is a separator, 46 is a feeding roller, 47 is a calling roller, 48 is a belt cleaner, 49 is a belt static eliminator, 50
Is a paper ejection roller.

In the image forming apparatus thus constructed, a digital copying machine capable of expressing gradation has appeared in recent years. Further, as the output is colorized, there is an increasing need for an output device having both higher gradation and higher resolution. In a conventional digital copying machine, such as a dither matrix method, which expresses gradations with or without dots for each pixel, when expressing, for example, 64 gradations, 8 × 8 is obtained. Pixels are needed, and there has been a problem that the resolution is reduced accordingly.

Recently, as a method for solving the above problem, the scanning beam is pulse-width-modulated or power-modulated to change to the gradation processing which is conventionally expressed by hitting or not hitting a dot. It has been proposed that the density of each dot is expressed in multiple stages so that the matrix size can be reduced to increase the resolution and obtain the same gradation.

[0010]

However, in this method, in order to obtain an image with higher resolution and higher gradation,
The number of data bits given to one dot is increasing more and more, and a new problem arises that a huge amount of image memory capacity is required. Recently, 8 as image data
Products that use bits and output one dot in 256 gradations have also appeared, but if, for example, an electrophotographic process is selected as the image forming process of the output device,
It is not powerful enough to express dots in 256 gradations, and depends on process conditions such as development and transfer.
The high gradation of dots does not always improve the gradation of the whole image, and the combination of the minute dither matrix method of about 1 × 2, 2 × 1 or 2 × 2 does It is better to disperse the dots as much as possible, for example, to make the dots concentrated, and to express the gradation by collecting multiple dots together. It has been found that stable image quality can be obtained without being affected by fluctuations.

Further, when the data of each n bit is grouped by 2 dots, that is, when the gradation of 2 n steps is expressed by the pixels of 2 dots, a 2-dot unit as shown in FIG. 18 is formed. To do. In this case, when trying to express an intermediate density, the toner adheres to the hatched portion in FIG. 18, and therefore, it looks like vertical stripes. This is not so annoying when the density gradually changes in a large area, but when representing a character having a high spatial frequency, for example, the vertical stripes are very annoying.

FIG. 19 shows an example in which characters are expressed using the pattern of FIG. In this example, since the density of the central part of the character line is high, toner adheres to both 1 and 2 of 2 pixel unit shown in FIG. Only one side of the body is filled, and the paper surface can be seen in the part 2 so that the image is very annoying.

Further, in a machine for transferring a plurality of images in an overlapping manner, at least an image memory for the drum interval is required. However, if the number of bits of each pixel is increased as described above in this system, a huge memory capacity increase will result. Become.

On the other hand, for a picture portion including a smooth gradation such as a photograph, the above-described dot concentration method is sufficient. ) May be anxious.

The present invention has been made on the basis of such a background, and it is possible to output a high gradation image without increasing the memory capacity, and also to select one of gradation and resolution depending on the image quality mode. It is an object of the present invention to provide an image forming apparatus that can output an image that emphasizes that.

[0016]

SUMMARY OF THE INVENTION The above object is to provide an image forming apparatus which receives n-bit image data in synchronization with a timing signal corresponding to a basic unit of a pixel and outputs a multi-gradation image according to the image data. , Write control means for reconstructing m × n bit image data according to m consecutive n bit image data, and 2 in units of m times the basic unit.
Output means for outputting gradations of m × n to the power of m. Further, the above-mentioned object is provided by the second means, which is provided with the image quality mode selection means for selecting any one of the plurality of image quality modes in the first means, and the value of m is changed by this image quality mode selection means. To be achieved.

[0017]

In the first means, the writing control means uses m
According to the image data of n consecutive bits, the image data of m × n bits are connected, while the output means outputs 2 bits.
M × n power gradation output.

In the second means, the image quality mode is selected by the image quality mode selection means and the value of m is changed to obtain an image output which emphasizes either gradation or resolution.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment will be described with reference to FIGS. In this embodiment, when two image data transferred at 4 bits are connected to each pixel unit to output 8 bits at 2 pixel units, that is, a 256-level dot gradation output (that is, the patent claims). In the range of m = 2, n = 4
In the other cases, for example, two image data transferred in 2 bits for each pixel unit are joined together by 4 bits to obtain 8 bits in 4 pixel units, that is, 2 bits.
To output 56 levels of gradation, or to combine 2 image data transferred in 3 bits for each pixel, 2 bits for 6 bits, that is, 64 levels of gradation output. It goes without saying that the concept can be extended and applied according to the specifications of the machine, such as when performing.

FIG. 1 shows a diagram for explaining the data flow of the entire machine. This is an example of a color image forming apparatus. Further, FIG. 2 is a diagram showing a state of the timing signal and the image data in each section A to C. First, a document is read by the image reading means 100 and analog signals are read, for example, R, G, B
Is output as digital image data with a resolution of 10 bits each. The spatial resolution of reading is determined by the required output image quality, and the current standard resolution is about 16 pixels / mm, and the reading sensor is selected correspondingly. In this case, 16 pieces of 10-bit image data are output per 1 mm. Here, detailed description of R, G, Bγ conversion and the like is omitted.

In the image processing means 101, mainly R,
Color conversion from G, B to Y, M, C, BK data and other processing are performed. The output from the image processing means 101 is generally equal to or slightly less than the number of bits of R, G, B data. In this example, the case where the processing result of the image processing means 101 is output in 8 bits is illustrated (the change in the number of bits is essentially unrelated to the present invention). The image data output from the image processing unit 101 is output in synchronization with the timing signal for indicating the delimiter of each pixel (A in FIG. 2). Next, the arithmetic processing means 10
The image data is arithmetically processed in 2 and converted into 4 bits for each pixel.

In the processing described in claim 3, since m = 2 at present, one of the continuous 8-bit image data is selected and the other is thinned out. The selected 8-bit image data is decomposed into, for example, upper 4 bits and lower 4 bits, and the image data storage means 1 is synchronized with the timing signal.
03 (FIG. 3). Such thinning-out processing is effective in the case of image data that has been averaged in advance by the image processing means 101. Also, the resolution is 1/2 due to thinning.
However, it is possible to express 256 gradations with 2 pixels, which is sufficiently practical for both resolution and gradation.

Further, the greatest advantage is that the image quality is not so different from the image data of 8 bits, but
The memory capacity required for the image data storage means 103 is 1/2
The point is that The 4-bit image output from the image data storage means 103 is connected again by the write control means 104 to the two 4-bit data, and assembled as 8-bit image data.
Outputs 6 levels of gradation. As the gradation output method, a pulse width modulation method, a power modulation method, a combination of both methods, or another method can be used.

Further, in the processing shown in claim 4, at present m
= 2, the average of 8-bit data of two adjacent pixels is calculated, decomposed into, for example, upper 4 bits and lower 4 bits, and output to the image data storage means 103 in synchronization with the timing signal (FIG. 4). The averaging process can also be realized by using the averaging process of the image processing unit 101 without the arithmetic processing unit 102 having the role. In this averaging process, the spatial resolution drops to 1/2, but no image data is missed.

In any of the above processes, if there is a resolution as illustrated here, an image quality that is almost satisfactory with respect to the resolution can be obtained, and an image (original) of 16 lines / mm cycle is obtained. Since it is not so general, the averaging processing described in claim 4 is sufficient.

Next, a second embodiment will be described with reference to FIGS. In this embodiment, in order to avoid the deterioration of the image quality such that the background portion is output in every predetermined cycle as shown in FIG. 18, the writing start position of the basic unit is shifted every scanning line as shown in FIG. [Though the pattern is staggered in the case of FIG. 5, the concept can be easily extended to a case other than m = 2, for example, m = 3 (see FIG. 7)], and an image without vertical stripes as shown in FIG. 6 is obtained. be able to.

This embodiment also provides a system for obtaining color output by one or more image forming systems,
The color moire due to the periodicity is avoided. In the case of an image forming apparatus that outputs in color, each color overlaps or separates due to the positional accuracy of the dots of each written color, which causes color unevenness or color moire.
If the same pattern (pattern as shown in FIGS. 18 and 19) is used for each color, the writing position must be controlled more strictly. Also, since the spatial frequency of each color differs depending on the original, the read image data of each color component has different periodicity, and color moire occurs. In the field of printing, the above color moiré is avoided by adding a screen angle to each color, but in this embodiment, the idea is applied, that is, if the cycle or direction of the writing start position of the basic unit is different for each color. By doing so, color moire can be avoided.

FIG. 8 is a block diagram according to the embodiment. This block diagram is the block diagram shown in FIG. 1 to which a start position control means 106 for controlling the start position of the writing of the block of the basic unit is added. Where LSYN
C indicates a line synchronization signal which is a timing signal for detecting the passage of the scanning beam by a photodetector and controlling the writing position in the scanning beam. Therefore, the writing position (writing position) for each scanning line is controlled by LSYNC. The head position control means 106 shifts the output timing of the image data from the writing control means 104 for each line by the LSYNC, sends it to the output means 105, and exposes it to output an image.

FIG. 9 is a timing chart of the portion C in FIG. The timing chart corresponds to the portion C in FIG. A timing signal for controlling the timing of writing is generated based on LSYNC. Here, in order to control the head position as shown in FIG. 5, the image data of the n-th line is sequentially generated in synchronization with the first timing signal and transferred to the output means 105. Then n
The image data of the + 1st line is sequentially generated in synchronization with the second timing signal and transferred to the output means 105. Similarly, the n + 2th line is synchronized with the first line, and so on, and the like is repeated to form a pattern as shown in FIG.

Now, using pulse width modulation, which is one of the methods for expressing the gradation of each dot, is as shown in FIG. Numerical value entered in the image data (1,128,25
6, 64) is image data, which indicates the density level to be expressed in one dot. The lighting time of the exposure beam changes according to the density level, and finally a toner image corresponding to the image data is formed, and the image density is determined. In the example of FIG. 10, the areas 1 and 2 in the image data 256 are the front black (or Y, M or C), and when 0, no dot is formed. Therefore, when the image data is 128, the toner adheres to the area of about 1. In this way, by combining two adjacent pixels each having 4 bits of data, it is possible to express gradations in 256 steps with 8 bits and density.

Now, also in the case of color output, the idea so far can be expanded and explained. That is, the circuit configuration can be the same as that of FIG. 8, and in the example shown in FIG. 21, a plurality of circuits may be provided for each color. Here, the head position control means 106 is changed for each color. For example, when a full-color image output is made with four colors of C, M, Y, and BK, color moire and the like can be avoided by changing the control of the leading position so as to form a pattern as shown in FIG. Can be loosened to some extent.

Next, a third embodiment will be described with reference to FIGS. In this embodiment, the image quality mode (for example, the pattern mode and the character mode) is set in advance, so that the user sets the image quality mode according to the type of the document, and the gradation or resolution according to the image quality mode is set. An image output that emphasizes one of them is obtained.
Further, the machine automatically determines the pattern portion or the character portion of the original area, and outputs the image in which either the gradation or the resolution is emphasized according to each area. Here, the image quality is switched by changing m in the present embodiment. Generally, when m in the picture part where the gradation is important is m picture and m in the character part where the resolution is important is m sentence, An optimal image can be obtained by setting m picture ≧ m sentence.

FIG. 12 is a block diagram of this embodiment. Although this block diagram is almost the same as that shown in FIG. 1, the difference is that the image quality mode signal is sent to the arithmetic processing means 102 and the writing control means 104, for example, the image quality mode signal indicating the picture mode. In this case, m pictures are changed to m pictures, adjacent m picture pixels are grouped together, and the m picture pixels can express a gradation of 2 m pictures × n stages (where N ≧ m picture × n). In the case of the image quality mode signal indicating the character mode, m → m sentences are set, and adjacent m sentences (m sentences <m pictures) are grouped together. The point is that gradations of m sentences × nth power can be expressed.

As a result, when the picture mode is designated even though the memory capacity of the image data storage means 103 is only n bits for each pixel, the resolution is lowered, but 2 m pictures × squared. It is possible to obtain a high-gradation image output in steps, and when the character mode is designated, it is possible to obtain a high-resolution image output although the gradation is lowered.

The following is a specific description of numerical values. If 256 gradations can be output with 2 pixels, and if the required image quality is sufficient to express a photograph or picture, m picture =
2, memory capacity of each pixel n = 4 bits (∵
Gradation = 2 2 × 4 = 2 8 = 256). On the other hand, when the original is characters, the required number of gradations is not so high, but high resolution is required. Therefore, in text mode, m sentences = 1
, The minimum unit of resolution is 1 dot, and the gradation is 2 × 1 ×
The fourth power = 2 to the fourth power = 16 gradations. This makes it possible to satisfy the required image quality for both the picture portion and the character portion.

FIG. 13 and FIG. 14 show respective data flows when the picture mode and the character mode are designated.
In the picture mode, the arithmetic processing means 102 selects, for example, every other 8-bit image data, distributes it to adjacent dots by 4 bits, and sends it to the image data storage means 103. The writing control means 104 reconstructs the image data of 2 pixels and 8 bits by the image data of 4 bits each of the adjacent dots. In the character mode, the arithmetic processing means 102
Then, for example, 8 bits of each image data are compressed to 4 bits (the number of gradations is reduced) and sent to the image data storage means 103. The writing control means 104 sends out image data of 4 bits for each pixel.

To meet the ninth aspect, the area determination signal of the area determination means 107 shown in FIG. 15 may be used as the image quality mode signal shown in FIG. In this case, the configuration corresponding to FIG. 12 is as shown in FIG. Further, the configuration of the area determination means 107 is as shown in FIG. The edge separation unit 111 detects whether the input image data 110 includes an edge of a character, the halftone dot separation unit 112 detects whether or not it is a halftone dot, and further determines whether or not it is a color character. The determination unit 113 detects them, the comprehensive determination unit 114 comprehensively determines them, and outputs a region determination signal.

FIG. 17 shows examples of output patterns in each mode. FIG. 10A shows an example of dot configuration in the pattern mode.
FIG. 7B shows an example of dot configuration in the character mode.

[0039]

According to the inventions of claims 1 to 5,
By outputting m consecutive n-bit image data as 2 × m × n gradation levels, a high-resolution and high-gradation image can be output without unnecessarily increasing the capacity of the image memory. An inexpensive image forming apparatus can be constructed. According to the invention of claim 6, in addition to the above, periodicity of high spatial frequency due to the pattern can be removed, and a smoother image output can be obtained. According to the invention described in claim 7, in addition to the above, color moiré can be removed by changing the pattern configuration for each color, and the writing position accuracy of each color can be loosened. According to the invention described in claim 8, in addition to the above, it is possible to specify the resolution priority or the gradation priority according to the original, and it is possible to output a desired image. According to the invention of claim 9, in addition to the above, the resolution and gradation of the picture portion and the character portion can be automatically switched, and even in one image, the picture portion has gradation priority and the character portion has resolution. An appropriate priority image can be output.

[Brief description of drawings]

FIG. 1 is a control block diagram according to a first embodiment of the present invention.

FIG. 2 is a timing chart of each part of the block shown in FIG.

FIG. 3 is an explanatory diagram showing control contents of the first embodiment.

FIG. 4 is an explanatory diagram showing control contents of the first embodiment.

FIG. 5 is an explanatory diagram showing a pixel pattern of a 2-dot unit.

FIG. 6 is an explanatory diagram showing an example of an output image according to the second embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a pixel pattern of a 2-dot unit.

FIG. 8 is a control block diagram according to a second embodiment of the present invention.

9 is a timing chart of a portion C in FIG.

FIG. 10 is a timing chart based on a pulse width modulation method.

FIG. 11 is an explanatory diagram showing a pixel pattern when a full-color image is created with four colors of C, M, Y, and BK.

FIG. 12 is a control block diagram according to a third embodiment of the present invention.

13 is a timing chart of each part of the control block shown in FIG.

14 is a timing chart of each part of the control block shown in FIG.

FIG. 15 is a control block diagram showing a modification of the third embodiment.

FIG. 16 is a block diagram showing a configuration of a region determination means.

FIG. 17 is an explanatory diagram of pixel patterns in a pattern mode and a character mode.

FIG. 18 is an explanatory diagram showing a defect of a 2-dot pixel pattern.

FIG. 19 is an explanatory diagram of an output image of a conventional example with a 2-dot pixel pattern.

FIG. 20 is a schematic diagram showing a general writing optical system.

FIG. 21 is a configuration diagram showing an example of a color image forming apparatus.

[Explanation of symbols]

 28 photodetector 100 image reading means 101 image processing means 102 arithmetic processing means 103 image data storage means 104 writing control means 105 output means 106 head position control means 107 area determination means 110 input image data 111 edge separation section 112 halftone dot separation Part 113 Color character determination unit 114 Overall determination unit

Claims (9)

[Claims] 1. An image forming apparatus that receives n-bit image data in synchronization with a timing signal corresponding to a basic unit of a pixel and outputs a multi-gradation image in accordance with the image data, and has m consecutive n-bits. Mx depending on the image data of
An image forming apparatus provided with a write control means for reconstructing n-bit image data and an output means for outputting a gradation of 2 m × n stages in units of m times the basic unit. .. 2. The n-bit image data according to claim 1, wherein the m-bit image data is one m × n-bit image data obtained by subjecting m × n-bit image data of each of the m pixels to arithmetic processing.
An image forming apparatus characterized in that the image data of × n bits is decomposed into n bits and transferred in time sequence. 3. The arithmetic processing according to claim 2, wherein the arithmetic processing by the arithmetic processing means is processing for selecting any one image data from the m × n bit image data of the m pixels. Image forming apparatus. 4. The image forming apparatus according to claim 2, wherein the arithmetic processing by the arithmetic processing means is a processing of arithmetically averaging image data of m × n bits of the m pixels. 5. The image forming apparatus according to claim 1, further comprising image data storage means for storing image data by allocating a storage capacity of n bits to one pixel. 6. The image forming apparatus according to claim 1, wherein the head position of a unit m times as large as the basic unit is shifted for each scanning. 7. The image forming apparatus according to claim 6, wherein a plurality of image data can be input, and the cycles of the leading positions of the plurality of image data are different from each other. 8. The image forming apparatus according to claim 1, further comprising image quality mode selection means for selecting any one of a plurality of image quality modes, and changing the value of m by the image quality mode selection means. .. 9. The apparatus according to claim 1, further comprising area separating means for judging the image quality of the original and separating the area, and changing the value of m according to the area separated by the area separating means. Image forming apparatus.