JPH1075357A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce stable gradation by avoiding gradation number of printed-out image data from being decreased even in the case of making gamma correction. SOLUTION: A CPU of an engine 54 forms an image a plurality of correction patterns where gradation of a noted dot is gradually changed by write dot number around the noted dot in advance onto a recording medium as gradation patterns in different turning directions, each density is detected by using an optical sensor and gamma correction data are generated by the write dot number, based on the detection result. Then a gamma correction section 52 references dots around the noted dot of image data applied with pseudo gradation processing from a printer controller 51 to discriminate the environment and any of the gamma correction data is selected depending on the discrimination result and the gamma correction data are used to correct the gradation of the noted dot of the image data to provide an output of a corresponding write level signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, a facsimile, etc., which modulates a light or ion stream in accordance with image data to irradiate a recording medium to form a dot image on the recording medium by an electrophotographic method. Related to various image forming apparatuses.

[0002]

2. Description of the Related Art Some image forming apparatuses such as a laser printer using an electrophotographic system have a printer controller and a printer engine which perform the following processing.

A printer controller develops vector-format image information sent from an external device such as a host computer into image data (bitmap data),
Alternatively, the image data of the original is read by an image reading device (scanner), temporarily stored in a frame memory, any one of the image data is read out at a predetermined timing, and γ correction (gradation correction) is performed for each dot. After correcting the non-linearity (write density or write size of dots) of the printer engine, pseudo tone processing such as dither processing is performed and sent to the printer engine.

The printer engine corrects the variation in density by performing γ correction again for each dot of the image data sent from the printer controller, and prints out the image data. That is, the laser beam is modulated (power modulation or pulse width modulation or the like) and scanned in accordance with the image data to form a dot image on a recording medium by an electrophotographic method.

[0005]

However, in such a conventional image forming apparatus, gamma correction is performed on input (read from the frame memory) image data before performing pseudo gradation processing. Therefore, there is a problem that the number of gradations of the image data to be printed is reduced.

For example, when performing dot concentration type dither processing as pseudo gradation processing, as shown in FIG. 11, in a high density part (solid part), the dot density and the dot size become large, so that a part of each dot becomes large. Although they overlap (shown by hatching), in the low-density portion (single dot portion), the dot density and the dot size are reduced, so that such overlap is eliminated.

Therefore, the dot γ characteristic (the relationship between the writing level (gradation) of the modulated dot based on the image data and the density) when the image data from the printer controller is directly printed out by the printer engine is shown by a solid line in FIG. As shown. In this case, the number of gradations of the image data read from the frame memory is 256 gradations.

Therefore, it is necessary to γ-correct image data read from the frame memory so that the dot γ characteristic (non-linearity) becomes the reference dot γ characteristic indicated by the broken line in FIG. The number of gradations of the image data printed and output by the engine is reduced to about 1/2 in each of the high density portion and the low density portion as shown in FIGS. Is reduced to about 2/3, which is about 170 gradations.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is intended to prevent the number of gradations of image data to be printed out from being reduced even if gamma correction is performed, and to reproduce stable gradation. The purpose is to do.

[0010]

SUMMARY OF THE INVENTION The present invention provides an image forming apparatus for modulating light or an ion stream according to image data to irradiate a recording medium to form a dot image on the recording medium by an electrophotographic method. To achieve the above object, the following means are provided.

According to a first aspect of the present invention, a plurality of .gamma. Correction patterns in which the gradation of the target dot is gradually changed according to the number of writing dots around the target dot are respectively provided as gradation patterns on the recording medium in the direction of rotation. Pattern forming means for forming images with different lengths, density detecting means for detecting the density of each gradation pattern created on a recording medium by the means using an optical sensor, and detecting the means Γ-correction data creating means for creating γ-correction data for each of the writing dot numbers based on the result, pseudo-gradation processing means for performing pseudo-gradation processing on input image data, and pseudo-gradation processing by the means Dot environment determining means for determining the environment of the dot by referring to surrounding dots with respect to the noted dot of the image data subjected to And selecting one of the gamma correction data for each writing dot number created by the gamma correction data creation means according to the result, and using the gamma correction data to correct the tone of the target dot of the image data. Γ correction means for outputting a corresponding write level signal.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the gradation pattern image forming means is provided with a gamma correction pattern in a case where there is a writing dot, based on a gamma correction pattern in a case where there is no writing dot around the target dot. This is a means for forming an image of each γ correction pattern such that the length of the correction pattern in the rotating direction of the recording medium is shorter.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the gradation pattern image forming means is arranged so that the gradation pattern forming means is located closer to the target dot than the gamma correction pattern when all the writing dots are present around the target dot. The means for forming each γ-correction pattern is such that the γ-correction pattern in the absence of some or all of the writing dots has a shorter length in the rotating direction of the recording medium.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the gradation pattern image forming means is provided for correcting γ when there are all write dots around the target dot and when there are no write dots. Than the pattern
This is a means for forming an image of each γ correction pattern such that the length of the γ correction pattern in the case where there is a part of writing dots around the target dot is shorter in the rotation direction of the recording medium. .

In the image forming apparatus according to the present invention, the gradation pattern image forming means includes a plurality of γ correction patterns in which the gradation of the target dot is gradually changed according to the number of writing dots around the target dot, as gradation patterns. An image is formed on the recording medium with the length in the direction of rotation being different, the density detecting means detects the density of each gradation pattern using an optical sensor, and the γ correction data creating means is based on the detection result. Γ correction data is created for each of the write dot numbers.

After that, the pseudo gradation processing means performs pseudo gradation processing on the input image data, and the dot environment judgment means refers to surrounding dots for the target dot of the image data, and determines the value of that dot. The environment is determined, and the γ correction unit selects one of the γ correction data for each writing dot number created by the γ correction data creation unit according to the determination result, and uses the γ correction data to select the γ correction data. The gradation of the target dot of the image data is corrected (γ correction) and a corresponding write level signal is output.

Therefore, even if the γ correction is performed, the number of gradations of the image data to be printed out does not decrease, and stable gradation can be reproduced. Further, since a plurality of γ correction patterns are formed as gradation patterns, not patch patterns, on a recording medium with different lengths in the rotation direction, an image data portion corresponding to the longer image formation pattern (the It is possible to improve the gradation property (accuracy of γ correction) of a portion that is γ corrected using γ correction data created based on the density detection result of the image forming pattern. If the image forming pattern is made as short as possible, the process control operation time can be reduced, and the amount of toner consumption at that time can be minimized.

It is to be noted that the gradation pattern image forming means performs γ when there is no writing dot around the dot of interest.
By forming each γ correction pattern such that the length of the γ correction pattern in the case where there is a writing dot is shorter in the rotation direction of the recording medium than the correction pattern,
The gradation of the low density portion of the image data can be improved.

The gradation pattern image forming means is configured to generate a gamma correction pattern in the case where there is no part or all of the writing dots around the target dot, based on the gamma correction pattern in the case where all the writing dots are present around the target dot. If each γ correction pattern is formed such that the length of the recording medium in the rotation direction is shorter, the high-density gradation of the image data can be improved.

The gradation pattern image forming means calculates the γ correction pattern based on the case where all the write dots are present around the target dot and the case where there is no write dot.
By forming each γ correction pattern such that the length of the γ correction pattern in the case where there is a part of writing dots around the target dot is shorter in the rotation direction of the recording medium, The low-density part and high-density gradation of data can be improved.

[0021]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 shows the first embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of a mechanism unit of the color image forming apparatus according to the embodiment.

In this color image forming apparatus, reference numeral 1 denotes a flexible belt-shaped photoconductor serving as an image carrier (recording medium), and the belt-shaped photoconductor 1 is bridged between rotating rollers 2 and 3. Each of the rotating rollers 2 and 3 rotates clockwise. Reference numeral 4 denotes a charging member serving as a charging unit;
Denotes a laser writing system unit serving as an image exposure unit.
Reference numerals 6 to 9 denote developing devices as developing means, each containing a toner of a specific color.

The laser writing system unit 5 is housed in a holding housing provided with a slit-shaped exposure opening on the upper surface, and is incorporated in the apparatus main body. In addition, as the laser writing system unit 5, a unit in which the light emitting unit and the convergent light transmitting body are integrated may be used. Charging member 4 and cleaning device 15
Is provided so as to face the rotating roller 2 of the two rotating rollers 2 and 3 on which the belt-shaped photoreceptor 1 is provided.

Each of the developing devices 6 to 9 contains, for example, each of yellow, magenta, cyan, and black toners, and has a developing sleeve that comes close to or comes into contact with the belt-shaped photosensitive member 1 at a predetermined position. It has a function of visualizing the latent image on the photoconductor 1 by non-contact development or contact development. An intermediate transfer belt 10 is a transfer image carrier (recording medium). The intermediate transfer belt 10 is provided between rotating rollers 11 and 12 and is rotated counterclockwise by driving a bias roller 13. You.

The belt-shaped photoconductor 1 and the intermediate transfer belt 10 are in contact with the rotating roller 3, and the first visible image on the belt-shaped photoconductor 1 is transferred to a bias roller provided in the intermediate transfer belt 10. 13, the image is transferred onto the intermediate transfer belt 10. Then, by repeating the same process, the second, third, and fourth visual images are respectively superimposed on the intermediate transfer belt 10 and transferred so as not to cause a positional shift.

A transfer roller 14 is provided so as to come into contact with and separate from the intermediate transfer belt 10. Reference numeral 15 denotes a cleaning device for the belt-shaped photoreceptor 1, reference numeral 16 denotes a cleaning device for the intermediate transfer belt 10, and a blade 16A of the cleaning device 16 is kept at a position separated from the surface of the intermediate transfer belt 10 during image formation. It is pressed against the surface of the intermediate transfer belt 10 as shown in FIG.

The process of forming a color image by the color image forming apparatus is performed, for example, as follows.
First, the formation of a multicolor image according to this embodiment is performed according to the following image forming system. For example, in an image reading device (not shown), data obtained by a color image data input unit (scanner) in which an image of an original document is scanned by an image sensor is subjected to arithmetic processing by an image data processing unit to generate image data (multi-valued bitmap data). ) Is created, and this image data is temporarily stored in the image memory.

Thereafter, the image data stored in the image memory is read out at the time of image formation and is input to the color image forming apparatus shown in FIG. That is, image data (color signals) output from an image reading apparatus separate from the color image forming apparatus (printer) is transmitted to a laser writing unit 5 via a printer controller and a gamma correction unit and a writing unit of an engine. , The laser writing unit 5 performs the following operation.

First, a laser beam modulated in accordance with image data is generated from a semiconductor laser (not shown), and the laser beam is deflected and scanned by a polygon mirror 5B rotated by a drive motor 5A and passes through an fθ lens 5C. The light path is bent by the mirror 5D, the charge is removed by the charge removing lamp 21 in advance, and the peripheral surface of the belt-shaped photosensitive member 1 uniformly charged by the charging member 4 is exposed to form an electrostatic latent image.

Here, the image pattern to be exposed is a single-color image pattern when a desired full-color image is separated into yellow, magenta, cyan, and black. Each of the electrostatic latent images formed on the belt-shaped photoreceptor 1 includes yellow, magenta, cyan,
After the black developing units 6 to 9 sequentially develop and visualize the image, form a monochromatic image to form a monochromatic image (dot image), and rotate in the counterclockwise direction while contacting the belt-shaped photoconductor 1 The image is transferred onto the transfer belt 10 and overlapped.

The images of yellow, magenta, cyan, and black superimposed on the intermediate transfer belt 10 are transferred to a transfer sheet which is conveyed to a transfer section from a sheet supply table 17 through a sheet supply roller 18 and a registration roller 19, and transferred to a transfer roller 14. Is transferred. Then, after the transfer is completed, the transfer paper is fixed by the fixing device 20 to complete a full-color image. The intermediate transfer belt 10 and the belt-shaped photoconductor 1 are seamless.

FIG. 3 is an enlarged view showing a part of the color image forming apparatus. There are six marks 41A to 41F at the end of the intermediate transfer belt 10, and the writing of the first color is started by detecting an arbitrary mark (for example, 41A) by the mark detection sensor 40. , The writing of the second color is started.

At this time, by controlling the number of marks 41B to 41F, the marks 41B to 41F cannot be used as write timing, and a corresponding signal from the mark detection sensor 40 is masked. By the way, a P sensor 22 which is an optical sensor for detecting the amount of toner (image density) on the belt-shaped photoconductor 1 is provided slightly upstream from a portion of the belt-shaped photoconductor 1 in contact with the intermediate transfer belt 10. Have been. Note that the P sensor 22 may be provided at a position where the image density on the intermediate transfer belt 10 can be detected.

FIG. 1 is a block diagram showing a configuration example of a control system of the color image forming apparatus. Vector-format image information sent from the outside (external device such as a host computer) is input to the printer controller 51. In the printer controller 51, a CPU (Central Processing Unit) (not shown) creates image data (bitmap data) based on external image information. It should be noted that, as image information in units of one dot, information of eight bits for each color in four colors of yellow, magenta, cyan, and black is included.

Next, the CP in the printer controller 51
U performs pseudo gradation processing (such as multi-value dither processing or multi-value error diffusion processing) on image data created based on image information in units of one dot, and converts the image data into 4-bit image data for each color. The image data is temporarily stored in a 4-bit frame memory for each color, and thereafter read out for each color and input to the gamma correction unit 52 of the engine 54 side. Note that the CPU in the printer controller 51 can also perform pseudo gradation processing on image data in units of one dot sent from the above-described image reading device.

The γ correction section 52 performs γ correction (gradation correction) on the input image data for each dot (dot of interest) by determining the surrounding dot environment (situation), and writes it as a write level signal. Send to section 53. Writing unit 5
In 3, the laser beam generated from the semiconductor laser in the laser writing unit 5 is modulated (power modulation or pulse width modulation, etc.) based on the sent write level signal, and the laser beam is A latent image is formed.

The CPU of the printer controller 51
Function as pseudo gradation processing means for performing pseudo gradation processing on input image data. The gamma correction unit 52 of the engine 54 refers to surrounding dots with respect to the target dot of the image data on which the pseudo gradation process has been performed by the CPU from the printer controller 51, and determines the environment (situation) of the dot. Dot environment determining means for determining,
According to the determination result, γ for each writing dot number described later
The function as a γ correction unit that selects one of the correction data, corrects the gradation of the dot of interest of the image data using the γ correction data, and outputs a corresponding write level signal.

Further, the CPU of the engine 54 sets a plurality of γ correction patterns in which the gradation of the target dot is gradually changed according to the number of writing dots around the target dot as gradation patterns on the belt-shaped photosensitive member 1. A gradation pattern image forming means for forming an image by changing the length in the rotation direction, and a density of each gradation pattern formed on the belt-shaped photoconductor 1 are detected by using a P sensor 22 which is an optical sensor. It functions as a density detection unit and a γ correction data generation unit that generates γ correction data for each of the write dot numbers based on the detection result.

The gradation pattern image forming means performs the processing shown in any of (1) to (3) in detail. (1) From the γ correction pattern when there is no writing dot around the target dot, γ when there is a writing dot
Each gamma correction pattern is imaged such that the length of the correction pattern in the rotation direction of the belt-shaped photoconductor 1 is shorter.

(2) The γ correction pattern when there is no part or all of the writing dots around the target dot, based on the γ correction pattern when all the writing dots are around the target dot.
Each gamma correction pattern is imaged such that the length of the correction pattern in the rotation direction of the belt-shaped photoconductor 1 is shorter.

(3) The gamma correction pattern in the case where there are some writing dots around the target dot is obtained from the gamma correction patterns in the case where all the writing dots are present around the target dot and in the case where all the writing dots are not present. Each gamma correction pattern is formed such that the length of the belt-shaped photoconductor 1 in the rotating direction is shorter in the pattern.

FIG. 4 shows an example of the configuration of a circuit for performing the optimum .gamma. Correction on the image data mainly subjected to the multi-value dither processing in the .gamma. Correction section 52, and FIG. It is a block diagram which shows the example of a structure of the circuit for performing the optimal (gamma) correction with respect to the image data which performed the multi-value error diffusion processing, respectively, and some circuits are overlapped and illustrated.

The γ correction section 52 includes a dot environment determination section 81,
100, a line buffer 82, a position matching latch 83,
It comprises a point-of-interest latch 84 and a γ correction table 85. The dot environment determination unit 81 includes OR gates 86 to 88,
It comprises a line buffer 89, a point-of-interest latch 90, latches for surrounding determination 91 to 98, and a determination unit 99. The dot environment determination unit 100 includes a line buffer 101, a point of interest latch 102, and surrounding determination latches 103 to 11.
0 and a judgment unit 111.

In the γ correction section 52, image data having a weight of 4 bits is sequentially sent from the printer controller 51 for each color, so that the OR gate 86 shown in FIG.
Is a bit (1) indicating whether or not the image data is written.
(Dot) data. That is, it is determined whether or not each bit of the input image data is all “0”, and if all the bits are “0”, “0 (dot not written dot)”
And if one of the bits is “1”, “1 (write dot)” is output. Here, the presence / absence of writing is used as a criterion for determination, but other levels may be used as boundaries.

The data output from the OR gate 86 is
It enters the surrounding determination latch 91 (i + 1), and sequentially shifts to the surrounding determination latches 92 and 93 in synchronization with the image synchronization clock. Also, the image data from the printer controller 51 enters the line buffer 82, and the OR gate 87 converts the image data delayed by one line into 1-bit data indicating the presence or absence of writing in the same manner as described above.

The data output from the OR gate 87 is
It enters the surrounding determination latch 94 (i), and sequentially shifts to the attention point latch 90 and the surrounding determination latch 95 in synchronization with the image synchronization clock. Further, the image data delayed by one line by the line buffer 82 enters another line buffer 89, and the image data further delayed by one line is converted by the OR gate 88 into 1-bit data indicating the presence or absence of writing in the same manner as described above. Convert.

The data output from the OR gate 88 is
It enters the surrounding determination latch 96 (i-1), and sequentially shifts to the surrounding determination latches 97 and 98 in synchronization with the image synchronization clock. The judgment unit 99 includes the surrounding judgment latches 91 to
The environment (the number of writing dots) is determined with reference to each data 98 (dots surrounding the target dot), and the result is used as γ as 3-bit code information (information for selecting optimal γ correction data). It is sent to the correction table 85.
Here, since the number of write dots is a number from “0” to “8”, when the number is “8”, code information indicating “7” is output.

On the other hand, the image data having a weight of 4 bits sent from the printer controller 51 also enters the surrounding determination latch 103 (i + 1) in FIG. Latch 104, 10
Shifting to 5. The printer controller 5
1 is stored in the line buffer 8 as described above.
2, the image data delayed by one line enters the surrounding determination latch 106 (i), and is sequentially shifted to the target point latch 102 and the surrounding determination latch 107 in synchronization with the image synchronization clock.

Further, the image data delayed by one line by the line buffer 82 is transferred to another line buffer 1.
01, the image data further delayed by one line enters the surrounding determination latch 108 (i-1), and is sequentially shifted to the surrounding determination latches 109 and 110 in synchronization with the image synchronization clock.

The judgment section 111 is provided with a surrounding judgment latch 103.
The environment (the average value of the gradation of each dot) with reference to each of the image data (dots around the dot of interest)
Is determined, and the result is converted to 3-bit code information (optimum γ
(Information for selecting correction data) to the following γ correction table 85. Here, each image data is represented by a numerical value in the range of “0” to “15” with 4 bits.
The result of the above determination is converted into 3 bits (upper 3 bits) and assigned to a numerical value in a range from “0” to “7”.

On the other hand, the image data having a 4-bit weight sent from the printer controller 51 passes through the line buffer 82 as described above, and then passes through the position matching latch 83 to the point latch 84 of interest. The data is latched and input to the gamma correction table 85.

The γ correction table 85 is provided by the dot environment determination unit 81 (mainly one that can correspond to image data subjected to multi-value dither processing) by a selection signal corresponding to the type of pseudo gradation processing from the printer controller 51. , Or the code information from the dot environment determination unit 100 (which can mainly correspond to the image data subjected to the multi-value error diffusion processing). For example, if the selection signal is “0 (for example, indicating multi-value dither processing)”, the code information from the dot environment determination unit 81 is determined. The code information from the unit 100 is selected.

Thereafter, one of gamma correction data for each write dot number, which will be described later, is selected according to the selected code information, and the 4-bit weight input from the point-of-interest point latch 84 is used by using the gamma correction data. Γ-correction is performed on the image data (dot of interest) having the following, and the writing level is variably set, and the corresponding 8-bit writing level signal is output to the writing unit 53.

The gamma correction of the image data subjected to the pseudo gradation process will be described below. 6A to 6I are explanatory diagrams showing different examples of the γ correction pattern. In this figure, ○ indicates a target dot (modulated dot) written at 256 levels (0 to 255) of write levels (gradations).
, And the hatched portions indicate dots (write dots) written at a write level of “255 (100%)”.

Each of the nine gamma correction patterns has 3 patterns.
Although this is a repetition of a × 3 matrix, the number of dots written around the dot of interest differs. Note that both the dot of interest (○) and its surrounding dots (shaded area) are 25
A gamma correction pattern written at six levels (0 to 255) of writing levels (gradations) can also be used.

The CPU 80 on the engine 54 side (see FIGS. 4 and 5)
) Are the γ values obtained by gradually changing the writing level of the target dot according to the number of writing dots around the target dot.
Each of the correction patterns is formed as a gradation pattern on the belt-shaped photoreceptor 1 as shown in any of the following (1) to (3) (here, the image formation pattern is in the rotational direction of the belt-shaped photoreceptor 1). The writing level of the target dot is changed so that the density gradually increases. At this time, a mark pattern (a uniform solid pattern with an intermediate density) indicating the detection start position of the P sensor 22 is added to the head of each gamma correction pattern (gradation pattern) as shown in FIG.

(1) As shown in FIG. 9A, the γ correction pattern when there is a writing dot is obtained from the γ correction pattern when there is no writing dot around the target dot (see FIG. 6A). 6 (see (b) to (i) of FIG. 6) so that the length of the belt-shaped photosensitive member 1 in the rotating direction is shorter (reducing the number of repetitions of the 3 × 3 matrix). Create a pattern.

(2) As shown in FIG. 9 (b), from the γ correction pattern (see FIG. 6 (i)) when all the writing dots are present around the target dot, one Each gamma correction pattern such that the length of the belt-shaped photosensitive member 1 in the rotation direction is shorter in the gamma correction pattern (see FIGS. 6A to 6H) when there is no part or all the writing dots. A pattern for use.

(3) As shown in FIG. 9C, a γ correction pattern when there are all write dots around the target dot and when there are no write dots (FIG. 6A )), The γ-correction pattern (see FIGS. 6B to 6H) in the case where there are some writing dots around the target dot is longer in the rotation direction of the belt-shaped photoconductor 1. Γ-correction patterns are formed so as to reduce the length.

Thereafter, the detection of the density of the gradation pattern is started from the time when the density of each mark pattern is detected using the P sensor 22. At this time, by measuring the time from the point at which the density of the mark pattern is detected by the P sensor 22, the writing level (gradation) of the target dot with respect to the density at each position of the gradation pattern sequentially detected by using the P sensor 22 Figure 8
Is calculated, and γ correction data is created based on the dot γ characteristic.

That is, the approximate expression for calculating the write level of the target dot after the γ correction is obtained by the least squares method based on the dot γ characteristics for each number of write dots around the target dot. Then, each of the approximation formulas has "0" to
By sequentially applying “15”, the write level of the target dot after the γ correction (8 bits, within the range of 0 to 255) is obtained, and each level and the write level of the target dot before the γ correction (4 bits, 0 Γ correction data indicating the relationship (within the range of ~ 15) is created and written to the internal memory of the γ correction table 85.

Therefore, according to the image forming apparatus of the first embodiment, the number of tones of the image data to be printed out does not decrease even if the γ correction is performed, and stable tone characteristics can be reproduced. Can be. Further, since a plurality of γ correction patterns are formed as gradation patterns instead of patch patterns on the belt-shaped photosensitive member 1 with different lengths in the rotation direction, the following (1) to (3) are shown. Thus, the gradation of the image data portion corresponding to the longer image forming pattern can be improved. If the image forming pattern is made as short as possible, the process control operation time can be reduced, and the toner consumption at that time can be minimized.

(1) The length of the belt-shaped photosensitive member 1 in the rotating direction of the gamma correction pattern when there is a writing dot is shorter than that when there is no writing dot around the target dot. By forming each γ correction pattern so as to make it possible, the gradation of the low density portion of the image data can be improved.

(2) From the γ correction pattern in the case where there are all writing dots around the target dot, the γ when there is no part or all of the writing dots around the target dot
By forming each γ correction pattern such that the length of the correction pattern in the rotation direction of the belt-shaped photoconductor 1 is shorter, high-density gradation of image data can be improved. .

(3) The gamma correction pattern in the case where there are some write dots around the target dot is obtained from the gamma correction pattern in the case where all the write dots are present around the target dot and in the case where all the write dots are not present. Improving the low-density part and high-density gradation of image data by forming each γ correction pattern such that the length of the pattern in the rotating direction of the belt-shaped photoconductor 1 is shorter. Can be.

Next, a second embodiment of the present invention will be described. Since the hardware configuration other than the γ correction unit 52 is the same as that of the above-described embodiment, FIGS. 1 to 3 will be referred to again. The printer controller 51 in the color image forming apparatus of this embodiment has a function of selectively performing dot concentration type multi-value dither processing or dot dispersion type multi-value dither processing on image data.

FIG. 10 shows an example of the configuration of a circuit for performing the optimum γ correction on image data on which either the dot concentration type or the dot distribution type multi-value dither processing has been performed in the γ correction section 52. It is a block diagram. γ correction unit 52
Are the dot environment determination unit 120 and the γ correction table 140
Consists of The dot environment determination unit 120 includes a line buffer 121, a point-of-interest latch 122, surrounding determination latches 123 to 130, and a determination unit 131.

In the γ correction section 52, the image data having a weight of 4 bits sequentially sent from the printer controller 51 for each color is read by the surrounding determination latch 128.
(I + 1) is entered, and sequentially shifted to the surrounding determination latch 129, the attention point latch 122, and the surrounding determination latch 130 in synchronization with the image synchronization clock. The image data from the printer controller 51 also enters the line buffer 121, and the image data delayed by one line enters the surrounding determination latch 123 (i), and is sequentially synchronized with the surrounding synchronization latch 124 (i) in synchronization with the image synchronization clock. 125,12
It shifts to 6,127.

The determining unit 131 includes a surrounding determining latch 123.
The environment (logical product of each image data and the number of writing dots) is determined by referring to each image data (dots surrounding the dot of interest) to 130, and the logical product of each image data corresponding to the determination result is determined. The information to be written is 1-bit code information, and the information corresponding to the number of write dots is 3-bit code information.
Send to 40.

Here, the surrounding determination latches 123 to 130
When the logical product of the respective image data is "0", the 1-bit code information is set to "0". If the logical product of the image data of the surrounding determination latches 123 to 130 is not "0", the 1-bit code information is set to "1". Further, when the above-mentioned 3-bit code information is transmitted, each image data has a 4-bit numerical value in the range of “0” to “15”.
Bit), and assigns it to a numerical value in the range of “0” to “7”.

On the other hand, the image data having a 4-bit weight sent from the printer controller 51 is shifted to the surrounding determination latches 128 and 129 and the point-of-interest latch 122 as described above, and is shifted to the line (main scanning). )
Gamma correction table 140 with three clock delays in the direction
Is input to

The gamma correction table 140 determines the type of the pseudo gradation process of the printer controller 51 based on the 1-bit code information from the determination unit 131. That is, if the 1-bit code information is "0", it is determined that the dot concentration type multi-value dither processing is performed, and if "1", it is determined that the dot dispersion type multi-value dither processing is performed.

Thereafter, according to the result and the 3-bit code information from the determination unit 131, one of the γ correction data for each writing dot number similar to the first embodiment is selected, and the γ correction is performed. The image data (dot of interest) having a 4-bit weight input from the point-of-interest latch 122 is γ-corrected using the data, the writing level is variably set, and the corresponding 8-bit writing level signal is written into the writing unit 53. Output to

The gamma correction of image data subjected to pseudo gradation processing (dot concentration type or dot dispersion type multi-value dither processing) is partially different from that of the first embodiment in pseudo gradation processing. The description is omitted because all the others are the same. Therefore, also in the second embodiment, the same effects as in the first embodiment can be obtained.

In the first and second embodiments, the gradation pattern and the mark pattern are transferred to the belt-shaped photosensitive member 1.
And the density is detected using the P sensor 22. The P sensor 22 or an optical sensor equivalent thereto is installed facing the surface of the intermediate transfer belt 10,
An image of the gradation pattern and the mark pattern may be formed on the intermediate transfer belt 10 via the belt-shaped photoreceptor 1, and the density may be detected by using the P sensor 22 or the optical sensor.

In the first and second embodiments, nine (all types) of γ correction patterns are prepared as γ correction patterns for the number of writing dots around the target dot.
It is not always necessary to prepare all of the gamma correction patterns, and it is possible to selectively prepare (for example, the number of write dots around the target dot is 1, 4, or 5) depending on the type of pseudo gradation processing, the accuracy of gamma correction, and the like. , 6 and 8 γ correction patterns).

Although the embodiment in which the present invention is applied to an electrophotographic image forming apparatus using a semiconductor laser for irradiating a laser beam has been described, the present invention is not limited to this, and irradiates light other than a laser beam. LED and EL
Alternatively, the present invention can be applied to an electrophotographic image forming apparatus using a recording head that irradiates an ion stream.

[0078]

As described above, according to the image forming apparatus of the present invention, since the number of gradations of the image data to be printed out does not decrease, stable gradation can be reproduced. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a control system of the color image forming apparatus illustrated in FIG. 2;

FIG. 2 is a diagram illustrating a configuration example of a mechanism of the color image forming apparatus according to the first embodiment of the present invention.

3 is an enlarged view showing a part of the color image forming apparatus shown in FIG. 2;

FIG. 4 is a block diagram showing a configuration example of a circuit for performing optimal γ correction on image data mainly subjected to multi-value dither processing in the γ correction unit 52 of FIG. 1;

FIG. 5 is a block diagram showing a configuration example of a circuit for performing optimal γ correction on image data mainly subjected to multi-level error diffusion processing.

6 is an explanatory diagram showing a different example of a gamma correction pattern (gradation pattern) formed on the belt-shaped photoconductor 1 of FIG.

FIG. 7 is an explanatory diagram showing a positional relationship between a mark pattern formed on the belt-shaped photoconductor 1 of FIG. 3 and a γ correction pattern.

FIG. 8 is a diagram illustrating an example of dot γ characteristics of a mark pattern and a γ correction pattern formed on the belt-shaped photoconductor 1 of FIG. 3;

9 is a diagram for explaining the length of each gamma correction pattern formed on the belt-shaped photoconductor 1 in FIG. 3 in the rotation direction.

FIG. 10 shows a configuration example of a circuit for performing optimal γ correction on image data subjected to multi-level dither processing of dot concentration type and dot dispersion type in the γ correction unit of the second embodiment of the present invention. FIG.

FIG. 11 shows dot densities in a high density portion (solid portion) and a low density portion (single dot portion) when dot concentrated dither processing is performed on image data by a printer controller of a conventional color image forming apparatus. It is a figure showing an example of a dot size.

FIG. 12 is a diagram showing an example of dot γ characteristics when image data from a printer controller of the color image forming apparatus is printed out by a printer engine.

FIG. 13 is an explanatory diagram for explaining a problem of the color image forming apparatus.

[Explanation of symbols]

1: Belt-shaped photoconductor 5: Laser writing system unit 6-9: Developing device 10: Intermediate transfer belt 13: Bias roller 14: Transfer roller 22: P sensor 51: Printer controller 52: γ correction unit 53: Writing unit 54: Engine 80: CPU 81, 100, 120: Dot environment judging unit 82, 89, 101, 121: Line buffer 83: Latch for position alignment 84, 90, 102, 122: Latch of interest point 85, 140: γ correction table 86 to 88: OR gate 91-98, 103-110, 123-130: Latch for surrounding determination 99, 111, 131: Judgment unit

Claims (4)

[Claims] 1. An image forming apparatus which modulates light or ion flow according to image data to irradiate a recording medium to form a dot image on the recording medium by an electrophotographic method, wherein the number of writing dots around a target dot is Separately, gradation pattern image forming means for forming a plurality of γ correction patterns in which the gradation of the target dot is gradually changed as gradation patterns on the recording medium with different lengths in the rotation direction, Density detecting means for detecting, using an optical sensor, the density of each gradation pattern created on the recording medium by the means; and gamma correction data for creating gamma correction data for each of the number of writing dots based on the detection result of the means. Correction data creation means, pseudo gradation processing means for performing pseudo gradation processing on input image data,
Dot environment determining means for determining the environment of the dot by referring to surrounding dots with respect to the target dot of the image data subjected to the pseudo gradation processing by the means, and the γ correction according to the determination result of the means. Selecting one of the gamma correction data for each writing dot number created by the data creation means, correcting the tone of the dot of interest of the image data using the gamma correction data, and writing a corresponding writing level signal An image forming apparatus, comprising: a γ-correction unit that outputs a signal. 2. A method according to claim 1, wherein said gradation pattern image forming means includes a γ image when there is no writing dot around the target dot.
The correction pattern is a means for imaging each of the γ correction patterns so that the length of the γ correction pattern in the case where there is a writing dot is shorter in the rotation direction of the recording medium. The image forming apparatus according to claim 1. 3. The gradation pattern image forming means according to claim 1, wherein said gradation pattern image forming means performs gamma correction when there is no part or all of the writing dots around the target dot, based on the gamma correction pattern when all the writing dots are around the target dot. 2. An image forming apparatus according to claim 1, wherein said gamma correction pattern is formed such that the length of the recording pattern in the direction of rotation of said recording medium is shorter. 4. The gradation pattern image forming means according to claim 1, wherein said gamma correction pattern includes a case where all of the writing dots are present around the target dot and a case where all of the writing dots are absent. 2. The image according to claim 1, wherein the .gamma.-correction pattern is a means for forming each of the .gamma.-correction patterns such that the length of the recording medium in the rotating direction is shorter. Forming equipment.