JPH1075367A - Image processing unit - 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 printer controller 51 applies pseudo gradation processing such as dot concentration or dot distribution multi-value dither processing to image data so as to reduce a data quantity, the resulting image data are stored in a frame memory, and then read and a gamma correction section 52 of the engine 54 applies gamma correction to the image data for each dot. In this case, the gamma correction section 52 references dots around a noted dot so as to discriminate an environment of the surrounding dots and selects any of a plurality of kinds of gamma correction data stored in an internal memory according to the result and sets a write level of a noted dot by using the selected gamma correction data and provides an output of a corresponding write signal to a write section 53.

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. 26, in a high density portion (solid portion), the dot density and the dot size increase, 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) and the density of the modulated dot based on the image data) 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 a broken line in FIG. 27. 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, there is provided a pseudo-gradation processing means for performing pseudo-gradation processing on input image data, and a method for processing a target dot of image data which has been subjected to pseudo-gradation processing by the means. Dot environment determining means for referring to surrounding dots and determining the environment of the dot, and performing γ correction for variably setting a writing level such as a writing density or a writing size of the target dot in accordance with the determination result of the means. Correction means.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the γ correction unit is provided with at least two types of γ correction units.
Γ correction data storage means for storing correction data, γ correction data selection means for selecting any of the above γ correction data according to the judgment result of the dot environment judgment means, γ selected by the means And a write level signal output means for setting a write level of the target dot using the correction data and outputting a corresponding write level signal.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the gamma correction data storage means is means for storing gamma correction data of different types depending on the surrounding dot environment with respect to the target dot. is there. The invention of claim 4 is
4. The image forming apparatus according to claim 2 or 3, wherein a predetermined type of gamma correction dot pattern is sequentially formed on a recording medium at a predetermined timing for each predetermined writing level, and Density detecting means for detecting the density of each dot pattern created on the recording medium by the means using an optical sensor, and gamma correction data creating means for creating gamma correction data based on the detection result of the means. It is provided.

According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the γ correction data creating means determines a dot γ characteristic based on a detection result of the density detecting means,
This is a means for creating γ correction data based on characteristics. According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, each of the γ correction data has the highest write level of the modulation dot and the lowest γ correction data based on the lowest γ correction data. A means is provided for creating new gamma correction data within the range of the writing level by calculation.

According to a seventh aspect of the present invention, in the image forming apparatus of the fourth aspect, the gamma correction pattern image forming means includes a gamma correction dot having no writing dots (dots written visually) at least around the modulation dots. A means for sequentially forming a pattern and a dot pattern for γ correction with a writing dot on a recording medium at a predetermined timing for each predetermined writing level, and γ correction data generating means,
Based on the detection result of the density detecting means, the dot γ characteristic of each dot pattern for γ correction is obtained, and
After obtaining the dot γ characteristics of the dot patterns other than the correction dot pattern from the respective dot γ characteristics by interpolation, it is means for creating different types of γ correction data based on the respective dot γ characteristics. is there.

According to an eighth aspect of the present invention, in the image forming apparatus of the fifth or seventh aspect, when the modulation of the light or the ion current is multi-level modulation, It is provided with means for allocating the writing level at equal intervals from the visualization start point to the target maximum density. According to a ninth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the γ correction unit sets the writing level of the target dot to be smaller as the number of write dots around the target dot, which is a result of the determination by the dot environment determining unit, is smaller. It is a means of raising the height.

According to a tenth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the dot environment determining means determines whether an environment of a surrounding dot with respect to the target dot is in a state where there is no writing dot, in a horizontal direction or a vertical direction. This is a means for determining whether the state is a certain state or an oblique state. According to an eleventh aspect of the present invention, in the image forming apparatus of the first or second aspect, the gamma correction unit includes a unit that changes a maximum writing level of the target dot in accordance with a result of the determination by the dot environment determining unit.

According to a twelfth aspect of the present invention, in the image forming apparatus according to the first or second aspect, when determining the environment of surrounding dots with respect to the target dot, the dot environment determining means may use data of each dot under an arbitrary condition. Is provided with means for binarization. According to a thirteenth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the dot environment determining means includes: a dot within a predetermined range of a previous line with respect to the target dot; a dot within a predetermined range on the left and right of the target dot; This is a means for judging the environment of dots within a predetermined range of the subsequent line with respect to the target dot.

According to a fourteenth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the dot environment determining means includes a dot within a predetermined range of the previous line with respect to the target dot, and a predetermined left or right position of the target dot. This is a means for judging the environment of the dots within the range. The invention of claim 15 is the invention of claim 1
Alternatively, in the image forming apparatus of (2), the dot environment determining means is means for determining an environment of a dot within a predetermined range of a line after the target dot and a dot within a predetermined range of left or right of the target dot. It is.

According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to fifteenth aspects, there is provided a dot range switching means for switching the predetermined range according to the type of pseudo gradation processing of the pseudo gradation processing means. It is. According to a seventeenth aspect of the present invention, in the image forming apparatus according to the sixteenth aspect, when the pseudo gradation processing of the pseudo gradation processing means is an error diffusion process, the predetermined range adjacent to the target dot is set. In the case of the dot concentration type dither processing, the predetermined range is switched to a predetermined range wider than the range in the case where the dot concentration type dither processing is performed so that the number of dots can be referred to.

The invention according to claim 18 is the image forming apparatus according to any one of claims 1 to 17, wherein the dot environment judging means judges the environment of surrounding dots with respect to the target dot based on the number of surrounding writing dots. It is provided with. According to a nineteenth aspect of the present invention, in the image forming apparatus according to any one of the first to seventeenth aspects,
It is provided with means for judging the environment of surrounding dots with respect to the target dot based on the average value of the surrounding dots.

According to a twentieth aspect of the present invention, in the image forming apparatus according to any one of the first to seventeenth aspects, the dot environment determining means determines an environment of surrounding dots with respect to the target dot based on the number of surrounding writing dots. Means, and means for determining the average value of the surrounding dots,
The correction means includes means for selecting one of the determination results of the dot environment determining means depending on the type of pseudo gradation processing of the pseudo gradation processing means.

According to a twenty-first aspect of the present invention, in the image forming apparatus according to any one of the second to eighth aspects, the gamma correction data selecting means is provided for performing the judgment result of the dot environment judging means and the pseudo gradation processing of the pseudo gradation processing means. This is a means for selecting any one of the γ correction data stored in the γ correction data storage means according to the type. According to a twenty-second aspect of the present invention, in the image forming apparatus according to any one of the first to twenty-first aspects, the gamma correction unit determines the type of the pseudo gradation processing of the pseudo gradation processing unit according to the result of the determination by the dot environment determination unit. This is provided with a pseudo gradation processing type discriminating means.

According to a twenty-third aspect of the present invention, in the image forming apparatus according to any one of the first to twenty-second aspects, the image in which the writing level of the dot of interest is subjected to pseudo gradation processing by the pseudo gradation processing means is provided to the γ correction means. A means for variably setting the number of variable steps larger than the multi-value number of one dot of data is provided. According to a twenty-fourth aspect of the present invention, in the image forming apparatus according to the first aspect, a γ characteristic setting unit that arbitrarily sets a dot γ characteristic is provided, and the γ correction unit sets the target dot according to the dot γ characteristic set by the γ characteristic setting unit. Is variably set.

According to a twenty-fifth aspect of the present invention, in the image forming apparatus of the first or second aspect, an image storage means for storing the image data subjected to the pseudo gradation processing by the pseudo gradation processing means, and the image data stored in the means. Image reading means for reading the read image data, and the dot environment determining means refers to surrounding dots for a target dot of the image data read by the image reading means, and determines the environment of the dot. Things.

In the image forming apparatus according to the present invention,
Pseudo gradation processing is performed on the input image data, and the dot environment determining means determines the environment (situation) of the surrounding dots by referring to surrounding dots for the target dot of the image data, and performs γ correction. Since the means variably sets (γ-correction) the writing level of the noted dot in accordance with the result of the determination, an intended dot density or dot size can be obtained regardless of the surrounding dot environment. Further, since the gamma correction is not performed before the pseudo gradation processing is performed on the input image data, the number of gradations of the image data to be printed out does not decrease, and stable gradation is reproduced. be able to. Further, the dot stability of the highlight part is improved.

In the image forming apparatus according to the present invention,
2. The image forming apparatus according to claim 1, wherein the gamma correction data selection means of the gamma correction means selects one of the gamma correction data in the gamma correction data storage means in accordance with the result of the determination by the dot environment determination means, and writes the selected data. The level signal output means is the γ
Since the write level of the target dot is set using the correction data and the corresponding write level signal is output, the intended dot density or dot size can be easily obtained.

In the image forming apparatus according to the third aspect of the present invention,
3. The image forming apparatus according to claim 2, wherein the gamma correction data storage means stores gamma correction data of different types for each surrounding dot environment with respect to the target dot, so that the gamma characteristic is arbitrarily set by adjusting the writing level. This makes it possible to prevent the occurrence of a gradation jump in a highlight portion and a shadow portion even when the tone (gradation) is changed.

According to a fourth aspect of the present invention, in the image forming apparatus of the second or third aspect, the γ-correction pattern image forming means forms a predetermined type of γ-correction dot pattern on a recording medium. An image is sequentially formed at a predetermined timing for each predetermined writing level, a density detecting unit detects the density of each dot pattern created on the recording medium using an optical sensor, and the γ correction data generating unit detects the density. Since the γ correction data is created based on the result (for example, the dot γ characteristic is obtained based on the detection result, and the γ correction data is created based on the dot γ characteristic), it is possible to cope with changes in environment and time. Image stability can be achieved.

In the image forming apparatus according to the present invention,
5. The image forming apparatus according to claim 4, wherein the writing level of the modulation dot in each of the γ correction data is the highest.
Based on the correction data and the lowest gamma correction data,
Since new γ-correction data within the range of each writing level is created by calculation, there is no need to create a corresponding γ-correction dot pattern on the recording medium in order to increase the accuracy of γ-correction, and the toner Is reduced.

In the image forming apparatus according to the present invention,
5. The image forming apparatus according to claim 4, wherein the γ-correction pattern image forming means includes a γ-correction dot pattern having no write dots and a γ-correction dot pattern having write dots at least around the modulation dots on a recording medium. Images are sequentially formed for each of the predetermined writing levels at predetermined timings, and the γ correction data generating means obtains the dot γ characteristics of each of the γ correction dot patterns based on the detection result of the density detecting means, Since the dot γ characteristics of the dot patterns other than the γ correction dot pattern are obtained by interpolating from the above dot γ characteristics, different types of γ correction data are created based on the above dot γ characteristics. Therefore, it is not necessary to create a corresponding .gamma. Correction dot pattern on the recording medium in order to increase the accuracy of the image formation, and the amount of discharged toner is reduced.

In the image forming apparatus according to the present invention,
8. The image forming apparatus according to claim 5, wherein, when the modulation of the light or the ion current is a multi-level modulation, the writing level of the modulated dot in the dot γ characteristic is set to a target maximum from the visualization start point. Since the distribution is performed at equal intervals up to the density, the stability of the image can be further improved. In the image forming apparatus according to the ninth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the γ correction unit sets the target dot to be smaller as the number of write dots around the target dot, which is a result of the determination by the dot environment determining unit, is smaller. Since the write level of is higher, more stable gradation can be reproduced.

According to a tenth aspect of the present invention, in the image forming apparatus of the first or second aspect, the dot environment determining means determines that an environment of surrounding dots with respect to the target dot is in a state where there is no writing dot, in the horizontal direction. Alternatively, it is determined whether the state is a state in the vertical direction or a state in the oblique direction, so that more stable gradation can be reproduced.

In the image forming apparatus according to the eleventh aspect of the present invention, in the image forming apparatus according to the first or second aspect, the γ correction means changes the maximum writing level of the target dot in accordance with the result of the determination by the dot environment determining means. Thus, more stable gradation can be reproduced.

In the image forming apparatus according to the twelfth aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the dot environment determining means determines the environment of surrounding dots with respect to the target dot, the data of each dot is used. 2 under any conditions
Since the value is converted to a value, even if the image data input to the dot environment determining means is multi-valued data, it is not necessary to have a memory for the weight, and the memory can be saved.

In the image forming apparatus according to a thirteenth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the dot environment judging means determines that a dot (for example, three dots) within a predetermined range of the previous line with respect to the target dot. Since the environment of a dot (for example, one dot) within a predetermined range on the left and right of the dot and a dot (for example, three dots) within a predetermined range of the succeeding line with respect to the target dot is determined, simulation of dither processing, error diffusion processing, and the like is performed. Image data subjected to gradation processing (dots of interest)
Can be effectively performed with a small range of environment judgment, and memory can be saved.

According to a fourteenth aspect of the present invention, in the image forming apparatus of the first or second aspect, the dot environment determining means includes a dot (for example, 5 dots) within a predetermined range of the preceding line with respect to the target dot; Since the environment of a dot (for example, 3 dots) within a predetermined range on the left or right of the target dot is determined, it is effective to perform γ correction of image data that has been subjected to pseudo gradation processing such as dither processing by determining the environment in a small range. And the memory can be saved.

According to a fifteenth aspect of the present invention, in the image forming apparatus of the first or second aspect, the dot environment determining means includes a dot within a predetermined range of the rear line with respect to the target dot (for example, 5 dots), and Since the environment of a dot (for example, 3 dots) within a predetermined range on the left or right of the target dot is determined, the gamma correction of image data that has been subjected to pseudo gradation processing such as dither processing is performed in a small range environment as described above. The determination can be performed effectively, and the memory can be saved.

In the image forming apparatus according to the sixteenth aspect of the present invention, in the image forming apparatus according to any one of the thirteenth to fifteenth aspects, the dot range switching means sets the predetermined range according to the type of pseudo gradation processing of the pseudo gradation processing means. Since the switching is performed, the gamma correction of the image data on which the pseudo gradation processing has been performed can be effectively performed with a smaller range of environment judgment, and further memory saving can be achieved.

In the image forming apparatus according to the seventeenth aspect, in the image forming apparatus according to the sixteenth aspect, the dot range switching means includes a predetermined range when the pseudo gradation processing of the pseudo gradation processing means is error diffusion processing. Is switched to a range in which a predetermined number of dots adjacent to the target dot can be referred to, and in the case of the dot concentration type dither processing, the predetermined range is switched to a predetermined range wider than the range, so that error diffusion processing and dot concentration type dither processing are performed. The gamma correction of the image data to which is applied can be effectively performed by the environment judgment in a small range.

In the image forming apparatus according to the eighteenth aspect, in the image forming apparatus according to the first or second aspect, the dot environment determining means determines the environment of the surrounding dots with respect to the target dot based on the number of surrounding writing dots. ,
Γ of image data subjected to pseudo gradation processing such as dither processing
The correction can be effectively performed by a small range of environment judgment, and the memory can be saved.

In the image forming apparatus according to the nineteenth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the dot environment determining means determines the environment of the surrounding dots with respect to the target dot based on the average value of the surrounding dots. Of image data that has been subjected to pseudo gradation processing such as multi-level error diffusion processing
The correction can be effectively performed by a small range of environment judgment, and the memory can be saved.

According to a twentieth aspect of the present invention, in the image forming apparatus of the first or second aspect, the dot environment determining means determines the environment of surrounding dots with respect to the target dot based on the number of surrounding writing dots. Judgment is made based on the average value of the surrounding dots, and the γ correction means selects one of the above judgment results according to the type of pseudo gradation processing of the pseudo gradation processing means. The gamma correction of the target dot is performed by using the gamma correction data of (1), and the writing level thereof can be set. That is, gamma correction of image data that has been subjected to pseudo gradation processing such as dither processing and error diffusion processing can be performed using a small range of environment determination and optimal gamma correction data, thereby saving memory.

According to the image forming apparatus of the present invention, in the image forming apparatus of any one of claims 2 to 8,
The γ correction data selection means selects one of the γ correction data stored in the γ correction data storage means according to the judgment result of the dot environment judgment means and the type of pseudo gradation processing of the pseudo gradation processing means. Since the selection is made, gamma correction of the target dot can be performed using the gamma correction data, and the writing level can be set. That is, γ of image data that has been subjected to pseudo gradation processing such as dither processing and error diffusion processing
The correction can be performed in a small range of environment judgment and using the optimal γ correction data, and the memory can be saved.

In the image forming apparatus according to the present invention, in the image forming apparatus according to any one of the first to twenty-first aspects, the gamma correcting means includes a pseudo-gradation processing means for pseudo-gradation processing means according to the judgment result of the dot environment judging means. Since the type of the gradation processing is determined, it is possible to perform the optimum γ correction without having to send the information indicating the type of the pseudo gradation processing from the outside.

In the image forming apparatus according to the twenty-third aspect, in the image forming apparatus according to any one of the first to twenty-second aspects, the write level of the dot of interest is image data obtained by performing pseudo gradation processing by pseudo gradation processing means. Variably set to a variable step number larger than the multi-value number of 1 dot,
The gamma characteristic can be set with high accuracy by adjusting the writing level, and even if the tone is changed, no gradation jump occurs in the highlight portion and the shadow portion.

According to a twenty-fourth aspect of the present invention, in the image forming apparatus of the first aspect, a γ characteristic setting means for arbitrarily setting a dot γ characteristic is provided, and the γ correction means comprises:
Since the dot writing level is variably set in accordance with the dot γ characteristic set by the γ characteristic setting means, it is also possible to easily set the γ characteristic by adjusting the writing level. No gradation jump occurs in the portion.

In the image forming apparatus according to the twenty-fifth aspect, in the image forming apparatus according to the first or second aspect, the pseudo gradation processing such as multi-value dither processing is performed by the pseudo gradation processing means to reduce the data amount. Since the image data is temporarily stored in the image storage unit and then read out, the surrounding dots are referred to the target dot of the image data, and the environment of the dot is determined, so that the capacity of the image storage unit (frame memory) is reduced. And low cost can be realized by memory saving.

[0049]

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 units 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 photosensitive member 1 and the intermediate transfer belt 10 are in contact with the rotating roller 3, and the first visible image on the belt-shaped photosensitive member 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 be in 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 away 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 the figure only during cleaning after transfer.

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). After the image data is subjected to the pseudo gradation processing, the 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 input to the color image forming apparatus shown in FIG. That is, when image data (color signal) output from an image reading device separate from the color image forming apparatus (printer) is input to the laser writing system unit 5, the laser writing system unit 5
Performs the following operation.

First, a laser beam modulated according to 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 driving 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 yellow, magenta, cyan, and black images superimposed on the intermediate transfer belt 10 are transferred to a transfer sheet which is conveyed to a transfer unit from a sheet supply table 17 through a sheet supply roller 18 and a registration roller 19, and transferred to a transfer sheet by 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 2 which is an optical sensor for detecting the amount of toner (image density) on the belt-shaped photoconductor 1 is located slightly upstream from the portion of the belt-shaped photoconductor 1 which is in contact with the intermediate transfer belt 10.
2 are provided. 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 (here, dot-concentration type multi-value dither processing is used) on image data created based on image information in units of one dot, and applies 4-bit image data for each color to the image data. After the conversion, the image data is temporarily stored in a 4-bit frame memory for each color, and then read out for each color and input to the γ correction unit 52 of the engine 54. 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 gamma correction unit 52 performs gamma correction on the input image data by determining the surrounding dot environment (situation) for each dot (dot of interest), and sends it to the writing unit 53 as a write level signal. The writing unit 53 modulates (power modulation, pulse width modulation, or the like) a laser beam generated from the semiconductor laser in the laser writing unit 5 based on the sent write level signal, and places the laser beam on the belt-shaped photoconductor 1. An electrostatic latent image is formed.

The CP in the printer controller 51
U functions as pseudo gradation processing means for performing pseudo gradation processing on image data and image reading means for reading image data stored in a frame memory in the printer controller 51. Further, the frame memory corresponds to an image storage unit that stores image data that has been subjected to pseudo gradation processing.

Further, the γ correction unit 52 refers to the surrounding dots with respect to the target dot of the image data read from the frame memory, that is, the image data subjected to the pseudo gradation process, and determines the environment of the dot. It functions as a dot environment determining means for determining (situation) and a γ correcting means for performing γ correction for variably setting a writing level such as a writing density or a writing size of a target dot according to the determination result.

FIG. 4 is a block diagram showing a configuration example of the γ correction unit 52. The gamma correction unit 52 has a circuit configuration for performing optimal gamma correction on image data that has been mainly subjected to dot concentration type multi-value dither processing, and includes a dot environment determination unit 61 and a line buffer 62. , Position matching latch 63, attention point latch 64, and γ correction table 6
Consists of five. The dot environment determination unit 61 determines whether the OR gate 6
6, line buffers 67, 68, attention point latch 6
9, a surrounding determination latch 70 to 77, and a determination unit 78.

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. Therefore, the OR gate 66 outputs 1 bit (1 bit) 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”. If all the bits are “0”, “0 (dot that is not a writing dot)” is set. For example, "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 66 is
It enters the surrounding determination latch 74 (d1) and sequentially stores the surrounding determination latches 72 (v1) and 75 in synchronization with the image synchronization clock.
Shift to (d2). On the other hand, the data passing through the OR gate 66 enters the line buffer 67, and the data delayed by one line is shifted to the surrounding determination latch 70 (h1), the attention point latch 69, and the surrounding determination latch 71 (h2). Go.

Further, the data that has passed through the line buffer 67 enters another line buffer 68, and the data delayed by one line is further supplied to the surrounding determination latches 76 (d3) and 7 (d3).
3 (v2) and 77 (d4). Here, the next determination unit 78 determines the surrounding determination latch 74 (d
1), 72 (v1), 75 (d2), 70 (h1), 7
1 (h2), 76 (d3), 73 (v2), 77 (d
The environment is determined with reference to each data (4) (dots surrounding the target dot).

The result of the determination (information for selecting the optimal γ correction data) is sent to the next γ correction table 65 as 2-bit code information. On the other hand, the image data having a 4-bit weight sent from the printer controller 51 passes through a line buffer 62 having a 4-bit weight, passes through a position matching latch 63, is latched by a target point latch 64, and It is input to the correction table 65.

The gamma correction table 65 selects gamma correction data in accordance with the code information from the determination unit 78, and uses the gamma correction data to input 4-bit weighted image data input from the point of interest latch 64. (Dot of interest) to γ
The write level is variably set by correcting the
A bit write level signal is output to the write unit 53.

FIG. 5 is a diagram showing the surrounding environment determination latches 74 (d 1), 72 (v 1), and 75 (d) in the dot environment determination section 61.
2), 70 (h1), 71 (h2), 76 (d3), 7
FIG. 9 is an explanatory diagram showing an example of the relationship between each data environment of 3 (v2) and 77 (d4) and each γ correction data selected by the γ correction table 65 according to each environment.

The gamma correction table 65 includes the surrounding determination latches 74 (d1), 72 (v1), 75 (d2), and 70 (h).
1), 71 (h2), 76 (d3), 73 (v2), 7
7 (d4) are all “0”, the γ correction data γc (see FIG. 9) is stored in the surrounding determination latch 70 (h
1), 71 (h2), 72 (v1), 73 (v2) are “0” and the surrounding determination latches 74 (d1) 75 (d2),
If any of 76 (d3) and 77 (d4) is “1”, the γ correction data γb is stored in the surrounding determination latch 70 (h
If at least one of 1), 71 (h2), 72 (v1), and 73 (v2) is “1”, the γ correction data γa is selected.

FIG. 6 is an explanatory diagram showing an example of a gamma correction pattern. This gamma correction pattern is a dot pattern, which is a repetition of a 2 × 2 matrix, and has 15 patterns. The writing level (laser beam modulation level) of the modulation dot (shown by ○) in each of the γ correction patterns is divided into 15 stages (pattern levels 1 to 15).

That is, from the γ correction section 52 to the writing section 5
The image data to be sent to 3 is 8-bit data, and the maximum writing level of the modulated dot is “255”, so that the writing level corresponding to pattern level 1 is “17”,
When the write level corresponding to pattern level 2 is “3”
4 ", and then increase by 17, and the write level corresponding to the pattern level 15 becomes" 255 ".

FIG. 7 is an explanatory diagram showing an example of the dot arrangement of various dot patterns, and FIG. 8 is a diagram showing an example of dot γ characteristics (the relationship between the writing level of the modulated dot and the density) for each dot arrangement. In FIG. 7, a circle represents dots (modulation dots) written at 15 levels of writing levels,
Indicates dots written at a writing level of “255 (100%)”.

This embodiment is based on the premise that dot concentration multi-value dither processing is performed on image data. For example, when forming each dot pattern as shown in FIG. In order to increase the writing level of the dot) in units of one dot and to increase the writing level of the surrounding dots (adjacent to the dot) when the dot reaches the writing level of 100%,
If the target dot is always a single dot, or if there is a write dot around the target dot, the write dot has a 100% write level.

In this embodiment, the environment of the surrounding dots with respect to the target dot is classified into three states: a state in which there is no writing dot, a state in the horizontal or vertical direction, and a state in which the dot is oblique. A single dot pattern (pattern S) as shown in FIG.
(c) Horizontal and vertical array patterns (patterns H, V1, V2) as shown in (d) and oblique array patterns (patterns D1, D2) as shown in (e) and (f) of FIG.

The dot γ characteristic shows a curve as shown in FIG. 8A when there is no writing dot (a dot written at a writing level of 100%) around the target dot. Draws a curve as shown in (2) of the figure, and draws a curve as shown in (3) of the figure when it is in the horizontal or vertical direction.

Here, the CPU 80 (see FIG. 4), which controls the sequence of the entire engine 54, applies the 15 gamma correction patterns (pattern levels 1 to 15) shown in FIG. Images are sequentially formed on the body 1 and the respective image densities (optical reflectances) are measured (detected) by the P sensor 22, and the dot γ characteristics as shown in (1) of FIG. 8 are derived from the results. The dot γ characteristic as shown in (3) of FIG. 8 is a function straight line obtained by an experiment in advance. Further, since the dot γ characteristic shown in (2) of FIG. 8 is related as an intermediate between the above γ characteristics,
It is determined based on each dot γ characteristic.

Subsequently, 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 shown in (1) to (3) of FIG.
Then, “0” to “15” are sequentially applied to the respective approximate expressions to determine the write level of the target dot after the γ correction (in the range of “0” to “255” because it is 8 bits). Correction data .gamma.c, .gamma.b, and .gamma.a (see FIG. 9) showing the relationship between the target dot and the writing level of the target dot before .gamma. Correction (because of 4 bits, within the range of "0" to "15").
Is written in the internal memory of the γ correction table 65.

FIG. 9 is a diagram showing the relationship between the write level before gamma correction and the write level after gamma correction of modulated dots (dots of interest) respectively corresponding to the dot gamma characteristic of each dot pattern shown in FIG. It is. γ correction table 65
When image data (data of the dot of interest) is input in a state where the γ correction data γc shown in FIG. 5 is selected, the following γ correction processing is performed on the data.

For example, when the writing level of the target dot is “15”, the data is γ-corrected using γ correction data γc, and the writing level after γ correction is set to γc15.
(255). When the writing level of the target dot is “7”, the data is γ-corrected using the γ correction data γc, and the writing level after γ correction is set to γc7.

The γ correction table 65 indicates that when the target dot data is input in a state where the γ correction data γb shown in FIG. 5 is selected, for example, when the write level of the target dot is “15”, the data is set to γ. Γ correction is performed using the correction data γb, and the write level after γ correction is set to γb15
To When the writing level of the target dot is “7”, the data is γ-corrected using the γ correction data γb, and the writing level after γ correction is set to γb7.

The γ correction table 65 indicates that when the data of the target dot is input in a state where the γ correction data γa shown in FIG. 5 is selected, for example, when the write level of the target dot is “15”, the data is set to γ. Γ correction is performed using the correction data γa, and the write level after γ correction is set to γa15
To When the writing level of the target dot is "7", the data is subjected to γ correction using the γ correction data γa, and the writing level after γ correction is set to γa7.

FIG. 10 is a diagram showing an example of dot γ characteristics based on image data subjected to multi-value dither processing. As can be seen from this figure, since there are many single dots in the highlight portion, area 1 changes when the γ correction table 65 changes the maximum value of the γ correction data γc. In the middle part, the ratio of single dots decreases and the number of combinations of oblique dots increases. Therefore, when the γ correction table 65 changes the maximum value of the γ correction data γb, the area 2 changes. Further, since the combination of left, right, top and bottom dots increases in the shadow portion, when the γ correction table 65 changes the maximum value of the γ correction data γa, the area 3 changes.

As described above, in the color image forming apparatus of this embodiment, the printer controller 51 performs dot concentration type multi-value dither processing on image data to reduce the data amount, and temporarily stores the image data in the frame memory. Since the image data is stored and read out, and the γ correction unit 52 performs γ correction on the image data for each dot, the capacity of the frame memory can be reduced and the cost can be reduced. Note that pseudo gradation processing other than dot concentration type multi-value dither processing may be performed on image data. In this case, the γ correction unit 5
It is necessary to change 2 to a circuit configuration for performing gamma correction on the image data on which the pseudo gradation processing has been performed for each dot.

The dot environment determination unit 6 of the γ correction unit 52
1 is referred to the surrounding dots for the target dot of the input image data, and the surrounding dot environment (whether there is no writing dot, in the horizontal or vertical direction, or in the oblique state). Is determined, and the γ correction table 65 stores the γ correction data stored in the internal memory according to the determination result (the γ correction data of different types is stored for each surrounding dot environment with respect to the target dot). Is selected, the writing level of the dot of interest is set using the γ correction data, and a corresponding writing signal is output. At this time, as the number of write dots around the target dot, which is the result of the determination, is smaller, the write level of the target dot is increased, or the maximum write level of the target dot is changed according to the result of the determination.

Therefore, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. Further, since the γ correction is not performed before the pseudo gradation processing is performed on the image data, the number of gradations of the image data to be printed out does not decrease, and stable gradation can be reproduced. . Further, the dot stability of the highlight part is improved. Further, it is possible to arbitrarily set the γ characteristic by adjusting the writing level of the engine 54, so that even if the tone (gradation) is changed, the gradation does not occur in the highlight portion and the shadow portion.

Further, the CPU 80 on the engine 54 side
The 15 types of γ correction patterns (predetermined types of γ correction dot patterns) shown in FIG. 6 are sequentially formed on the belt-shaped photosensitive member 1 at a predetermined timing, and the density of each pattern is set to P. Detection is performed using the sensor 22, and γ correction data γc is created based on the detection result (a dot γ characteristic is determined based on the detection result, and γ correction data γc is created based on the dot γ characteristic). In addition, it is possible to cope with changes in environment and time, and to stabilize an image. If the P sensor 22 is installed so as to face the surface of the intermediate transfer belt 10, it is possible to form fifteen gamma correction patterns on the intermediate transfer belt 10.

Further, the CPU 80 on the engine 54 side
Is the γ correction data γa at which the writing level of the modulated dot is the highest among the γ correction data γa, γb, and γc stored in the internal memory of the γ correction unit 52, and γ which is the lowest.
Based on the correction data γc, new γ correction data γb within the range of each writing level is created by calculation, so that the corresponding γ correction pattern is changed to the belt-shaped photoconductor 1 in order to increase the accuracy of γ correction. No need to image on top,
Waste toner is reduced.

When the dot environment determining section 61 determines the environment of the surrounding dots with respect to the target dot, the data of each dot is binarized under arbitrary conditions. It is not necessary to have a memory for the weight of multi-value data). Further, the dot environment determination unit 61
Since the environment of three dots on the front line, one dot on the left and right of the target dot, and three dots on the rear line for the target dot is determined for the target dot, dot concentration type multi-value dither processing is performed. The gamma correction of the image data (dots of interest) can be effectively performed with a small range of environment judgment, and only a small amount of memory is required.

The number (reference range) of the dots of the preceding line, the left and right dots of the noted dot, and the dots of the following line with respect to the noted dot may be changed with respect to the noted dot.

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 according to the present embodiment has a function of selectively performing various pseudo gradation processes such as a multi-value dither process and a multi-value error diffusion process on image data by an external command or the like. have. Further, the γ correction section 52 has a circuit configuration for performing an optimum γ correction on the image data subjected to any pseudo gradation processing.

FIG. 11 shows an example of the configuration of a circuit for performing optimal γ correction on image data which has been mainly subjected to multi-value dither processing in the γ 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 4-bit weight is sequentially sent from the printer controller 51 for each color.
Reference numeral 6 converts the image data into 1-bit (1 dot) data indicating the presence or absence of writing. That is, it is determined whether or not each bit of the input image data is all “0”. If all the bits are “0”, “0 (dot that is not a writing dot)” is set. For example, "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 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. OR gate 88
Is output from the surrounding determination latch 96 (i-
1), and sequentially shifted to the surrounding determination latches 97 and 98 in synchronization with the image synchronization clock.

Here, the judging section 99 judges the environment (the number of write dots) by referring to each data (surrounding dots with respect to the target dot) of the surrounding judgment latches 91 to 98, and judges the result as a 3-bit data. Γ correction table 85 as code information (information for selecting optimal γ correction data)
Send to Here, the number of write dots is from “0” to
Since the number is “8”, code information indicating “7” is output at the time of “8”.

On the other hand, the image data having a 4-bit weight sent from the printer controller 51 is shown in FIG.
Also enters the surrounding determination latches 103 (i + 1), sequentially in synchronization with the image synchronization clock.
It shifts to 05. Further, since the image data from the printer controller 51 also enters the line buffer 82 as described above, the image data delayed by one line enters the surrounding determination latch 106 (i), and is sequentially focused in synchronization with the image synchronization clock. The shift to the point latch 102 and the surrounding determination latch 107 is performed.

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.

Here, the judging section 111 judges the environment (average value of the density or size of each dot) with reference to each image data (dots surrounding the target dot) of the surrounding judgment latches 103 to 110. , And the result as 3-bit code information (information for selecting the optimal γ correction data)
To the next γ correction table 85. Here, since each image data has a 4-bit numerical value in the range of “0” to “15”, the above-described determination result is converted into 3 bits (upper 3 bits) and converted into the range of “0” to “7”. To the numbers.

On the other hand, the image data having a weight of 4 bits 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 gamma correction table 85 is supplied from the dot environment determination unit 81 (which can mainly 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, gamma correction data is selected in accordance with the selected code information, and the 4-bit weighted image data (attention dot) input from the attention point latch 84 is gamma corrected using the gamma correction data. Then, the write level is variably set, and a corresponding 8-bit write level signal is output to the write unit 53.

Hereinafter, gamma correction of image data subjected to multi-value dither processing will be described. 13 to 15 are explanatory diagrams illustrating different examples of the γ correction patterns. Each of these γ
The correction pattern is a dot pattern and is a repetition of a 2 × 2 matrix, and there are 15 types. The writing level (laser beam modulation level) of the modulation dot (shown by ○) in each of the γ correction patterns is divided into 15 stages (pattern levels 1 to 15).

That is, from the γ correction section 52 to the writing section 5
The image data to be sent to 3 is 8-bit data, and the maximum writing level of the modulated dot is “255”, so that the writing level corresponding to pattern level 1 is “17”,
When the write level corresponding to pattern level 2 is “3”
4 ", and then increase by 17, and the write level corresponding to the pattern level 15 becomes" 255 ".

In the gamma correction pattern shown in FIG. 13, no writing dot exists around the modulation dot.
In the γ correction pattern shown in FIG. 14, four write dots (dots indicated by hatching are write dots around modulation dots, but the matrix portion where two write dots exist is omitted from the illustration). Exists).
In the gamma correction pattern shown in FIG. 15, all the dots around the modulation dot are writing dots.

FIGS. 16 to 18 correspond to FIGS. 13 and 1, respectively.
FIG. 16 is a diagram illustrating an example of dot γ characteristics (a relationship between a writing level of a modulation dot and a density) of each γ correction pattern in FIG. 15.

The CPU 80 on the engine 54 side (see FIGS. 11 and 12) applies the 15 patterns (pattern levels 1 to 15) shown in FIG. 13 on the belt-shaped photosensitive member 1 shown in FIG. Images are sequentially formed, and the respective image densities are measured (detected) by the P sensor 22. From the result, a dot γ characteristic as shown in FIG. 16 is derived. In this case, the density (measurement result) of the gamma correction pattern of pattern level 1 in FIG. 13 is a1, and the density of the gamma correction pattern of pattern level 2 is a
2. Similarly, the density of the gamma correction pattern at the pattern level 15 is a15.

Further, 15 patterns (pattern levels 1 to 15) of γ correction patterns shown in FIG. 14 are sequentially formed on the belt-shaped photosensitive member 1, and the respective image densities are measured by the P sensor 22. From the result, a dot γ characteristic as shown in FIG. 17A is derived, and since the start is not white, the vertical axis is normalized from “0” as shown in FIG. 17B. In this case, the density of the gamma correction pattern at pattern level 1 in FIG. 14 is b1, the density of the gamma correction pattern at pattern level 2 is b2, and similarly, the density of the gamma correction pattern at pattern level 15 is b15.

Further, 15 kinds of gamma correction patterns (pattern levels 1 to 15) shown in FIG. 15 are sequentially formed on the belt-shaped photosensitive member 1, and the respective image densities are measured by the P sensor 22. A dot γ characteristic as shown in FIG. 18A is derived from the result, and since the start is not white, the vertical axis is normalized from “0” as shown in FIG. 18B. In this case, the density of the gamma correction pattern at pattern level 1 in FIG. 15 is c1, the density of the gamma correction pattern at pattern level 2 is c2, and similarly, the density of the gamma correction pattern at pattern level 15 is c15.

FIG. 19 shows the number of surrounding writing dots (number of surrounding dots) with respect to the modulation dot (dot of interest) and FIG.
FIG. 19 is a diagram showing the relationship between the maximum density a15, b15, and c15 of the γ correction pattern at the pattern level 15 in FIGS.

The CPU 80 of the engine 54 plots the maximum densities a15, b15, and c15 of the gamma correction patterns at the respective pattern levels 15 obtained by the above-described processing, and performs the least square method or spline conversion from the three densities. , The density with respect to the number of surrounding dots during that period is calculated. Thus, the degree of deviation between a straight line (reference line) connecting “0” and the maximum density “MAX” can be determined.

From the dot γ characteristics shown in FIGS. 16 to 18, the intermediate dot γ characteristics are also calculated by the least square method or spline transformation. For example, for the number s of surrounding dots up to “4”, (a1 × (4-s) + b1 ×
s) / 4 (ax × (4-s) + bx × s) / 4
Similarly, the number of surrounding dots s from “4” to “8” is calculated by S
= S−4, and an interpolation formula (x = 1 to 15) expressed by the formula of (bx × (4-S) + cx × S) / 4 such as (b1 × (4-S) + c1 × S) / 4 ).

FIG. 20 shows a dot γ according to a user's instruction.
Operation procedure by user when setting characteristics and CPU 80
FIG. 6 is an explanatory diagram for explaining a processing operation by the. For example, on the screen of a computer connected to the color image forming apparatus, the user moves the density of the modulation dot relative to the writing level (0 to 255) after the gamma correction using the mouse to move the points P1, P2, P3, etc. up and down. By doing so, it can be variably set.

The points P1, P2, and P3 are representative points, and there may be any number of points. However, since there is a spline correction between the points, there is no need to carelessly increase the points. The information of the dot γ characteristic is sent to the color image forming apparatus when the state is determined, and the color image forming apparatus creates γ correction data. For example, as shown in FIG. 21, position information of P0, P1x / P1, P2x / P2, and P3, that is, each point is a straight line point (for example, P
Information indicating what percentage of displacement from the position (1, P2) is sent to the color image forming apparatus.

In the color image forming apparatus, the CPU 80 of the engine 54 uses the intermediate γ characteristics obtained from the respective γ characteristics of FIGS. 16 to 18 and the information indicating the% displacement as shown in FIG. The density for the 19 reference lines is obtained, and the maximum writing level of the target dot is obtained using γ correction data corresponding to the surrounding dot information (information indicating the number of surrounding dots) as shown in FIG.

The creation and storage of the γ correction data are as described in the first embodiment. That is, an approximate expression for calculating the write level of the target dot after the γ correction is obtained by the least squares method from each dot γ characteristic described above. Then, each of the approximation formulas has "0" to
By sequentially applying “14”, 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 Γ-correction data indicating the relationship between “0” and “15” for bits is created and written to the internal memory of the γ-correction table 85.

As described above, in the color image forming apparatus of this embodiment, the printer controller 51 performs pseudo gradation processing such as multi-value dither processing and multi-value error diffusion processing on image data to reduce the data amount. The image data is temporarily stored in the frame memory and then read out, and the γ correction unit 52 performs γ correction on the image data for each dot, so that the capacity of the frame memory can be reduced and the cost can be reduced.

The dot environment determination unit 8 of the γ correction unit 52
The reference numeral 1,100 refers to the surrounding dots with respect to the target dot and determines the environment of the surrounding dots.
5 corresponds to each γ of the internal memory in accordance with one of the judgment results.
One of correction data (gamma correction data of different types is stored for each environment of surrounding dots with respect to the target dot), and the writing level of image data (dot of interest) is determined using the gamma correction data. And outputs a corresponding write signal. At this time, the smaller the number of surrounding write dots for the target dot, which is the result of the above determination, the higher the write level of the target dot,
The maximum writing level of the dot of interest is changed according to the above determination result.

Therefore, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. Further, since the γ correction is not performed before the pseudo gradation processing is performed on the image data, the number of gradations of the image data to be printed out does not decrease, and stable gradation can be reproduced. . Further, the dot stability of the highlight part is improved. Further, it is possible to arbitrarily set the dot γ characteristic by adjusting the writing level of the engine 54, and the gradation does not occur in the highlight portion and the shadow portion even when the tone (gradation) is changed. .

Further, the CPU 80 on the engine 54 side
The 15 types of γ correction patterns (dot patterns for γ correction of a predetermined type) shown in FIGS. 13 to 15 are sequentially formed on the belt-shaped photosensitive member 1 at a predetermined timing, and the respective patterns are formed. Is detected using the P sensor 22, and γ correction data is created based on the detection result (a dot γ characteristic is obtained based on the detection result, and γ correction data is created based on the dot γ characteristic). ) So
It is possible to cope with changes in environment and time, and to stabilize images.

In this case, a .gamma. Correction pattern having no writing dots around the modulation dots (FIG. 13) and a .gamma. Correction pattern having the writing dots (FIGS. 14 and 15) are respectively provided on the belt-shaped photosensitive member 1. , The density of each pattern is detected using the P sensor 22, and the dot γ characteristic of each γ correction pattern is obtained based on each detection result. In order to improve the accuracy of the γ correction, the dot γ characteristics of the γ correction pattern other than the pattern are obtained by interpolating from the above dot γ characteristics, and different types of γ correction data are created based on the dot γ characteristics. In addition, there is no need to form a corresponding gamma correction pattern on a recording medium, and the amount of discharged toner is reduced.

Further, when the dot environment determination section 81 determines the environment of surrounding dots with respect to the target dot,
Since the data of each dot is binarized under arbitrary conditions,
There is no need to have a memory for the weight of the image data (multi-valued data) input here.

The dot environment determining unit 81 determines the environment of the surrounding dots with respect to the target dot by the number of write dots around the dot, and the dot environment determining unit 100 determines the environment of the surrounding dots with respect to the target dot by averaging the surrounding dots. Each value is determined based on the value.
The determination result from the dot environment determination unit 81 or the determination from the dot environment determination unit 100 depends on the type of the pseudo gradation process of the printer controller 51 (actually, a selection signal according to the type of the pseudo gradation process from the printer controller 51). One of the results is selected, and the writing level of the dot of interest is set using the gamma correction data of the writing level according to the selected judgment result, so that the pseudo gradation such as multi-value dither processing or multi-value error diffusion processing is used. Γ correction of the processed image data (dot of interest) can be performed with a small range of environment judgment and optimal γ
The correction can be performed effectively using the correction data, and only a small amount of memory is required.

Further, the dot γ characteristic can be arbitrarily set according to a user's instruction, and the γ correction section 52 can variably set the writing level of the target dot in accordance with the dot γ characteristic. , The dot γ characteristic can be easily set.

Note that the γ correction table 85 selects the judgment result from the dot environment judgment unit 81 or the judgment result from the dot environment judgment unit 100 by a selection signal from the printer controller 51 according to the type of pseudo gradation processing. But,
It is also possible to determine the type of the pseudo gradation process of the printer controller 51 according to the result of these determinations, and to select one of the above respective determination results according to the result. Then, the optimum γ correction can be performed without receiving a selection signal according to the type of the pseudo gradation processing from the printer controller 51.

Next, a third 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 each of the above-described embodiments, 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. The γ correction unit 5
Reference numeral 2 denotes a circuit configuration for performing the optimum γ correction on the image data subjected to any of the above-described multi-value dither processing.

FIG. 22 shows an example of the configuration of a circuit for performing the optimum γ correction on the image data on which either the dot concentration type or the dot dispersion 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 4-bit weight sequentially transmitted 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 judgment section 131 includes a surrounding judgment 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 the line (main scanning) is read. )
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 processing 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, optimal gamma correction data is selected according to the result and the 3-bit code information from the determination unit 131, and the 4-bit weighted image data (from the point-of-interest point latch 122) is selected using the gamma correction data. The writing level is variably set by performing gamma correction on the target dot, and a corresponding 8-bit writing level signal is output to the writing unit 53.

The gamma correction of the image data that has been subjected to the pseudo gradation processing (dot concentration type or dot dispersion type multi-value dither processing) is the same as that of the first or second embodiment described above. The description is omitted because all the other types are the same except for some differences.

As described above, in the color image forming apparatus of this embodiment, the printer controller 51 performs dot concentration type or dot dispersion type multi-value dither processing on image data to reduce the data amount, and Once stored in the frame memory and read out, the γ correction unit 52 performs γ correction on the image data for each dot, so that the capacity of the frame memory can be reduced and the cost can be reduced.

The dot environment determination unit 1 of the γ correction unit 52
Reference numeral 20 refers to the surrounding dot for the target dot and refers to the surrounding dot environment (5 to
The dot, the left two dots of the target dot, and the right one dot are determined, and the γ correction table 140 determines the determination result (including the information for determining the type of the pseudo gradation process of the printer controller 51). Accordingly, one of the γ correction data in the internal memory is selected, the writing level of the image data (dot of interest) is set using the γ correction data, and the corresponding writing signal is output. In addition, the gamma correction of the image data subjected to the multi-value dither processing of the dot dispersion type can be effectively performed by using the optimum gamma correction data with a small range of environment judgment, and only requires a small-capacity memory.

Further, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. Further, since the gamma correction is not performed before performing the pseudo gradation processing on the image data, the number of gradations of the image data to be printed out does not decrease, and the stable gradation can be reproduced. . Further, the dot stability of the highlight part is improved. Further, the engine 54
It is possible to arbitrarily set the dot γ characteristic by adjusting the writing level of, so that even if the tone (gradation) is changed, the gradation jump does not occur in the highlight portion and the shadow portion.

Further, when the gamma correction table 140 selects any one of the gamma correction data, the dot environment determination unit 1
20, the type of the pseudo gradation process of the printer controller 51 is determined in accordance with the 1-bit code information of the determination result, and the 3-bit code information (of the determination result and the determination result of the dot environment determination unit 120) is determined. Since any one of the γ correction data is selected according to the information indicating the number of writing dots), there is no need to have the printer controller 51 send a selection signal according to the type of the pseudo gradation processing.

Furthermore, effects other than the above-described effects, that is, effects similar to those of the above-described first or second embodiment can be obtained. Note that the number (reference range) of the dots on the previous line and the dots on the left or right of the target dot can also be changed with respect to the target dot.

Next, a fourth 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 each of the above-described embodiments, 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 multi-value error diffusion processing on image data. The γ correction unit 52 has a circuit configuration for performing an optimum γ correction on the image data on which any of the above-described pseudo gradation processing has been performed.

FIG. 23 shows an example of the configuration of a circuit for performing the optimum γ correction on the image data subjected to the multi-value dither processing in the γ correction section 52. 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 processed image data, respectively, and some circuits are overlapped and illustrated.

The gamma correction section 52 is provided by the dot environment determination section 15.
0, 170, and a gamma correction table 180. The dot environment determination unit 150 includes a line buffer 151, a point-of-interest latch 152, and surrounding-area determination latches 153 to 15.
9 and a judgment unit 160.

In the γ correction unit 52, the 4-bit weighted image data sequentially transmitted from the printer controller 51 for each color enters the surrounding determination latch 158 (i + 1) in FIG. In synchronization with the surroundings, the latch 159 for determining the surroundings, the point-of-interest latch 15
2 and is input to the γ correction table 180 with a delay of three clocks in the line (main scanning) direction.

The image data from the printer controller 51 also enters the line buffer 151, and the image data delayed by one line enters the surrounding determination latch 153 (i). Shifting to latches 154, 155, 156, 157 is performed.

The judgment section 160 includes a surrounding judgment latch 153.
To 159, the environment (the number of dots to be written) is determined by referring to the image data (dots surrounding the target dot), and the result is converted into 3-bit code information (information for selecting the optimal γ correction data). ) To the gamma correction table 180. In this case, since each image data has a 4-bit numerical value in the range of “0” to “15”, the above determination result is converted into 3 bits (upper 3 bits) to “0”.
To a numerical value in the range from "7" to "7".

On the other hand, image data having a 4-bit weight sequentially transmitted from the printer controller 51 for each color enters the surrounding determination latch 176 (i + 1) shown in FIG. 24, and is focused in synchronization with the image synchronization clock. Point latch 1
72 and is input to the γ correction table 180 with a delay of two clocks in the line direction. Further, the image data from the printer controller 51 also enters the line buffer 171, and the image data delayed by one line enters the surrounding determination latch 173 (i), and sequentially rotates in synchronization with the image synchronization clock. 175.

The judgment section 177 includes a surrounding judgment latch 173.
The environment (the number of dots to be written) is determined by referring to each of the image data (dots surrounding the target dot) to 156, and the result is converted into 3-bit code information (information for selecting optimal γ correction data). ) To the gamma correction table 180. In this case, since each image data has a 4-bit numerical value in the range of “0” to “15”, the above determination result is converted into 3 bits (upper 3 bits) to “0”.
To a numerical value in the range from "7" to "7".

The gamma correction table 180 is based on a dot environment determining unit 150 (corresponding to image data on which dot concentration type multi-value dither processing has been performed) by a selection signal corresponding to the type of pseudo gradation processing from the printer controller 51. ) Or the dot environment determination unit 17
Any one of the code information from 0 (corresponding to the image data subjected to the multi-level error diffusion processing) is selected. For example, if the selection signal is “0 (indicating multi-value dither processing of dot concentration type)”, the code information from the dot environment determining unit 150 is “1” (indicating multi-value error diffusion processing). The code information from the environment determining unit 170 is selected.

Thereafter, γ-correction data is selected in accordance with the selected code information, and the 4-bit weighted image data (dot of interest) from the point-of-interest latch 152 or 172 is corrected using the γ-correction data. Then, the write level is variably set, and a corresponding 8-bit write level signal is output to the write unit 53. Note that the gamma correction of image data that has been subjected to pseudo gradation processing (dot concentration type multi-value dither processing and multi-value error diffusion processing) is described in the first to third embodiments and the types of pseudo gradation processing. Are the same except for some differences, and a description thereof will be omitted.

As described above, in the color image forming apparatus of this embodiment, the printer controller 51 performs the dot concentration type multi-value dither process or the multi-value error diffusion process on the image data to reduce the data amount. Since the data is temporarily stored in the frame memory and then read out, and the γ correction section 52 performs γ correction on the image data for each dot, the capacity of the frame memory can be reduced and the cost can be reduced.

The dot environment determination unit 1 of the γ correction unit 52
50 and 170 refer to the surrounding dots of the target dot to determine the surrounding dot environment, and the γ correction table 180 determines each γ correction data (target dot) in the internal memory according to one of the determination results. Γ correction data of different types are stored for each environment of the surrounding dots of the image data), and the writing level of the image data (dot of interest) is set by using the γ correction data. Γ correction of the image data subjected to the dot concentration type and the multi-value error diffusion processing can be effectively performed with a small range of environment judgment and using the optimal γ correction data, and a small capacity can be obtained. You just need to have memory.

Further, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. Further, since the gamma correction is not performed before performing the pseudo gradation processing on the image data, the number of gradations of the image data to be printed out does not decrease, and the stable gradation can be reproduced. . Further, the dot stability of the highlight part is improved. Further, the engine 54
It is possible to arbitrarily set the dot γ characteristic by adjusting the writing level of, so that even if the tone (gradation) is changed, the gradation jump does not occur in the highlight portion and the shadow portion.

Furthermore, effects other than the above-described effects, that is, effects similar to those of the above-described first to third embodiments can be obtained. In the fourth embodiment, the determination unit 177 of the dot environment determination unit 170 shown in FIG. 24 determines, with respect to the target dot (indicated by 〇), The environment of three dots and one dot to the left of the target dot was determined. Half of the six adjacent dots of the six dots adjacent to the target dot were respectively surrounded by solid lines in (b) to (h) of FIG. Of course, the environment of the dot may be determined.

That is, the environment of three dots in the previous line and one dot to the right of the target dot with respect to the target dot is determined, and two dots in the previous line, one dot to the right of the target dot, and The environment of one dot on the line may be determined, or the environment of one dot on the previous line, one dot on the right of the target dot, and two dots on the subsequent line may be determined.

Alternatively, the environment of three dots in the rear line and one dot to the right of the target dot with respect to the target dot is determined, and the environment of three dots in the rear line and one dot to the left of the target dot with respect to the target dot is determined. , And one dot on the previous line, one dot on the left of the dot of interest,
The environment of two dots of the following line may be determined, or the environment of two dots of the preceding line, one dot to the left of the noted dot, and one dot of the following line may be determined for the noted dot.

In the fourth embodiment, two dot environment determining units 150 and 170 are provided. However, the dot environment determining unit 170 is omitted, and the function of the dot environment determining unit 170 is replaced by the dot environment determining unit 150. It is also possible to keep waiting and reduce costs. In this case, the printer controller 5
A selection signal corresponding to the type of the pseudo gradation processing from No. 1 is input to the determination section 160 as a mask signal, and the determination section 160 performs the following processing.

That is, when the mask signal is "0" (indicating dot concentration type multi-value dither processing), the above-mentioned processing is performed by referring to the dots of the surrounding determination latches 153 to 159. If the mask signal is “1” (indicating multi-level error diffusion processing), the surrounding determination latches 154-1
Refer to dots 56 and 159 (the surrounding determination latch 15
3, 157, and 158 are masked), and the same processing as the above-described determination unit 177 is performed.

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. However, 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.

[0163]

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. Further, according to the image forming apparatus of claim 2 or later, the stability of image quality can be improved,
The dot γ correction of the image data can be made compatible with various kinds of pseudo gradation processing, and the cost can be reduced.

[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 illustrating a configuration example of a γ correction unit 52 in FIG. 1;

5 shows an example of the relationship between the environment of each data of the surrounding determination latches 70 to 77 in the dot environment determination unit 61 of FIG. 4 and each γ correction data selected by the γ correction table 65 according to each environment. FIG.

FIG. 6 is an explanatory diagram showing an example of a γ correction pattern.

FIG. 7 is an explanatory diagram showing dot arrangement examples of various dot patterns.

FIG. 8 is a diagram illustrating an example of dot γ characteristics (a relationship between a writing level and a density of a modulated dot) for each dot arrangement.

9 is a diagram showing a relationship between a write level before γ correction and a write level after γ correction of modulated dots respectively corresponding to the dot γ characteristic of each dot pattern shown in FIG. 8;

FIG. 10 is a diagram illustrating an example of a dot γ characteristic based on image data subjected to multi-value dither processing.

FIG. 11 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 according to the second embodiment of the present invention;

FIG. 12 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.

FIG. 13 is an explanatory diagram illustrating an example of a gamma correction pattern.

FIG. 14 is an explanatory diagram showing another example.

FIG. 15 is an explanatory view showing still another example.

FIG. 16 is a diagram illustrating an example of dot γ characteristics of the γ correction pattern in FIG. 13;

FIG. 17 is a diagram illustrating an example of dot γ characteristics of the γ correction pattern in FIG. 14;

FIG. 18 is a diagram illustrating an example of dot γ characteristics of the γ correction pattern in FIG. 15;

FIG. 19 shows the number of surrounding writing dots (the number of surrounding dots) with respect to the modulated dots and the maximum densities a15 and b1 of the γ correction patterns at the pattern level 15 in FIGS.
FIG. 5 is a diagram showing a relationship between C5 and c15.

20 is an explanatory diagram for describing an operation procedure by the user when setting the dot γ characteristic according to a user's instruction and a processing operation by the CPU 80 of FIG. 11;

21 is information (computer information) indicating what percentage of displacement from the position of points P1 and P2 shown in FIG. 20;
FIG. 4 is an explanatory diagram showing an example of a relationship between the information and the information (surrounding dot information) indicating the number of writing dots around modulation dots.

FIG. 22 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 third embodiment of the present invention. FIG.

FIG. 23 is a block diagram showing a configuration example of a circuit for performing optimal γ correction on image data on which dot concentration type multi-value dither processing has been performed in the γ correction unit according to the fourth embodiment of the present invention; is there.

FIG. 24 is a block diagram showing an example of a configuration of a circuit for performing an optimal γ correction on image data that has also been subjected to multi-level error diffusion processing.

FIG. 25 is a diagram illustrating an example of different reference ranges for the determination unit of FIG. 24 to determine the environment of a dot around a dot of interest.

FIG. 26 shows dot densities in a high density portion (solid portion) and a low density portion (single dot portion) when dot concentration type 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. 27 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. 28 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 unit 10: intermediate transfer belt 13: bias roller 14: transfer roller 51: printer controller 52: gamma correction unit 53: writing unit 61, 81, 100, 120, 150, 170: dot environment determination unit 62, 67, 68, 82, 89, 101, 121, 15
1,171: Line buffer 63,83: Latch for position alignment 64,69,84,90,102,122,152,1
72: Point-of-interest latch 65, 85, 140, 180: γ correction table 66, 86-88: OR gate 70-77, 91-98, 103-110, 123-1
30, 153 to 159, 173 to 176: Peripheral judgment latch 78, 99, 111, 131, 160, 177: Judgment unit 80: CPU

Claims (25)

[Claims] An image forming apparatus modulates 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. Pseudo gradation processing means for performing pseudo gradation processing, and dot environment determination means for referring to surrounding dots for a target dot of image data subjected to pseudo gradation processing by the means and determining the environment of the dot When,
Gamma correction means for performing gamma correction for variably setting a writing level such as a writing density or a writing size of the dot of interest in accordance with a determination result of the means. 2. The gamma correction data storage means, wherein the gamma correction means stores at least two types of gamma correction data,
Γ correction data selection means for selecting any of the γ correction data according to the determination result of the dot environment determination means, and the writing level of the target dot using the γ correction data selected by the means. 2. The image forming apparatus according to claim 1, further comprising: a write level signal output unit configured to output a corresponding write level signal. 3. The γ-correction data storage means is means for storing γ-correction data of different types depending on the surrounding dot environment with respect to the target dot.
The image forming apparatus as described in the above. 4. The image forming apparatus according to claim 2, wherein a predetermined type of dot pattern for gamma correction is sequentially formed on the recording medium at a predetermined timing for each predetermined write level. Correction pattern imaging means,
Density detecting means for detecting the density of each dot pattern created on the recording medium by the means using an optical sensor, and gamma correction data creating means for creating gamma correction data based on the detection result of the means; An image forming apparatus comprising: 5. A method according to claim 1, wherein said γ correction data generating means obtains a dot γ characteristic based on a detection result of said density detecting means and generates γ correction data based on the dot γ characteristic. The image forming apparatus according to claim 4. 6. The image forming apparatus according to claim 4, wherein
Based on the γ correction data in which the write level of the modulated dot is the highest and the γ correction data in the lowest among the γ correction data, new γ correction data within the range of each write level is created by calculation. An image forming apparatus comprising: 7. The γ correction pattern image forming means sets a γ correction dot pattern having no write dots and a γ correction dot pattern having write dots at least around the modulation dots on the recording medium. Γ correction data generating means obtains the dot γ characteristic of each γ correction dot pattern based on the detection result of the density detection means. Means for interpolating the dot γ characteristics of the dot patterns other than the γ correction dot patterns from the respective dot γ characteristics, and then generating different types of γ correction data based on the respective dot γ characteristics. The image forming apparatus according to claim 4, wherein 8. The γ correction data creation means, when the modulation of the light or the ion current is multi-level modulation, sets the writing level of the modulated dot in the dot γ characteristic at equal intervals from the visualization start point to the target maximum density. 8. The image forming apparatus according to claim 5, further comprising a allocating unit. 9. The method according to claim 1, wherein the gamma correction unit increases the writing level of the target dot as the number of surrounding write dots for the target dot, which is the result of the determination by the dot environment determining unit, decreases. Item 1 or 2
The image forming apparatus as described in the above. 10. The dot environment determination means determines whether the environment of surrounding dots with respect to a target dot is a state in which there is no writing dot, a state in which the writing dot is in the horizontal or vertical direction, or a state in which the writing dot is oblique. The image forming apparatus according to claim 1, wherein the image forming apparatus is a unit. 11. The image forming apparatus according to claim 1, wherein the γ correction unit includes a unit that changes a maximum writing level of the dot of interest according to a determination result of the dot environment determination unit. 12. The apparatus according to claim 1, wherein said dot environment determining means includes means for binarizing data of each dot under an arbitrary condition when determining an environment of surrounding dots with respect to a target dot. 3. The image forming apparatus according to 1 or 2. 13. The method according to claim 1, wherein the dot environment determining means includes: a dot within a predetermined range of the preceding line with respect to the target dot; a dot within a predetermined range to the left and right of the target dot; 3. The image forming apparatus according to claim 1, wherein the image forming apparatus determines a dot environment. 14. The dot environment judging means is means for judging an environment of a dot within a predetermined range of a previous line with respect to a target dot and a dot within a predetermined range to the left or right of the target dot. 3. The image forming apparatus according to claim 1, wherein: 15. The dot environment judging means is means for judging an environment of a dot within a predetermined range of a line following a target dot and a dot within a predetermined range of left or right of the target dot. 3. The image forming apparatus according to claim 1, wherein: 16. The image forming apparatus according to claim 13, further comprising a dot range switching unit that switches the predetermined range according to a type of pseudo gradation processing of the pseudo gradation processing unit. An image forming apparatus comprising: 17. The method according to claim 17, wherein, when the pseudo gradation processing of the pseudo gradation processing means is error diffusion processing, the dot range switching means sets the predetermined range to a range in which a predetermined number of dots adjacent to a target dot can be referred to. 17. The image forming apparatus according to claim 16, wherein the unit switches the predetermined range to a predetermined range wider than the range in the case of dot concentration type dither processing. 18. The apparatus according to claim 1, wherein said dot environment determining means has means for determining an environment of a surrounding dot with respect to a target dot based on the number of surrounding writing dots. The image forming apparatus as described in the above. 19. The apparatus according to claim 1, wherein said dot environment determining means includes means for determining an environment of a surrounding dot with respect to a target dot based on an average value of the surrounding dots. The image forming apparatus as described in the above. 20. The dot environment judging means has means for judging the environment of surrounding dots with respect to a target dot by the number of surrounding writing dots, and means for judging by the average value of the surrounding dots. 18. The apparatus according to claim 1, wherein the gamma correction unit includes a unit that selects one of the determination results of the dot environment determination unit according to a type of pseudo gradation processing of the pseudo gradation processing unit. The image forming apparatus according to claim 1. 21. Each of the gamma correction data selection means stored in the gamma correction data storage means according to a result of the determination by the dot environment determination means and a type of pseudo gradation processing by the pseudo gradation processing means. The image forming apparatus according to claim 2, wherein the image forming apparatus is a unit that selects one of the γ correction data. 22. A method according to claim 19, wherein said gamma correction means includes a pseudo gradation processing type discriminating means for discriminating a kind of pseudo gradation processing of said pseudo gradation processing means in accordance with a judgment result of said dot environment judgment means. The image forming apparatus according to any one of claims 1 to 21. 23. The gamma correction unit variably sets the writing level of the target dot with a variable step number larger than the multi-valued number of one dot of the image data subjected to pseudo gradation processing by the pseudo gradation processing unit. The image forming apparatus according to claim 1, further comprising a unit configured to perform the operation. 24. The image forming apparatus according to claim 1, further comprising: γ characteristic setting means for arbitrarily setting a dot γ characteristic, wherein the γ correction means focuses on the dot γ characteristic set by the γ characteristic setting means. An image forming apparatus wherein a dot writing level is variably set. 25. An image forming apparatus according to claim 1, wherein said image processing means stores image data subjected to pseudo gradation processing by said pseudo gradation processing means, and image data stored in said means. Image reading means for reading the image data, wherein the dot environment determining means refers to surrounding dots with respect to a target dot of the image data read by the image reading means, and determines the environment of the dot. An image forming apparatus comprising: