JP3737593B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to various image forming apparatuses such as a copying machine, a printer, and a facsimile machine that form a dot image on a recording medium by electrophotographic method by irradiating a recording medium by modulating light or ion flow according to image data.
[0002]
[Prior art]
Some image forming apparatuses such as laser printers using an electrophotographic system have a printer controller and a printer engine that perform the following processes.
[0003]
The printer controller develops vector-format image information sent from an external device such as a host computer into image data (bitmap data), or reads image data of a document by an image reading device (scanner) to generate a frame memory. In this case, the printer engine nonlinearity (dot writing density or writing size) is corrected by reading one of the image data at a predetermined timing and performing γ correction (tone correction) for each dot. Thereafter, pseudo gradation processing such as dither processing is performed and the result is sent to the printer engine.
[0004]
The printer engine corrects variations in density by performing γ correction again for each dot on the image data sent from the printer controller, and prints out the image data. That is, a laser beam is modulated (power modulation or pulse width modulation) according to the image data and scanned to form a dot image on a recording medium by electrophotography.
[0005]
[Problems to be solved by the invention]
However, in such a conventional image forming apparatus, since γ correction is performed on the input image data (read out from the frame memory) before performing the pseudo gradation processing, the image is output. There has been a problem that the number of gradations of image data is reduced.
[0006]
For example, when performing dot concentration type dither processing as pseudo gradation processing, as shown in FIG. 26, in the high density portion (solid portion), the dot density and the dot size increase, so that a part of each dot overlaps (oblique line) However, in the low density portion (single dot portion), the dot density and the dot size are conversely reduced, so that such overlapping does not occur.
[0007]
Accordingly, the dot γ characteristics (the relationship between the modulation dot writing level (gradation) and the density based on the image data) when the image data from the printer controller is directly printed out by the printer engine as shown by the solid line in FIG. Become. In this case, the number of gradations of the image data read from the frame memory is 256 gradations.
[0008]
Therefore, it is necessary to γ-correct the image data read from the frame memory so that the dot γ characteristic (nonlinearity) becomes the reference dot γ characteristic shown by the broken line in FIG. For example, as shown in FIGS. 28A and 28B, the number of gradations of the output image data is reduced to about ½ in the high density portion and the low density portion, respectively. It is reduced to 2/3 and becomes about 170 gradations.
[0009]
The present invention has been made in view of the above points, and is intended to prevent the number of gradations of image data printed out from being reduced even when γ correction is performed, and to reproduce stable gradation. Objective.
[0010]
[Means for Solving the Problems]
The present invention provides an image forming apparatus that forms a dot image on a recording medium by electrophotographic method by irradiating a recording medium by modulating light or ion flow according to image data. Each means is provided.
[0011]
  According to the first aspect of the present invention, pseudo gradation processing means for performing pseudo gradation processing on input image data, and a target dot of multi-value image data subjected to pseudo gradation processing by the means are described. A dot environment determining unit that refers to surrounding dots and determines the environment of the dot, and a γ correction that variably sets a writing level such as a writing density or a writing size of the target dot according to a determination result of the unit A correction means, and the γ correction means is a γ correction data storage means for storing at least two types of γ correction data., DeΓ correction data selection means for selecting one of the γ correction data according to the determination result of the network environment determination means, and the writing level of the target dot is set using the γ correction data selected by the means And a write level signal output means for outputting a corresponding write level signal.The γ correction data selecting means is means for selecting γ correction data in which the writing level of the target dot is set higher as the number of surrounding writing dots with respect to the target dot, which is the determination result of the dot environment determining means, is smaller. The correcting means is means for increasing the writing level of the target dot as the number of surrounding writing dots with respect to the target dot, which is the determination result of the dot environment determining means, is small.Is.
[0012]
  According to a second aspect of the present invention, there is provided a pseudo gradation processing means for performing pseudo gradation processing on input image data, and a target dot of multi-valued image data subjected to pseudo gradation processing by the means. A dot environment determining unit that refers to surrounding dots and determines the environment of the dot, and a γ correction that variably sets a writing level such as a writing density or a writing size of the target dot according to a determination result of the unit A correction unit, and a γ correction unit that stores at least three or more types of γ correction data, and any one of the γ correction data according to the determination result of the dot environment determination unit. Γ correction data selection means to be selected, and a write level for setting the write level of the target dot using the γ correction data selected by the means and outputting a corresponding write level signal. Whether or not the dot environment judgment means is in a state where there are no dots to be written, in a horizontal or vertical direction, or in an oblique state. And the γ correction data selection means when the dot environment determination means determines that the surrounding dot environment relative to the target dot of the multi-valued image data is in a state where there are no writing dots. If it is determined that the first γ correction data in which the writing level of the target dot is set high is the state where the writing dot is in the horizontal direction or the vertical direction, the writing level of the target dot is higher than that of the first γ correction correction data. If the second γ correction data set to be low is determined to be in a state where the writing dot is oblique, the writing level of the target dot It is obtained by the means for selecting a third γ correction data is set during the write level of the first and second γ correction data, respectively.
[0013]
  ClaimAccording to a third aspect of the present invention, in the image forming apparatus according to claim 1 or 2, a γ correction pattern for sequentially forming a predetermined type of γ correction dot pattern on a recording medium at a predetermined timing for each writing level. Image forming means, density detection means for detecting the density of each dot pattern created on the recording medium by the means using an optical sensor, and gamma correction for creating gamma correction data based on the detection result of the means And data creation means.
[0014]
  Claim4The invention of claim3In this image forming apparatus, the γ correction data creating means is a means for obtaining dot γ characteristics based on the detection result of the density detecting means and creating γ correction data based on the dot γ characteristics.
  Claim5The invention of claim3In the image forming apparatus, a new γ correction within the range of each writing level based on the γ correction data with the highest modulation dot writing level and the γ correction data with the lowest modulation dot among the γ correction data. Means for creating data by calculation are provided.
[0015]
  Claim6The invention of claim3In the image forming apparatus, the γ correction pattern image forming means includes at least a dot pattern for γ correction that has no writing dots (dots that are visibly written) around a modulation dot and a dot pattern for γ correction that has writing dots. On the recording medium at a predetermined timing for each predetermined writing level, and the γ correction data generating means uses the dot γ of the dot pattern for each γ correction based on the detection result of the density detecting means. After obtaining the characteristics and interpolating the dot γ characteristics of the dot patterns other than the respective γ correction dot patterns from the respective dot γ characteristics, different types of γ correction data are obtained based on the respective dot γ characteristics. It is a means to create.
[0016]
  According to a seventh aspect of the present invention, in the image forming apparatus according to the fourth or sixth aspect, when the light or ion current modulation is multi-level modulation, the γ correction data creation means sets the modulation dot writing level in the dot γ characteristics. It is equipped with a means for allocating at regular intervals from the visual start point to the target maximum density.is there.
[0017]
  Claim 8The invention of claim1 or 2In this image forming apparatus, the γ correction means includes means for changing the maximum writing level of the target dot in accordance with the determination result of the dot environment determination means.
[0023]
  Claim 9The invention of claim 1 to claim 18In any of the image forming apparatuses, the γ correction unit is provided with a pseudo gradation processing type determination unit that determines the type of pseudo gradation processing of the pseudo gradation processing unit according to the determination result of the dot environment determination unit It is.
[0024]
  Claim10The invention of claim 1 to claim 19In any one of the image forming apparatuses, the γ correction unit can change the writing level of the target dot to be larger than the multi-value number of one dot of the multi-value image data subjected to the pseudo-gradation processing by the pseudo-gradation processing unit. Means for variably setting the number of steps is provided.
[0025]
  Claim11The invention of claimAny one of 1-10The image forming apparatus includes an image storage unit that stores multi-valued image data that has been subjected to pseudo gradation processing by the pseudo gradation processing unit, and an image reading unit that reads out the image data stored in the unit. The environment determining means refers to surrounding dots with respect to the target dot of the image data read by the image reading means, and determines the environment of the dots.
[0026]
  In the image forming apparatus according to the first aspect, the pseudo gradation processing is performed on the input image data, and the dot environment determining means refers to the surrounding dots for the target dot of the multi-valued image data. The environment (situation) of the surrounding dots is determined, and the γ correction means variably sets (γ correction) the writing level of the target dot according to the determination result. At this time, the γ correction unit selects one of the γ correction data in the γ correction data storage unit according to the determination result of the dot environment determination unit.(The smaller the number of surrounding writing dots for the target dot, which is the determination result of the dot environment determining means, is, the more the gamma correction data set with the higher writing level of the target dot is selected)The writing level signal output means sets the writing level of the target dot using the γ correction data.(The smaller the number of surrounding writing dots for the attention dot, the higher the writing level of that attention dot)Outputs the corresponding write level signal. Therefore, the intended dot density or dot size can be easily obtained regardless of the surrounding dot environment. Also, since γ correction is not performed before the input image data is subjected to pseudo gradation processing, the number of gradations of the image data to be printed is not reduced, and stable gradation is reproduced. be able to. In addition, the dot stability in the highlight portion is improved.
[0028]
  In the image forming apparatus according to the invention of claim 2,Pseudo gradation processing is performed on the input image data, and the dot environment determination means refers to the surrounding dots for the target dot of the multi-valued image data and determines the environment of the surrounding dot (the target dot Whether the surrounding dot environment is a state in which there is no writing dot, a state in the horizontal or vertical direction, or a state in which the dot is oblique)), and the γ correction means determines the above attention according to the determination result. Set the dot writing level variably. At this time, the γ correction unit selects one of the γ correction data in the γ correction data storage unit according to the determination result of the dot environment determination unit (the multi-value image data is selected by the dot environment determination unit). When it is determined that the environment of surrounding dots with respect to the target dot is in a state where there is no writing dot, the first γ correction data in which the writing level of the target dot is set high is used as the writing dot in the horizontal direction or the vertical direction. When it is determined that the state is in the direction, the second γ correction data in which the writing level of the target dot is set lower than the first γ correction correction data is determined to be the state in which the writing dots are oblique. In this case, the third γ correction data in which the writing level of the target dot is set between the writing levels of the first and second γ correction data is selected), The writing level signal output means sets the writing level of the target dot using the γ correction data and outputs a corresponding writing level signal. Therefore, the same effect as the invention of claim 1 can be obtained.
[0029]
  Claim3, 4In the image forming apparatus according to the present invention,1Or2In this image forming apparatus, the γ correction pattern image forming means sequentially forms a predetermined type of γ correction dot pattern on the recording medium at a predetermined timing for each predetermined writing level, and the density detecting means records it. The density of each dot pattern created on the medium is detected using an optical sensor, and γ correction data creation means creates γ correction data based on the detection result (for example, dot γ characteristics based on the detection result) Therefore, γ correction data is created based on the dot γ characteristics), so that it is possible to cope with changes in the environment and time and to improve image stability.
[0030]
  Claim5In the image forming apparatus according to the present invention,3In the image forming apparatus, a new γ correction within the range of each writing level based on the γ correction data with the highest modulation dot writing level and the γ correction data with the lowest modulation dot among the γ correction data. Since the data is created by calculation, it is not necessary to create a corresponding dot pattern for γ correction on the recording medium in order to increase the accuracy of γ correction, and waste toner is reduced.
[0031]
  Claim6In the image forming apparatus according to the present invention,3In the image forming apparatus, the γ correction pattern image forming means includes at least predetermined γ correction dot patterns having no writing dots around the modulation dots and γ correction dot patterns having writing dots on the recording medium. The image is sequentially formed for each predetermined writing level at the timing, and the γ correction data creation means obtains the dot γ characteristics of the dot pattern for each γ correction based on the detection result of the density detection means, and for each γ correction After obtaining the dot γ characteristics of dot patterns other than the dot patterns from each dot γ characteristic, different types of γ correction data are created based on the dot γ characteristics. Therefore, it is not necessary to create a corresponding γ correction dot pattern on the recording medium, and the amount of waste toner is reduced.
[0032]
  In the image forming apparatus according to the seventh aspect of the present invention, in the image forming apparatus according to the fourth or sixth aspect, the γ correction data generating means is configured such that when the light or ion current modulation is multi-value modulation, the modulated dot in the dot γ characteristics Since the writing level is assigned at regular intervals from the visual start point to the target maximum density, image stability can be further improved.it can.
[0034]
  Claim8In the image forming apparatus according to the present invention,1 or 2In this image forming apparatus, the γ correction unit changes the maximum writing level of the target dot in accordance with the determination result of the dot environment determination unit, so that more stable gradation can be reproduced.
[0045]
  Claim9In the image forming apparatus according to the present invention,8In any of the image forming apparatuses, since the γ correction unit determines the type of the pseudo gradation process of the pseudo gradation processing unit according to the determination result of the dot environment determination unit, the type of the pseudo gradation process is indicated. Optimal γ correction can be performed without having to send information from the outside.
[0046]
  Claim10In the image forming apparatus according to the present invention,9In any of the image forming apparatuses, the writing level of the target dot is variably set to a variable step number larger than the multi-value number of one dot of the multi-value image data subjected to the pseudo-gradation processing by the pseudo-gradation processing means. Therefore, it is possible to set the γ characteristic with high accuracy by adjusting the writing level, and even if the tone is changed, the gradation skip does not occur in the highlight portion and the shadow portion.
[0048]
  Claim11In the image forming apparatus according to the present invention,Any one of 1-10In the image forming apparatus, pseudo-gradation processing such as multi-value dither processing is performed by the pseudo-gradation processing means, and the multi-value image data whose data amount is reduced is temporarily stored in the image storage means and then read out. Since surrounding dots are referred to the target dot and the environment of the dot is determined, the capacity of the image storage means (frame memory) can be reduced, and the cost can be reduced by saving memory.
[0049]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 2 is a diagram showing a configuration example of a mechanism unit of the color image forming apparatus according to the first embodiment of the present invention.
[0050]
In this color image forming apparatus, reference numeral 1 denotes a flexible belt-like photoconductor that is an image carrier (recording medium), and the belt-like photoconductor 1 is installed between rotating rollers 2 and 3. The rotating rollers 2 and 3 are driven to rotate clockwise.
Reference numeral 4 denotes a charging member as charging means, and 5 denotes a laser writing system unit as image exposure means. Reference numerals 6 to 9 denote developing devices as developing means, each of which accommodates a specific color toner.
[0051]
The laser writing system unit 5 is housed in a holding housing having a slit-shaped exposure opening on the upper surface, and is incorporated in the apparatus main body.
As the laser writing system unit 5, a unit in which the light emitting unit and the convergent light transmission body are integrated may be used.
The charging member 4 and the cleaning device 15 are provided to face the rotating roller 2 of the two rotating rollers 2 and 3 on which the belt-like photosensitive member 1 is installed.
[0052]
Each of the developing devices 6 to 9 stores, for example, toners of yellow, magenta, cyan, and black, respectively, and includes developing sleeves that are close to or in contact with the belt-like photoreceptor 1 at a predetermined position, and each belt-like photoreceptor. 1 has a function of visualizing the latent image on 1 by non-contact development or contact development.
Reference numeral 10 denotes an intermediate transfer belt which is a transfer image carrier (recording medium). The intermediate transfer belt 10 is provided between the rotation rollers 11 and 12 and is rotated counterclockwise by the drive of the bias roller 13. The
[0053]
The belt-like photoreceptor 1 and the intermediate transfer belt 10 are in contact with the rotating roller 3, and a first visible image on the belt-like photoreceptor 1 is transferred by a bias roller 13 provided in the intermediate transfer belt 10. The image is transferred onto the intermediate transfer belt 10.
Then, by repeating the same process, the second, third, and fourth images are superimposed on the intermediate transfer belt 10 and transferred so as not to cause positional deviation.
[0054]
A transfer roller 14 is provided so as to be in contact with and away from the intermediate transfer belt 10.
Reference numeral 15 denotes a cleaning device for the belt-shaped photoreceptor 1, and 16 denotes a cleaning device for the intermediate transfer belt 10. A blade 16 </ b> A of the cleaning device 16 is maintained at a position spaced apart from the surface of the intermediate transfer belt 10 during image formation. Only during cleaning after transfer, it is pressed against the surface of the intermediate transfer belt 10 as shown in the figure.
[0055]
A color image forming process by the color image forming apparatus is performed as follows, for example.
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 apparatus (not shown), data obtained by a color image data input unit (scanner) that scans an image of an original document is scanned by an image data processing unit to obtain image data (multi-valued bitmap). Data) is created, and this image data is subjected to pseudo gradation processing and then temporarily stored in the image memory.
[0056]
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 apparatus 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 is performed.
[0057]
First, a laser beam modulated in accordance with image data is generated from a semiconductor laser (not shown), the laser beam is deflected and scanned by a polygon mirror 5B rotated by a drive motor 5A, passes through an fθ lens 5C, and then mirror 5D. Thus, the light path is bent, the charge is removed by the charge removing lamp 21 in advance, and the belt member 1 is uniformly charged by the charging member 4 and is exposed on the peripheral surface to form an electrostatic latent image.
[0058]
Here, the image pattern to be exposed is a single-color image pattern when a desired full-color image is color-separated into yellow, magenta, cyan, and black.
Each electrostatic latent image formed on the belt-like photoreceptor 1 is developed in order by each of the yellow, magenta, cyan, and black developing devices 6 to 9 constituting the rotary developing unit to be visualized as a single color. After being converted into a single color image (dot image), the image is transferred onto the intermediate transfer belt 10 that rotates counterclockwise while being in contact with the belt-shaped photoconductor 1 and superimposed.
[0059]
The yellow, magenta, cyan, and black images superimposed on the intermediate transfer belt 10 are transferred by the transfer roller 14 to the transfer paper conveyed from the paper supply table 17 to the transfer unit via the paper supply roller 18 and the registration roller 19. The
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-like photoreceptor 1 are seamless.
[0060]
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. When the mark detection sensor 40 detects an arbitrary mark (for example, 41A), writing of the first color is started, and the mark 41A goes around once again. When the color is detected, writing of the second color is started.
[0061]
At this time, the marks 41B to 41F are not used as the write timing by managing the number of marks, and the corresponding signal from the mark detection sensor 40 is masked.
By the way, a P sensor 22 that is an optical sensor for detecting the toner amount (image density) on the belt-like photosensitive member 1 is provided slightly upstream from the portion of the belt-like photosensitive member 1 that is in contact with the intermediate transfer belt 10. Yes. The P sensor 22 may be provided at a position where the image density on the intermediate transfer belt 10 can be detected.
[0062]
FIG. 1 is a block diagram illustrating 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 image information from the outside. Note that image information in units of dots includes information of 8 bits for each color of four colors of yellow, magenta, cyan, and black.
[0063]
Next, the CPU in the printer controller 51 performs pseudo gradation processing (here, dot-concentrated multi-value dither processing is used) on image data created based on image information in units of dots. After each color is converted to 4-bit image data, the image data is temporarily stored in a 4-bit frame memory for each color, and then read for each color and input to the γ correction unit 52 on the engine 54 side. Note that the CPU in the printer controller 51 can also perform pseudo gradation processing on image data in units of one dot sent from the above-described image reading apparatus.
[0064]
The γ correction unit 52 determines the surrounding dot environment (situation) of each input image (dot of interest) for each dot (target dot), corrects γ, and sends the data to the writing unit 53 as a write level signal.
In the writing unit 53, the laser beam generated from the semiconductor laser in the laser writing system unit 5 is modulated (power modulation or pulse width modulation) based on the write level signal sent to the belt-like photosensitive member 1. An electrostatic latent image is formed.
[0065]
  The CPU in the printer controller 51 functions as a pseudo gradation processing unit that performs pseudo gradation processing on image data and an image reading unit that reads out image data stored in a frame memory in the printer controller 51. .
  The frame memory has been subjected to pseudo gradation processing.Multi-valuedThis corresponds to image storage means for storing image data.
[0066]
  Further, the γ correction unit 52 has been subjected to image data read from the frame memory, that is, pseudo gradation processing.Multi-valuedA dot environment determination unit that refers to surrounding dots with respect to a target dot of image data and determines the environment (situation) of the dot, and a write level such as a write density or a write size of the target dot according to the determination result It functions as a γ correction means for performing γ correction that is variably set.
[0067]
  FIG. 4 is a block diagram illustrating a configuration example of the γ correction unit 52.
  The γ correction unit 52 is mainly subjected to dot concentration type multi-value dither processing.Multi-valuedIt has a circuit configuration for performing optimum γ correction on image data, and includes a dot environment determination unit 61, a line buffer 62, a position matching latch 63, a point of interest latch 64, and a γ correction table 65.
  The dot environment determination unit 61 includes an OR gate 66, line buffers 67 and 68, a point of interest latch 69, surrounding determination latches 70 to 77, and a determination unit 78.
[0068]
Since the γ correction unit 52 sequentially sends image data having a 4-bit weight from the printer controller 51 for each color, the OR gate 66 has 1 bit (1 dot) indicating whether or not the image data is written. Convert to data. That is, it is determined whether each bit of the input image data is “0”. If all the bits are “0”, “0 (dots that are not writing dots)” is set, and any bit is “1”. “1 (write dot)” is output. Here, the presence / absence of writing is used as a criterion for determination, but other levels may be used as boundaries.
[0069]
The data output from the OR gate 66 enters the surrounding determination latch 74 (d1) and sequentially shifts to the surrounding determination latches 72 (v1) and 75 (d2) in synchronization with the image synchronization clock.
On the other hand, the data past 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.
[0070]
Further, the data passed through the line buffer 67 enters another line buffer 68, and the data delayed by one line is shifted to the surrounding determination latches 76 (d3), 73 (v2), 77 (d4). .
Here, the next determination unit 78 includes surrounding determination latches 74 (d1), 72 (v1), 75 (d2), 70 (h1), 71 (h2), 76 (d3), 73 (v2), 77. The environment is determined with reference to each data (d4) (dots surrounding the target dot).
[0071]
Then, the determination result (information for selecting optimum 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 the 4-bit weight sent from the printer controller 51 passes through the line buffer 62 having the 4-bit weight, and is latched by the point-of-interest latch 64 through the position matching latch 63. It is input to the correction table 65.
[0072]
The γ correction table 65 selects γ correction data in accordance with the code information from the determination unit 78, and uses the γ correction data to input image data having a 4-bit weight (attention dot) that is input from the attention point latch 64. ) Is corrected, the write level is variably set, and a corresponding 8-bit write level signal is output to the write unit 53.
[0073]
FIG. 5 shows surrounding determination latches 74 (d1), 72 (v1), 75 (d2), 70 (h1), 71 (h2), 76 (d3), 73 (v2), 77 in the dot environment determination unit 61. It is explanatory drawing which shows an example of the relationship between the environment of each data of (d4), and each (gamma) correction data which the (gamma) correction table 65 selects according to each environment.
[0074]
The gamma correction table 65 includes surrounding determination latches 74 (d1), 72 (v1), 75 (d2), 70 (h1), 71 (h2), 76 (d3), 73 (v2), and 77 (d4). If all the data is “0”, the gamma correction data γc (see FIG. 9) is used as the surrounding judgment latch 70 (h1), 71 (h2), 72 (v1), and 73 (v2) is “0”. If any of the determination latches 74 (d1) 75 (d2), 76 (d3), and 77 (d4) is “1”, the γ correction data γb is used as the surrounding determination latches 70 (h1) and 71 (h2). , 72 (v1) and 73 (v2) are respectively “1”, the γ correction data γa is selected.
[0075]
FIG. 6 is an explanatory diagram showing an example of a γ correction pattern.
This γ correction pattern is a dot pattern, which is a 2 × 2 matrix repetition, and there are 15 patterns. The writing level (laser beam modulation level) of the modulation dot (shown by ◯) in each γ correction pattern is divided into 15 levels (pattern levels 1 to 15).
[0076]
That is, the image data sent from the γ correction unit 52 to the writing unit 53 is 8-bit data, and the maximum writing level of the modulation dot is “255”. Therefore, the writing level corresponding to the pattern level 1 is “17”. The write level corresponding to level 2 is “34”, and is increased by 17 thereafter, and the write level corresponding to pattern level 15 is “255”.
[0077]
FIG. 7 is an explanatory diagram showing examples of dot arrangement of various dot patterns, and FIG. 8 is a diagram showing an example of dot γ characteristics (relationship between modulation dot writing level and density) for each dot arrangement.
In FIG. 7, ◯ indicates dots (modulation dots) written at 15 write levels, and ■ indicates dots written at a write level of “255 (100%)”.
[0078]
This embodiment is based on the premise that image data is subjected to dot concentration type multi-value dither processing. For example, when each dot pattern as shown in FIG. When the writing level is increased in units of one dot, and the dot reaches the writing level of 100%, the writing level of surrounding dots (adjacent to the dot) is increased. When there is a writing dot around the target dot, the writing dot has a writing level of 100%.
[0079]
In this embodiment, the surrounding dot environment with respect to the target dot is classified into three categories: a state where there is no writing dot, a state where the dot is in the horizontal or vertical direction, and a state where it is oblique, respectively. A single dot pattern (pattern S) as shown in FIG. 6B, horizontal and vertical arrangement patterns (patterns H, V1, V2) as shown in FIGS. An oblique arrangement pattern (patterns D1, D2) as shown in FIG.
[0080]
The dot γ characteristic shows a curve as shown in (1) of FIG. 8 when there are no writing dots (dots written at a writing level of 100%) around the target dot, and in the case of being oblique, If the curve is as shown in (2) in the horizontal or vertical direction, the curve as shown in (3) of FIG.
[0081]
Here, the CPU 80 (see FIG. 4) for performing sequence control of the entire engine 54 has the fifteen (pattern levels 1 to 15) γ correction patterns shown in FIG. 6 on the belt-like photoreceptor 1 shown in FIG. Then, each image density (optical reflectance) is measured (detected) by the P sensor 22, and the dot γ characteristic as shown in FIG. 8A is derived from the result. Further, the dot γ characteristic as shown in (3) of FIG. 8 is a function straight line obtained in advance by experiments. Further, since the dot γ characteristic shown in (2) of FIG. 8 is related as an intermediate between the above γ characteristics, it is obtained based on each dot γ characteristic.
[0082]
Subsequently, an approximate expression for calculating the writing level after γ correction of the target dot is obtained by the least square method based on the dot γ characteristics shown in (1) to (3) of FIG. Then, “0” to “15” are sequentially applied to the approximate expressions to obtain the writing level after γ correction of the target dot (within the range of “0” to “255” because of 8 bits). Γ correction data γc, γb, γa (see FIG. 9) showing the relationship between the target dot and the writing level of the target dot before γ correction (in the range of “0” to “15” because of 4 bits). Write to the internal memory of table 65.
[0083]
FIG. 9 is a diagram showing the relationship between the writing level before γ correction and the writing level after γ correction of the modulation dot (target dot) corresponding to the dot γ characteristics of each dot pattern shown in FIG.
When image data (target dot data) is input with the γ correction data γc shown in FIG. 5 selected, the γ correction table 65 performs the following γ correction processing on the data.
[0084]
For example, when the writing level of the target dot is “15”, the data is γ corrected using the 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.
[0085]
In the γ correction table 65, when the dot data of interest is input with the γ correction data γb shown in FIG. 5 selected, for example, when the writing level of the dot of interest is “15”, the γ correction data γb Is used to make γ correction, and the writing level after γ correction is set to γb15. 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.
[0086]
In the γ correction table 65, when the dot data of interest is input with the γ correction data γa shown in FIG. 5 selected, for example, when the writing level of the dot of interest is “15”, the γ correction data γa And γ correction using, and the writing level after γ correction is set to γa15. When the writing level of the target dot is “7”, the data is γ-corrected using the γ correction data γa, and the writing level after γ correction is set to γa7.
[0087]
FIG. 10 is a diagram showing an example of the dot γ characteristic by the image data subjected to the multi-value dither processing.
As can be seen from this figure, since there are many single dots in the highlight portion, the area 1 changes when the γ correction table 65 changes the maximum value of the γ correction data γc. In the middle portion, the ratio of single dots decreases, and the number of oblique dot combinations increases. Therefore, when the γ correction table 65 changes the maximum value of the γ correction data γb, the area 2 changes. Furthermore, since there are many combinations of left and right and upper and lower dots in the shadow portion, the area 3 changes when the γ correction table 65 changes the maximum value of the γ correction data γa.
[0088]
As described above, in the color image forming apparatus of this embodiment, after the printer controller 51 performs dot concentration type multi-value dither processing on the image data to reduce the amount of data and temporarily stores the image data in the frame memory. Since the reading and γ correction unit 52 γ corrects 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 the image data. In this case, it is necessary to change the γ correction unit 52 to a circuit configuration for performing γ correction for each dot on the image data subjected to the pseudo gradation processing.
[0089]
In addition, the dot environment determination unit 61 of the γ correction unit 52 refers to the surrounding dot with respect to the target dot of the image data, and the surrounding dot environment (the state where there is no writing dot, horizontal direction or vertical direction) The γ correction table 65 determines the γ correction data in the internal memory according to the determination result (the type varies depending on the surrounding dot environment for the target dot). γ correction data is stored), the writing level of the target dot is set using the γ correction data, and a corresponding writing signal is output. At this time, the write level of the target dot is increased as the number of surrounding write dots with respect to the target dot, which is the determination result, is decreased, or the maximum write level of the target dot is changed according to the determination result.
[0090]
Therefore, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. In addition, 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 is not reduced, and a stable gradation can be reproduced. . In addition, the dot stability in the highlight portion is improved. Furthermore, it becomes possible to arbitrarily set the γ characteristic by adjusting the writing level of the engine 54, and even if the tone (gradation) is changed, gradation skip does not occur in the highlight portion and the shadow portion.
[0091]
Further, the CPU 80 on the engine 54 side sequentially forms the 15 γ correction patterns (predetermined types of γ correction dot patterns) shown in FIG. 6 on the belt-like photoreceptor 1 at a predetermined timing. Then, the density of each pattern is detected using the P sensor 22, and γ correction data γc is created based on the detection result (the dot γ characteristic is obtained based on the detection result, and the dot γ characteristic is determined based on the dot γ characteristic). (gamma correction data γc is created), it is possible to cope with changes in the environment and time, and to improve image stability. If the P sensor 22 is installed facing the surface of the intermediate transfer belt 10, fifteen patterns for γ correction can be formed on the intermediate transfer belt 10.
[0092]
Furthermore, the CPU 80 on the engine 54 side has the lowest γ correction data γa with the highest modulation dot writing level among the γ correction data γa, γb, and γc stored in the internal memory of the γ correction unit 52. Based on the γ correction data γc, new γ correction data γb within the range of each writing level is created by calculation. Therefore, in order to increase the accuracy of γ correction, a corresponding γ correction pattern is used as a belt-shaped photoconductor. Therefore, it is not necessary to form an image on 1 and toner waste is reduced.
[0093]
In addition, when the dot environment determination unit 61 determines the environment of the surrounding dots with respect to the target dot, the data of each dot is binarized under an arbitrary condition. Therefore, the image data (multi-value data) input here It is not necessary to have memory for weights).
Further, since the dot environment determination unit 61 determines the environment of 3 dots in the previous line with respect to the noticed dot, 1 dot on each side of the noticed dot, and 3 dots in the back line with respect to the noticed dot, the dot concentration type Therefore, the γ correction of the image data (dot of interest) subjected to the multi-value dither processing can be effectively performed by the environmental judgment in a small range, and only a small memory is required.
[0094]
It should be noted that the number of dots (reference range) of the preceding line with respect to the attention dot, the left and right dots of the attention dot, and the dot of the rear line with respect to the attention dot may be changed.
[0095]
Next explained is the second embodiment of the invention. Since the hardware configuration other than the γ correction unit 52 is the same as that of the above-described embodiment, reference will be made to FIGS. 1 to 3 again.
The printer controller 51 in the color image forming apparatus of this embodiment has a function of selectively performing various pseudo gradation processing such as multi-value dither processing and multi-value error diffusion processing on image data by an external command or the like. have. Further, the γ correction unit 52 has a circuit configuration for performing an optimal γ correction on any pseudo-gradation processed image data.
[0096]
FIG. 11 shows a configuration example of a circuit for performing optimal γ correction on image data that has been mainly subjected to multi-value dither processing in the γ correction unit 52, and FIG. 12 shows mainly multi-value errors in the γ correction unit 52. FIG. 3 is a block diagram showing a configuration example of a circuit for performing optimum γ correction on image data that has been subjected to diffusion processing, and a part of the circuits is shown in an overlapping manner.
[0097]
The γ correction unit 52 includes dot environment determination units 81 and 100, a line buffer 82, a position matching latch 83, a point of interest latch 84, and a γ correction table 85.
The dot environment determination unit 81 includes OR gates 86 to 88, a line buffer 89, an attention point latch 90, surrounding determination latches 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, surrounding determination latches 103 to 110, and a determination unit 111.
[0098]
In this γ correction unit 52, image data having a 4-bit weight is sequentially sent from the printer controller 51 for each color, so that the OR gate 86 in FIG. 1 dot) data. That is, it is determined whether each bit of the input image data is “0”. If all the bits are “0”, “0 (dots that are not writing dots)” is set, and any bit is “1”. “1 (write dot)” is output. Here, the presence / absence of writing is used as a criterion for determination, but other levels may be used as boundaries.
[0099]
The data output from the OR gate 86 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.
Further, 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 / absence of writing in the same manner as described above.
[0100]
The data output from the OR gate 87 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 OR gate 88 converts the image data delayed by one line into 1-bit data indicating the presence / absence of writing in the same manner as described above. Convert.
The data output from the OR gate 88 enters the surrounding determination latch 96 (i-1) and sequentially shifts to the surrounding determination latches 97 and 98 in synchronization with the image synchronization clock.
[0101]
Here, the determination unit 99 determines the environment (the number of written dots) with reference to each data (peripheral dots with respect to the target dot) of the surrounding determination latches 91 to 98, and the result is expressed as 3-bit code information ( Information for selecting optimum γ correction data) is sent to the γ correction table 85. Here, since the number of written dots is a number from “0” to “8”, code information indicating “7” is output when “8”.
[0102]
On the other hand, the 4-bit weighted image data sent from the printer controller 51 also enters the surrounding determination latch 103 (i + 1) in FIG. 12, and sequentially determines the surrounding determination latches 104, in synchronization with the image synchronization clock. Shift to 105.
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 successively noticed in synchronization with the image synchronization clock. The point latch 102 and the surrounding determination latch 107 are shifted.
[0103]
Further, the image data delayed by one line by the line buffer 82 enters another line buffer 101, and the image data delayed by one line enters the surrounding determination latch 108 (i-1), and is synchronized with the image synchronization clock. Then, the shift to the surrounding determination latches 109 and 110 is sequentially performed.
[0104]
Here, the determination unit 111 determines the environment (the average value of the density or size of each dot) with reference to the image data (the surrounding dots with respect to the target dot) of the surrounding determination latches 103 to 110, and the result Is sent to the next γ correction table 85 as 3-bit code information (information for selecting optimal γ correction data). Here, since each image data represents a numerical value in the range of “0” to “15” with 4 bits, the determination result is converted into 3 bits (upper 3 bits) and the range of “0” to “7” is obtained. Sort into the numbers.
[0105]
On the other hand, the image data having a 4-bit weight sent from the printer controller 51 passes through the line buffer 82 as described above, and then is latched by the point of interest latch 84 through the position matching latch 83. It is input to the γ correction table 85.
[0106]
The γ correction table 85 is code information from the dot environment determination unit 81 (which can deal mainly with 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. (Determination result) or code information from the dot environment determination unit 100 (mainly capable of handling image data subjected to multilevel error diffusion processing) is selected. For example, if the selection signal is “0 (for example, indicates multilevel dither processing)”, the code information from the dot environment determination unit 81 is determined. If the selection signal is “1 (for example, indicates multilevel error diffusion processing)”, the dot environment determination is performed. The code information from the unit 100 is selected.
[0107]
Then, γ correction data is selected according to the selected code information, and the γ correction data is used to γ-correct the image data (attention dot) having a 4-bit weight input from the attention point latch 84. The write level is variably set, and a corresponding 8-bit write level signal is output to the writing unit 53.
[0108]
Hereinafter, γ correction of image data that has been subjected to multilevel dither processing will be described.
13 to 15 are explanatory diagrams showing different examples of the γ correction pattern.
Each γ correction pattern is a dot pattern, which is a 2 × 2 matrix repetition, and there are 15 patterns. The writing level (laser beam modulation level) of the modulation dot (shown by ◯) in each γ correction pattern is divided into 15 levels (pattern levels 1 to 15).
[0109]
That is, the image data sent from the γ correction unit 52 to the writing unit 53 is 8-bit data, and the maximum writing level of the modulation dot is “255”. Therefore, the writing level corresponding to the pattern level 1 is “17”. The write level corresponding to level 2 is “34”, and is increased by 17 thereafter, and the write level corresponding to pattern level 15 is “255”.
[0110]
Further, in the γ correction pattern shown in FIG. 13, there are no writing dots around the modulation dots. In the γ correction pattern shown in FIG. 14, four writing dots (dots shown by hatching are writing dots around the modulation dot, but the matrix portion where two writing dots are present is omitted. Exist). In the γ correction pattern shown in FIG. 15, all dots around the modulation dot are writing dots.
[0111]
FIGS. 16 to 18 are graphs showing examples of dot γ characteristics (relationship between modulation dot writing level and density) of the γ correction patterns of FIGS. 13, 14, and 15, respectively.
[0112]
The CPU 80 (see FIGS. 11 and 12) on the engine 54 side sequentially forms the fifteen (pattern levels 1 to 15) γ correction patterns shown in FIG. 13 on the belt-like photoreceptor 1 shown in FIG. Then, each image density is measured (detected) by the P sensor 22, and a dot γ characteristic as shown in FIG. 16 is derived from the result. In this case, the density (measurement result) of the γ correction pattern at pattern level 1 in FIG. 13 is a1, the density of the γ correction pattern at pattern level 2 is a2, and similarly, the density of the γ correction pattern at pattern level 15 is a15. It becomes.
[0113]
Further, the fifteen (pattern levels 1 to 15) γ correction patterns shown in FIG. 14 are sequentially formed on the belt-like photosensitive member 1, and the respective image densities are measured by the P sensor 22, and the results are shown in FIG. Since the dot γ characteristic as shown in FIG. 17A is derived and the start is not white, the vertical axis is normalized from “0” as shown in FIG. In this case, the density of the γ correction pattern of pattern level 1 in FIG. 14 is b1, the density of the γ correction pattern of pattern level 2 is b2, and similarly the density of the γ correction pattern of pattern level 15 is b15.
[0114]
Further, fifteen (pattern levels 1 to 15) γ correction patterns shown in FIG. 15 are sequentially formed on the belt-like photosensitive member 1, and the respective image densities are measured by the P sensor 22, and the results are shown in FIG. Since the dot γ characteristic as shown in FIG. 18A is derived and the start is not white, the vertical axis is normalized from “0” as shown in FIG. In this case, the density of the γ correction pattern of pattern level 1 in FIG. 15 is c1, the density of the γ correction pattern of pattern level 2 is c2, and similarly the density of the γ correction pattern of pattern level 15 is c15.
[0115]
FIG. 19 is a line showing the relationship between the number of surrounding writing dots (number of surrounding dots) with respect to the modulation dot (target dot) and the maximum density a15, b15, c15 of the pattern for γ correction at the pattern level 15 in FIGS. FIG.
[0116]
The CPU 80 on the engine 54 side plots the maximum densities a15, b15, and c15 of the pattern for γ correction at each pattern level 15 obtained by the above-described processing, and from these three densities, the least square method or the spline conversion is performed between them. The density with respect to the number of surrounding dots is calculated. As a result, the degree of deviation between “0” and the straight line (reference line) connecting the maximum density “MAX” is known.
[0117]
Also, the dot γ characteristics intermediate between them are calculated from the dot γ characteristics of FIGS. 16 to 18 by the least square method or spline conversion. For example, the number of surrounding dots s up to “4” can be expressed by the equation (ax × (4-s) + bx × s) / 4, such as (a1 × (4-s) + b1 × s) / 4. Similarly, according to the interpolation formula (x = 1 to 15), the number of surrounding dots s from “4” to “8” is set to S = s−4, and (b1 × (4-S) + c1 × S) / 4. As shown in (bx × (4-S) + cx × S) / 4.
[0118]
FIG. 20 is an explanatory diagram for explaining an operation procedure by the user and a processing operation by the CPU 80 when setting the dot γ characteristic according to the user's instruction.
For example, on the screen of a computer connected to this color image forming apparatus, the user moves the points P1, P2, P3, etc. up and down using the mouse to adjust the density of the modulation dot to the writing level (0 to 255) after γ correction. Can be variably set.
[0119]
The points P1, P2, and P3 are representative points, and there may be any number of points. However, since the points are subjected to spline correction, it is not necessary to increase them excessively.
The dot γ characteristic information is sent to the color image forming apparatus when the state is fixed, and γ correction data is created on the color image forming apparatus side. For example, the position information of P0, P1x / P1, P2x / P2, and P3 as shown in FIG. 21, that is, information indicating the percentage of displacement of each point from the position of a straight point (for example, P1 and P2) is colored. Send to image forming device.
[0120]
In the color image forming apparatus, the CPU 80 on the engine 54 side uses the intermediate γ characteristics obtained from the respective γ characteristics shown in FIGS. 16 to 18 and information indicating the percentage displacement as shown in FIG. The density for the line 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.
[0121]
The creation and storage of γ correction data is as described in the first embodiment. That is, an approximate expression for calculating the writing level after the γ correction of the target dot is obtained by the least square method from each dot γ characteristic described above. Then, “0” to “14” are sequentially applied to each of the approximate expressions to obtain the writing level after γ correction of the target dot (within the range of “0” to “255” because of 8 bits). And γ correction data indicating the relationship between the target dot and the writing level of the target dot before γ correction (in the range of “0” to “15” because of 4 bits), are written in the internal memory of the γ correction table 85.
[0122]
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 the image data to reduce the data amount, and the image data Is stored in the frame memory and then read out, and the γ correction unit 52 γ corrects the image data for each dot, so that the capacity of the frame memory can be reduced and the cost can be reduced.
[0123]
Further, the dot environment determination units 81 and 100 of the γ correction unit 52 refer to the surrounding dots with respect to the target dot to determine the environment of the surrounding dots, and the γ correction table 85 responds to any of the determination results. Each of the γ correction data in the internal memory (gamma correction data of a different type for each surrounding environment of the dot of interest is stored), and image data ( The write level of the target dot) is set and the corresponding write signal is output. At this time, the write level of the target dot is increased as the number of surrounding write dots with respect to the target dot, which is the determination result, is decreased, or the maximum write level of the target dot is changed according to the determination result.
[0124]
Therefore, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. In addition, 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 is not reduced, and a stable gradation can be reproduced. . In addition, the dot stability in the highlight portion is improved. Furthermore, it becomes possible to arbitrarily set the dot γ characteristics by adjusting the writing level of the engine 54, and even if the tone (gradation) is changed, gradation skip does not occur in the highlight portion and the shadow portion. .
[0125]
Further, the CPU 80 on the engine 54 side applies 15 kinds of γ correction patterns (predetermined types of γ correction dot patterns) shown in FIGS. 13 to 15 to the belt-like photosensitive member 1 at a predetermined timing. Are sequentially formed, and the density of each pattern is detected using the P sensor 22, and γ correction data is created based on the detection result (the dot γ characteristic is obtained based on the detection result, and the dot γ characteristic is obtained. (Gamma correction data is created based on the above), it is possible to cope with changes in the environment and time, and to achieve image stability.
[0126]
In this case, a γ correction pattern (FIG. 13) having no writing dots around the modulation dots and a γ correction pattern (FIGS. 14 and 15) having writing dots are respectively formed on the belt-like photoreceptor 1 at predetermined timings. Images are sequentially formed, 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. Interpolate the dot γ characteristics of the γ correction pattern from each dot γ characteristic and create different types of γ correction data based on each dot γ characteristic. Therefore, it is not necessary to form the γ correction pattern on the recording medium, and the waste toner is reduced.
[0127]
Furthermore, when the dot environment determination unit 81 determines the environment of surrounding dots with respect to the target dot, the data of each dot is binarized under an arbitrary condition. It is not necessary to have memory for the weight of (data).
[0128]
In addition, the dot environment determination unit 81 determines the surrounding dot environment for the target dot by the number of surrounding writing dots, and the dot environment determination unit 100 determines the surrounding dot environment for the target dot by the average value of the surrounding dots. However, the γ correction table 85 is determined by the dot environment determining unit 81 based on the type of pseudo gradation processing of the printer controller 51 (actually, a selection signal corresponding to the type of pseudo gradation processing from the printer controller 51). Since either the result or the determination result from the dot environment determination unit 100 is selected and the writing level of the target dot is set using the γ correction data of the writing level corresponding to the selected determination result, the multi-value dither processing or Γ correction of image data (attention dot) that has been subjected to pseudo gradation processing such as multi-level error diffusion processing Effectively performed using and optimum γ correction data in decision need only have a memory of small capacity.
[0129]
Further, the dot γ characteristic can be arbitrarily set according to a user instruction, and the γ correction unit 52 can variably set the writing level of the target dot in accordance with the dot γ characteristic. Characteristics can be set easily.
[0130]
Note that the γ correction table 85 selects the determination result from the dot environment determination unit 81 or the determination result from the dot environment determination unit 100 based on a selection signal corresponding to the type of pseudo gradation processing from the printer controller 51. It is also possible to determine the type of pseudo gradation processing of the printer controller 51 according to the determination result, and to select one of the determination results according to the result. By doing so, optimum γ correction can be performed without having the printer controller 51 send a selection signal corresponding to the type of pseudo gradation processing.
[0131]
  Next, the present inventionFirst reference exampleWill 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, reference is again made to FIGS.
  thisReference exampleThe printer controller 51 in the color image forming apparatus has a function of selectively performing dot concentration type multi-value dither processing or dot dispersion type multi-value dither processing on image data. Further, the γ correction unit 52 has a circuit configuration for performing an optimal γ correction on the image data subjected to any of the multi-value dither processing.
[0132]
FIG. 22 is a block diagram showing a configuration example of a circuit for performing optimum γ correction on image data subjected to either the dot concentration type or the dot dispersion type multi-value dither processing in the γ correction unit 52. is there.
The γ correction unit 52 includes a dot environment determination unit 120 and a γ correction table 140.
The dot environment determination unit 120 includes a line buffer 121, an attention point latch 122, surrounding determination latches 123 to 130, and a determination unit 131.
[0133]
In this γ correction unit 52, image data having a 4-bit weight sequentially sent from the printer controller 51 for each color enters the surrounding determination latch 128 (i + 1), and sequentially surrounds in synchronization with the image synchronization clock. The determination is shifted to the determination latch 129, the point of interest latch 122, and the surrounding determination latch 130.
Further, 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 sequentially determines the surrounding determination latches 124, in synchronization with the image synchronization clock. Shift to 125, 126, 127.
[0134]
The determination unit 131 refers to each image data (peripheral dots with respect to the target dot) of the surrounding determination latches 123 to 130 to determine the environment (logical product of each image data and the number of writing dots), and the determination result The information corresponding to the logical product of each image data is sent to the γ correction table 140 as 1-bit code information, and the information corresponding to the number of written dots is sent as 3-bit code information.
[0135]
If the logical product of the image data in the surrounding determination latches 123 to 130 is “0”, the 1-bit code information is set to “0”. When 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”. Furthermore, when sending the above 3-bit code information, each image data is 4 bits and represents a numerical value in the range of “0” to “15”. Therefore, the judgment result is converted into 3 bits (upper 3 bits). The values are assigned to values ranging from “0” to “7”.
[0136]
On the other hand, the 4-bit weighted image data 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 in the line (main scanning) direction. The data is input to the γ correction table 140 with a delay of 3 clocks.
[0137]
The γ correction table 140 determines the type of pseudo gradation processing of the printer controller 51 based on 1-bit code information from the determination unit 131. That is, if the 1-bit code information is “0”, it is determined as dot-intensive multi-value dither processing, and if it is “1”, it is determined as dot-dispersed multi-value dither processing. Thereafter, optimal γ correction data is selected in accordance with the result and 3-bit code information from the determination unit 131, and image data having a 4-bit weight from the point of interest latch 122 using the γ correction data ( The target dot) is γ-corrected and its writing level is variably set, and a corresponding 8-bit writing level signal is output to the writing unit 53.
[0138]
It should be noted that the γ correction of image data that has been subjected to pseudo gradation processing (dot concentration type or dot dispersion type multi-value dither processing) has the same kind of pseudo gradation processing as in the first or second embodiment. Since all other parts are the same, the description is omitted.
[0139]
  Like thisReference exampleIn the color image forming apparatus, the printer controller 51 performs dot concentration type or dot dispersion type multi-value dither processing on the image data to reduce the amount of data, and the image data is temporarily stored in the frame memory and then read out. Since the correction unit 52 γ-corrects the image data for each dot, the capacity of the frame memory can be reduced and low cost can be realized.
[0140]
Also, the dot environment determination unit 120 of the γ correction unit 52 refers to the surrounding dots with respect to the target dot, and the surrounding dot environment (5 dots in the previous line with respect to the target dot, two dots to the left of the target dot , Right one dot environment), and the γ correction table 140 includes each γ correction data in the internal memory according to the determination result (including information for determining the type of pseudo gradation processing of the printer controller 51). Is selected, and the γ correction data is used to set the writing level of the image data (dot of interest) and output the corresponding writing signal, so that the dot concentration type and dot dispersion type multi-value dither processing Γ correction of the image data subjected to the above can be effectively performed using a small range of environment judgment and optimal γ correction data, and only a small capacity memory is required.
[0141]
Further, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. In addition, 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 is not reduced, and a stable gradation can be reproduced. . In addition, the dot stability in the highlight portion is improved. Furthermore, it becomes possible to arbitrarily set the dot γ characteristics by adjusting the writing level of the engine 54, and even if the tone (gradation) is changed, gradation skip does not occur in the highlight portion and the shadow portion. .
[0142]
Further, when the γ correction table 140 selects any of the γ correction data, the type of pseudo gradation processing of the printer controller 51 is determined according to the 1-bit code information in the determination result of the dot environment determination unit 120. Since each of the γ correction data is selected according to the determination result and the 3-bit code information (information indicating the number of written dots) of the determination result and the determination result of the dot environment determination unit 120, the printer controller 51 It is not necessary to send a selection signal according to the type of pseudo gradation processing.
[0143]
Furthermore, effects other than the effects described above, that is, effects similar to those of the first embodiment or the second embodiment described above can be obtained.
Note that the number (reference range) of the dot on the previous line and the left or right dot of the attention dot can be changed with respect to the attention dot.
[0144]
  Next, the present inventionSecond reference exampleWill 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, reference is again made to FIGS.
  thisReference exampleThe printer controller 51 in the color image forming apparatus 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 optimal γ correction on the image data subjected to any of the pseudo gradation processes.
[0145]
FIG. 23 shows a configuration example of a circuit for performing optimum γ correction on the image data subjected to the multi-value dither processing in the γ correction unit 52, and FIG. 24 shows the multi-value error diffusion processing in the γ correction unit 52. FIG. 4 is a block diagram showing a configuration example of a circuit for performing an optimal γ correction on the image data that has been processed, and some of the circuits are shown in duplicate.
[0146]
The γ correction unit 52 includes dot environment determination units 150 and 170 and a γ correction table 180.
The dot environment determination unit 150 includes a line buffer 151, an attention point latch 152, surrounding determination latches 153 to 159, and a determination unit 160.
[0147]
In this γ correction unit 52, image data having a 4-bit weight sequentially sent from the printer controller 51 for each color enters the surrounding determination latch 158 (i + 1) in FIG. 23 and is synchronized with the image synchronization clock. Are sequentially shifted to the surrounding determination latch 159 and the point-of-interest latch 152 and input to the γ correction table 180 with a delay of 3 clocks in the line (main scanning) direction.
[0148]
Further, 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), and sequentially determines the surrounding determination latches 154 in synchronization with the image synchronization clock. Shift to 155, 156, 157.
[0149]
The determination unit 160 refers to each image data (peripheral dots with respect to the target dot) of the surrounding determination latches 153 to 159 to determine the environment (the number of written dots) and uses the result as 3-bit code information (optimum). Information for selecting correct γ correction data) to the γ correction table 180. In this case, since each image data represents a numerical value in the range of “0” to “15” with 4 bits, the above determination result is converted into 3 bits (upper 3 bits) and the range of “0” to “7”. Sort into the numbers.
[0150]
On the other hand, the 4-bit weighted image data sequentially sent from the printer controller 51 for each color enters the surrounding determination latch 176 (i + 1) in FIG. 24, and the point of interest latch 172 is synchronized with the image synchronization clock. And is input to the γ correction table 180 with a delay of two clocks in the line direction.
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 determines the surrounding determination latches 174 in synchronization with the image synchronization clock. Shifted to 175.
[0151]
The determination unit 177 refers to each image data (peripheral dots with respect to the target dot) of the surrounding determination latches 173 to 156 to determine the environment (the number of written dots), and determines the result as 3-bit code information (optimum). Information for selecting correct γ correction data) to the γ correction table 180. In this case, since each image data represents a numerical value in the range of “0” to “15” with 4 bits, the above determination result is converted into 3 bits (upper 3 bits) and the range of “0” to “7”. Sort into the numbers.
[0152]
The gamma correction table 180 is supplied from the dot environment determination unit 150 (which can handle image data subjected to dot concentration type multi-value dither processing) by a selection signal corresponding to the type of pseudo gradation processing from the printer controller 51. Either the code information (judgment result) or the code information from the dot environment judgment unit 170 (which can deal with the image data subjected to the multi-value error diffusion processing) is selected. For example, if the selection signal is “0 (indicates dot concentration type multi-value dither processing)”, the code information from the dot environment determination unit 150 is “1” (indicates multi-value error diffusion processing). The code information from the environment determination unit 170 is selected.
[0153]
  After that, γ correction data is selected according to the selected code information, and the γ correction data is used to γ-correct image data (attention dot) having a 4-bit weight from the attention point latch 152 or 172 and The write level is variably set, and a corresponding 8-bit write level signal is output to the writing unit 53.
  Note that the γ correction of image data that has been subjected to pseudo gradation processing (dot-concentrated multi-value dither processing and multi-value error diffusion processing) is the above-described first method., SecondSince all of the embodiments are the same except that the type of pseudo gradation processing is partially different from that of the embodiment, description thereof is omitted.
[0154]
  Like thisReference exampleIn the color image forming apparatus, the printer controller 51 performs dot concentration type multi-value dither processing or multi-value error diffusion processing on the image data to reduce the data amount, and the image data is temporarily stored in the frame memory and then read out. Since 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.
[0155]
Further, the dot environment determination units 150 and 170 of the γ correction unit 52 refer to the surrounding dots with respect to the target dot to determine the environment of the surrounding dots, and the γ correction table 180 responds to any of the determination results. Each of the γ correction data in the internal memory (gamma correction data of a different type for each surrounding environment of the dot of interest is stored), and image data ( The target dot) writing level is set and the corresponding writing signal is output, so that the γ correction of the image data subjected to the dot concentration type and the multi-value error diffusion processing can be performed in a small range of environment and the optimum γ correction data Can be done effectively with a small amount of memory.
[0156]
Further, the intended dot density or dot size can be obtained regardless of the surrounding dot environment for the target dot. In addition, 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 is not reduced, and a stable gradation can be reproduced. . In addition, the dot stability in the highlight portion is improved. Furthermore, it becomes possible to arbitrarily set the dot γ characteristics by adjusting the writing level of the engine 54, and even if the tone (gradation) is changed, gradation skip does not occur in the highlight portion and the shadow portion. .
[0157]
  Furthermore, effects other than the above-described effects, that is, the above-described first, SecondEffects similar to those of the embodiment can also be obtained.
  In addition, thisReference exampleThen, the determination unit 177 of the dot environment determination unit 170 in FIG. 24 has three dots in the previous line with respect to the target dot (indicated by a circle) as shown by a solid line in FIG. However, the environment of half the dots adjacent to each other among the 6 dots adjacent to the target dot is determined as shown by the solid lines in FIGS. Of course.
[0158]
That is, the environment of 3 dots in the previous line with respect to the noticed dot and 1 dot on the right of the noticed dot is judged, or 2 dots in the previous line with respect to the noticed dot, 1 dot on the right of the noticed dot, 1 on the back line. The environment of the dots 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 rear line may be determined with respect to the target dot.
[0159]
Alternatively, the environment of 3 dots on the back line and the 1 dot to the right of the attention dot is determined with respect to the attention dot, or the environment of 3 dots on the back line and the 1 dot on the left of the attention dot is determined with respect to the attention dot. Or the environment of 1 dot on the previous line with respect to the attention dot, 1 dot on the left of the attention dot, and 2 dots on the rear line, 2 dots on the previous line with respect to the attention dot, 1 on the left of the attention dot You may judge the environment of 1 dot of a dot and a back line.
[0160]
  Also thisReference exampleIn this case, the two dot environment determination units 150 and 170 are provided. However, the dot environment determination unit 170 can be omitted, and the dot environment determination unit 150 can wait for the function of the dot environment determination unit 170 to reduce the cost. .
  In this case, a selection signal corresponding to the type of pseudo gradation processing from the printer controller 51 is input to the determination unit 160 as a mask signal, and the determination unit 160 performs the following processing.
[0161]
That is, when the mask signal is “0 (indicating dot-concentrated multi-value dither processing)”, the above-described processing is performed by referring to the dots of the surrounding determination latches 153 to 159. When the mask signal is “1 (indicating multi-value error diffusion processing)”, the dots of the surrounding determination latches 154 to 156 and 159 are referred to (the dots of the surrounding determination latches 153, 157 and 158 are masked). The same processing as that of the determination unit 177 described above is performed.
[0162]
As described above, the embodiment in which the present invention is applied to an electrophotographic image forming apparatus using a semiconductor laser that irradiates a laser beam has been described. However, the present invention is not limited thereto, and an LED that irradiates light other than a laser beam, The present invention can also be applied to an electrophotographic image forming apparatus using a recording head that irradiates an EL or ion stream.
[0163]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, since the number of gradations of image data to be printed out is not reduced, stable gradation can be reproduced. Further, according to the image forming apparatus of the second and subsequent aspects, the stability of the image quality can be improved, the dot γ correction of the image data can be applied to various pseudo gradation processes, and the cost can be reduced. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a control system of the color image forming apparatus illustrated in FIG.
FIG. 2 is a diagram illustrating a configuration example of a mechanism unit of the color image forming apparatus according to the first embodiment of the invention.
3 is an enlarged view showing a part of the color image forming apparatus shown in FIG. 2;
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. It is explanatory drawing shown.
FIG. 6 is an explanatory diagram showing an example of a γ correction pattern.
FIG. 7 is an explanatory diagram showing a dot arrangement example of various dot patterns.
FIG. 8 is a diagram showing an example of dot γ characteristics (relationship between modulation dot writing level and density) for each dot arrangement;
9 is a diagram showing a relationship between a writing level before γ correction and a writing level after γ correction of a modulation dot corresponding to the dot γ characteristic of each dot pattern shown in FIG. 8;
FIG. 10 is a diagram illustrating an example of dot γ characteristics 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 optimum γ correction on image data mainly subjected to multi-value dither processing in a γ correction unit according to the second embodiment of the present invention;
FIG. 12 is a block diagram showing an example of the configuration of a circuit for performing optimum γ correction on image data that has been mainly subjected to multilevel error diffusion processing.
FIG. 13 is an explanatory diagram showing an example of a γ correction pattern.
FIG. 14 is an explanatory view showing another example.
FIG. 15 is an explanatory view showing still another example.
16 is a diagram showing an example of dot γ characteristics of the γ correction pattern of FIG. 13;
17 is a diagram showing an example of dot γ characteristics of the γ correction pattern of FIG. 14;
18 is a diagram showing an example of dot γ characteristics of the γ correction pattern of FIG.
FIG. 19 is a diagram showing the relationship between the number of surrounding writing dots (number of surrounding dots) with respect to the modulation dot and the maximum densities a15, b15, c15 of the γ correction pattern at the pattern level 15 in FIGS.
20 is an explanatory diagram for explaining an operation procedure by the user when setting the dot γ characteristics according to a user instruction and a processing operation by the CPU 80 of FIG. 11;
FIG. 21 shows the relationship between the information (computer information) indicating the percentage displacement from the positions of the points P1 and P2 shown in FIG. 20 and the information (peripheral dot information) indicating the number of writing dots around the modulation dot. It is explanatory drawing.
FIG. 22 is a configuration example of a circuit for performing optimum γ correction on image data subjected to dot concentration type and dot dispersion type multi-value dither processing in the γ correction unit of the third embodiment of the present invention; FIG.
FIG. 23 is a block diagram illustrating a configuration example of a circuit for performing optimum γ correction on image data on which dot concentration type multi-value dither processing has been performed in a γ correction unit according to a fourth embodiment of the present invention; is there.
FIGS. 24A and 24B are block diagrams respectively showing configuration examples of circuits for performing optimal γ correction on image data that has also been subjected to multilevel error diffusion processing. FIGS.
FIG. 25 is a diagram illustrating different examples of reference ranges for the determination unit of FIG. 24 to determine the environment of dots around a target dot.
FIG. 26 shows dot densities in a high density part (solid part) and a low density part (single dot part) 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 which shows the example of dot size.
FIG. 27 is a diagram showing an example of dot γ characteristics when image data from the printer controller of the color image forming apparatus is printed out by the printer engine.
FIG. 28 is an explanatory diagram for explaining the problem of the color image forming apparatus.
[Explanation of symbols]
1: Belt-shaped photoconductor 5: Laser writing system unit
6-9: Developing device 10: Intermediate transfer belt
13: Bias roller 14: Transfer roller
51: Printer controller 52: γ correction unit
53: Writing section
61, 81, 100, 120, 150, 170: Dot environment determination unit
62, 67, 68, 82, 89, 101, 121, 151, 171: line buffer
63, 83: Latch for position alignment
64, 69, 84, 90, 102, 122, 152, 172: attention point latch
65, 85, 140, 180: γ correction table
66, 86-88: OR gate
70 to 77, 91 to 98, 103 to 110, 123 to 130, 153 to 159, 173 to 176: surrounding judgment latch
78, 99, 111, 131, 160, 177: determination unit
80: CPU

Claims (11)

In an image forming apparatus that irradiates a recording medium by modulating light or ion flow according to image data, and forms a dot image on the recording medium by an electrophotographic method.
Pseudo gradation processing means for performing pseudo gradation processing on input image data, and surrounding dots with respect to the target dot of the multi-valued image data subjected to pseudo gradation processing by the means, Dot environment determining means for determining the environment of the dot, and γ correction means for performing γ correction for variably setting a writing level such as a writing density or a writing size of the target dot according to a determination result of the means,
The γ correction means is a γ correction data storage means for storing at least two types of γ correction data, and a γ correction for selecting any one of the γ correction data according to the determination result of the dot environment determination means. and data selection means, Ri Do and a write level signal output means for outputting a write level signal corresponding to set the write level of the target dot with a γ correction data selected by said means,
The γ correction data selection unit is a unit that selects γ correction data in which the writing level of the target dot is set higher as the number of surrounding writing dots with respect to the target dot, which is the determination result of the dot environment determination unit, is smaller.
The γ correcting means, images forming device you being a means for increasing the write level of the noted dot smaller the number of peripheral write dot for the target dot is a determination result of the dot environment determination means. In an image forming apparatus that irradiates a recording medium by modulating light or ion flow according to image data, and forms a dot image on the recording medium by an electrophotographic method.
Pseudo gradation processing means for performing pseudo gradation processing on input image data, and surrounding dots with respect to the target dot of the multi-valued image data subjected to pseudo gradation processing by the means, Dot environment determining means for determining the environment of the dot, and γ correction means for performing γ correction for variably setting a writing level such as a writing density or a writing size of the target dot according to a determination result of the means,
The γ correction means stores γ correction data storage means for storing at least three types of γ correction data, and γ correction for selecting any of the γ correction data according to the determination result of the dot environment determination means. Data selection means, and write level signal output means for setting the write level of the target dot using the γ correction data selected by the means and outputting the corresponding write level signal,
The dot environment determination means is a means for determining whether the environment of surrounding dots with respect to the target dot is a state where there is no writing dot, a state where it is in a horizontal direction or a vertical direction, or a state where it is oblique,
When the dot environment determination unit determines that the environment of surrounding dots with respect to the target dot of the multivalued image data is in a state where there is no writing dot, the γ correction data selection unit writes the target dot. When it is determined that the first γ correction data set at a high level is in a state where the writing dot is in the horizontal direction or the vertical direction, the writing level of the target dot is lower than that of the first γ correction correction data. When it is determined that the set second γ correction data indicates that the writing dot is oblique, the writing level of the target dot is set between the writing levels of the first and second γ correction data. An image forming apparatus, wherein the third γ correction data is selected.   3. The image forming apparatus according to claim 1, wherein a predetermined type of γ correction dot pattern is sequentially formed on the recording medium at a predetermined timing for each predetermined writing level. Density detection means for detecting the density of each dot pattern created on the recording medium by the means using an optical sensor; and γ correction data creation for creating γ correction data based on the detection result of the means And an image forming apparatus.   4. The γ correction data creation means is means for obtaining dot γ characteristics based on a detection result of the density detection means and creating γ correction data based on the dot γ characteristics. Image forming apparatus.   4. The image forming apparatus according to claim 3, wherein, within each γ correction data, based on γ correction data having the highest write level of the modulation dot and γ correction data having the lowest level, the write dot is within a range of each write level. An image forming apparatus comprising means for creating new γ correction data by calculation. The γ correction pattern image forming means generates a γ correction dot pattern having at least a writing dot around a modulation dot and a γ correction dot pattern having a writing dot at a predetermined timing on the recording medium. It is a means to create images sequentially for each writing level,
The γ correction data creation means obtains the dot γ characteristics of the respective γ correction dot patterns based on the detection result of the density detection means, and the dot γ characteristics of dot patterns other than the respective γ correction dot patterns. 4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a means for creating different types of γ correction data based on the dot γ characteristics after the interpolation is obtained from the dot γ characteristics.   The γ correction data creation means has means for allocating modulation dot writing levels in the dot γ characteristics at equal intervals from a visual image starting point to a target maximum density when the light or ion current modulation is multilevel modulation. The image forming apparatus according to claim 4, wherein: The γ correcting means, an image forming apparatus according to claim 1, wherein further comprising means for changing the results the maximum write level of the target dot according to the judgment of the dot environment determination means. 2. The pseudo gradation processing type determining means for determining the type of pseudo gradation processing of the pseudo gradation processing means in accordance with the determination result of the dot environment determining means. to an image forming apparatus according to any one of 8. The γ correction means variably sets the writing level of the target dot with a variable step number larger than the multi-value number of one dot of the multi-value image data subjected to the pseudo-gradation processing by the pseudo-gradation processing means. the image forming apparatus according to any one of claims 1 to 9, characterized in that it has a. 11. The image forming apparatus according to claim 1 , wherein image storage means for storing multivalued image data subjected to pseudo gradation processing by the pseudo gradation processing means, and storage in the means. Image reading means for reading out the image data that has been read,
An image forming apparatus, wherein the dot environment determining unit refers to a surrounding dot with respect to a target dot of the image data read by the image reading unit and determines the environment of the dot.

Images