JPH09326926A - Image processor and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain gradation conversion with high image quality at all times by setting a medium tone density to form a dither pattern in the multi-value dither method to be an optimum value in following to a change in the process condition of the processor. SOLUTION: An optimum medium tone level 2041 is set under a current environment by allowing an initial processing section 215 to generate a correction image actually to detect the density at application of power to the processor. A received image signal after that is subject to multi-value dither processing in a dither processing section 202 and converted into prescribed gradation. The gradation is converted into a prescribed density level based on the medium tone level 2041 in a level conversion section 204 and the result is modulated and outputted from a section 205.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and a method thereof, for example, an image processing apparatus and a method thereof capable of recording a multi-gradation image by multi-value dither processing.

[0002]

2. Description of the Related Art In a conventional image processing apparatus, each pixel is represented by multi-values such as 8 bits from the viewpoints of reduction of memory capacity, speeding up of data transfer, and recording ability of a recording apparatus. A so-called binarization method for compressing image data such as a natural image into a 1-bit representation is widely used.

Typical examples of this binarization method include an error diffusion method and a systematic dither method. Especially in laser printers, from the viewpoint of high resolution of the recording device,
The systematic dither method (hereinafter referred to as the dither method) is generally used.

In recent years, colorization of image recording apparatuses has progressed, and there is an increasing need to print and record natural images expressed in gray scale with high image quality. However, an image represented by binary values has limitations in terms of gradation and resolution. Therefore, a so-called multi-valued dither method, which uses a multi-valued recording method capable of expressing three or more levels of gradation per pixel, has been receiving attention. For example, in a laser printer,
This multilevel recording method is realized by PWM (pulse width modulation method).

[0005]

In the case of the above-mentioned conventional multi-valued dither method, halftone pixel values are used when forming a dither pattern. Then, the image quality after conversion is greatly influenced by the density adopted as the halftone, that is, the image density actually formed as the halftone. However, there is no effective method for determining the optimum density as the density corresponding to this halftone. Further, even if the optimum halftone density is once determined, the halftone density itself changes in time series due to process conditions and the like, so that high image quality cannot be maintained during gradation conversion by the multi-value dither method. There was a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to make a halftone density value forming a dither pattern in a multilevel dither method follow a change in process conditions of an apparatus. The present invention provides an image processing apparatus and a method thereof that can always perform gradation conversion with high image quality by setting an optimum value.

[0007]

As one means for achieving the above object, the image processing apparatus of the present invention has the following arrangement.

That is, a multilevel dither means for performing multilevel dither processing on an input image signal and converting it into a signal of a predetermined level number, and a signal of a predetermined level number output by the multilevel dither means, An image processing apparatus comprising: a level converting means for converting to a corresponding predetermined density level; and an image forming means for forming an image based on a predetermined density level signal output by the level converting means. A correction image forming means for forming a correction image by means, a density detecting means for detecting the density of the formed correction image, and the level converting means based on the density of the correction image detected by the density detecting means. The control means for setting an intermediate density level among the predetermined density levels in 1.

As one method for achieving the above object, the image processing method of the present invention includes the following steps.

That is, a multi-value dither process for performing multi-value dither processing on an input image signal and converting it into a signal of a predetermined level number, and a signal of a predetermined level number output from the multi-value dither process, An image processing method comprising: a level converting step of converting to a corresponding predetermined density level; and an image forming step of forming an image by an image forming means based on a predetermined density level signal output from the level converting step. A correction image forming step of forming a correction image by the image forming means, a density detection step of detecting the density of the formed correction image, and a level conversion step in the level conversion step based on the detected density of the correction image. And a control step of setting an intermediate density level among the predetermined density levels.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings.

In the present embodiment, an example in which the present invention is applied to an image processing apparatus using electrophotography will be described. In the present embodiment, the input density level is an 8-bit image signal.

FIG. 1 is a side sectional view of an image processing apparatus according to this embodiment. In the figure, reference numeral 100 denotes a semiconductor laser, which receives an 8-bit image signal transmitted from an external host computer in a multi-valued image processing unit 1000 described later and is driven by an image signal subjected to multi-valued dither processing as described later. As a result, the laser beam light L is emitted.

At this time, the photoconductor drum 105 is uniformly charged to a predetermined polarity by the charger 104, and the laser beam light L scans the photoconductor drum 105 via the polygon mirror 101, the lens 102, and the mirror 103, An electrostatic latent image is formed on the drum 105. Then, the developing device 10
A required developing bias voltage is applied to 6 to develop the latent image, and a toner image is formed on the photosensitive drum 105.

On the other hand, the transfer paper P is fed at a predetermined timing, and a transfer bias voltage (+1.8 KV) having a polarity opposite to that of the toner (eg, positive polarity) (+1.8 KV) is generated immediately before the leading edge of the transfer paper P reaches the transfer start position. The toner image on the photoconductor drum 105 is transferred to the transfer sheet P, and the transfer sheet P is electrostatically attracted to the surface of the transfer drum 107. After that, the photoconductor drum 105 is cleaned by the cleaner 10.
By 8, the residual toner is removed.

The transfer paper P on which the image is formed as described above is separated from the transfer drum 107, and the fixing roller 10
The image is fixed by passing through 9. Finally, the transfer paper P is discharged to a paper discharge tray (not shown).

A density sensor 1005 detects the density of patches formed on the transfer drum 107, as will be described later.

FIG. 2 shows a detailed block configuration of the multivalued image processing unit 1000 in this embodiment, and its operation will be briefly described. In the present embodiment, a case where 2-bit dither processing with a matrix size of 3 × 3 is performed on input 8-bit image data will be described. That is, the input image data of 256 gradations is converted into 4 gradations by the multi-value dither processing.

In the figure, 201 is a density correction unit,
The LUT 2011 generated as described below is held and the input 8-bit data (256 gradations) is stored in the LU.
By referring to T2011, it is converted into 8-bit data of 28 gradations having density levels adapted to the current device environment. Reference numeral 202 denotes a dither processing unit, which has 8 gradations of 8
Grayscale conversion is performed by performing multivalued dither processing described later on the bit data, and a 2-bit signal indicating four grayscales is output. The level signal output from the dither processing unit 202 is temporarily stored in the buffer 203 and then output in synchronization with the image clock.

Reference numeral 204 denotes a level conversion unit, which refers to an intermediate level 2041 to be described later with respect to four gradations indicated by a 2-bit signal obtained as a result of the multi-valued dither processing in the dither processing unit 202, and a PWM unit 205 in the subsequent stage. The signal is converted to a 4-level 8-bit signal that can be output at.

An 8-bit image signal and an image clock 212 are input to the PWM unit 205. Then, first, the 8-bit image signal is supplied to the image clock PC by the latch circuit 206.
The D / A converter 2 is synchronized with the rise of LK212.
It is converted into an analog voltage at 07 and the analog comparator 2
09 to one terminal. On the other hand, the image clock 212
The triangular wave generated by the triangular wave generator 208 is also input to the other terminal of the analog comparator 209. Then, in the analog comparator 209, the analog voltage and the two signals of the triangular wave are compared with each other to output a pulse width modulated (PWM) signal, which is inverted by the inverter 210.
The WM signal is obtained. The semiconductor laser 100 is driven by inputting this PWM signal to a laser driving unit (not shown), and image formation is performed by the above-described process.

An initial processing unit 215 performs initial processing for multi-valued dither, which will be described later, when the power of the apparatus is turned on, and sets the LUT 2011 in the density correction unit 201 and the intermediate level 2041 in the level conversion unit 204. Set.
Reference numeral 220 denotes a CPU, which comprehensively controls each component of the apparatus including the initial processing unit 215 according to a control program stored in the ROM 221. A RAM 222 is used as a work area for the CPU 220.

Next, the principle of the multi-valued dither processing in this embodiment will be described. As described above, in the present embodiment, a case will be described in which 2-bit dither processing with a matrix size of 3 × 3 is performed on input 8-bit image data.

In the case of 2-bit dither, since the output image has four levels of gradation in the depth direction, the four levels in this output image will be referred to as level 0, level 1, level 2 and level in the order of increasing density. Call 3. That is, 1 of the output image
Pixels are represented by four levels of level 0, level 1, level 2 and level 3.

FIG. 3 shows an example of a dither threshold matrix in this embodiment. The numbers in the matrix represent the threshold value of each square, and when the density of the input image exceeds the threshold value, the density level of the square increases by one. Three threshold values are set for each square. From the smallest value, the threshold value from level 0 to level 1, the threshold value from level 1 to level 2, and the value from level 2 to level 3 Represents a threshold. Specifically, for example, assuming that image data of a single density is input, the dither pattern of 9 pixels output corresponding to the dither matrix is such that as the density increases, the pixel corresponding to the central cell in the figure is first displayed. The density level of changes to level 1, level 2 and level 3, then the pixel corresponding to the center right cell changes to level 1, level 2 and level 3, and then the pixel corresponding to the lower right cell changes level. 1, level 2, level 3. . . And so on. Then, when the input density level exceeds the maximum threshold value “27” in the upper right square, all 9 pixels become level 3. That is, the multi-valued dither processing according to the present embodiment makes it possible to represent all 28 gradations in units of 3 × 3 pixels.

The manner of this gradation change is shown in FIG. FIG. 4A to FIG. 4I are all 2 that can be expressed in this embodiment.
Of the eight gradations, the states of gradations 1 to 9 are shown. Hereinafter, the respective states shown in (a) to (i) will be referred to as state 1, state 2,
... state 9 It should be noted that the case where all pixels are at level 0 is referred to as state 0.

The states shown in FIG. 4 correspond to the threshold matrix shown in FIG. For example, in the state 1 shown in FIG. 4A, the pixel corresponding to the central cell of the matrix (hereinafter,
The central pixel) is at level 1. Similarly, the state 2 shown in FIG. 4B is a state in which the central pixel is at level 2, the state 3 shown in FIG. 4C is a state in which the central pixel is at level 3, and FIG. State 4 shown in d) indicates that the central pixel is in level 3 and the central right pixel is in level 1. In addition, states 10 to 27 (not shown)
Is similarly determined corresponding to the threshold matrix.

Here, a detailed configuration of the dither processing unit 202 shown in FIG. 2 is shown in FIG. 5 and will be described below.

In FIG. 5, image data indicating 28 gradations is input to each of the mass processing units 401 to 409 corresponding to each square of the 3 × 3 dither matrix in this embodiment. Here, the detailed configuration of the mass 1 processing unit 401 is shown in FIG. In FIG. 6, first, the threshold value of the cell 1 is input from the memory 504 to the comparators 1, 501 and 2 of 501 to 503, respectively. Each comparator 501-50
In 3, the input data is compared with each threshold value, and the result is input to the level generation unit 505.
The level generator 505 generates and outputs a 2-bit signal indicating any one of levels 1 to 4 according to the value of the input signal 506. In addition, in the mass 2 processing unit 402 to the mass 9 processing unit 409 in FIG.
The same processing is performed by the same configuration as 01. The memory 504 may be secured in the ROM 221.

In this way, each mass processing unit 401-40
The level signal 410 output from 9 is input to the selector 413. On the other hand, the signal 406 indicating the current position of the input data is also input to the selector 413 from the counter 412 that counts the number of pixels in the main scanning direction and the sub scanning direction.
The selector 413 uses the position signal 406 as a selection signal, selects one of the nine level signals sent from each of the mass processing units 401 to 409, and outputs it as a 2-bit level signal.

As described above, the 2-bit dither processing in this embodiment is performed.

Now, let us consider a case where the above-mentioned respective states shown in FIG. 4 are actually formed and the concentration thereof is measured. For example, among four density levels in one pixel, level 0 is 00h, level 4 is ffh, and intermediate level values (8-bit values corresponding to level 1 and level 2) are 00h to f.
The image is actually formed by setting an appropriate value between fh. In this case, the concentration change measured in each state of FIG. 4 is as shown in the graph of FIG. 7, for example. In FIG. 7, the horizontal axis represents the gradation of dither, that is, each state shown in FIG. 4, the vertical axis represents the measured density value, and the curve connecting the points plotting the density from state 0 to state 9 It is shown.

Here, in the case of the states 1 to 3, since the dots are constituted as the isolated points as shown in FIGS. 4A to 4C, the density value measured in this state is the density of the isolated dots. It depends on the characteristics. Further, since the states 1 to 3 correspond to the density value of the highlight portion, the density change in the state is visually inconspicuous.

On the other hand, the change in density from state 3 to state 6 is
As shown in (d) to (f) of FIG. 4, the pixel adjacent to the central pixel changes from level 1 to level 3 and is expressed. In these states, if the intermediate level value which is the output level corresponding to the level 1 and the level 2 is not appropriate, the density variation amounts are not equal as shown in states 3 to 6 in FIG. It may be too large or too small. This causes problems such as impairing the gradation of the image and generating pseudo contours.

Similarly, when the density changes from the state 6 to the state 9, the amount of density change is greatly influenced by the output intermediate level value. These changes in density are shown in FIG.
(A) to (c), it depends on the density characteristics when a dot grows in the vicinity of a certain dot. In addition, state 1
The change in density above 0 is also affected by similar characteristics.

Therefore, in the multi-valued dither processing, it is necessary to particularly consider the density characteristic generated in the states 3 and above. That is, of the four output level values converted by the level conversion unit 204, the intermediate level values corresponding to level 1 and level 2 must be set to appropriate values according to these density characteristics.

Therefore, in the present embodiment, when the power of the apparatus is turned on, the first and second processes described below are executed in the initial processing section 215 as multi-valued dither initial processing, so that it is optimal under the current apparatus environment. Enables multi-valued dither processing. Hereinafter, the multi-valued dither initializing process according to this embodiment will be described with reference to the flowchart in FIG.

First, the intermediate level setting process which is the first process will be described.

When the image processing apparatus is turned on, first, in step S151, the image signal indicating the first corrected image as shown in FIG. 10 is read from the ROM 221. In the corrected image, a patch having a predetermined density is formed in each of the areas 601 to 612, and nothing is formed in the area other than the patch.

On each of the patches 601 to 612 shown in FIG. 10, the density level corresponding to the dither pattern created as follows is placed. First, as shown in FIG. 11, the central pixel of the dither matrix is set to level 3 (ffh).
In this state, the density of the adjacent center right pixel is set to d, and the density d is changed to create a dither pattern corresponding to each density of the patches 601 to 612. Originally d
It is ideal to change 256 steps from the density of 00h to ffh. However, due to the restriction of the patch area, in reality
The density levels corresponding to the individual patches 601 to 612 are set.

First, values (approximate values) close to the optimum output density levels corresponding to Level 1 and Level 2 are acquired in advance according to the density characteristics of the output device and stored in the ROM 221. Hereinafter, a method of acquiring the approximate values of level 1 and level 2 will be described.

First, d in FIG. 11 is 00h to ffh.
The dither pattern varied up to is formed, and the density value for each state is measured. Here, the measurement result is, for example, as shown in FIG.
Is obtained as follows. In FIG. 12, the horizontal axis is the value of d, and the vertical axis is the measured density value of the patch. And the density is 0
The density corresponding to 0h is Dmin, the density corresponding to density ffh is Dmax, and D1 = Dmin + (Dmax-Dmin) / 3 D2 = Dmin + 2 * (Dmax-Dmin) / 3 is set to D1 and D2. As can be seen from the above equation and FIG. 12, D1 and D2 are values that divide the difference between Dmax and Dmin into three equal parts. Here, in FIG. 12, the values of d that take D1 and D2 are x1 and x2, respectively. These x1 and x2 are the approximate values of Level 1 and Level 2 in the present embodiment,
It is stored in the ROM 221 in advance.

Then, d is 00, x1-8, x1-4, x1, x1 + 4, x1 + 8, x2 with respect to the obtained x1 and x2.
Twelve ways of -8, x2-4, x2, x2 + 4, x2 + 8, ff (all units are hexadecimal (h)) are set. Then, in the above-described first corrected image shown in FIG. 10, the twelve dither patterns corresponding to the density d are the patches 601 to 601.
612 respectively. Hereinafter, twelve patches corresponding to respective densities d will be referred to as patch 1 to patch 12, respectively.

Here, a case has been described in which the density of the central right pixel of the dither matrix as shown in FIG. 11 is set to d, and the patches 1 to 12 are created by changing the density d. However, the patch 1 to the patch 12 can be similarly created not only for the central right pixel of the dither matrix but for any pixel adjacent to the central pixel, the density of any pixel may be d.

Then, in step S152, patches 1 to 12 in the first corrected image are actually formed on the photosensitive drum 107. That is, a latent image corresponding to the first corrected image shown in FIG. 10 is formed on the photosensitive drum 107. Then, the toner image is developed through the above process.
Although formed, the transfer paper P is not conveyed in this intermediate level setting process, so that the toner is directly placed on the transfer drum 107, so that toner images corresponding to the patches 1 to 12 are formed on the transfer drum 107. To be done.

Next, in step S153, the transfer drum 10
The densities of patches 1-12 formed on 7 are measured. FIG. 13 shows how the density of the patch is measured. FIG. 13 is a view of the transfer drum 107 seen obliquely, in which 105 is a photosensitive drum and 106 is a developing device. The twelve patches 1004 on the transfer drum 107 are the density sensor 100.
5, each concentration is measured.

Then, in step S154, the intermediate level value of the density level to be output in the multi-valued dither of the present embodiment is calculated based on the measurement result in step S153. Hereinafter, the intermediate level calculation method in step S154 will be described.

For example, assume that the density measurement result in step S153 is as shown in FIG. Twelve black circles in the figure are density values obtained by measuring the patches 1 to 12. Here, as in the case of FIG. 12 described above, the density of the patch 1 corresponding to the density 00h is Dmin, the density of the patch 12 corresponding to the density ffh is Dmax, and D1 = Dmin + (Dmax−Dmin) / 3 D2 = Dmin + 2 * (Dmax-Dmin) / 3. Further, the values of d having the density values closest to D1 and D2 are defined as x'1 and x'2. In the case of FIG. 14, namely,
x'1 = x1 + 8 and x'2 = x2-4. In the present embodiment, these x'1 and x'2 are obtained as optimum intermediate level values for level 1 and level 2.

Then, in step S155, the obtained intermediate level values x'1 and x'2 are set as the intermediate level 2041 in the level converting section 204 shown in FIG.

Steps S151 to S155 described above
Is the first process (intermediate level setting process) in the multi-valued dither initial processing of this embodiment.

Next, the LUT creating process which is the second process will be described.

First, in step S156, the image signal indicating the second corrected image as shown in FIG.
Read more. In the second corrected image, 13
Eight patches indicated by 01 to 1308 are included, and each patch includes states 0, 4, 8, 12, 16, 2 described above.
Dither patterns corresponding to 0, 24, and 27 are listed in order.

In step S157, the density level value of each patch 1301 to 1308 is converted for each square of the dither pattern according to the result of the first process. That is, according to the result of the first process,
The conversion of level 0 → 00h, level 1 → x′1, level 2 → x′2, and level 3 → ffh is performed for each square.

Then, in step S158, the converted patches 1301 to 1308 are formed on the transfer drum 107 as shown in FIG. 13 in the same manner as the first process, and in step S159, the density sensor 1005 detects each patch. Measure the concentration value of.

Then, the process proceeds to step S160, and based on the measured density value of the second corrected image in step S159, a LUT (look-up) for approximating a linear relationship between the level value of the input image data and the output density level value. Up table). Then, this LUT is stored in the density correction unit 201 shown in FIG.
011 is set.

Steps S156 to S161 described above
Is a second process (LUT creation process) in the multi-valued dither initial process of this embodiment.

As described above, the density correction unit 201 includes
LUT 201 generated in the second process described above
1 is set and the input 8-bit data (25
By referring to the LUT 2011 for 6 gradations, 28 density levels adapted to the current device environment can be obtained.
It can be converted into 8-bit gradation data. Then, as described above, the dither processing unit 202 performs multi-value dither processing, and converts each pixel into four gradations of level 0 to level 3.

Then, in the level conversion section 204, the intermediate level values 2041 (x'1, x'2) of the multi-valued dither calculated in the above-mentioned first process are set, and the four gradation levels to be inputted are set. The level signal (level 0 to level 3) is changed to level 0 → by referring to the intermediate level value 2041.
00h, level 1 → x'1, level 2 → x'2, level 3 →
It can be converted into an ffh 8-bit signal. Therefore, it becomes possible to perform image formation by using the intermediate level value in the multi-value dither as the optimum value for the current device environment.

As described above, according to the present embodiment, the optimum intermediate threshold level in the multi-valued dither processing in the current environment can be determined when the power of the apparatus is turned on. The formation can be maintained.

In this embodiment, the matrix size is 3
Although the description has been given by taking the 2-bit dither of × 3 as an example, it is needless to say that the present invention can be applied to a matrix of arbitrary size and multi-value dither depending on the number of bits.

Further, in the present embodiment, an example in which the image data after the multi-value dither processing is formed by PWM has been described, but it goes without saying that the image is formed by another method such as an area gradation method by an ink jet method. Is also good.

In the present embodiment, the so-called monochrome image forming apparatus in which the image processing apparatus holds only one developing device has been described, but the present invention is of course applicable to a full-color image processing apparatus. . In this case, the multilevel dither initializing process may be performed for each color component to set an intermediate level value for each color component, and similarly, an LUT may be created for each color component.

<Other Embodiments> Incidentally, even when the present invention is applied to a system composed of a plurality of devices (eg, host computer, interface device, reader, printer, etc.), a device composed of one device ( For example, it may be applied to a copying machine, a facsimile machine, etc.).

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

Further, by executing the program code read by the computer, not only the functions of the above-described embodiment are realized, but also the OS (operating system) running on the computer based on the instruction of the program code. It is needless to say that this also includes a case where the above) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instructions of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the above-mentioned storage medium, the storage medium stores the program code corresponding to the above-mentioned flow chart. Briefly, in the memory map example of FIG. Each module shown will be stored in the storage medium. That is, at least "first patch formation module (S151, S1 in FIG. 9
52) "" First patch density detection module (same S
153) "" Intermediate level value calculation module (same S
154), "second patch density conversion module (corresponding to S156 and S157)", "second patch forming module (corresponding to S158)", "second patch density detecting module (corresponding to S159)" and " The program code of each module of “LUT creation module (corresponding to S160)” may be stored in the storage medium.

[0070]

As described above, according to the present invention, by setting the optimum intermediate level value in the multi-valued dither in accordance with the current apparatus environment, it is possible to always maintain high quality image formation. it can.

[0071]

[Brief description of drawings]

FIG. 1 is a side sectional view of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a multi-valued image processing unit in this embodiment.

FIG. 3 is a diagram showing an example of a threshold matrix in the multi-value dither processing of this embodiment.

FIG. 4 is a diagram for explaining the principle of multi-valued dither processing in this embodiment.

FIG. 5 is a block diagram showing a detailed configuration of a dither processing unit in this embodiment.

FIG. 6 is a block diagram showing a detailed configuration of a mass 1 processing unit in the present embodiment.

FIG. 7 is a diagram showing an example of density change after multi-value dither processing.

FIG. 8 is a diagram showing dots growing in the vicinity of a certain dot.

FIG. 9 is a flowchart showing a multi-valued dither initializing process in this embodiment.

FIG. 10 is a diagram showing a first corrected image example in the present embodiment.

FIG. 11 is a diagram showing an example of a dither pattern for calculating each patch density in the first corrected image.

FIG. 12 is a table showing an example of density change measured in advance to obtain an intermediate level approximation value in the present embodiment.

FIG. 13 is a perspective view of a peripheral portion of a transfer drum in the present embodiment.

FIG. 14 is a diagram showing an example of concentration measurement in a first process of multi-value dither initial processing in the present embodiment.

FIG. 15 is a diagram showing a second corrected image example in the present embodiment.

FIG. 16 is a diagram showing an example of a memory map when the present invention is applied to a storage medium.

[Explanation of symbols]

 100 semiconductor laser 104 charging device 105 photosensitive drum 106 developing device 107 transfer drum 108 cleaner 201 density correction unit 202 dither processing unit 204 level conversion unit 205 PWM unit 215 initial processing unit 220 CPU 221 ROM 222 RAM 1000 multi-value image processing unit 1005 density Sensor

Claims (12)

[Claims] 1. A multi-level dither means for performing multi-level dither processing on an input image signal and converting it into a predetermined level number of signals, and a predetermined level number of signals output by the multi-level dither means, An image processing apparatus comprising: a level conversion unit that converts a corresponding predetermined density level; and an image forming unit that forms an image based on a predetermined density level signal output by the level conversion unit. A correction image forming means for forming a correction image by means, a density detecting means for detecting the density of the formed correction image, and the level converting means based on the density of the correction image detected by the density detecting means. And a control unit that sets an intermediate density level among the predetermined density levels in 1. 2. The image processing apparatus according to claim 1, wherein the predetermined density level includes a maximum density level, a minimum density level, and at least one intermediate density level which is a level between them. 3. The image processing apparatus according to claim 1, wherein the corrected image is composed of a plurality of dither patterns. 4. The corrected image is composed of a plurality of dither patterns formed by setting a specific pixel in the dither matrix to the highest level and changing a pixel level adjacent to the specific pixel within a predetermined range. Claim 3
The image processing apparatus according to any one of the preceding claims. 5. The control means sets the density value of the dither pattern in which the adjacent pixel has the lowest level and the density value of the dither pattern in which the adjacent pixel has the highest level in the corrected image for the predetermined number of levels. The image processing apparatus according to claim 4, wherein an adjacent pixel level corresponding to a density value obtained by equally dividing the image density into the intermediate density level is set as the intermediate density level. 6. The image processing apparatus according to claim 4, wherein the predetermined range in which the adjacent pixel level is changed in the corrected image is set near an adjacent pixel level corresponding to a predetermined density. 7. A correction unit that corrects an input image signal by referring to a table, the correction image forming unit forms a second correction image, and the control unit includes the density detection unit. The image processing apparatus according to claim 1, wherein a table in the correction unit is created based on the density of the second corrected image detected by the. 8. The second corrected image is a multi-level dither pattern, and the control means sets the input image signal level to be linear with an image density value formed by the image forming means. The image processing apparatus according to claim 7, wherein a table in the correction unit is created. 9. The image processing apparatus according to claim 1, wherein the image forming unit forms an image for each color component, and the control unit sets an intermediate level for each color component. 10. The image processing apparatus according to claim 1, wherein the image forming unit forms an image on a transfer material. 11. A multi-level dither process for performing multi-level dither processing on an input image signal to convert it into a predetermined level number of signals, and a predetermined level number of signals output from the multi-level dither process, An image processing method comprising: a level conversion step of converting to a corresponding predetermined density level; and an image forming step of forming an image by an image forming means based on a predetermined density level signal output from the level conversion step. A correction image forming step of forming a correction image by the image forming unit, a density detection step of detecting a density of the formed correction image, and a level conversion step in the level conversion step based on the detected density of the correction image. An image processing method comprising: a control step of setting an intermediate density level among predetermined density levels. 12. A code for a multi-value dither process for performing multi-value dither processing on an input image signal and converting it into a signal of a predetermined level, and a signal of a predetermined level output from the multi-value dither process. And a code of a level converting step for converting the respective to a corresponding predetermined density level, and a code of an image forming step for forming an image by the image forming means based on the predetermined density level signal output from the level converting step are stored. A code for a correction image forming step for forming a correction image by the image forming means, a code for a density detecting step for detecting the density of the formed correction image, and the detected correction A control process code for setting an intermediate density level among the predetermined density levels in the level conversion process based on the image density. A computer-readable memory according to claim Rukoto.