JPH11314401A - Image processor and processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep linearity in the relationship of image data vs quantity of light appropriately when pulse width modulation(PWM) is performed at high speed in an electrophotographic imaging system. SOLUTION: PWM is performed while setting minimum/maximum pulse widths in a PWM section 212 for gradation stressed 400 line region. For resolution stressed 800 line region, PWM is performed in a PWM section 212 after minimum/maximum image data is set at an LUT 211. Consequently, an appropriate gradation reproducibility is provided for the 400 line region and an image can be formed while sustaining resolution for the 800 line region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an image processing apparatus and an image processing method.

[0002]

2. Description of the Related Art In a conventional electrophotographic image processing apparatus, a laser is driven by a signal which has been subjected to pulse width modulation (PWM) based on image data, and the photosensitive member is scanned by the laser emission. A visible image was obtained by forming a latent image and developing and transferring the latent image.

FIG. 10 shows a configuration of a conventional pulse width modulation circuit for performing pulse width modulation. The pulse width modulation circuit shown in FIG. 1 outputs a pulse signal having a pulse width corresponding to the level of an input image signal, and inputs the pulse signal to a laser driver for driving a laser in a printer unit.

A conventional pulse width modulation circuit is an 800-line PWM circuit unit 4 for a character / thin line region requiring more resolution.
11 and two PWM circuit units 412 of a 400-line PWM circuit unit 412 for a photograph area that requires more gradation.

[0005] 800 line PWM circuit section 41 for characters / thin lines
In No. 1, PWM is performed at a resolution of 800 dpi, and is used in an area where importance is placed on the resolution, which is determined as a character / thin line area by an area determination unit (not shown) in the document image. 800
The line PWM circuit section 411 includes a D / A conversion section 401, a triangular wave generation circuit 402, and a comparator 403.

[0008] For example, an 8-bit image signal input to the 800-line PWM 411 is interpolated by an interpolation circuit (not shown) into an image signal having a cycle of an integer multiple (twice in the conventional example) to 800 dpi. Has been converted.
Then, first, the input 800 dpi image signal is D /
D / A conversion is performed in the A conversion unit 401. Then, a triangular wave having the same cycle as the clock from the oscillator 407 is generated by the triangular wave generation circuit 402, and the D /
The output after the A conversion is compared with the triangular wave, and the H level is output only when the output of D / A is large.

On the other hand, a 400-line PWM circuit 41 for photography
In No. 2, PWM is performed at a resolution of 400 dpi, and is used in an area where importance is placed on gradation, which is determined as a photographic area by an area determination unit (not shown) in the document image. 400 lines P
The WM circuit unit 412 includes a D / A conversion unit 404, a triangular wave generation circuit 405, and a comparator 406.

In a 400-line PWM circuit section 412, for example, an 8-bit image signal inputted is D / A converted by a D / A conversion section 404, and a clock having the same cycle as the image signal from the oscillator 407 is divided by a frequency dividing circuit 408. The triangular wave generation circuit 405 generates a triangular wave having the same cycle as the clock divided by 2. The comparator 406 compares the output after the D / A conversion with the triangular wave, and outputs an H level only when the output of the D / A is large.

In the selector 407, based on a 400/800 line switching signal from an area determination unit (not shown),
Either the 0-line PWM output or the 800-line PWM output is selected.

The operation of the above-described 800-line PWM unit 411 is shown in a timing chart of FIG. 800 line PW
The M section 411 compares the triangular wave with the output of the D / A conversion circuit 401, and finds that the portion where the D / A output is high is 800 lines
This is the output of the M unit 411. For example, if the image signal level is 0
When the image data input to the D / A conversion circuit 401 is FFh when represented by 0h to FFh, as shown in 51, the output of the D / A conversion circuit 401 is smaller than the triangular wave in all regions of one pixel. Therefore, all pixels are at H level (laser ON). If the input image data is 00h, as shown at 52, the output of the D / A conversion circuit 401 is smaller than the triangular wave in all regions of one pixel, so that all pixels are at L level (laser off). If the input image data is 7Fh, as shown at 53, only the region where the output of the D / A conversion circuit 401 is larger than the triangular wave is at the H level (laser ON). This comparator output is P
The laser is input to the laser driver as a WM signal, and the laser is turned on only when the PWM signal is at the H level.

Incidentally, based on FIG.
11 has been described, but the operation of the 400-line PWM unit 412 is also the same as that of the 800-line PWM unit 411 shown in FIG.

The image data input to the above-described pulse width modulation circuit is input after well-known image processing such as an LUT for performing gamma correction.

[0013]

However, the conventional image processing apparatus has the following problems.

Due to its characteristics, a laser driven by a laser driver based on a PWM signal does not start laser emission unless a drive pulse having a certain width is input to the laser driver. This is because laser emission does not start unless the current applied to the laser exceeds a predetermined threshold current ITH (corresponding to a predetermined number of carriers). For this reason, when the drive pulse is small, laser emission may not be obtained in some cases. Therefore, in a conventional image processing apparatus, normally, a bias current that does not exceed the threshold current is supplied to the laser in advance, and the amount of current required to reach the threshold current by the switching current (drive current by a PWM pulse) is reduced. Thus, the response of the laser emission was accelerated.
Thus, laser emission can be obtained even if the PWM pulse is small.

However, since the threshold current changes depending on the temperature, for example, if the bias current is set to about the same as the threshold current, laser emission may be caused by the bias current depending on the temperature. For this reason, the set value of the bias current has to be reduced to some extent, and therefore, even if the bias current is supplied, there is a problem that a drive pulse having a constant width is still required for laser emission.

Furthermore, when the duty of the H level of the PWM output in which the laser is on in one pixel is large, there is a problem that the laser is fully turned on for one pixel despite the laser off area. This is PWM
This is because the laser driver cannot respond completely because the output off time is short.

FIG. 12 shows the relationship between image data proportional to the H level duty of the PWM output and the amount of light output from the laser, which remarkably represent these developments. In the figure, when the image data is in the range of 00h to 30h, there is no laser emission and the light amount is constant. When the image data is in the range of 30h to B0h, the relationship between the image data and the light amount is linear. However, when the image data is in the range of B0h to D0h, the slope sharply increases, and the image data is D0h to F0h.
In the range of Fh, the maximum light amount has been reached.

For this reason, in the conventional image processing apparatus, the pulse width corresponding to the image data of 00h to FFh is corrected so that the relationship between the pulse width and the light amount becomes linear as shown by 30h to B0h in FIG. I was able to. That is, when the image data is 00h, the actual pulse width is 30h.
And set the pulse width of FFh to B
By setting to be equivalent to 0h, the relationship between image data and light amount could be kept linear.

However, when the PWM becomes faster and the one-pixel period becomes shorter, the duty of the minimum pulse width for starting laser emission further increases, so that the duty of the maximum pulse width that can maintain the linearity of the image data to the light amount becomes small. turn into. That is, since the linear region of the image data versus the light amount becomes narrower as the PWM becomes faster, there is a restriction that the pulse width corresponding to 00h must be set large and the pulse width change in units of 01h must be reduced. However, it becomes difficult to maintain the linearity.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has an image processing apparatus and a system capable of always maintaining appropriate linearity in the relationship between image data and light quantity even when performing high-speed PWM. The aim is to provide a method.

[0021]

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

That is, input means for inputting image data,
Area determination means for determining first and second areas based on the image data; first and second correction means for performing density correction on the image data of the first and second areas, respectively; First and second modulating means for modulating the pulse width based on the image data of the first and second areas, respectively;
An image forming unit that forms an image based on a pulse width modulated by the first and second modulation units, wherein the first modulation unit is provided for the first area. , The minimum and maximum pulse widths are set, and for the second region, the second correction means sets the minimum and maximum image data.

For example, the first region is an image region where importance is placed on gradation, and the second region is an image region where importance is placed on resolution.

[0024]

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

First Embodiment Apparatus Overview An electrophotographic digital copying machine will be described as an example of an image processing apparatus according to the present embodiment. FIG. 1 shows a schematic sectional view of the apparatus, and FIG. 2 shows a schematic functional configuration of the digital copying machine. The overall configuration and image forming process of the digital copying machine will be described in detail.

In FIG. 1, reference numeral 100 denotes a reader unit for reading an original image, and 200 denotes a printer unit for printing the original image. First, when a copy key (not shown) is depressed, the reader unit 100 exposes and scans the original 30 placed on the original platen glass 31 with the exposure lamp 32, thereby scanning the reflected light image from the original 30 with a CCD or the like. To obtain a color separation image signal of R, G, B. The full-color sensor 34 separates the original 30 into a number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. The image signal output from the full-color sensor 34 is input to an image processing unit 35, and a laser drive signal is generated by performing various image processing described later.

FIG. 2 shows a functional block configuration of the image processing unit 35. In the figure, an image signal output from a full-color sensor 34 is input to an analog signal processing unit 201, where gain and offset are adjusted, and then, for example, 8 bits (00h to 00h) for each color component in an A / D conversion unit 202. FF
h: 256 gradations).
The shading correction unit 203 optimizes the gain for each sensor cell using a signal obtained by reading the reference white plate 106 for each color in order to eliminate sensitivity variations in the CCD sensor cells arranged in a line on the full-color sensor 34. A well-known shading correction is applied.

Next, in the line delay section 204, a spatial shift contained in the image signal output from the shading correction section 203 is corrected. This spatial shift is caused by the line sensors on the full-color sensor 34 being arranged at a predetermined distance from each other in the sub-scanning direction. Specifically, based on the B color component signal, the R and G color component signals are line-delayed in the sub-scanning direction, and the phases of the three color component signals are synchronized.

Then, in the input masking section 205,
The color space of the image signal output from the line delay unit 204 is converted into the NTSC standard color space by the matrix operation of Expression (1). In other words, the color space of each color component signal output from the full-color sensor 34 is determined by the spectral characteristics of the filter of each color component, but is converted into the NTSC standard color space.

[0030]

(Equation 1)

Next, the LOG conversion unit 206 is, for example, a ROM
It converts the RGB luminance signal output from the input masking unit 205 into a CMY density signal. Line delay memory 2
07 indicates that the black character determination unit (not shown) has the input masking unit 2
05 to the control signals UCR, FILTER, SEN
LOG conversion unit 2 for the period (line delay) for generating
The image signal output from 06 is delayed.

In the masking / UCR unit 208,
The black component signal K is extracted from the image signal output from the line delay memory 207, and further, a matrix operation for correcting the color turbidity of the recording color material of the printer unit 200 is performed on the YMCK image signal, and each reading of the reader unit 100 is performed. For each operation,
For example, an 8-bit color component image signal is output in the order of M, C, Y, and K. The matrix coefficients used for the matrix operation are set by the CPU 213 in the image processing unit 35.

Output Filter (Spatial Filter Processing Unit) 20
9 performs edge enhancement or smoothing processing on the image signal output from the masking / UCR unit 208 according to a control signal from the CPU 213.

Reference numeral 210 denotes an interpolation unit which generates 800 dpi image data to be used for 800-line PWM in the PWM unit 212. In the interpolation section 210, image data to be output at 400 dpi is set to through according to the determination signal from the area determination section 216.

The LUT 211 is for matching the density of the original image with the density of the output image. In this embodiment, the LUT 211 is provided for 800 lines and for 400 lines, respectively.
Switching is performed according to a determination signal from the area determination unit 216. The LUT 211 is constituted by, for example, a RAM, etc.
The conversion table is set by the CPU 213.

The pulse width modulation (PWM) unit 212 has a capacity of 800 lines / 400 according to the area attribute of the input image signal.
By performing pulse width modulation of the line, a pulse signal having a pulse width corresponding to the level of image data is output. The present embodiment is characterized in that the minimum and maximum pulse widths are adjusted at this time, and the details will be described later.

An area determination unit 216 performs a well-known area determination process of detecting a photograph area or a character / thin line area based on an input document image signal, and sends a 400/800 line switching signal to the PWM unit 212. A region determination signal is generated.

The pulse signal output from the PWM unit 212 is input to a laser driver 41 for driving a laser 42 in the printer unit 200. Reference numeral 217 denotes a pattern generator which converts sample image data to be described later into a PW
Output to M section 212. The components in the image processing unit 35 are controlled by the CPU 213 according to a control program stored in the ROM 214. RAM 21
Reference numeral 5 is used as a work area of the CPU 213.

The laser beam emitted from the laser 42 as described above causes the printer unit 20 of the digital copying machine to
0 is performed. Returning to FIG. 1, the laser beam E emitted from the semiconductor laser 42 in the laser exposure optical system 3 is swept by the rotating polygon mirror 3a, and the lens 3b such as an f / θ lens and the photosensitive drum as the image carrier A spot image is formed on the photosensitive drum 1 by the fixed mirror 3c which is directed in one direction. Thus, the laser beam E
Scans the photosensitive drum 1 in a direction (main scanning direction) substantially parallel to the rotation axis of the photosensitive drum 1 and repeatedly scans in the rotation direction (sub-scanning direction) to form an electrostatic latent image.

In the printer unit 200, the photosensitive drum 1 as an image carrier is made of amorphous silicon, selenium, OP
C, and the like, are rotatably supported in the direction of the arrow, and have a pre-exposure lamp 11, a corona charger 2 as a charging unit, a laser exposure optical system 3, a surface potential sensor 12, Four different developing units 4y, 4c, 4m, 4
bk, the photosensitive drum light intensity detecting means 13, the transfer device 5, and the cleaning device 6 are arranged.

At the time of image formation in the printer section 200, the photosensitive drum 1 is rotated in the direction of the arrow, is uniformly discharged by the pre-exposure lamp 11, and is uniformly charged by the primary charger 2. Thereafter, exposure scanning is performed with the laser light E modulated in accordance with the above-described image information signal, whereby an electrostatic latent image corresponding to the image information signal is formed.

Next, by operating a predetermined developing unit, the electrostatic latent image on the photosensitive drum 1 is reversely developed with a two-component developer composed of toner and carrier. To form a charged visible image (toner image). The developing devices are eccentric cams 24y, 24c, 24m, 2
By the operation of 4bk, the photosensitive drum 1 is selectively approached in accordance with each separation color. Here, the reversal development is a development method in which a toner charged to the same polarity as the latent image is attached to a region of the photoconductor exposed to light, and the toner is visualized. The toners used in the present embodiment are yellow, magenta, and cyan color toners, and are formed by using a styrene copolymer resin as a binder and dispersing color materials of each color.

Further, the toner image on the photosensitive drum 1 is transferred from a recording material cassette 7 to a recording material supplied to a position facing the photosensitive drum 1 via a transport system and a transfer device 5. The transfer device 5 includes a transfer drum 5a as a recording material carrier, a transfer brush charger 5b as a transfer unit, an attraction roller 5g opposed to an attraction brush charger 5c for electrostatically adsorbing the recording material, and an inner charger 5d. A recording material carrying sheet 5f made of a dielectric is integrally formed in a cylindrical shape in a peripheral opening area of a transfer drum 5a which is rotatably driven and has an outer charger 5e and a transfer peeling sensor 5h. It is stretched. The recording material supporting sheet 5f uses a dielectric sheet such as a polycarbonate.

As the drum-shaped transfer device 5, that is, the transfer drum 5a is rotated, the toner image on the photosensitive drum 1 is transferred onto a recording material carried on a recording material carrying sheet 5f by a transfer brush charger 5b. You. When the transfer of the desired number of color toner images onto the recording material is completed, the recording material is separated from the transfer drum 5a by the separation claw 8a and the separation pushing roller 8
The toner image is separated by the action of b and the separation charger 5h, discharged to the tray 10 via the heat roller fixing device 9, and provided as a full-color image. A density sensor 22 detects the density of the sample formed on the recording material as described later, and provides the density to the CPU 213 in the image processing unit 35.
As a result, as will be described later in detail,
The creation and control of the UT 211 are performed.

On the other hand, the post-transfer photosensitive drum 1 is cleaned of residual toner on the surface thereof by a cleaning device 6 including a cleaning blade 6a and a squeeze sheet, and is subjected to an image forming process again.

Further, in order to prevent scattering of powder on the recording material carrying sheet 5f of the transfer drum 5a and adhesion of oil on the recording material, etc., the fur brush 14 and the recording medium carrying sheet 5f are used. The cleaning is performed by the action of the backup brush 15 facing 14. Such cleaning is performed before or after image formation, and is performed as needed when a jam (paper jam) occurs. [PWM Processing] Hereinafter, the operation of the PWM unit 212 in the present embodiment will be described in detail. In the PWM unit 212,
The 400-line PWM in which the tone reproducibility is important and the 800-line PWM in which the resolution is important are performed. Line PWM and 800 Line PWM
Are realized by different methods. FIG. 3 shows the configuration of the PWM unit 212, which will be described in detail below. In FIG. 3, reference numeral 703 denotes a 400-line PWM unit that performs pulse width modulation for 400 lines, and an image signal of an area determined by the area determination unit 216 as a photographic area is converted into 400-line image data such as 8 Sent in bit units. In the 400-line PWM unit 703, pulse width modulation is performed by a clock having the same cycle as the image signal obtained by dividing the clock from the oscillator 704 into two by the frequency dividing circuit 705. 400-line PWM unit 703
4 is shown in FIG. 8-bit image data is D
The D / A conversion is performed by the / A conversion circuit 801, and the triangular wave generation circuit 802 generates a triangular wave having the same cycle as the input clock for 400 lines. The offset generation circuit 804 is a circuit for giving an offset component to the triangular wave, and determines the offset amount using the volume 805. In the present embodiment, the image data 00h, that is, the pulse width of the minimum pulse can be determined by the offset adjustment. In addition, by dividing the output of the D / A conversion circuit 801 with the volume 803 for the 00h adjustment, the FFh adjustment for adjusting the image data FFh, that is, the pulse width of the maximum pulse width can be performed.

In this embodiment, the 400 line PWM 00
FIG. 5 shows the state of the / FF adjustment. Since the output of the D / A conversion circuit 801 at the image data 00h is constant, the minimum pulse width changes as indicated by 91 by changing the offset amount with the volume 805. That is, when the offset amount of the triangular wave is increased, the minimum pulse width is reduced.
Also, as shown in 92, D / A at the time of image data FFh
The maximum pulse width is adjusted by adjusting the output of the conversion circuit 801 with the volume 803. That is, the lower the FFh level, the narrower the maximum pulse width. in this way,
The comparator 806 compares the offset-adjusted triangular wave and the divided D / A output, thereby executing the 400-line PWM of the present embodiment.

In the present embodiment, by performing the 00 / FF adjustment as described above, the relationship between the amount of laser light and the image data is controlled to be linear. However, since the relationship between the amount of light and the actual output density is not linear, tone correction is further performed using a conversion table of the LUT 211 described later.

As described above, by appropriately performing the 00 / FF adjustment at the time of the 400-line PWM, it becomes possible to perform the pulse width modulation while appropriately maintaining the tone reproducibility.

When setting the minimum pulse width of 400 lines,
Although an example has been described in which the triangular wave has an offset component, the minimum pulse width can be similarly controlled by making the D / A output variable for image data of 00h, for example. -800 line PWM Next, 800 line PWM in the present embodiment will be described. Laser 4 by pulse generated by 800 line PWM
When driving the pulse No. 2, the pulses have a high frequency, that is, the individual pulse widths become narrow. Then, as described in the conventional example, it is difficult to reliably respond to the laser emission due to the emission characteristics of the laser 42. This problem cannot be solved by applying the 00 / FFh adjustment by volume adjustment or the like as described in the above-described 400-line PWM. Therefore, in the present embodiment, the minimum / maximum pulse width is adjusted by the LUT 21 so that an appropriate laser emission response can be obtained at all levels of image data even with 800-line PWM.
1 is performed. Hereinafter, the method will be described.

In FIG. 3, reference numeral 702 denotes an 800-line PWM unit for performing pulse width modulation for 800 lines, and an image signal of an area determined by the area determination unit 216 to be a character / thin line area is
The image data is transmitted, for example, in units of 8 bits as image data of 800 lines. Here, the image signal cycle is 400 lines P described above.
Since it is the same as the WM unit 703, the interpolation unit 210 interpolates at a cycle of an integral multiple (twice in this embodiment) to 800 dpi.
After passing through the LUT 211, pulse width modulation is performed. In the 800-line PWM unit 702, the oscillator 704
The pulse width modulation is performed at the same cycle as the clock from. 80
FIG. 6 shows a detailed configuration of the 0-line PWM unit 702. D / A
The conversion circuit 1001 performs D / A conversion of the interpolated image data, and the triangular wave generation circuit 1002 generates a triangular wave having the same cycle as the input 800-line clock. Then, the comparator 1003 compares the triangular wave and the D / A output to perform 800-line PWM.

Returning to FIG. 3, the 400-line PWM output and the 800-line PWM output obtained as described above are switched by the selector 706 by the 400/800 line switching signal from the area determination section 216 and output to the laser driver 41. Is done.

However, according to the above-described configuration of the 800-line PWM unit 702, the 800-line PWM does not have a linear relationship between the amount of laser light and image data such as 400 lines. Accordingly, in the present embodiment, the relationship between the entire range of image data (00h to FFh) and the actual output image density is detected, and the range of image data for which a linear relationship is obtained is applied to the entire image data range. It is characterized by the following. Hereinafter, the processing will be described. ● Gradation control at 800 lines FIG. 7 is a 4-limit chart showing how gradation is reproduced.
In the figure, a first quadrant shows a reader characteristic for converting a document density into a density signal, a second quadrant shows a characteristic of an LUT 211 for converting a density signal into a laser output signal, and a third quadrant.
The quadrant indicates a printer characteristic for converting the laser output signal to the output density, the fourth quadrant indicates the relationship between the original density and the output density,
That is, it shows a comprehensive gradation characteristic in the image processing apparatus. The number of gradations that can be expressed in the present embodiment is 256 gradations because the image signal is processed as an 8-bit digital signal. In the image processing apparatus of the present embodiment, in order to make the gradation characteristic shown in the fourth quadrant linear, the amount of distortion of the printer characteristic in the third quadrant is replaced by L in the second quadrant.
It is corrected by the UT 211. The LUT 211 is generated by a calculation described later. That is, the reader unit 10
0 is read by the LUT 211
After that, the signal is converted into a signal corresponding to the dot width by the PWM 212 and sent to the laser driver 41.

In this embodiment, a tone reproduction means using pulse width modulation processing is used. Then, a latent image having a gradation characteristic due to a dot area change is formed on the photosensitive drum 1 by laser scanning, and a gradation image is obtained through a process of development, transfer, and fixing. ● LUT control on 800 lines FIG. 8 shows an example using the reader unit 100 according to the present embodiment.
A flowchart of the gradation control on the 00 line is shown and described below.

First, in step S1201, when a start switch is turned on from an operation panel (not shown), the flow advances to step S1202, and the pattern generator 21
7, a sample pattern image of 256 gradations of the designated color as shown in FIG. 9 is formed on the recording material and printed out.

Next, in step S 1203, the printout sample is placed again on the platen glass 31 of the lead portion, illuminated by the light source 32, and
, The image signal of the printout sample is read. And step S12
At 04, the density sensor 22 detects the relationship between laser output and image density, that is, each pattern density in a 256-gradation pattern image, so as to correspond to the position coordinate information of the reader signal in the second quadrant of FIG. For example, RA
Take it into a memory such as M215. It is generally known that an optical system using a full-color sensor 34 using a CCD has good measurement reproducibility by performing shading correction.

Next, in step S1205, the LUT 211 is calculated and set using the density data of 256 gradations in the memory. Here, the 800 line PW of the present embodiment
In M, since the 00h adjustment is not performed, laser emission does not start unless the pulse width does not reach a certain value, in other words, if the image data does not reach a certain value or more. Therefore, in the printout sample shown in FIG. 9, the density is not reproduced up to image data of a certain density. Further, when the image data exceeds a certain value, the density to be reproduced is saturated and remains at a constant value. Therefore, in step S1205, the LUT 211 is set such that the image data value at which the density starts to be reproduced becomes 00h and the image data value at which the density is saturated becomes FFh. For example, when the relationship between the image data and the light amount that is the laser output is obtained with the characteristics shown in FIG. 12 shown in the conventional example, the laser output when the image data is 00h has the density actually reproduced. LU to be equivalent to 30h to start
T211 is set, and the laser output of FFh is set to B0h.
By setting the LUT 211 to be substantial, the relationship between image data and laser output can be kept linear.

Thus, in other words, the 800-line P
In the WM, the LUT 211 performs not only the gradation correction but also the 00 / FF adjustment. In the 800-line PWM of the present embodiment, by performing such gradation correction, the number of gradations that can be expressed is reduced as compared with the case of the above-described 400 lines. it can.

As described above, according to the present embodiment,
When the LUT is controlled based on the actually measured image density value for the resolution-oriented image data to be represented by 800 lines, the resolution is considered by considering the relationship between the image data and the output density to be linear. , And appropriate gradation reproducibility can be obtained. Furthermore, since the minimum and maximum pulse widths of 800 lines are also set by the LUT, there is no need to provide an adjustment mechanism for setting the minimum / maximum pulse width, and 800 line PWM adjustment can be performed at low cost.

<Other Embodiments> Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), a device including one device (for example, For example, the present invention may be applied to a copying machine, a facsimile machine, and the like.

An 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 implements 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, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, 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. ) May perform some or all of the actual processing, and the processing may realize 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.

[0066]

As described above, according to the present invention, a dedicated pulse width adjusting mechanism is provided by setting the minimum pulse width and the maximum pulse width in the high resolution area by using the LUT for performing gradation correction. Therefore, appropriate pulse width adjustment can be performed at low cost. Therefore, even when high-speed PWM is performed, the linearity in the relationship between the image data and the light amount can always be appropriately maintained, the appropriate gradation is maintained in the region where importance is placed on the gradation, and the resolution is maintained in the region where importance is placed on the resolution. In this way, it is possible to form appropriate images while maintaining the image quality.

[0067]

[Brief description of the drawings]

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

FIG. 2 is a functional block diagram of an image processing unit according to the embodiment.

FIG. 3 is a block diagram illustrating a configuration of a pulse width modulation unit according to the present embodiment.

FIG. 4 is a diagram illustrating a configuration of a 400-line pulse width modulation circuit according to the present embodiment.

FIG. 5 is a diagram for explaining setting of a minimum / maximum pulse width in 400-line pulse width modulation of the present embodiment.

FIG. 6 is a diagram illustrating a configuration of an 800-line pulse width modulation circuit according to the present embodiment.

FIG. 7 is a fourth-limit chart showing gradation reproducibility in the present embodiment.

FIG. 8 is a flowchart illustrating a tone correction process according to the embodiment.

FIG. 9 is a view showing a sample print output for gradation correction in the embodiment.

FIG. 10 is a diagram showing a configuration of a conventional pulse width modulation circuit.

FIG. 11 is a diagram for explaining conventional pulse width modulation processing.

FIG. 12 is a diagram showing the relationship between conventional image data and the amount of laser light.

[Explanation of symbols]

 211 LUT 212 PWM section 702 800-line PWM section 703 400-line PWM section 704 Oscillator 705 Divider circuit 706 Selector 801 and 1001 D / A converter 802 and 1002 Triangular wave generation circuit 803 and 805 Volume 804 Offset circuit 806 and 1003 Comparator

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 1/407 H04N 1/40 101E

Claims (28)

[Claims] An input unit for inputting image data; an area determining unit for determining first and second areas based on the image data; and a density correction for the image data of the first and second areas. First and second correction means for performing the following, first and second modulation means for modulating a pulse width based on the image data of the first and second areas, respectively, and the first and second modulation means Image forming means for forming an image based on the pulse width modulated by the means, wherein a minimum and a maximum pulse width are set in the first modulating means for the first area. An image processing apparatus, wherein the second correction unit sets minimum and maximum image data for the second area. 2. The image processing apparatus according to claim 1, wherein the first area is an image area where importance is placed on gradation, and the second area is an image area where importance is placed on resolution. apparatus. 3. The image processing apparatus according to claim 2, wherein in the image forming unit, the second area is formed with a higher resolution than the first area. 4. The apparatus according to claim 1, wherein the first and second correction means perform density correction on the image data of the first and second areas based on first and second conversion tables, respectively. Item 2. The image processing apparatus according to Item 1. 5. A pattern generating means for generating a predetermined gradation pattern; a density detecting means for detecting the density of the gradation pattern formed by the image forming means; The image processing apparatus according to claim 4, further comprising: a table creating unit that creates the second conversion table by using a table. 6. The image forming unit according to claim 1, wherein the first and second image forming units include:
A beam is generated based on the pulse width modulated by the modulating means, and an image is formed based on the exposure of the beam. The table creating means makes the relationship between the image data and the beam output substantially linear. The image processing apparatus according to claim 5, wherein the minimum and maximum values of the image data are set as described above. 7. The image forming unit according to claim 1, wherein the first and second image forming units include:
A beam is generated based on the pulse width modulated by the modulating means, and an image is formed based on the exposure of the beam. The first modulating means generates a first reference signal having a predetermined period. A signal generation unit; an analog conversion unit configured to convert the image data into an analog signal to generate an analog signal; a comparison unit configured to compare the first reference signal with the analog signal; 2. The image processing apparatus according to claim 1, further comprising setting means for setting the minimum and maximum pulse widths so that the relationship becomes substantially linear. 8. The setting means includes: adding means for adding an offset value to the first reference signal to set a minimum pulse width; and attenuating means for attenuating the analog signal to set a maximum pulse width. The image processing apparatus according to claim 7, comprising: 9. A minimum value setting means for setting a minimum value of the analog signal to set a minimum pulse width, and an attenuating means for attenuating the analog signal to set a maximum pulse width. The image processing apparatus according to claim 7, comprising: 10. The second modulating means includes: a reference signal generating means for generating a second reference signal having a predetermined period; an analog converting means for converting the image data into an analog signal to generate an analog signal; 2. The image processing apparatus according to claim 1, further comprising a comparing unit that compares a reference signal with the analog signal. 11. An interpolating means for interpolating image data so that an image period in the second area is an integral multiple of the first area, wherein the second correcting means comprises: 2. The image processing apparatus according to claim 1, wherein a density correction is performed on the image data interpolated by (1). 12. The image processing apparatus according to claim 11, wherein the interpolation unit interpolates the image data so that a resolution of an image cycle in the second area is twice as large as that of the first area.
The image processing apparatus according to any one of the preceding claims. 13. The image processing apparatus according to claim 12, wherein said interpolating means interpolates image data of said second area input at an image cycle of said first area. 14. An input step of inputting image data; an area determining step of determining first and second areas based on the image data; and an image of the first area based on a first conversion table. A first correction step of performing density correction on data; and a first step of setting a minimum and a maximum pulse width and modulating the pulse width based on the corrected image data of the first area.
A second correction step of performing density correction on image data of the second area based on a second conversion table in which minimum and maximum image data are set; and an image of the second area. A second modulation step of modulating a pulse width based on data; and an image forming step of forming an image based on the pulse width modulated by the first and second modulation steps. Image processing method. 15. The image processing apparatus according to claim 14, wherein the first area is an image area where importance is placed on gradation, and the second area is an image area where importance is placed on resolution. Method. 16. The image forming process according to claim 16, wherein:
16. The image processing method according to claim 15, wherein the region is formed with a higher resolution than the first region. 17. A pattern forming step of forming a predetermined gradation pattern on a recording medium, a pattern reading step of reading a recording medium on which the gradation pattern is formed, and a density of the read gradation pattern. 15. A density detecting step of detecting the density pattern, and a table generating step of generating the second conversion table based on the density of the gradation pattern detected in the density detecting step. The image processing method described in the above. 18. In the image forming step, a beam is generated based on the pulse width modulated by the first and second modulation steps, and an image is formed based on the exposure of the beam. 18. The image processing method according to claim 17, wherein in the step, a minimum value and a maximum value of the image data are set such that a relationship between the image data and the beam output becomes substantially linear. 19. In the image forming step, a beam is generated based on the pulse width modulated by the first and second modulation steps, and an image is formed based on the exposure of the beam. 15. The image processing method according to claim 14, wherein in the modulating step, the minimum and maximum pulse widths are set so that the relationship between the image data and the beam output becomes substantially linear. 20. An interpolation step of interpolating image data such that an image cycle in the second area is an integral multiple of the first area, and in the second correction step, 15. The image processing method according to claim 14, wherein density correction is performed on the image data interpolated in the step. 21. A computer-readable memory storing a program code for image processing, wherein: a code for an input step of inputting image data; and an area discrimination for discriminating first and second areas based on the image data. A code of a step, a code of a first correction step for performing density correction on the image data of the first area based on the first conversion table, and an image data of the first area after the correction. Modulate the pulse width by setting the minimum and maximum pulse width
A code of a modulation step of: a code of a second correction step of performing density correction on image data of the second area based on a second conversion table in which minimum and maximum image data are set; A code for a second modulation step of modulating the pulse width based on the image data of the area, and a code for an image formation step of forming an image based on the pulse widths modulated by the first and second modulation steps. , A computer readable memory. 22. An input unit for inputting image data, a correction unit for performing density correction on the image data, and comparing the image data corrected by the correction unit with a first pattern signal of a predetermined cycle. And a pulse for selectively outputting a second pulse width modulation signal generated by comparing the generated first pulse width modulation signal with the second pattern signal having a different period from the first pattern signal. Width modulation means; and adjustment means for adjusting a dynamic range of the first pattern signal. In the pulse width modulation processing by the first pattern signal,
The relative signal level between the image data and the first pattern signal is adjusted by adjusting the first pattern signal by the adjusting means, and the pulse width modulation process by the second pattern signal is performed by the correcting means. An image processing apparatus, wherein a relative signal level between the image data and the second pattern signal is adjusted by correcting the image data. 23. The image processing apparatus according to claim 22, wherein a cycle of the first pattern signal is longer than a cycle of the second pattern signal. 24. The image processing apparatus according to claim 22, further comprising image forming means for forming an image based on the pulse width modulation signal output by said pulse width modulation means. 25. The image processing apparatus according to claim 25, further comprising: a determination unit configured to determine an image tone of the image data input by the input unit, wherein the pulse width modulation unit performs the first pulse width modulation according to an output of the determination unit 23. A signal according to claim 22, wherein the signal and the second pulse width modulation signal are selectively output.
The image processing apparatus according to any one of the preceding claims. 26. The image processing apparatus according to claim 26, wherein the correction unit includes a first conversion table for image data pulse-width modulated by the first pattern signal, and a first conversion table for image data pulse-width modulated by the second pattern signal. 23. The image processing apparatus according to claim 22, further comprising a second conversion table having a different correction characteristic from the conversion table. 27. A pattern generating means for generating a predetermined gradation pattern; a density detecting means for detecting the density of the gradation pattern formed by the image forming means; 27. The image processing apparatus according to claim 26, further comprising: a table creating unit that creates the second conversion table by using the table. 28. An inputting step of inputting image data, a correcting step of performing density correction on the image data, and comparing the image data corrected by the correcting step with a first pattern signal of a predetermined period. And a pulse for selectively outputting a second pulse width modulation signal generated by comparing the generated first pulse width modulation signal with the second pattern signal having a different period from the first pattern signal. A width modulation step; and an adjustment step of adjusting a dynamic range of the first pattern signal. In the pulse width modulation processing using the first pattern signal,
The relative signal level between the image data and the first pattern signal is adjusted by adjusting the first pattern signal in the adjusting step, and in the pulse width modulation process using the second pattern signal, An image processing method, comprising: adjusting a relative signal level between the image data and the second pattern signal by correcting the image data.