JPH08265520A - Image forming device - Google Patents

Abstract

PURPOSE: To properly correct the image data despite of the different modulation systems by correcting the image data based on the γdata stored in response to every modulation system after it is indicated whether the image data show the binary images or the multilevel images. CONSTITUTION: The γ data used for the binary or multilevel images which are read out of a ROM 31a of a main control part 31 are supplied and stored into a conversion table part 51 of an image output part 46 via a secondary control part 33 in response to the binary or multilevel image processing mode respectively. Then the image data obtained by converting the image data supplied from an image expansion part are outputted to a pulse modulation circuit 52 according to the contents of the stored γ data. Thereby, the proper γ correction is applied to the image data regardless of a pulse width modulation system of every pixel that is used for the binary images or a pixel connection type pulse width modulation system that is used for the multilevel images.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image from a digital image signal.

[0002]

2. Description of the Related Art A digital copying machine is composed of a scanner section and a printing section, and its printing is the same as that of a laser beam printer. A semiconductor laser is used as a light source to directly modulate image data to be recorded into image data. The laser light output is horizontally scanned by the polygon mirror. Then, the image data is written as an electrostatic latent image on the photosensitive drum that rotates at a low speed. To briefly explain the printing process, first,
The photoconductor drum is uniformly charged by the charger. When the laser light is irradiated onto the area, the electric charge is removed from the area exposed to the light. This is an electrostatic latent image. A charged toner is attached to this by electrostatic force to form a visible image. Next, the transfer device applies an electric field from the back surface of the paper to transfer the visible image on the photoconductor drum to the paper. Finally, heat and pressure are applied by the fixing device to fix the toner image on the paper.
Printing is performed by repeating the above process.

In a digital copying machine, there are an area gradation method and a density gradation method as a method of reproducing the halftone of one pixel. The area gradation method expresses gradation by changing the area of the toner adhering to each pixel, and the density gradation method changes the toner density adhering to one pixel in order to faithfully reproduce the original density. To express gradation.

Among them, the pulse width modulation method for realizing the area gradation method is proportional to the density per pixel of the original read by the scanner unit while keeping the laser light output from the laser diode as the semiconductor laser constant. Then, the gradation is expressed by modulating the corresponding pulse width, that is, the exposure time (see FIG. 7). For example, processing is performed using a pulse width modulation circuit capable of controlling each pixel every 1/256 of one pixel period.

In this system, since the surface potential of the photosensitive drum is brought into a saturated state when the laser light output is in the ON state, it is hard to be influenced by the change of the laser light output by the temperature and the change of the sensitivity of the photosensitive drum. It is excellent in stability, and multivalued one pixel can be performed relatively easily. The circuit configuration can be relatively simplified.

However, even if a pulse width modulation circuit capable of obtaining an ideal pulse width by performing pulse width modulation can be produced, the laser diode is driven using the signal, but the actual circuit is used. However, because of the influence of the frequency response of the laser driver circuit and the limit value of the size of the laser spot system, pulse width modulation is not performed as an accurate area gradation of one pixel.

Therefore, the exposure time of the laser beam to the photosensitive drum and the toner adhesion amount (output density) do not have a linear relationship but a non-linear curve (this curve is called a γ curve. This relationship is also a γ characteristic. : See FIG. 8). In order to ensure this linearity, it is necessary to make the exposure time corresponding to the output density data, that is, the relationship between the pulse widths non-linear to correct.

Due to the above problem, when the target value of the number of gradations is set to 256 gradations, for example, 2 pixels are obtained by one pixel pulse width modulation.
It is difficult to express 56 gradations, and it is necessary to perform gradation processing in combination with other pseudo halftone processing. In this case, the number of gradations depends on the pseudo halftone processing, and the gradation processing of the printer section can reinforce it and perform the pseudo halftone expression to alleviate the problem.

Pulse width modulation in units of one pixel (front reference (left side reference) position control for each pixel: FIG. 9A and FIG.
0 (see (a) and (b)), gradation can be expressed without lowering the resolution when considering a small area, but when viewing the entire surface image such as halftone, the intermediate exposure is performed. Since there are many parts, the density unevenness is conspicuous due to the influence of process conditions.

As means for correcting this, the rise of the laser spot is sharpened to reduce the intermediate exposure area, and pixel combination type pulse width modulation (reference position control of adjacent two pixels, that is, front reference (left reference) and rear reference) is performed. The position control of the reference (right side reference) is alternately performed for each pixel: (b) of FIG. 9 and (a) and (b) of FIG. 11) are performed to reduce the intermediate exposure area to reduce the density unevenness. Things are possible. However, in this case, there is a drawback that the apparent resolution is lowered.

Therefore, in the digital copying machine, when the image read by the scanner is a character image, the characteristics of the two modulation systems, that is, the one-pixel unit pulse width modulation system and the pixel combination type pulse width modulation system are utilized. The one-pixel unit pulse width modulation method is used, and in the case of a photographic image, the pixel combination type pulse width modulation method is used.

However, the output image densities using both the one-pixel unit pulse width modulation method and the pixel combination type pulse width modulation method are the same when the laser exposure time, that is, the pulse width, is used for laser exposure. Despite that, they are different when compared. This is because the ratio of the intermediate exposure area to the photosensitive drum is lower in the pixel combination type pulse width modulation method than in the one pixel unit pulse width modulation method.

In order to output a stable halftone density, the printing section must ensure linearity in the output density of the image data from the scanner section. That is, it is necessary to make the relationship between the pulse widths corresponding to the image data non-linear and correct. In the case of the 1-pixel unit pulse width modulation system, see A in FIG. 12, and in the case of the pixel combination type pulse width modulation system, see B in FIG.

Therefore, whether the pulse width modulation method of one pixel unit used in the case of a binary image or the pixel combination type pulse width modulation method used in the case of a multi-valued image is used, an appropriate γ What can be corrected is demanded.

[0015]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks, and even if a pulse width modulation method of one pixel unit used in the case of a binary image is used, a pixel combination used in the case of a multivalued image is used. Type pulse width modulation method,
An object of the present invention is to provide an image forming apparatus capable of performing proper γ correction.

[0016]

An image forming apparatus of the present invention forms an image by using a generating means for generating a laser beam according to image data, and whether the image data is a binary image or a multi-valued image. Instructing means for instructing, the first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the pulse width modulation method for one pixel used in the case of a binary image, and the multivalued image A memory for storing second γ data different from the first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the image data for the pixel combination type pulse width modulation method used in Means for correcting a binary image by the instructing means, the image data is corrected by the first γ data stored in the storage means, and the instructing means displays a multivalued image. In the meantime, a correction means for correcting the image data by the second γ data stored in the storage means, and a pulse signal having a pulse width corresponding to the image data corrected by the correction means are output. The output means and the control means for generating the laser beam by the generation means for a time corresponding to the pulse signal output by the output means.

The image forming apparatus of the present invention forms an image by using a generating means for generating a laser beam according to the image data, and supplies the image data of either a binary image or a multivalued image. Means for instructing whether the image data supplied by the supplying means is a binary image or a multi-valued image, and the density indicated by the image data for the pulse width modulation method of one pixel unit used in the case of a binary image and the density The first γ such as conversion data with the exposure time corresponding to
Data and second γ data different from the first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the image data for the pixel combination pulse width modulation method used in the case of a multi-valued image And a storage unit that stores the image data when the binary image is instructed by the instruction unit, the image data supplied by the supply unit is corrected by the first γ data stored in the storage unit, A correction means for correcting the image data received by the receiving means by the second γ data stored in the storage means when the multivalued image is instructed by the instructing means. Output means for outputting a pulse signal having a pulse width corresponding to the image data, and a time corresponding to the pulse signal output by the output means for the laser by the generating means. And a control means for generating the over arm.

The image forming apparatus of the present invention forms an image by using a generating means for generating a laser beam according to the image data, and the image data is a binary image having no gradation such as characters or a photograph. A first means such as instruction means for instructing whether the image is a multi-valued image having gradations, conversion data of the density indicated by the image data for the one-pixel unit pulse width modulation method used in the case of a character image, and the exposure time corresponding thereto Second γ data different from the first γ data such as conversion data of the density of the image data and the exposure time corresponding to the γ data of the pixel combination type pulse width modulation method used for the photographic image. When a character image is instructed by the storage means for storing data and the instructing means, the image data is corrected by the first γ data stored in the storage means, Correction means for correcting the image data by the second γ data stored in the storage means when a photographic image is designated by the correction means, and a pulse width corresponding to the image data corrected by the correction means. It is composed of output means for outputting a pulse signal and control means for causing the generation means to generate a laser beam for a time corresponding to the pulse signal output by the output means.

The image forming apparatus of the present invention forms an image by using a generating means for generating a laser beam according to image data. Supplying means for supplying any image data of a certain multi-valued image, instructing means for instructing whether the image data supplied by the supplying means is a binary image or a multi-valued image, one pixel unit used in the case of a binary image Image data for the pixel combination pulse width modulation method used in the case of a multivalued image and the first γ data such as conversion data of the density indicated by the image data for the pulse width modulation method and the corresponding exposure time. Is stored by the storage means for storing the first γ data different from the first γ data such as the conversion data of the density indicated by and the corresponding exposure time,
When the value image is instructed, the image data supplied by the supplying means is corrected by the first γ data stored in the storage means, and the multivalued image is instructed by the instructing means. At this time, the image data received by the receiving means is stored in the storage means.
Correction means for correcting the .gamma. Data, output means for outputting a pulse signal having a pulse width corresponding to the image data corrected by the correction means, and time corresponding to the pulse signal output by the output means, the generating means. And a control means for generating a laser beam.

The image forming method of the present invention forms an image by generating a laser beam according to image data. In the image forming method, a binary image having no gradation such as characters or a multivalue having gradation such as a photograph is used. If any of the image data of the image is supplied and the supplied image data is a binary image,
The image data is corrected by the first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the image data for the pulse width modulation method for each pixel, or the supplied image data is multi-valued. In the case of image data, the image data is second γ data different from the first γ data such as conversion data of the density indicated by the image data for the pixel combination type pulse width modulation method and the exposure time corresponding thereto. The pulse signal having the pulse width corresponding to the corrected image data is output, and the laser beam is generated for the time corresponding to the output pulse signal.

[0021]

According to the present invention, an image is formed by using a generating means for generating a laser beam in accordance with image data, and the indicating means indicates whether the image data is a binary image or a multi-valued image. The first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the pulse width modulation method of one pixel unit used in the case The second γ data different from the first γ data such as the conversion data of the density indicated by the image data for the width modulation method and the exposure time corresponding thereto is stored in the storage means, and the second γ data is stored by the instruction means.
When the value image is instructed, the image data is corrected by the first γ data stored in the storage means, and when the instructing means is instructing the multivalued image, the image data is corrected. Is corrected by the second γ data stored in the storage means, and output means for outputting a pulse signal having a pulse width corresponding to the corrected image data, and a pulse signal output by the output means The laser beam is generated by the generating means for a corresponding time.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view showing the internal structure of a digital copying machine as an image processing apparatus. That is, the digital copying machine includes a scanner unit 1 for optically reading the image information of the original O, and a printer engine for outputting an image read by the scanner unit 1 onto a recording material, that is, a copy sheet P ( The printing section) 2 is provided.

In the scanner unit 1, the original to be copied is placed on the original placing table 3, and the original O placed on the original placing table 3 is fluorescent as a light source extending in the sub-scanning direction. The reflected light from the original O illuminated by the lamp 4 and illuminated by the fluorescent lamp 4 is photoelectrically converted by the CCD sensor 5 as a photoelectric conversion element, and image information is converted into an image signal by the reflected light. Above fluorescent lamp 4
A reflector 6 for efficiently focusing the illumination light from the fluorescent lamp 4 on the original O is disposed on the side of the original O, and the original O is interposed between the fluorescent lamp 4 and the CCD sensor 5. From the above to the CCD sensor 5,
That is, a plurality of mirrors 7, 8, 9 for bending the optical path through which the reflected light from the original O passes and a lens 10 for converging the reflected light on the light collecting surface of the CCD sensor 5.
Are arranged.

The optical system for guiding the reflected light from the exposure lamp 4 and the original O to the CCD sensor 5 includes carriages 11 and 12.
And is conveyed in the main scanning direction by a pulse motor (not shown). The fluorescent lamp 4 illuminates the area of the original O in the sub-scanning direction, and the carriages 11 and 12 are moved in the main scanning direction to illuminate the areas of the original O in the sub-scanning direction one after another so that the entire area of the original O is covered. It will be illuminated by the fluorescent lamp 4.

On the upper part of the document placing table 3, there is arranged a document cover 13 for bringing the document O into close contact with the document placing table 3.
The pressing of the original O can be replaced with, for example, an SDF, that is, a semi-automatic document feeder, or an ADF, that is, an automatic document feeder, depending on the size of the digital copying machine or the copying capability.

The image forming portion as the printer engine 2 is provided with a photosensitive drum 14 which is cylindrical and is rotated in a desired direction via a motor (not shown) and charged to a desired potential. . When the photosensitive drum 14 is irradiated with the laser beam, the potential of the region irradiated with the laser beam is changed, and an electrostatic latent image is formed on the photosensitive drum 14.

Around the photosensitive drum 14, a charging device 15 for applying a desired electric potential to the photosensitive drum 14, a laser unit 16 for outputting a laser beam modulated to the photosensitive drum 14 according to image data, A developing device 17 that supplies a visualization agent, that is, toner to the electrostatic latent image formed on the photoconductor drum 14 by the laser beam from the laser unit 16 to develop the latent image, and the photoconductor drum 14 developed by the developing device 17. The recording material fed from the recording material feeding unit, which will be described later, the visualized toner image of
That is, a transfer device 18 for transferring the copy paper P and a peeling device 19 for peeling the copy paper P from the photosensitive drum 14 are arranged.

The laser unit 16 includes a semiconductor laser oscillator 24 for generating a laser beam, and a polygon mirror 25 for converting the laser beam supplied from the semiconductor laser oscillator 24 through a collimator lens (not shown) into a beam for each line. An fθ lens 26 that changes the laser beam from the polygon mirror 25 into parallel light for each scanning line, a mirror 27 that reflects the parallel light from this lens 26 and guides it to the photosensitive drum 14, and the polygon mirror 25 are rotated. It is configured by a mirror motor 28 that operates.

On the downstream side of the peeling device 19 in the rotation direction of the photoconductor drum 14, the toner remaining on the surface of the photoconductor drum 14 of the photoconductor drum 14 is removed and the photoconductor drum 14 is irradiated by the laser beam. A cleaner unit 20 for erasing the potential change generated above for the next image formation.
Is arranged.

A recording material is fed between the developing device 17 and the transfer device 18 so as to feed the copy paper P onto which the toner image formed on the photosensitive drum 14 is transferred, toward the transfer device 18. The part 21 is arranged. In addition, the transfer device 18
A fixing device 22 for fixing the toner image on the copy sheet P is provided in the direction in which the copy sheet P on which the toner image is transferred is separated from the photoconductor drum 14. Between the fixing device 22 and the transfer device 18, a carrying device 23 for carrying the copy paper P toward the fixing device 22 is arranged.

In such a digital copying machine, an image is processed by the control system shown in FIG. 3, and the control of the image processing is executed. In FIG. 3, reference numeral 31 is a main control unit that controls the present digital copying machine. The main control unit 31 is connected to four sub-control units 32 to 34 that control the respective units, and the main control unit 31 manages an operation panel 35 that issues various image processing instructions and an image processing area. The area management unit 36 is connected to an image processing unit 37 including an image quality improvement unit that improves the image quality of the captured image data, an image editing unit that edits the image data, and an image processing unit that processes the image data, and controls these. are doing. Further, the main controller 31 is connected to a buffer 38 that temporarily stores image data.

The sub-control unit 32 controls a light source control unit 40 for controlling the light source intensity of the fluorescent lamp 4, a mechanism driving unit 42 for controlling a mechanical input unit mechanism 41 such as the sheet feeding mechanism shown in FIG.
Connected to an A / D converter 43 that converts the analog image data converted by the CCD sensor 5 that detects reflected light rays and converts the image into image data, and a correction unit 44 that corrects the image signal such as shading. Is
It controls these. The light source control unit 40 is connected to the exposure lamp 4 which is a light source, the light intensity of the exposure lamp 4 is controlled, and the mechanism driving unit 42 is connected to the input unit mechanism 41 such as a pulse motor for moving the carriage. The pulse motor is driven. Therefore, the entire area of the document O is illuminated with appropriate illumination light.

The sub-control unit 33 expands the edited or processed image data for image formation, and stores the image data in the image expansion unit 45 and the image data from the image expansion unit 45 (image data from the scanner). ) Is output as a pulse signal (image data for a printer) as a laser modulation signal to realize halftone reproduction by the area gradation method, a drive system for a motor, a solenoid, etc. in the laser unit 16. Is connected to and controls a mechanism driving unit 49 that drives the output unit mechanism 48.

The sub-control unit 34 is connected to the data transmission / reception unit 50 and controls data transmission / reception with an external device. The main controller 31 has a ROM (Read Only Memory) 31a built therein. In the ROM 31a, the first γ data (conversion data of the density indicated by the image data and the exposure time corresponding thereto) for the pulse width modulation method of one pixel unit used in the case of a binary image having no gradation such as characters. Etc.) as a binary image conversion table of the actual image density for the image data, and the first γ data for the pixel combination type pulse width modulation method used in the case of a multi-valued image with gradations such as photographs. Two tables are registered, which are conversion tables for multivalued images of actual image densities for different image data as the second γ data. The image data is expressed in 256 levels from code value 00H to code value FFH corresponding to the density.

The above-mentioned multi-valued image processing or binary image processing is switched depending on whether this device is used in the copying machine mode (designation of multi-valued image processing) or the printer mode (designation of binary image processing) ( For example, an instruction is given from the operation panel 35).

In the above-mentioned digital copying machine, the original O is illuminated by the fluorescent lamp 4, and the reflected light beam reflected from the original O is imaged on the CCD sensor 5 and converted into an analog electric signal. This analog image signal is converted into a digital signal by the A / D conversion unit 43 and supplied to the correction unit 44 for shading correction. In this correction unit 44, the shading-corrected image signal is temporarily stored in the buffer 38 and output to the image processing unit 37.

The operation of the above arrangement will be described below. In the image processing unit 37, the image quality of the image signal from the buffer 38 is improved by an image improving unit (not shown), the improved image signal is edited by using an image editing unit (not shown), and the edited image signal is edited. The processed image signal is processed by an image processing unit (not shown), and the image development unit 45
Is output to

As shown in FIG. 1, the image output section 46 is composed of a conversion table section 51, a pulse width modulation circuit 52, a laser driver 53, an auto power controller 54, and a reference voltage setting circuit 55.

The conversion table section 51 is composed of a memory such as a RAM and is composed of a binary image γ data or a multi-valued image read from the ROM 31a of the main control section 31 according to the binary image processing or the multi-valued image processing. The image γ data is supplied and stored via the sub-control unit 33, and the stored γ data is stored.
According to the content of the data, the image data supplied from the image developing unit 45 (image density data represented by 8 bits per pixel of the original document) is converted and output. The image data output from the conversion table unit 51 is supplied to the pulse width modulation circuit 52.

The pulse width modulation circuit 52 includes a main controller 3
1. Image data supplied from the conversion table unit 51 according to the positioning selection signal, the clock, and the reference data supplied from the sub-control unit 33 (image density data represented by 8 bits per pixel of the original document) Is modulated into a pulse signal having a pulse width corresponding to the image data value (exposure time corresponding to image density data). The pulse width of the pulse signal increases in proportion to the increase in the image density data, and each pixel is controlled every 1/256 of one pixel period. The pulse signal output from the pulse width modulation circuit 52 is supplied to the laser driver 53.

In this case, in the case of a binary image, the positioning selection signal for each pixel is based on the left side reference, and a pulse signal as shown in FIG. 10 (a) is output.

Further, in the case of a multi-valued image, the left side reference and the right side reference are alternated in the positioning selection signal for each pixel, and a pulse signal as shown in FIG. 11 (a) is output. Has become.

Therefore, when the γ data for the binary image is supplied to the conversion table section 51, as shown in FIG. 4A, the image density D1 of the image data supplied to the conversion table section 51 is changed. On the other hand, a pulse signal with a pulse width t2 is output from the pulse width modulation circuit 52, and a pulse signal with a pulse width t4 is output from the pulse width modulation circuit 52 with respect to the image density D2 of the image data supplied to the conversion table unit 51. Is output, and the pulse signal having the pulse width t6 is output from the pulse width modulation circuit 52 with respect to the image density D3 of the image data supplied to the conversion table unit 51.

Further, when the γ data for the multivalued image is supplied to the conversion table section 51, as shown in FIG. 4B, the image density D1 of the image data supplied to the conversion table section 51 is changed. On the other hand, a pulse signal of pulse width t1 is output from the pulse width modulation circuit 52, and the image density D2 of the image data supplied to the conversion table unit 51 is
The pulse width modulation circuit 52 outputs a pulse signal having a pulse width t3, and the pulse width modulation circuit 52 outputs a pulse signal having a pulse width t5 with respect to the image density D3 of the image data supplied to the conversion table section 51. It

The laser driver 53 drives the laser diode 24 with the voltage value supplied from the auto power controller 54 for a period (time) corresponding to the pulse width of the pulse signal supplied from the pulse width modulation circuit 52. Yes (supply drive current to laser diode 24)
Thus, a laser beam having a desired beam diameter is generated for a period corresponding to the pulse signal.

That is, as shown in FIG. 7, by changing the laser output period with a pulse signal corresponding to the image density to be printed for one dot width of the image to be printed, the toner adhering to each pixel is The area is changed (area gradation) to express gradation.

The auto power controller 54 supplies a power supply voltage corresponding to a reference voltage from the reference voltage setting circuit 55 and a monitor output output from a monitor diode (not shown) of the laser diode 24 to the laser. It is supplied to the driver 53. Even if the ambient temperature changes due to feedback of the monitor output, a constant laser beam can be output.

The reference voltage setting circuit 55 includes the main controller 3
1 outputs a different reference voltage to the auto power controller 54 depending on whether the binary image processing or the multi-valued image processing indicated by the control signal supplied from the sub-control unit 33. This is for setting the drive current in the vicinity of the oscillation start current so that the laser driver 53 can rapidly oscillate the laser diode 24.
The reference voltage corresponding to the binary image processing is lower than the reference voltage corresponding to the multivalued image processing. The intensity of the laser beam from the laser diode 24 can be changed by the reference voltage.

As shown in FIG. 5, the pulse width modulation circuit 52 has an input circuit 61, a ramp wave generator 62, a reference generator 63, a register 64, a digital-analog converter 65, an inverter circuit 66, and a comparator 67. , And an output circuit 68.

The input circuit 61 generates various timing signals corresponding to the left side reference, the right side reference, or the center reference according to the positioning selection signal and the clock supplied from the sub control unit 33. These timing signals are supplied to the ramp wave generator 62, the reference generator 63, the register 64, and the output circuit 68.

The ramp wave generating section 62 is the input circuit 61.
(A) of FIG. 6 according to the timing signal supplied from
A ramp wave as shown in (d) is generated. The ramp wave from the ramp wave generator 62 is supplied to the comparator 67.

The reference generator 63 has a configuration shown in FIG.
A reference signal as reference data supplied from the sub control unit 33 as shown in (d) is generated according to the timing signal supplied from the input circuit 61. The reference signal from the reference generator 63 is supplied to the comparator 67.

The register 64 is responsive to the timing signal supplied from the input circuit 61 to convert the conversion table section 51.
Image data (8-bit digital value: code) supplied from The image data stored in the register 64 is supplied to the digital-analog converter 65.

The digital-analog converter 65 converts the digital image data supplied from the register 64 into analog image data. The analog image data output from the digital-analog converter 65 is inverted by the inverter circuit 66 and then supplied to the comparator 67.

The comparator 67 compares the ramp wave from the ramp wave generator 62 with the reference signal from the reference generator 63 to determine the rising edge (first of the dot clock period) of the output pulse, and the digital signal is output. -The falling edge of the output pulse is determined by comparing the image data supplied from the analog conversion section 65 via the inverter circuit 66 with the reference signal from the reference generation section 63, and these determined rising edges are determined. And a pulse generated by the falling edge. The pulse signal output from the comparison unit 67 is supplied to the output circuit 68.

The output circuit 68 outputs the pulse signal supplied from the comparison section 67 according to the timing signal supplied from the input circuit 61. This output circuit 6
The pulse signal output from 8 is supplied to the laser driver 53.

The comparing section 67 is shown in FIG. 5 and FIG. 6 (b).
As shown in (e), it is composed of a comparator 71, a comparator 72, and an FF circuit 73. The comparator 71 is
The ramp wave from the ramp wave generator 62 is compared with the reference signal from the reference generator 63, and when the ramp wave crosses the reference signal (point a in (a) and (d) of FIG. 6), “H It outputs a "level signal", and this output is supplied to the clock terminal of the FF circuit 73.

The comparator 72 compares the image data supplied from the digital-analog converter 65 via the inverter circuit 66 with the reference signal from the reference generator 63, and when the ramp wave crosses the image data ( Figure 6
(Points b) shown in (a) and (d)), an "H" level signal is output, and this output is supplied to the reset terminal of the FF circuit 73.

The FF circuit 73 rises by the signal from the comparator 71 and falls by the signal from the comparator 72.
It outputs a pulse signal as shown in (c) and (f) of FIG.

First, the binary (character) image processing as the print mode will be described. That is, the print mode (binary image processing) is instructed by the operation panel 35, and the print data from the external device is supplied to the data transmitting / receiving unit 50.

As a result, the main control section 31 has the ROM 31a.
The γ data for the binary image is read from and output to the conversion table unit 51 in the image output unit 46 via the sub-control unit 33. Further, the main control unit 31 sends a positioning selection signal (a signal indicating the left reference) corresponding to the binary image processing via the sub control unit 33 to the pulse width modulation circuit 52 in the image output unit 46.
Output to.

Therefore, the conversion table unit 51 stores the γ data for the binary image. Further, the main control unit 31 outputs the print data supplied to the data transmitting / receiving unit 50 to the conversion table unit 51 of the image output unit 46 via the buffer 38, the image processing unit 37, and the image developing unit 45.

As a result, the conversion table section 51 converts the supplied image data using the γ data for the binary image and outputs it to the pulse width modulation circuit 52. The pulse width modulation circuit 52 modulates a pulse signal on the left side having a pulse width corresponding to the image data value of the supplied image data, and outputs the pulse signal to the laser driver 53. The laser driver 53 uses the voltage value supplied from the auto power controller 54 for a period (time) corresponding to the pulse width of the supplied pulse signal,
The laser diode 24 is driven.

An image is formed on the sheet P in the image forming section by using the laser beam generated by the laser diode 24. Further, multi-valued (photo) image processing in the copying machine mode will be described.

That is, the copying machine mode (multi-valued image processing) is instructed through the operation panel 35, other copying conditions are set, the original O is placed on the original placing table 3, and the copy key is turned on. As a result, the main control unit 31 is
The γ data for the multivalued image is read from a and output to the conversion table unit 51 in the image output unit 46 via the sub control unit 33. Further, the main control unit 31 outputs a positioning selection signal (alternately outputs a signal indicating a left side reference and a signal indicating a right side reference) corresponding to multi-valued image processing to a pulse in the image output unit 46 via the sub control unit 33. Output to the width modulation circuit 52.

Therefore, the conversion table section 51 stores the γ data for the multivalued image. Further, the main control section 31 controls the exposure lamp 4, the input section mechanism 41, the CCD sensor 5 and the like to read the original O. The analog image signal converted by the CCD sensor 5 is converted into digital image data by the A / D conversion unit 43, and then the image is passed through the correction unit 44, the buffer 38, the image processing unit 37, and the image expansion unit 45. It is output to the conversion table unit 51 of the output unit 46.

As a result, the conversion table section 51 converts the supplied image data by using the γ data for the multivalued image and outputs it to the pulse width modulation circuit 52. The pulse width modulation circuit 52 alternately modulates, for each pixel, a left reference pulse signal and a right reference pulse signal having a pulse width corresponding to the image data value of the supplied image data, and outputs the pulse signal to the laser driver 53. The laser driver 53 drives the laser diode 24 with the voltage value supplied from the auto power controller 54 for a period (time) corresponding to the pulse width of the supplied pulse signal.

An image is formed on the paper P in the image forming section by using the laser beam generated by the laser diode 24. As described above, the γ data used in the processing of a binary image having no gradation such as characters and the processing of a multi-valued image having gradation such as a photograph is changed.

As a result, an appropriate pulse width modulation method for each pixel, which is used for a binary image, or a pixel combination type pulse width modulation method used for a multivalued image is used. γ correction can be performed.

[0070]

As described above, even when the pulse width modulation method for each pixel used in the case of a binary image is used, the pixel combination type pulse width modulation method used in the case of a multi-valued image is used. Even in such a case, it is possible to provide an image forming apparatus capable of performing proper γ correction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image output unit of a digital copying machine for explaining an embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of a digital copying machine.

FIG. 3 is a block diagram showing a schematic configuration of a control system of a digital copying machine.

FIG. 4 is a diagram for explaining characteristics of pulse width with respect to image density.

FIG. 5 is a block diagram showing a schematic configuration of a pulse width modulation circuit.

FIG. 6 is a diagram for explaining a comparison content by a comparison unit and a pulse signal output.

FIG. 7 is a diagram for explaining a laser output and a spot diameter (toner area) with respect to a pulse width in a 1-dot width of an image to be printed.

FIG. 8 is a diagram for explaining a γ characteristic showing a relationship between a laser beam exposure time and a toner adhesion amount.

FIG. 9 is a diagram for explaining a print pattern for each pixel by a 1-pixel unit pulse width modulation method and a pixel combination type pulse width modulation method.

FIG. 10 is a diagram for explaining a pulse width and a laser output according to a one-pixel unit pulse width modulation method.

FIG. 11 is a diagram for explaining a pulse width and a laser output by a pixel combination type pulse width modulation method.

FIG. 12 is a diagram for explaining characteristics of pulse width with respect to image density.

[Explanation of symbols]

 1 ... Scanner part 2 ... Printer engine 5 ... CCD sensor 24 ... Laser diode 31 ... Main control part 31a ... ROM 32, 33 ... Sub control part 37 ... Image processing part 45 ... Image development part 51 ... Conversion table part 52 ... Pulse width Modulation circuit 53 ... Laser driver 54 ... Auto power controller 55 ... Reference voltage setting circuit

Claims (5)

[Claims] 1. An image forming apparatus for forming an image using a generating means for generating a laser beam according to image data, and an indicating means for instructing whether the image data is a binary image or a multivalued image, and a binary image. The first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the pulse width modulation method of one pixel unit used in the case Storage means for storing second γ data different from the first γ data such as conversion data of the density indicated by the image data for the width modulation method and the exposure time corresponding to the density, and a binary value by the instructing means. The image data is stored in the storage means when the image is instructed.
Correcting means for correcting the image data by the second γ data stored in the storing means when the multivalued image is instructed by the instructing means, and the correcting means. Output means for outputting a pulse signal having a pulse width corresponding to the image data corrected by the output means, and control means for generating a laser beam by the generation means for a time corresponding to the pulse signal output by the output means. An image forming apparatus characterized by the above. 2. An image forming apparatus for forming an image using a generation means for generating a laser beam according to image data, and a supply means for supplying image data of either a binary image or a multivalued image. Instructing means for instructing whether the image data supplied by the supplying means is a binary image or a multi-valued image, and the density indicated by the image data for the pulse width modulation method of one pixel unit used in the case of a binary image, and the density corresponding thereto. The first γ data such as the conversion data with the exposure time and the density indicated by the image data for the pixel combination type pulse width modulation method used in the multi-valued image and the conversion data with the corresponding exposure time. Storage means for storing the first γ data and second γ data different from the first γ data, and image data supplied by the supply means when a binary image is instructed by the instructing means. Is corrected by the first γ data stored in the storage means, and when the multivalued image is instructed by the instructing means, the image data received by the receiving means is stored in the storage means. Corresponding to the correction means for correcting with the second γ data, an output means for outputting a pulse signal having a pulse width corresponding to the image data corrected by the correction means, and a pulse signal output by this output means. An image forming apparatus comprising: a control unit for generating a laser beam by the generation unit for a time. 3. An image forming apparatus for forming an image using a generating means for generating a laser beam according to image data, wherein the image data has a binary image without gradation such as characters or gradation such as a photograph. Instructing means for instructing whether the image is a multi-valued image, and first γ data such as conversion data of the density indicated by the image data and the exposure time corresponding to the image data for the pulse width modulation method for each pixel used in the case of a character image And second γ data different from the first γ data such as the conversion data of the density indicated by the image data and the exposure time corresponding to the image data for the pixel combination type pulse width modulation method used for a photographic image. The storage means for storing the image data, and the first image data stored in the storage means when the character image is instructed by the instructing means.
Correcting means for correcting the image data by the second γ data stored in the storing means when the photographic image is instructed by the instructing means, and the correcting means. Output means for outputting a pulse signal having a pulse width corresponding to the corrected image data; and control means for generating a laser beam by the generation means for a time corresponding to the pulse signal output by the output means. An image forming apparatus characterized by the above. 4. An image forming apparatus for forming an image using a generating means for generating a laser beam according to image data, wherein a binary image having no gradation such as characters or a multivalued image having gradation such as a photograph. Supply means for supplying any one of the image data, instruction means for instructing whether the image data supplied by the supply means is a binary image or a multi-valued image, and a pulse for each pixel used in the case of a binary image. The first γ data such as the conversion data of the density indicated by the image data for the width modulation method and the exposure time corresponding thereto and the image data for the pixel combination type pulse width modulation method used in the multi-valued image are shown. Storage means for storing the first γ data different from the first γ data such as the conversion data of the density and the exposure time corresponding thereto, and the binary image by the instructing means, The image data supplied by the supply means is corrected by the first γ data stored in the storage means, and the image received by the receiving means when the multivalued image is instructed by the instructing means. Correction means for correcting the data by the second γ data stored in the storage means, output means for outputting a pulse signal having a pulse width corresponding to the image data corrected by the correction means, and this output means An image forming apparatus comprising: a control unit that generates a laser beam by the generation unit for a time corresponding to the pulse signal output by the image forming apparatus. 5. An image forming apparatus for forming an image by generating a laser beam according to image data, which is either a binary image having no gradation such as characters or a multivalued image having gradation such as a photograph. Image data is supplied, and when the supplied image data is a binary image, the image data is converted into the density indicated by the image data for the pulse width modulation method in pixel units and the exposure time corresponding to the density. When the image data corrected by the first γ data such as data or supplied is multi-valued image data, the image data corresponds to the density indicated by the image data for the pixel combination type pulse width modulation method and the density Correction with the second γ data different from the first γ data such as the conversion data with the exposure time to be output, and outputting a pulse signal having a pulse width corresponding to the corrected image data. Time corresponding to that pulse signal, an image forming method characterized by generating a laser beam.