JPS62183669A - Picture processor - Google Patents

Abstract

PURPOSE:To constantly perform an optimum picture conversion processing and to obtain a good output picture by generating a signal of a prescribed pulse duration and correcting a signal characteristic of a processing circuit according to the detected level. CONSTITUTION:Before the operation of a picture forming mode, the operation of a control mode is performed, a photosensitive member 9 is rotated, an electrifyer 10 is also operated, and a scanner 18 is also rotated. A digital video signal of a check mode A is generated, and a CPU 22 adjusts a bias adjusting means 24 of a triangular wave generating means correspondingly to a surface potential V1' of the photosensitive member 9. Then, the digital video signal for the check mode B is generated and the CPU 22 adjusts a dynamic range of an analog video signal by a dynamic range adjusting means 25 correspondingly to the surface potential V2' of the photosensitive member 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image processing apparatus that performs gradation processing on a human-generated image signal to form an output image.

[Prior Art] In order to obtain gradation when a digital image signal is binarized to form an image using, for example, a laser beam printer, the digital image signal is first converted into an analog signal.
The applicant of the present application has previously proposed a method of generating a binary signal subjected to pulse width modulation by comparing this converted signal with a pattern signal such as a triangular wave.

FIG. 2 shows a concrete example of this method. The digital video signal is connected to the video clock VK in latch 1.
is latched and synchronized.

This video clock VK is the master Kurotsuta MK.
This is a clock whose frequency is divided by two using a flip-flop 5. This video signal is converted into an analog video signal by the D/A converter 2. The output of the D/A converter 2 is converted into a voltage level by a resistor 3 and then input to one input terminal of a comparator 4. On the other hand, the master clock MK is subjected to a predetermined frequency division by a period switching signal from a frequency divider 6, and roughly divided by two by a flip-flop 7 to J- to produce a clock signal with a duty ratio of 50%. This has a period with the same magnification as the frequency division ratio of the frequency divider 6 with respect to the video clock VK. This clock is turned into a triangular wave by the triangular wave generating means 8, which is inputted to the other input terminal of the comparator 4 mentioned above, and is compared with the analog video signal and subjected to one-pulse width modulation. This pulse width modulation signal E is input to the drive circuit 21, and the drive circuit 21 drives the semiconductor laser 17 in blinking modulation to output the laser beam 11 in response to the pulse width modulation signal. The laser beam 11 emitted from the semiconductor laser 17 is scanned by a scanner 18 composed of a rotating polygon mirror, a galvano mirror, or the like. In addition, 19 is a lens for forming a point-like image of the laser beam 11 on the photoreceptor 9;
0 is a mirror for folding the optical path.

Further, 9 is a drum-shaped electrophotographic photoreceptor that rotates in the direction of the arrow, and the photoreceptor 9 is first uniformly charged by a charger 10.
Next, the photoreceptor 9 is scanned and exposed in a direction substantially perpendicular to the direction of rotation of the photoreceptor 9 with a laser beam 11 that is blinking and modulated in accordance with the modulation signal. The electrostatic latent image thus formed on the photoreceptor 9 is developed and visualized by the developing device 12 .

The visible toner image formed on the photoreceptor 9 is transferred to the transfer 1F electronics 1.
6. The visible toner image transferred to the transfer material 14 is fixed by a fixing device (not shown);
The toner remaining on the photoreceptor 9 after transfer is removed by a cleaning device 15.
removed and cleaned. Thereafter, the charge remaining on the photoreceptor 9 is eliminated by the discharge light from the lamp 16, and the above steps are repeated again.

Further, the relationship between the level of the analog video signal and the level of the triangular wave may be as shown in FIGS. 3(a), (b), and (c) depending on the type of image to be obtained.

[Problems to be Solved by the Invention] For example, in FIG. 3(a), the relationship between the white level α of the analog video signal and the maximum value of the triangular wave may be due to some reason such as thermal characteristics of the triangular wave generating means. If there is a fluctuation, even if the amount of fluctuation is minute, the gradation in an area with low image density will fluctuate greatly. Conversely, if the relationship between the black level β of the analog video signal and the minimum value of the triangular wave fluctuates, there is a problem in that the gradation in areas of high image density will fluctuate greatly. Further, even if the relationship between the white and black levels of the analog video signal and the triangular wave does not change, even a small deviation will have a large effect on the image, so it is difficult to adjust it even using a synchroscope. Furthermore, even if the relationship between the white and black levels of the analog video signal and the triangular wave is constant, for example, in the case of a laser beam printer, the laser emission power, the response of the laser emission, the E-V characteristics of the photoreceptor, etc. There has been a problem in that the gradation varies greatly, especially in areas where the image density is light and dark, due to variations and fluctuations in the image density.

The present invention has been made to improve the above-mentioned points,
An object of the present invention is to provide an image processing device that forms #L output images by calibrating the characteristics of a circuit that forms images.

[Means for Solving the Problem] As a means for solving this problem, for example, the image processing apparatus shown in FIG. It includes a CPU that calculates a calibration value, and an adjustment means that changes signal characteristics based on the output from the CPU.

[Operation] With the configuration shown in FIG. 1, a signal with a predetermined pulse width is generated, an output image is formed from the signal, and
The density level of the output image is detected, and the signal characteristics of the processing circuit are calibrated based on the detected level.

[Example code] FIG. 1 is a block diagram of the image processing apparatus of this embodiment.

Components having the same functions as those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted.

In the figure, 22 is a CPU that controls each circuit, and 26 is a ROM in which an operating program of the flowchart of FIG. 6, which will be described later, is stored. Further, 27 is a RAM used as a work area when the CPU 22 operates.

30 is a selector, and according to instructions from the CPU 22,
The digital video signal and the check mode signal included in the signal line 31 from the CPU 22 are also connected to the signal line 31.
is selected based on selection information included in the selection information and output to latch 1. 9 is a drum-shaped electrophotographic photoreceptor that rotates in the direction of the arrow. The photoreceptor 9 is first uniformly charged by a charger 10,
Next, the photoreceptor 9 is scanned and exposed in a direction substantially perpendicular to the direction of rotation of the photoreceptor 9 with a laser beam 11 that is blinking and modulated in accordance with the modulation signal.

The electrostatic latent image thus formed on the photoreceptor 9 is developed and visualized by the developing device 12 . In this embodiment, the developing device 12 is a developing device that performs so-called reversal development in which toner is attached to the portion of the photoreceptor 9 exposed to the laser beam, the so-called bright area.
The toner 2 supplies to the photoreceptor 9 is charged to the same polarity as the photoreceptor charging polarity by the charger 10 . Conversely, the laser beam 11 is modulated so as to expose the portion of the photoreceptor 9 to which the toner is to be attached.

In any case, the visible toner image formed on the photoreceptor 9 is
The image is transferred onto a transfer material 14 by a transfer charger 13 . The visible toner image transferred to the transfer material 14 is fixed by a fixing device (not shown), while the toner remaining on the photoreceptor 9 after transfer is removed and cleaned by a cleaning device 15. Thereafter, the charge remaining on the photoreceptor 9 is eliminated by the discharge light from the lamp 16, and the above steps are repeated again.

Laser beam 11 is emitted from semiconductor laser 17 .

The semiconductor laser 17 is driven by a drive circuit 21 to which a pulse width modulation signal E outputted from the comparator 4 is applied, and emits a laser beam 11 that is blink-modulated in accordance with this modulation signal. be. When forming an image corresponding to a digital video signal on the photoreceptor 9 (image forming mode), the modulation signal E is a signal corresponding to the digital video signal. In any case, the semiconductor laser 1
A laser beam 11 emitted from the laser beam 7 is scanned by a scanner 18 such as a rotating polygon mirror or a galvanometer mirror. 19
2 is a lens for forming a point-like image of the laser beam 11 on the photoreceptor 9, and 20 is a mirror for bending the optical path.

In the image forming mode, an image can be obtained by subjecting the digital video signal to pulse width modulation through the processing described above, supplying the pulse width modulation signal E to the drive circuit 21 and driving the semiconductor laser 17.

Now, in this embodiment, the control mode operation is performed prior to the image forming mode operation described above.

In the control mode, the photoreceptor 9 rotates and the charger 1
0 is also activated and the scanner 18 is also rotated. However, in this mode, the developing device 12 and the transfer charger 13 may be operated or not, but it is preferable that the static elimination lamp 16 be operated.

Furthermore, in the control mode of this embodiment, the output image is calibrated by adjusting the bias of the triangular wave generating means (hereinafter referred to as check mode A) and adjusting the dynamic range of the analog log video signal (hereinafter referred to as check mode B). This processing step is shown in the flowchart of FIG. 6, and its operation will be explained below. Further, this control mode is started after a control signal is transmitted to the CPU 22.

First, check mode A is implemented. In step S1, a digital video signal of check mode A as shown in FIG. 4(a) is generated, a triangular wave synchronized with this digital video signal is generated, and the triangular wave is compared by the comparator 4, and the triangular wave shown in FIG. 4(b) is generated. As shown, a semiconductor laser 17 is driven by a pulse width modulated signal. The thus emitted laser beam 11 exposes and scans the photoreceptor 9. Next, in step S2, the potential sensor 23 detects the surface potential v1 of the photoreceptor 9 that has been exposed and scanned.

Here, the CPU 22 adjusts the bias adjusting means 24 of the triangular wave generating means in accordance with the detected surface potential Vl' of the photoreceptor 9, and adjusts the surface potential v1' of the photoreceptor to a predetermined difference from the desired surface potential v1. Adjust until the value is equal to or less than the value (step S3.4).

Here, the digital video signal in check mode A is a signal in which the time during which the semiconductor laser 17 is off is longer than the time during which the semiconductor laser 17 is emitting light, and is a signal at an arbitrarily set level in advance. Further, the desired surface potential v1 can be easily set in advance based on the characteristics of the photoreceptor 9 and the level of the digital video signal of the set check mode A. In any case, the bias of the triangular wave C is adjusted by adjusting the bias adjustment means 24 until the difference between the desired surface potential (1) and the actual surface potential Vl' on the photoreceptor 9 becomes equal to or less than a preset value. adjust.

When check mode A is completed as described above, check mode B will be processed in steps 35 and thereafter.

In step S5, a digital video signal for check mode B as shown in FIG. Surface potential IJq'
is detected by the potential sensor 23 in the same way as check code A.

Here, the CPU 22 adjusts the dynamic range of the analog video signal using the dynamic range adjusting means 25 in accordance with the detected surface potential V2' of the photoreceptor 9, and adjusts the surface potential V2' of the photoreceptor 9 to a desired surface potential 2. Adjust until the difference becomes less than or equal to a predetermined value (steps S7 and 8).
).

Here, the digital video signal in check mode B is a signal in which the time during which the semiconductor laser 17 is emitting light is longer than the time during which it is off, and is a signal at an arbitrarily set level in advance.

Further, the desired surface potential (2) can be easily set in advance based on the characteristics of the photoreceptor 9 and the level of the digital video signal of the set check mode B.

When each check mode process is completed as described above, the semiconductor laser 17 is stopped in step S9, and the series of check mode processes is ended.

Now, it has been explained that the calibration is performed so that the difference between the potential on the photoreceptor 9 and the desired potential is less than or equal to a preset value Δ■, but the value of ΔV will be explained below.

In Figure 5, when a positively charged photoreceptor is actually used, when the dynamic range of the triangular wave is 1■,
The change in the surface potential Vs of the photoreceptor due to the potential difference ΔV Δv=vp −VC between the peak vP of the triangular wave and the potential VC in check mode A is shown. In this embodiment, as shown in FIG.
The surface potential VS on the photoconductor 9 is 400V when ΔV is completely turned off, and as ΔV increases, the surface potential VS of the photoconductor decreases.If each circuit is adjusted to a potential of 350V±IOV, a very stable image can be obtained. It was confirmed that it was possible to obtain At that time, Δ■ was 0.05±0.01V.

This is because by adjusting the surface potential of the photoreceptor 9, it is possible to adjust the laser emission power, the responsiveness of the laser emission, and the adverse effects on the image due to variations and fluctuations in the EV characteristics of the photoreceptor. Another major reason why it has become possible to obtain stable images is that the adjustment latitude for obtaining good images becomes wider when the voltage is adjusted.

In addition, in this example, the analog video signal and triangular wave were adjusted using two parameters: the bias of the triangular wave and the dynamic range of the analog video signal, but there are other ways to adjust the amplitude and bias of the triangular wave while keeping the analog video signal constant. Any method may be used as long as it can adjust the relationship between the analog video signal and the triangular wave.

Furthermore, when the control mode ends, or after entering the standstill state, the operation of the image forming mode is started when an image forming command (print command) is input.

Note that the above control mode may be performed in conjunction with the operation of turning on the power switch (main switch) of the device.
Alternatively, it may be performed in conjunction with the operation of turning on the image forming operation command switch (print switch), and furthermore, it may be performed in conjunction with the operation of turning on the image forming operation command switch (print switch), and furthermore, it may be performed between the transfer material conveyance and the subsequent transfer material conveyance, corresponding to the so-called paper gap area. (that is, the time between the end of laser beam exposure of the photoreceptor corresponding to the previous image and the start of laser beam exposure of the photoreceptor corresponding to the next image).

Or on the side of the area of the photoreceptor where the image to be transferred is formed (
A test area may be provided in the scanning direction of the laser beam, and a sample image may be formed in this test area to perform the above-described control. In this case, after or before the scanning of one line of the photoreceptor by the laser beam modulated by the modulation signal corresponding to the recorded information is completed, the laser beam modulated by the signal C or the test area scan. Therefore, in this case, the control mode and the image forming mode are performed in parallel.

Also, the control mode does not necessarily have to be automatic;
By pressing the control mode switch, the potential of the photoreceptor in check modes A and H may be displayed, and the relationship between the analog video signal and the triangular wave may be adjusted by adjusting the volume.

The above example is a laser beam printer, which uses an LED array in which many small light emitting diodes (LEDs) are lined up, and each LED in this array is controlled to blink in response to a modulation signal to expose an electrophotographic photoreceptor. The present invention can also be applied to an image processing apparatus that forms an image by doing this.

Furthermore, in the above example, so-called reversal development is adopted in which the toner is attached to the exposed area of the photoreceptor, but the toner is attached to the unexposed area of the photoreceptor, the so-called dark area (therefore, the toner is not charged). It goes without saying that this embodiment can also be applied to an image forming apparatus to which a normal development method (in which the photoreceptor is charged to a polarity opposite to that of the photoconductor 10) is applied.

[Effects of the Invention] As explained above, according to the present invention, by calibrating the characteristics of the circuit in the process of processing human-powered image signals, it is possible to always perform optimal image conversion processing and select an extremely good output image. It becomes possible to

[Brief explanation of drawings]

Figure 1 is a diagram for explaining this embodiment, Figure 2 is a block diagram of an image processing device previously proposed by the applicant, and Figures 3 (a) to (C) are analog video signals and triangular waves. Figures 4 (a) to (d) are diagrams showing examples of pulse width modulation in tick mode, Figure 5 is a diagram showing the surface potential of the photoreceptor, and Figure 6 is a diagram showing an example of the relationship between It is a flowchart at the time of control mode. In the figure, 1... latch section, 2... D/A converter,
3... Resistor, 4... Comparator, 5.7... Flip-flop, 6... Frequency divider, 8... Triangular wave generating means, 9... Photoreceptor, 10... Charger , 11...
Laser beam, 12...Developer, 13...Transfer separator, 14...Transfer member, 15...Cleaner, 16.
...Lamp, 17...Semiconductor laser, 18...Scanner, 19...Lens, 20...Mirror, 21...
Drive circuit, 22...CPU. 23... Potential sensor, 24... Bias adjustment means,
25...Dynamic range adjustment means, 26...R
OM, 27...RAM. Patent applicant Canon Co., Ltd. Figure 3 β□ Figure 1 Figure 4 Figure 6

Claims (2)

[Claims] (1) An image processing device that forms a pulse width modulated signal from an input image signal and a pattern signal of a predetermined period, and forms an output image based on the pulse width modulated signal,
A signal generating means for generating a signal with a predetermined pulse width; a detecting means for detecting the gray level of an output image formed by the signal having a predetermined pulse width generated from the signal generating means; an image processing apparatus, comprising: a calibration means for calibrating the characteristics of the input image signal or the pattern signal of the predetermined period based on the gray level detected by the image processing apparatus. (2) The image processing apparatus according to claim 1, wherein the pattern signal is a triangular wave signal.