JPH0660181A - Image forming device - Google Patents

Abstract

PURPOSE:To correct a fog of an edge part and an edge emphasis effect. CONSTITUTION:The device is provided with a detection means 1 forming a latent image of a prescribed pattern on a latent image medium, developing the image by a development section to detect a level of an edge part of the pattern latent image and a spatial digital filter 2 processing a digital picture signal when a printer is in operation based on the detected value of the detection means 1 to correct the edge part.

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 such as a copying machine or a printer.

[0002]

2. Description of the Related Art Image forming apparatuses include copying machines, printers, etc., and FIG. 50 shows an example of an electrophotographic laser printer. Laser light emitted from the laser oscillator 1 and having an intensity corresponding to a binary digital image signal is deflected in the main scanning direction by the rotating polygon mirror 3 via the mirror 2 and the photoconductor via the fθ lens 4 and the mirror 5. The drum 6 is irradiated. The photoconductor drum 6 is uniformly charged by the charging charger 7, and an image is written and an electrostatic latent image is formed by the exposure with the laser light.

This electrostatic latent image is developed with a developer by a developing device 8 to form a visible image, which is transferred by a transfer charger 9 onto a transfer paper P fed from a paper feeding device. The transfer paper P is separated from the photoconductor drum 6 by the separation charger 10 and the visible image is fixed by the fixing device 11. Also,
After the transfer paper P is separated from the photosensitive drum 6, the cleaning device 12 removes the residual toner. In the developing device, for example, a developing bias voltage is applied from a high-voltage power source to a developing roller serving as a developing electrode, and the developing roller supplies a two-component developer containing toner and carrier or a one-component developer to the photosensitive drum 6. What develops the electrostatic latent image on the photoconductor drum 6 is used.

Further, an image is read by a scanner on a pixel-by-pixel basis, the image signal is quantized into a multi-valued digital image signal to express gradation, and then binarized, and the binarized signal is used for electrophotography. 2. Description of the Related Art In an image forming apparatus that records an image with a printer, an image processing method has been proposed in which a low-pass digital filter enhances a low frequency region of a spatial frequency in a digital image signal during image recording to correct an edge effect.

[0005]

Generally, in the image forming apparatus such as the electrophotographic laser printer described above, a low electric field is generated around the charge holding portion of the photosensitive drum due to its electrostatic characteristics, and this is the developing device as it is. By being developed by the above method to form a visible image, an edge enhancing effect that the edge portion becomes low density or white spot appears. For example, even if the image to be recorded has a good rise and fall characteristic as shown in FIG. 51, the photosensitive drum is exposed by the binary digital image signal of the image, and electrostatic latent An image is formed, and the electric field strength thereof is such that unevenness appears at the edge portion of the electrostatic latent image as shown in FIG. This electrostatic latent image is developed by a developing device to become a visible image, and this visible image has a strong contrast of light and shade at the edge portion.

Further, this edge enhancement effect is influenced not only by the electric field strength of the electrostatic latent image on the photosensitive drum but also by the developing electric field, and further as a developer.
When a component type developer is used, it is influenced by the resistance of the carrier and the specific charge (Q / M) of the toner in the two component type developer, and varies with time. The edge enhancement effect is likely to occur when the carrier resistance value is high.

Generally, the developing characteristics of the developer change with time depending on the degree of deterioration of the developer, that is, the change of the resistance value of the carrier. The developer does not emphasize a specific frequency of the electrostatic latent image in the initial stage of use, and has a flat developing characteristic for all frequencies of the electrostatic latent image. However, the developer causes a phenomenon in which the carrier adheres to the toner and does not separate from the toner (spent phenomenon) depending on the use, which increases the resistance value of the carrier as shown by a characteristic curve a in FIG. For this reason, an edge enhancement effect is produced, and even if an image to be recorded has a good rise and fall characteristic in the developing device, the electrostatic latent image on the photosensitive drum has irregularities at the edge portion. It has a developing property of developing into a visible image.

Further, in the developer, the carrier coating film may be shaved and the resistance value of the carrier may drop as shown by a characteristic curve b in FIG. When the resistance value of the carrier is low, the developing device has a developing property in which the edge portion of the visible image formed on the photosensitive drum is chipped (blurred), and a sharp image cannot be obtained.

If the effective distance between the developing electrode of the developing device and the photosensitive drum is narrowed, the resistance value of the carrier is low, or a carrier having a low resistance value is used, the carrier is formed on the photosensitive drum. The edges of the visible image may be blurred. Further, when a sharp characteristic cannot be obtained as the exposure characteristic for the photoconductor drum, the edge portion of the visible image formed on the photoconductor drum is blurred.

For example, as shown in FIG. 53, even if the image to be recorded has a good rising and falling characteristics, the photosensitive drum is exposed by the binary digital image signal of the image. An electrostatic latent image is formed, and the electric field strength thereof is such that the edge portion of the electrostatic latent image is recessed as shown in FIG. This electrostatic latent image is developed by a developing device to become a visible image, and the visible image has a weak contrast of light and shade at the edge portion.

The edge enhancement effect is preferable when a text image is recorded because the sharpness of the image is emphasized, but when recording a photographic image, the contrast is enhanced when the continuous gradation of the image is expressed. Is emphasized too much and the quality of the recorded image becomes poor. Although the edge enhancement effect is due to the enhancement of the developing electric field, the edge enhancement effect may be further enhanced due to the deterioration of the developer.

It has been found that the edge enhancement effect is improved by applying an AC (alternating current) voltage to the developing electrode as the developing bias voltage. Generally, when a two-component developer composed of carrier and toner is used, the developing bias voltage has an amplitude of 2 KV and a rectangular wave of A near a frequency of 2 KHZ.
The C voltage is used. However, even if the AC voltage is applied to the developing electrode as the developing bias voltage, the edge enhancement effect cannot be sufficiently corrected due to a change over time.

After all, the edge enhancement effect and the blurring of the edge portion are affected by the exposure characteristics, the photoreceptor characteristics, the development characteristics and the developer characteristics, and also change with time. Further, in the above image processing method, the edge enhancement effect is corrected without looking at the visible image formed on the photoconductor, so that the variation of the characteristics of the photoconductor, the exposure, and the developer is not taken into consideration. The effect cannot be corrected correctly.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which can improve the above-mentioned drawbacks and can correct an edge enhancement effect and an edge blurring to obtain an image with good gradation and good image quality. .

[0015]

In order to achieve the above object, the invention according to claim 1 forms a latent image by writing a digital image signal on a latent image carrier in a printer and forms the latent image. In an image forming apparatus that performs an image forming operation of visualizing by a developing unit, a latent image of a predetermined pattern is formed on the latent image carrier as shown in FIG. 1 and then visualized by the developing unit. Detecting means 1 for detecting the level of the edge portion of the pattern image, and a spatial digital filter for correcting the edge portion by processing the digital image signal during the image forming operation of the printer based on the detection value of the detecting means 1. 2 and.

According to a second aspect of the invention, an image forming operation is performed in which a latent image is formed on the latent image carrier by writing a digital image signal on the latent image carrier and the latent image is visualized by a developing unit. In the image forming apparatus, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects an edge enhancement level of the pattern visualized image; And a low-pass digital filter that enhances the low frequency region of the spatial frequency in the digital image signal based on the value to correct the edge enhancement.

According to a third aspect of the present invention, a printer performs an image forming operation in which a latent image is formed on a latent image carrier by writing a digital image signal and the latent image is visualized by a developing unit. In the image forming apparatus, a detection unit for detecting an edge missing level of the pattern image after the latent image of the predetermined pattern is formed on the latent image carrier and visualized by the developing unit, and the detection unit And a high-pass digital filter that corrects edge deficiency by enhancing the high frequency region of the spatial frequency in the digital image signal based on the value during the image forming operation of the printer.

In a fourth aspect of the invention, an image forming operation is performed in which a latent image is formed by writing a digital image signal on a latent image carrier by a printer and the latent image is visualized by a developing unit. In the image forming apparatus, a detection means for detecting a level state of the pattern image after forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, and a detection value of the detection means. Based on the above, during the image forming operation of the printer, the low frequency region of the spatial frequency in the digital image signal is enhanced to correct the edge enhancement, and the high frequency region of the spatial frequency in the digital image signal is enhanced to correct the edge defect. And a spatial digital filter for performing.

According to a fifth aspect of the present invention, a printer performs an image forming operation in which a latent image is formed on a latent image carrier by writing a digital image signal and the latent image is visualized by a developing unit. In the image forming apparatus, after forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, the toner adhesion amount of this pattern visible image is detected by a photo sensor to calculate an edge enhancement level. Edge enhancement level detecting means, and a low-pass digital for performing edge enhancement correction by enhancing the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge enhancement level detecting means. And a filter.

In a sixth aspect of the invention, an image forming operation is performed in which a latent image is formed on a latent image carrier by a printer by writing a digital image signal and the latent image is visualized by a developing unit. In the image forming apparatus, after forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, the toner adhesion amount of the visual image of the pattern is detected by a photo sensor to calculate an edge defect level. Edge defect level detecting means, and a high-pass digital for correcting the edge defect by enhancing the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge defect level detecting means. And a filter.

According to a seventh aspect of the invention, an image forming operation is performed in which a latent image carrier is formed by writing a digital image signal on a latent image carrier by a printer and the latent image is visualized by a developing unit. In the image forming apparatus, after a latent image of a predetermined pattern is formed on the latent image carrier and visualized in the developing unit, the toner adhesion amount of the pattern visualized image is detected by a photo sensor to detect the level of the edge portion. Edge portion level detecting means for calculating, and based on the detection value of the edge portion level detecting means, to enhance the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer to perform edge enhancement correction, And a spatial digital filter that corrects an edge defect by enhancing a high frequency region of a spatial frequency in the image signal.

According to an eighth aspect of the invention, an image forming operation is performed in which a latent image is formed by writing a digital image signal on a latent image carrier by a printer and the latent image is visualized by a developing unit. In the image forming apparatus, a detection unit configured to form a latent image of a predetermined pattern on the latent image carrier and visualize the toner in the developing unit by a photo sensor after the latent image is visualized in the developing unit; The edge emphasis level detecting means for calculating the edge emphasis level from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern image detected by the means, and the edge emphasis level detecting means. A low-pass digitizer that enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detected value to correct edge enhancement. It is obtained by a filter.

According to a ninth aspect of the invention, an image forming operation is performed in which a latent image carrier is formed by writing a digital image signal on a latent image carrier by a printer and the latent image is visualized by a developing unit. In the image forming apparatus, a detection unit configured to form a latent image of a predetermined pattern on the latent image carrier and visualize the toner in the developing unit by a photo sensor after the latent image is visualized in the developing unit; The edge missing level detecting means for calculating the edge missing level from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern visible image detected by the means, and the edge missing level detecting means A high-pass digital device that corrects edge deficiency by enhancing the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detected value. It is obtained by a filter.

According to a tenth aspect of the invention, a printer performs an image forming operation of forming a latent image on a latent image carrier by writing a digital image signal and visualizing the latent image by a developing unit. In the image forming apparatus, a detection unit configured to form a latent image of a predetermined pattern on the latent image carrier and visualize the toner in the developing unit by a photo sensor after the latent image is visualized in the developing unit; An edge portion level detecting means for calculating the level of the edge portion from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern visible image detected by the means, and the edge portion level detecting means Based on the detection value of the digital image signal during the image forming operation of the printer, the low frequency region of the spatial frequency in the digital image signal is enhanced to correct the edge enhancement, By enhancing the high frequency region of the spatial frequency in the signal is obtained by a spatial digital filter for correcting the edge chipping.

According to an eleventh aspect of the present invention, an image forming operation is performed in which a latent image carrier is formed on a latent image carrier by a printer to form a latent image and the latent image is visualized by a developing unit. In the image forming apparatus, a detection unit configured to form a latent image of a predetermined pattern on the latent image carrier and visualize the toner in the developing unit by a photo sensor after the latent image is visualized in the developing unit; An edge for calculating the edge emphasis level from the information of the area by calculating the area of the pattern visible image based on the reference level with the toner adhesion amount average value near the center of the pattern visible image detected by the means as a reference level. An emphasis level detecting means and a low frequency range of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge emphasis level detecting means. Strong let it is obtained by a low pass digital filter for correcting the edge enhancement.

According to the twelfth aspect of the present invention, an image forming operation is performed in which a latent image is formed by writing a digital image signal on the latent image carrier by the printer and the latent image is visualized by the developing unit. In the image forming apparatus, a detection unit configured to form a latent image of a predetermined pattern on the latent image carrier and visualize the toner in the developing unit by a photo sensor after the latent image is visualized in the developing unit; An edge for calculating an edge defect level from the information of the area by calculating the area of the pattern image based on the reference level with the toner adhesion amount average value in the vicinity of the center of the pattern image detected by the means as a reference level. The high level region of the spatial frequency in the digital image signal is generated during the image forming operation of the printer based on the defect level detecting unit and the detection value of the edge defect level detecting unit. Strong let it is obtained by a high-pass digital filter for correcting the edge chipping.

According to a thirteenth aspect of the present invention, a printer performs an image forming operation of forming a latent image on a latent image carrier by writing a digital image signal and visualizing the latent image by a developing unit. In the image forming apparatus, a detection unit configured to form a latent image of a predetermined pattern on the latent image carrier and visualize the toner in the developing unit by a photo sensor after the latent image is visualized in the developing unit; The toner adhesion amount average value near the central portion of the pattern visible image detected by the means is used as a reference level, the area of the pattern visible image is calculated based on the reference level, and the edge level is calculated from the information of the area. Edge part level detection means, and enhances the low frequency range of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge part level detection means. Thereby corrects the edge enhancement, the said enhanced the high frequency region of the spatial frequency in the digital image signal is obtained by a spatial digital filter for correcting the edge chipping.

The invention according to claim 14 is the invention as defined in claims 2, 5,
In the image forming apparatus described in 8 or 11, the correction is performed in the photo forming mode but not in the character forming mode.

The invention of claim 15 is the same as claim 1,
The image forming apparatus according to 8, 11, or 14 is provided with a developing bias applying unit that applies a DC or AC developing bias to the developing unit, and an amplitude of the developing bias applied from the developing bias applying unit to the developing unit and / Or the frequency is controlled based on the detection value of the detection means to correct the edge enhancement.

The invention described in claim 16 is,
In the image forming apparatus described in 9 or 12, the correction is performed in the character forming mode and not in the photo forming mode.

The invention according to claim 17 is the invention according to claim 4, 7,
In the image forming apparatus described in 10 or 13, the edge enhancement correction and the edge lack correction are executed in accordance with the switching between the photo formation mode and the character formation mode.

The invention described in claim 18 is,
The image forming apparatus described in 8 or 11 is provided with a judging means for judging that the life of the developer has come when the edge enhancement level detected by the detecting means exceeds a specified value.

The invention described in claim 19 is,
The image forming apparatus described in 9 or 12 is provided with a determination unit that determines that the life of the developer has come when the edge defect level detected by the detection unit exceeds a specified value.

The invention according to claim 20 is the invention according to claim 4, 7,
The image forming apparatus described in Item 10 or 13 is provided with a determination unit that determines that the life of the developer has come when the level of the edge portion detected by the detection unit exceeds a specified value.

The invention described in claim 21 is,
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
Or the image forming apparatus according to item 14, wherein the detection unit forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then transfers the latent image to an intermediate transfer body to transfer the latent image onto the intermediate transfer body. The level of the edge portion of the pattern image is detected.

The invention described in claim 22 is,
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
Or the image forming apparatus according to item 14, wherein the detection unit forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing unit, and then transfers it to a transfer body to form a pattern on the transfer body. The level of the edge portion of the visible image is detected.

In a twenty-third aspect of the invention, a printer performs an image forming operation of forming a latent image on a latent image carrier by writing a digital image signal and visualizing the latent image by a developing unit. In the image forming apparatus, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing unit, and then detects the level of the edge portion of the pattern visualized image with an image sensor, And a spatial digital filter that processes the digital image signal and corrects the edge portion during the image forming operation of the printer based on the detection value of the detection unit.

According to the twenty-fourth aspect of the present invention, a direct-current or alternating-current developing bias is applied to the developing portion from the developing bias applying means in the printer, and a latent image is formed on the latent image carrier by writing an image signal. In an image forming apparatus for performing an image forming operation in which the latent image is visualized by the developing unit, a latent image having a predetermined pattern is formed on the latent image carrier, and the latent image carrier is visualized by the developing unit. Detecting means for detecting the level of the edge portion of the visible image by the image pickup device, and controlling the developing bias applying means on the basis of the detection value of the detecting means to control the amplitude and / or the amplitude of the developing bias during the image forming operation of the printer. A correction means for correcting the edge portion by changing the frequency is provided.

According to a twenty-fifth aspect of the present invention, in the image forming apparatus according to the first or the second aspect, the detection means forms a latent image of each color of a predetermined pattern on the latent image carrier in sequence to form a latent image. The latent image of 1 is visualized with the developer of each color in the developing section to form a color image of a predetermined pattern, and then the level of the edge portion of the color image is detected at once by the color image pickup device.

[0040]

According to the invention described in claim 1, the detecting means 1 forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and thereafter detects the level of the edge portion of the pattern visualized image. The spatial digital filter 2 processes the digital image signal based on the detection value of the detection means 1 during the image forming operation of the printer to correct the edge portion.

According to the second aspect of the invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and thereafter detects the edge enhancement level of the pattern visible image, and low pass The digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the detection means to correct the edge emphasis.

According to the third aspect of the present invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and thereafter detects the edge defect level of this pattern visible image, and high pass The digital filter enhances the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the detection means, and corrects the edge defect.

According to the fourth aspect of the present invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing section, and thereafter detects the level state of the pattern visualized image.
Then, the spatial digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the detection means to correct the edge emphasis, and the high frequency of the spatial frequency in the digital image signal. The edge is corrected by increasing the area.

According to the fifth aspect of the invention, the edge emphasis level detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then the toner adhesion amount of the pattern visualized image is measured. The edge enhancement level is calculated by the sensor and the low-pass digital filter enhances the low frequency range of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge enhancement level detection means to enhance the edge enhancement. Make a correction.

According to the sixth aspect of the present invention, the edge defect level detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing unit, and then the toner adhesion amount of the pattern visualized is measured. The sensor detects the edge missing level and calculates the edge missing level, and the high-pass digital filter enhances the high frequency range of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge missing level detecting means to detect the edge missing. Make a correction.

According to the seventh aspect of the invention, the edge level detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then the toner adhesion amount of the pattern visualized is measured. The level of the edge part is calculated by detecting with the sensor. Then, the spatial digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge level detecting means to correct the edge emphasis, and the spatial frequency of the image signal The high frequency range is enhanced to correct edge defects.

According to the present invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then detects the toner adhesion amount of the pattern visualized by a photo sensor. Then, the edge emphasis level detecting means calculates the edge emphasis level from the information of the toner adhesion amount average value near the center and the toner adhesion amount peak value of the edge portion in the pattern image detected by the detection means. Then, the low-pass digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the edge enhancement level detection means to correct the edge enhancement.

According to a ninth aspect of the present invention, the detection means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then detects the toner adhesion amount of the visualized pattern by a photo sensor. Then, the edge deficiency level detection means calculates the edge deficiency level from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern image detected by the detection means. Then, the high-pass digital filter enhances the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the edge defect level detecting means to correct the edge defect.

According to the tenth aspect of the invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and thereafter, the toner adhesion amount of the pattern visualized image is detected by the photosensor. Then, the edge portion level detecting means calculates the level of the edge portion from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern image detected by the detecting means. Then, the spatial digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the edge level detection means to correct the edge emphasis, and the spatial frequency in the digital image signal is corrected. Edges are corrected by enhancing the high frequency range of.

In the eleventh aspect of the present invention, the detection means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then detects the toner adhesion amount of the visualized pattern by a photo sensor. Then, the area of the pattern image is calculated on the basis of the average value of the toner adhesion amount in the vicinity of the central portion of the pattern image detected by the edge emphasis level detecting means by the detecting means, and the area of the pattern image is calculated from the information of this area. Calculate the edge emphasis level. Then, the low-pass digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the edge enhancement level detection means to correct the edge enhancement.

According to the twelfth aspect of the present invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and thereafter the toner adhesion amount of the pattern visualized image is detected by the photosensor. Then, the area of the pattern image is calculated based on the reference level with the toner adhesion amount average value in the vicinity of the central portion in the pattern image detected by the edge defect level detecting means as the reference level, and from this area information Calculate the edge missing level. Then, the high-pass digital filter enhances the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the edge defect level detecting means to correct the edge defect.

According to the thirteenth aspect of the present invention, the detection means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and thereafter, the toner adhesion amount of the pattern visualized image is detected by the photosensor. Then, the area of the pattern image is calculated based on the reference level with the toner adhesion amount average value in the vicinity of the central portion in the pattern image detected by the edge level detecting means detected by the detecting means, and from this area information Calculate the edge level. Then, the spatial digital filter enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer on the basis of the detection value of the edge level detection means to correct the edge emphasis, and the spatial frequency in the digital image signal is corrected. Edges are corrected by enhancing the high frequency range of.

According to the invention of claim 14, claim 2
In the image forming apparatus described in 5, 8, or 11, the correction is performed in the photo forming mode but not in the character forming mode.

According to the invention of claim 15, claim 1,
In the image forming apparatus described in 2, 8, 11 or 14, the developing bias applying unit applies a DC or AC developing bias to the developing unit, and the amplitude and / or frequency of the developing bias is based on the detection value of the detecting unit. The edge enhancement is controlled and corrected.

In the sixteenth aspect of the invention, the third and third aspects are provided.
In the image forming apparatus described in 6, 9, or 12, the correction is performed in the character forming mode and not in the photo forming mode.

According to the seventeenth aspect of the invention, the fourth and fifth aspects are provided.
In the image forming apparatus described in item 7, 10 or 13, the edge enhancement correction and the edge defect correction are executed in accordance with the switching between the photo formation mode and the character formation mode.

According to the invention described in claim 18,
In the image forming apparatus described in 5, 8, or 11, the determining unit determines that the life of the developer has come when the edge enhancement level detected by the detecting unit exceeds a specified value.

In the nineteenth aspect of the invention, the third and third aspects are provided.
In the image forming apparatus described in 6, 9, or 12, the determining unit determines that the life of the developer has come when the edge defect level detected by the detecting unit exceeds a specified value.

According to the invention of claim 20, claim 4
In the image forming apparatus described in item 7, 10 or 13, the determination unit determines that the developer has reached the end of its life when the level of the edge portion detected by the detection unit exceeds a specified value.

According to the invention of claim 21, claim 1,
2,3,4,5,6,7,8,9,10,11,12,
In the image forming apparatus described in 13 or 14, the detection means forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing section, and then transfers it to the intermediate transfer body to form the pattern on the intermediate transfer body. The level of the edge part of the visible image is detected.

According to the invention of claim 22, claim 1,
2,3,4,5,6,7,8,9,10,11,12,
In the image forming apparatus described in 13 or 14, the detection means forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in a developing unit, and then transfers it to a transfer body, and a pattern image on the transfer body. The level of the edge part of is detected.

In the twenty-third aspect of the present invention, the detection means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then the level of the edge portion of this pattern visualized image is picked up by the image pickup device. Then, the spatial digital filter processes the digital image signal during the image forming operation of the printer based on the detection value of the detection means to correct the edge portion.

According to the twenty-fourth aspect of the present invention, the detecting means forms a latent image of a predetermined pattern on the latent image carrier and visualizes it in the developing section, and then the level of the edge portion of this pattern visualized image is picked up by the image pickup device. The edge portion is detected by detecting and correcting the edge portion by controlling the developing bias applying means based on the detection value of the detecting means to change the amplitude and / or frequency of the developing bias during the image forming operation of the printer.

According to a twenty-fifth aspect of the present invention, in the image forming apparatus according to the first or the second aspect, the detection means sequentially forms a latent image of each color of a predetermined pattern on the latent image carrier to successively form these latent images. After the image is visualized with the developer of each color in the developing section to form a color image of a predetermined pattern, the level of the edge portion of this color image is detected at once by the color image pickup device.

[0065]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows the outline of a color copying apparatus according to the first embodiment of the present invention, and FIG. 3 shows a magnified portion around a photosensitive drum and an intermediate transfer belt. A color image reading device (hereinafter referred to as a color scanner) 1 illuminates a document 3 on a document table 2 with an illumination lamp 4, and a reflected light image thereof is transmitted through a mirror group 5 to 7 and a lens 8 to a color sensor 9.
Then, the color image information of the original is image-separated for each of blue, green, and red to be read and converted into an electrical image signal.
The color sensor 9 is a color separation unit that separates color image information of an original into, for example, blue, green, and red, and an image pickup that converts the image information of each color separated by the color separation unit into an electrical image signal. It is composed of a device, for example CCD, and 3
Simultaneous color reading is performed. The blue, green, and red color-separated image signals obtained by the color sensor 9 are subjected to color conversion processing by an image processing unit (not shown) based on the intensity level thereof, and black (hereinafter referred to as BK) and cyan. (Hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) color image data.

An electrophotographic color image recording apparatus (hereinafter referred to as a color printer) 10 forms visible images of BK, C, M and Y by the color image data from the image processing section and makes a final color copy. create. Where BK,
Color scanner 1 for obtaining C, M, Y image data
2 receives the scanner start signal in timing with the operation of the color printer 10 from the control unit, and in FIG. 2, the illumination lamp 4 and the optical systems 5 to 7 move in the left arrow direction to move the original on the original table 2. Scanning is performed, and image data of one color is obtained each time the document is scanned. Color scanner 1
By repeating such an operation four times in total, the image processing section sequentially obtains image data of four colors of BK, C, M and Y. Then, every time image data of each color is obtained, the color printer 2 sequentially forms a visible image by the image data and superimposes them to create a four-color full-color image.

Next, the color printer 10 will be described. The writing optical unit 11 converts the color image data from the image processing unit into an optical signal to convert the color image data into an optical signal.
An electrostatic latent image is formed by performing optical writing corresponding to the original image on the second image. The writing optical unit 11 includes a laser 13, a light emission drive control unit (not shown) that controls the light emission of the laser 13, a polygon mirror 14, a motor 15 for rotating the polygon mirror 14, an f / θ lens 16, a reflection mirror 17, and the like. Has been done.

The photoconductor drum 12 rotates counterclockwise as indicated by an arrow, around which a photoconductor cleaning device (including a pre-cleaning charge eliminator 18) 19, a charge elimination lamp 20, a charger 21, a potential sensor 22, BK developing device 2
3, a C developing device 24, an M developing device 25, a Y developing device 26, a development density pattern detector 27, an intermediate transfer belt 28 and the like are arranged. Each of the developing devices 23 to 26 includes the photosensitive drum 1.
Developing sleeve 23 that rotates by bringing the ears of the developer into contact with the surface of the photosensitive drum 12 to develop the electrostatic latent image on the second electrostatic latent image.
a, 24a, 25a, 26a, and developing paddles 23b, 24 that rotate to scoop up and agitate the developer inside
b, 25b, 26b and toner concentration detection sensors 23c, 24c, 25c, 2 for detecting the toner concentration of the developer
6c and the like. In the standby state, all of the four developing devices 23 to 26 have the developing sleeves 23a, 24a, 25.
Although the developer on a and 26a is in a state of cutting off (development inoperative), the order of each development operation of the developing devices 23 to 26 (B
K, C, M, Y image formation order) is BK, C, M, Y
The order is to develop the electrostatic latent image. However, the order of image formation of each color is not limited to this, and may be any order.

At the start of the copying operation, the photosensitive drum 12
Rotates and is uniformly charged by the charger 21. Then, the color scanner 1 starts the reading for obtaining the BK image data at a predetermined timing, the image processing unit obtains the BK image data from the image data from the color scanner 1, and the writing optical based on the BK image data. The unit 11 performs optical writing with a laser beam on the photoconductor drum 12 to form a latent image. Hereinafter, the electrostatic latent image based on this BK image data is referred to as a BK latent image. Similarly, the electrostatic latent image based on the C, M, and Y image data is also a C latent image, an M latent image, and a Y latent image.
It is called a latent image. In order to make this BK latent image developable from its tip, the developing sleeve 23a starts to rotate before the tip of the latent image reaches the developing position of the BK developing device 23, and the developer is spiked. Develop the latent image with BK toner. After that, the developing operation of the BK latent image area on the photoconductor drum 12 is continued, but when the trailing edge of the latent image passes the BK developing position, the developer is quickly cut off on the developing sleeve 23a of the BK developing device 23. To make the development inoperative. This is completed at least before the leading edge of the C latent image by the next C image data arrives. The developer is cut off by changing the rotation direction of the developing sleeve 23a to the opposite direction to that during the developing operation. At this time, the other developing units 24 to 26 remain in the non-developing state.

The BK toner image on the photoconductor drum 12 is transferred onto the surface of the intermediate transfer belt 28 which is driven at the same speed as the photoconductor drum 12 (hereinafter, from the photoconductor drum 12 to the intermediate transfer belt 28). Toner image transfer is called belt transfer). The belt transfer is performed by the transfer bias roller 2 which is in contact with the intermediate transfer belt 28 forming an electrode in a state where the photosensitive drum 12 and the intermediate transfer belt 28 are in contact with each other.
9 is applied by applying a predetermined bias voltage. After the BK toner image is transferred, the photoconductor drum 12 is subjected to charge removal and cleaning by a photoconductor cleaning device 19 including a pre-cleaning charge remover 18, and is uniformly charged again by a charger 21. It should be noted that the intermediate transfer belt 28 is formed by transferring the BK, C, M, and Y toner images sequentially formed on the photosensitive drum 12 to the same surface in order and transferred.
A belt transfer image of color superposition is formed, and then this belt transfer image is collectively transferred to a transfer paper. The structure and operation of the intermediate transfer belt unit will be described later.

On the side of the photosensitive drum 12, the BK image forming process is followed by the C image forming process. In this C image forming process, the color scanner 1 starts reading for obtaining C image data at a predetermined timing. , The image processing unit obtains C image data from the image data from the color scanner 1 and
Based on the image data, the writing optical unit 11 performs optical writing on the photoconductor drum 12 with laser light, and C
Form a latent image.

With respect to the developing position of the C developing device 24, the developing sleeve 24a starts rotating after the rear end portion of the previous BK latent image has passed and before the leading end of the C latent image has reached the developing position. The C latent image is developed with C toner. After that,
The C developing device 24 continues to develop the C latent image area on the photosensitive drum 12, but when the rear end of the C latent image passes,
As in the case of the K developing device 23, the developer on the C developing sleeve 24a is cut off. This is also completed before the leading edge of the next M latent image arrives. The C toner image on the photosensitive drum 12 is transferred to the surface of the intermediate transfer belt 28 that is driven at the same speed as the photosensitive drum 12. Photoconductor drum 12
After the transfer of the C toner image, the photoconductor cleaning device 19 including the pre-cleaning charge eliminator 18 removes the charge and the cleaning, and the charger 21 charges the charge uniformly again.

On the photosensitive drum 12 side, the C image forming process is followed by the M image forming process. In this M image forming process, the color scanner 1 starts reading for obtaining M image data at a predetermined timing, and The image processing unit obtains M image data from the image data from the scanner 1, and the writing optical unit 11 causes the photoconductor drum 12 based on the M image data.
An optical latent image is formed by performing optical writing with a laser beam.

In the M developing device 25, the developing sleeve 25a starts rotating after the trailing edge of the C latent image has passed and before the leading edge of the M latent image has reached the developing position. The M latent image is developed with M toner. After that, M
The developing device 25 continues to develop the M latent image area on the photoconductor drum 12, but when the rear end portion of the M latent image passes, as in the case of the C developing device 24, on the M developing sleeve 25a. The developer is cut off. This is also completed before the leading edge of the next Y latent image arrives. The M toner image on the photoconductor drum 12 is transferred onto the surface of the intermediate transfer belt 28 that is driven at the same speed as the photoconductor drum 12. The photoconductor drum 12 is M
After the transfer of the toner image, the photoconductor cleaning device 19 including the pre-cleaning static eliminator 18 performs static elimination and cleaning, and the charger 21 again uniformly charges the toner image.

On the side of the photosensitive drum 12, the M image forming process is followed by the Y image forming process. In this Y image forming process, the color scanner 1 starts reading for obtaining Y image data at a predetermined timing, and the color image forming process is performed. The image processing unit obtains Y image data from the image data from the scanner 1, and the writing optical unit 11 causes the photoconductor drum 12 based on the Y image data.
Then, optical writing is performed by laser light to form a Y latent image.

In the Y developing device 26, the developing sleeve 26a starts rotating after the rear end portion of the previous M latent image has passed and before the leading end of the Y latent image reaches the developing position, and the developing sleeve 26a starts developing. And the Y latent image is developed with Y toner. After that, Y
The developing device 26 continues to develop the Y latent image area on the photoconductor drum 12, but when the trailing end of the Y latent image passes, the developing device 26 is on the Y developing sleeve 26a as in the case of the M developing device 25. The developer is cut off. This is also completed after the trailing edge of the Y latent image has arrived. The Y toner image on the photosensitive drum 12 is transferred to the intermediate transfer belt 28 that is driven at the same speed as the photosensitive drum 12.
Is transferred to the surface of.

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 28 includes a driving roller 31, a belt transfer bias roller 29, and driven roller groups 32 and 3.
The drive roller 31 is driven by a drive motor (not shown) to rotate the intermediate transfer belt 28. The belt cleaning device 35 includes a brush roller 35.
a, a rubber blade 35b, a contact / separation mechanism 35c for the intermediate transfer belt 28, and the like. After the BK image of the first color is belt-transferred, the C image, the M image, and the Y image are transferred to the belt transfer bias roller 29. When the brush roller 35a and the rubber blade 35b are in contact with each other,
It is separated from the belt transfer bias roller 29 by 5c.

The paper transfer unit 36 is composed of a paper transfer bias roller 36a, a roller cleaning blade 36b, a contact / separation mechanism 36c for the intermediate transfer belt 28, and the like. Although the paper transfer bias roller 36 a is normally separated from the intermediate transfer belt 28,
When the four-color superposed images formed on the transfer paper are collectively transferred to the transfer paper, they are pressed by the contact / separation mechanism 36c at a timing to come into contact with the intermediate transfer belt 28, and the paper transfer bias roller 36a receives a predetermined amount. The bias voltage is applied from the bias power source to the paper transfer bias roller 36a and the intermediate transfer belt 2
8 on the intermediate transfer belt 28 to the transfer paper passing between
Transfer the color superimposition image.

In this case, the transfer paper is the transfer paper cassette 37-
The selected one of 40 is fed to the registration roller 45 by one of the paper feed rollers 41 to 44, or is fed from the manual paper feed tray 46 to the registration roller 45 by the paper feed roller 41. The transfer paper is fed at the timing when the leading end of the four-color superimposed image on the intermediate transfer belt 28 reaches the paper transfer position.

The movement of the intermediate transfer belt 28 is 1
The following constant speed forward movement method, skip forward movement method, and reciprocating movement (quick return) method can be considered as the operation method after the belt transfer of the BK toner image of the color is completed up to the rear end portion. A method, or a method in which these are efficiently combined (in terms of copy speed, etc.) according to the copy size is used.

1) -Constant speed forward movement method Even after the intermediate transfer belt 28 has transferred the BK toner image, it continues to move forward at a constant speed. On the photoconductor drum 12 side, when the BK image front end position on the intermediate transfer belt 28 again reaches the belt transfer position of the contact portion with the photoconductor drum 12, the front end part of the next C toner image is just at the belt transfer position. An image is formed with a timing so that the image becomes dark. As a result, the C image is accurately aligned with the BK image and is transferred onto the intermediate transfer belt 28 in a superposed manner. After that, the M image forming process and the Y image forming process are performed by similar operations, and a belt transfer image of four colors is obtained on the intermediate transfer belt 28. Following the step in which the intermediate transfer belt 28 performs the belt transfer of the Y toner image of the fourth color, the four-color superimposed toner image is collectively transferred to the transfer paper as described above while moving forward.

2) Skip Forwarding Method After the BK toner image is transferred to the intermediate transfer belt 28, the intermediate transfer belt 28 is separated from the photosensitive drum 12 and is skipped at high speed in the forward direction to move a predetermined amount. Return to speed. Then, the intermediate transfer belt 28 is brought into contact with the photosensitive drum 12 again. On the photoconductor drum 12 side, when the BK image front end position on the intermediate transfer belt 28 reaches the belt transfer position again, the timing is adjusted so that the front end portion of the next C toner image comes to the belt transfer position. It is formed. as a result,
The C image is accurately aligned with the BK image and transferred onto the belt in a superimposed manner. After that, the M image forming process and the Y image forming process are performed by similar operations, and a belt transfer image of four colors is obtained on the intermediate transfer belt 28. The intermediate transfer belt 28 collectively transfers the four-color superposed toner image onto the transfer paper at the same forward speed as the belt transfer process of the Y toner image of the fourth color.

3) Reciprocating (quick return) system When the intermediate transfer belt 28 finishes the belt transfer of the BK toner image, it is separated from the photosensitive drum 12 and stops the forward movement, and at the same time, returns in the reverse direction at a high speed. In this return, the front end position of the BK image on the intermediate transfer belt 28 passes through the position corresponding to the belt transfer in the opposite direction, and after moving for a preset distance, it is stopped and becomes a standby state. Next, on the side of the photoconductor drum 12, when the front end portion of the C toner image reaches a predetermined position before the belt transfer position, the intermediate transfer belt 28 is restarted in the forward direction and comes into contact with the photoconductor drum 12 again. . Also in this case, the condition is controlled such that the C image accurately overlaps the BK image on the intermediate transfer belt 28. After that, the M image forming process and the Y image forming process are performed by similar operations, and a belt transfer image of four colors is obtained on the intermediate transfer belt 28. Following the belt transfer process of the Y toner image of the fourth color, the intermediate transfer belt 28 moves forward at the same speed without returning, and transfers the four-color superimposed toner image to the transfer paper in a batch.

The transfer paper on which the four-color superposed toner images are collectively transferred from the intermediate transfer belt 28 is conveyed to the fixing device 48 by the paper conveying unit 47 and is controlled to a predetermined temperature of the fixing device 48. The toner image is fused and fixed by the fixing roller 48a and the pressure roller 48b and is carried out to the copy tray 49 as a full-color copy. Further, the photoconductor belt 12 after the belt transfer is uniformly discharged by the pre-cleaning static eliminator 18 by the photoconductor cleaning device 19, and the surface is cleaned by the brush roller 19a and the rubber blade 19b. The surface of the intermediate transfer belt 28 after the toner image is transferred onto the transfer paper is cleaned by the cleaning unit 36, and at this time, the cleaning unit 36 is pressed by the contact / separation mechanism 36c.

At the time of repeat copying in which copying is continuously performed, the operation of the color scanner 1 and the image formation on the photosensitive drum 12 are started following the Y (fourth color) image forming process for the first sheet, and at a predetermined timing. Proceed to the second BK (first color) image formation process. Further, the intermediate transfer belt 28 has its surface cleaned by the cleaning device 35 following the step of collectively transferring the four-color superimposed image onto the first transfer sheet, and the second BK toner image is transferred onto the surface by the cleaning device 35. It
After that, the same operation as that for the first sheet is performed, and thereafter, the same operation is performed for each sheet.

The transfer sheet cassettes 37 to 40 store transfer sheets of various sizes, and the sheet feeding rollers 41 to 44 are provided.
Thus, the transfer paper is fed to the registration roller 45 at a timing from the transfer paper cassette in which the transfer paper of the size specified by the operation panel (not shown) is stored. The manual feed tray 46 is used for feeding OHP paper or thick paper in the manual feed mode.

The above-described operation is the operation in the copy mode for obtaining a full-color copy in four colors.
When obtaining a copy in the color copy mode, the same operation as described above is performed for the number of colors and the number of times designated by the operation unit. Also, in the case of the monochromatic copy mode for obtaining a monochromatic copy, only the monochromatic developing device is in the development operation (development of developer) state until the copying of a predetermined number of sheets is completed,
The intermediate transfer belt 28 is driven in the forward direction at a constant speed while being in contact with the photosensitive drum 12, and the belt cleaning unit 35 is also kept in contact with the intermediate transfer belt 28 to perform a copying operation.

Next, the image processing section will be described. Figure 4
Shows the circuit configuration of the first embodiment. In FIG. 4, 50 is a shading correction circuit, 51 is an RGBγ correction circuit, 5
2 is an image separation circuit, 53 is an MTF correction circuit, 54 is a color conversion UCR correction circuit, 55 is a scaling circuit, 56 is an image processing circuit, 57 is an MTF filter circuit, 58 is a γ correction circuit, and 59 is gradation processing. Circuit.

The original to be copied is color-separated into R, G, B by the color scanner 1 and read. The R, G, B image signals from the color scanner 1 are sent to the shading correction circuit 50 in the color scanner 1. Fluctuations due to unevenness of the image pickup element, unevenness of the illumination lamp 4, etc. are corrected. The R, G, and B image signals from the shading correction circuit 50 are corrected or converted by the RGBγ correction circuit 51 via the interface 60 to have desired characteristics such as linear relationship with the reflectance and density of the original. The MTF correction circuit 53 corrects the deterioration of the MTF characteristic of the input system, especially the MTF characteristic in the high frequency range.

The image separation circuit 52 is an RGBγ correction circuit 51.
It is determined whether the document image is a character image, a halftone image, a photographic image, a chromatic color, an achromatic color, or the like based on the image signal from the MTF filter 57.
, The gradation processing, etc. are determined.

The color conversion UCR correction circuit 54 corrects the difference between the color separation characteristics of the input system and the spectral characteristics of the color material of the output system for the R, G, B image signals from the MTF correction circuit 53, and faithful color reproduction. A color correction unit for calculating the amount of Y, M, and C color materials required for the above, and a UCR processing unit for replacing the overlapping portion of the Y, M, and C color image signals with the BK image signal. . The color correction unit of the color conversion UCR correction circuit 54 performs color correction processing by the following matrix calculation.

[0092]

[Equation 1]

Here, y, m, and c represent the Y, M, and C image signals, and Rc, Gc, and Bc represent the complements of the R, G, and B image signals. The matrix coefficient aij is determined by the spectral characteristics of the input system and the output system (color material). Further, although the first-order masking equation is given as the arithmetic expression of the color correction processing here, the color correction is performed with higher accuracy by using a quadratic term such as Bc ² , Bc × Gc or a higher-order term. be able to. Further, the calculation formula of the color correction process may be changed depending on the hue, or the Neugayber equation may be used as the calculation formula of the color correction process. In any of the arithmetic expressions, Y, M, and C image signals are obtained from Rc, Gc, and Bc (or R, G, and B image signals).

On the other hand, the UCR of the color conversion UCR correction circuit 54
The processing unit performs UCR processing using the following formula. y ′ = y−α · min (y, m, c) m ′ = m−α · min (y, m, c) c ′ = c−α · min (y, m, c) bk = α · min (Y, m, c) In this equation, α is a coefficient that determines the amount of UCR,
When α = 1, 100% UCR processing is performed. α may be a constant value. For example, by making α close to 1 in the high density area and close to 0 in the highlight area, the image in the highlight area can be smoothed. Also, bk
Is a BK image signal.

The scaling circuit 55 is a color conversion UCR correction circuit 54.
This is a circuit for enlarging and reducing an image with respect to the image signal from, and a three-point convolution method or the like is used. The image processing circuit 56 receives the image signal from the scaling circuit 55,
Performs processing such as repeating and erasing the specified area, and
The TF filter 57 performs a process for changing the frequency characteristic such as edge enhancement and smoothing according to the user's preference such as a sharp image or a soft image for the image signal from the image processing circuit 56.

The γ correction circuit 58 corrects the image signal from the MTF filter 57 according to the developing characteristic and the light attenuation characteristic of the photosensitive drum, and the gradation processing circuit 59 responds to the image signal from the γ correction circuit 58. Perform dither processing. The image signal from the gradation processing circuit 59 is transferred to the printer 10 via the I / F 61.
The I / Fs 60 and 61 are provided for processing the image signal from the scanner 1 by an external image processing device or outputting the image signal from the external image processing device by the printer 10. .

These image processing circuits 51 to 59 are CPUs.
63, the ROM 64, and the RAM 65 are controlled via the bus 66, the CPU 63 is connected to the system controller 67 via the serial I / F, and a command is transmitted from an operation unit (not shown) or the like, and image processing is performed according to the command. Control the circuits 51 to 59.

In the printer 10, the developer is a two-component type developer including a carrier having a particle size of 50 μm and a high resistance coating film, and a toner having particle sizes of 5 μm, 7.5 μm and 10 μm. . Further, the photosensitive drum 12 is 1
A full-color image of a predetermined reference pattern is formed at a predetermined timing other than the image forming operation for obtaining one color copy, as in the image forming operation. That is, the photoconductor drum 12 is uniformly charged by the charger 21, and the writing optical unit 11 sequentially exposes each color image of the reference pattern to form an electrostatic latent image.

In this case, the CPU 67 executes Y, Y for the reference pattern full-color image stored in the ROM 64.
The image signals of M, C, and BK are sequentially read and the printer 1
0, and the writing optical unit 11 outputs the Y, M,
By sequentially converting the image signals of C and BK into optical signals and performing optical writing corresponding to the full-color image of the reference pattern on the photoconductor drum 12, the electrostatic latent images of Y, M, C, and BK are placed at the same position. Are sequentially formed.

The electrostatic latent images of BK, C, M and Y are respectively developed by BK developing device 23, C developing device 24, M developing device 25 and Y.
The developing device 26 visualizes the respective visible images of BK, C, M, and Y, and the respective visible images are successively formed at the same position to form a full-color image of the reference pattern.
As shown in FIGS. 5 and 6, the full-color image 68 of the reference pattern is illuminated by a light source 69 composed of a fluorescent lamp when passing through a fixed reading position, and the reflected light is formed on a reading plate 71 by an imaging lens 70. An image is formed on the image pickup device 72 including a CCD. The intermediate transfer drum 28
Is separated from the photosensitive drum 12 when the full-color image 68 of the reference pattern is created.

The CCD 72 converts the light and shade of the color image 68 into an electric signal. Here, a CCD of 5000 pixels is used and has a high resolution of 400 dpi (16 dots / mm). The reading plate 71 has a built-in A / D converter, and the analog image signal from the CCD 72 is A / D converted by the A / D converter and output as a 6-bit (64 gradation) digital image signal. . Further, in order to correct the fluctuation of the brightness of the fluorescent lamp 69 and the unevenness of the incident light on the CCD 72, the CCD 72 reads the reference white plate and corrects the read signal for the color image 68 (shading correction) by the read signal. If this is done, an image signal without variations can be obtained.

Light source 69, imaging lens 70 and CCD 72
Is fixed to the machine body, the photosensitive drum 12 rotates in the direction of the arrow, and the CCD 72 reads the color image 68 on the photosensitive drum 12 line by line. This gives C
A two-dimensional image signal is obtained from the CD 72. FIG. 7 shows a reference pattern color image 68, an imaging lens 70, and a CCD.
A part of 72 is enlarged and shown, and the color image 68 of the reference pattern is an image of 400 dpi (16 dots / mm), and FIG. 7 shows the 3 × 3 pixels. Color image 68
The image of the reflected light from the imaging lens 70 is 1: 0.110.
The image is reduced on the CCD 72 at a reduction ratio of 2.

FIGS. 8 and 9 show one line in the main scanning direction of the output signal of 64 gradations of the CCD 72 for the color image 68 of the reference pattern. FIG. 8 shows a case where there is an edge enhancement effect, and the output signal of the CCD 72 has a high value at both ends of one line in the main scanning direction. FIG. 9 shows a case where there is an edge defect, and the output signal of the CCD 72 has a low value at both ends of one line in the main scanning direction. FIG. 10 shows the output signal of the CCD 72 for the color image 68 of the reference pattern in the sub-scanning direction.

CCD 7 for the central portion of color image 68
The average value of the two output signals is Vsp. CPU 63
The output signals Vo and Vsp of the CCD 72 for the first pixel (the pixel first written on the photosensitive drum 12 by the writing optical unit 11) are compared, and when Vo is larger than Vsp, it is determined that there is an edge enhancement effect. Vo is Vs
If it is smaller than p, it is determined that there is an edge defect.

Then, when there is an edge enhancement effect or an edge deficiency, the CPU 63 integrates the output signal of the CCD 72 for the edge portion of the color image 68 with a value larger than the reference value or smaller than the reference value with reference to Vsp. Then, the absolute value is obtained. The integration is performed by the CCD 7 for the entire edge portion of the color image 68 as shown in FIG.
2 output signals. When the output signal of the CCD 72 with respect to the edge portion of the color image 68 is larger than the reference value, it means that there is an edge enhancement effect.
In the output signal of the CCD 72 for the eight edge portions, the larger value than the reference value is integrated to obtain the absolute value. The result is the edge emphasis level indicating the edge strong effect. When the output signal of the CCD 72 for the edge portion of the color image 68 is smaller than the reference value, there is an edge defect, and the output signal of the CCD 72 for the edge portion of the color image 68 is integrated by an amount smaller than the reference value. The result of obtaining the value indicates the level of edge chipping.

A color CCD is used as the CCD 72, and it has about 1,000 light receiving elements each having a size of several tens of μm. The light receiving element of the CCD 72 is integrated with the G, B, and R filters. 12
As shown in (1), one light receiving element in the CCD 72 is covered with filters of three colors (G, B, R), and each pixel is an independent pixel. The light receiving element of the CCD 72 is tilted to the right by 45 degrees, and the amounts of light incident on the G, B, and R pixels are averaged.

The photosensitive drum 12 is of each color (C, M, Y, B
An electrostatic latent image is formed by writing by the writing optical unit 11 for each K), and each of the electrostatic latent images of BK, C, M, and Y is developed by BK developing device 23, C developing device 24, M developing device 2, respectively.
5. BK, C, M, Y visualized by Y developing device 26
Of the reference pattern, and by sequentially forming these visible images at the same position.
It becomes 8. The fluorescent light 69 irradiates the color image 68 with light, and the reflected light is C through the imaging lens 70.
It is detected by the CD 72. In this case, the CCD 72 reads the color image 68 in one scan.

By the writing by the writing optical unit 11, the electrostatic latent images of C, M, Y, and BK are sequentially formed on the photosensitive drum 12 without overlapping, and the BK developing devices 2 are formed.
3, C developing device 24, M developing device 25, Y developing device 26 to visualize, C, M, Y, BK of each visible image CCD 72
May be sequentially detected.

In the first embodiment, the edge enhancement effect and the edge lack correction are performed by the spatial digital filter.
The spatial digital filter has a function of separating frequency components of one-dimensional, two-dimensional and three-dimensional data. This frequency component is the set of spatial frequencies involved in the change in gray level during a certain spatial distance. If the spatial digital filter is a high-pass digital filter, high frequency detailed information is emphasized, and as a result, low frequency detailed information is attenuated. If the spatial digital filter is a low-pass digital filter, it has the opposite effect.

In the first embodiment, the matrix coefficient of the spatial digital filter is determined according to the two-dimensional data obtained by the CCD 72. The MTF filter 57 is used as a spatial digital filter. This first embodiment is useful when a sharp image having no edge enhancement effect is desired. When an image signal as shown in FIG. 8 is obtained from the CCD 72, M is generated during the image forming operation of the printer 10.
The TF filter 57 is used as a low pass digital filter so as to correct the edge enhancement.

When an image signal as shown in FIG. 9 is obtained from the CCD 72, the MTF filter 57 is used as a high-pass digital filter so that a sharp image can be obtained during the image forming operation of the printer 10. to correct. Since the ID of the edge portion of the image is not always the same in the main scanning direction and the sub scanning direction, the spatial digital filter takes a free matrix arrangement in the main scanning direction and the sub scanning direction to obtain a sufficient edge enhancement effect. Edge defect correction can be performed.

FIG. 13 shows an example of a two-dimensional low-pass digital filter for correcting the edge enhancement effect. Here, the low-pass digital filter has a numerical array that enhances the low frequency region of the spatial frequency of the image as each threshold value in the 3 × 3 matrix configuration. Further, the characteristic curve shown by the solid line in FIG. 14 shows the spatial frequency characteristic of the image by the image signal processed by the low-pass digital filter. The characteristic curve shown by the dotted line in FIG. 14 shows the spatial frequency characteristic of the edge portion in the image when no processing by the spatial digital filter is performed.

As described above, when the spatial frequency of the edge portion is high in the original image, image signal processing using a low-pass digital filter for smoothing the spatial frequency characteristic of the edge portion is necessary for the correction. Become. CPU63
When it is determined that there is an edge enhancement effect as described above, the MTF filter 57 is used as a low-pass digital filter to perform image signal processing during the image forming operation of the printer 10, and this image signal processing is specifically as follows. To be done.

First, depending on the size of the low-pass digital filter to be used, the digital image signals Da, Db, Dc, Dd in the 3 × 3 pixel area centered on the target pixel to be processed as shown in FIG. Dx, De, Df,
Dg and Dh are extracted. Here, Dx is a digital image signal of the pixel of interest. Next, the digital image signal Dx of the pixel of interest and the digital image signals Da of the pixels around it,
Considering Db, Dc, Dd, De, Df, Dg, and Dh, each threshold value in the low-pass digital filter, for example, 1, 2, 1, 2, 2, 2, 1, as shown in FIG.
The processed data Dx ′ of the pixel of interest can be obtained by the following arithmetic expression using 2 and 1.

Dx ′ = 1/16 × {Da × 1 + Db × 2 + Dc × 1 + Dd × 2 + Dx × 4 + De × 2 + Df × 1 + Dg × 2 + Dh × 1} (1) The arithmetic processing of the equation (1) is an image processing circuit. This is performed for all the image signals from 56, and the CPU 63 integrates the threshold value of the low-pass digital filter with an edge enhancement level (in the output signal of the CCD 72 for the edge portion of the color image 68, a value larger than the reference value is integrated to obtain an absolute value The result of
Set according to. The spatial frequency of the image is uniquely determined by the ratio between the center value of the threshold values of the low-pass digital filter and the threshold values of the peripheral pixels. When the central value of the threshold value of the low pass digital filter is increased, the image has a high MTF in the high frequency region of the spatial frequency.

By the image signal processing by such a low-pass digital filter, the rising edge as shown in FIG.
From the input image having a sharp falling edge, a smooth image of rising edges and falling edges as shown in FIG. 17 can be obtained. Therefore, the image signal processing by the low-pass digital filter has the spatial frequency characteristic such that the edge portion is rounded as shown by the characteristic curve shown by the solid line in FIG. Since the edge enhancement effect is generated due to the electric characteristics, the edge enhancement effect of the recorded image is lost as a result, and a recorded image close to the input image can be obtained.

FIG. 18 shows an example of a two-dimensional high-pass digital filter for correcting an edge defect. Here, the high-pass digital filter has a numerical array that enhances the high frequency region of the spatial frequency of the image as each threshold value in the 3 × 3 matrix configuration. Further, the characteristic curve shown by the solid line in FIG. 19 shows the spatial frequency characteristic of the image by the image signal processed by the high pass digital filter. The characteristic curve shown by the dotted line in FIG. 19 shows the spatial frequency characteristic of the edge portion in the image when no processing by the spatial digital filter is performed.

As described above, when the spatial frequency of the edge portion is low in the original image, image signal processing using a high-pass digital filter for smoothing the spatial frequency characteristic of the edge portion is necessary for the correction. Become. CPU63
When it is determined that there is an edge defect as described above, the MTF filter 57 is used as a high-pass digital filter to perform image signal processing during the image forming operation of the printer 10, and this image signal processing is specifically as follows. Done.

First, depending on the size of the high-pass digital filter to be used, the digital image signals Da, Db, Dc, Dd in the 3 × 3 pixel area centering on the target pixel to be processed as shown in FIG. Dx, De, Df,
Dg and Dh are extracted. Here, Dx is a digital image signal of the pixel of interest. Next, the digital image signal Dx of the pixel of interest and the digital image signals Da of the pixels around it,
Considering Db, Dc, Dd, De, Df, Dg, and Dh, each threshold value in the low-pass digital filter, for example, -1, -1, -1, -1, 9, as shown in FIG.
The processed data Dx ′ of the target pixel is obtained by the following arithmetic expression using −1, −1, −1, −1.

Dx ′ = 1/1 × {Da × (−1) + Db × (−1) + Dc × (−1) + Dd × (−1) + Dx × 9 + De × (−1) + Df × (−1) + Dg × c (−1) + Dh × (−1)} (2) The arithmetic processing of the equation (2) is performed on all the image signals from the image processing circuit 56, and the CPU 63 uses the high pass digital filter. The threshold value is the edge missing level (the result of calculating the absolute value by integrating the output signal of the CCD 72 for the edge portion of the color image 68, which is smaller than the reference value).
Set according to. In the high-pass digital filter, the sum of matrix coefficients is always 1. Generally, a high-pass digital filter has a large matrix coefficient in the center, and a small positive or negative matrix coefficient surrounds it. The spatial frequency of the image is uniquely determined by the ratio between the center value of the threshold values of the high-pass digital filter and the threshold values of the peripheral pixels. When the central value of the threshold value of the high pass digital filter is increased, the image has a high MTF in the high frequency region of the spatial frequency.

By the image signal processing by such a high-pass digital filter, the rising edge as shown in FIG.
From the input image with a gentle fall, an image with a clear rise and fall as shown in FIG. 22 is obtained. Therefore, although the image signal processing by the high-pass digital filter has a spatial frequency characteristic with a clear edge portion as shown by the characteristic curve shown by the solid line in FIG. 19, the electrostatic characteristic of the photosensitive drum 12 when the printer 10 records an image. As a result, edge defects occur, and as a result, edge defects in the recorded image are eliminated and a recorded image close to the input image can be obtained.

In the first embodiment, a latent image of a predetermined pattern is formed on the photosensitive drum 12 and visualized by the developing units 23 to 26, and then the level of the edge portion of the visualized pattern is set to C.
Detected by the CD 72, based on the detected value of the CCD 72, the spatial digital filter 57 is used during the image forming operation of the printer 10.
Since the edge part is corrected by processing the digital image signal with, the edge enhancement effect and the blurring of the edge part due to the temporal change of the developer, the photosensitive drum 12, the writing system, etc. are corrected, and the gradation is adjusted. You can get a good image of. Further, since the CCD 72 detects the level of the edge of the pattern image, the edge level detection accuracy is high. That is, the color image 68 can be read by a photo sensor, but in that case, it is impossible to detect the edge level of the color image 68 of 400 dpi (16 dots / mm) for each dot, and it is not possible to detect the edge level. It will detect the number of pixels and output the average value.
The edge level detection accuracy becomes low. However, in the first embodiment, the level of the edge portion of the pattern image is set to the CCD 72.
The edge level of the color image 68 of 400 dpi (16 dots / mm) can be detected for each dot, and the edge level detection accuracy is high.

The second embodiment of the present invention is the same as the first embodiment, except that the edge emphasis effect and the edge defect are corrected by the spatial digital filter, and the edge emphasis effect and the edge defect are corrected by controlling the developing bias voltage. The developing bias voltage is an AC with a DC voltage superimposed.
Voltage.

The electric resistance of the carrier of the two-component developer is determined by the coating material of the carrier for the purpose of imparting and stabilizing the triboelectric charge of the toner. As a coating material for the carrier, Teflon, silicon, or a stainless steel resin is generally used, and carbon or the like is used as a resistance imparting agent. A characteristic curve a in FIG. 23 shows a latent image frequency vs. development density characteristic of a developing device which performs development with an insulating magnetic brush. As is clear from this characteristic, the developing device that develops with an insulating magnetic brush emphasizes the developing electric field of a specific frequency,
Edge enhancement effect can be obtained. This edge enhancement effect does not give good results for photographic images. That is, since the image of the photograph is an image in which a wide range of frequencies exist continuously, the edge enhancement effect by the developing device that develops with the insulating magnetic brush emphasizes the minute step of the image frequency,
An unnatural image with graininess is reproduced.

The characteristic curve b in FIG. 23 shows the latent image frequency vs. development density characteristic of the developing device for developing with a conductive magnetic brush.
As is clear from this characteristic, the developing device for developing with the conductive magnetic brush does not emphasize the developing electric field of a specific frequency. However, the insulating magnetic brush has a higher resistance value of the carrier than the conductive magnetic brush, and since the carrier is generally coated with the coating agent, deterioration of the developer due to abrasion of the coating film of the carrier is less likely to occur. It has a long life.

A method is known in which an AC voltage on which a DC voltage is superimposed is used as the developing bias voltage. This method facilitates the development of the latent image by activating the movement of the toner, and the relative speed between the photoconductor and the developer can be set small. The edge enhancement effect can be alleviated, and uniform development can be performed. And so on. Explaining in detail, as the developing bias voltage A
By using the C voltage, even in the case of the insulating magnetic brush, the developing characteristics similar to those of the conductive magnetic brush are exhibited, the emphasis of the developing electric field of the specific frequency is eliminated, and a smooth image without the edge enhancement effect can be obtained.

FIG. 24 shows the developing characteristics a to d of the developing device. In the developing characteristic a, a DC voltage is applied as the developing bias voltage, and the peripheral speed ratio between the photosensitive drum and the developing sleeve is 1.
8 is the developing characteristic in the case of 8. The developing characteristic b is a developing characteristic when a DC voltage is applied as the developing bias voltage and the peripheral speed ratio between the photosensitive drum and the developing sleeve is 3.0. The developing characteristic c is a developing characteristic when a DC voltage is superimposed as a developing bias voltage and an AC voltage having a peak value of 1.8 KV is applied, and the peripheral speed ratio between the photosensitive drum and the developing sleeve is 1.8. . The developing characteristic d is an AC having a peak value of 0.5 KV when a DC voltage is superimposed as a developing bias voltage.
This is a developing characteristic when a voltage is applied and the peripheral speed ratio between the photosensitive drum and the developing sleeve is 1.8.

From these developing characteristics a to d, the developing characteristics of the developing device depend on whether a DC voltage is applied as the developing bias voltage and an AC voltage on which the DC voltage is superimposed is applied as the developing bias voltage ( It can be seen that the image density) changes. Further, in the developing device, when the peripheral speed ratio between the photosensitive drum and the developing sleeve is 1.8, the developing bias voltage is changed from the AC voltage to the direct current voltage, so that the developing ability is lowered and the AC developing bias voltage is increased. The developing ability changes by changing the peak value of the voltage. Therefore, the peripheral speed ratio between the photosensitive drum and the developing sleeve, the charging potential of the photosensitive drum, the potential of the developing sleeve (equal to the developing bias voltage when the developing bias voltage is a DC voltage, and the developing bias voltage is a DC voltage). If the AC voltage is a superposed AC voltage, it is equal to the DC voltage of the developing bias voltage), and the image forming process conditions such as the exposure amount must be changed according to the developing characteristics of the developing device to correct the output image density. .

It is also known that a smooth image having no edge enhancement effect can be obtained when the developing bias voltage is an AC voltage on which a DC voltage is superimposed. It is known that the edge enhancement effect is better when the amplitude and frequency of the AC component of the developing bias voltage are higher, but there are saturation points where both the amplitude and frequency become the same when the amplitude and frequency become higher than a certain value. In addition, the edge enhancement effect greatly changes in relation to the amplitude and frequency of the AC component of the developing bias voltage when the carrier is covered or uncoated, and the edge emphasis effect is greatly changed depending on the resistance value of the carrier.

The developer may have a spent resistance (a phenomenon in which the carrier and the toner are attached to each other) to increase the resistance value of the carrier as the running is repeated, and the coating film of the carrier may be scraped to decrease the resistance value of the carrier. In general, the edge enhancement effect is better when the carrier resistance value is lower as shown in FIG. 25, and even when the document bias voltage is the same AC voltage, the higher the carrier resistance value is, the more difficult it is for the effect to appear. The amplitude and frequency of the AC voltage must be increased.

FIG. 26 shows the relationship between the edge emphasis level Ex and the peak value (amplitude) Vpp of the AC component of the developing bias voltage. From this relationship, it can be seen that the edge enhancement effect is better when Ex is smaller. Normally, the relationship between Ex and Vpp is a characteristic of being convex downward as shown by the characteristic curve a in FIG. 26, and Ex becomes the optimum value (minimum value) when Vpp reaches a certain value. Further, the relationship between Ex and Vpp is such that when the resistance value of the developer becomes low, Vpp becomes Vpp as shown by the characteristic curve b in FIG.
When the resistance value of the developer becomes higher, on the contrary, when the resistance value of the developer becomes higher, the value shifts to the larger Vpp as shown by the characteristic curve c in FIG. In this way, the optimum value of Vpp changes depending on the resistance value of the developer.

FIG. 27 shows the relationship between Ex and the frequency fb of the AC component of the developing bias voltage. From this relationship, it can be seen that the edge enhancement effect is better when Ex is smaller. Normal,
The relationship between Ex and fb is a characteristic of being convex downward as shown by a characteristic curve a in FIG. 27, and Ex becomes an optimum value (minimum value) when fb becomes a certain value (the optimum value is wide. May exist). The relationship between Ex and Vpp shifts to a smaller value of fb as shown by the characteristic curve b in FIG. 27 when the resistance value of the developer decreases, and conversely when the resistance value of the developer increases, the characteristics shown in FIG. Shift to the larger fb as indicated by the curve c. Thus, the optimum value of fb changes depending on the resistance value of the developer.

FIG. 28 shows a processing flow in which the CPU 63 controls the application condition of the developing bias voltage from the output signal of the CCD 72. The CPU 63 sequentially reads the Y, M, C, and BK image signals for the full-color image of the reference pattern stored in the ROM 64 at a predetermined timing other than the image forming operation of the printer 10 and outputs them to the printer 10 to write optical signals. The unit 11 sequentially converts the Y, M, C, and BK image signals into optical signals and performs optical writing on the photoconductor drum 12 corresponding to a full-color image of a predetermined pattern, whereby Y, M, C, and BK Each electrostatic latent image is sequentially formed at the same position. The electrostatic latent images of BK, C, M, and Y are visualized by the BK developing device 23, the C developing device 24, the M developing device 25, and the Y developing device 26, respectively.
Each visible image of Y becomes a full-color image 68 of the reference pattern by sequentially forming each visible image at the same position. The intermediate transfer belt 28 is separated from the photosensitive drum 12 when the color image 68 is created.

The CPU 63 uses the CC for the color image 68.
The output signal of the D72 is taken in, and the output signal of the CCD 72 for the first pixel (the pixel first written on the photosensitive drum 12 by the writing optical unit 11) and the color image 6
The average value Vsp of the output signal of the CCD 72 for the vicinity of the central portion of 8 is compared. When Vsp is larger than the output signal of the CCD 72 for the edge portion of the color image 68, the edge enhancement effect is shown, and when Vsp is smaller than the output signal of the CCD 72 for the edge portion of the color image 68, the edge is missing. When Vo is equal to Vsp, the developing bias voltage is left as it is. In the developing units 23 to 26, a developing bias voltage composed of an AC voltage on which a DC voltage is superimposed is applied to the developing sleeves 23 a to 26 a from a high voltage power source, and the high voltage power source supplies the developing bias voltage to the CPU 63.
Controlled by.

When Vo is larger than Vsp, the CPU 63 determines that there is an edge enhancement effect, and the CC for all the edge portions of the color image 68 is based on Vsp.
Regarding the output signal of D72, the amount larger than the reference value is integrated to obtain the absolute value as the edge emphasis level Sx1.
Next, the CPU 63 controls the high voltage power supply based on the edge emphasis level Sx1 to set the amplitude Vpp and frequency fb of the AC component of the developing bias voltage to predetermined values ΔVpp and Δfb.
Adjust higher one by one.

Further, when Vo is smaller than Vsp, the CPU 63 determines that there is an edge defect, and the CCD 7 for all the edge portions of the color image 68 with Vsp as a reference.
For the two output signals, the smaller value than the reference value is integrated to obtain the absolute value as the edge-missing level Sx2. Next, the CPU 63 controls the high-voltage power supply based on the edge defect level Sx2 to adjust the amplitude Vpp and the frequency fb of the AC component of the developing bias voltage to decrease by a predetermined value ΔVpp, Δfb.

By such adjustment of Vpp and fb, the printer 10 performs the image forming operation with Vpp and fb adjusted to the optimum values, and the color copy without the edge enhancement effect and the edge loss can be obtained. . In the second embodiment, a latent image of a reference pattern is formed on the photosensitive drum 12 and visualized by a developing unit, and then the level of the edge portion of this pattern visualized image is detected by the CCD 72, and the detection value of the CCD 72 is detected. Since the edge portion is corrected by changing the amplitude and frequency of the developing bias during the image forming operation of the printer 10 based on the above, the edge enhancement effect and the edge due to the temporal change of the developer, the photosensitive drum 12, the writing system, etc. It is possible to obtain a sharp and smooth image without blurring of parts. In addition, the level of the edge portion of the pattern image is CCD7.
Since the detection is performed at 2, the detection accuracy at the edge level is high.

In the second embodiment, both Vpp and fb are adjusted according to the edge enhancement effect and the presence / absence of edge deficiency, but only one of Vpp and fb may be adjusted. In the second embodiment, Vp
The adjustments of p and fb may be repeated until Sx1 and Sx2 reach specified values.

In the second embodiment, the CCD 7
After adjusting Vpp and fb based on the output signal of No. 2 to set the developing bias voltage, an electrostatic latent image having a predetermined pattern is formed by the developing bias voltage as in the first embodiment. After visualizing with a developing device, C
The threshold value of the spatial digital filter 57 may be set as described above based on the output signal of the CCD 72 detected by the CD 72. By doing so, a better image can be obtained. That is, the correction of Vpp and fb corrects the main scanning direction and the sub scanning direction to be the same, but since the ID differs depending on the direction in the actual image, the direction of the image can be adjusted by adjusting the threshold value of the spatial digital filter 57. Even a difference in ID due to can be corrected, and a better image can be obtained. Further, although the CCD 72 is a reduction image forming type, a close contact type may be used. By doing so, the space for the image forming optical system is not required, and the size can be reduced.

In the third embodiment of the present invention, a photo sensor (hereinafter referred to as P sensor) is used instead of the CCD 72 in the first embodiment. FIG. 29 shows the photosensitive drum 12.
The relationship between the above toner adhesion amount and the output signal voltage of the P sensor is shown. As can be seen from this relationship, the output signal voltage of the P sensor becomes lower as the toner adhesion amount on the photosensitive drum 12 increases.

As described above, the CPU 63 controls the Y for the full-color image of the reference pattern stored in the ROM 64 at a predetermined timing other than the image forming operation of the printer 10.
The image signals of M, C, and BK are sequentially read and the printer 1
0, and the writing optical unit 11 outputs the Y, M,
By sequentially converting the image signals of C and BK into optical signals and performing optical writing corresponding to a full-color image of a predetermined pattern on the photoconductor drum 12, each electrostatic latent image of Y, M, C, and BK is placed at the same position. Are sequentially formed. This BK, C, M,
The Y electrostatic latent images are visualized by the BK developing device 23, the C developing device 24, the M developing device 25, and the Y developing device 26 to become the BK, C, M, and Y visible images, respectively. A full-color image 68 of the reference pattern is formed by successively forming the visible images at the same position. The intermediate transfer belt 28 is separated from the photosensitive drum 12 when the color image 68 is created.

As shown in FIG. 30, the P sensor 73 reads the color image 68 on the photosensitive drum 12 along the rotation direction (sub-scanning direction) of the photosensitive drum 12, and the output signal voltage thereof is shown in FIG. 31, for example. A one-dimensional spatial digital filter is used as the MTF filter 57 because the one-dimensional data has such a waveform. The output signal voltage of the P sensor 73 is the portion A of the color image 68 with respect to the front end and the color image 68.
The portion B with respect to the rear end portion is lower than the portion with respect to the central portion of the color image 68. This is because the densities of the front end portion and the rear end portion of the color image 68 are the same as the central portion of the color image 68. It is higher than that, that is, the edge enhancement effect is shown.

The output signal voltage of the P sensor 73 is shown in FIG.
As shown in FIG. 3, a portion A with respect to the leading end of the color image 68
And the portion B for the rear end of the color image 68 may be higher than the portion for the central portion of the color image 68, which means that, as shown in FIG. This indicates that the density is lower than the density of the central portion of the color image 68, that is, the edge is missing.

Similar to the first embodiment, the CPU 63 compares the output signal Vo and Vsp of the P sensor 73 for the first pixel (pixel first written on the photosensitive drum 12 by the writing optical unit 11) and Vo is compared. If it is larger than Vsp, it is judged that the edge enhancement effect is present, and if Vo is smaller than Vsp, it is judged that there is an edge defect. Then, when there is an edge enhancement effect or an edge lack, the CPU 63 integrates the output signal of the P sensor 73 for the edge portion of the color image 68 with a value larger than the reference value or smaller than the reference value with reference to Vsp. The edge enhancement level or the edge missing level is obtained by obtaining the absolute value of the threshold value, and the MTF filter 57 is used as a low-pass digital filter or a high-pass digital filter during the image forming operation of the printer 10, and the threshold value is used as the edge enhancement level or the edge missing. Set according to the level.

In the third embodiment, the latent image of the reference pattern is formed on the photosensitive drum 12 and visualized in the developing portion, and then the level of the edge portion of the visualized pattern is measured by the P sensor 73.
The edge portion is corrected by the spatial digital filter 57 during the image forming operation of the printer 10 based on the detection value of the P sensor 73.
2. It is possible to obtain a sharp and smooth image without the edge enhancement effect and the blurring of the edge portion due to the temporal change of the writing system.

In the third embodiment, as shown in FIG. 46, the P sensor 73 displays the color image 68 along the reading line L parallel to the width direction (main scanning direction) of the photosensitive drum 12 when stopped. You may read it. Further, as shown in FIG.
May be read by a plurality of reading lines L, L2 ... In parallel with the width direction (main scanning direction) of the photoconductor drum 12 when stopped, and a one-dimensional spatial digital filter may be used as the MTF filter 57.

FIG. 34 shows a part of a circuit portion in the fourth embodiment of the present invention, and FIG. 35 shows an operation flow of the fourth embodiment. In the fourth embodiment, the edge enhancement effect is corrected but the blur of the edge portion is not corrected. As in the third embodiment, the color image of the reference pattern ( A P sensor pattern) 68 is formed in step S1, and this color image 68 is read by the P sensor 73 in step S2. P sensor 73
Is amplified by the amplifier 74, sampled by the sampling circuit 75, A / D converted by the A / D converter 76, and sent to the comparison operation circuit 77.

The comparison operation circuit 77 executes A / D in step S3.
The edge enhancement level Ex is calculated from the output signal of the converter 76, and the MTF filter 5 is calculated by the CPU 63 in step S4.
The threshold value of 7 is determined according to the edge emphasis level Ex, and the MTF filter 57 is set as a low pass digital filter. Then, during the copying operation in which the scanner 1 reads the original and the printer 10 performs the image forming operation, the image signal from the γ correction circuit 58 is passed through the low-pass digital filter 57 in step S5 to correct the edge enhancement effect, and the edge is corrected. A color copy with no emphasis effect can be obtained.

The comparison operation circuit 77 uses the edge emphasis level Ex.
44, the peak value (minimum value) Veg of the input signal from the P sensor 73 with respect to the edge portions (the front end portion and the rear end portion in the sub-scanning direction) of the color image 68 of the reference pattern and the reference pattern are calculated as shown in FIG. Average value Vsp of the input signal from the P sensor 73 for the central portion of the color image 68 is calculated and standardized (Vsp / Veg is calculated), or (Vs
p-Veg) to obtain the edge enhancement level Ex
To calculate. The smaller the edge emphasis level Ex, the better the edge emphasis effect.

In the fourth embodiment, the latent image of the reference pattern is formed on the photosensitive drum 12 and visualized in the developing section, and then the level of the edge portion of the visualized pattern is measured by the P sensor 73.
The edge emphasis effect is corrected by the spatial digital filter 57 during the image forming operation of the printer 10 based on the detection value of the P sensor 73. Therefore, the developer, the photoconductor drum 12, the writing system, etc. may vary with time. It is possible to obtain a smooth image without the edge enhancement effect.

In the fifth embodiment of the present invention, in the fourth embodiment, as shown in FIG.
The edge emphasis level Ex is calculated by using p as a reference level (0 level) and obtaining the area of the region surrounded by the edge portion (hatched portion in FIG. 45) by the trapezoidal method or the like. The smaller the edge emphasis level Ex is, the better the edge emphasis effect is, and the more the sampling number of the sampling circuit 75 is, the higher the accuracy is.

FIG. 36 shows the operation flow of the sixth embodiment of the present invention. In the sixth embodiment, the CPU 63 of the fourth embodiment is advanced from step S4 to step S5.
Read the Y, M, C, and BK image signals for the full-color image of the reference pattern stored in the ROM 64 sequentially and output them to the printer 10 through the low-pass digital filter 57, and the writing optical unit 11 outputs the Y, By sequentially converting the M, C, and BK image signals into optical signals and performing optical writing corresponding to a full-color image of a predetermined pattern on the photosensitive drum 12, Y,
The electrostatic latent images of M, C, and BK are sequentially formed at the same position. Each of the electrostatic latent images of BK, C, M, and Y is B
The K developing device 23, the C developing device 24, the M developing device 25, and the Y developing device 26 visualize the respective images of BK, C, M, and Y, and these respective visible images are sequentially superposed at the same position. By being formed, the full-color image 68 of the reference pattern is obtained.

This color image 68 is read by the P sensor 73 in step S7, and the output signal of the P sensor 73 is amplified by the amplifier 74, the sampling circuit 75 and the A / D converter 7.
It is sent to the comparison operation circuit 77 via 6. The comparison operation circuit 77 calculates the edge enhancement level Ex from the output signal of the A / D converter 76 in the same manner as described above in step S8, and the CPU 6
In step S9, it is determined whether or not the edge emphasis level Ex is between the upper limit value Ves and the lower limit value Vee in step S9.

If the edge emphasis level Ex is not between the upper limit value Ves and the lower limit value Vee, the CPU 63 counts the number of times the threshold value of the low-pass digital filter 57 is set by the counter N in step S10, In S11, it is determined whether the counter N is 5 times or less. If the counter N is 5 times or less, the process returns to step S4. When the counter N reaches 6 times or more, the CPU 63 determines that the life of the developer in the developing device has reached the end, and displays the replacement of the developer on the display unit in step S14.

Further, the CPU 63 determines that the edge emphasis level Ex
Is between the upper limit value Ves and the lower limit value Vee, the threshold value of the low-pass digital filter 57 is determined according to the edge emphasis level Ex in step S12. Then, during the copying operation in which the scanner 1 reads the original document and the printer 10 performs the image forming operation, the image signal from the γ correction circuit 58 is passed through the low-pass digital filter 57 in step S13 to correct the edge enhancement effect, and the edge is corrected. A color copy with no emphasis effect can be obtained.

FIG. 37 shows the operation flow of the seventh embodiment of the present invention. In the seventh embodiment, the edge defect is corrected but the edge enhancement effect is not corrected. In the fourth embodiment, the comparison operation circuit 77 is used to make the A / D converter 7
The edge missing level Ex is calculated from the output signal of 6 instead of the edge emphasis level, the CPU 63 determines the threshold of the MTF filter 57 according to the edge missing level Ex, and the MTF filter 57 replaces the low pass digital filter. It is set as a high-pass digital filter.

The comparison operation circuit 77 detects the edge missing level Ex.
48, the peak value (maximum value) Veg of the input signal from the P sensor 73 with respect to the edge portion (the front end portion and the rear end portion in the sub scanning direction) of the color image 68 of the reference pattern and the reference pattern are calculated as shown in FIG. Average value Vsp of the input signal from the P sensor 73 for the central portion of the color image 68 is calculated and standardized (Vsp / Veg is calculated), or (Vs
p-Veg) to obtain the edge defect level Ex
To calculate. The smaller the edge missing level Ex, the better the edge missing.

In the seventh embodiment, the latent image of the reference pattern is formed on the photosensitive drum 12 and visualized in the developing portion, and then the edge portion level of the visualized pattern is measured by the P sensor 73.
Is detected by the spatial digital filter 57 during the image forming operation of the printer 10 based on the detection value of the P sensor 73.
2. It is possible to obtain a sharp image without any edge chipping due to a change with time in a writing system or the like.

In the eighth embodiment of the present invention, in the seventh embodiment, the comparison operation circuit 77 sets Vsp as the reference level (0 level) as shown in FIG. ) Is calculated by the trapezoidal method or the like to obtain the edge defect level Ex.
The smaller the edge missing level Ex, the better the edge missing.

FIG. 38 shows the operation flow of the ninth embodiment of the present invention. In the ninth embodiment, in the sixth embodiment, the edge arithmetic level Ex is calculated as described above from the output signal of the A / D converter 76 by the comparison operation circuit 77 instead of the edge emphasis level, and the CPU 63 causes the MTF to be calculated. The threshold value of the filter 57 is determined according to the edge missing level Ex, and the MTF filter 57 is set as a high pass digital filter instead of the low pass digital filter.

FIG. 39 shows the operation flow of the tenth embodiment of the present invention. In the tenth embodiment, the edge emphasis effect and the blurring of the edge portion are corrected, and the color image 68 of the reference pattern is formed in step S1 during the non-image forming operation of the printer 10 as in the above embodiment. This color image 68 is read by the P sensor 73 in step S2. The output signal of the P sensor 73 is amplified by the amplifier 74 and sampled by the sampling circuit 75.
A / D converter 76 performs A / D conversion and comparison operation circuit 7
Sent to 7.

The comparison operation circuit 77 executes A / D in step S3.
From the output signal of the converter 76, the level Ex (edge emphasis level, edge lack level) of the edge portion is calculated in the same manner as in the fourth and seventh embodiments (or in the same manner as in the fifth and eighth embodiments). Then, the CPU 63 determines in step S4 whether or not the level Ex of the edge portion is between the upper limit value Ves and the lower limit value Vee. If the level Ex of the edge portion is between the upper limit value Ves and the lower limit value Vee, the CPU 63 leaves the threshold value of the MTF filter 57 unchanged in step S8, the scanner 1 reads the document, and the printer 10 performs the image forming operation. In the copying operation for performing the step S9, the image signal from the γ correction circuit 58 passes through the MTF filter 57 in step S9 to obtain a sharp and smooth image.

Further, the CPU 63 controls the level E of the edge portion.
If x is not between the upper limit value Ves and the lower limit value Vee, the peak level Veg of the edge portion as shown in FIG. 44 and the level Vsp of the central portion are compared in step S5.

If Veg> Vsp, the CPU 63 determines the threshold value of the MTF filter 57 according to the edge level Ex at step S7, sets the MTF filter 57 as a high-pass digital filter, and the scanner 1 During a copying operation in which the printer 10 performs an image forming operation by reading an original, the image signal from the γ correction circuit 58 is subjected to edge defect correction by passing through the high-pass digital filter 57 in step S10, and a color copy without edge defect is obtained. can get.

If Veg> Vsp is not satisfied, the CPU 63 determines the threshold value of the MTF filter 57 according to the edge level Ex in step S6 and sets the MTF filter 57 as a low-pass digital filter. During a copying operation in which the document is read and the printer 10 performs an image forming operation, the image signal from the γ correction circuit 58 is passed through the low-pass digital filter 57 in step S11 to correct the edge enhancement effect, and the color without the edge enhancement effect is obtained. You get a copy.

40 and 41 show the operation flow of the eleventh embodiment of the present invention. In the eleventh embodiment, the edge enhancement effect and the blurring of the edge portion are corrected. In the tenth embodiment, steps S6 to S6 are performed.
21. The CPU 63 advances to step 21, and Y, M, C, B for the full-color image of the reference pattern stored in the ROM 64
The K image signals are sequentially read and output to the printer 10 through the low-pass digital filter 57, and the writing optical unit 11 outputs the Y, M, C, and BK in step S22.
Image signals are sequentially converted into optical signals, and the photosensitive drum 12
By performing optical writing corresponding to a full-color image of a predetermined pattern, the electrostatic latent images of Y, M, C, and BK are sequentially formed at the same position. The electrostatic latent images of BK, C, M and Y are respectively developed by BK developing device 23, C developing device 24 and M.
After being visualized by the developing device 25 and the Y developing device 26, BK,
The C, M, and Y visible images are formed, and the developed images are sequentially overlapped at the same position to form a full-color image 68 of the reference pattern.

This color image 68 is printed in step S23.
The output signal of the P sensor 73 read by the sensor 73 is sent to the comparison operation circuit 77 via the amplifier 74, the sampling circuit 75, and the A / D converter 76. The comparison operation circuit 77 calculates the edge enhancement level Ex from the output signal of the A / D converter 76 in the same manner as described above in step S24,
In step S25, the U63 determines whether or not the edge emphasis level Ex is between the upper limit value Ves and the lower limit value Vee.

If the edge emphasis level Ex is not between the upper limit value Ves and the lower limit value Vee, the CPU 63 counts with the counter N how many times the threshold value of the low-pass digital filter 57 is set in step S26, In S27, it is determined whether the counter N is 5 times or less. If the counter N is 5 times or less, the process returns to step S6. When the counter N reaches 6 times or more, the CPU 63 determines that the life of the developer in the developing device has reached the end, and causes the display unit to display the replacement of the developer in step S28.

Further, the CPU 63 determines that the edge emphasis level Ex
Is between the upper limit value Ves and the lower limit value Vee, the threshold value of the low-pass digital filter 57 is determined according to the edge emphasis level Ex in step S29. Then, during the copying operation in which the scanner 1 reads the document and the printer 10 performs the image forming operation, the image signal from the γ correction circuit 58 is passed through the low-pass digital filter 57 in step S11 to correct the edge enhancement effect, and the edge is corrected. A color copy with no emphasis effect can be obtained.

Further, in step S7 to step S12, the CPU 63 sequentially reads out the Y, M, C, and BK image signals for the full-color image of the reference pattern stored in the ROM 64, and the high-pass digital filter 5
7 to the printer 10, and the writing optical unit 11 sequentially converts the Y, M, C, and BK image signals into optical signals in step S13, and the photosensitive drum 12 outputs light corresponding to the full-color image of the reference pattern. By writing, electrostatic latent images of Y, M, C, and BK are sequentially formed at the same position. The electrostatic latent images of BK, C, M, and Y are visualized by the BK developing device 23, the C developing device 24, the M developing device 25, and the Y developing device 26, respectively.
Each visible image of Y becomes a full-color image 68 of the reference pattern by sequentially forming each visible image at the same position.

This color image 68 is printed in step S14.
The output signal of the P sensor 73 read by the sensor 73 is sent to the comparison operation circuit 77 via the amplifier 74, the sampling circuit 75, and the A / D converter 76. In step S15, the comparison operation circuit 77 calculates the edge missing level Ex from the output signal of the A / D converter 76 in the same manner as described above,
The U63 determines in step S16 whether or not the edge missing level Ex is between the upper limit value Ves and the lower limit value Vee.

If the edge emphasis level Ex is not between the upper limit value Ves and the lower limit value Vee, the CPU 63 counts the number of times the threshold value of the low-pass digital filter 57 is set by the counter N in step S17, and the step In S18, it is determined whether the counter N is 5 times or less. If the counter N is 5 times or less, the process returns to step S6. Further, when the counter N reaches 6 times or more, the CPU 63 determines that the life of the developer in the developing device has reached the end, and displays the replacement of the developer on the display unit in step S19.

Further, the CPU 63 causes the edge missing level Ex
If is between the upper limit value Ves and the lower limit value Vee, the threshold value of the high-pass digital filter 57 is determined according to the edge missing level Ex in step S20. Then, during the copying operation in which the scanner 1 reads the original and the printer 10 performs the image forming operation, the image signal from the γ correction circuit 58 is passed through the high-pass digital filter 57 in step S10 to correct the edge defect effect, and the edge edge effect is corrected. You can get a perfect color copy.

FIG. 42 shows a part of the circuit portion of the twelfth embodiment of the present invention, and FIG. 43 shows the operation flow of the twelfth embodiment. In the twelfth embodiment, the blur of the edge portion is corrected and the edge emphasis effect is not corrected.
U63 controls the high voltage power source in step S1 to set the direct current component Vdc of the developing bias voltage, the amplitude Vpp of the AC component and the frequency fb to initial values. Next, the color image 68 of the reference pattern is formed in step S2 during the non-image forming operation of the printer 10 as in the above embodiment.
8 is read by the P sensor 73 in step S3.
The output signal of the P sensor 73 is amplified by the amplifier 74 and sampled by the sampling circuit 75, and the A / D
It is A / D converted by the converter 76 and sent to the comparison operation circuit 77.

The comparison operation circuit 77 executes A / D in step S4.
The edge emphasis level Ex is calculated from the output signal of the converter 76 as described above, and the edge emphasis level Ex is D / A converted by the D / A converter 78 to be the developing bias control circuit 79.
Sent to. The developing bias control circuit 79 executes step S
In step 5, it is judged whether or not the edge emphasis level Ex is less than or equal to a predetermined level Vl. If the edge emphasis level Ex is not less than or equal to the predetermined level Vl, the high voltage power source is controlled in step S6 to control the DC component of the developing bias voltage. Vdc, the amplitude Vpp of the AC component and the frequency fb are set to predetermined values ΔVdc and ΔVp.
p and Δfb will be listed.

Then, the developing bias control circuit 79 outputs Vp
p is the upper limit value Vppmax or more and fb is the upper limit value fbm
It is determined whether or not the condition of being ax or more is satisfied, and if this condition is not satisfied, the process returns to step S2, and if the condition is satisfied, the process proceeds to step S8. Further, the developing bias control circuit 79 proceeds to step S8 when the edge emphasis level Ex is equal to or lower than the predetermined level Vl. In step S8, the developing bias control circuit 79 determines the DC component Vdc of the developing bias voltage, the amplitude Vpp of the AC component, and the frequency fb as they are, and the CPU 63 determines M in step S9.
The threshold of the TF filter 57 is set to the edge emphasis level E
Determined according to x, the MTF filter 57 is set as a low-pass digital filter. Then, during the copying operation in which the scanner 1 reads the original and the printer 10 performs the image forming operation, the image signal from the γ correction circuit 58 is output in step S10.
Then, the edge enhancement effect is corrected by passing through the low-pass digital filter 57, and a color copy without the edge enhancement effect is obtained.

In the above embodiment, when writing the image of the reference pattern on the photosensitive drum 12, any of a fluorescent lamp, a light emitting diode and a laser may be used as the light source, but the wavelength and intensity of the light from the light source may be changed. It is necessary that the photosensitive drum 12 is not deteriorated. In the above embodiment, it is possible to detect and correct the edge enhancement effect and the edge deficiency even when it is used as a copying machine (performing the copying operation).

In the above embodiment, the photosensitive drum 12 is used.
Although the image 68 of the upper reference pattern is detected by the CCD 72 or the P sensor 73, the image 68 of the reference pattern on the photosensitive drum 12 is transferred to the intermediate transfer belt 28 and then C
The CCD 72 or the P sensor 73 is used for detection, or the image 68 of the reference pattern on the photosensitive drum 12 is transferred onto the transfer paper via the intermediate transfer belt 28, and then the CCD 7 is transferred.
Alternatively, it may be detected by the 2 or P sensor 73.

When the visible images of the respective colors of the reference pattern are sequentially formed and detected by the CCD 72 or the P sensor 73, the reflection intensities of the visible images of the respective colors are different from each other (for example, the detection voltage of the CCD 72 or the P sensor 73). Is higher than that of BK), it is effective to change the calculation level of the edge portion for each color.

Also, in the photo forming mode for copying a photo, a smooth image without the edge enhancement effect is required.
In the character forming mode for copying a line drawing or a character, an image with a sharp edge is required. Therefore, in each of the other embodiments of the present invention, in the fourth to sixth embodiments, the correction is performed in the photo forming mode and not in the character forming mode. Further, in each of the other embodiments of the present invention, in the seventh to ninth embodiments and the twelfth embodiment, the correction is not performed in the photo forming mode, but is performed in the character forming mode.
Further, in each of the other embodiments of the present invention, in the tenth and eleventh embodiments, the correction of the edge enhancement effect and the correction of the edge defect are switched according to the switching between the photo formation mode and the character formation mode. I am trying to do it.

[0181]

As described above, according to the first aspect of the present invention, a latent image is formed by writing a digital image signal on the latent image carrier by the printer, and the latent image is visualized by the developing unit. In the image forming apparatus that performs the image forming operation of
Based on the detection means for detecting the level of the edge portion of the visible image of the pattern after the latent image of the predetermined pattern is formed on the latent image carrier and visualized by the developing section, Since the digital image signal is processed during the image forming operation of the printer and the spatial digital filter for correcting the edge portion is provided, it is possible to optimize the state of the edge portion due to the temporal change of the developer, the photoconductor, the writing system and the like. It is possible to obtain an image with good image quality that has been corrected for gradation.

According to the second aspect of the invention, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for carrying out the above, a detection means for forming a latent image of a predetermined pattern on the latent image carrier, visualizing the latent image on the latent image carrier, and then detecting an edge emphasis level of the pattern visible image; A low-pass digital filter that enhances the low-frequency region of the spatial frequency in the digital image signal based on the detection value of the printer and corrects the edge emphasis. It is possible to obtain a smooth image without the edge enhancement effect due to the temporal variation of the system.

According to the third aspect of the invention, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing the above, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and detects an edge-missing level of the pattern image, and the sensing unit. A high-pass digital filter that corrects edge deficiency by enhancing the high frequency region of the spatial frequency in the digital image signal based on the detection value of It is possible to obtain a sharp image with no edge chipping due to aging of the system.

According to the invention described in claim 4, an image forming operation in which a latent image is formed by writing a digital image signal on the latent image carrier by the printer and the latent image is visualized by the developing section. In the image forming apparatus for carrying out the above, a detecting means for detecting a level state of the pattern image after forming a latent image of a predetermined pattern on the latent image carrier and visualizing the latent image in the developing section, On the basis of the detected value, during the image forming operation of the printer, the low frequency region of the spatial frequency in the digital image signal is enhanced to correct the edge enhancement, and the high frequency region of the spatial frequency in the digital image signal is enhanced to cut edges. Since it is equipped with a spatial digital filter that corrects, there is no edge enhancement effect or edge chipping due to changes over time in the developer, photoconductor, writing system, etc. and it is sharp and smooth. Image can be obtained.

According to the invention described in claim 5, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus, the latent image of a predetermined pattern is formed on the latent image carrier and visualized by the developing unit, and then the toner adhesion amount of the pattern image is detected by a photo sensor to detect the edge enhancement level. And an edge emphasis level detecting means for calculating the edge emphasis level detecting means, and based on the detection value of the edge emphasis level detecting means, enhances the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer to correct the edge emphasis. Since it is equipped with a low-pass digital filter, it is possible to obtain a smooth image without the edge enhancement effect due to changes over time in the developer, photoconductor, writing system, etc.

According to the invention described in claim 6, an image forming operation in which a latent image is formed by writing a digital image signal on the latent image carrier by the printer and the latent image is visualized by the developing section. In the image forming apparatus for performing the above, after forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, the toner adhesion amount of the visual image of the pattern is detected by a photo sensor to detect an edge defect level. Edge defect level detecting means for calculating the edge defect level and correcting the edge defect by enhancing the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge defect level detecting means. Since it has a high-pass digital filter, it is possible to obtain a sharp image without any edge chipping due to changes over time in the developer, photoconductor, writing system and the like.

According to the invention described in claim 7, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing the above, after forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, the toner adhesion amount of the pattern visual image is detected by a photo sensor to detect the edge portion. Edge level detection means for calculating a level, and based on the detection value of the edge level detection means, enhance the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer to correct the edge enhancement. And a spatial digital filter that corrects an edge deficiency by enhancing the high frequency region of the spatial frequency in the image signal. It can optimally correct the state of the edge portion due to change over time of obtaining the image quality good image fully equipped gradation.

According to the invention described in claim 8, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects the toner adhesion amount of the patterned image by a photo sensor, Edge emphasis level detection means for calculating an edge emphasis level from information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern image detected by the detection means, and this edge emphasis level detection A low-pass for correcting the edge emphasis by enhancing the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the means. Since a digital filter,
It is possible to obtain a smooth image without the edge enhancement effect due to changes over time in the developer, photoconductor, writing system and the like.

According to the invention described in claim 9, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects the toner adhesion amount of the patterned image by a photo sensor, An edge missing level detecting means for calculating an edge missing level from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern image detected by the detecting means, and the edge missing level detecting means. High-pass for enhancing the high frequency region of the spatial frequency in the digital image signal to correct the edge defect during the image forming operation of the printer based on the detection value of the means. Since a digital filter,
It is possible to obtain a sharp image with no edge chipping due to changes over time in the developer, photoconductor, writing system, etc.

According to the tenth aspect of the invention, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects the toner adhesion amount of the patterned image by a photo sensor, An edge portion level detecting means for calculating the level of the edge portion from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the pattern visible image detected by the detecting means, and the edge portion level detecting means. Based on the detection value of the detection means, the low frequency region of the spatial frequency in the digital image signal is enhanced during the image forming operation of the printer to correct the edge enhancement, Equipped with a spatial digital filter that enhances the high frequency range of the spatial frequency in the image signal and corrects edge deficiencies, it optimally corrects the edge condition due to changes over time in the developer, photoconductor, writing system, etc. As a result, it is possible to obtain an image with good image quality and gradation.

According to the eleventh aspect of the present invention, an image forming operation in which a latent image is formed by writing a digital image signal on the latent image carrier by the printer and the latent image is visualized by the developing unit. In the image forming apparatus for performing, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects the toner adhesion amount of the patterned image by a photo sensor, The area of the pattern image is calculated on the basis of the toner adhesion amount average value in the vicinity of the central portion of the pattern image detected by the detecting means as a reference level, and the edge enhancement level is calculated from the information of the area. Edge enhancement level detecting means and a low spatial frequency in the digital image signal during image forming operation of the printer based on the detection value of the edge enhancement level detecting means. Since a low pass digital filter which enhanced the frequency correcting the edge emphasis can be the developer, photoreceptor, the edge enhancement effect with time variation, such as writing system obtain without smooth image.

According to the twelfth aspect of the invention, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects the toner adhesion amount of the patterned image by a photo sensor, The area of the pattern image is calculated on the basis of the toner adhesion amount average value in the vicinity of the center of the pattern image detected by the detecting means as a reference level, and the edge defect level is calculated from the information of this area. And a high frequency spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge defect level detecting unit. Since a high-pass digital filter which enhanced the frequency correcting the edge chipping, the developer can photoreceptor, edge chipping due to change over time, such as writing system obtain without sharp images.

According to the thirteenth aspect of the invention, an image forming operation in which a latent image is formed by writing a digital image signal on the latent image carrier by the printer and the latent image is visualized by the developing unit. In the image forming apparatus for performing, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes the latent image on the latent image carrier, and then detects the toner adhesion amount of the patterned image by a photo sensor, The area of the pattern image is calculated on the basis of the toner adhesion amount average value in the vicinity of the central portion of the pattern image detected by the detecting means as a reference level, and the level of the edge portion is calculated from the information of the area. Edge portion level detecting means for calculating, and a low frequency range of spatial frequency in the digital image signal during image forming operation of the printer based on the detection value of the edge portion level detecting means. Since it is provided with a spatial digital filter that performs edge enhancement correction by enhancing the spatial frequency in the digital image signal and enhances the high frequency region of the spatial frequency in the digital image signal, the developer, the photoconductor, the writing system, etc. It is possible to optimally correct the state of the edge portion due to aging and obtain an image with good image quality and gradation.

According to the fourteenth aspect of the invention, in the image forming apparatus of the second, fifth, eighth or eleventh aspect, since the correction is performed in the photo forming mode and not in the character forming mode, a photographic image is formed. Is effective for.

According to a fifteenth aspect of the present invention, in the image forming apparatus according to the first, second, eighth, eleventh or fourteenth aspect, a developing bias applying means for applying a direct-current or alternating-current developing bias to the developing section is provided. Since the amplitude and / or the frequency of the developing bias applied from the developing bias applying unit to the developing unit is controlled based on the detection value of the detecting unit to correct the edge emphasis, the correction effect of the edge emphasis is improved. .

According to the sixteenth aspect of the invention, in the image forming apparatus of the third, sixth, ninth or twelfth aspect, the correction is performed in the character forming mode and not in the photo forming mode. Is effective for.

According to the seventeenth aspect of the invention, in the image forming apparatus of the fourth, seventh, tenth or thirteenth aspect, the edge enhancement correction and the edge defect correction are switched between the photo formation mode and the character formation mode. Run according to
It is effective for forming a photographic image and a character image.

According to the eighteenth aspect of the present invention, in the image forming apparatus according to the second, fifth, eighth or eleventh aspect, the life of the developer is reached when the edge emphasis level detected by the detecting means becomes a specified value or more. Since a judgment means for judging that the developer has come is provided, it is possible to accurately know the replacement time of the developer.

According to a nineteenth aspect of the present invention, in the image forming apparatus according to the third, sixth, ninth or twelfth aspect, the life of the developer is reached when the edge defect level detected by the detecting means exceeds a specified value. Since a judgment means for judging that the developer has come is provided, it is possible to accurately know the replacement time of the developer.

According to the twentieth aspect of the present invention, in the image forming apparatus according to the fourth, seventh, tenth or thirteenth aspect, when the level of the edge portion detected by the detecting means exceeds a specified value, the developer Since the judgment means for judging the end of life has been provided, it is possible to accurately know when to replace the developer.

According to the invention of claim 21, claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 1
In the image forming apparatus described in 2, 13, or 14, the detection unit forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing unit, and then transfers it to an intermediate transfer member to transfer the intermediate image. Since the level of the edge of the pattern image on the transfer body is detected, the state of the edge due to changes over time of the developer, photoconductor, writing system, etc. is optimally corrected to provide an image with good gradation and good image quality. Can be obtained.

According to the invention of claim 22, claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 1
2. The image forming apparatus according to 2, 13 or 14, wherein the detecting means forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing section, and then transfers it to a transfer body. Since the level of the edge part of the upper pattern image is detected, the state of the edge part due to aging of the developer, photoconductor, writing system, etc. is optimally corrected to obtain an image with good gradation and good image quality. be able to.

According to the twenty-third aspect of the invention, an image forming operation of forming a latent image by writing a digital image signal on the latent image carrier by the printer and visualizing the latent image by the developing unit. In the image forming apparatus for performing the following, a detection unit that forms a latent image of a predetermined pattern on the latent image carrier, visualizes it in the developing unit, and then detects the level of the edge portion of the visualized pattern with an image sensor. , And a spatial digital filter that corrects the edge portion by processing the digital image signal during the image forming operation of the printer based on the detection value of the detection means, so that the edge portion of the pattern image with high accuracy can be obtained. By detecting the level, it is possible to optimally correct the state of the edge portion due to the temporal change of the developer, photoconductor, writing system, etc., and obtain an image with good gradation and good image quality.

According to the twenty-fourth aspect of the present invention, in the printer, a developing bias applying unit applies a developing bias of DC or AC to the developing unit to form a latent image by writing an image signal on the latent image carrier. Then, in an image forming apparatus that performs an image forming operation of making the latent image visible by the developing unit, after forming a latent image of a predetermined pattern on the latent image carrier and making the latent image visible by the developing unit. Detecting means for detecting the level of the edge portion of the pattern image with an image sensor, and the developing bias applying means on the basis of the detection value of the detecting means to control the amplitude of the developing bias during the image forming operation of the printer and And / or a correction means for correcting the edge portion by changing the frequency, so that the level of the edge portion of the pattern image can be detected with high accuracy to change the developer, the photoconductor, the writing system, etc. with time. Quality good image fully equipped gradation optimally correct the state of the edge portion with can be obtained.

According to the invention of claim 25, claim 1
Alternatively, in the image forming apparatus according to the second aspect, the detecting unit sequentially forms a latent image of each color in a predetermined pattern on the latent image carrier, and the latent image is visualized by the developer of each color in the developing unit. After the image is formed into a color image having a predetermined pattern, the level of the edge portion of this color image is detected by the color image pickup element at once, so that the level of the edge portion of the color image can be detected efficiently.

[Brief description of drawings]

FIG. 1 is a block diagram showing an invention according to claim 1.

FIG. 2 is a sectional view showing the outline of a first embodiment of the present invention.

FIG. 3 is a sectional view showing a part of the first embodiment.

FIG. 4 is a block diagram showing a circuit configuration of the first embodiment.

FIG. 5 is a perspective view showing a reference pattern color image detection unit in the first embodiment.

FIG. 6 is a side view showing the reference pattern color image detection unit.

FIG. 7 is an enlarged perspective view showing a part of the reference pattern color image detection unit.

FIG. 8 is a waveform diagram showing an example of a CCD output signal voltage according to the first embodiment.

FIG. 9 is a waveform chart showing another example of the CCD output signal voltage.

FIG. 10 is a waveform chart showing another example of the CCD output signal voltage.

FIG. 11 is a plan view showing a reference pattern color image of the first embodiment.

FIG. 12 is a diagram showing a part of the CCD according to the first embodiment.

FIG. 13 is a diagram showing an example of coefficients of the spatial digital filter of the first embodiment.

FIG. 14 is a characteristic diagram for explaining the correction of the edge enhancement effect of the first embodiment.

FIG. 15 is a diagram for explaining image processing by the spatial digital filter according to the first embodiment.

FIG. 16 is a diagram showing an example of an input image according to the first embodiment.

FIG. 17 is a diagram showing an example of an image after processing by the spatial digital filter of the first embodiment.

FIG. 18 is a diagram showing another example of coefficients of the spatial digital filter of the first embodiment.

FIG. 19 is a characteristic diagram for explaining the edge defect correction of the first embodiment.

FIG. 20 is a diagram for explaining image processing by the spatial digital filter according to the first embodiment.

FIG. 21 is a diagram showing another example of the input image according to the first embodiment.

FIG. 22 is a diagram showing another example of an image after being processed by the spatial digital filter of the first embodiment.

FIG. 23 is a characteristic diagram showing frequency characteristics of the developing device in the first embodiment.

FIG. 24 is a characteristic diagram showing developing characteristics of the developing device in the first embodiment.

FIG. 25 is a characteristic diagram showing the relationship between carrier resistance and edge enhancement level in the first embodiment.

FIG. 26 is a characteristic diagram showing the relationship between the amplitude of the developing bias voltage and the edge emphasis level according to the first embodiment.

FIG. 27 is a characteristic diagram showing the relationship between the frequency of the developing bias voltage and the edge emphasis level according to the first embodiment.

FIG. 28 is a flowchart showing an operation flow of the second embodiment of the present invention.

FIG. 29 is a characteristic diagram showing characteristics of a P sensor.

FIG. 30 is a plan view showing a reference pattern image detecting portion according to the third embodiment of the present invention.

FIG. 31 is a waveform chart showing an example of a P sensor output signal of the third embodiment.

FIG. 32 is a plan view showing a reference pattern image detection unit of the third embodiment.

FIG. 33 is a waveform chart showing an example of a P sensor output signal of the third embodiment.

FIG. 34 is a block diagram showing a circuit portion of a fourth embodiment of the present invention.

FIG. 35 is a flow chart showing an operation flow of the fourth embodiment.

FIG. 36 is a flowchart showing an operation flow of the sixth embodiment of the present invention.

FIG. 37 is a flowchart showing the operation flow of the seventh embodiment of the present invention.

FIG. 38 is a flowchart showing the operation flow of the ninth embodiment of the present invention.

FIG. 39 is a flowchart showing an operation flow of the tenth embodiment of the present invention.

FIG. 40 is a flowchart showing a part of the operation flow of the eleventh embodiment of the present invention.

FIG. 41 is a flowchart showing another portion of the operation flow of the eleventh embodiment.

FIG. 42 is a block diagram showing a circuit portion of a twelfth embodiment of the present invention.

FIG. 43 is a flowchart showing the operation flow of the twelfth embodiment.

FIG. 44 is a waveform diagram showing an output signal example of the P sensor.

FIG. 45 is a waveform diagram showing an output signal example of the P sensor.

FIG. 46 is a plan view showing another example of the reference pattern image detection unit.

FIG. 47 is a plan view showing another example of the reference pattern image detection unit.

FIG. 48 is a waveform chart showing an example of the output signal of the P sensor.

FIG. 49 is a waveform diagram showing an output signal example of the P sensor.

FIG. 50 is a schematic view showing a conventional laser printer.

FIG. 51 is a diagram showing an example of an input image of the laser printer.

FIG. 52 is a diagram showing an example of electric field strength on a photosensitive drum of the laser printer.

FIG. 53 is a diagram showing an example of an input image of the laser printer.

FIG. 54 is a diagram showing an example of electric field strength on a photosensitive drum of the laser printer.

FIG. 55 is a characteristic diagram showing resistance characteristics of carriers.

[Explanation of symbols]

 1 Detection means 2 Spatial digital filter

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display area H04N 1/29 Z 9186-5C

Claims (25)

[Claims] 1. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for detecting the level of the edge portion of the visible image of the pattern after the latent image of the predetermined pattern is formed on the latent image carrier and visualized by the developing portion, and the detecting means based on the detection value of the detecting means. An image forming apparatus comprising: a spatial digital filter that processes the digital image signal and corrects an edge portion during an image forming operation of a printer. 2. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing the latent image on the developing portion, and then detecting the edge enhancement level of the visible image of the pattern, and the printer based on the detection value of the detecting means. An image forming apparatus, comprising: a low-pass digital filter which enhances a low frequency region of a spatial frequency in the digital image signal and corrects edge enhancement during the image forming operation. 3. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing the latent image on the latent image carrier, and detecting the edge defect level of the visible image of the pattern, and the printer based on the detection value of the detecting means. An image forming apparatus, comprising: a high-pass digital filter that enhances a high frequency region of a spatial frequency in the digital image signal to correct an edge defect during the image forming operation. 4. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for detecting the level state of the latent image of the pattern after the latent image of the predetermined pattern is formed on the latent image carrier and visualized in the developing section, and the printer of the printer based on the detection value of the detecting means. A spatial digital filter that enhances the low frequency region of the spatial frequency in the digital image signal during image forming operation to correct edge enhancement and enhances the high frequency region of the spatial frequency in the digital image signal to correct edge deficiency; An image forming apparatus comprising: 5. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. An edge emphasis level detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, and thereafter detecting the toner adhesion amount of the pattern image by a photo sensor to calculate an edge emphasis level. And a low-pass digital filter that corrects edge enhancement by enhancing the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge enhancement level detection means. An image forming apparatus characterized by. 6. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. An edge deficiency level detection means for calculating a toner deficiency level by detecting a toner adhesion amount of the pattern observable image with a photo sensor after forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section. And a high-pass digital filter that corrects edge deficiency by enhancing the high frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge deficiency level detection means. An image forming apparatus characterized by. 7. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Edge portion level detection, in which a latent image of a predetermined pattern is formed on the latent image carrier and visualized at the developing portion, and then the toner adhesion amount of this pattern image is detected by a photo sensor to calculate the edge portion level. Means for enhancing the low frequency range of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge part level detection means to correct the edge enhancement, and the spatial frequency in the image signal. And a spatial digital filter that corrects edge deficiency by enhancing the high frequency range of the image forming apparatus. 8. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section and then detecting the toner adhesion amount of the visible image of this pattern by a photo sensor; and the pattern detected by this detecting means. Edge emphasis level detection means for calculating an edge emphasis level from the information of the toner adhesion amount average value in the vicinity of the central portion and the toner adhesion amount peak value of the edge portion in the visible image, and based on the detection value of the edge emphasis level detection means And a low-pass digital filter that corrects edge enhancement by enhancing the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer. An image forming apparatus comprising. 9. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section and then detecting the toner adhesion amount of the visible image of this pattern by a photo sensor; and the pattern detected by this detecting means. Edge defect level detection means for calculating an edge defect level from the information of the toner adhesion amount average value near the central portion and the toner adhesion amount peak value of the edge portion in the visible image, and based on the detection value of the edge defect level detection means And a high-pass digital filter that enhances the high frequency region of the spatial frequency in the digital image signal and corrects edge deficiency during image forming operation of the printer. An image forming apparatus comprising. 10. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section and then detecting the toner adhesion amount of the visible image of this pattern by a photo sensor; and the pattern detected by this detecting means. Based on the detection value of the edge part level detection means for calculating the level of the edge part from the information of the toner adhesion amount average value near the central part and the toner adhesion amount peak value of the edge part in the visible image. During the image forming operation of the printer, the low frequency region of the spatial frequency in the digital image signal is enhanced to correct the edge emphasis, and the spatial frequency in the digital image signal is corrected. By enhancing the high frequency range image forming apparatus characterized by comprising a spatial digital filter for correcting the edge chipping. 11. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section and then detecting the toner adhesion amount of the visible image of this pattern by a photo sensor; and the pattern detected by this detecting means. Edge emphasis level detection means for calculating the area of the pattern visible image based on the reference level with the average value of the toner adhesion amount near the central portion of the visible image as a reference level, and calculating the edge emphasis level from the information of this area, Based on the detection value of the edge emphasis level detecting means, the low frequency region of the spatial frequency in the digital image signal is enhanced during the image forming operation of the printer to enhance the edge emphasis. An image forming apparatus characterized by comprising a low-pass digital filter for performing positive. 12. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section and then detecting the toner adhesion amount of the visible image of this pattern by a photo sensor; and the pattern detected by this detecting means. An edge deficiency level detecting means for calculating an area of the pattern imaginary image based on the reference level with the toner adhesion amount average value in the vicinity of the central portion of the imaginary image as a reference level and calculating an edge deficiency level from information of the area, Based on the detection value of the edge-missing level detecting means, the high frequency region of the spatial frequency in the digital image signal is enhanced during the image forming operation of the printer so that the edge missing An image forming apparatus comprising the high-pass digital filter for performing positive. 13. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. Detecting means for forming a latent image of a predetermined pattern on the latent image carrier and visualizing it in the developing section, and then detecting the toner adhesion amount of the visible image of the pattern by a photo sensor; and the pattern detected by the detecting means. Edge portion level detection means for calculating an area of the pattern visualized image based on the reference level with an average value of toner adhesion amount near the central portion in the visualized image and calculating the level of the edge portion from the information of the area. Correction of edge enhancement by enhancing the low frequency region of the spatial frequency in the digital image signal during the image forming operation of the printer based on the detection value of the edge level detection means Performed, the image forming apparatus characterized by comprising a spatial digital filter for by enhancing high frequency region of the spatial frequency of the edge chipping correction in the digital image signal. 14. The image forming apparatus according to claim 2, 5, 8 or 11, wherein the correction is performed in a photo forming mode and not in a character forming mode. 15. The image forming apparatus according to claim 1, 2, 8, 11 or 14, further comprising: a developing bias applying unit for applying a direct-current or alternating-current developing bias to the developing unit, and the developing bias applying unit applies the developing bias to the developing unit. An image forming apparatus, characterized in that the amplitude and / or frequency of a developing bias applied to a developing section is controlled based on a detection value of the detecting means to correct edge enhancement. 16. The image forming apparatus according to claim 3, 6, 9 or 12, wherein the correction is performed in the character forming mode and not in the photo forming mode. 17. The image forming apparatus according to claim 4, 7, 10, or 13, wherein edge enhancement correction and edge defect correction are executed in response to switching between a photo formation mode and a character formation mode. Image forming apparatus. 18. An image forming apparatus according to claim 2, 5, 8 or 11, further comprising a judging means for judging that the life of the developer has come when the edge emphasis level detected by the detecting means exceeds a specified value. An image forming apparatus characterized by being provided. 19. The image forming apparatus according to claim 3, 6, 9 or 12, further comprising a judging means for judging that the life of the developer has come when the edge defect level detected by the detecting means exceeds a specified value. An image forming apparatus characterized by being provided. 20. The image forming apparatus according to claim 4, 7, 10 or 13, wherein when the level of the edge portion detected by the detecting means exceeds a specified value, it is determined that the developer has reached the end of its life. An image forming apparatus comprising: 21. Claims 1, 2, 3, 4, 5, 6, 7,
In the image forming apparatus described in 8, 9, 10, 11, 12, 13 or 14, the detection means forms a latent image of a predetermined pattern on the latent image carrier and visualizes the latent image on the latent image carrier, and then the intermediate image is formed. An image forming apparatus characterized by transferring to a transfer body and detecting a level of an edge portion of a pattern image on the intermediate transfer body. 22. Claims 1, 2, 3, 4, 5, 6, 7,
In the image forming apparatus described in 8, 9, 10, 11, 12, 13 or 14, the detection unit forms a latent image of a predetermined pattern on the latent image carrier, and transfers the image after the latent image is visualized in the developing unit. An image forming apparatus, which is transferred to a body and detects a level of an edge portion of a pattern image on the transfer body. 23. An image forming apparatus for performing an image forming operation of forming a latent image by writing a digital image signal on a latent image carrier by a printer and visualizing the latent image by a developing unit. A detection means for detecting the level of the edge portion of the pattern image after the latent image of a predetermined pattern is formed on the latent image carrier and visualized by the developing section by the image sensor, and the detection value of the detection means. An image forming apparatus, comprising: a spatial digital filter which processes the digital image signal and corrects an edge portion based on the image forming operation of the printer. 24. In the printer, a developing bias applying means applies a developing bias of DC or AC to the developing portion to form a latent image by writing an image signal on the latent image carrier, and the latent image is developed. In an image forming apparatus that performs an image forming operation of visualizing by a unit, a latent image of a predetermined pattern is formed on the latent image carrier and visualized by the developing unit, and then an edge portion of the pattern visual image is formed. By detecting the level with an image sensor, and controlling the developing bias applying means based on the detection value of the detecting means to vary the amplitude and / or frequency of the developing bias during the image forming operation of the printer. An image forming apparatus comprising: a correction unit that corrects an edge portion. 25. An image forming apparatus according to claim 1 or 2, wherein said detection means successively forms a latent image of each color in a predetermined pattern on said latent image carrier to successively develop said latent image. An image forming apparatus, characterized in that a level of an edge portion of a color image is detected at one time by a color image pickup device after being visualized with a developer of each color to form a color image of a predetermined pattern.