JP3526230B2 - Image forming method and apparatus, and storage medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus for forming an image on a recording medium, and a storage medium storing a control program for controlling the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as a method of adjusting image processing characteristics in an image forming apparatus such as a copying apparatus or a printer apparatus, an image forming apparatus is activated and one specific gradation test pattern is printed on a recording paper or the like. After forming on the recording medium,
The density of the gradation test pattern formed on the recording medium is read by an image reading unit (reader), and the read image information is fed back to an image forming condition such as γ correction (LUT) to obtain an image. Techniques for improving quality stability are known.

[0003]

However, in the above-mentioned conventional example, when the input of the reader is usually 8 bits, the ISO brightness of the white background of the document is 81% (density D = 0. 07), the luminance signal is 25
It becomes 5. This is set so that the luminance signal of a general blank sheet becomes 255. However, the ISO of the read manuscript
Brightness (whiteness) of 81% or more (density D = 0.0
7), the luminance signal sticks to 255.

As described above, in the above-mentioned conventional example, when the above-described processing is performed using a recording medium having a high whiteness, the information of the extreme highlight is lost, and if it is fed back as it is, a pseudo contour appears in the highlight portion. was there.

[0005] The present invention has been made in view of such problems of the prior art described above, it is an purpose of that, the recording medium used in the tone correction of the image forming apparatus
White paper with low density can be used as a body
The choices of the body are expanded, and it is compared to the gradation correction of the image forming device.
It is an object of the present invention to provide an image forming method, an image forming apparatus , and a storage medium that can obtain a good image in which pseudo contours, fogging, and roughness are suppressed even if a recording medium having high whiteness is used .

[0006]

[0007]

The image forming method of the present invention to achieve the above Symbol purpose Means for Solving the Problems] is adjusted using the first white reference
Read the original image under the adjusted first image reading condition.
The first reading step to be performed and the image obtained in the first reading step
An image forming machine that forms an image with a printer based on an image signal
And a tone test pattern with a second white reference
As a draft, read under the second image reading condition and execute the gradation test pattern.
A second reading step of generating a turn reading signal, and the gradation
The tone of the printer is adjusted using the test pattern read signal.
Printer gradation correction step for correction, and the first image reading
Depending on the density of the original that gives the specified read signal level under certain conditions
Also the predetermined reading signal level under the second image reading condition
Change the image reading conditions to reduce the density of the original
And a further step .

Further, the image forming apparatus of the present invention to achieve the above Symbol purpose was adjusted using the first white reference
First, the image of the original is read under the first image reading condition
And the image signal obtained by the first reading means.
An image forming means for forming an image on the printer based on the second;
The gradation test pattern with the white reference of
Read under the image reading conditions of 2 and read the gradation test pattern
Second reading means for generating a signal, and the gradation test pattern
A screen correction signal is used to correct the gradation of the printer.
Linter gradation correction means and predetermined according to the first image reading condition
The reading signal level of
The predetermined reading signal level is obtained under the image reading condition
Image reading condition changing means for setting the density of the original to be small is provided.

[0009]

[0010]

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[0018]

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[0020]

[0021]

[0022]

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[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a vertical sectional side view showing the structure of an image forming apparatus (an electrophotographic digital copying machine in this embodiment) according to a first embodiment of the present invention. 2 is a block diagram showing a configuration of a processing circuit for processing an electric signal from a full color sensor (CCD or the like) in the image forming apparatus shown in FIG.

In FIG. 1, the image forming apparatus includes a reader unit R.
When a copy key (not shown) is pressed, the original document 30 placed on the original platen glass 31 is exposed and scanned by the exposure lamp 32 in the reader unit R to expose the original document 30. The reflected light image from is collected on a full color sensor 34 such as a CCD to obtain a color separated image signal. The full-color sensor 34 decomposes the original 30 into a large number of pixels and generates photoelectric conversion signals corresponding to the densities of the pixels. Then, the read image information is recorded on the recording paper, which is a recording material, in the printer unit P and is output.

In FIG. 2, the image signal output from the full-color sensor 34 is input to the analog signal processing unit 201 and adjusted in gain and offset, and then, in the A / D conversion unit 202, for each color component, for example, 8 bits. (0-25
(5 levels: 256 gradations) converted into RGB digital signals, and the shading correction unit 203 uses the signal obtained by reading the reference white plate 106 for each color to eliminate variations in the sensitivity of the sensor cell group of the full-color sensors 34 arranged in a line. Therefore, a known shading correction process is performed by optimizing the gain corresponding to each sensor cell.

The line delay section 204 corrects the spatial deviation contained in the image signal output from the shading correction section 203. This spatial shift is caused by the line sensors of the full-color sensor 34 being arranged at a predetermined interval in the sub-scanning direction. Specifically, with the B (blue) color component signal as a reference, the R (red) and G (green) color component signals are line-delayed in the sub-scanning direction to synchronize the phases of the three color component signals.

The input masking unit 205 calculates the color space of the image signal output from the line delay unit 204 by the matrix calculation of the following expression (1), NTSC (Natio).
nal Television System Com
Mittee: Converts to the standard color space of the American Television System Committee. That is, the full-color sensor 34
The color space of each color component signal output from is determined by the spectral characteristics of the filter of each color component, but this is converted to the NTSC standard color space.

[0037]

[Equation 1] However, Ro, Go, Bo: output image signals Ri, Gi, Bi: input image signal from an external input unit 213 to a CRT of a computer (not shown)
The color original image information displayed on the display is input to the image forming apparatus as an image signal.

The LOG conversion unit 206 is composed of a look-up table (LUT) including, for example, a ROM (Read Only Memory), and converts the RGB luminance signal output from the input masking unit 205 into a CMY density signal. In the line delay memory 207, the black character determination unit (not shown) outputs the control signal UC from the output of the input masking unit 205.
The image signal output from the LOG conversion unit 206 is delayed by the period (line delay) for creating R, FLTER, SEN, and the like.

The masking / UCR unit 208 extracts the black component signal K from the image signal output from the line delay memory 207, and further performs a matrix calculation for correcting the color turbidity of the recording color material of the printer unit P as a YMCK image signal. Apply to
For each reading operation of the reader unit R, in the order of M, C, Y, K,
For example, an 8-bit color component image signal is output. The matrix coefficient used for the matrix calculation is the CPU 21
4 is set.

The .gamma.-correction unit 209 masks the image signal in order to match it with the ideal gradation characteristics of the printer unit P.
Density correction is performed on the image signal output from the UCR unit 208. The output filter (spatial filter processing unit) 210 is C
The image signal output from the γ correction unit 209 is subjected to edge enhancement or smoothing processing according to the control signal from the PU 214.

The LUT 211 is used to match the density of the original image with the density of the image, and is composed of, for example, a RAM (random access memory) or the like, and its conversion table is set by the CPU 214. The pulse width modulator (PWM) 212 outputs a pulse signal having a pulse width corresponding to the level of the input image signal, and the pulse signal is input to the laser driver 41 that drives the laser light source (semiconductor laser) 42. .

A pattern generator 215 is mounted on this image forming apparatus, the gradation pattern shown in FIG. 5 is registered, and a signal can be directly passed to the pulse width modulator 212. .

In FIG. 1, a laser light E emitted from a laser light source (semiconductor laser) 42 is swept by a rotary polygon mirror 3a, and a lens 3b such as an f / θ lens and the laser light E are exposed as an image carrier. A spot image is formed on the photosensitive drum 1 by the fixed mirror 3c that is directed in the direction of the drum 1. Thus, the laser beam E scans the photosensitive drum 1 in a direction substantially parallel to the rotation axis of the photosensitive drum 1 (main scanning direction), and repeatedly scans the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 (sub scanning direction). By doing so, an electrostatic latent image is formed.

In the printer section P, the photosensitive drum 1 as an image carrier is made of amorphous silicon, selenium, OPC.
Etc. on the surface, rotatably carried in the direction of the arrow in the figure,
Around the photosensitive drum 1, a pre-exposure lamp 11, a primary charging device (corona charging device) 2 as a charging device, a laser exposure optical system 3, a surface potential sensor 12, and a developing device 4 having different colors from each other.
y, 4c, 4m, 4bk, light amount detecting means 1 on the photosensitive drum
3, a transfer device 5, and a cleaning device 6 are arranged.

In the printer section P, during image formation, the photosensitive drum 1 is rotated in the direction of the arrow in the drawing, uniformly discharged by the pre-exposure lamp 11, and then uniformly charged by the primary charger 2. After that, the laser beam E modulated corresponding to the above-mentioned image information signal is exposed and scanned, whereby an electrostatic latent image corresponding to the image information signal is formed.

Next, a predetermined developing device among the developing devices 4y, 4c, 4m, and 4bk is operated, and the electrostatic latent image on the photosensitive drum 1 is reversely developed by a two-component developer consisting of toner and carrier. As a result, a negatively-charged visible image (toner image) based on resin is formed on the photosensitive drum 1.
Each developing device 4y, 4c, 4m, 4bk is adapted to selectively approach the photosensitive drum 1 according to each separated color by the operation of the corresponding eccentric cams 24y, 24c, 24m, 24bk. Here, the reversal development is a development method in which toner charged with the same polarity as the latent image is attached to the region of the photoconductor exposed to light to visualize the latent image.

Further, the toner image on the photosensitive drum 1 is transferred from the recording material cassette 7 to the recording material supplied to the position facing the photosensitive drum 1 via the conveying system and the transfer device 5.
In the present embodiment, the transfer device 5 includes a transfer drum 5a as a recording material carrier, a transfer brush charger 5b as a transfer unit, and an adsorption brush charger 5 for adsorbing a recording material.
c, the inner charging device 5d, the outer charging device 5e, the recording material carrying sheet 5f, and the suction roller 5 facing the suction brush charging device 5c.
g, a transfer peeling sensor 5h, and a separation charger 5j. The transfer drum 5a is axially supported so as to be rotationally driven, and a recording material carrying sheet 5f made of a dielectric material is integrally stretched in a cylindrical shape in an opening area of its peripheral surface. The recording material carrying sheet 5f uses a dielectric sheet such as polycarbonate.

As the transfer drum 5a of the drum-shaped transfer device 5 is rotated, the toner image on the photosensitive drum 1 is recorded on the recording material carrying sheet 5 by the transfer brush charger 5b.
The image is transferred onto the recording material carried by f. When the transfer of the toner images of the desired number of colors to the recording material is completed in this way, the recording material is separated from the transfer drum 5a by the separation claw 8a and the separation push-up roller 8.
It is separated by the action of b and the separation charging device 5j, is discharged to the tray 10 through the heat roller fixing device 9, and is provided as a full-color image.

After the transfer, the photosensitive drum 1 is cleaned of residual toner on the surface thereof by a cleaning device 6 including a cleaning blade 6a and a squeegee sheet, and is again subjected to an image forming process.

Further, in order to prevent scattering of powder on the recording material carrying sheet 5f of the transfer drum 5a and adhesion of oil on the recording material, the fur brush 14 and the recording material carrying sheet 5f are used to interpose a fur brush. Cleaning is performed by the action of the backup brush that faces 14. Such cleaning is performed before or after image formation, and at any time when a jam (clogging of recording material) occurs.

FIG. 3 is a block diagram showing a gradation correction process. In FIG. 3, the reproduction of gradation is shown in a 4-limit chart.

In FIG. 3, the first quadrant (I) shows the reader characteristic for converting the document density into the density signal, and the second quadrant (I).
I) is an LU for converting the density signal to the laser output signal
The data characteristic of T211 (see FIG. 2) is shown, the third quadrant (III) shows the printer γ characteristic for converting the laser output signal into the output density, and the fourth quadrant (IV) shows the relationship between the document density and the output density. 7 shows the total gradation characteristics of the image forming apparatus according to the present embodiment. The number of gradations is 256 because it is processed by an 8-bit digital signal. In the image forming apparatus according to the present embodiment, the printer characteristic of the third quadrant is bent by the LUT 211 of the second quadrant in order to make the gradation characteristic of the fourth quadrant rear.

In FIG. 2, the signal converted by the LUT 211 is converted into a signal corresponding to the dot width by the pulse width modulator (PWM) 212 and sent to the laser driver 41. Then, a latent image having a gradation characteristic is formed on the photosensitive drum 1 by laser scanning, and a gradation image is obtained through the steps of development, transfer, and fixing. The image forming apparatus according to the present embodiment has a pattern generator 215 for outputting on the photosensitive drum 1.
Built in.

The toners used in this embodiment are yellow (y), magenta (m) and cyan (c).
This toner is formed by dispersing color materials of respective colors using a styrene-based copolymer resin as a binder. Further, in the present embodiment, the gradation reproducing means by the pulse width modulation processing is used.

FIG. 4 is a flowchart showing the operation procedure in the image forming apparatus according to this embodiment.

When it is judged from the operation panel (not shown) of the image forming apparatus shown in FIG. 1 that the maximum density or gradation is abnormal and the start switch is turned on, the pattern generator 215 (FIG. 2),
As shown in FIG. 5, a 256 gradation image pattern from "00" to "FF" is output. This printout sample is placed again on the document table glass 31 of the reader unit R in FIG. 1, illuminated by the document exposure lamp 32, and converted into a reflected light amount signal (Ro, Go, Bo) by the full color sensor 34. In order to convert the brightness to the density, the “brightness (i) → density (D) conversion table shown in FIG. 6 is used. When the LUT is actually created, the density of the paper is 0, and the target maximum density is Further conversion to obtain 255. Density data is
The relationship between the laser output and the density is obtained based on the position coordinate information, and the LUT is created based on the relationship between the output level and the density.

Conventionally, the input of the reader unit is usually 8 bits.
Is the ISO brightness of the white background of the document (whiteness)
Is 81% (density D = 0.07), the luminance signal is 2
55. This is set so that the brightness of a general white paper is within 255 levels.

However, when the whiteness of the original is 81% or more (density D = 0.07 or less, for example, hammer mill ISO brightness 85%), the whiteness is 81% or more (density D (= 0.07 or less), the signal sticks to the 255 level.

Therefore, when the above gradation correction is performed using a paper whose density is D = 0.04 and the actual density of the gradation pattern is as shown in FIG. 7, the density of the background is When 0 and the maximum density (Dmax) 1.3 are read at the 255 level, the brightness is overflowed up to the density of 0.07 and the data cannot be read. Therefore, the density data is read as shown in FIG.

When an LUT is created with this density data, FIG.
When the output is carried out through this LUT, the actual density becomes as shown in FIG. 10, and there is a density step between the outputs 0 and 1. This causes not only low density pseudo contours but also deterioration such as “fog” and “roughness”, and significantly deteriorates image quality.

In this embodiment, the density of 0.02 becomes 255 in luminance (the whitest paper does not become 255).
As described above, when the gradation correction is executed, the gain of the analog signal processing circuit 201 in FIG. 2 is lowered so that the brightness of the white background becomes 250 levels.

When the gradation pattern as shown in FIG. 7 is read by performing the above-mentioned processing, it is read after passing through the “luminance (i) → density (D) conversion table” shown in FIG. The density is as shown in FIG. White background is 0,
When the maximum density (Dmax) 1.3 is converted to be 255, the read density becomes as shown in FIG. 12, and when the LUT is created from this density data, it becomes as shown in FIG.

When an image is formed using this LUT, the output density becomes as shown in FIG. 14, and a beautiful gradation characteristic can be obtained. As described above, only when the gradation correction pattern is read, by lowering the gain of the analog conversion processing, a good image in which “pseudo contour”, “fog”, “roughness” and the like are suppressed can be obtained.

Further, the same effect can be obtained even if the gain is reduced and the luminance data is reduced in the A / D converter 202 of FIG.

(Second Embodiment) In the first embodiment described above, the analog signal processing unit 201 reduces the gain so that the brightness is not saturated. However, the present invention is not limited to this. The brightness may not be saturated by reducing the light amount of the R original exposure lamp 32.
In this case, the principle is similar to that of the first embodiment described above.

In this way, by reducing the light amount of the original exposure lamp 32 only when the gradation correction pattern is read, a good image in which "pseudo contour", "fog", "roughness" and the like are suppressed can be obtained. It was

(Third Embodiment) In the present embodiment,
By increasing the scanning speed of the reader unit R and shortening the time of light entering the full-color sensor 34 per pixel, the brightness of the paper with high whiteness is not saturated. Normally, scanning was performed at a scanning speed of 200 mm / s of 180 mm / s.

By performing the above processing, a good image in which "pseudo contour", "fog", "roughness" and the like were suppressed was obtained.

[0069]

According to the present onset Akira As described above in detail, according to the present invention, the field
As a recording medium used for gradation correction of an image forming apparatus, low density
Since white paper can be used, the choice of recording media is wide.
Therefore , for example, even if the paper has a high degree of whiteness , the gradation is corrected after the brightness is not saturated, so that it is possible to obtain a good image with less "pseudo contour", "fog", and "roughness". Play.

[0070]

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing a configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a processing circuit that processes an electric signal from a full color sensor in the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a gradation correction process in the image forming apparatus according to the first embodiment of the invention.

FIG. 4 is a flowchart showing an operation procedure in the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a printout sample in the image forming apparatus according to the first embodiment of the invention.

FIG. 6 is a diagram showing a luminance (i) → density (D) conversion table used in the image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a diagram showing the densities of output samples in the image forming apparatus according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a read density in a conventional setting.

FIG. 9 is a diagram showing an LUT in a conventional setting.

FIG. 10 is a diagram showing a density after LUT in a conventional setting.

FIG. 11 is a diagram showing reading densities in the image forming apparatus according to the first embodiment of the present invention.

FIG. 12 is a diagram showing corrected read densities in the image forming apparatus according to the first embodiment of the present invention.

FIG. 13 is a diagram showing an LUT in the image forming apparatus according to the first embodiment of the present invention.

FIG. 14 is a diagram showing post-LUT density in the image forming apparatus according to the first embodiment of the present invention.

[Explanation of symbols]

R reader section P printer section 1 photosensitive drum 2 Corona charger (primary charger) 3 Laser exposure optical system 3a rotating polygon mirror 3b lens 3c fixed mirror 4y developing device 4c Developing device 4m developing device 4bk developing device 5 Transfer device 5a transfer drum 5b Transfer brush charger 5c Adsorption brush charger 5d Inner charger 5e Outside charger 5f Recording material carrying sheet 5g suction roller 5h Transfer peeling sensor 5j Separating charger 6 cleaning device 6a cleaning blade 7 Recording material cassette 8a Separation claw 8b Separate push up roller 9 Heat roller fixing device 10 trays 11 Pre-exposure lamp 12 Surface potential sensor 13 Light amount detection means on photosensitive drum 14 fur brush 24y eccentric cam 24c eccentric cam 24m eccentric cam 24bk eccentric cam 30 manuscripts 31 Platen glass 32 Original exposure lamp 34 Full color sensor 41 laser driver 42 Laser light source (semiconductor laser) 106 standard white plate 201 Analog signal processor 202 A / D converter 203 Shading correction unit 204 line delay section 205 Input masking section 206 LOG converter 207 line delay memory 208 Masking and UCR section 209 γ correction unit 210 output filter 211 LUT (look-up table) 212 PWM (pulse width modulation circuit) 213 External input section 214 CPU (central processing unit) 215 pattern generator

─────────────────────────────────────────────────── ───Continuation of front page (56) Reference JP-A-8-190630 (JP, A) JP-A-7-264411 (JP, A) JP-A-62-111564 (JP, A) JP-A-7- 184006 (JP, A) JP 11-205593 (JP, A) JP 63-258160 (JP, A) JP 9-107477 (JP, A) JP 64-61172 (JP, A) JP-A-6-46208 (JP, A) JP-A-63-127664 (JP, A) JP-A-5-114962 (JP, A) JP-A-7-25070 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/00 303 G03G 21/00 370-512 G03G 15/04-15/04 120 G03G 15/043 H04N 1/04 101 H04N 1/407

Claims (9)

(57) [Claims] 1. A first adjusted using a first white reference.
The first image is read under the following image reading conditions.
Printer on the basis of the read process and an image signal obtained by said first reading step
Image forming step of forming an image by using a gradation test pattern having a second white reference as an original
Read under the second image reading condition
A second reading step for generating a reading signal; and the printer using the gradation test pattern reading signal.
A printer tone correction step of correcting the tone of the image, and a predetermined read signal level is obtained under the first image reading condition.
Under the second image reading condition rather than the density of the original to be read.
Decrease the density of the original to obtain a constant reading signal level
And a step of changing the image reading condition . 2. The image reading condition changing step comprises the first step.
Under the second image reading condition compared to the image reading condition
The image forming method according to claim 1, further comprising: a gain changing step of reducing a gain of a circuit for obtaining the read signal.
Law . 3. The image reading condition changing step comprises the first step .
Under the second image reading condition compared to the image reading condition
The image forming method according to claim 1, characterized in Rukoto to have a light quantity changing step of decreasing the amount of light that illuminates the serial document. 4. The image reading condition changing step comprises the first step .
Under the second image reading condition compared to the image reading condition
Exposure that shortens the exposure time per pixel for reading the document
The image forming method according to claim 1, characterized in Rukoto to have a time changing process. 5. A first adjusted using a first white reference.
The first image is read under the following image reading conditions.
A reading unit and a printer based on the image signal obtained by the first reading unit
Image forming means for forming an image by using a gradation test pattern having a second white reference as an original
Read under the second image reading condition
Second reading means for generating a read signal and the printer using the gradation test pattern read signal
And a printer gradation correction unit for correcting the gradation of the image, and a predetermined read signal level is obtained under the first image reading condition.
Under the second image reading condition rather than the density of the original to be read.
Decrease the density of the original to obtain a constant reading signal level
An image forming apparatus, comprising an image reading condition changing means for. 6. The image reading condition changing means comprises the first
Under the second image reading condition compared to the image reading condition
The image forming apparatus according to claim 5, further comprising a gain changing unit that lowers a gain of a circuit that obtains the read signal . 7. The image reading condition changing means is the first
Under the second image reading condition compared to the image reading condition
The image forming apparatus according to claim 5, characterized in Rukoto of having a light quantity changing means for reducing the amount of light that illuminates the serial document. 8. The image reading condition changing means is the first
Under the second image reading condition compared to the image reading condition
Exposure that shortens the exposure time per pixel for reading the document
The image forming apparatus according to claim 5, characterized in Rukoto to have a time changing means. 9. An image forming method according to any one of claims 1 to 4.
Computer-readable program for realizing
A storage medium characterized by holding a code .