JPH07131649A - Image forming device - Google Patents

Abstract

PURPOSE:To provide any peculiar operational effects to form high-gradation images even when density is partially changed by any trouble even with the same density output. CONSTITUTION:The start switch of gradation correction is turned on at a step S21. Plural gradation test patterns are formed and outputted by a pattern generator 29 at a step S22. The outputted gradation test patterns are read and defined as read density data at a step S23, and the relation between a laser output level in the case of reading the gradation test pattern and the density value of the read gradation test pattern is calculated corresponding to the coordinate of each gradation test pattern and stored in a memory at a step S24. Continuously, the average of the plural positions of the same density data of the respective plural gradation test patterns is calculated at a step S25, the characteristic of gamma correction of a printer is decided for each density and a gamma-LUT 25 is set at a step S26 corresponding to the relation between the laser output level and the read density.

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.

[0002]

2. Description of the Related Art Conventionally, the following method has been known as a method for adjusting the image processing characteristics of an image forming apparatus such as a copying machine or a printer. That is, the image forming apparatus is activated to form one specific gradation test pattern on the recording material, and then the density of the gradation test pattern formed on the recording material is read by the image reading means, A method has been known in which, on the basis of image information, feedback is made to a means for determining an image forming condition such as a γ correction means. By this method, it was possible to stabilize the image quality according to the characteristic variation due to durability and the environmental condition variation.

[0003]

However, in the above-mentioned conventional example, in the image forming apparatus, for example, when the center of the drum is deviated, light and shade appear in the drum cycle, and uneven charging occurs due to dirt on the charger. When density unevenness is partially observed due to some inconvenience such as occurrence, even if uniform density is output on the entire surface of the recording material, the density changes depending on the location of the recording material.

Therefore, when the density unevenness as described above occurs, if the density data of one specific gradation test pattern is used to feed back to the image forming condition as in the conventional case, the optimum image quality is obtained. There was a drawback that I could not do it.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and as one means for solving the above-mentioned problems, the following structure is provided. That is, image forming means for forming an image, pattern forming means for forming at least two specific gradation test patterns, reading means for reading at least two gradation test patterns formed by the pattern forming means, and Storage means for storing density data of the gradation test pattern read by the reading means, averaging means for averaging the density data stored by the storage means at corresponding gradation levels, and averaging by the averaging means. And a gradation correction unit for performing gradation correction using the density data of each gradation level thus obtained, and the gradation correction by the gradation correction unit is performed by setting a look-up table for performing γ correction. It is characterized by

Further, the image forming means is characterized in that the image forming conditions are controlled by a look-up table for γ correction set by the gradation correcting means.

[0007]

With the above construction, even if the density is partially changed due to some inconvenience even with the same density output, a unique effect that an image having excellent gradation and stable image quality can be formed is obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. <First Embodiment> A schematic configuration of an embodiment according to the present invention is shown in FIG.
Shown in. In FIG. 1, an image signal is a laser driver 10
By driving the semiconductor laser 103 at 2, it is converted into laser light. Laser light from the semiconductor laser 103 is scanned by the polygon mirror 1 and reflected by the reflection mirror 2, so that the photosensitive drum 4 is irradiated with the laser light and scanned. The photosensitive drum 4 on which a latent image has been formed by scanning with laser light rotates in the direction of the arrow shown in the figure. Then, development is performed for each color by the rotary developing device 3 (in FIG. 1, a development state with yellow toner is shown).

On the other hand, the transfer paper is wound around the transfer drum 5 to be Y (yellow), M (magenta), C (cyan),
It is rotated once in the order of Bk (black), and the transfer is completed after a total of four rotations. When the transfer is completed, the transfer paper leaves the transfer drum 5 and is fixed by the fixing roller pair 7,
The color image print is completed.

Further, 301 is a read original, 302 is an original table glass, 303 is a light source, 304 is a color separation optical system, 2
1 is a CCD. The toner used in this example is
Yellow, magenta, and cyan toners are used, and a styrene copolymer resin is used as a binder, and a color image print is formed by dispersing color materials of respective colors.

Next, the image signal processing section of this embodiment will be described with reference to FIG. In FIG. 2, the luminance signal of the original image read by the CCD 21 is input to the A / D converter 22 and converted into a digital luminance signal. This digital luminance signal is sent to the shading unit 23, and C
The shading correction is performed for the light amount unevenness due to the sensitivity variations of the individual elements of the CD 21. By performing the shading correction, the measurement reproducibility of the CCD 21 is improved. The luminance signal corrected by the shading unit 23 is further LOG
The conversion unit 24 performs LOG conversion. Then, the LOG-converted signal is converted into a gamma lookup table (γ-LU
T) 25, and the γ-LUT 25 is used to convert the image signal so that the original image density at the time of initial setting of the printer 100 and the output image density processed according to the γ characteristic match.

The image signal thus converted becomes a signal whose pulse width is modulated by the pulse width modulation circuit 26 and is input to the laser driver 102, and the semiconductor laser 10 shown in FIG.
3 is driving. Further, 28 is a CPU and 29 is a pattern generator, which generates various gradation test patterns described later. An operation panel 30 is used in the procedure described below.

In this embodiment, for all colors, the gradation reproduction means by the pulse width conversion processing in which the pixels are arranged in the sub-scanning direction is used, and the gradation characteristic due to the dot area change is provided on the photosensitive drum 4 by the scanning of the laser light. An electrostatic latent image is formed, and a gradation image is obtained through processes such as development, transfer and fixing. Next, FIG. 3 shows a four-limit chart showing characteristics for reproducing the density of the original image.

In FIG. 3, the quadrant I shows the reading characteristic for converting the document density into the density signal, and the quadrant II shows the characteristic of the γ-LUT 25 for converting the density signal into the laser output signal. The third quadrant shows the characteristics of the printer that converts the laser output signal to the printer output density, and the fourth quadrant shows the relationship between the document density and the printer output density, that is, the characteristics shown in the fourth quadrant are 3 shows the overall gradation characteristics of the copying machine of the embodiment.

In the present embodiment, in order to make the gradation characteristics linear as shown in the fourth quadrant of FIG. 3, the distortion of the recording characteristics of the printer section shown in the third quadrant is shown in the second quadrant. It is corrected by the γ-LUT 25. Since the image signal is processed as an 8-bit digital signal in this embodiment, the number of gradations is 256.

Hereinafter, with reference to FIG. 4, C in this embodiment will be described.
The process of setting the γ-LUT 25 by the PU 28 will be described. FIG. 4 shows the γ-L by the CPU 28 in this embodiment.
It is a flowchart which shows the process of UT25 setting. First, in step S21, from the operation panel 30 of FIG.
Specify the color for which you want to correct the gradation characteristics, and turn on the gradation correction start switch. Then step S
In step 22, the pattern generator 29 shown in FIG. 2 forms and outputs a plurality of gradation test patterns of 256 gradations of the designated color on the recording material, shifted in the sub-scanning direction.

FIG. 5 shows an example in which two gradation test patterns of a designated single color are output on the recording material. In FIG. 5, the upper left end of the gradation test pattern is “white” and the lower right end is “black”, and the density gradually increases from the upper left end to the lower right end in the meantime. In addition, in FIG. 5, the display of the intermediate portion is partially omitted. Next, in step S23, step S2
The gradation test pattern output in FIG.
Place it on the platen glass 302 as the read document 301,
The light is illuminated by the light source 303 and then converted into a reflected light amount signal by the CCD 21 through the color separation optical system 304. Then, the reflected light amount signal is LOG-converted by the LOG converter 24 shown in FIG. 2, and is read by the CPU 28 as read density data.

Next, in step S24, the relationship between the laser output level at the time of reading the gradation test pattern and the density value of the read gradation test pattern is obtained in correspondence with the coordinates of each gradation test pattern, Memory 32
To store. Then, in step S25, an average of a plurality of portions of the same density data of each of the plurality of gradation test patterns as shown in FIG. 5 is obtained.

Then, in step S26, the printer characteristics shown in the third quadrant of FIG. 3 are obtained from the relationship between the laser output level and the read density obtained in step S24. By exchanging the input and output relationships of the printer characteristics with each other, the γ correction characteristics of the printer shown in the second quadrant II are determined for each density, and all γ−
Set the LUT 25.

This completes the setting of the γ-LUT 25 in this embodiment. Γ set as described above
-By using the LUT 25 in the image signal processing unit shown in FIG. 2 to perform γ correction, it becomes possible to perform density correction in consideration of the current printer characteristics. As described above, according to the present embodiment, a plurality of gradation test patterns are formed, and the LUT for γ correction is reset by averaging the density data at a plurality of locations for each of the formed test patterns. Even when the output partially changes the density due to some inconvenience, this can be effectively corrected, and an image with excellent gradation can be formed.

<Second Embodiment> In the first embodiment described above, by forming at least two gradation test patterns in the sub-scanning direction as shown in FIG. 5, it is possible to cope with density unevenness in the sub-scanning direction. Although the gradation correction is realized, the density difference may occur also in the main scanning direction. Therefore, in the second embodiment, the gradation correction is realized by forming a plurality of gradation test patterns in the main scanning direction.

The structure and processing procedure of the second embodiment are almost the same as those of the first embodiment described above, but the second embodiment is replaced by the plurality of gradation test patterns shown in FIG. 5 of the first embodiment. Then, the gradation test pattern shown in FIG. 6 is used. The gradation test pattern shown in FIG. 6 has 256 specified colors.
At least two pattern images of gradation are formed on the recording material by shifting in the main scanning direction. In FIG. 6, the upper left corner of the gradation test pattern is “white” and the lower right corner is “black”, and the density gradually increases from the upper left corner to the lower right corner during that time. Incidentally, in FIG. 6, the display of the intermediate portion is partially omitted.

As described above, also in the second embodiment, the same effect as in the first embodiment can be obtained. <Third Embodiment> In the above-described first embodiment, the gradation correction for the designated single color has been described, but the gradation correction is necessary for all the color toner types used. Therefore, the third
In the embodiment, gradation correction is simultaneously performed for all colors of yellow, magenta, cyan and black.

The configuration of the third embodiment is the same as the first embodiment described above.
It is common to FIGS. 1 and 2 shown in the embodiment. Hereinafter, with reference to FIG. 7, the γ-LUT 25 in the third embodiment.
The setting process of will be described. FIG. 7 is a flow chart showing the process of setting the γ-LUT 25 in the third embodiment. First, in step S31, a tone correction start switch is turned on from the operation panel. Then, the process proceeds to step S32, and the pattern generator 29 shown in FIG.
Thus, a plurality of gradation test patterns of 16 gradations for all colors are formed on the recording material and shifted in the sub-scanning direction, and are output. FIG. 8 shows an example in which two gradation test patterns of all colors are output on the recording material.

Next, in step S33, the gradation test pattern (FIG. 8) output in step S32 is placed on the platen glass 302 as a read original 301, illuminated by a light source 303, and then CC through a color separation optical system 304.
At D21, it is converted into a reflected light amount signal. Then, the reflected light amount signal is LOG-converted by the LOG converter 24 shown in FIG.
The CPU 28 takes in the read density data.

Next, in step S34, the relationship between the laser output level at the time of reading the gradation test pattern and the density value of the read gradation test pattern is obtained in correspondence with the coordinates of each gradation test pattern, Memory 32
To store. Subsequently, in step S35, an average of a plurality of portions of the same density data of each of the plurality of gradation test patterns as shown in FIG. 8 is obtained.

Then, in step S36, the printer characteristics shown in the third quadrant of FIG. 3 are obtained from the relationship between the laser output level and the read density obtained in step S34. By exchanging the input / output relations of the printer characteristics with each other, the γ
The correction characteristic is determined for each density, and the γ-LUT 25 is created. As a result, all γ-LUT25 for 256 gradations can be obtained.
To set.

When the data of the γ-LUT 25 is created in step S36, for example, the γ-LUT 25 has all 25 data.
If there are 6 gradations, data for 256 gradations must be set from 16 gradation data of the gradation test pattern. Therefore, in order to improve primary interpolation or accuracy, high-order interpolation and high-order interpolation are performed. It is desirable to make an approximation. Above is the third
The setting of the γ-LUT 25 in the embodiment is completed.

As described above, according to the third embodiment, the same effect as that of the first embodiment can be obtained not only for a single color but for all colors. <Fourth Embodiment> An example in which the above-described first to third embodiments are combined will be described as a fourth embodiment according to the present invention.

For example, an example in which four or more gradation test patterns are formed on a recording material can be considered by combining the first embodiment and the second embodiment. The gradation test pattern output by this example is shown in FIG. The gradation correction method is similar to that of the above-described first embodiment and the like. As described above, according to the fourth embodiment, it is possible to form an image which is more excellent in gradation than the effect of the first embodiment.

<Fifth Embodiment> Further, in the above-mentioned first to fourth embodiments, the full-color digital copying machine has been described, but the present invention is not limited to the above example, and a monochrome digital copying machine is used. It is also effective in copying machines. In a fifth embodiment according to the present invention, an example applied to a monochrome digital copying machine will be described.

FIG. 10 shows a schematic block diagram of a monochrome digital copying machine. The main constituent parts are common to those of FIGS. 1 and 2 in the first embodiment, and such common structures are denoted by the same reference numerals as in the first embodiment, and the description thereof is omitted. Figure 1
In the fifth embodiment shown in FIG. 0, since there is no need for multiple transfer because it is monochrome, the main difference from FIG. 1 of the first embodiment is that there is no transfer drum.

The method of realizing the gradation correction in the fifth embodiment is the same as that in the above-mentioned first embodiment. As described above, in the fifth embodiment, the same effect as that of the first embodiment can be obtained even in the case of monochrome. Although the laser beam printer has been mainly described in the above first to fifth embodiments, the present invention is not limited to these examples, and other images such as an inkjet printer and a dot matrix printer can be used. It is also applicable to a forming device.

In the present invention, gradation correction is performed by resetting the gamma look-up table, and various image forming conditions are controlled according to the result of this gradation correction. In addition to the laser light amount and the laser emission time, the potential of the primary charger, the developing bias, and the like can be considered. Other image forming conditions include a distance between an inkjet head and a recording material when applied to an inkjet printer, and a sublimation ink ribbon of a sublimation type head when applied to a dot matrix printer.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0036]

As described above, according to the present invention,
Even when the same density is output, even if the density partially changes due to some inconvenience, this part can be effectively corrected, and an image with excellent gradation can be formed.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment according to the present invention.

FIG. 2 is a block diagram showing a detailed configuration of an image signal processing unit in the present embodiment.

FIG. 3 is a fourth limit chart showing the gradation reproduction characteristics in the present embodiment.

FIG. 4 is a graph of γ in the first and second embodiments according to the present invention.
6 is a flowchart of LUT creation processing.

FIG. 5 is a diagram showing a grayscale test pattern output in the first embodiment according to the present invention.

FIG. 6 is a diagram showing a gradation test pattern output in the second embodiment according to the present invention.

FIG. 7 is a flowchart of a γ-LUT creation process according to the third embodiment of the present invention.

FIG. 8 is a diagram showing a gradation test pattern output in a third embodiment according to the present invention.

FIG. 9 is a diagram showing a grayscale test pattern output in a fourth embodiment according to the present invention.

FIG. 10 is a diagram showing a schematic configuration of a fourth embodiment according to the present invention.

[Explanation of symbols]

 1 polygon mirror 2 mirror 3 developing device 4 photosensitive drum 5 transfer drum 7 fixing roller pair 21 CCD 102 laser driver 103 semiconductor laser 301 read original 302 original platen glass 303 light source 304 color separation optical system

Claims (3)

[Claims] 1. An image forming unit for forming an image, a pattern forming unit for forming at least two specific gradation test patterns, and a reading unit for reading at least two gradation test patterns formed by the pattern forming unit. Storage means for storing the density data of the gradation test pattern read by the reading means; averaging means for averaging the density data stored by the storage means at corresponding gradation levels; An image forming apparatus comprising: a gradation correction unit that corrects a gradation of an image formed by the image forming unit by using density data of each gradation level averaged by the unit. 2. The image forming apparatus according to claim 1, wherein the gradation correction by the gradation correction unit is performed by setting a look-up table for γ correction. 3. The gradation correction by the gradation correction means controls the image forming condition of the image forming means according to the preset γ correction look-up table. The image forming apparatus described.