JP2000089531A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a gradation conversion table having high reliability in all gradation. SOLUTION: This image forming device is constituted so that the first gradation conversion table obtained at a set-up time and the second gradation conversion table obtained at the executing time of a job are synthesized and an image forming condition is controlled. Besides it is provided with a first gradation extension means 11 extending the number of gradation of the first gradation conversion table, a second gradation extension means 12 extending the number of gradation of the second gradation conversion table and a synthesis means 13 synthesizing the first gradation conversion table extended by the extension means 11 and the second gradation conversion table extended by the extension means 12 so as to prepare the third gradation conversion table.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for controlling an image forming condition by synthesizing a first gradation conversion table obtained at the time of setup and a second gradation conversion table obtained at the time of job execution. About.

[0002]

2. Description of the Related Art Conventionally, in tone correction of an image forming apparatus, a multi-tone toner patch is formed at the time of setup such as when power is turned on, and a tone for obtaining an output tone corresponding to a read tone from a density detection value. A tone conversion table is generated (see JP-A-63-113568). However, fluctuations in density can occur during job execution after setup, and it is necessary to correct this.

However, since there is no time margin at the time of job execution as at the time of setup, it is difficult to generate a multi-tone toner patch and obtain a tone conversion table from its density detection value. Therefore, by forming a toner patch with a small number of gradations (for example, two gradations) and correcting the gradation conversion table generated from the density detection value of the toner patch, a high-precision gradation conversion table can be generated in a short time. I am trying to do it.

This technique requires a memory for separately storing a gradation conversion table generated during setup and a gradation conversion table generated during job execution. Therefore, from the viewpoint of generating a gradation conversion table with high accuracy even from toner patches having a small number of gradations and saving memory capacity, a gradation conversion table generated during setup and a gradation conversion table generated during job execution are used. A technique for synthesizing is disclosed (see Japanese Patent Application Laid-Open No. 5-336267).

[0005]

However, as described above, in the technique of synthesizing the tone conversion table generated at the time of setup and the tone conversion table generated at the time of job execution, the tone conversion table before the synthesis is combined. If the table is saturated, the grayscale conversion table obtained by synthesis also becomes saturated in the middle of the grayscale, and there is a problem that accurate conversion cannot be performed at all grayscales that can be represented by image data.

FIG. 9 is a diagram for explaining the effect of saturation. That is, (a) is a gradation conversion table generated during job execution, (b) is a gradation conversion table generated during setup, and (c) is a gradation conversion table after synthesis.

In order to combine the gradation conversion tables, first, an output gradation Cout with respect to the input gradation Cin is obtained by using the gradation conversion table at the time of job execution shown in FIG. Subsequently, the value of the output gradation Cout is applied to the input gradation Cin of the gradation conversion table at the time of setup shown in FIG. 9B, and the output gradation Cout corresponding to the input gradation Cin is obtained.

The input gradation Cin → the output gradation Cout of the gradation conversion table at the time of job execution → the input gradation Cin → the output gradation Cout of the gradation conversion table at the time of setup is performed for all gradations. A combined tone conversion table composed of an output tone Cout at the setup time and an input tone Cin at the time of job execution shown in (c) is created.

Here, in the gradation conversion table at the time of job execution shown in FIG. 9A, the output gradation Cout is saturated to 255 before the input gradation Cin reaches 255. Therefore, when synthesizing the gradation conversion table, the saturated portion is saturated at an output gradation lower than 255.

When a tone conversion table is created by such synthesis, for example, if the setup performed the first time in the morning deviates in density for some reason, an accurate tone conversion table after synthesis can be generated. Therefore, accurate gradation correction cannot be performed. Also, the density may be returned to the original state after a while,
It takes time to absorb the shift amount in the gradation conversion table created at the time of job execution, and it is difficult to accurately correct a large density change.

[0011]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus made to solve such a problem. That is, the present invention is an image forming apparatus that combines the first gradation conversion table obtained at the time of setup and the second gradation conversion table obtained at the time of job execution, and controls image forming conditions. First gradation extending means for extending the number of gradations in the gradation conversion table, second gradation extending means for extending the number of gradations in the second gradation conversion table, and first gradation extension Combining means for combining the first gradation conversion table extended by the means and the second gradation conversion table extended by the second gradation extending means to generate a third gradation conversion table; Have.

In the present invention, the number of gradations in the first gradation conversion table is extended by the first gradation extending means,
Since the number of gradations in the second gradation conversion table is extended by the second gradation extension means, even if any gradation conversion table is saturated, the gradation is extended by the extension of the number of gradations. It is not necessary to do so, and saturation can be avoided in the third gradation conversion table obtained by combining.

In the image forming apparatus of the present invention, the detection value obtained by detecting the density of the toner patch at the time of set-up and the detection value obtained by detecting the density of the toner patch at the time of executing the job satisfy a predetermined threshold value. If it exceeds, execution of the job is suspended, and the first gradation conversion table is re-created.

According to the present invention, when the density detection value of the toner patch at the time of the setup and the density detection value of the toner patch at the time of executing the job exceed a predetermined threshold, the first gradation performed at the time of the setup again. Since the conversion table is re-created, if the density detection value is deviated for some reason only during the setup, the tone conversion table can be re-created in a state where it has returned to the normal state thereafter. The accuracy of the gradation conversion table can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image forming apparatus of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. That is, the image forming apparatus detects the density of the toner patch formed on the transfer belt B by the light receiving sensor S, controls the image forming condition based on the detected value, and the LUT for gradation correction. (Look Up Table) 2, a pattern generator 3 for generating a reference wave such as a triangular wave, and a pulse width by comparing the gradation corrected image data with reference to the LUT 2 and the reference wave in the pattern generator 3. Modulation signal (PWM signal)
, A laser driver 5 that controls the output of laser light based on the PWM signal, and K (black), C (cyan), M (magenta), and Y based on a signal from the laser driver 5. (Yellow) photoconductors 61, 62, 63, and 64 for developing each color.

The image forming apparatus according to the present embodiment includes a first gradation expanding unit 11 and a second gradation expanding unit 12 as program processing executed by the CPU 1.
It is characterized in that it has the synthesizing means 13.

In the image forming apparatus of this embodiment, the LUT 2 is used for performing the gradation correction.
For example, a combination of a first gradation conversion table generated in a setup performed when the power of the apparatus is turned on and a second gradation conversion table generated in executing a job is used.

Here, the first gradation expanding means 11 expands the number of gradations of the first gradation conversion table generated at the time of setup, and the second gradation expanding means 12 generates the number of gradations at the time of job execution. The number of gradations in the second gradation conversion table is extended.
Further, the synthesizing unit 13 synthesizes the first gradation conversion table and the second gradation conversion table in which the number of gradations has been expanded, and generates an LUT 2 that is a third gradation conversion table.

Here, the generation by synthesis of the LUT 2 is shown in FIG.
Will be described along the flowchart of FIG. In the following description, reference numerals not shown in FIG. 2 refer to FIG. 1 unless otherwise specified.

First, as a start of setup, as shown in step S101, a toner patch for image density detection is created. At the time of this setup, for example, a toner patch having 12 gradations is created on the transfer belt B.

Next, as shown in step S102, the density of the toner patch is detected by the light receiving sensor S. Next, in step S103, the density detection value of the toner patch having 12 gradations is expanded to 256 gradations, and a first density conversion table is created by abutting against the target density curve.

In step S104, the first gradation expanding means 11 performs a process of expanding the number of gradations in the first gradation conversion table to an output image (for example, 8 bits) or more.

A specific example in the creation of the first gradation conversion table at the time of this setup will be described. FIG. 3 is a diagram showing the relationship between the input gradation Cin and the detection value Radc of the optical sensor S. The plot in this figure is the actually detected density value of the toner patch of 12 gradations detected. The density detection values of the 12-tone toner patch are linearly interpolated to 25.
A density detection value of a toner patch corresponding to six gradations is created.

FIG. 4 is a diagram showing an example of creating a first gradation conversion table by a butting process. That is, as shown in FIG. 4A, in order to interpolate a difference between a density detection value (current Radc) of a toner patch corresponding to 256 gradations which has been linearly interpolated first and a target Radc, first, as shown in FIG. The target Radc corresponding to the input gradation Cin for which the LUT is to be determined is determined as shown in FIG. 7, and then the current Radc equal to the target Radc is determined as shown in FIG. Thereafter, as shown in the figure, an input tone Cin corresponding to the current Radc, which is the same as the target Radc, is obtained, and the input tone Cin is output to the output tone Cou.
Let t.

FIG. 4 (b) shows that the processes (1) to (4) of FIG.
4 shows an LUT obtained by obtaining a relationship with out, that is, a first gradation conversion table.

Next, the creation of an LUT during job execution will be described. First, as shown in step S105 of FIG. 2, a toner patch for image density detection is created. At the time of job execution, there is no time
A toner patch having a gradation is formed on the transfer belt B.

Next, as shown in step S106, the density of the toner patch is detected by the light receiving sensor S. Next, in step S107, the amount of change from the respective set-up values is calculated from the density detection values of the two gradations, and Poi at the two gradations is calculated using a predetermined table.
Find nt_LUT.

Thereafter, in step S108, a second gradation conversion table is created by calculating the LUT values of the other gradations from the Point_LUT of the two gradations by using coefficients, and the second gradation extending means 12 Then, a process of extending the number of gradations of the second gradation conversion table to an output image (for example, 8 bits) or more is performed.

A specific example of creating the second gradation conversion table at the time of executing this job will be described. FIG. 5 is a diagram showing an example in which a second gradation conversion table is created from the detected toner patch density values of two gradations.

First, as shown in FIG. 5A, the density detection values of the toner patches of the low gradation (CinA) and the high gradation (CinB) are obtained, and the density detection values of each gradation obtained at the time of the setup are calculated. ΔRadc (CinA), ΔRadc (C
inB) is calculated.

Next, as shown in FIG. 5B, .DELTA.Radc (CinA) and .DELTA.R corresponding to the two gradations CinA and CinB.
Each Point_LUT is obtained from adc (CinB). This Point_LUT is obtained from a table showing the relationship between ΔRadc and ΔLUT shown in FIG.

Next, as shown in FIG. 5C, the output gradation Cout for the other input gradation Cin is calculated from the Point_LUT for the two gradations obtained previously using a predetermined coefficient or an approximate expression. Then, as shown in FIG. 5D, the output gradation Cout in each input gradation Cin expanded to several gradations is linearly interpolated to create a second gradation conversion table.

In the present embodiment, the first tone conversion table created at the time of setup and the second tone conversion table created at the time of job execution are combined by the combining means 13 (step S109 shown in FIG. 2). A third gradation conversion table, that is, LUT2 is generated.

Next, the synthesis procedure will be described. 7A and 7B are diagrams for explaining the combination. FIG. 7A shows a second gradation conversion table generated at the time of job execution, FIG. 7B shows a first gradation conversion table generated at the time of setup, and FIG. It is a gradation conversion table.

To perform the composition, first, the number of gradations of the output gradation Cout of the second gradation conversion table created at the time of executing the job shown in FIG. I do. In this example, the area is extended to 511, whereby the saturated portion indicated by the broken line in the figure is extended based on the inclination in front.

Next, the number of gradations of the input gradation Cin of the first gradation conversion table created at the setup shown in FIG. 7B is extended by the first gradation extending means 11. In this case, the output gradation Cout shown in FIG. 7A is expanded to 511, and the input gradation Cin of the first gradation conversion table is used.
Is also extended to 511. As a result, the portion indicated by the one-dot chain line in the drawing is extended based on the front inclination.

Then, an output gradation Cout for the input gradation Cin shown in FIG. 7A is obtained, and the value of the output gradation Cout is applied to the input gradation Cin shown in FIG. An output gradation Cout with respect to Cin is obtained.

The input gradation Cin → the output gradation Cout of the gradation conversion table at the time of executing the job → the input gradation Cin → the output gradation Cout of the gradation conversion table at the time of the setup is performed for all the gradations. A combined tone conversion table composed of an output tone Cout at the setup time and an input tone Cin at the time of job execution shown in (c) is created.

By such a combination, the saturated portion shown by the broken line in FIG. 7C is eliminated, and it is possible to obtain the output gradation Cout for all the input gradations Cin.

FIG. 7A shows an example of the expansion of the number of gradations.
Only the output gradation Cout of the second gradation conversion table generated during job execution shown in FIG. 7 and the input gradation Cin of the first gradation conversion table generated during setup shown in FIG. The input gradation Cin of the second gradation conversion table generated at the time of job execution shown in FIG. 7A and the output gradation Cout of the first gradation conversion table generated at the time of setup shown in FIG. If expansion is not performed as it is, it is possible to automatically create an LUT including the number of gradations before expansion of both input and output after synthesis.

Next, the flow of creating a table in the image forming apparatus according to the present embodiment will be described. FIG. 8 is a flowchart illustrating the table creation. First, step S20
As shown in FIG. 1, a first tone conversion table is created from multi-tone toner patches created in the setup.

Next, as shown in step S202,
The first gradation conversion table created by the setup is stored as a reference value. Thereafter, as shown in step S203, two toner patches of highlight and halftone are created at the time of job execution.

In step S204, the values detected by the optical sensors of the two toner patches created in step S203 are compared with the reference values for setup stored in step S202.

In step S205, step S204
As a result of the comparison, it is determined whether or not the difference is equal to or more than a predetermined value. If the difference is equal to or more than the predetermined value, the process returns to step S201, and the first gradation conversion table is created again using the multi-gradation toner patches to be set up. In other words, if the detected toner patch value at the time of job execution deviates from the reference value at the time of setup by a predetermined value or more, it is considered that a reference value different from normal has been created due to some influence at the time of setup, and the process is performed again at the time of setup. A first gradation conversion table is created.

On the other hand, if the result of the comparison does not exceed the predetermined value in step S205, the flow advances to step S206, where the two toner patches of highlight and halftone created at the time of job execution are detected based on the values detected by the optical sensor. A second gradation conversion table is created. That is, in this case, the reference values created in steps S201 to S202 are regarded as reliable, and the second gradation conversion table at the time of job execution is created. After that, the second gradation conversion table and the first gradation conversion table are combined, and an image is formed using the third gradation conversion table.

By creating such a table, even when the first gradation conversion table is created when the environment is unstable, such as when the power is turned on, it can be created again by subsequent judgment, and when the job is executed, Image formation can be performed using a highly reliable gradation conversion table.

The update of the gradation conversion table at the time of job execution is performed at the following timing. That is, for example, in the four-color image forming mode, Y
(Yellow), M (magenta), C (cyan), K (black)
When the gradation patch data of all the colors is completed, the gradation conversion table is synthesized, and in the three-color image forming mode, all three colors of Y (yellow), M (magenta), and C (cyan) are used. The tone conversion table is synthesized when the tone patch data of all the colors have been prepared. In the monochrome (black) image forming mode, the tone conversion table is synthesized when the K (black) tone patch data is obtained. Perform synthesis.

Thus, the next print 1 at the end of the synthesis
A new gradation conversion table is used from the color. At this time, the job is interrupted even during the continuous job execution by storing the tone conversion table used at the time of executing the job and the tone conversion table used at the calculation (synthesis) process independently. A new gradation conversion table can be created without using it, and it can be used from the next print first color.

[0049]

As described above, the image forming apparatus of the present invention has the following effects. In other words, the first tone conversion table created at the time of setup and the second tone conversion table created at the time of job execution are combined to form a third tone conversion table.
When the gradation conversion table is created, a conversion table corresponding to all gradations that can be expressed by image data can be created, and accurate image formation can be performed.
Even if the first gradation conversion table is created when the environment is unstable, such as during setup, the first gradation conversion table and the second gradation conversion table are always created in a stable state by re-creation. It is possible to improve the image quality by the high reliability of the third gradation conversion table after the combination.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a flowchart illustrating LUT synthesis.

FIG. 3 is a diagram showing a relationship between an input gradation Cin and a detection value Radc of an optical sensor.

FIG. 4 is a diagram showing an example of creating a first gradation conversion table by a butting process.

FIG. 5 is a diagram illustrating an example in which a second gradation conversion table is created from two-tone toner patch density detection values.

FIG. 6 is a diagram illustrating a relationship between ΔRadc and ΔLUT.

FIG. 7 is a diagram illustrating a synthesis procedure.

FIG. 8 is a flowchart illustrating table creation.

FIG. 9 is a diagram illustrating the effect of saturation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CPU, 2 ... LUT, 3 ... pattern generator, 4 ... pulse width modulation circuit, 5 ... laser driver, 11 ... 1st gradation expansion means, 12 ... 2nd gradation expansion means, 13 ... synthesis means

Claims (3)

[Claims] 1. An image forming apparatus which combines a first gradation conversion table obtained at a setup time and a second gradation conversion table obtained at a job execution time, and controls image forming conditions. A first gradation extending means for extending the number of gradations in the gradation conversion table; a second gradation extending means for extending the number of gradations in the second gradation conversion table; and the first gradation Combining means for combining the first gradation conversion table extended by the extension means and the second gradation conversion table extended by the second gradation extension means to generate a third gradation conversion table An image forming apparatus comprising: 2. The combining means according to claim 3, wherein
2. The image forming apparatus according to claim 1, wherein when generating the gradation conversion table, the number of gradations is matched with the number of gradations of the output image. 3. An image forming apparatus which combines a first gradation conversion table obtained at the time of setup and a second gradation conversion table obtained at the time of job execution, and controls image forming conditions. When the detection value obtained by performing the density detection of the patch and the detection value obtained by performing the density detection of the toner patch during execution of the job exceed a predetermined threshold,
An image forming apparatus for recreating the first gradation conversion table.