JP2003150006A - Color image forming device, image density control method, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device that uses a combination of a color sensor and a density sensor, thereby decreasing the number of times that density control is exerted by the color sensor and reducing transfer material consumption, and is excellent in density stability in comparison with the conventional density control using only a density sensor. SOLUTION: The color image forming device has a first density detection means for detecting the density of an unfixed toner image formed on an image carrier or a transfer material carrier, and a second density detection means for detecting the density of a fixed toner image formed on the transfer material. The device corrects the first density detection means based upon the detection result of the second density detection means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color printer,
The present invention relates to an electrophotographic color image forming apparatus such as a color copying machine.

[0002]

2. Description of the Related Art In recent years, a color image forming apparatus such as a color printer or a color copying machine which employs an electrophotographic system or an inkjet system is required to have a high quality output image. In particular, the density gradation and the stability thereof have a great influence on the judgment of the quality of an image made by a human.

However, in the color image forming apparatus, the density of the obtained image fluctuates when the environment changes or each part of the apparatus fluctuates due to long-term use. In particular, in the case of an electrophotographic color image forming apparatus, even a slight environmental change may cause a change in density, which may impair the color balance. Therefore, it is necessary to have a means for always maintaining a constant density.

Therefore, a toner image for density detection (hereinafter referred to as a patch) is formed on each of the toners of respective colors on an intermediate transfer body or a photoconductor, and the density of the unfixed toner patch is compared with a density detection sensor for an unfixed toner (hereinafter referred to as a density detection sensor). The density is detected by the density sensor, and the density of the image is controlled by feeding back the process conditions such as the exposure amount and the developing bias based on the detection result to control the density.

However, the density control using the density sensor is to detect a patch by forming it on an intermediate transfer body or a drum, and to detect the color balance of an image by transferring and fixing the patch on a transfer material performed thereafter. It has no control over changes. This change cannot be dealt with by the density control using the density sensor.

Therefore, a color image forming apparatus in which a sensor (hereinafter referred to as a color sensor) for detecting the density or the color of the patch on the transfer material is installed on the transfer material can be considered.

This color sensor uses, for example, three or more types of light sources having different emission spectra such as red (R), green (G), and blue (B) as light emitting elements, or the light emitting elements are white (W). Using a light source that emits light, the spectral transmittances of red (R), green (G), blue (B), etc. on the light receiving element are different 3
It is configured by forming more than one kind of filter. As a result, three or more different outputs such as RGB output can be obtained.

[0008]

However, in order to perform control using the color sensor, a patch must be formed on the transfer material, and the transfer material and toner are consumed.
Therefore, the implementation frequency cannot be increased so much. Therefore, it is necessary to perform effective density control while minimizing the number of times of control using the color sensor.

The present invention has been made in view of the above circumstances, and by using a color sensor and a density sensor in combination, the number of times of density control using the color sensor is reduced to reduce the consumption of the transfer material. An object of the present invention is to provide a color image forming apparatus that suppresses the color density and has excellent density stability as compared with the conventional density control using only the density sensor.

[0010]

The present invention can solve the above-mentioned problems by providing the following constitutions.

(1) First density detecting means for detecting the density of the unfixed toner image formed on the image carrier or the transfer material carrier, and the fixed toner image formed on the transfer material. A color image forming apparatus having a second density detecting means for detecting density, wherein the first density detecting means corrects based on a detection result of the second density detecting means. Color image forming apparatus.

(2) In the color image forming apparatus described in the above item (1), regarding the black toner, the first density is obtained by using a value obtained by detecting the black monochrome toner image by the second density detecting means. The detection means is corrected, and for cyan, magenta and yellow toners, a mixed color toner image composed of three colors of cyan, magenta and yellow and a monochrome toner image are detected by the second density detection means, and the mixed color toner image is obtained. And a detection result of monochromatic black are compared, and the first density detecting unit is corrected according to the detection result.

(3) First density detecting means for detecting the density of the unfixed toner image formed on the image carrier or the transfer material carrier, and the fixed toner image formed on the transfer material. An image density control method for a color image forming apparatus having a second density detecting means for detecting the density, wherein the first density detecting means is corrected based on a detection result of the second density detecting means. For the step and the black toner, the first density detecting means is corrected using a value obtained by detecting the black monochrome toner image by the second density detecting means, and for the cyan, magenta and yellow toners, cyan is used. A step of detecting a mixed color toner image of three colors of magenta, magenta, and yellow and a toner image of single color black by the second density detecting means, and a detection result of the mixed color toner image and single color black Comparison, according to the result, the image density control method of the color image forming apparatus characterized by comprising a step of correcting the first density detecting unit.

(4) A storage medium storing a program for implementing the image density control method for a color image forming apparatus according to the above item (3).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a color image forming apparatus and an image density control method of the present invention will be described below.

FIG. 1 is a sectional view showing the overall structure of a color image forming apparatus in Embodiment 1, FIG. 2 is an explanatory view showing the structure of a density sensor, and FIG. 3 is an explanatory view showing the structure of a color sensor. 4 is a flow chart showing a correction method of the density sensor in the first embodiment, FIG. 5 is an explanatory view showing a correction patch pattern formed on the transfer material used in the first embodiment, and FIG. FIG. 7 is a graph showing the relationship between the density sensor output and the color sensor output / correction output.
FIG. 8 is a flow chart showing the correction method of the density sensor in the second embodiment, and FIG. 8 is an explanatory diagram showing the correction patch pattern used in the second embodiment.

(Embodiment 1) FIG. 1 is an example of an electrophotographic color image forming apparatus, which is a tandem color image forming apparatus using an intermediate transfer member 27. The color image forming apparatus includes an image forming section shown in FIG. 1 and an image processing section (not shown).

The operation of the image forming section in the electrophotographic color image forming apparatus will be described below with reference to FIG.

The image forming unit forms an electrostatic latent image by the exposure light that is turned on based on the exposure time converted by the image processing unit, develops the electrostatic latent image to form a monochromatic toner image, and the monochromatic toner image is formed. Toner images are overlaid to form a multicolor toner image,
This multicolor toner image is transferred to the transfer material 11, and the transfer material 1
1, which fixes the multicolor toner image on the sheet feeding unit 21,
The photoconductors (22Y, 2Y, 2Y) for each station arranged in parallel for the development color
2M, 22C, 22K), injection charging means (23Y, 23M, 23C, 23K) as primary charging means, toner cartridges (25Y, 25M, 25C, 25K), developing means (26Y, 26M, 26C, 26K), intermediate The transfer member 27, the transfer roller 28, the cleaning unit 29, the fixing unit 30, the density sensor 41, and the color sensor 42 are included.

The photosensitive drums (photosensitive members) 22Y, 22
M, 22C, and 22K are formed by applying an organic photoconductive layer on the outer circumference of an aluminum cylinder, and are rotated by the driving force of a drive motor (not shown). The drive motors are photosensitive drums 22Y, 22M, and 22C. 22K is rotated counterclockwise in accordance with the image forming operation.

As the primary charging means, four injection chargers 23Y, 23M and 23C for charging the yellow (Y), magenta (M), cyan (C) and black (K) photoconductors for each station. 23K, each injection charger has a sleeve 23YS, 23MS, 23CS,
23 KS is provided.

Photosensitive drums 22Y, 22M, 22C, 22
The exposure light for K is supplied to the scanner units 24Y, 24M, 24C, 2
4K, the photosensitive drums 22Y, 22M, 22C,
The electrostatic latent image is formed by selectively exposing the surface of 22K.

As developing means, in order to visualize the electrostatic latent image, yellow (Y), magenta (M), cyan (C) and black (K) development is carried out at each station. 4
The developing device 26Y, 26M, 26C, 26K is provided, and each developing device has a sleeve 26YS, 26MS,
6CS and 26KS are provided. Each developing device is detachably attached.

The intermediate transfer member 27 includes the photosensitive drums 22Y and 2Y.
2M, 22C and 22K, which rotate clockwise when forming a color image,
The toner rotates with the rotation of M, 22C, and 22K, and a single-color toner image is transferred. Then, a transfer roller 28, which will be described later, comes into contact with the intermediate transfer body 27 to nip and convey the transfer material 11, and the multicolor toner image on the intermediate transfer body 27 is transferred to the transfer material 11.

The transfer roller 28 contacts the transfer material 11 at the position 28a while transferring the multicolor toner image on the transfer material 11, and is separated to the position 28b after the printing process.

The fixing section 30 melts and fixes the transferred multicolor toner image while the transfer material 11 is being conveyed. As shown in FIG. 1, the fixing roller 31 and the transfer material 11 heat the transfer material 11. A pressure roller 32 for pressing the fixing roller 31 to the fixing roller 31 is provided. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and each has a heater 3 inside.
3, 34 are built in. That is, the transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32, and is subjected to heat and pressure to fix the toner on the surface.

After the toner image is fixed, the transfer material 11 is discharged to a paper discharge tray (not shown) by a discharge roller (not shown), and the image forming operation is completed.

The cleaning means 29 is an intermediate transfer member 27.
The toner remaining on the upper surface is cleaned, and the waste toner after transferring the multicolor toner image of four colors formed on the intermediate transfer member 27 to the transfer material 11 is stored in the cleaner container.

The density sensor 41 is arranged toward the intermediate transfer body 27 in the color image forming apparatus of FIG.
The density of the toner patch formed on the surface of the intermediate transfer body 27 is measured. An example of the configuration of the density sensor 41 is shown in FIG.
Shown in. An infrared light emitting element 51 such as an LED, a photodiode, a light receiving element 52 such as Cds, an IC (not shown) for processing received light data, and a holder (not shown) for accommodating them.

The light receiving element 52a detects the intensity of irregularly reflected light from the toner patch 64, and the light receiving element 52b detects the intensity of specularly reflected light from the toner patch 64. By detecting both the regular reflection light intensity and the irregular reflection light intensity, it is possible to detect the densities of the toner patch 64 from high density to low density. An optical element such as a lens (not shown) may be used for coupling the light emitting element 51 and the light receiving element 52.

In the color image forming apparatus of FIG. 1, the color sensor 42 is arranged downstream of the fixing section 30 of the transfer material conveying path toward the image forming surface of the transfer material 11, and is formed on the transfer material 11. The RGB output values of the colors of the mixed color patch after fixing are detected. By arranging the image inside the color image forming apparatus, it becomes possible to automatically detect the image after fixing before discharging the image to the paper discharging unit.

FIG. 3 shows an example of the configuration of the color sensor 42. The color sensor 42 includes a white LED 53 and a charge storage sensor 54a with an RGB on-chip filter. The white LED 53 is incident on the transfer material 11 on which the patch after fixing is formed at an angle of 45 degrees, and the intensity of diffused reflection light in the 0 degree direction is detected by the charge storage type sensor 54a with an RGB on-chip filter. The light receiving portion of the charge storage sensor 54a with the RGB on-chip filter is 54
RGB is an independent pixel like b.

The charge storage type sensor of the RGB on-chip filter-equipped charge storage type sensor 54 may be a photodiode. Several sets of three RGB pixels may be lined up. Alternatively, the incident angle may be 0 degree and the reflection angle may be 45 degrees. Furthermore, LEDs that emit RGB three colors
And a sensor without a filter may be used.

FIG. 4 shows the density sensor 4 according to this embodiment.
3 is a flowchart showing a correction method of No. 1. The color sensor 42 is used for the correction in this embodiment. That is, since the toner image fixed on the transfer material is required, it is preferable to reduce the execution frequency as much as possible. In the present embodiment, when the user desires to execute the correction control, the correction control is performed manually by the user.

First, in step S1, a sensor correction patch pattern fixed on the transfer material is formed.

FIG. 5 shows a correction patch pattern formed on the transfer material.

The correction patch patterns are yellow gradation patches 611, 612, 613, 614, magenta gradation patches 621, 622, 623, 624, cyan gradation patches 631, 632, 633, 634, and black gradation patches. A total of 16 gradation patches 641, 642, 643, 644
It is an individual.

Next, in step S2, step S
The density of the toner patch formed by the color sensor 42
Detect by.

Here, the detected density detection result is a value that includes the effects of variations in the transferability of the toner image on the transfer material and fluctuations in the fixability, so it is the same as when unfixed toner is detected by the density sensor. It is a highly accurate value by comparison.

Next, in step S3, step S
A toner patch is formed on the intermediate transfer member 27 under the same conditions as in 1. The patch pattern is the same as in step S1.

Next, in step S4, step S3
The density of the toner patch formed in step 3 is detected by the density sensor 41.

Next, in step S5, the density sensor 4
The output of 1 is corrected.

The method of correcting the density sensor 41 will be described below with reference to FIG. The horizontal axis in FIG. 6 indicates the concentration sensor 4
1 represents the detection result of 1. The vertical axis indicates the color sensor 42.
Represents the detection result of. The white circle point P in the figure is the step S.
2 shows the relationship between the detection result of 2 (the result of detecting the toner patch on the transfer material by the color sensor) and the detection result of step S4 (the result of detecting the toner patch on the intermediate transfer material 27 by the density sensor). . The straight line A represents the case where the output of the density sensor is equal to the output of the color sensor, that is, the case where there is no measurement error of the density sensor (since the color sensor detects the density on the transfer material, the density detection accuracy is high. Therefore, there is no color sensor measurement error).
In the figure, the point P and the straight line A do not match. That is, it means that a slight measurement error occurs in the density sensor.

Next, the correction table (curve C in the figure) of the density sensor 41 is calculated. The correction table C is a curve that passes through the point P, and the tone density that does not form a patch (tone between patches) is calculated by spline interpolation between the origin and the point P. The correction table C is calculated for each color (yellow, magenta, cyan, black). Further, the calculation of the correction table is executed by a main body CPU (not shown), and the calculated correction table C is stored in a main body memory (not shown, which uses a nonvolatile memory).

The correction method of the density sensor 41 has been described above.

The normal image density control is performed by the density sensor 4
1 is used regularly.

In the color image forming apparatus of this embodiment, the image density control is executed when the power is turned on, when the developing device or the photosensitive drum is replaced, or every time a predetermined number of sheets are printed.
That is, it is executed when the fluctuation of the concentration is predicted. At this time, the output of the density sensor 41 is corrected each time by the correction table C that has already been calculated. Further, the method of image density control performed here may be a conventionally known method. For example, a plurality of predetermined patterns (halftone patterns, etc.) patches in which development conditions (bias, etc.) or charging conditions, etc. are changed in multiple stages are formed on an intermediate transfer member, and the density of the patch pattern is detected, A method of calculating the developing condition and the charging condition for obtaining a desired density may be used. As another example, a plurality of patches are formed with a gradation pattern of a plurality of stages, the density gradation characteristics of the engine are calculated from the density curves, and a step for obtaining a predetermined gradation characteristic is obtained according to the calculation result. A method of calculating a tone correction lookup table may be used. In any case of performing the image density control, the output of the density sensor is corrected by the correction table C described above.

When variations in transfer conditions and fixing conditions are predicted (for example, when the intermediate transfer member or the fixing device is replaced, or when the installation location of the device, that is, the operating environment is changed), the user can perform the above-mentioned operation. The correction of the density sensor 41 is executed, and the correction table C is updated.

In this embodiment, the output density value of the density sensor is corrected by the correction table C. However, when the relationship between the output voltage value of the density sensor and the density is previously provided as a density conversion table, the density conversion is performed. A new density conversion table may be created by multiplying the table by the correction table C.

Furthermore, the density conversion table of the density sensor may be created directly from the relationship between the detected density value of the color sensor and the output voltage value of the density sensor.

In any of the above methods, the correction of the density detecting means for detecting the density of the unfixed toner image is performed on the basis of the detection result of the density detecting means for detecting the density of the toner image after fixing formed on the transfer material. It is within the scope of the present invention to do so.

As described above, according to the present embodiment, it is possible to provide the color image forming apparatus which suppresses the consumption of the transfer material required for the density control and is excellent in the density stability as compared with the conventional density control using only the density sensor. .

(Embodiment 2) In the present embodiment, an example in which the detection accuracy of the color sensor 42 does not decrease, that is, the correction accuracy of the density sensor 41 does not deteriorate even when the light receiving characteristics of the color sensor 42 have large variations. explain.

Spectral reflectance of color toner (wavelength characteristic for absorption of light) and RG generally used for color sensor
The transmission spectral characteristics of the B filter do not match. Therefore, when there are variations in the spectral characteristics of the RGB filters used in the color sensor, the toner amount of the color toner and the sensor output differ for each sensor. In this embodiment, a method will be described in which, even in such a case, the color sensor accurately detects the amount of toner on the transfer material, and the density sensor is accurately corrected.

The present embodiment is an extension of the first embodiment, and the overall structure of the color image forming apparatus used is the same as that of FIG. 1 and its explanation is omitted.

The method of correcting the density sensor 41 in this embodiment will be described below with reference to the flowchart of FIG.

First, in step S101, a sensor correction patch pattern fixed on the transfer material is formed.

FIG. 8 shows a correction patch pattern used in this embodiment.

The correction patch patterns are black gradation patches 641, 642, 643, 644, and yellow, magenta, and cyan mixed-color toner patches 651, 65.
There are a total of eight, 2,653,654.

Here, the feature of the present embodiment is that the mixed color toner patches 651, 652, 653, 654 are used for detecting the color toners. In addition, the mixed color toner patch 651,
652, 653, and 654 are black gradation patches 64
It is a patch formed with a predetermined color mixture ratio where the output values of the color sensors 1, 642, 643, and 644 are expected to be substantially the same. Incidentally, the toner patches 641 and 651, 64
2 and 652, 643 and 653, 644 and 654 respectively correspond.

Next, in step S102, the density of the black gradation patches 641, 642, 643, 644 among the toner patches formed in step S101 is detected by the color sensor 42. Black toner patches generally have flat spectral characteristics (light absorption characteristics) with respect to wavelength, and therefore are not affected by filter variations of the color sensor. Therefore, the black toner density detection is performed in the same manner as in the first embodiment.

Next, in step S103, the color patches of the mixed color gradation patches 651, 652, 653, 654 among the toner patches formed in step S101 are set in the color sensor 4.
2 to detect.

In step S104, step S1
Black monochromatic toner patch detected in 02 and step S
The sensor output values of the mixed color patch detected in 103 are compared, and if all the R, G, and B sensor output values match, the process proceeds to step S106.

If the R, G, and B sensor output values do not match, the color mixing ratio of the color mixing toner patch is adjusted in step S105.

The adjustment method is as follows when the output value of R is high.
The amount of complementary cyan toner is reduced, and if it is low, the amount of cyan toner is increased. Similarly, magenta toner is adjusted for G output, and yellow toner is adjusted for B output. In addition, the color mixture ratio is adjusted by the color mixture gradation patch 65.
1, 652, 653, 654 are independently performed.

After adjusting the color mixture ratio, the process returns to step S101.

The adjustment of the color mixture ratio is repeatedly executed until the output values of all the color mixture patches become equal to the black patch.

In step 106, the density values of yellow, magenta and cyan are calculated. A predetermined conversion table is used to calculate the density.

The conversion table is composed of a combination of the density of black monochromatic toner and the monochromatic densities of yellow, magenta and cyan toners having the same spectral characteristics.

Next, in step S107, a toner patch is formed on the intermediate transfer member 27.

The patch pattern is the same as that of the first embodiment, and four gradation patches of yellow, magenta, cyan, and black are formed, 16 in total. The black toner patch has the same conditions as in step S101. As for the yellow, magenta, and cyan patches, a mixed color patch of yellow, magenta, and cyan toners having the same density and spectral characteristics of the black monochrome toner is formed under the same conditions. Let it be done.

Next, in step S108, step S
The density sensor 41 detects the density of the toner patch formed by 107.
Detect with.

Finally, in step S109, the output of the density sensor 41 is corrected. The correction method is the same as in the first embodiment.

The above is the correction method for the density sensor 41 in this embodiment.

Incidentally, the normal image density control is carried out periodically by using the density sensor 41 as in the first embodiment.

As described above, according to this embodiment, the color sensor 42
Even when there is a large variation in the light receiving characteristics of the color sensor 42, the detection accuracy of the color sensor 42 does not decrease, that is, the correction accuracy of the density sensor 41 does not decrease, and further, the consumption of the transfer material required for the density control is suppressed and only the density sensor is used. It is possible to provide a color image forming apparatus having excellent density stability as compared with the conventional density control using.

In this embodiment, when the color toner is detected by the color sensor, the toner mixture ratio is adjusted and the detection is repeatedly executed until the sensor output values of the black single color toner and the mixed color toner become equal. Other methods may be used to calculate the toner mixture ratio. For example, by performing a regression calculation on the toner mixture ratio of a mixed color patch in which the output is equal to the black single color patch and the output is the same, by forming a plurality of types of mixed color patches in which the toner mixture ratio is changed in multiple stages in advance. You may ask. In any case,
Any method that uses a color-mixed patch when detecting the density of color toner with a color sensor and that compares the detection value of the color-mixed patch with the output of a black single-color patch does not violate the gist of the present invention.

The present embodiment is an optimum method for accurately correcting the density sensor even when the light receiving characteristics of the color sensor have a large variation. When the characteristics and the spectral characteristics of the filter of the color sensor are almost equal to each other, or when the accuracy of the correction of the density sensor is not so high, the first embodiment in which the usage amount of the transfer material and the toner is small and the processing is completed in a short time is applied. Is preferred.

That is, the optimum method may be selected according to the configuration of the color image forming apparatus using the present invention.

Furthermore, in the present embodiment, only the example in which the density detection position of the density sensor is on the intermediate transfer member has been described, but the installation position of the density sensor is not limited to this. Specifically, it may be on another image carrier such as a photoconductor or on a transfer material carrier such as a transfer belt.
In other words, it may be any place where an unfixed toner image can be formed.

[0081]

As described above, according to the present invention,
By correcting the density sensor using the color sensor, the consumption of transfer material required for density control is suppressed, and
It is possible to provide a color image forming apparatus having excellent density stability as compared with the conventional density control using only the density sensor.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a color image forming apparatus according to a first embodiment.

FIG. 2 is an explanatory diagram showing a configuration of a concentration sensor.

FIG. 3 is an explanatory diagram showing a configuration of a color sensor.

FIG. 4 is a flowchart showing a method of correcting the density sensor according to the first embodiment.

FIG. 5 is an explanatory diagram showing a correction patch pattern formed on the transfer material used in the first embodiment.

FIG. 6 is a graph showing the relationship between the density sensor output and the color sensor output / correction output in the first embodiment.

FIG. 7 is a flowchart showing a correction method for the density sensor according to the second embodiment.

FIG. 8 is an explanatory diagram showing a correction patch pattern used in the second embodiment.

[Explanation of symbols]

11 Transfer material 22 Photoreceptor, photosensitive drum 26 developing means 27 Intermediate transfer body 30 fixing device 41 Concentration sensor 42 color sensor

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 115 G03G 15/08 115 (72) Inventor Tomoaki Nakai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon In-house F-term (reference) 2G059 AA01 BB06 BB09 CC19 EE02 EE13 GG02 HH01 JJ02 JJ11 KK01 MM05 MM10 MM14 2H027 DA09 DE02 DE07 DE10 EB04 EC03 EC20 HB09 2H030 AA03 AD04 AD16 BB36 BB56 GA63 DB08 DA35 DA08 DA49

Claims (4)

[Claims] 1. A first density detecting means for detecting a density of an unfixed toner image formed on an image carrier or a transfer material carrier, and a density of a fixed toner image formed on a transfer material. A color image forming apparatus having a second density detecting unit for detecting a color, wherein the first density detecting unit performs correction based on a detection result of the second density detecting unit. Image forming apparatus. 2. The color image forming apparatus according to claim 1, wherein, with respect to black toner, a value obtained by detecting a black monochrome toner image by the second density detecting means is used, and the first density detecting means is used. For cyan, magenta, and yellow toners, cyan, magenta, and
The mixed toner image of three colors of yellow and the toner image of monochromatic black are detected by the second density detecting means, the detection results of the mixed toner image and monochromatic black are compared, and the first image is detected according to the result. A color image forming apparatus, characterized in that the density detecting means is corrected. 3. A first density detecting means for detecting a density of an unfixed toner image formed on an image carrier or a transfer material carrier, and a density of a fixed toner image formed on a transfer material. An image density control method for a color image forming apparatus having a second density detecting means for detecting a step of correcting the first density detecting means based on a detection result of the second density detecting means. With respect to black toner, the first density detecting means is corrected using a value obtained by detecting a black monochrome toner image by the second density detecting means, and cyan, magenta and yellow toners are cyan, The step of detecting the mixed color toner image composed of three colors of magenta and yellow and the monochrome image of the monochrome toner by the second density detecting means, and the detection result of the mixed color toner image and the monochrome black are compared. Compare
A step of correcting the first density detecting means according to the result, and a method of controlling the image density of the color image forming apparatus. 4. A storage medium storing a program for realizing an image density control method of a color image forming apparatus according to claim 3.