JP2015039108A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate correction data which can be used up to a reference maximum density even when the density characteristics of an image forming apparatus is changed.SOLUTION: A correction data generation section 31 performs processing of: (a) measuring density characteristics; (b) generating temporary gray level correction data making the density characteristics liner while changing the maximum density of the density characteristics to a reference maximum density lower than the maximum density; (c) generating base gray level correction data making the density characteristics liner while maintaining the maximum density of the density characteristics; (d) generating additional gray level correction data used for an additional gray level correction executed after a gray level correction based on the base gray level correction data so that the gray level correction based on the base gray level correction data and the additional gray level correction data, and the gray level correction based on the temporary gray level correction data are the same. Then, an image processing section 33 performs a gray level correction on a print image on the basis of the base gray level correction data and the additional gray level correction data.

Description

  The present invention relates to an image forming apparatus.

  In general, in an electrophotographic image forming apparatus, even if dots are grown corresponding to pixel values in an image, the pixel value and the toner density are not proportional.

  In addition, since the relationship between the pixel value and the toner density varies depending on the machine difference of the image forming apparatus, environmental conditions, etc., it is necessary to adjust the density characteristics for each machine to print at a toner density proportional to the pixel value. is there.

  In a certain density adjustment method, an image forming apparatus prints a test chart on a sheet, reads the printed test chart with a scanner or the like, and generates gradation correction data based on the read result (see, for example, Patent Document 1). ).

  In this method, the operation of printing and reading the test chart is complicated, so that it is not actually executed. For this reason, the image forming apparatus often automatically adjusts the gradation correction data periodically. In this case, the image forming apparatus forms an adjustment toner pattern on the intermediate transfer member, measures the density of the adjustment toner pattern with a density sensor, and adjusts the gradation correction data based on the measurement result.

JP 2008-26552 A

  When adjusting the gradation correction data based on the measurement result of the density of the adjusted toner pattern on the intermediate transfer member, in order to form the adjusted toner pattern after correcting the pixel value using the gradation correction data before adjustment When the toner density decreases due to changes over time, the maximum density of toner density may not reach the reference maximum density (for example, ID (Image Density) = 1.4) even if density adjustment is performed.

  FIG. 7 is a diagram for explaining adjustment of gradation correction data. FIG. 7A is a diagram illustrating an example of the relationship between the pixel value and the toner density when the tone correction data is generated using the test chart. FIG. 7B is a diagram illustrating the relationship between the target pixel value and the toner density. FIG. 7C is a diagram illustrating an example of gradation correction data obtained from the relationship between the pixel value and the toner density illustrated in FIG. 7A and the target relationship illustrated in FIG. . FIG. 7D is a diagram illustrating an example of the relationship between the pixel value after the density characteristic change and the toner density.

  For example, in the density characteristics shown in FIG. 7A, the maximum value Xmax of the pixel value (for example, 255 for 8-bit data) becomes the reference maximum density, and the pixel value and the toner density are proportional to each other. When the tone correction data is generated, the result is as shown in FIG.

  Thereafter, as shown by the solid line in FIG. 7D, the density characteristics change, and when the density is lower than in the case of FIG. 7A (broken line in FIG. 7D), the density is shown in FIG. 7C. When the adjustment toner pattern is generated using the gradation correction data, as shown in FIG. 7D, the density at Ymax corresponding to the maximum value Xmax of pixel values (that is, the maximum density after gradation correction) is obtained. It becomes lower than the standard maximum density.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that generates correction data that can be used up to a reference maximum density even when density characteristics change.

  The image forming apparatus according to the present invention includes: (a) measuring density characteristics; and (b) changing the maximum density of the density characteristics to a reference maximum density lower than the maximum density while linearizing the density characteristics. And (c) generating base gradation correction data that linearizes the density characteristic while maintaining the maximum density of the density characteristic, and (d) gradation based on the base gradation correction data. The additional gradation correction data used for the additional gradation correction executed after the correction are gradation correction based on the base gradation correction data and the additional gradation correction data, and gradation correction based on the provisional gradation correction data. And a correction data generation unit that generates the same and the image processing unit that performs gradation correction of a print image based on the base gradation correction data and the additional gradation correction data.

  According to the present invention, it is possible to obtain an image forming apparatus that generates correction data that can be used up to the reference maximum density even if the density characteristic changes.

FIG. 1 is a side view showing a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a flowchart for explaining the operation of the image forming apparatus shown in FIGS. 1 and 2 when generating gradation correction data. FIG. 4 is a diagram for explaining processing at the time of tone correction data generation in the image forming apparatus shown in FIGS. 1 and 2. FIG. 5 is a flowchart for explaining the operation of the image forming apparatus shown in FIGS. 1 and 2 when adjusting the gradation correction data. FIG. 6 is a diagram for explaining processing at the time of gradation correction data adjustment in the image forming apparatus shown in FIGS. 1 and 2. FIG. 7 is a diagram for explaining adjustment of gradation correction data.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image forming apparatus of this embodiment has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, an exposure device 2, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are photoconductors of four colors of black, magenta, cyan, and yellow. The exposure device 2 is a device that forms an electrostatic latent image by irradiating the surfaces of the photosensitive drums 1a to 1d with laser light. The exposure apparatus 2 is a laser diode that is a light source of laser light, and an optical element that guides the laser light to the photosensitive drums 1a to 1d (lens, mirror, light on the surface of the photosensitive drums 1a to 1d along the main scanning direction). A polygon mirror for scanning, and a polygon motor for rotating the polygon mirror.

  The developing devices 3a to 3d attach the toner in the toner cartridge to the electrostatic latent images on the photosensitive drums 1a to 1d and develop the toner images to form toner images. The photosensitive drum 1a and the developing device 3a develop black, the photosensitive drum 1b and the developing device 3b develop magenta, and the photosensitive drum 1c and the developing device 3c develop cyan. Then, yellow development is performed by the photosensitive drum 1d and the developing device 3d.

  The intermediate transfer belt 5 is an annular intermediate transfer member that contacts the photosensitive drums 1a to 1d and transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 5 is stretched around a driving roller 6 and a tension roller 7, and rotates around in the direction from the contact position with the photosensitive drum 1 d to the contact position with the photosensitive drum 1 a by the driving force from the driving roller 6. To go.

  The transfer roller 8 brings the conveyed paper into contact with the intermediate transfer belt 5 and transfers the toner image on the intermediate transfer belt 5 to the paper. The sheet on which the toner image is transferred is conveyed to a fixing device (not shown), and the toner image is fixed on the sheet.

  The density sensor 9 irradiates the intermediate transfer belt 5 with light and detects the reflected light. In particular, the density sensor 9 detects the density and position of the adjustment toner pattern on the intermediate transfer belt 5 during the adjustment process. The density sensor 9 is a reflective optical sensor.

  The cleaning unit 10 is a cleaning roller, for example, and removes residual toner on the intermediate transfer belt 5.

  FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus according to the embodiment of the present invention.

  As shown in FIG. 2, the image forming apparatus includes a controller 21, a printing device 22, an image reading device 23, and a storage device 24.

  The controller 21 has an ASIC (Application Specific Integrated Circuit) and / or a microcomputer, and controls each unit in the image forming apparatus based on hardware and / or software and operates as various processing units.

  The controller 21 operates as a correction data generation unit 31, a correction data adjustment unit 32, and an image processing unit 33.

  The correction data generation unit 31 (a) measures the density characteristic (toner density characteristic with respect to the pixel value) of the image forming apparatus, and (b) changes the maximum density of the density characteristic to a reference maximum density lower than the maximum density. And (c) generating base gradation correction data that linearizes the density characteristics while maintaining the maximum density of the density characteristics, and (d) base The additional gradation correction data used for the additional gradation correction executed after the gradation correction based on the gradation correction data is the gradation correction based on the base gradation correction data and the additional gradation correction data, and the provisional gradation correction data. Is generated so as to be the same as the gradation correction based on.

  Specifically, the correction data generation unit 31 causes the printing device 22 to print the test chart, causes the image reading device 23 to read the printed test chart image, and determines the density characteristics based on the reading result of the test chart image. taking measurement.

  The correction data adjustment unit 32 measures density characteristics using (e) base gradation correction data, and (f) adjusts additional gradation correction data based on the density characteristics.

  Specifically, the correction data adjustment unit 32 forms an adjustment toner pattern on the intermediate transfer belt 5 at a gradation to which the base gradation correction data is applied, and the adjustment toner pattern formed on the intermediate transfer belt 5 The density is measured by the density sensor 9 to measure density characteristics.

  Further, the correction data adjustment unit 32 does not adjust the base gradation correction data, but adds the maximum density after gradation correction based on the base gradation correction data and the additional gradation correction data to be the reference maximum density. Adjust the tone correction data.

  The correction data adjustment unit 32 automatically adjusts the additional gradation correction data when the adjustment timing based on a predetermined schedule arrives. The correction data adjustment unit 32 also adjusts the additional gradation correction data even when an adjustment request by an operation by a user or a service person is detected.

  The image processing unit 33 performs gradation correction of the print image based on the base gradation correction data and the additional gradation correction data.

  The printing device 22 is an internal device that prints an image based on image data after image processing by the image processing unit 33 in the controller 21 with the mechanical configuration shown in FIG.

  The image reading device 23 is an internal device that optically reads a document image from a document and generates color image data of the document image.

  The storage device 24 is a non-volatile storage device such as a flash memory, and stores the above-described gradation correction data and the like.

  Next, the operation of the image forming apparatus will be described.

(1) Generation of gradation correction data

  FIG. 3 is a flowchart for explaining the operation of the image forming apparatus shown in FIGS. 1 and 2 when generating gradation correction data. FIG. 4 is a diagram for explaining processing at the time of tone correction data generation in the image forming apparatus shown in FIGS. 1 and 2. FIG. 4A is a diagram illustrating an example of the relationship between the pixel value and the toner density when the tone correction data is generated using the test chart. FIG. 4B is a diagram illustrating a relationship between the linear pixel value and the toner density when the maximum density is set to the reference maximum density. FIG. 4C is a diagram illustrating an example of provisional gradation correction data obtained from the relationship between the pixel value and the toner density illustrated in FIG. 4A and the target relationship illustrated in FIG. is there. FIG. 4D is a diagram illustrating a relationship between the linear pixel value and the toner density when the maximum density is maintained. FIGS. 4E and 4F are diagrams illustrating examples of base gradation correction data and additional gradation correction data.

  The correction data generation unit 31 controls the printing device 22 to print a test chart on a sheet (step S1). The test chart includes 64-gradation patches for each color of black, magenta, cyan, and yellow.

  Next, after the user places the paper on which the test chart is printed on the image reading device 23, the correction data generation unit 31 controls the image reading device 23 to display an image of the test chart printed on the paper. To obtain RGB image data of each patch in the test chart (step S2). Thereby, for example, density characteristics as shown in FIG. 4A are obtained for each color of black, magenta, cyan, and yellow.

  For each color, the correction data generation unit 31 generates provisional gradation correction data as shown in FIG. 4C for correcting the density characteristics to the density characteristics as shown in FIG. 4B. At the same time (step S3), base gradation correction data as shown in FIG. 4 (E) for correcting the density characteristics as shown in FIG. 4 (D) is generated (step S4).

  For each color, the correction data generation unit 31 generates additional gradation correction data as shown in FIG. 4F from the temporary gradation correction data and the base gradation correction data (step S5). At this time, as shown in FIG. 4, an output Y based on the input / output relationship of the base gradation correction data with respect to the input X is obtained as an input to the additional gradation correction data. The additional gradation correction data is generated so as to be the same as the output Y by the provisional gradation correction data.

  The correction data generation unit 31 stores the base gradation correction data and the additional gradation correction data in the storage device 24 (step S6).

  Then, when printing the print image based on the print request, the image processing unit 33 reads the base gradation correction data and the additional gradation correction data from the storage device 24, sets a certain pixel value as the input X, and uses the base gradation correction data. The output t for the input X in the correction data is used as an input for the additional gradation correction data, and the output Y for the input t in the additional gradation correction data is used as the pixel value after the gradation correction.

(2) Adjustment of gradation correction data

  FIG. 5 is a flowchart for explaining the operation of the image forming apparatus shown in FIGS. 1 and 2 when adjusting the gradation correction data. FIG. 6 is a diagram for explaining processing at the time of gradation correction data adjustment in the image forming apparatus shown in FIGS. 1 and 2. FIG. 6A is a diagram illustrating an example of the relationship between the pixel value after the density characteristic change and the toner density. FIG. 6B is a diagram illustrating a relationship between the linear pixel value and the toner density when the maximum density is set to the reference maximum density. 6C and 6D are diagrams illustrating examples of the base gradation correction data and the adjusted additional gradation correction data.

  First, the correction data adjustment unit 32 controls the printing device 22 to form an adjustment toner pattern on the intermediate transfer belt 5 based on the base gradation correction data (step S21). The adjustment toner pattern includes eight gradation patches, which are fewer than the gradation of the test chart, for each color of black, magenta, cyan, and yellow.

  That is, when adjusting the gradation correction data, gradation correction is performed using only the base gradation correction data without using the additional gradation correction data, and the pixel value of each patch is determined.

  Then, the correction data adjustment unit 32 uses the density sensor 9 of the printing device 22 to measure the density of each patch of the adjusted toner pattern (step S22).

  The correction data adjustment unit 32 adjusts the additional gradation correction data based on the measured density (Step S23).

  For example, when the density in the density characteristic decreases from the broken line to the solid line shown in FIG. 6A, the density characteristic as shown in FIG. 6B is obtained with the base gradation correction data and the additional gradation correction data. The additional gradation correction data is adjusted from the broken line shown in FIG. 6D to the solid line without changing the base gradation correction data (FIG. 6C).

  Then, the correction data adjustment unit 32 updates the additional gradation correction data stored in the storage device 24 with the adjusted additional gradation correction data (step S24).

  Similarly, after the adjustment, when the print image is printed based on the print request, the image processing unit 33 reads the base gradation correction data and the additional gradation correction data from the storage device 24, and inputs a certain pixel value X The output t for the input X in the base gradation correction data is used as the input for the additional gradation correction data, and the output Y for the input t in the additional gradation correction data is used as the pixel value after the gradation correction.

  As described above, according to the above embodiment, the correction data generation unit 31 measures (a) the density characteristic, and (b) changes the maximum density of the density characteristic to the reference maximum density lower than the maximum density. (C) generating base gradation correction data that linearizes the density characteristics while maintaining the maximum density of the density characteristics, and (d) base level correction data. The additional gradation correction data used for the additional gradation correction executed after the gradation correction based on the tone correction data is changed into the gradation correction based on the base gradation correction data and the additional gradation correction data and the provisional gradation correction data. It is generated so that the gradation correction based on it is the same. Then, the image processing unit 33 performs gradation correction of the print image based on the base gradation correction data and the additional gradation correction data.

  Thereby, even if the density characteristic of the printing apparatus 22 changes, correction data that can be used up to the reference maximum density (that is, a combination of base gradation correction data and additional gradation correction data) is generated.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above embodiment, the intermediate transfer belt 5 is used as an intermediate transfer member. However, even when an intermediate transfer member of another form is used, adjustment of gradation correction data is executed in the same manner.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

5 Intermediate transfer belt (an example of an intermediate transfer member)
9 Density Sensor 23 Image Reading Device 31 Correction Data Generation Unit 32 Correction Data Adjustment Unit 33 Image Processing Unit

Claims (4)

(A) measuring density characteristics; (b) generating provisional gradation correction data for linearly changing the density characteristics while changing the maximum density of the density characteristics to a reference maximum density lower than the maximum density; c) generating base gradation correction data that linearizes the density characteristics while maintaining the maximum density of the density characteristics; and (d) additional gradation correction executed after gradation correction based on the base gradation correction data. The additional gradation correction data used in the above is generated so that the gradation correction based on the base gradation correction data and the additional gradation correction data is the same as the gradation correction based on the provisional gradation correction data. A correction data generation unit;
An image processing unit that performs gradation correction of a print image based on the base gradation correction data and the additional gradation correction data;
An image forming apparatus comprising:   The method further comprises: (e) measuring a density characteristic using the base gradation correction data; and (f) a correction data adjusting unit that adjusts the additional gradation correction data based on the density characteristic. The image forming apparatus according to 1.   The correction data adjusting unit adjusts the maximum density after gradation correction based on the base gradation correction data and the additional gradation correction data to be the reference maximum density without adjusting the base gradation correction data. 3. The image forming apparatus according to claim 2, wherein the additional gradation correction data is adjusted. An image reader, an intermediate transfer member, and a density sensor;
The correction data generation unit prints a test chart, causes the image reading device to read the image of the printed test chart, measures the density characteristic based on the reading result of the image of the test chart,
The correction data adjustment unit causes an adjustment toner pattern to be formed on the intermediate transfer body at a gradation to which the base gradation correction data is applied, and the density of the adjustment toner pattern formed on the intermediate transfer body is set to the density Measuring the concentration characteristics by measuring with a sensor;
The image forming apparatus according to claim 2, wherein:

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