JPH09172546A - Gamma conversion correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the device whose print-out image quality is proper even when a read characteristic of an image and a printer characteristic are changed. SOLUTION: In the usual operation, image data of an original read by an image read section A are transferred to a gamma memory 44 via a usual mode section 42a and an image processing section B, in which the data are gamma- transformed and the resulting data are transferred to a printer section D. On the other hand, in the case of gamma-transformation correction, image data of a reference pattern read by an image read section A are stored in a memory 43 and gamma-transformed by the gamma memory 44 and the transformed data are printed out by the printer section D. The printed image is read again by the image read section A and fed to a gamma calculation comparison section 42b as print paper image data, where the resulting data are compared with data stored in a memory 43 and a density difference is obtained. Depending on the obtained density difference, a gamma parameter of the gamma memory 44 is rewritten. Thus, the succeeding print density of the printer section D is made proper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a γ-conversion correction device which is applied to an image forming apparatus such as a copying machine or a printer and corrects γ conversion (density conversion) of image data. Further, the present invention can be applied to a printer that prints digital image data on a transfer paper to determine the output characteristics of the transfer paper that has been printed out, particularly the characteristics relating to the density.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus, a γ conversion performed for image quality processing is performed in order to output an optimum copy density for image data from an image reading section. (Linearity) conversion processing is performed. However, there is a problem that the above-mentioned γ characteristic is changed due to the deterioration of the image reading unit and the printer unit due to the temperature and the number of times of operation, and the optimum density output cannot be realized. In order to solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 62-183675 introduces a technique for setting the characteristics of the image reading unit and the printer unit and performing γ conversion.

[0003]

By the way, when performing the γ conversion in order to improve the image quality in the image forming apparatus, it is necessary to have the γ parameter according to the input / output characteristics of the printer and the scanner. In addition, changes in characteristics occur due to deterioration due to temperature and the number of operating times, making it difficult to output the target concentration. For this reason, it is important to easily respond to changes in the characteristics. On the other hand, in the γ conversion, an optimum image cannot be obtained only by linearly converting the image density,
It is necessary to have a γ parameter that corresponds to the nature of the image (eg, characters, pictures, etc.). However, it is not preferable to have each of the above two γ parameters in the memory, because the cost immediately increases.

The present invention has been made under such a background, and it is a first object of the present invention to provide an apparatus in which the image quality to be printed out is appropriate even if the reading characteristic of the image or the printer characteristic is changed. To aim. A second object of the present invention is to provide a device capable of surely realizing the correction of the density deviation due to the deterioration of the printer section. A third object of the present invention is to provide an apparatus capable of omitting the labor of manually transferring the printed transfer paper to the reading position when correcting the γ conversion. A fourth object of the present invention is to provide a device capable of automatically performing the γ conversion correction when the γ conversion correction is required due to deterioration of the printer unit.

[0005]

According to a first aspect of the present invention, an image reading unit that reads a reference test pattern and outputs image data corresponding to the reference test pattern, and image data output from the image reading unit. Γ conversion means for γ-converting the density of the data into a predetermined density, printing means for printing the image data γ-converted by the γ conversion means, and image data of the reference test pattern read by the image reading means. Storage means for storing, comparison means for comparing the image data stored in the storage means with image data obtained by reading the print image printed by the printing means again by the image reading means, and based on the comparison result of the comparison means. The first object is achieved by including a correction unit that corrects the predetermined density data that the γ conversion unit performs the γ conversion.

According to a second aspect of the present invention, in the γ conversion correction apparatus according to the first aspect, the counting means for counting the number of times the printing means has been operated, and when the counting means reaches a certain count value, The second object is achieved by including a warning unit that notifies that the correction of the γ conversion unit is necessary. According to a third aspect of the invention, in the γ conversion correction device according to the first aspect, after the printing by the printing means, there is provided a transportation means for transporting the printed sheet again to the reading position of the image reading means. Thus, the third object is achieved.

According to a fourth aspect of the present invention, in the γ conversion correction apparatus according to the first aspect, the counting means for counting the number of times of operation of the printing means, and after printing by the printing means,
And a conveying unit that conveys the printed sheet again to the reading position of the image reading unit. When the count value of the counting unit reaches a predetermined value, the γ conversion unit is corrected. The fourth object is achieved by causing the printed sheet to be conveyed again to the reading position of the image reading means by the conveying means.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the γ conversion correction apparatus of the present invention will be described in detail below with reference to FIGS. 1 to 8. FIG. 1 is a schematic cross-sectional view of an image forming apparatus to which a γ conversion correction device according to a first embodiment of the present invention is applied. FIG. 2 is a sectional view of an image reading unit of the image forming apparatus. FIG. 3 is a block diagram of a data processing system of the image forming apparatus. In the first embodiment, as shown in FIGS. 1 and 3, an image reading unit A that reads an image of a document and outputs image data corresponding to the reading, and an image read by the image reading unit A. An image processing unit B that performs predetermined image processing on the data, an image quality processing unit C that performs γ conversion or the like on the image data processed by the image processing unit B as described below, and the image quality processing unit C.
The printer unit D for printing the data after the γ conversion and the main control unit E including a CPU (central processing unit) for controlling these units.

The image reading section A, as shown in FIG.
A contact glass 1 for placing a document is provided, the contact glass 1 is illuminated by light sources 2a and 2b, and reflected light (document image) from the document is reflected by the mirrors 3, 4,
An image is formed on the light receiving surface of the CCD image sensor 9 through 5, 6, and 7 and the lens 8. Light source 2a,
2 and the mirror 3 are mounted on a scanning body 11 which moves the lower surface of the contact glass 1 in parallel with the contact glass 1 in the sub-scanning direction (left and right direction in FIG. 2). Main scanning is performed by solid-state scanning of the CCD image sensor 9, and the entire document is scanned. The image processing unit B amplifies the image signal read by the CCD image sensor 9, and A / D
Processing such as conversion and shading correction is performed. The digital image signal processed by the image processing unit B is sent to the image quality processing unit described later.

As shown in FIG. 3, the image quality processing section C comprises a changeover switch 41, a γ calculation section 42, a memory 43, and a γ memory 44. The γ calculation unit 42 includes a normal mode unit 42a and a γ calculation comparison unit 42a.
A main control unit E is connected to the image quality processing unit C.
The main control unit E supplies a write enable signal and a read enable signal for reading and writing to the γ memory 44, and a γ conversion correction signal for instructing the image quality processing unit C to perform γ conversion correction. We are supplying.

The printer section D is provided with a laser writing unit 12 which receives image data from the image quality processing section C. In this laser writing unit 12,
It is equipped with a laser diode that is a laser light source and a polygon mirror that rotates at high speed by a motor. The laser light output from the laser writing unit 12 illuminates the photosensitive drum 14 of the image forming system. Around the photosensitive drum 14, a charging charger 15, an eraser 16, a developing unit 17, a separation claw 20,
A cleaning unit 21 is provided. The peripheral surface of the photosensitive drum 14 is uniformly charged to a high potential by the charging charger 15. When the peripheral surface of the photosensitive drum 14 is irradiated with the laser light, the electric potential of the irradiated portion is lowered. The laser light is turned on / off in accordance with black / white of recording / reproduction, and the laser irradiation energy on the surface of the photoconductor drum 14 is controlled by pulse width modulation. As a result, a potential distribution corresponding to the gradation level of the recorded image, that is, an electrostatic latent image is formed on the surface of the photosensitive drum 14. When the portion on which the electrostatic latent image is formed passes through the developing unit 17, toner adheres according to the level of the potential, and the electrostatic latent image becomes a visualized toner image. The transfer paper 22 is transferred at a predetermined timing to the portion where the toner image is formed, and then the transfer paper is separated from the photosensitive drum 14 by the separation charger 19 and the separation claw 20. The separated transfer paper is heated and fixed by the transport belt 24 and the fixing roller 25 having a built-in heater, and then the transfer paper is discharged to the paper discharge tray 26.

Further, in the first embodiment, the printed transfer paper is operated by the separation claw 29 so that the paper discharge tray 26 is discharged.
Is not discharged to the feedback rollers 30a, 30
It is configured so that it is conveyed onto the contact glass 1 by b and 30c and can be read by the image reading unit A again.

Next, the operation of the first embodiment having such a configuration will be described below. First, prior to the description of the operation, the γ conversion of the image quality processing unit C according to the present embodiment will be described with reference to FIG. As shown in FIG. 4, when the image is read by the image reading unit A, the exposure sensitivity (reading characteristic) is non-linear, so the output density Ko does not become linear with respect to the input density Do. Similarly, since the printer characteristic of the printer unit D is also non-linear, the density Kp after the γ conversion and the density Dp of the transfer paper are not linear as shown in FIG. Therefore, the γ conversion corrects the density deviation based on this non-linearity. In order to perform this γ conversion, the image quality processing unit C determines a γ parameter determined by the image reading characteristics of the image reading unit A and the printer characteristics of the printer unit D (see FIG. 4).
Read density level from "Ko" to "Kp"
Need to be converted to. Therefore, the γ parameter is as shown in FIG.
As shown in, the read density level “Ko” is made to correspond to addresses 0 to 255 in the γ memory 44, and data “Kp” is stored in advance at each address.

Next, a description will be given of a case where the first embodiment is a normal copy mode in which a document is read by the image reading section A and printed by the printer section D. In this case,
The main control unit E controls the image quality processing unit D so as to perform a normal operation. That is, the image data read by the image reading unit A is subjected to image processing by the image processing unit B,
The data is transferred to the γ memory 44 via the normal mode unit 42a of the γ calculation unit 42. In the γ memory 44, the transferred image data is γ-converted and the γ-converted data is transferred to the printer unit D, so that the printer unit D can perform printing with an appropriate density.

By the way, the reading characteristics of the image reading section A and the printer characteristics (printing characteristics) of the printer section D may change with temperature and deterioration. For example, when it changes like the dotted line in FIG.
In the parameter, the density changes from "Do" to "Dp", and the density shift (Dp-Do) occurs, and the target density cannot be output from the printer unit C. Therefore, the currently set γ parameter is corrected. There is a need to. Therefore,
The case where the first embodiment corrects the γ parameter will be described with reference to FIG. In this case, it is realized by setting the γ conversion correction mode. That is, when this mode is set, the γ conversion correction mode signal is supplied from the main control unit E to the image quality processing unit C, and the main control unit E controls the following units so as to perform γ conversion correction. To control.

First, the image data read by the image reading unit A is subjected to various processes such as amplification, A / D conversion, shading correction, etc. in the image processing unit B, and then sent to the memory 43. In this case, the image read by the image reading unit A is a reference test pattern as shown in FIG.
It has 6 density gradations. The density level is sampled from the predetermined 256 points of the reference test pattern, and the value is stored in the memory 43 as reference image data. For the density level at each point, the average density of each pixel within m × m is used as the reference density level for each gradation. The above-mentioned image data from the image processing unit B is simultaneously sent to the normal mode unit 42 of the γ calculation unit 42.
Since it is γ converted by the γ parameter stored in the γ memory 44 via a and supplied to the printer unit D,
The converted image data is printed out on the transfer paper.

Next, the transfer paper on which the reference test pattern is printed is read again by the image reading section A, and n density levels are sampled in the same manner as described above, and as transfer paper image data, .gamma. It is sent to the calculation comparison unit 42b. The γ calculation comparison unit 42b compares the reference image data (curve in FIG. 7) stored in the memory 43 with the transfer paper image data (curve in FIG. 7). As shown in FIG.
When the transfer paper image data is deviated from the reference image data, the reading characteristic or the printer characteristic is changed, and the target density is not output with the current γ parameter (curve in FIG. 7). Therefore, the γ calculation comparison unit 4
In 2b, as shown in FIG. 7, the concentration deviation Zn is calculated for each of the n concentration levels to determine the correction γ parameter. The concentration deviation Zn is obtained from the curves. With the current γ parameter, a Zn component concentration shift occurs, so the curve in FIG. 7 shifted by Zn from the current γ parameter is calculated as the correction value γ parameter. The determined γ parameter is written in the γ memory 44 and rewritten with the current γ parameter. As a result, the reading characteristics and
It is possible to perform γ conversion corresponding to both changes in printer characteristics. Further, according to such γ conversion correction, it is possible to easily change the γ parameter with a small memory capacity.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, similarly to the first embodiment, the γ conversion correction operation can be performed by setting the γ conversion correction mode, and the operation number counter that counts the operation number of the printer unit D can be performed. When the count value of the operation number counter F reaches a constant value, it is determined that the printer unit D is deteriorated, and the operation number counter F determines γ with respect to the main control unit E.
A signal for requesting conversion correction is output. When this request signal is received, the main control unit E instructs the warning unit G to generate a warning display and a warning sound for performing γ conversion correction (magnification correction). The number of times the printer unit D is operated is the number of transfer sheets output from the printer unit D, but this is an example, and in the case of a page printer, the rotation number of the drum, the operating time, the number of output characters, etc. are counted. You may do it. According to the second embodiment having such a configuration, the γ conversion correction of the image quality processing unit C can be surely performed according to the density deviation due to the deterioration of the printer unit D. If the γ-conversion correction operation is performed for each print, it is possible to always realize highly accurate density reproduction for the original.

Next, a third embodiment of the present invention will be described. In the third embodiment, similarly to the first embodiment, it is possible to perform the γ conversion correction operation by setting the γ conversion correction mode, and at the time of the γ conversion correction mode, the printed transfer paper is printed. However, as shown in FIG. 1, due to the action of the separation claw 29, the paper is not discharged to the paper discharge tray 26 but is conveyed to the reading position on the contact glass 1 by the feedback rollers 30a, 30b, 30c, and again,
The image is read by the image reading section B. After this reading, the transfer paper is ejected to the paper ejection tray 32 outside the copying machine by the conveyor belt 31. According to the third embodiment having such a configuration, in the γ conversion correction mode, it is not necessary to manually transfer the transfer paper discharged to the paper discharge tray 26 to the contact glass 1, and automation can be achieved. It is possible to realize the uniformity of the document position on the contact glass 1.

Next, a fourth embodiment of the present invention will be described. The fourth embodiment is a combination of the above-described second embodiment and third embodiment. That is, in the fourth embodiment, the number of operations of the printer unit D is counted by the operation number counter F, and when the count value reaches a certain value, the operation number counter F is compared with the main control unit E. A request signal for γ conversion correction is sent. Then, the main control unit E issues a warning display of γ conversion correction (magnification correction) to the warning unit G, and at the same time,
Normally, the transfer paper discharged onto the paper discharge tray 26 is controlled to be conveyed onto the contact glass 1, and the γ conversion correction mode is set. As a result, the image quality processing unit C can perform the γ conversion correction without manually carrying the paper on which the reference test pattern is printed on the contact glass 1. According to the fourth embodiment having such a configuration, when the γ conversion correction becomes necessary due to the deterioration of the printer unit D, the automatic correction can be realized.

[0021]

According to the first aspect of the present invention, the reference image data read and stored in the reference test pattern is compared with the image data obtained by re-reading the image printed by γ-converting the image data obtained by reading the reference test pattern. Since the density data at the time of γ conversion is corrected based on this comparison result, the printed image quality becomes appropriate with respect to changes due to temperature and deterioration of reading characteristics and printer characteristics. According to the second aspect of the present invention, the number of times the printing unit is operated is counted, and when the predetermined count value is reached, it is notified that the γ conversion correction is necessary. The deviation can be surely corrected.

According to a third aspect of the present invention, when the γ conversion is corrected,
Since the printed transfer paper is conveyed again to the image reading position, it is not necessary to manually transfer the printed transfer paper discharged to the paper ejection tray to the image reading position, which can be automated and The reading position can be made uniform. According to a fourth aspect of the present invention, the number of times the printing unit is operated is counted, and when the count value reaches a predetermined value, γ conversion correction is performed, and at this time, the printed sheet is conveyed again to the reading position. Since this is done, it becomes possible to automatically correct the density deviation due to deterioration of the printing means.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus to which a γ conversion correction apparatus according to a first embodiment of the present invention is applied.

FIG. 2 is a sectional view of an image reading unit of the image forming apparatus.

FIG. 3 is a block diagram of a data processing system of the image forming apparatus.

FIG. 4 is a diagram for explaining γ conversion in an image quality processing unit.

FIG. 5 is a diagram showing an example of a γ memory.

FIG. 6 is a diagram showing an example of a reference test pattern.

FIG. 7 is a diagram for explaining density deviation and its correction.

FIG. 8 is a block diagram of a second embodiment of the present invention.

[Explanation of symbols]

 A image reading unit B image processing unit C image quality processing unit D printer unit E main control unit F operating count counter G warning unit 42 γ calculation unit 42a normal mode unit 42b γ calculation comparison unit 43 memory 44 γ memory

Claims (4)

[Claims] 1. An image reading unit for reading a reference test pattern and outputting image data corresponding to the reference test pattern, and a density of image data output from the image reading unit to γ conversion into data having a predetermined density. Γ converting means, a printing means for printing the image data γ converted by the γ converting means, a storing means for storing the image data of the reference test pattern read by the image reading means, and a storing means for storing in the storing means. Comparing means for comparing the image data with the image data read by the image reading means again for the print image printed by the printing means; and based on the comparison result of the comparing means, the γ conversion means
And a correction means for correcting predetermined density data to be converted. 2. A counting means for counting the number of times the printing means has been operated, and when the counting means reaches a certain count value,
The γ conversion correction device according to claim 1, further comprising: a warning unit that notifies that the correction of the γ conversion unit is necessary. 3. The .gamma. Conversion correcting apparatus according to claim 1, further comprising a transporting unit that transports the printed sheet again to the reading position of the image reading unit after printing by the printing unit. 4. A counting means for counting the number of times of operation of the printing means, and a carrying means for carrying the printed paper again to the reading position of the image reading means after printing by the printing means, When the count value of the counting means reaches a predetermined value, the γ
2. The .gamma. Conversion correcting apparatus according to claim 1, wherein the conversion unit is corrected, and at this time, the sheet printed by the conveying unit is conveyed again to the reading position of the image reading unit.