JP3912864B2 - Image processing apparatus and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and an image forming apparatus that read a document image using a CCD line sensor and perform range correction processing on image data obtained by the reading.
[0002]
[Prior art]
In recent years, image forming apparatuses such as digital copying machines and facsimiles have begun to spread rapidly. These image forming apparatuses are provided with a scanner, and in order to output a high-quality image, these image forming apparatuses are required to perform various types of image processing on image data input by the scanner.
[0003]
One of the image processes is automatic density adjustment. Currently, image forming apparatuses having this automatic density adjustment function have been announced by various companies. Here, the automatic density adjustment will be briefly described.
[0004]
First, an original image is read by being divided into a plurality of lines by an optical system, and image data in units of lines corresponding to the original image is acquired. That is, the original image is irradiated with the light beam, and the reflected light of the light beam reflecting the image of the original image is input to the CCD line sensor. This CCD line sensor photoelectrically converts an image of a document image reflected on a light beam and outputs it as image data. That is, this CCD line sensor sequentially outputs image data corresponding to the original image in line units.
[0005]
The image data output from the CCD line sensor is subjected to shading correction by a shading correction unit, and shading corrected image data is output. Based on the shading corrected image data output from the shading correction unit, the density histogram of the shading corrected image data is generated by the density histogram generation unit. A correction reference value for correcting the density range is calculated by the correction reference value calculation unit based on the density histogram created by the density histogram creation unit. The density range correction unit that corrects the density range of the image data performs density range correction processing on the shading-corrected image data output from the shading correction unit according to the correction reference value provided from the correction reference value calculation unit. Then, the range-corrected image data, that is, the image data whose density has been adjusted is output. In this way, automatic density adjustment is realized in line units.
[0006]
Currently available image forming apparatuses include those that perform range correction processing at the time of pre-scanning and those that execute range correction processing in real time in parallel with the image forming processing operation.
[0007]
Further, in an image forming apparatus having such an automatic density adjustment function, image data that has been subjected to automatic density adjustment, that is, image data that has undergone range correction processing is stored in a page memory. And it is provided to an external device etc. as needed.
[0008]
[Problems to be solved by the invention]
However, in the line unit range correction process, there is always a limit to the optimum range correction process performed on each line unit image data. Therefore, an inappropriate range correction process may be performed on the image data of a specific line. For example, when a plurality of originals having different background density levels are arranged in the sub-scanning direction and range correction processing is performed on image data obtained from these originals, a portion where the background density is reproduced and a portion where the background density is not reproduced vary. There was such a problem.
[0009]
Further, when the range correction process is executed during the pre-scan, there is a problem that the image reading time increases.
[0010]
Furthermore, when the image data acquired by the image forming apparatus is received by an external apparatus such as a personal computer and processed by the external apparatus, the image data provided from the image forming apparatus is range corrected image data. There was also a problem that the processing of image data was restricted.
[0011]
SUMMARY OF THE INVENTION An object of the present invention is to provide the following image processing apparatus and image forming apparatus in view of the above-described circumstances.
[0012]
(1) An image processing apparatus and an image forming apparatus capable of performing an excellent range correction process without requiring a pre-scan.
[0013]
(2) An image processing apparatus and an image forming apparatus capable of providing image data convenient for image editing by an external apparatus.
[0014]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, an image processing apparatus and an image forming apparatus of the present invention are configured as follows.
[0015]
(1) An image processing apparatus according to the present invention reads a document image by dividing it into a plurality of lines and provides image data in units of lines corresponding to the document image, and the document provided from the reading unit The image data corresponding to the line corresponding to the image is stored, and if necessary, the image data corresponding to the original image corresponding to the line is stored, and the line corresponding to the original image provided from the reading means. A correction reference value calculating means for calculating a correction reference value in line units corresponding to the original image based on the image data in units, and providing a correction reference value in line units corresponding to the original image; The correction reference value for the original image is determined based on the correction reference value in line units corresponding to the original image provided from the reference value calculating means, and the determined correction reference value for the original image is provided. A correction reference value determining unit that performs density adjustment on the image data in line units corresponding to the document image provided from the storage unit based on the correction reference value of the document image provided from the correction reference value determining unit. Range correction means for performing range correction processing and providing density range corrected image data.
[0016]
(2) An image processing apparatus according to the present invention reads a document image by dividing it into a plurality of lines and provides image data in line units corresponding to the document image, and the document provided from the reading unit The image data corresponding to the line corresponding to the image is stored, and if necessary, the image data corresponding to the original image corresponding to the line is stored, and the line corresponding to the original image provided from the reading means. An image discriminating unit for discriminating the type of image data of each line unit based on the unit image data, and providing a discrimination result; and an image in line units corresponding to the original image provided from the reading unit. Correction reference value calculation means for calculating a correction reference value for each line corresponding to the original image based on the data, and providing a correction reference value for each line corresponding to the original image; Based on the discrimination result provided from the image discrimination means and the correction reference value provided from the correction reference value calculation means, a correction reference value for each image type is generated, and the correction reference value for each image type is generated. Based on the determination result provided from the correction reference value generating means and the image determining means, the image type having the highest ratio of the entire original image is specified, and the specified image type is determined as the original type. This is determined as the image type, and the correction reference value for the determined image type is selected from the correction reference values for each image type provided from the correction reference value generating means, and the selected correction reference value Is determined as the correction reference value of the original image, the correction reference value determining means for providing the determined correction reference value of the original image, and the correction reference value of the original image provided from the correction reference value determining means Based performs density range correction process on the image data in line units of the document image equivalent provided from the storage means, and a range correcting means for providing a density range corrected image data.
[0017]
(3) An image processing apparatus according to the present invention reads a document image by dividing it into a plurality of lines and provides image data in units of lines corresponding to the document image, and the document provided from the reading unit The image data corresponding to the line corresponding to the image is stored, and if necessary, the image data corresponding to the original image corresponding to the line is stored, and the line corresponding to the original image provided from the reading means. An image discriminating unit for discriminating the type of image data of each line unit based on the unit image data, and providing a discrimination result; and an image in line units corresponding to the original image provided from the reading unit. Correction reference value calculation means for calculating a correction reference value for each line corresponding to the original image based on the data, and providing a correction reference value for each line corresponding to the original image; Based on the discrimination result provided from the image discrimination means and the correction reference value provided from the correction reference value calculation means, a correction reference value for each image type is generated, and the correction reference value for each image type is generated. The correction reference value generation means for providing the image data, and the image data in line units corresponding to the original image provided from the storage means based on the correction reference value for each type of image provided from the correction reference value generation means. On the other hand, there is provided range correction means for performing density range correction processing for each type of image and providing density range corrected image data.
[0018]
(4) The image forming apparatus of the present invention reads a document image by dividing it into a plurality of lines and provides image data in line units corresponding to the document image, and the document provided from the reading unit The image data corresponding to the line corresponding to the image is stored, and if necessary, the image data corresponding to the original image corresponding to the line is stored, and the line corresponding to the original image provided from the reading means. A correction reference value calculating means for calculating a correction reference value in line units corresponding to the original image based on the image data in units, and providing a correction reference value in line units corresponding to the original image; The correction reference value for the original image is determined based on the correction reference value in line units corresponding to the original image provided from the reference value calculating means, and the determined correction reference value for the original image is provided. A correction reference value determining unit that performs density adjustment on the image data in line units corresponding to the document image provided from the storage unit based on the correction reference value of the document image provided from the correction reference value determining unit. A range correction unit that performs a range correction process and provides density range corrected image data and an image forming unit that forms an image based on the density range corrected image data provided from the range correction unit are provided.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
FIG. 1 is a diagram showing a schematic configuration of a digital copying machine as an image forming apparatus according to an embodiment of the present invention.
[0021]
As shown in FIG. 1, the digital copying machine includes an apparatus main body 10. In the apparatus main body 10, a scanner unit 4 that functions as an image reading unit and a printer unit 6 that functions as an image forming unit are provided.
[0022]
On the upper surface of the apparatus main body 10, a document placing table 12 made of transparent glass on which a reading object, that is, a document D is placed, is provided. An automatic document feeder (hereinafter referred to as “ADF”) 7 that automatically conveys a document onto a document table 12 is disposed on the upper surface of the apparatus body 10. The ADF 7 is disposed so as to be openable and closable with respect to the document placing table 12, and also functions as a document presser that brings the document D placed on the document placing table 12 into close contact with the document placing table 12.
[0023]
The ADF 7 is provided with a document tray 8, an empty sensor 9, a pickup roller 14, a paper feed roller 15, an aligning roller pair 16, a conveyance belt 18, and the like. The document tray 8 receives a document D to be set. The empty sensor 9 detects the presence or absence of a document. The pick-up roller 14 takes out documents one by one from the document tray 8. The paper feed roller 15 conveys the extracted document. The aligning roller pair 16 aligns the leading edge of the document. The conveying belt 18 is disposed so as to cover almost the entire document placing table 12 and conveys the document. A plurality of documents set on the document tray 8 are sequentially taken out from the bottom page, that is, the last page, and aligned by the aligning roller pair 16, and then a predetermined position on the document table 12 by the conveying belt 18. It is conveyed to.
[0024]
A reversing roller 20, a non-reversing sensor 21, a flapper 22, and a paper discharge roller 23 are disposed at the end of the ADF 7 opposite to the aligning roller pair 16. A document D read by a scanner unit 4 to be described later is sent out from the document placing table 12 by a conveyor belt 18 and is passed through a reverse roller 20, a flapper 21, and a sheet discharge roller 22 on a document discharge unit 24 on the upper surface of the ADF 7. To be discharged. When the back side of the document D is read, by switching the flapper 22, the document D transported by the transport belt 18 is reversed by the reverse roller 20, and then again on the document placement table 12 by the transport belt 18. Sent to a predetermined position.
[0025]
The scanner unit 4 disposed in the apparatus main body 10 is configured to deflect an exposure lamp 25 as a light source for illuminating the document D placed on the document table 12 and reflected light from the document D in a predetermined direction. A first mirror 26 is provided. More specifically, the exposure lamp 25 and the first mirror 26 are attached to a first carriage 27 disposed below the document table 12.
[0026]
The first carriage 27 is arranged in parallel to the document table 12. Further, the first carriage 27 is reciprocated below the document table 12 by a drive motor via a toothed belt (not shown).
[0027]
A second carriage 28 that is movable in parallel with the document table 12 is disposed below the document table 12. A second mirror 30 and a third mirror 31 that sequentially deflect the reflected light from the document D deflected by the first mirror 26 are attached to the second carriage 28 at right angles to each other. The second carriage 28 is driven by the toothed belt that drives the first carriage 27 with respect to the first carriage 27 and at the half speed of the original carriage 12 with respect to the first carriage 27. Is moved in parallel.
[0028]
Also, below the document table 12, an imaging lens 32 that focuses the reflected light from the third mirror 31 on the second carriage 28, and the reflected light focused by the imaging lens is received and photoelectrically received. A CCD line sensor 34 for conversion is disposed. The imaging lens 32 is disposed so as to be movable via a drive mechanism in a plane including the optical axis of the light deflected by the third mirror 31, and when it moves, it reflects the reflected light to the CCD line sensor 34. An image is formed at a desired magnification on the light receiving surface. The CCD line sensor 34 photoelectrically converts incident reflected light and outputs an electrical signal (analog signal) corresponding to the read original D. That is, the CCD line sensor 34 sequentially outputs electrical signals corresponding to predetermined lines of the document D. When the document D is read by dividing the document D into n lines, the electrical signal output from the CCD line sensor 34 is an electrical signal for n lines corresponding to the document D.
[0029]
On the other hand, the printer unit 6 includes a laser exposure unit 40. The laser exposure unit 40
A semiconductor laser 41, a polygon mirror 36, a polygon motor 37, and an optical system 42 are provided. The polygon mirror 36 is a scanning member that continuously deflects the laser light emitted from the semiconductor laser 41. The polygon motor 37 rotates the polygon mirror 36 at a predetermined rotation speed. The optical system 42 deflects the laser light from the polygon mirror 36 and guides it to a photosensitive drum 44 described later. The laser exposure unit 40 having such a configuration is fixedly supported by a support frame (not shown) of the apparatus main body 10.
[0030]
The semiconductor laser 41 is controlled to be turned on / off according to the image data of the document D read by the scanner unit 4 or facsimile transmission / reception document information. Laser light output from the semiconductor laser 41 by this on / off control is directed to the photosensitive drum 44 via the polygon mirror 36 and the optical system 42. The laser beam scans the circumferential surface of the photosensitive drum 44, whereby an electrostatic latent image is formed on the circumferential surface of the photosensitive drum 44.
[0031]
The printer unit 6 is provided with a rotatable photosensitive drum 44 as an image carrier disposed almost at the center of the apparatus main body 10. The peripheral surface of the photosensitive drum 44 is exposed by laser light from the laser exposure unit 40 to form a desired electrostatic latent image. Further, around the photosensitive drum 44, a charging charger 45, a developing device 46, a peeling charger 47, a transfer charger 48, a peeling claw 49, a cleaning unit 50, and a static eliminator 51 are arranged in this order. The charging charger 45 charges the drum peripheral surface to a predetermined charge. The developing device 46 supplies toner as a developer to the electrostatic latent image formed on the circumferential surface of the photosensitive drum 44 and develops it with a predetermined image density. The peeling charger 47 separates a transfer material fed from a paper cassette, which will be described later, that is, a copy paper P, from the photosensitive drum 44. The transfer charger 48 transfers the toner image formed on the photosensitive drum 44 onto the paper P. The peeling claw 49 is for peeling the copy paper P from the circumferential surface of the photosensitive drum 44. The cleaning unit 50 cleans the toner remaining on the circumferential surface of the photosensitive drum 44. The static eliminator 51 neutralizes the peripheral surface of the photosensitive drum 44.
[0032]
An upper cassette 52, a middle cassette 53, and a lower cassette 54 that can be pulled out from the apparatus main body are arranged in a stacked state in the lower part of the apparatus main body 10, respectively. Copy papers of different sizes are loaded in each of these cassettes. In addition, a large capacity feeder 55 is provided on the side of these cassettes. The large capacity feeder 55 contains about 3000 sheets of frequently used copy paper P, for example, A4 size copy paper P. It is stored. A paper feed cassette 57 that also serves as a manual feed tray 56 is detachably mounted above the large capacity feeder 55.
[0033]
In the apparatus main body 10, a conveyance path 58 extending from each cassette and the large-capacity feeder 55 through a transfer portion located between the photosensitive drum 44 and the transfer charger 48 is formed. A fixing device 60 is provided at the end of the conveyance path 58. A discharge port 61 is formed in the side wall of the apparatus main body 10 facing the fixing device 60. A discharge tray 62 is attached to the discharge port 61.
[0034]
In the vicinity of the upper cassette 52, the middle cassette 53, the lower cassette 54, the paper feed cassette 57, and the large-capacity feeder 55, there is provided a pickup roller 63 that takes out the paper P one by one from the cassette or the large-capacity feeder. The conveyance path 58 is provided with a plurality of paper feed roller pairs 64 that convey the copy paper P taken out by the pickup roller 63 through the conveyance path 58.
[0035]
A registration roller pair 65 is provided on the upstream side of the photosensitive drum 44 in the conveyance path 58. The registration roller pair 65 corrects the inclination of the taken copy paper P and aligns the front end of the toner image on the photoconductive drum 44 with the front end of the copy paper P so that the moving speed of the peripheral surface of the photoconductive drum 44 The copy paper P is fed to the transfer unit at the same speed. A pre-aligning sensor 66 for detecting the arrival of the copy paper P is provided in front of the registration roller pair 65, that is, on the paper feed roller 64 side.
[0036]
The copy paper P picked up one by one from each cassette or large-capacity feeder 55 by the pickup roller 63 is sent to the registration roller pair 65 by the paper feed roller pair 64. The copy paper P is fed to the transfer section after the leading edge is aligned by the registration roller pair 65.
[0037]
In the transfer portion, the developer image formed on the photosensitive drum 44, that is, the toner image, is transferred onto the paper P by the transfer charger 48. The copy paper P to which the toner image has been transferred is peeled from the peripheral surface of the photosensitive drum 44 by the action of the peeling charger 47 and the peeling claw 49, and is transferred to the fixing device 60 via the conveyance belt 67 constituting a part of the conveyance path 52. Be transported. Then, after the developer image is melted and fixed on the copy paper P by the fixing device 60, the copy paper P is discharged onto the paper discharge tray 62 through the discharge port 61 by the paper feed roller pair 68 and the paper discharge roller pair 69. .
[0038]
Below the conveyance path 58, there is provided an automatic duplex device 70 that reverses the copy paper P that has passed through the fixing device 60 and sends it again to the registration roller pair 65. The automatic duplexer 70 is provided with a temporary stacking unit 71, a reverse path 72, a pickup roller 73, and a paper feed roller 75. The temporary stacking unit 71 stacks the copy paper P temporarily. The reversing path 72 is formed by branching from the conveying path 58, and reverses the copy paper P that has passed through the fixing device 60 and guides it to the temporary stacking unit 71. The pick-up roller pair 65 takes out the copy sheets P collected in the temporary stacking unit 71 one by one. The paper feed roller 75 feeds the paper to the registration roller pair 65 through the conveyance path 74. In addition, a branching gate 76 that selectively distributes the copy paper P to the discharge port 61 or the reversing path 72 is provided at a branch portion between the conveyance path 58 and the reversing path 72.
[0039]
When performing double-sided copying, the copy paper P that has passed through the fixing device 60 is guided to the inversion path 72 by the sorting gate 76 and is temporarily accumulated in the temporary accumulation unit 71 in the inverted state. Then, the sheet is fed to the registration roller pair 65 through the conveyance path 74 by the pickup roller 73 and the paper feed roller pair 75. Further, after the copy paper P is aligned by the registration roller pair 65, the copy paper P is sent again to the transfer unit, and the toner image is transferred to the back surface of the copy paper P. Thereafter, the copy paper P is discharged onto the paper discharge tray 62 via the conveyance path 58, the fixing device 60, and the paper discharge roller 69.
[0040]
The digital copying machine is further provided with an operation panel 80 and a main control unit 90 as shown in FIG.
[0041]
The operation panel 80 is provided with a print key 81, an input unit 82, a panel CPU 83, and a numeric keypad 84. The print key 81 receives an instruction to start copying. The input unit 82 receives various instructions for the digital copying machine, and includes a push button switch and a touch panel 82a (not shown). The touch panel 82a accepts setting of a copying magnification, designation of partial copying, designation of a partial copying area, and setting / changing of an upper limit density threshold value and a lower limit density threshold value which will be described later. The panel CPU 83 controls the entire operation panel 80. The numeric keypad 84 is for setting the number of copies.
[0042]
Next, the control system of the digital copying machine shown in FIG. 1 will be described with reference to FIG.
[0043]
As shown in FIG. 2, the digital copying machine is provided with three CPUs: a main CPU 91 in the main control unit 90, a scanner CPU 100 in the scanner unit 4, and a printer CPU 110 in the printer unit 6.
[0044]
The main CPU 91 performs bidirectional communication with the printer CPU via the shared RAM 95. The main CPU 91 issues an operation instruction, and the printer CPU 110 returns a status status in response thereto. The printer CPU 110 and the scanner CPU 100 perform serial communication. The printer CPU 110 issues an operation instruction, and the scanner CPU 100 returns a status status in response thereto. Incidentally, the operation panel 80 is connected to the main CPU 91.
[0045]
The main control unit 90 includes a main CPU 91, a ROM (read only memory) 92, a RAM (random access memory) 93, an NVM (nonvolatile random access memory) 94, a shared RAM 95, an image processing unit 96, and a multi-value page memory control unit 97. , A multi-value page memory 98, a system I / F 99, and the like are provided.
[0046]
The main CPU 91 controls the entire main control unit 90. The ROM 92 stores a control program. The RAM 93 temporarily stores data. The NVRAM 94 is a non-volatile memory backed up by a battery, and holds data on the NVM 94 when the power is turned off. The shared RAM 95 is used for bidirectional communication between the main CPU 91 and the printer CPU 110.
[0047]
The image processing unit 96 performs various types of image processing on the image data sent from the scanner unit 4, and performs, for example, a range correction process described later. The multi-value page memory control unit 97 stores image data in the multi-value page memory 98 and reads image data stored in the multi-value page memory 98. The multi-value page memory 98 has an area where image data for a plurality of pages can be stored, and stores compressed image data for each page. The system I / F 99 is for connecting an external device (not shown) and the image forming apparatus to each other. For example, the system I / F 99 transmits image data stored in the multi-level page memory 98 to the external device.
[0048]
The scanner unit 4 includes a scanner CPU 100, a ROM 101, a RAM 102, a CCD driver 103, a scan motor driver 104, an A / D conversion circuit 105, a shading correction unit 106, a line memory 107, and the like. The scanner CPU 100 controls the entire scanner unit 4. The ROM 101 stores various control programs and the like. The CCD driver 103 drives the CCD line sensor 34. The scan motor driver 104 controls the rotation of a motor that moves the exposure lamp 25, the mirrors 26, 27, 28, and the like. The A / D conversion circuit 105 converts an analog signal corresponding to a predetermined line of the document D output from the CCD line sensor 34 into a digital signal. That is, the A / D conversion circuit 105 sequentially outputs image data for one line of a document converted into a digital signal. The shading correction unit 106 corrects the fluctuation of the threshold level for the image data for one line of the document output from the CCD line sensor 34 due to the ambient temperature change or the like. The line memory 107 sequentially stores the shading corrected image data for one line of the document output from the shading correction unit.
[0049]
The printer unit 6 includes a printer CPU 110, a ROM 11, a RAM 112, a laser driver 113, a polygon motor driver 114, a paper transport unit 115, a development process unit 116, a fixing control unit 117, an option unit 118, and the like. The printer CPU 110 controls the entire printer unit 6. Various control programs and the like are recorded in the ROM 111. The laser driver 113 turns on / off the light emitted by the semiconductor laser 41. The polygon motor driver 114 controls the rotation of the polygon motor 37 of the laser unit 40. The paper transport unit 115 controls the transport of the paper P through the transport path 58. The development process unit 116 executes a development process of charging, development, and transfer using the charging charger 45, the developing device 46, and the transfer charger 48. The fixing control unit 117 controls the fixing device 60.
[0050]
Further, the image processing unit 96, the multi-value page memory control unit 97, the line memory 107, and the laser driver 113 are connected by an image data bus 120.
[0051]
Here, with reference to FIG. 3, the image processing unit 96 and its periphery for realizing the entire uniform range correction process 1 will be described. This whole surface uniform range correction process No. 1 does not require a pre-scan operation, and performs a range correction process using a predetermined correction reference value for each page of a document image.
[0052]
First, the image processing unit 96 and its periphery will be described with reference to FIG. As shown in FIG. 3, the image processing unit 96 includes a histogram creation unit 201, a reference value calculation unit 202, a reference value determination unit 203, a range correction unit 204, an image quality improvement processing unit 205, an enlargement / reduction processing unit 206, a floor An adjustment processing unit 207, a timing signal generation unit 208, a clock generation unit 209, and the like are provided.
[0053]
First, the multi-value page memory control unit 97, the multi-value page memory 98, and the system I / F 99 will be described. The multi-value page memory control unit 97 is sequentially provided with shading corrected image data for one line of the original stored in the line memory 107. The multi-value page memory control unit 97 sequentially stores the shading corrected image data for one line of the document at a predetermined address of the multi-value page memory 98. As a result, the shading corrected image data for one page of the document is stored in the multi-level page memory. Further, the multi-value page memory control unit 98 calls up the shading-corrected image data for one page of the document from the multi-value page memory 98 and provides it to the range correction unit 204 or the system I / F 99 as necessary.
[0054]
In other words, the image data provided from the system I / F 99 to the outside is image data as acquired by the scanner unit 4, that is, so-called raw image data. Therefore, the image data can be freely edited outside the system that receives the raw image data via the system I / F 99.
[0055]
Further, the multi-value page memory control unit 97 can directly and randomly read image data from the multi-value page memory 98. Thus, it can be used for data processing in the main CPU 91 using image data, automatic adjustment of the scanner unit 4, correction of gamma characteristics, and the like.
[0056]
The page memory control unit 97 has a multi-value page memory for a plurality of pages, and can store and read image data simultaneously in parallel.
[0057]
Further, the page memory control unit 97 directly transfers the shading corrected image data for one line of the document provided from the line memory 107 to the range correction unit 204 without storing it in the multi-level page memory as necessary. provide.
[0058]
In general, image data provided from the outside is input via a system interface from the process after image processing. However, considering the case where it is desired to use image processing, image data provided from the outside is stored in the multi-value page memory 98 via the system I / F 99.
[0059]
Subsequently, a histogram creation unit 201, a reference value calculation unit 202, a reference value determination unit 203, a range correction unit 204, an image quality improvement processing unit 205, an enlargement / reduction processing unit 206, a gradation processing unit 207, a timing signal generation unit 208, The clock generation unit 209 will be described.
[0060]
The histogram creation unit 201 is sequentially provided with shading-corrected image data for one line of the original stored in the line memory 107. The histogram creation unit 201 creates a density histogram of the shading-corrected image data, that is, a density histogram for one line of the document, based on the shading-corrected image data. Further, the histogram creation unit 201 sequentially provides the result of the density histogram for one line of the document to the reference value calculation unit 202.
[0061]
The reference value calculation unit 202 calculates the temporary white reference value R10 and the temporary black reference value R20 for one line of the document in real time based on the result of the density histogram for one line of the document provided from the histogram creation unit 201. . The reference value calculation unit 202 provides the temporary white reference value R10 and the temporary black reference value R20 for one line of the document to the reference value determination unit 203.
[0062]
The reference value determination unit 203 determines the actual white reference value R11 and the black reference value R21 based on the temporary white reference value R10 and the temporary black reference value R20 for one line of the document provided from the reference value calculation unit 202. . Then, the reference value determination unit 203 provides the white reference value R11 and the black reference value R21 to the range correction unit 204.
[0063]
The range correction unit 204 performs range correction processing on the image data based on the white reference value R11 and the black reference value R21 provided from the reference value determination unit 203. The image data to be subjected to the range correction process is the shading corrected image data for one page of the document provided from the multi-value page memory 98 under the control of the multi-value page memory control unit 97. Furthermore, the range correction unit 204 provides the range-corrected image data to the image quality improvement processing unit 205.
[0064]
The image quality improvement processing unit 205 includes a low-pass filter and a high-frequency emphasis circuit (not shown). The image quality improvement processing unit 205 performs image quality improvement processing on the range-corrected image data provided from the range correction unit 204. Further, the image quality improvement processing unit 205 provides the image quality improvement processed image data to the enlargement / reduction processing unit 206.
[0065]
The enlargement / reduction processing unit 206 performs enlargement / reduction processing on the image quality improved image data provided from the image quality improvement processing unit 205 as necessary. Then, the enlargement / reduction processing unit 206 provides the gradation processing unit 207 with the enlarged / reduced image data.
[0066]
The gradation processing unit 207 performs image gradation processing on the enlarged / reduced image data provided from the enlargement / reduction processing unit 206 using a dither method or an error diffusion method. The gradation processing unit 207 provides the gradation processed image data to the printer unit 6.
[0067]
The printer unit 6 executes image forming processing based on the gradation processed image data provided from the gradation processing unit 207.
[0068]
Further, the timing signal generation unit 208 generates a timing signal based on the clock signal from the clock generation unit 209. The clock signal generated from the clock generation unit 209 and the clock signal generated from the timing signal 208 are provided to each block in the image processing unit 96.
[0069]
Next, the entire uniform range correction process 1 executed in the configuration shown in FIG. 3 will be described.
[0070]
Operation mode parameters are set in advance in the multi-value page memory control unit 97, the histogram reference value calculation unit 202, and the reference value determination unit 204. When the copy operation is started, the scanner unit 4 (strictly, the line memory 107) provides shading corrected image data for one line of the original to the multi-value page memory control unit 97 and the histogram creation unit 201. . Accordingly, the shading corrected image data for one line of the original is sequentially stored in the multi-value page memory 98 under the control of the multi-value page memory control unit 97. Further, the multi-value page memory control unit 97 calls the shading-corrected image data for a plurality of lines from the multi-value page memory 98, that is, the shading-corrected image data for one page of the document, as necessary. 204.
[0071]
On the other hand, the histogram creating unit 201 creates a density histogram of the shading-corrected image data, that is, a density histogram for one line of the document, based on the shading-corrected image data for one line of the document. Further, the histogram creation unit 201 sequentially provides the result of the density histogram for one line of the document to the reference value calculation unit 202.
[0072]
The reference value calculation unit 202 calculates the temporary white reference value R10 and the temporary black reference value R20 for one line of the document in real time based on the result of the density histogram for one line of the document provided from the histogram creation unit 201. . The reference value calculation unit 202 provides the temporary white reference value R10 and the temporary black reference value R20 for one line of the document to the reference value determination unit 203.
[0073]
The reference value determination unit 203 sequentially accumulates the temporary white reference value R10 and the temporary black reference value R20 for one document line provided from the reference value calculation unit 202, and stores a plurality of lines for forming the accumulated one page of the document. Based on the temporary white reference value R10 and the temporary black reference value R20, an actual white reference value R11 and a black reference value R21 for one page of the document are determined. Then, the reference value determination unit 203 provides the white reference value R11 and the black reference value R21 to the range correction unit 204.
[0074]
The range correction unit 204 is based on the white reference value R11 and the black reference value R21 provided from the reference value determination unit 203, and the shading corrected image data for one page of the document provided from the multi-value page memory control unit 97. A range correction process is performed on The range correction unit 204 provides range-corrected image data.
[0075]
Thus, range correction processing using uniform correction reference values (R11, R21) can be performed on image data corresponding to one page of the document. Therefore, the problem caused by the conventional range correction process is improved. That is, when a plurality of originals having different background densities are arranged in the sub-scanning direction and range correction processing is performed on image data obtained from these originals, a portion where the background density is reproduced and a portion where the background density is not reproduced are fluctuated. The problem is improved.
[0076]
Next, with reference to FIG. 4, the image processing unit 96 and its periphery for realizing the whole surface uniform range correction processing part 2 will be described. This whole surface uniform range correction processing No. 2 does not require a pre-scan operation, and automatically switches between reproducing the background density and not reproducing according to the type of the document, and is predetermined for each page of the document image. The range correction process is performed based on the correction reference value.
[0077]
The image processing unit 96 includes a histogram creation unit 201, a reference value calculation unit 202, a reference value determination unit 203, a range correction unit 204, an image quality improvement processing unit 205, an enlargement / reduction processing unit 206, a gradation processing unit 207, a timing signal. A generation unit 208, a clock generation unit 209, and the like are provided. The reference value determination unit 203 includes a character image processing unit 211, a photographic image processing unit 212, a temporary reference value holding unit 213, a temporary reference value holding unit 214, a reference value determination unit 215, and the like.
[0078]
First, the multi-value page memory control unit 97, the multi-value page memory 98, and the system I / F 99 will be described. The multi-value page memory control unit 97 is sequentially provided with shading corrected image data for one line of the original stored in the line memory 107. The multi-value page memory control unit 97 sequentially stores the shading corrected image data for one line of the document at a predetermined address of the multi-value page memory 98. As a result, the shading corrected image data for one page of the document is stored in the multi-level page memory. Further, the multi-value page memory control unit 98 calls up the shading-corrected image data for one page of the document from the multi-value page memory 98 and provides it to the range correction unit 204 or the system I / F 99 as necessary.
[0079]
In other words, the image data provided from the system I / F 99 to the outside is image data as acquired by the scanner unit 4, that is, so-called raw image data. Therefore, the image data can be freely edited outside the system that receives the raw image data via the system I / F 99.
[0080]
Subsequently, a histogram creation unit 201, a reference value calculation unit 202, a reference value determination unit 203, a range correction unit 204, an image quality improvement processing unit 205, an enlargement / reduction processing unit 206, a gradation processing unit 207, a character image processing unit 211, The photographic image processing unit 212, the first data holding unit 212, the second data holding unit 213, the reference value determination unit 215, the timing signal generation unit 208, and the clock generation unit 209 will be described.
[0081]
The histogram creation unit 201 is sequentially provided with shading-corrected image data for one line of the original stored in the line memory 107. The histogram creation unit 201 creates a density histogram of the shading-corrected image data, that is, a density histogram for one line of the document, based on the shading-corrected image data. Further, the histogram creation unit 201 sequentially provides the result of the density histogram for one line of the document to the reference value calculation unit 202.
[0082]
The reference value calculation unit 202 calculates the temporary white reference value R10 and the temporary black reference value R20 for one line of the document in real time based on the result of the density histogram for one line of the document provided from the histogram creation unit 201. . Then, the reference value calculation unit 202 provides the temporary white reference value R10 and the temporary black reference value R20 for one line of the document to the character image processing unit 211 and the photographic image processing unit 212. The reference value calculation unit 202 performs image discrimination processing for one document line based on the density histogram result for one document line provided from the histogram creation unit 201. Then, the reference value calculation unit 202 provides the determination processing result R30 of the image determination processing for one document line to the character image processing unit 211, the photographic image processing unit 212, and the reference value determination unit 215. The image discrimination process will be described in detail later.
[0083]
The character image processing unit 211 provides the temporary reference value holding unit 213 with the provisional white reference value R10 and the provisional black reference value R20 of the character image area provided from the reference value calculation unit 202. The temporary reference value holding unit 213 compares the temporary white reference value R10 (background portion) with a smaller value than the temporary white reference value R10 and the temporary black reference value R20 in the character image area of the previous line, and the temporary black reference value R20. (Character part) updates a large value. That is, the temporary reference value holding unit 213 provides the updated temporary white reference value R10 and temporary black reference value R20 of the character image region to the reference value determination unit 215.
[0084]
The photographic image processing unit 212 provides the temporary white reference value R10 and the temporary black reference value R20 of the photographic image region provided from the reference value calculation unit 202 to the temporary reference value holding unit 214. Similarly, the temporary reference value holding unit 214 compares the temporary white reference value R10 (background portion) with a smaller value than the temporary white reference value R10 and the temporary black reference value R20 in the photographic image area of the previous line. The reference value R20 (character part) is updated to a large value. That is, the temporary reference value holding unit 213 provides the updated temporary white reference value R10 and temporary black reference value R20 of the photographic image area to the reference value determination unit 215.
[0085]
The reference value determination unit 215 counts the number of lines of the character image and the number of lines of the photographic image per page of the document. The reference value determination unit 215 determines that the document is a character image when the number of lines of the character image per page of the document is larger than the number of lines of the photographic image. Conversely, if the number of lines of a photographic image per page of the document is greater than the number of lines of a character image, the document is determined as a photographic image. When it is determined that the document is a character image, the temporary white reference value R10 and the temporary black reference value R20 provided from the temporary reference value holding unit 213 are used as actual reference values. Conversely, when the document is determined to be a photographic image, the temporary white reference value R10 and the temporary black reference value R20 provided from the temporary reference value holding unit 214 are used as the actual reference values.
[0086]
The range correction unit 204 performs range correction processing on the image data based on the white reference value R11 and the black reference value R21 provided from the reference value determination unit 203. The image data to be subjected to the range correction process is the shading corrected image data for one page of the document provided from the multi-value page memory 98 under the control of the multi-value page memory control unit 97. Furthermore, the range correction unit 204 provides the range-corrected image data to the image quality improvement processing unit 205.
[0087]
The image quality improvement processing unit 205 includes a low-pass filter and a high-frequency emphasis circuit (not shown). The image quality improvement processing unit 205 performs image quality improvement processing on the range-corrected image data provided from the range correction unit 204. Further, the image quality improvement processing unit 205 provides the image quality improvement processed image data to the enlargement / reduction processing unit 206.
[0088]
The enlargement / reduction processing unit 206 performs enlargement / reduction processing on the image quality improved image data provided from the image quality improvement processing unit 205 as necessary. Then, the enlargement / reduction processing unit 206 provides the gradation processing unit 207 with the enlarged / reduced image data.
[0089]
The gradation processing unit 207 performs image gradation processing on the enlarged / reduced image data provided from the enlargement / reduction processing unit 206 using a dither method or an error diffusion method. The gradation processing unit 207 provides the gradation processed image data to the printer unit 6.
[0090]
The printer unit 6 executes image forming processing based on the gradation processed image data provided from the gradation processing unit 207.
[0091]
Further, the timing signal generation unit 208 generates a timing signal based on the clock signal from the clock generation unit 209. The clock signal generated from the clock generation unit 209 and the clock signal generated from the timing signal 208 are provided to each block in the image processing unit 96.
[0092]
Next, the whole surface uniform range correction process No. 2 will be described with reference to the flowchart of FIG.
[0093]
Operation mode parameters are set in advance in the multi-value page memory control unit 97, the histogram reference value calculation unit 202, and the reference value determination unit 204 (ST10). When the copy operation is started (ST12), the scanner unit 4 (strictly, the line memory 107) sends the shading corrected image data for one line of the original to the multi-value page memory control unit 97 and the histogram creation unit 201. Is provided (ST14). Accordingly, under the control of the multi-value page memory control unit 97, shading corrected image data for one line of the original is sequentially stored in the multi-value page memory 98 (ST16). Further, the multi-value page memory control unit 97 calls the shading-corrected image data for a plurality of lines, that is, the shading-corrected image data for one page of the original from the multi-value page memory 98 as necessary (ST18). This is provided to the range correction unit 204.
[0094]
On the other hand, the histogram creating unit 201 creates a density histogram of the shading-corrected image data, that is, a density histogram for one line of the document, based on the shading-corrected image data for one line of the document. Further, the histogram creation unit 201 sequentially provides the result of the density histogram for one line of the document to the reference value calculation unit 202.
[0095]
The reference value calculation unit 202 calculates a temporary white reference value and a temporary black reference value for one document line in real time based on the density histogram result for one document line provided from the histogram creation unit 201 (ST20). ). Then, the reference value calculation unit 202 provides the temporary white reference value and the temporary black reference value for one line of the document to the character image processing unit 211 and the photographic image processing unit 212. The reference value calculation unit 202 performs image discrimination processing for one document line based on the density histogram result for one document line provided from the histogram creation unit 201 (ST20). Then, the reference value calculation unit 202 provides the result of the image discrimination processing for one line of the document to the character image processing unit 211, the photographic image processing unit 212, and the reference value determination unit 215.
[0096]
The reference value determining unit 203 holds the temporary white reference value and the temporary black reference value of each of the character image area and the photographic image area, and counts the number of character lines and the number of photographic lines in one page of the document (ST22). Further, this document is determined to be a character document or a photo document according to the ratio of the number of character lines and the number of photo lines in one page of the document. Then, according to the determination result, the temporary white reference value and the temporary black reference value of the character image area, or the temporary white reference value and the temporary black reference value of the photographic image area are selected, and the selected reference value is the actual white reference value. The reference value and the black reference value are set (ST24).
[0097]
Then, the range correction process is executed with the set white reference value and black reference value (ST26). Thereafter, the next-stage image processing is performed (ST28), and the printing processing is performed (ST30).
[0098]
This makes it possible to automatically switch between when the background density is reproduced and when it is not reproduced at the ratio of the document discrimination result, and to perform range correction using a uniform reference value that improves the reproducibility of the document. When a plurality of originals with different background density levels are arranged in the sub-scanning direction and range correction processing is performed on image data obtained from these originals, a portion where the background density is reproduced and a portion where the background density is not reproduced The problem of fluctuations is improved.
[0099]
The outline of the image reproduced by the entire surface uniform range correction process described above is shown in FIGS. FIG. 6 is a diagram illustrating a state in which the entire surface uniform range correction process is performed on a document image in which the ratio of the photographic image is higher than that of the character image. In such a case, the document image is determined as a photographic image. Then, a whole surface uniform range correction process is performed as a photographic image.
[0100]
FIG. 7 is a diagram illustrating a state in which the entire surface uniform range correction process is performed on a document image in which a character image occupies a higher ratio than a photographic image. In such a case, the document image is determined as a character image. Then, the entire surface uniform range correction process is performed as a character image.
[0101]
Next, image type range correction processing will be described with reference to the flowchart shown in FIG. In this range correction processing for each image type, a character image area and a photographic image area in one page of a document are discriminated, a range correction process appropriate for the character image area is performed on the character image area, and a photographic image area is applied to the photographic image area. A range correction process suitable for the above is performed. This range correction process for each image type is realized by the configuration shown in FIG.
[0102]
First, operation mode parameters are set in advance in the multi-value page memory control unit 97, the histogram reference value calculation unit 202, and the reference value determination unit 204 (ST40). When the copy operation is started (ST42), the scanner unit 4 (strictly, the line memory 107) sends the shading corrected image data for one line of the document to the multi-value page memory control unit 97 and the histogram creation unit 201. Is provided (ST44). Accordingly, the shading corrected image data for one line of the original is sequentially stored in the multi-value page memory 98 under the control of the multi-value page memory control unit 97 (ST46). Further, the multi-value page memory control unit 97 calls the shading-corrected image data for a plurality of lines from the multi-value page memory 98, that is, the shading-corrected image data for one page of the document as needed (ST48). This is provided to the range correction unit 204.
[0103]
On the other hand, the histogram creating unit 201 creates a density histogram of the shading-corrected image data, that is, a density histogram for one line of the document, based on the shading-corrected image data for one line of the document. Further, the histogram creation unit 201 sequentially provides the result of the density histogram for one line of the document to the reference value calculation unit 202.
[0104]
The reference value calculation unit 202 calculates the temporary white reference value and the temporary black reference value for one document line in real time based on the density histogram result for one document line provided from the histogram creation unit 201 (ST50). ). Then, the reference value calculation unit 202 provides the temporary white reference value and the temporary black reference value for one line of the document to the character image processing unit 211 and the photographic image processing unit 212. The reference value calculation unit 202 performs image discrimination processing for one document line based on the density histogram result for one document line provided from the histogram creation unit 201 (ST50). Then, the reference value calculation unit 202 provides the result of the image discrimination processing for one line of the document to the character image processing unit 211, the photographic image processing unit 212, and the reference value determination unit 215.
[0105]
The reference value determining unit 203 holds the temporary white reference value and the temporary black reference value of the character image region and the photographic image region, respectively (ST52). Then, the temporary white reference value and the temporary black reference value of the character image area are selected as the character image area, and the temporary white reference value and the temporary black reference value of the photograph image area are selected as the photographic image area. The actual white reference value and black reference value are set (ST54).
[0106]
Then, a range correction process is executed with the white reference value and the black reference value set for each of the character image area and the photographic image area (ST56). Thereafter, the next stage image processing is performed (ST58), and the printing processing is performed (ST60).
[0107]
As a result, the character image area included in one page of the original image is subjected to a range correction process suitable for the character image area, and the photographic image area is subjected to a range correction process suitable for the photographic image area.
[0108]
9 and 10 schematically show images reproduced by the image type-specific range correction process described above. FIG. 9 is a diagram illustrating a state in which a range correction process for each image type is performed on a document image in which the proportion of a photographic image is higher than that of a character image. Even in such a case, the entire document is not determined as a photographic image, the photographic image area is subjected to a range correction process suitable for the photographic image area, and the character image area is subjected to a range correction process suitable for the character image area. .
[0109]
FIG. 10 is a diagram illustrating a state in which a range correction process for each image type is performed on a document image in which a character image occupies a higher ratio than a photographic image. Even in such a case, the entire original is not determined as a character image, the photographic image area is subjected to a range correction process suitable for the photographic image area, and the character image area is subjected to a range correction process suitable for the character image area. .
[0110]
According to the present invention, image data after being input / output to / from the image memory by the multi-value page memory control unit having the external system interface and the CPU interface is processed by the scanner unit that reads the image in dot units using the line sensor. By performing the range correction process, the optimal density reproduction can be realized without pre-scanning and without imposing a burden on the CPU, without any erroneous image identification and character collapse due to the automatic density adjustment process. .
[0111]
As a result, even if originals such as newspapers or thinly written characters are copied side by side, the original and the background that you want to reproduce with the background density remaining are deleted according to the ratio of the original discrimination result of the histogram reference value calculation section of the original. It is possible to automatically discriminate the original to be made and to realize optimum density reproduction.
[0112]
In addition, because of the use of a multi-value page memory, printer products with a multi-value engine can perform the same image processing in both the normal copy mode and the electronic sort mode using the page memory. It becomes possible to do.
[0113]
In addition, since the multi-level page memory control unit can output raw multi-level image data from a scanner unit that does not perform image processing according to the characteristics of the image product using an external system interface, It is also possible to respond to requests for free image data editing by applications.
[0114]
Furthermore, since the multi-level page memory can be used, application to scanner automatic adjustment, separate image processing (image area identification processing, etc.) and the like is also possible.
[0115]
Next, an outline of the image discrimination process will be described with reference to FIGS. The image discrimination process described below is performed by the main CPU 91.
[0116]
First, a method of determining character character will be described with reference to the density histogram of FIG.
[0117]
The character-likeness is determined by determining the background peak P11 [i], the division numbers P11 [i-1] and P11 [i + 1] before and after the background peak P11, the character peak P12 [i], and the character peak P12. The division number P12 [i−1] and P12 [i + 1] is calculated based on the ratio of the total number.
[0118]
For character distinction, a character frequency discrimination threshold (cth) is provided as a character like condition register. When the above sum is equal to or greater than the character frequency discrimination threshold, it is determined that the document is a character image. It is assumed that the character frequency determination threshold is stored in advance in the ROM 92 or the like.
[0119]
In other words, the character quality is determined as follows.
[0120]
WA1 = P11 [i-1] + P11 [i] + P11 [i + 1]
WA1 = P12 [i-1] + P12 [i] + P12 [i + 1]
WA = WA1 + WA2
If WA ≧ cth, the document is determined to be a character-like document. In other cases, it is determined that the document does not look like text.
[0121]
When it is determined that the document is a character-like document, an intermediate density determination threshold value (pth) is then provided as a processing register for the intermediate density range A, and this intermediate density determination threshold value is compared with the histogram value of the intermediate density range A. The character document and the character / photo document are discriminated. The intermediate density range A is a range between a division number P11 [i + 3] that is three divisions larger than the base peak P11 and a division number P12 [i-3] that is three divisions smaller than the character peak P12. When all the histogram values in the intermediate density range A are smaller than the intermediate density determination threshold value (all histograms in the intermediate density range A <pth), it is determined as a character document. In other cases, it is determined as a text / photo original.
[0122]
Next, a method for determining the photographic quality will be described with reference to the density histogram of FIG.
[0123]
For discrimination of photographic quality, a white width discrimination coefficient is provided as a condition register, and the histogram value of the photo original discrimination range B divided into three before and after the background peak P21 is a photo original discrimination threshold Z (Z = background peak value P1 × white width discrimination). If the coefficient is greater than (16), it is determined that the document is a photograph. In other cases, it is determined that the document does not look like a photo. It is assumed that the white width discrimination coefficient is stored in advance in the RAM 93 or the like.
[0124]
A document that cannot be discriminated by the above-described image discrimination, that is, a manuscript that does not correspond to either a character image or a photographic image is discriminated as a character / photo image as shown in FIG.
[0125]
Next, the density histogram creation unit 201 will be described.
[0126]
14 and 15 show an outline of the density histogram created by the density histogram creation unit 205. FIG. For example, when a single image of A4 (210 × 297 [mm]) is read, if it is read at 400 [dpi], the total number of pixels G is as follows.
[0127]
G = 210 × 297 × (400 / 25.4) ² (1) Each pixel having the number G of pixels has a density, and here, the density is expressed by 8 bits. The horizontal axis in FIG. 14 indicates density, and the vertical axis indicates frequency (number of pixels). In this embodiment, the lower density level and the highest density level that are the target of the density level are equally divided into 256 levels (00h to FFh), and the lowest density level is set to a density level of 00h. This highest density level is set as the density level of FFh. FIG. 14 shows the relationship between density and frequency by simplifying the density in 256 levels to 16 levels. By adopting 16 divisions in this way, the hardware is greatly simplified. In addition, the amount of information necessary as a histogram even in 16 divisions is sufficiently secured in the automatic density adjustment function. FIG. 15 shows an equal 16-division method, where division number 0 is a pixel value range from 00h to 0Fh, division number 1 is a pixel value range from 10h to 1Fh, and so on.
[0128]
Before describing the histogram creation unit 205 in detail, the range correction of the correction reference value calculation unit 206 and the range correction unit 207 will be described. Range correction is a function used for background cutting or the like as a background portion in an automatic exposure function in an analog copying machine.
[0129]
Generally, when a document is read digitally and a density histogram is created, the result is as shown in FIG. In the case of a manuscript such as a newspaper, the background density is considerable, so that one peak is formed in the background density portion as indicated by M in FIG. Here, in the analog copying machine, the brightness of the exposure lamp is controlled to eliminate the background density portion, but in the digital copying machine, the same effect is obtained by the following signal processing.
[0130]
To explain with a simple example, density DW and DB corresponding to the peak points of M peak and N peak shown in FIG. 16 are obtained, and the density histogram is distributed as shown in FIG. 17 by performing the following calculation. Convert. The densities DB and DB are called correction reference values, in particular the density DB is called a white reference value, and the density DB is called a black reference value. The densities DW and DB are calculated by the correction reference value calculation unit 206 based on the histogram of each scanning line created by the histogram creation unit 205.
[0131]
DN = (DI−DW) × FFh / (DB−DW) (2)
Here, DI is the input pixel density, DN is the corrected pixel density, and FFh is the maximum pixel density. That is, the range (density width) between M and N in FIG. 16 is expanded to the range of 00h to FFh.
[0132]
Next, the histogram creation method will be outlined. The following formula is a basic calculation formula for creating a histogram, and the histogram is created for each main scanning line. Each time one line of histogram creation processing is completed, a reference value for range correction is obtained, and the range correction processing is performed based on the reference value. The total number of data constituting the histogram is always a constant value.
[0133]
A ′ = A−αA + αB (3)
A ′: corrected frequency (number of pixels) corresponding to each density of the current line
A: Frequency corresponding to each concentration calculated up to the previous line
B: Frequency corresponding to each concentration of the current line
α: Weight coefficient
The weighting factor α is a value multiplied by the frequency value accumulated in each line, and indicates a contribution rate to the histogram. As shown in FIG. 18, the value of α is set corresponding to the number of lines, and 14 values (1, 1/2, 1/4, 1/8, 1/16, 1/32,..., 1 / 2048, 1/4096, 1/8192).
[0134]
Next, the histogram creation unit 205 will be described. The histogram creation unit 205 first calculates A ′ = (A ′) + αB for each input pixel during one line reading, and secondly, the pixel density is input from one line reading to the next line reading. If not, calculate (A ′) = A−αA for the frequency of each density in the histogram. In this way, the histogram creation unit 205 generates a corrected frequency value A ′ = A−αA + αB for the current line. A correction reference value calculation unit 206 calculates a reference value for range correction from the histogram created in this way.
[0135]
Also, two modes, mode 0 and mode 1, are provided for histogram creation, and one mode is selected as necessary.
[0136]
Mode 0: Weighting coefficient fluctuation addition mode depending on the number of sub-scanning lines
Mode 1: Weighting factor constant addition mode for input pixels
In mode 0, as described above, the coefficient α is changed in accordance with the count number of the main scanning line, and a histogram is created. Mode 1 creates a histogram with a constant coefficient regardless of the count value of the main scanning line.
[0137]
FIG. 19 is a block diagram showing a detailed configuration of the histogram creation unit 205. Pixel density signals IDAT4 to IDAT7 from the scanner unit 4 are input to one terminal of the switch 141, and output data signals CDT00 to CDT03 from the counter 142 are input to the other terminal. The switch 141 selects one of the input signals according to a selection signal from a timing signal generator (not shown), and outputs the selected signals SLDT0 to SLDT3 to the selector 145 and a clock generator (not shown). Here, the pixel density signals IDAT4 to IDAT7 are the upper 4 bits of the pixel density, and IDAT0 to 3 are ignored. The timing signal CTL0 from the timing signal generator becomes high during each line, that is, when the pixel density signal is not read, and the switch 141 selects and outputs the signal from the counter 142.
[0138]
The counter 142 supplies a necessary value (count value) to the clock generation unit and the selector 145 when calculating “(A ′) = A−αA”. When the pixel density signal is not read, the counter 142 generates a 4-bit count value for selecting and generating the outputs of the clock generator in order. The counter 142 receives the counter clock signal CT1CK from the timing signal generator and is cleared by the counter clear signal CT1CL from the timing signal generator. The counter clear signal CT1CL becomes low level when the pixel density signal is read, and the counter 142 is cleared.
[0139]
The clock generator selects and outputs one of the 16 outputs FCK0 to FCK in the cycle of the input clock signal MCK according to the selection input signals SLDT0 to SLDT3. FIG. 20 shows the relationship between the input and output signals of the clock generator.
[0140]
Histogram register (flip-flop) 144 ₁ ~ 144 _F Latches and outputs the corrected frequency (WDAT) for each pixel density when the input clock signals FCK0 to FCKF rise. The input signal WDAT is “A′−αA” or “(A ′) + αB” described above. Histogram register 144 ₁ ~ 144 _F The corrected frequency signals H0 to HF are also output to the correction reference value calculation unit 206.
[0141]
The selector 145 is a histogram register 144 ₁ ~ 144 _F The frequency (number of pixels) corresponding to each of the 16 levels of density H0 to HF is input, and according to the input signals SLDT0 to SLDT3 from the switch 141, of the 16 data of H0 to HF (each bus width is 26 bits) One data is selected and a signal HSDT is output.
[0142]
As shown in the timing chart of FIG. 26, the sub-scanning line number counter 153 receives the line synchronization signal HDEN from the timing signal generator. Accordingly, count value signals FDAT00 to FDAT12 are output from the sub-scanning line number counter 153 to the clock generator 152. The sub-scanning line number counter 153 is cleared every time one page of the document is scanned by the clear signal CRST from the main CPU 91.
[0143]
The clock generation unit 152 receives the output signals FDAT0 to FDAT12 from the sub-scanning line number counter 153 and the pixel synchronization clock signal GCK from the scanner unit 4. Accordingly, the signal HCK is output from the clock generation unit 152 to the counter 151 and the addition value generation unit 150. The clock generator 152 outputs one clock of the input pixel synchronization clock signal when the value of the signal FDAT is any one of 1, 3, 7, F, 1F, 3F, 7F, 1FF, 3FF, 7FF, FFF, and 1FFF. To do. The clock generator 152 is composed of an AND circuit, and when all the line number signals FDAT are “1”, that is, when FDAT = 1, 3 (11), 7 (111), F (1111),. Is output.
[0144]
The counter 151 receives the clock signal HCK from the clock generator 152. Accordingly, the counter 151 outputs count value signals CDT20 to CDT23 to the selector 147 in the mode 0. The counter 151 is also cleared for each page by a clear signal CRST from the main CPU 91. The count values CDT20 to CDT23 are values for selecting α as shown in FIG.
[0145]
The fixed coefficient value register 155 outputs a fixed coefficient value in mode 1. The switch 156 is switched according to the mode signal SL1 from the CPU 91, and is set on the counter 151 side in the mode 0, and is set on the register 155 side in the mode 1.
[0146]
The subtraction value generation unit 146 outputs “αA” when calculating “(A ′) = A−αA”. The subtraction value generator 146 receives the output signal HSDT from the selector 145 and generates a value obtained by dividing the signal HSDT by a power of 2 (shifts the signal HSDT).
[0147]
The selector 147 determines “αA” of the operation “(A ′) = A−αA” performed between the lines, that is, when the pixel signal is not read, according to the input signals SSL0 to SSL3. That is, when the value of the input signals SSL0 to SSL3 is “1”, the selector 147 is (signal HSDT value) / 2, and when the input value is “2”, (signal HSDT value) / 22,. When the input value is C, (value of signal HSDT) / 213 is output.
[0148]
The subtraction unit 149 performs subtraction “(A ′) = A−αA”. The subtraction unit 149 receives the density signal HSDT (A in the above equation) from the selector 145, receives the subtraction number signal SDT (αA in the above equation) from the selector 147, and outputs the signal YDAT as the subtraction result. .
[0149]
The addition value generation unit (shift register) 150 generates “αB” when calculating “A ′ = (A ′) + αB”. The addition value generation unit 150 receives the clock signal HCK from the clock generation unit 152 and outputs the signal XDAT to the addition unit 148. The addition value generation unit 150 is also cleared for each page by a clear signal CRST from the main CPU 91. FIG. 21 shows an output example of the addition value generation unit 150. When the clear signal CRST is input, the initial value output is 2000H, and after that, every time the clock signal HCK from the clock generation unit 152 is input, 1/2 of the current value is obtained. Output. Since this output is a hexadecimal number, for example, 1/2 of the current value 2000H is 1000H, and 1/2 of the current value 1000H is 800H. FIG. 22 shows changes in each signal corresponding to changes in the signal FDAT.
[0150]
The adding unit 148 performs addition A ′ = (A ′) + αB. The frequency signal HSDT from the selector 145 and the addition data signal XDAT from the addition value generation unit 150 are input to the addition unit 148, and a signal ZDAT is output as a result of the addition. FIG. 23 shows an addition example of the signal ZDAT.
[0151]
The switch 154 switches operations between (A ′) = A−αA and A ′ = (A ′) + αB. The addition result signal ZDAT from the addition unit 148 is input to one terminal of the switch 154, and the subtraction result signal YDAT from the subtraction unit 149 is input to the other terminal, and one input is input according to the selection signal CTL1. The selection result signal WDAT is selected from the histogram register 144. ₁ ~ 144 _F Is output.
[0152]
Next, the creation of a histogram with the configuration shown in FIG. 19 will be described with reference to the timing charts of FIGS. 24, 25, and 26.
[0153]
FIG. 24 is a timing chart showing a state when “A ′ = (A ′) + αB” is calculated for each input pixel during one line reading. The signal MCK is a main clock and is synchronized with the pixel signal. The signal VDEN is a page synchronization signal. The signal HDEN is a line synchronization signal. Pixel density signals IDAT4 to IDAT7 from the scanner unit 4 are the upper 4 bits of the pixel density and are input to the switch 141. In this case, the sub-scan valid signal CTL0 is enabled (low level), and the switch 141 sends the inputs IDAT4 to IDAT7 to the selector 145 and the clock generator 143.
[0154]
The selector 145 selects the histogram signals 144 according to the pixel signals IDAT4 to IDAT7, that is, the value of the selected input signal. ₁ ~ 144 _F Output (frequency) is selected and the selected frequency signal HSDT is output. The signal HSDT is added with a coefficient (XDAT) weighted according to the number of lines by the adder 148. In this case, since the switch 154 is set on the adder 148 side by the input signal CTL1, the addition result signal ZDAT is stored in the histogram register 144. ₁ ~ 144 _F Return to.
[0155]
Next, the clock generation unit 143 outputs clock signals FCK0 to FCKF according to the pixel signals IDAT4 to IDAT7. Each histogram register 144 ₁ ~ 144 _F Is latched, that is, stores the value of the output signal WDAT of the switch 154 at the rising edge of each of the clock signals FCK0 to FCKF. By performing the above processing for each pixel in one line, a histogram for one line is generated, a reference value for pixel density adjustment is calculated, and the reference value is used for processing in the next line.
[0156]
Next, during one line reading to the next line reading, that is, when no pixel density signal is input, “(A ′) = A−αA” is calculated for the frequency of each density in the histogram.
[0157]
FIG. 25 is a timing chart showing the state of the subtraction process. The switch 141 is switched to the counter 142 side by the selection signal CTL0, and the switch 154 is switched to the subtractor 149 side by the selection signal CTL1. The selector 147 subtracts each histogram value by a coefficient (in mode 0) or a fixed coefficient (in mode 1) determined by the number of sub-scanning counters. After this subtraction operation is completed, the operation moves to a normal histogram creation operation. By repeating the operation described above, a histogram with a variable total data amount is created each time each main scanning line is read.
[0158]
As described above, a histogram can be obtained for each main scanning line, and automatic density adjustment in real time using the histogram can be performed. Further, by multiplying the frequency by a weighting factor that changes according to the number of read lines and accumulating the frequency, a histogram with a variable total data amount is created each time each main scanning line is read. Further, when the weighting coefficient is fixed, a histogram corresponding to a sudden density change of the document image can be obtained.
[0159]
【The invention's effect】
According to the present invention, the following image processing apparatus and image forming apparatus can be provided.
[0160]
(1) An image processing apparatus and an image forming apparatus capable of performing an excellent range correction process without requiring a pre-scan.
[0161]
(2) An image processing apparatus and an image forming apparatus capable of providing image data convenient for image editing by an external apparatus.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a digital copying machine as an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram for explaining a control system of the digital copying machine.
FIG. 3 is a diagram illustrating an internal configuration of an image processing unit and a peripheral configuration of the image processing unit for realizing the entire uniform range correction process 1;
FIG. 4 is a diagram illustrating an internal configuration of an image processing unit and a peripheral configuration of the image processing unit for realizing a whole surface uniform range correction process No. 2;
FIG. 5 is a flowchart for explaining a whole surface uniform range correction process;
FIG. 6 is a diagram illustrating a state in which an entire uniform range correction process is performed on a document image in which a photographic image is higher than a character image.
FIG. 7 is a diagram illustrating a state in which a uniform image range correction process is performed on a document image in which a character image occupies a higher proportion than a photographic image.
FIG. 8 is a flowchart for explaining image type range correction processing;
FIG. 9 is a diagram illustrating a state in which a range correction process for each image type is performed on a document image in which a proportion of a photographic image is higher than that of a character image.
FIG. 10 is a diagram illustrating a state in which range correction processing for each image type is performed on a document image in which a character image occupies a higher proportion than a photographic image.
FIG. 11 is a diagram illustrating an example of a density histogram of an original mainly composed of character images.
FIG. 12 is a diagram showing an example of a density histogram of a document mainly composed of photographic images.
FIG. 13 is a diagram illustrating an example of a density histogram of a document including a character image and a photographic image.
FIG. 14 is a diagram illustrating an example of a density histogram created by a histogram creation unit based on image data read by a scanner.
FIG. 15 is a diagram for explaining a density histogram;
FIG. 16 is a diagram for explaining a correction reference value calculated by a correction reference value calculation unit and a range correction process in the range correction unit;
FIG. 17 is a diagram for explaining a correction reference value calculated by a correction reference value calculation unit and a range correction process in the range correction unit;
FIG. 18 is a diagram for explaining the number of sub-scanning lines in mode 0 and the coefficient α corresponding to the number of lines.
FIG. 19 is a diagram illustrating a schematic configuration of a histogram creation unit.
FIG. 20 is a diagram for explaining timing of an output clock signal corresponding to an input pixel density in a clock generation unit of a histogram creation unit.
FIG. 21 is a diagram illustrating an example of an output in an addition value generation unit of a histogram creation unit.
FIG. 22 is a diagram illustrating changes in each signal corresponding to changes in the signal FDAT.
FIG. 23 is a diagram illustrating an example of addition of a signal ZDAT.
FIG. 24 is a timing chart for explaining the operation of the histogram creation unit.
FIG. 25 is a timing chart for explaining the operation of the histogram creation unit following FIG. 24;
FIG. 26 is a timing chart for explaining the operation of the histogram creation unit following FIG. 25;
[Explanation of symbols]
4 ... Scanner section
6 ... Printer section
90 ... Main control unit
91 ... Main CPU
96. Image processing unit
97: Multi-level page memory control unit
98 ... Multi-level page memory
99 ... System I / F
201: Histogram creation unit
202... Reference value calculation unit
203: Reference value determining unit
204: Range correction unit

Claims (6)

A reading unit that divides and reads a document image into a plurality of lines, and provides image data in units of lines corresponding to the document image;
Storage means for storing image data in line units corresponding to the original image provided from the reading means, and providing image data in line units corresponding to the original image as necessary;
Based on the line unit image data corresponding to the original image provided from the reading unit, the type of image data of each line unit is determined, and the type determination result of the image data of each line unit is provided. Image discrimination means;
Based on the image data in line units corresponding to the original image provided from the reading means, a correction reference value in line units corresponding to the original image is calculated, and correction in line units corresponding to the original image is performed. A correction reference value calculation means for providing a reference value;
Correction for each type of image based on the result of determining the type of image data for each line unit provided from the image determining unit and the correction reference value for each line unit provided from the correction reference value calculating unit. A correction reference value generating means for generating a reference value and providing a correction reference value for each type of image;
Based on the correction reference value for each image type provided from the correction reference value generating means , the density range correction for each image type is performed on the image data corresponding to the original image corresponding to the original image provided from the storage means. A range correction unit that performs processing and provides density range corrected image data;
An image processing apparatus comprising: A reading unit that divides and reads a document image into a plurality of lines, and provides image data in units of lines corresponding to the document image;
Storage means for storing image data in line units corresponding to the original image provided from the reading means, and providing image data in line units corresponding to the original image as necessary;
Based on the line unit image data corresponding to the original image provided from the reading unit, the type of image data of each line unit is determined, and the type determination result of the image data of each line unit is provided. Image discrimination means;
Based on the line unit image data corresponding to the document image provided from the reading unit, a line unit density histogram corresponding to the document image is generated, and the line unit density histogram corresponding to the document image. A density histogram generating means for providing information on;
Based on the density histogram information corresponding to the original image corresponding to the original image provided from the density histogram generating means, a correction reference value for the original image equivalent to the line unit is calculated, and the original image equivalent value is calculated. Correction reference value calculation means for providing a correction reference value in line units;
Correction for each type of image based on the result of determining the type of image data for each line unit provided from the image determining unit and the correction reference value for each line unit provided from the correction reference value calculating unit. A correction reference value generating means for generating a reference value and providing a correction reference value for each type of image;
Based on the correction reference value for each image type provided from the correction reference value generating means , the density range correction for each image type is performed on the image data corresponding to the original image corresponding to the original image provided from the storage means. A range correction unit that performs processing and provides density range corrected image data;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, further comprising an output unit that outputs the image data stored in the storage unit to the outside. A reading unit that divides and reads a document image into a plurality of lines, and provides image data in units of lines corresponding to the document image;
Storage means for storing image data in line units corresponding to the original image provided from the reading means, and providing image data in line units corresponding to the original image as necessary;
Based on the line unit image data corresponding to the original image provided from the reading unit, the type of image data of each line unit is determined, and the result of determining the type of image data for each line is provided. Image discrimination means;
Based on the image data in line units corresponding to the original image provided from the reading unit, a correction reference value in line units corresponding to the original image is calculated, and correction in line units corresponding to the original image is performed. A correction reference value calculation means for providing a reference value;
Correction for each type of image based on the result of determining the type of image data for each line unit provided from the image determining unit and the correction reference value for each line unit provided from the correction reference value calculating unit. A correction reference value generating means for generating a reference value and providing a correction reference value for each type of image;
Based on the correction reference value for each image type provided from the correction reference value generating means , the density range correction for each image type is performed on the image data corresponding to the original image corresponding to the original image provided from the storage means. A range correction unit that performs processing and provides density range corrected image data;
Image forming means for forming an image based on density range corrected image data provided from the range correcting means;
An image forming apparatus comprising: A reading unit that divides and reads a document image into a plurality of lines, and provides image data in units of lines corresponding to the document image;
Storage means for storing image data in line units corresponding to the original image provided from the reading means, and providing image data in line units corresponding to the original image as necessary;
Based on the line unit image data corresponding to the original image provided from the reading unit, the type of image data of each line unit is determined, and the type determination result of the image data of each line unit is provided. Image discrimination means;
Based on the line unit image data corresponding to the original image provided from the reading unit, a line unit density histogram corresponding to the original image is generated, and the line unit density histogram corresponding to the original image. A density histogram generating means for providing information on;
Based on the density histogram information corresponding to the original image corresponding to the original image provided from the density histogram generating means, a correction reference value for the original image corresponding to the original line is calculated. Correction reference value calculation means for providing a correction reference value in line units;
Correction for each type of image based on the result of determining the type of image data for each line unit provided from the image determining unit and the correction reference value for each line unit provided from the correction reference value calculating unit. A correction reference value generating means for generating a reference value and providing a correction reference value for each type of image;
Based on the correction reference value for each image type provided from the correction reference value generating means, the density range correction for each image type is performed on the image data corresponding to the original image corresponding to the original image provided from the storage means. Range correction means for processing and providing density range corrected image data;
Image forming means for forming an image based on density range corrected image data provided from the range correcting means;
An image forming apparatus comprising:   And an output means for outputting the image data stored in the storage means to the outside. The image forming apparatus according to claim 4 or 5.

Images