JP2005094556A - Color correction coefficient generation method for image forming apparatus, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a difference between an original and a copied image caused by a change with the passage of time in a scanner part or in a printer part, to obtain a wide correction range only in the printer part to deal with a change such that a correction range is lacked, and to correct even a color such as a secondary or third color in RGB that is hardly corrected only by the printer part, representing an image in YMCK. <P>SOLUTION: An original image is read from the original (S103), a first color correction coefficient is generated on the basis of the original image (S104), and a copied original is outputted on the basis of the original image (S107). A copied original image is then read from the copied original (S108), and a second color correction coefficient is generated on the basis of the copied original image (S109). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color correction coefficient generation method of an image forming apparatus and an image forming apparatus that perform color correction of a read image and an output image.

Conventionally, reference color chart data is stored in advance in a memory of an image forming apparatus, formed on a sheet as an image, and data obtained by reading the sheet with a scanner unit is compared with reference color chart data. There has been a technique of correcting the color of an output image (see Patent Document 1).
JP-A-7-22203

  In the above technique, since the reference color chart is obtained from the memory, it is impossible to correct the color change that occurs when the scanner unit reads the document.

  An object of the present invention is to prevent a difference between a document and a duplicated image caused by a change with time of a scanner unit or a printer unit, and to correct a change in color of both the scanner unit and the printer unit or one of them, It is to obtain a wide correction range that can cope with a change in which the correction range is insufficient only by the printer unit.

  The present invention reads a document image from a document, generates a first color correction coefficient based on the document image, outputs a copied document based on the document image, and reads the copied document image from the copied document. There is provided a color correction coefficient generation method for an image forming apparatus, which generates a second color correction coefficient based on the copied original image.

  The present invention also provides a reading unit that reads a document and generates a document image signal, and a first color correction coefficient generation unit that generates a first color correction coefficient based on the document image signal read by the reading unit. An output unit that outputs a duplicate document based on the document image signal, and a second color based on a copy document image signal generated by reading the duplicate document output from the output unit by the reading unit. An image forming apparatus having a second color correction coefficient generation unit that generates a correction coefficient is provided.

  The present invention also provides a document conveying device, a reading unit that reads a document image from a document provided as a part of the document conveying device, and generates a reading color correction coefficient based on the document image read by the reading unit. An image forming apparatus having a read color correction coefficient generating unit is provided.

  By preventing the difference between the original and the duplicated image caused by changes over time in the scanner unit and printer unit, it is possible to correct changes in the color of both the scanner unit and printer unit or one of them. It is possible to realize a wide correction range that can cope with a change that would cause shortage.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an appearance of a digital color copying machine 1 as an image forming apparatus that reads a color image on a document and forms a duplicated image thereof. The copying machine 1 has a main body 2, an ADF (auto document feeder: automatic document feeder) 4 as a document feeder, and an operation panel 6.

  The main body 2 includes a scanner unit 8 described later and a printer unit 10 described later. The scanner unit 8 reads a color image of a document. The printer unit 10 prints a duplicate image of the color image read by the scanner unit 8 on a sheet.

  The ADF 4 is provided on the scanner unit 8 at the upper part of the main body 2 and conveys a document.

  The operation panel 6 is disposed on the front side of the ADF 4. The operation panel 6 includes a liquid crystal display unit 62 and a print key 64, and inputs instructions and set values to the copying machine.

  FIG. 2 is a diagram schematically showing the internal configuration of the ADF 4 and the scanner unit 8.

  First, the configuration of the ADF 4 will be described. The ADF 4 includes a transport belt 41, a driving roller 42, a driven roller 43, a patch sensor 44, a document tray 45, a pickup roller 46, a paper feed roller 47, a paper sensor 48, an aligning roller 49, a paper discharge tray 51, and a paper discharge roller 52. .

  The conveyor belt 41 is wound around a driving roller 42 and a driven roller 43 that are spaced apart from each other, and runs endlessly along the document table 81 of the scanner unit 8.

  The drive roller 42 is driven by a pulse motor (not shown).

  The driven roller 43 rotates according to the rotation of the conveyance belt 41 driven by the driving roller 42.

  The patch sensor 44 is provided in the vicinity of the driven roller 43 and detects a patch of the traveling conveyor belt 41.

  A document is placed on the document tray 45.

  The pickup roller 46 is provided at one end of the ADF 4 and takes out the documents set on the document tray 45 one by one.

  The paper feed roller 47 winds the taken out original and feeds it toward the original table.

  The paper sensor 48 detects the paper conveyed to the paper feed roller 47.

  The aligning roller 49 temporarily aligns the document before conveying the sheet by the conveying belt 41.

  The paper discharge roller 52 discharges the sent document to the paper discharge tray 51.

  The paper discharge tray 51 accommodates the original to be discharged.

  The paper sensor 48 detects the paper conveyed from the paper feed roller 47, and the operation of the aligning roller 49 is controlled based on the paper.

  FIG. 3 is a view showing a surface of the transport belt 41 facing the document table 81, that is, a front surface. Incidentally, here, the surface that contacts the driving roller 42 and the driven roller 43 is the back surface.

  Here, a color patch and a gray scale patch are provided. Here, the patches are seven colors of yellow 410y, magenta 410m, cyan 410c, black 410k, red 410r, green 410g, and blue 410b. The gray scale patches 411 to 420 have 10 gradations. In addition, a black bar 422 for specifying the position of the patch and the gray scale is provided.

  Each patch and each gray scale as a document are provided so that the driving roller 42 and the driven roller 43 do not overlap with the portion where the conveying belt 41 hits from the back side.

  This is to prevent the patches and gray scale from becoming dirty. The driving roller 42 is controlled so that the patch and the gray scale are not seen from the document table 81 when the document is read so that the patch and the gray scale are not read together with the document when the document is read.

  Next, the configuration of the scanner unit 8 will be described. The scanner unit 8 includes a document table 81, an exposure lamp 82, a first mirror 83, a first carriage 84, a second carriage 85, a second mirror 86, a third mirror 87, an imaging lens 88, a CCD type color image sensor (hereinafter referred to as a CCD type image sensor). (Referred to as a CCD) 89.

  The document table 81 is formed of a light-transmitting member such as glass so that the CCD 89 can read the placed document.

  The exposure lamp 82 exposes the document through the document table 81.

  The first carriage 84 includes a first mirror 83. The second carriage 85 includes a second mirror 86 and a third mirror 13. The first carriage 84 and the second carriage 85 are driven by a scanner motor (not shown) to move the exposure lamp 82, the first mirror 83, the second mirror 86, and the third mirror 87.

  The first mirror 83, the second mirror 86, and the third mirror 87 guide reflected light from the exposed document to the imaging lens 88.

  The imaging lens 88 forms an image of the reflected light from the original on the CCD 89.

  The CCD 89 converts the incident light from the imaging lens 88 into an electrical signal corresponding to the three primary colors of RGB light.

  FIG. 4 shows a block diagram of the electric system of the copying machine 1. The electrical system of the copying machine 1 includes a CPU 100, a liquid crystal display unit 62, a print key 64, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 104, a page memory 108, a printer controller 110, an HDD (Hardware). Disk drive) The controller 112, HDD 114, external interface 116, timer 118, counter 120, image processing unit 200, ADF 4, scanner unit 8, printer unit 10 and the like.

  The CPU 100 as the first color correction coefficient generation unit and the second color correction coefficient generation unit controls the operation of the copying machine 1 including generation of a color correction coefficient described later. The CPU 100 controls the operation of each roller according to the patch position detected by the patch sensor 44 of the ADF 4 and the paper position detected by the paper sensor 48. Once the conveyor belt 41 has traveled and patches have been detected by the patch sensor 44, the number of pulses sent to the pulse motor that drives the drive roller 42 is started. When the conveyance belt 41 rotates once and the patch is detected again by the patch sensor 44, the count is stopped, and the counted number of pulses is stored in the RAM 104. In this way, the number of pulses required to run the conveyor belt 41 once is obtained, and the patch can be moved to a desired position by adjusting the rotation angle of the drive roller 42 based on this.

  The liquid crystal display unit 62 has a touch panel on which various mode selection screens and the like are displayed, and inputs instructions and set values from the user to the copying machine.

  When the print key 64 is pressed by the user, the CPU 100 starts the copying operation of the copying machine 1.

  The ROM 102 stores a control program and the like.

  The RAM 104 temporarily stores data.

  The page memory 108 has an area where image information for a plurality of pages can be stored, and is formed so that image data can be stored for each page.

  The HDD 114 connected to the CPU 100 and the image processing unit 200 via the HDD controller 112 uses a magnetic disk or the like, and can hold image data for a long time.

  The external interface 116 transmits and receives image data and status status to and from a computer connected to a LAN or the Internet.

  In addition, the printer controller 110 connected to the external interface 116 is connected to the page memory 108, the image processing unit 200, and the printer unit 10, and matches the image data input and output by each.

  The timer 118 provides time information to the CPU 100.

  The counter 120 counts the number of sheets on which the printer unit 10 has formed an image.

  The image processing unit 200 performs image processing on an image input from the scanner unit 8 or the external interface 116.

  FIG. 5 is a block diagram of the image processing unit 200. The image processing unit 200 includes an A / D conversion circuit 202, a shading correction circuit 204, a line memory 206, a parameter calculation unit 208, a scanner color correction unit 210, a color conversion unit 212, a filter processing unit 214, an output image processing unit 216, and a printer. The color correction unit 218 is configured.

  The A / D conversion circuit 202 converts R, G, and B analog signals output from the CCD 89 into digital signals.

  The shading correction circuit 204 corrects variation in the threshold level with respect to the output signal from the CCD 89 due to variations in the CCD 89 or changes in ambient temperature.

  The line memory 206 temporarily stores the shading corrected digital signal from the shading correction circuit 204.

  The parameter calculation unit 208 refers to the RGB image data output from the line memory 206, the scanner reference value data and the printer reference value data stored in the ROM 102, and sends them to the scanner color correction unit 210 and the printer color correction unit 218. The color correction parameter to be provided is calculated.

  The scanner color correction unit 210 performs color correction processing such as shading correction and gamma correction on the RGB image data from the line memory 206 based on the color correction parameters described above.

  The color conversion unit 212 converts the RGB image data corrected by the scanner color correction unit 210 into cyan (C), magenta (M), yellow (Y), and black (K) data.

  The filter processing unit 214 performs filter processing such as enlargement / reduction, background removal, noise removal, and edge enhancement on the YMCK image data output from the color conversion unit 212.

  The output image processing unit 216 performs gradation processing, halftone processing, and the like on the YMCK image data output from the filter processing unit 214.

  The printer color correction unit 218 performs color correction processing on the output image data from the output image processing unit 216 based on correction parameters described later.

  The RGB image data corrected by the scanner color correction unit 210 can also be stored in the page memory 108.

  In the scanner color correction unit 210, correction is performed based on Equation 1 below.

Here, R, G, and B are RGB values input to the scanner color correction unit 210, and R ′, G ′, and B ′ are RGB values output from the scanner color correction unit 210. In addition, a value calculated by the parameter calculation unit 208 is used for a correction coefficient matrix including 12 coefficients a _{1 to} a ₄ , b _{1 to} b ₄ , and c _{1 to} c ₄ .

  The operation of the copying machine 1 having such a configuration will be described with reference to FIG.

  With the scanner / print selection key displayed on the liquid crystal display unit 62 of the operation panel 6 on which a document is placed on the document table 81 of the scanner unit 8, it is selected whether to scan or copy, and the print key 64 is pressed. Then, the scanner unit 8 starts reading the image of the document. That is, the exposure lamp 82 irradiates the original with light. The light reflected by the document is read by the CCD 89 via the first mirror 83, the second mirror 86, the third mirror 87, and the imaging lens 88 that perform a predetermined operation (step 1: hereinafter referred to as S1). .

  The reflected light of the original read by the CCD 89 is converted into an electrical signal corresponding to the three primary colors of RGB light, and the generated image data is sent to the image processing unit 200. Further, scanner color correction such as shading correction and gamma correction is performed using the scanner color correction matrix read from the RAM 104 (S2).

  The scanner color corrected image data is stored in the page memory 108 (S3).

  Here, the processing is divided depending on whether only scanning or copying is selected with the scanner / print selection key on the operation panel 6 (S4).

  If copying is selected (YES in S4), the image data stored in the page memory 108 is read into the image processing unit 200 again, and the print color is corrected using the print color correction matrix read from the RAM 104. (S5).

  Based on the image data that has undergone print color correction, the printer unit 10 forms an image (S6).

  If it has been selected to scan only in S4 (NO in S4), the scanner color corrected image data stored in the page memory 108 is stored in the HDD 114 via the HDD controller 112 (S7).

  Next, how the matrix used for color correction is generated will be described based on the flowchart shown in FIG.

  When the start of the color correction adjustment operation is instructed, it is determined whether or not the scanner color correction adjustment is selected (S101).

  If the adjustment is selected (YES in S101), the patch of the ADF 4 is moved to a position where it can be read by the scanner unit 8 (S102).

  When the patch is moved to a position where it can be read by the scanner unit 8, the scanner unit 8 reads the patch or gray scale to obtain image data as a first developed image (S103).

  Image data including patches and gray scales read by the scanner unit 8 is compared with the scanner reference value data stored in the ROM 102, and a scanner color correction matrix as a first color correction coefficient is generated (S104).

  The scanner color correction matrix generated in this way is stored in the RAM 104 (S105).

  If it is determined that the scanner color correction matrix generation process has been completed, or if it is determined in S1 that the scanner color correction adjustment is not performed, it is determined whether the printer color correction adjustment is selected. (S106).

  If it has been selected not to perform adjustment (NO in S106), the color correction process is terminated. If the printer color correction adjustment is selected (YES in S106), an image including a patch or gray scale read by the scanner unit 8 is printed on a sheet as a duplicate document (S107).

  When a sheet on which a duplicate image is printed is placed on the document table 81 as a document and the print key 64 is pressed, the scanner unit 8 reads a patch or gray scale copied on the sheet. (S108).

  The read original image data as a copied original image is compared with the printer reference value data stored in the ROM 102, and a printer color correction matrix as a second color correction coefficient is generated (S109).

  The generated printer color correction matrix is stored in the RAM 104 (S110).

  By the above operation, it is possible to correct a color change that occurs when the scanner unit reads a document.

  The scanner color correction matrix should have a property as shown in the following Equation 2, for example.

Here, R ₀ , G ₀ and B ₀ are printer reference value data stored in the ROM 102. In order to establish this relationship, each coefficient is obtained by minimizing the left side of Equation 3 below, that is, by the least square method.

  By using the scanner color correction matrix and printer color correction matrix created as described above, colors that are difficult to be corrected only by the printer unit that expresses an image in YMCK, such as RGB secondary colors and tertiary colors, can be obtained. Correction can be performed.

  In addition, by providing patches in advance on the ADF transport belt as described above, it is possible to eliminate the need to prepare a color chart when performing color correction.

  For example, the color correction operation may be performed periodically at predetermined time intervals.

  Further, since the color change of the output image is mainly related to the number of images formed, it may be performed every predetermined number of images formed.

  Alternatively, the color correction button displayed on the liquid crystal display unit 62 of the operation panel 6 may be touched.

  Further, at this time, it is selectively instructed whether to adjust the scanner color correction or to adjust the printer color correction. However, if the printer color correction is automatically adjusted, a mechanism for automatically placing the paper on which the duplicate image is printed by the printer unit 10 on the document table 81 of the scanner unit 8 is required.

  The color correction adjustment is not limited to using a patch provided on the transport belt 41 of the ADF 4, and a test chart may be prepared separately.

Perspective view of copying machine 1 Sectional view of ADF 4 and scanner unit 8 Illustration of the front surface of the conveyor belt 41 Block diagram of copier 1 Block diagram of the image processing unit 200 Flow chart of operation of copying machine 1 Flow chart for generating a matrix used for color correction

Explanation of symbols

1 Copier 2 Body 4 ADF
6 Operation Panel 108 Page Memory 200 Image Processing Unit 202 A / D Conversion Circuit 204 Shading Correction Circuit 206 Line Memory 208 Parameter Calculation Unit 210 Scanner Color Correction Unit 212 Color Conversion Unit 214 Filter Processing Unit 216 Output Image Processing Unit 218 Printer Color Correction Unit

Claims (11)

Read the original image from the original,
A first color correction coefficient is generated based on the original image,
A duplicate manuscript is output based on the manuscript image,
Read the copied manuscript image from this duplicate manuscript,
A color correction coefficient generation method for an image forming apparatus, characterized in that a second color correction coefficient is generated based on the copy original image. 2. The color correction coefficient generation method for an image forming apparatus according to claim 1, wherein at least one of the first color correction coefficient or the second color correction coefficient is calculated by a least square method. A reading unit that reads a document and generates a document image signal;
First color correction coefficient generation means for generating a first color correction coefficient based on the original image signal read by the reading unit;
An output unit that outputs a duplicate document based on the document image signal;
Second color correction coefficient generating means for generating a second color correction coefficient based on a copy original image signal generated by reading the duplicate original output from the output unit by the reading unit;
An image forming apparatus comprising:   4. The image forming apparatus according to claim 3, wherein at least one of generation of the first color correction coefficient and generation of the second color correction coefficient can be selected.   The image forming apparatus according to claim 3, wherein the document is provided as a part of the image forming apparatus. The image forming apparatus includes a document conveying device,
The image forming apparatus according to claim 3, wherein the original is provided as a part of the original conveying apparatus. A document feeder,
A reading unit for reading a document image from a document provided as a part of the document conveying device;
An image forming apparatus comprising: a read color correction coefficient generation unit configured to generate a read color correction coefficient based on the original image read by the reading unit.   The image forming apparatus according to claim 7, wherein the original is positioned not to be read when another original is read. The document conveying device has a document conveying belt,
The image forming apparatus according to claim 7, wherein the original is provided on the original conveying belt. The document conveying device has a driving device for driving the document conveying belt,
The image forming apparatus according to claim 9, wherein the driving device does not overlap a back side of a portion of the conveyance belt where the document is provided. Read the document image from the document provided as part of the document transport device,
A color correction coefficient generation method for an image forming apparatus, wherein a read color correction coefficient is generated based on the read original image.

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