WO2019017127A1 - Image reading device, image forming device, and image reading method - Google Patents

Abstract

This image reading device (1) includes: a plurality of light sources (52) which respectively include a first source light source which emits light having a first spectrum and a second source light source which emits light having a second spectrum, and emit white light; an image reading unit (50) which generates image data (ID) according to reflection light from a manuscript (P); and a correction value determination unit which calculates a total correction value (α3) for calibrating the amount of the light having the first spectrum by using the ratio of a reflection light amount of the light having the first spectrum from a calibration manuscript prepared in advance so as to calibrate the light having the second spectrum and a calibration reference value set as a reference of the reflection light amount of the light having the first spectrum. The correction value determination unit determines a partial correction value with respect to one light source (52) among the plurality of light sources (52), and calculates the total correction value by using the partial correction value and correction value relationship information that indicates a relationship between the partial correction value and the total correction value.

Description

Image reading apparatus, image forming apparatus, and image reading method

The present invention relates to an image reading apparatus, an image forming apparatus, and an image reading method, and more particularly, to a technology for achieving accurate color reproduction using a white LED as a light source for image reading.

Conventionally, in order to realize accurate color reproduction, a technology has been proposed in which color patches are printed, and the printed color patches are detected by a sensor to calibrate the image forming process. Patent Document 1 facilitates calibration of a color sensor for suppressing the influence of deterioration of sensor output due to change in output due to time-dependent change or ambient temperature change of light emitting unit and light receiving unit constituting a color sensor, and contamination of the sensor surface. It proposes technology. On the other hand, it has also been proposed to adopt a plurality of LEDs as a light source of the image reading unit to increase the light quantity in response to the demand for higher resolution and higher speed in image reading.

JP 2005-39364 A

However, Patent Document 1 has not sufficiently considered the error of color reproduction due to the variation of a plurality of light sources for image reading.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a technique for easily suppressing an error in color reproduction caused by variations in a plurality of light sources for image reading.

The present invention provides an image reading apparatus for reading an image on a document. The image reading apparatus includes a first source light source emitting light having a first spectrum and a second source light source emitting light having a second spectrum, the light having the first spectrum and Image data according to a plurality of light sources for emitting white light including light having the second spectrum, light having the first spectrum from the document, and reflected light of the light having the second spectrum An image reading unit for generating the second spectrum, a reflected light quantity of the light having the first spectrum from the calibration original prepared in advance for calibration of the light having the second spectrum, and the first spectrum A correction value determination unit for determining an overall correction value for calibrating the light quantity having the first spectrum as a ratio to a calibration reference value set as a standard of the reflected light quantity of light having; The value determination unit is configured to determine the amount of reflected light of the first spectrum from the calibration document when one of the plurality of light sources is turned on, and the first spectrum for the one light source. A partial correction value for calibrating the light quantity having the first spectrum is determined as a ratio to a calibration reference value set as a standard of the reflected light quantity of light having the first correction value, the partial correction value and the total correction value The total correction value is determined using the correction value relation information representing the relation with the above and the partial correction value.

An image forming apparatus according to the present invention includes the image reading apparatus and an image forming unit that forms an image based on the image data, and the image forming unit uses the entire correction value to generate the image data. And a calibration unit configured to calibrate image data generated according to the reflected light of the light having the first spectrum.

The present invention provides an image reading method for reading an image on a document. The image reading method uses a plurality of light sources respectively including a first source light source emitting light having a first spectrum and a second source light source emitting light having a second spectrum, Irradiating white light including light having a spectrum of: and light having the second spectrum; reflected light of light having the first spectrum from the original and light having the second spectrum An image reading step of generating image data according to the image data, a reflected light amount of light having the first spectrum from the calibration original prepared in advance for calibration of the light having the second spectrum, A correction value determination for determining an overall correction value for calibrating the light quantity having the first spectrum as a ratio to a calibration reference value set as a standard of the reflected light quantity of light having the first spectrum And the step of determining the correction value includes the step of reflecting the amount of reflected light of the first spectrum from the calibration document when one of the plurality of light sources is turned on; A partial correction value for calibrating the light amount having the first spectrum is determined as a ratio to a calibration reference value set as a reference of the reflected light amount of the light having the first spectrum for the light source, and the portion The method further includes the step of determining the entire correction value using correction value relation information representing a relation between the correction value and the entire correction value and the partial correction value.

According to the present invention, it is possible to easily suppress an error in color reproduction caused by the variation of a plurality of light sources for image reading.

FIG. 1 is a schematic configuration view showing an entire configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 1 is a cross-sectional view showing an entire configuration of an image forming apparatus 1 according to an embodiment. 5 is a flowchart showing the contents of a light source calibration process procedure of the image forming apparatus 1 according to an embodiment. 5 is a flowchart showing the contents of a light source calibration process procedure of the image forming apparatus 1 according to an embodiment. 5 is a flowchart showing the contents of an LED calibration processing procedure of the image forming apparatus 1 according to an embodiment. It is a graph which shows the relationship between the frequency characteristic of the patch for calibration of cyan and the frequency band of red light concerning one embodiment. It is a graph which shows the relation between the frequency characteristic of the patch for calibration of magenta concerning one embodiment, and the frequency band of green light. It is a graph which shows the relationship between the frequency characteristic of the patch for calibration of yellow which concerns on one Embodiment, and the frequency band of blue light. It is a graph which shows the relationship between the frequency characteristic of the patch for calibration of cyan and the frequency band of red light concerning one embodiment. It is a flow chart which shows the contents of B correction value alpha calculation processing concerning one embodiment.

Hereinafter, modes for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described with reference to the drawings.

FIG. 1 is a block diagram showing a functional configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 includes a control unit 10, an image forming unit 20, a storage unit 40, and an image reading unit 50.

The control unit 10 includes a main storage unit such as a RAM and a ROM, and a processor such as an MPU (Micro Processing Unit) and a CPU (Central Processing Unit). The control unit 10 also has a controller function related to interfaces such as various I / O, USB (Universal Serial Bus), bus, and other hardware, and controls the entire image forming apparatus 1.

The storage unit 40 is a storage device including a hard disk drive or a flash memory, which is a non-temporary recording medium, and stores control programs and data of processing executed by the control unit 10. In the present embodiment, the storage unit 40 further stores calibration image data CI and B reference value data Bref as calibration data CD for printing an adjustment document for CMYK calibration. The calibration image data CI is stored in the storage unit 40 as RGB data.

The image reading unit 50 reads an image from a document and generates an image data ID which is digital data. The image reading unit 50 includes a light source driver 51 and a plurality of white light sources 52 for irradiating the document P with light. In the present embodiment, the image reading unit 50 includes two white light sources 52. The plurality of white light sources 52 are arranged in the main scanning direction. The light source driver 51 is an LED driver that drives each LED of the white light source 52. The light source driver 51 performs on / off drive control of the white light source 52. Since the plurality of white light sources 52 are provided, it is possible to realize an increase in scanning speed and an increase in resolution while suppressing a decrease in S / N ratio leading to a granular feeling by increasing the light amount.

The white light source 52 is a white light source including a blue LED 52a and a yellow phosphor 52b. The blue LED 52a functions as a source of blue light of the three primary colors. The yellow phosphor 52b is a phosphor that functions as a source light source that emits blue light from the blue LED 52a and emits red light and green light. Thus, the white light source 52 can emit red light, green light and blue light, and thus functions as a white LED.

However, the inventor of the present invention has found that the brightness and the spectrum of the blue light vary depending on the chromaticity rank in the white LED. The chromaticity rank indicates the color variation. In other words, the spectrum of red light and green light emitted as photoluminescence by phosphors is small in fluctuation of the spectrum, while the spectrum of blue light is relatively fluctuated relatively to red light and green light with small fluctuation in spectrum. I found a thing. This is presumed to be due to the structure of the white LED described above.

In the present embodiment, the storage unit 40 stores B reference value data Bref that is a calibration reference value of blue light. In the B reference value data Bref, reference value data used when both of the two white light sources 52 are turned on, and reference value data used when one of the two white light sources 52 is turned on And are included.

The image sensor 53 has a plurality of light receiving elements 53a. The image sensor 53 is a line sensor having a plurality of light receiving elements 53a. The plurality of light receiving elements 53a are arranged in the main scanning direction. The plurality of light receiving elements 53a generate charges photoelectrically converted according to the intensity of each incident light. The generated charge is transferred by an analog shift register (not shown). Each transferred charge is converted by the charge-to-voltage conversion amplifier into an analog electrical signal which is a voltage signal. Thus, the image sensor 53 can output an analog electric signal for each pixel in the main scanning direction.

The image reading unit 50 further includes a signal processing unit 54, an AGC processing unit 55, and a white reference plate (not shown). The signal processing unit 54 amplifies the analog electrical signal with the gain set by the AGC processing unit 55 and stored in the storage unit 40, and A / D converts the amplified analog electrical signal to generate digital data. The generated digital data is an image data ID. As described above, the image forming unit 20 forms and discharges an image on a print medium based on the image data ID. The image data ID is data having a range width of the minimum value “0” and the maximum value “255”.

In the present embodiment, the AGC processing unit 55 is a gain adjustment unit that sets the optimum gain and offset value for each of the plurality of light receiving elements 53a using the black reference signal and the white reference signal. The black reference signal is an analog electrical signal of the light receiving element 53a when the white light source 52 is off. The white reference signal is an analog electric signal of the light receiving element 53a when the white reference plate (not shown) is illuminated instead of the document P. The AGC processing unit 55 sets an offset value such that the value of the image data ID when the black reference signal is A / D converted becomes the minimum value “0”. The AGC processing unit 55 sets the gain such that the value of the image data ID when the white reference signal is A / D converted using this offset value is the maximum value “255”.

Thereby, the fluctuation of the analog electrical signal due to increase or decrease of the reflected light between the black reference signal and the white reference signal can be effectively used from the minimum value "0" to the maximum value "255" of the image data ID. It becomes. However, when there is a variation in the luminance of RGB of the white light source 52 due to the individual difference of the white light source 52, for example, the detected RGB gradation is the same even if the RGB gradation of the document is the same. Not necessarily. Specifically, for example, when the amount of light of B of the white light source 52 is larger than the amount of light of R or G, the amount of reflected light of B increases even if the gradation of RGB of the document is the same.

The image forming unit 20 includes a color conversion processing unit 21, a density sensor 22 for calibration, an exposure unit 23, developing units 24c to 24k, and charging units 25c to 25k. The color conversion processing unit 21 performs color conversion of image data ID, which is RGB data, into CMYK, and executes halftone processing to generate CMYK halftone data.

FIG. 2 is a cross-sectional view showing the overall configuration of the image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 of the present embodiment is a tandem type color printer. In the image forming apparatus 1, photosensitive drums 26 m, 26 c, 26 y and 26 k are arranged in a line in the casing 70 corresponding to each color of magenta, cyan, yellow and black. The photosensitive drums 26m, 26c, 26y and 26k are image carriers. Developing portions 24m, 24c, 24y and 24k are disposed adjacent to the photosensitive drums 26m, 26c, 26y and 26k, respectively.

The laser beams Lm, Lc, Ly and Lk for respective colors are irradiated from the exposure unit 23 to the photosensitive drums 26m, 26c, 26y and 26k. By this irradiation, electrostatic latent images are formed on the photosensitive drums 26m, 26c, 26y and 26k. The developing units 24m, 24c, 24y and 24k adhere the toner to the electrostatic latent images formed on the surfaces of the photosensitive drums 26m, 26c, 26y and 26k while stirring the toner. Thus, the developing process is completed, and toner images of the respective colors are formed on the surfaces of the photosensitive drums 26m, 26c, 26y and 26k.

The image forming apparatus 1 has an endless intermediate transfer belt 27a. The intermediate transfer belt 27a is stretched around a tension roller 27c, a drive roller 27b and a driven roller 27d. The intermediate transfer belt 27a is driven to circulate by the rotation of the drive roller 27b.

For example, the black toner image on the photosensitive drum 26k is primarily transferred to the intermediate transfer belt 27a by holding the intermediate transfer belt 27a between the photosensitive drum 26k and the primary transfer roller 29k and driving the intermediate transfer belt 27a to circulate. Ru. The same applies to the three colors of cyan, yellow and black. A full-color toner image is formed on the surface of the intermediate transfer belt 27a by performing primary transfer so as to be superimposed on each other at a predetermined timing. Thereafter, the full-color toner image is secondarily transferred onto the printing paper P supplied from the paper feed cassette 60, and is fixed on the printing paper P in a known fixing process.

FIG. 3A is a flowchart showing the contents of the first light source calibration process of the image forming apparatus 1 according to one embodiment. FIG. 3B is a flowchart showing the contents of the second light source calibration process of the image forming apparatus 1 according to one embodiment. The first light source calibration process is a light source calibration process using both of the two white light sources 52. The second light source calibration process is a simplified light source calibration process using only one of the two white light sources 52. The first light source calibration process is performed at the time of adjustment before shipping of the image forming apparatus 1, and is also performed by the user as needed after shipping. The second light source calibration process is performed periodically or according to the situation on the user side after shipment of the image forming apparatus 1.

In step S100, the control unit 10 executes a first LED calibration process. The first LED calibration process is an LED calibration process performed by lighting only one of the two white light sources 52.

FIG. 4 is a flowchart showing the contents of the LED calibration processing procedure of the image forming apparatus 1 according to an embodiment. In step S111, the user uses the image forming apparatus 1 to print the adjustment document for CMYK calibration. In the present embodiment, the adjustment document for CMYK calibration is a document to be printed using the calibration image data CI read from the storage unit 40. The calibration image data CI is RGB data for calibration. The calibration RGB data includes C calibration R gradation data, M calibration G gradation data, Y calibration B gradation data, and K calibration RGB (gray) gradation data. Printing of the adjustment document for CMYK calibration is performed using a user interface for execution provided in a preset calibration menu (not shown).

The C calibration R gradation data is data for printing a plurality of patches representing each gradation of R. The M calibration G gradation data, the Y calibration B gradation data, and the K calibration RGB (gray) gradation data are data for printing a plurality of patches representing the respective gradations of MYK. The calibration RGB data is configured to print all the patches on one print medium which is preset using these data. As described above, the image forming apparatus 1 outputs the adjustment document for CMYK calibration based on the calibration image data CI.

In step S112, the user scans the adjustment document for CMYK calibration using the image reading unit 50 of the image forming apparatus 1. The image reading unit 50 reads an image from the adjustment document for CMYK calibration and generates print image data for calibration which is digital data. The proofreading print image data is generated as RGB image data based on the absorption characteristics of RGB light in the CMYK proofreading adjustment document. The calibration print image data may be generated by forming a patch on the intermediate transfer belt 27 a and using the calibration density sensor 22.

In step S113, the image forming apparatus 1 detects the RGB reflected light amount based on the printing image data for calibration. The RGB reflected light amount corresponds to the gradation value of the calibration print image data RGB. Specifically, the RGB reflected light amount is the light absorption amount Ar of red light in the patch of each gradation of the known cyan adjustment original, the absorption amount Ag of green light in the patch of each gradation of the known magenta adjustment original, and the known yellow adjustment This corresponds to the absorption amount Ab of blue light in the patch of each gradation of the original, and the absorption amount of RGB in the patch of each gradation of the known gray adjustment original. The light absorption amount Ar of red light corresponds to the gradation value of R. The green light absorption amount Ag corresponds to the gradation value of G. The blue light absorption amount Ab corresponds to the gradation value of B. The light absorption amount of RGB corresponds to the gradation value of RGB.

FIG. 5A is a graph showing the relationship between the frequency characteristics of the cyan calibration patch and the frequency band of red light according to one embodiment. FIG. 5B is a graph showing the relationship between the frequency characteristics of the calibration patch for magenta and the frequency band of green light according to one embodiment. The horizontal axes shown in FIGS. 5A and 5B indicate the wavelength of light, and the vertical axes indicate the amount of reflected light.

FIG. 5A shows an example of the reflection spectrum Rc of the cyan calibration patch of the cyan adjustment original and the absorption spectrum Sr of the cyan calibration patch. The cyan calibration patch of the cyan adjustment original is also referred to as a C calibration patch. The light absorption amount Ar indicates the amount of light absorbed by the cyan calibration patch of the cyan adjustment original, that is, the peak value of the amount of light not reflected. The light absorption amount Ar peaks in the red light wavelength band.

FIG. 5B shows an example of the reflection spectrum Rm of the magenta calibration patch of the magenta adjustment document and the absorption spectrum Sg of the magenta calibration patch. The magenta calibration patch of the magenta adjustment original is also referred to as an M calibration patch. The light absorption amount Ag indicates the amount of light absorbed by the magenta calibration patch of the magenta adjustment document, that is, the peak value of the amount of light not reflected. The light absorption amount Ag peaks in the green light wavelength band.

The absorption amount Ar of red light shown in FIG. 5A is detected by the image sensor 53, and is used for calibration of the image forming unit 20 by comparing the relationship between the gradation of the cyan calibration patch and the absorption amount Ar of red light. The absorption amount Ag of green light shown in FIG. 5B is detected by the image sensor 53, and is used for calibration of the image forming unit 20 by comparing the relationship between the gradation of the magenta calibration patch and the absorption amount Ag of green light. Specifically, the gradation of cyan corresponds to the area ratio of cyan dots, and the area ratio of cyan dots increases as the gradation of cyan increases. In other words, as the gradation of cyan is higher, the red light is absorbed by the cyan dot, and the absorption amount Ar of the red light becomes larger. The same applies to the gradation of magenta.

In step S114, the image forming apparatus 1 performs CM calibration based on the RG reflected light amount. In the present embodiment, CM calibration is performed as calibration of dot area rates of cyan toner and magenta toner in halftone processing. Specifically, for example, when the detection result of the light absorption amount Ar of the patch formed by the R gradation data for C calibration is larger than the set light absorption amount which is a known light absorption amount set in advance, the light absorption amount Ar is It is calibrated to reduce the area ratio so as to approach the set absorbance. That is, when the area ratio of cyan dots is high, calibration is performed so that the area ratio is decreased so that the light absorption amount Ar approaches the set light absorption amount. As a result, in the image forming apparatus 1, the scan result of the print image actually formed is calibrated so as to approach the calibration RGB data.

In step S115, the image forming apparatus 1 executes K calibration based on the RGB reflected light amount. The K calibration is performed in the present embodiment as a calibration of the dot area rate of the gray patch by the black toner in the halftone process. Specifically, for example, when the detection result of the light absorption amount (not shown) of the patch formed by the K gradation data for K calibration is larger than the set absorption amount which is a known light absorption amount set in advance, It is calibrated to reduce the area ratio so that the absorbance approaches the set absorbance. That is, when the area ratio of the black dots is high, calibration is performed so as to reduce the area ratio so that the light absorption amount approaches the set light absorption amount.

In step S116, the image forming apparatus 1 executes Y calibration based on the B reflected light amount. In the present embodiment, Y calibration is performed as calibration of the dot area ratio of yellow toner in halftone processing. The basic method is the same as the CM calibration performed based on the RG reflected light amount shown in step S114. However, this is different from the CM calibration based on the RG reflected light amount shown in step S114 in that Y calibration B gradation data is corrected using a B correction value α acquired by a method described later. The B calibration data for Y calibration corresponds to the detection result of the light absorption amount Ab of the patch. The B correction value α is an overall correction value α3 described later.

FIG. 6A is a graph showing the relationship between the frequency characteristic of the yellow calibration patch and the frequency band of blue light according to one embodiment. FIG. 6B is a graph showing the relationship between the frequency characteristics of the cyan calibration patch and the frequency band of blue light according to one embodiment. FIG. 6A shows an example of the reflection spectrum Ry of the yellow calibration patch of the yellow adjustment original and the absorption spectrum Sb of the yellow calibration patch. The yellow calibration patch is also referred to as a Y calibration patch. The light absorption amount Ab indicates the amount of light absorbed by the yellow calibration patch of the yellow adjustment original, that is, the peak value of the amount of light not reflected. The light absorption amount Ab peaks in the wavelength band of blue light.

FIG. 6B shows an example of the reflection spectrum Rc of the cyan calibration patch of the cyan adjustment original and the absorption spectrum Sb of the yellow calibration patch. The cyan calibration patch is also referred to as a C calibration patch. That is, it is a graph showing the relationship between the reflection spectrum Rc of the cyan calibration patch shown in FIG. 5A and the absorption spectrum Sb of the yellow calibration patch shown in FIG. 6A. According to the reflection spectrum Rc of the cyan calibration patch, blue light having a wavelength in the range of 400 nm to 500 nm is reflected with almost no absorption.

FIG. 7 is a flowchart showing the contents of the B correction value α calculation process according to one embodiment. In step S121, the user scans the adjustment document for scanner C calibration. The image forming apparatus 1 is provided with an adjustment document for scanner CMYK calibration, and calibration is performed in the same manner as the image forming unit 20. However, the B correction value α calculation process is generally used in a general scanner in that the variation of the blue light amount of the white light source 52 is detected using the adjustment document for scanner C calibration used for the calibration of cyan (red light). It is different from calibration. The scanner C calibration adjustment document is a calibration document having an example of a patch prepared in advance for the calibration of light having the second spectrum.

In step S122, the image reading unit 50 detects the B reflected light amount from the C calibration patch of the adjustment document for scanner C calibration. B The scanner C calibration adjustment original used for red light calibration is used to detect the amount of reflected light because the wavelengths of the red light and blue light are largely different, so the scanner C calibration adjustment original is blue light Because it reflects almost without absorbing it.

Specifically, for example, as shown in FIG. 6A, when the B reflected light amount Lb1 from the Y calibration patch of the adjustment document for scanner Y calibration is detected, blue light is absorbed by the Y calibration patch. The variation detection amount e1 of the light amount Lb1 also decreases. On the other hand, in the present embodiment, as shown in FIG. 6B, since the B reflected light amount Lb1 from the C calibration patch is detected, blue light is not absorbed by the C calibration patch, and the B reflected light amount Lb2 varies. The detection amount e2 also increases. Thereby, the variation of the blue light quantity of the white light source 52 can be detected with high accuracy.

In step S123, the control unit 10 functions as a correction value determination unit. The correction value determination unit determines the B correction value α. The B correction value α is calculated as a ratio of the B reference value data Bref read from the storage unit 40 by the control unit 10 to the gradation value RGB_Bc value according to the B reflection light amount. The B reference value data Bref is a light amount to be detected when the blue light amount of the white light source 52 is a reference value. Specifically, the B correction value α is determined as a value obtained by dividing the B reference value data Bref by the gradation value RGB_Bc value (α = Bref / RGB_Bc). In this example, reference value data used when one of the white light sources 52 of the B reference value data Bref is turned on is used.

In step S124, the control unit 10 stores the B correction value α in the storage unit 40. The B correction value α is a ratio of the gradation value to be detected when the blue light quantity of the white light source 52 is a reference value to the gradation value actually detected. Specifically, for example, assuming that the RGB_Bc value, which is the actual detection amount, is 1 / 2.2 of the gradation value to be detected when the blue light amount of the white light source 52 is a reference value, B The correction value α is 1.2 (α = 1 / 1.2 / 1/2). As a result, the partial correction value α1 that is the B correction value of one of the two white light sources 52 is obtained.

In step S200 (see FIG. 3), the control unit 10 executes a second LED calibration process. The second LED calibration process is an LED calibration process performed by lighting only the other of the two white light sources 52. The contents of the second LED calibration process are the same as the first LED calibration process except for the white light source 52 to be lit. As a result, the B partial correction value α2 of the other white light source 52 of the two white light sources 52 is acquired.

In step S300, the control unit 10 executes both LED calibration processing. Both LED calibration processes are LED calibration processes performed by lighting both of two white light sources 52. The contents of both LED calibration processes are the same as the first LED calibration process and the second LED calibration process except for the white light source 52 to be lit and the B reference value data Bref. In this example, reference value data used when both of the white light sources 52 of the B reference value data Bref are turned on is used. As a result, the B overall correction value α3 which is the correction value α at the time of lighting of both white light sources 52 is calculated.

In step S400, the control unit 10 executes measurement target LED selection processing. The measurement target LED selection process is a process of selecting a white light source 52 having a B-portion maximum correction value αL which is the largest correction value α among the B-portion correction values α1 or α2 out of the two white light sources 52. The measurement target LED is a white light source 52 to be measured in the second light source calibration process.

In step S500, the control unit 10 executes a table generation process. In the table generation process, the control unit 10 generates a table indicating the correspondence between the B overall correction value α3 when both white light sources 52 are lit and the B portion maximum correction value αL of the selected white light source 52.

The wavelength of the LED generally changes to the longer wavelength side as the temperature becomes higher. In this example, since the two white light sources 52 use the same LED in the same manner in the same temperature environment, the change in the wavelength of the white light source 52 having the B partial maximum correction value αL is used Thus, the B whole correction value α3 can be estimated. Thereby, it is possible to estimate the change of the entire B correction value α when both LEDs are lit based on the change of one of the B partial correction values α1 or α2. The LEDs have very close characteristics when they have chips diced from the same wafer, and can improve estimation accuracy.

The present invention executes the first light source calibration process at the time of adjustment before shipment and prepares the above-described table, thereby enabling execution of the second light source calibration process that is simple and consumes less power after shipment. . However, in consideration of aging and the like, it may be performed after shipment if necessary. The table stores correction value relationship information representing the relationship between the B-portion maximum correction value αL and the overall correction value α3.

In the second light source calibration process, only one of the two white light sources 52 is turned on and measured, and a table is used to estimate the B overall correction value α3 when both LEDs are turned on. In step S610 shown in FIG. 3B, the control unit 10 executes measurement target LED measurement processing. In the measurement target LED measurement process, the control unit 10 turns on the measurement target LED, executes the LED calibration process, and acquires the B-portion maximum correction value αL.

In step S620, the control unit 10 executes a calibration process using this B-portion maximum correction value αL. The control unit 10 estimates the B overall correction value α3 when both LEDs are lit, using the B portion maximum correction value αL to be measured and the LED table. The estimation can be performed by interpolation or extrapolation based on a table.

The image forming apparatus 1 uses the B entire correction value α3 to calculate the light amount when the blue light amount of the white light source 52 is the reference value even if the blue light amount of the white light source 52 fluctuates from the reference value. It can be estimated. Thus, the control unit 10 can function as a calibration unit that calibrates image data using the B entire correction value α3.

As described above, the image forming apparatus 1 according to the present embodiment can easily suppress an error in color reproduction due to the variation of a plurality of light sources for image reading without installing new hardware. .

The present invention can be implemented not only in the above embodiment but also in the following modifications.

Modified Example 1: Although the above embodiment is calibrated by adjusting the dot area ratio, it may be calibrated by adjusting, for example, the exposure energy, the charging bias, and the developing bias. Although it is possible to calibrate the variation of the light amount of RGB of the light source by adjusting the AGC, the calibration in the image forming process as described above has an advantage of not narrowing the dynamic range of RGB at the time of image reading.

Modified Example 2 In the above embodiment, it has a blue LED that emits light having a first spectrum, and a yellow phosphor that is excited by the light having a first spectrum to emit light having a second spectrum. Although a white light source 52 is used, the white light source 52 is not limited to this example. Blue LEDs are also referred to as source light sources.

Modified Example 3 In the above embodiment, the image reading unit of the CCD system is adopted, but the invention is not limited to the CCD system, and another system such as the CIS system may be adopted. In the CIS method, since RGB source light sources are generally used, the present invention can also be applied to suppress variations in RGB source light sources. In this case, the white light source 52 comprises a source light source emitting light having a first spectrum, a source light source emitting light having a second spectrum, and a source light source emitting light having a third spectrum. It will have.

Furthermore, the white light source 52 does not necessarily have to be composed of three source light sources of RGB, for example, a combination of a blue source light source and a yellow source light source, a combination of a red source light source and a blue green source light source, It may be a combination of a green source light source and a purple source light source. The combination of the blue and yellow source light sources is the spectrum of RG. The combination of the red and blue-green source light sources is the spectrum of the GB. The combination of the green source light and the purple source light is the spectrum of RB.

The white light source 52 generally comprises a first source light source emitting light having a first spectrum and a second source light source emitting light having a second spectrum, the light having a first spectrum Any light source may be used as long as it emits white light including light having a second spectrum. Furthermore, as in the above embodiment, the second source light source may be a phosphor that is excited by light having a first spectrum to emit light having a second spectrum.

Modification 4: In the above embodiment, the adjustment document for scanner C calibration is used as an example of a patch prepared in advance for the calibration of light having the second spectrum, but it is an adjustment document for scanner M calibration May be However, it is generally preferable to use a scanner C calibration adjustment document, which has a lower absorptivity in the blue light band than the scanner M calibration adjustment document.

Modification 5: Although the present invention is applied to the image forming apparatus in the above embodiment, the present invention is also applicable to a dedicated scanner or other image reading apparatus.

Claims (8)

An image reading apparatus for reading an image on a document,
A light source having a first spectrum, and a second light source having a second spectrum, the light source having a first spectrum and a second spectrum having a second spectrum. A plurality of light sources for emitting white light including light having light;
An image reading unit that generates image data according to the light having the first spectrum from the document and the reflected light of the light having the second spectrum;
As a reference of the reflected light quantity of the light having the first spectrum and the reflected light quantity of the light having the first spectrum from the calibration original prepared in advance for calibration of the light having the second spectrum A correction value determination unit that determines an overall correction value for calibrating the light quantity having the first spectrum as a ratio to the set calibration reference value;
Equipped with
The correction value determination unit is configured to determine the amount of light reflected from the calibration document when the one light source of the plurality of light sources is turned on, and the first light source with respect to the one light source. A partial correction value for calibrating the light quantity having the first spectrum is determined as a ratio to a calibration reference value set as a standard of the reflected light quantity of light having a spectrum of An image reading apparatus for determining the overall correction value using correction value relationship information representing a relationship with a correction value and the partial correction value. The image reading apparatus according to claim 1,
The image reading apparatus, wherein the one light source is a light source selected as the light source with the largest partial correction value among the plurality of light sources. The image reading apparatus according to claim 1,
The image reading device, wherein the plurality of light sources have chips diced from the same wafer. The image reading apparatus according to claim 1,
The image reading apparatus, wherein the second source light source is a phosphor that is excited by the light having the first spectrum and emits the light having the second spectrum. The image reading apparatus according to claim 4,
The first source light source is a blue LED,
The image reading apparatus wherein the phosphor is a yellow phosphor. The image reading apparatus according to claim 4,
The image reading apparatus wherein the proofreading original is a cyan proofreading original. An image reader according to claim 1;
An image forming unit that forms an image based on the image data;
Equipped with
The image forming apparatus has a calibration unit that calibrates image data generated according to reflected light of light having the first spectrum among the image data, using the entire correction value. An image reading method for reading an image on a document,
Using a plurality of light sources each comprising a first source light source emitting light having a first spectrum and a second source light source emitting light having a second spectrum, and light having the first spectrum Irradiating the white light including the light having the second spectrum;
An image reading step of generating image data in accordance with the light having the first spectrum from the document and the reflected light of the light having the second spectrum;
As a reference of the reflected light quantity of the light having the first spectrum and the reflected light quantity of the light having the first spectrum from the calibration original prepared in advance for calibration of the light having the second spectrum The processor executes a correction value determination step of determining an overall correction value for calibrating the light amount having the first spectrum as a ratio to the set calibration reference value;
In the correction value determination step, a reflected light amount of light having the first spectrum from the calibration document when one light source of the plurality of light sources is turned on, and the first light source with respect to the one light source A partial correction value for calibrating the light quantity having the first spectrum is determined as a ratio to a calibration reference value set as a standard of the reflected light quantity of light having a spectrum of An image reading method comprising the step of determining the total correction value using correction value relation information representing a relation with a correction value and the partial correction value.

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