JP2023180080A - Computer program, image processing device, image reading device, and image processing method - Google Patents

Abstract

To provide a computer program, an image processing device, an image reading device and an image processing method which can suppress a change in the hue of a photographed image.SOLUTION: A computer program causes a computer to execute processing of: acquiring a correction table for visible light for correcting image data obtained by performing photography under a visible light environment and a correction table for prescribed light for correcting prescribed light image data obtained by performing photography under a prescribed light environment; calculating a correction coefficient on the basis of the acquired correction table for visible light and correction table for prescribed light; and correcting the correction table for prescribed light on the basis of the calculated correction coefficient.SELECTED DRAWING: Figure 1

Description

The present invention relates to a computer program, an image processing device, an image reading device, and an image processing method.

The authenticity of target media such as credit cards, driver's licenses, and passports is generally determined by visual inspection. For example, a predetermined light (eg, UV light) is irradiated, and the authenticity is determined by whether or not a specific pattern can be visually confirmed.

On the other hand, authentication can also be automated. Patent Document 1 describes whether a predetermined location of a target medium is irradiated with ultraviolet rays (UV light) and whether dots of decolorizing ink are decolorized or not, and whether dots of normal ink (non-decolorable ink) remain. A system has been disclosed that determines authenticity based on whether the item is false or not.

Additionally, when importing a captured image of the target medium using UV light, it is necessary to read the captured image of a white plate (reference plate) in advance and create a correction table, and then perform shading correction using the created correction table. This suppresses uneven lighting.

JP 2021-144528 Publication

However, since the white plate used when creating the correction table does not necessarily have a uniform fluorescence rate (emission rate) of each RGB component for a given light, the RGB balance of the correction table may be disrupted. If a correction table with an unbalanced RGB is used, and if external light enters in addition to the predetermined light, the color tone of the photographed image will change due to external influences, which will affect the accuracy of authenticity determination.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a computer program, an image processing device, an image reading device, and an image processing method that can suppress changes in the tint of a photographed image.

The present application includes multiple means for solving the above-mentioned problems. To give one example, a computer program instructs a computer to use visible light for correcting image data obtained by photographing in a visible light environment. A correction coefficient is calculated based on a correction table and a predetermined light correction table for correcting predetermined light image data obtained by photographing under a predetermined light environment, and the predetermined light correction table is based on the calculated correction coefficient. Correct or execute processing.

According to the present invention, it is possible to suppress changes in color of a photographed image.

1 is a diagram showing an example of the configuration of a scanner device. FIG. 3 is a diagram showing an example of shading correction. It is a figure showing an outline of a correction table for visible light and a correction table for UV light. It is a figure which shows an example of the correction method of the correction table for UV light. It is a figure which shows an example of the correction table for UV light after correction|amendment. FIG. 3 is a diagram illustrating an example of a method for calculating an adjustment value. It is a figure which shows the influence of external light in the case of a comparative example. It is a figure showing the influence of external light of this embodiment. FIG. 3 is a diagram illustrating an example of a processing procedure of the scanner device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on drawings showing embodiments thereof. FIG. 1 is a diagram showing an example of the configuration of a scanner device 100. The scanner device 100 as an image reading device includes a light source section 10 for UV (ultraviolet) light as predetermined light, a light source section 20 for visible light, an imaging section 30, and an image processing section 50 as an image processing device. The image processing section 50 includes a control section 51 that controls the entire image processing section 50, an interface section 52, a memory 53, an output section 54, and a storage section 55. The storage unit 55 stores a computer program (program product) 56, a visible light correction table 57, a UV light correction table 58, and the like. The computer program 56 can be stored in the storage unit 55 by reading the computer program 56 recorded on a recording medium (for example, an optically readable disk storage medium such as a CD-ROM) using a recording medium reading unit. The computer program 56 may be downloaded from an external device and stored in the storage unit 55.

The UV light source unit 10 includes a light source that irradiates UV light onto a target medium (for example, a credit card, driver's license, passport, etc.) whose authenticity is to be determined. For example, a UV-LED can be used as the light source. The wavelength range of ultraviolet rays can be divided into UV-A (wavelength: 320-380 nm), UV-B (wavelength: 280-320 nm), and UV-C (wavelength: 200-280 nm). UV-A (wavelength: 320 to 380 nm) and a light source in the UV-A wavelength range can be used, but are not limited thereto.

The visible light light source section 20 includes a light source that irradiates a medium when the scanner device 100 reads a photographed image of a normal medium (for example, a document such as a document). For example, a white LED can be used as the light source. Visible light is electromagnetic waves within a wavelength range that is perceived as light by the human eye, with the lower limit of the wavelength range being approximately 360 to 400 nm and the upper limit being approximately 760 to 830 nm.

The imaging unit 30 includes an image sensor (eg, CCD: Charge Coupled Device, CMOS: Complementary Metal Oxide Semiconductor), an amplifier, an A/D converter, and the like. In the following, the imaging unit 30 will be described as a CCD image sensor. The imaging unit 30 obtains image data obtained by photographing a target medium by amplifying an analog signal taken in from an image sensor with an amplifier and converting the amplified analog signal into a digital signal with an A/D converter. The imaging section 30 outputs image data to the interface section 52.

The interface unit 52 acquires image data from the imaging unit 30 and stores the acquired image data in the memory 53.

The control unit 51 includes a required number of CPUs (Central Processing Units), MPUs (Micro-Processing Units), GPUs (Graphics Processing Units), and the like. The control unit 51 can execute processing determined by the computer program 56. That is, the processing by the control unit 51 is also the processing by the computer program 56. By executing the computer program 56, the control unit 51 executes various processes such as a correction table generation process, a correction coefficient calculation process to be described later, a correction process for the UV light correction table 58, and shading correction.

The memory 53 can be configured with a semiconductor memory such as an SRAM (Static Random Access Memory), a DRAM (Dynamic Random Access Memory), or a flash memory. The computer program 56 can be loaded into the memory 53 and the control unit 51 can execute the computer program 56.

The storage unit 55 can be configured with, for example, a hard disk or a semiconductor memory.

The output unit 54 outputs shading-corrected image data (scanned image).

FIG. 2 is a diagram showing an example of shading correction. FIG. 2A shows an overview of shading correction, and FIG. 2B shows a correction formula for shading correction. Shading correction is a function for correcting non-uniform factors such as uneven illuminance distribution of lenses and light sources, and uneven sensitivity for each pixel of a CCD, and also for maintaining white balance. A white plate (also referred to as a reference plate or white reference plate) having a uniform reflectance is installed on a glass table on which a medium (such as a manuscript) is placed, and the white plate is read in advance to generate a correction table. The correction table holds signal values obtained by imaging a white plate with a CCD. The signal value obtained by imaging a white plate with a CCD has a difference from the white reference value K due to the above-mentioned non-uniformity factor.

Therefore, as shown in FIG. 2A, each signal value in the correction table is corrected to a constant (white reference value) K. In order to correct each signal value in the correction table to a constant (white reference value) K, a correction formula is used as shown in FIG. 2B. If the pixel value of the image before correction is Iin, the pixel value of the image after correction is Iout, and K is a constant (white reference value), the correction formula is Iout=Iin・K/(correction table). can be expressed. Note that the correction formula is just an example, and is not limited to this. Note that different correction tables are generated depending on the light source used. In this embodiment, a visible light correction table 57 is used when a white LED is used, and a UV light correction table 58 is used when a UV-LED is used as the predetermined light.

Next, the visible light correction table 57 and the UV light correction table 58 will be explained.

FIG. 3 is a diagram showing an outline of the visible light correction table 57 and the UV light correction table 58. When generating the visible light correction table 57, the luminescence rate of each RGB component of the white plate is uniform (uniform due to the characteristics of the human eye). That is, since the luminescence rate of each RGB component with respect to visible light of the white plate is uniform, the histogram of the signal values (for example, 0 to 255) of each RGB component in the visible light correction table 57 is relatively well balanced. There is also no significant difference in the average value of the signal values of each RGB component.

On the other hand, when generating the UV light correction table 58, the white plate does not necessarily have a uniform fluorescence rate (emission rate) of each RGB component with respect to UV light. The fluorescence rate of RGB depends on the base material of the white plate, and for example, as shown in FIG. 3, the fluorescence rate of the R component may be lower than the fluorescence rate of other GB components. In addition, although the case where the fluorescence rate of R component is smaller than the fluorescence rate of other components is demonstrated below, the fluorescence rate of G component or B component may be small. When the fluorescence rate of the R component is smaller than the fluorescence rate of other components, the histogram of the signal values (for example, 0 to 255) of each RGB component in the UV light correction table 58 is out of balance. Furthermore, the average value of the signal values of the R component is smaller than the average value of the signal values of each of the GB components. Therefore, the signal values of the G and B components (correction table values) of the UV light correction table 58 are large, and the signal values of the R component (correction table values) are small.

In shading correction, pixel values are corrected by multiplying them by the reciprocal of the signal value (correction table value) in the correction table, so if a correction table with an imbalance of RGB is used, only the small components in the correction table will be corrected to larger values. As a result, only some of the RGB components are strongly corrected, and as a result, the color tone of the photographed image changes. In the following, a method of correcting the UV light correction table 58 will be described in order to suppress changes in the tint of a photographed image.

FIG. 4 is a diagram showing an example of a method of correcting the UV light correction table 58. The control unit 51 reads the visible light correction table 57 from the storage unit 55 and calculates statistical values of signal values for each RGB of the read visible light correction table 57. The statistical value can be, for example, an average value, median value, mode value, etc., but in this embodiment, the average value is used. The average values of RGB are expressed as A _VR , A _VG , and A _VB . In the example of FIG. 4, A _VR =108, A _VG =146, and A _VB =120.

The control unit 51 reads the UV light correction table 58 from the storage unit 55 and calculates statistical values of the signal values for each RGB of the read UV light correction table 58. The statistical value can be, for example, an average value, median value, mode value, etc., but in this embodiment, the average value is used. The average values of RGB are represented by A _UR , A _UG , and A _UB . In the example of FIG. 4, A _UR =40, A _UG =127, and A _UB =114.

The control unit 51 calculates a correction coefficient based on statistical values (for example, average values) of signal values held by the visible light correction table 57 and the UV light correction table 58. The correction coefficient may be calculated for each RGB. Let G _R , G _G , and G _B be correction coefficients for each of the RGB components.

The correction coefficient G _R can be calculated using the formula G _R =(A _VR /A _UR )·adj. (A _VR /A _UR ) is a magnification of the average value of the R component of the visible light correction table 57 with respect to the average value of the R component of the UV light correction table 58. In the example of FIG. 4, (A _VR /A _UR )=108/40. adj is an adjustment value. The adjustment value adj is a numerical value less than 1, and is used to prevent a portion of the signal values of the UV light correction table 58 corrected based on the correction coefficient from exceeding 255, thereby preventing so-called overexposure. The adjustment value may be a fixed value, or may be calculated as described below.

The correction coefficient G _G can be calculated using the formula G _G =(A _VG /A _UG )·adj. (A _VG /A _UG ) is a magnification of the average value of the G component of the visible light correction table 57 with respect to the average value of the G component of the UV light correction table 58. In the example of FIG. 4, (A _VG /A _UG )=146/127. adj is an adjustment value.

The correction coefficient G _B can be calculated using the formula G _B =(A _VB /A _UB )·adj. (A _VB /A _UB ) is a magnification of the average value of the B component of the visible light correction table 57 with respect to the average value of the B component of the UV light correction table 58. In the example of FIG. 4, (A _VB /A _UB )=120/114. adj is an adjustment value.

As described above, it is possible to correct the UV light correction table 58, which is out of RGB balance, so that it has the same RGB balance as the visible light correction table 57. In this way, the corrected UV light correction table 58 can make the fluorescence rate (emission rate) of each RGB component relatively uniform, like the visible light correction table 57.

Further, the control unit 51 may adjust the correction coefficient with a predetermined adjustment value. This makes it possible to prevent so-called overexposure.

FIG. 5 is a diagram showing an example of the UV light correction table 58 after correction. FIG. 5 describes the case of Bayer array, which is one way of arranging pixels of an image sensor of an image sensor. In the Bayer array, half of all pixels are G component pixels, and columns in which RG is repeated and columns in which GB is repeated are arranged alternately. The signal values of the RGB components of the UV light correction table 58 before correction are expressed in RGB. The signal values of the RGB components of the UV light correction table 58 after correction can be expressed as R×G _R , G×G _G , and B× _GB , respectively. Note that the arrangement is not limited to the Bayer arrangement, and may be a diagonal Bayer arrangement, a quad Bayer arrangement, or the like.

As described above, the control unit 51 can correct the signal values held in each of the uncorrected UV light correction tables 58 for each RGB based on the calculated correction coefficients G _R , G _G , and G _B .

FIG. 6 is a diagram illustrating an example of a method for calculating an adjustment value. The control unit 51 calculates statistical values (for example, average values) and deviation values of the signal values held by the UV light correction table 58 before correction, and calculates adjustment values based on the calculated statistical values and deviation values. be able to. The control unit 51 may adjust the correction coefficient using the calculated adjustment value.

Specifically, the average value of the signal values of the B component in the UV light correction table 58 before correction is set to _AUB , and the standard deviation of the signal values of the B component is set to σB. When { _GB ·(A _UB +3σB)}>255, the adjustment value AdB of the B component is set to AdB=255/{ _GB ·(A _UB +3σB)}. Further, when {G _B ·(A _UB +3σB)}≦255, AdB=1.

Let _AUG be the average value of the G component signal values in the UV light correction table 58 before correction, and let σG be the standard deviation of the G component signal values. When {G _G ·(A _UG +3σG)}>255, the adjustment value AdG of the G component is set to AdG=255/{G _G ·(A _UG +3σG)}. Further, when {G _G ·(A _UG +3σG)}≦255, AdG=1.

The average value of the signal values of the R component in the UV light correction table 58 before correction is defined as _AUR , and the standard deviation of the signal values of the R component is defined as σR. When {G _R ·(A _UR +3σR)}>255, the adjustment value AdR of the R component is set to AdR=255/{G _R ·(A _UR +3σR)}. Further, if {G _R ·(A _UR +3σR)}≦255, AdR=1.

The adjustment value adj can be the minimum value of AdB, AdG, and AdR.

Using the corrected UV light correction table 58, the control unit 51 can perform shading correction on the UV light image data obtained by photographing with UV light (UV light source unit 10). If the pixel value of the image before correction is Iin, the pixel value of the image after correction is Iout, and K is a constant (white reference value), the correction formula for shading correction is Iout=Iin・K/(after correction) UV light correction table 58).

Next, the influence of environmental factors on captured images will be explained. Below, the influence of external light will be explained as an example of environmental factors.

FIG. 7 is a diagram showing the influence of external light in a comparative example. A comparative example shows a case where a UV light correction table 58 before correction is used. It is assumed that a captured image of the medium to be authenticated is obtained by irradiating the medium to be authenticated with UV light. The photographed image is a scanner image subjected to shading correction using the UV light correction table 58 before correction. This figure schematically shows an example of the spectrum of each RGB component in each of predetermined areas A and B of a photographed image when there is no external light and no external light enters the surface of the medium when scanning the medium with a scanner device. .

When scanning a medium with a scanner device, if external light enters, for example, a predetermined region B on the surface of the medium, RGB uniform and minute white light, the spectrum of each RGB component in the predetermined region A will be the same as in the case without external light. It is. However, the spectrum of each RGB component in the predetermined area B where external light has entered actually only increases uniformly for each RGB color, so the balance of RGB does not change, but the UV light correction table before correction Since the signal value (correction table value) of the R component of 58 is small, only the small component is greatly corrected (corrected by the reciprocal of the correction table value), and the R component of external light is corrected to be strong. Therefore, the intensity of the RG component in the absence of external light and the intensity of the RG component in the presence of external light are reversed. Therefore, the color tone of the photographed image changes due to the influence of external light.

The example in FIG. 7 shows a case where a part of the captured image is affected by external light, but similarly when the entire captured image is affected by external light, the R component of the external light becomes strong and the captured image The color tone of the entire image changes. Note that the overall distribution of RGB components in the predetermined region B shifts slightly to the right with external light compared to without external light.

FIG. 8 is a diagram showing the influence of external light in this embodiment. When there is no external light, it is the same as the comparative example in FIG. When external light enters a predetermined region B on the surface of the medium when scanning a medium with a scanner device, the spectrum of each RGB component in the predetermined region A is the same as in the case without external light. Furthermore, since the balance of the RGB components in the corrected UV light correction table 58 is relatively uniform, the spectrum of each RGB component in the predetermined region B where the external light has entered is determined by the specific component ( For example, R, G, B) are not greatly corrected. Therefore, the spectrum of each RGB component in the absence of external light is equivalent to the spectrum of each RGB component in the presence of external light, and changes in color can be suppressed.

The example in FIG. 8 shows a case where a part of the captured image is affected by external light, but similarly, when the entire captured image is affected by external light, a specific component of the external light (e.g. , R, G, B) are not greatly corrected, and changes in the color tone of the entire captured image can be suppressed. Note that the overall distribution of RGB components in the predetermined region B shifts slightly to the right with external light compared to without external light.

As described above, the control unit 51 uses a visible light correction table for correcting image data obtained by photographing in a visible light environment and predetermined light image data obtained by photographing in a predetermined light environment. Obtain a predetermined light correction table for correction, calculate a correction coefficient based on the obtained visible light correction table and predetermined light correction table, and correct the predetermined light correction table based on the calculated correction coefficient. can do.

FIG. 9 is a diagram showing an example of a processing procedure of the scanner device 100. For convenience, the main body of processing will be described as the control unit 51 below. The control unit 51 acquires the visible light correction table 57 and the UV light correction table 58 (S11), calculates the average value of the signal values for each RGB in the visible light correction table 57 (S12), and calculates the average value of the signal values for each RGB in the visible light correction table 57. The average value of the signal values for each RGB in the correction table 58 is calculated (S13).

The control unit 51 calculates a magnification of the average value for each RGB based on the calculated average value (S14), and calculates an adjustment value for rounding (S15). Refer to FIG. 6 for calculation of the adjustment value. The control unit 51 calculates a correction coefficient for each RGB based on the calculated magnification and adjustment value (S16). See FIG. 4 for calculation of the correction coefficient.

The control unit 51 corrects the UV light correction table 58 using the calculated correction coefficient (S17), and ends the process. Refer to FIG. 5 for the correction of the UV light correction table 58.

According to the present embodiment, it is possible to suppress changes in color of a photographed image. Further, in a general scanner device, there is no need to separately provide a sensor for detecting external light, and the influence of external light can be reduced. Since it is possible to reduce the influence of external light on the photographed image of the medium for authentication, it is expected that the accuracy of authentication using the photographed image will be improved.

(Additional note 1) The computer program includes a visible light correction table for correcting image data obtained by shooting in a visible light environment and predetermined light image data obtained by shooting in a predetermined light environment. A correction coefficient is calculated based on a predetermined light correction table for correcting the predetermined light correction table, and the predetermined light correction table is corrected based on the calculated correction coefficient.

(Additional Note 2) In the computer program of Addendum 1, the computer program causes the computer to calculate a correction coefficient based on statistical values of signal values held in each of the visible light correction table and the predetermined light correction table; A process of correcting the signal value held in the predetermined light correction table based on the correction coefficient is executed.

(Supplementary note 3) The computer program in the computer program of Supplementary note 1 or 2 causes the computer to execute a process of adjusting the correction coefficient with a predetermined adjustment value.

(Additional Note 4) In the computer program according to any one of Appendices 1 to 3, the computer program calculates statistical values and deviation values of the signal values held in the correction table for predetermined light, and calculates the calculated statistical values and deviation values. A process of calculating an adjustment value based on the deviation value and adjusting the correction coefficient using the calculated adjustment value is executed.

(Additional Note 5) In any of the computer programs set forth in Appendix 1 to Appendix 4, the computer program causes the computer to calculate the correction coefficient for each of R (red), G (green), and B (blue). Let it run.

(Supplementary Note 6) In the computer program according to any one of Supplementary Notes 1 to 5, the predetermined light includes UV light.

(Additional Note 7) The computer program in any one of Appendixes 1 to 6 causes the computer to execute a process of performing shading correction using the predetermined light correction table corrected for the predetermined light image data. .

(Additional Note 8) The image processing device includes a visible light correction table for correcting image data obtained by shooting in a visible light environment and a correction table for correcting predetermined light image data obtained by shooting in a predetermined light environment. A calculation unit that calculates a correction coefficient based on a correction table for a predetermined light to perform the correction, and a correction unit that corrects the correction table for a predetermined light based on the calculated correction coefficient.

(Additional Note 9) The image reading device includes a light source unit that emits predetermined light, an imaging unit, and a control unit, and the imaging unit is configured to capture images obtained by photographing under a predetermined light environment irradiated by the light source unit. The predetermined light image data is output to the control unit, and the control unit includes a visible light correction table for correcting image data obtained by photographing in a visible light environment and a visible light correction table for correcting the predetermined light image data. Calculate a correction coefficient based on the predetermined light correction table of , correct the predetermined light correction table based on the calculated correction coefficient, and use the predetermined light correction table corrected for the predetermined light image data. Correct shading.

(Additional Note 10) The image processing method includes a visible light correction table for correcting image data obtained by shooting in a visible light environment and a correction table for correcting predetermined light image data obtained by shooting in a predetermined light environment. A correction coefficient is calculated based on a predetermined light correction table for the purpose of the correction, and the predetermined light correction table is corrected based on the calculated correction coefficient.

Items described in each embodiment can be combined with each other. Moreover, the independent claims and dependent claims recited in the claims may be combined with each other in any and all combinations, regardless of the form in which they are cited. Further, although the scope of claims uses a format in which claims refer to two or more other claims (multi-claim format), the invention is not limited to this format. It may be written using a multi-claim format that cites at least one multi-claim.

10 Light source section for UV light 20 Light source section for visible light 30 Imaging section 50 Image processing section 51 Control section 52 Interface section 53 Memory 54 Output section 55 Storage section 56 Computer program 57 Correction table for visible light 58 Correction table for UV light

Claims (10)

to the computer,
A visible light correction table for correcting image data obtained by photographing in a visible light environment and a predetermined light correction table for correcting predetermined light image data obtained by photographing in a predetermined light environment. Calculate the correction coefficient based on
correcting the predetermined light correction table based on the calculated correction coefficient;
A computer program that performs a process. to the computer,
Calculating a correction coefficient based on statistical values of signal values held by each of the visible light correction table and the predetermined light correction table,
correcting the signal value held in the predetermined light correction table based on the calculated correction coefficient;
The computer program according to claim 1, which causes the computer program to execute a process. to the computer,
adjusting the correction coefficient with a predetermined adjustment value;
The computer program according to claim 1 or 2, which causes the computer program to execute a process. to the computer,
Calculating statistical values and deviation values of signal values held by the predetermined light correction table,
Calculate the adjustment value based on the calculated statistical value and deviation value,
adjusting the correction coefficient with the calculated adjustment value;
The computer program according to claim 1 or 2, which causes the computer program to execute a process. to the computer,
Calculating the correction coefficient for each of R (red), G (green), and B (blue);
The computer program according to claim 1 or 2, which causes the computer program to execute a process. The predetermined light includes UV light.
The computer program according to claim 1 or claim 2. to the computer,
performing shading correction using a predetermined light correction table corrected for the predetermined light image data;
The computer program according to claim 1 or 2, which causes the computer program to execute a process. A visible light correction table for correcting image data obtained by photographing in a visible light environment and a predetermined light correction table for correcting predetermined light image data obtained by photographing in a predetermined light environment. a calculation unit that calculates a correction coefficient based on the
a correction unit that corrects the predetermined light correction table based on the calculated correction coefficient;
Image processing device. A light source unit that emits predetermined light, an imaging unit, and a control unit,
The imaging unit includes:
outputting predetermined light image data obtained by photographing under a predetermined light environment irradiated by the light source unit to the control unit;
The control unit includes:
Calculating a correction coefficient based on a visible light correction table for correcting image data obtained by photographing in a visible light environment and a predetermined light correction table for correcting the predetermined light image data;
correcting the predetermined light correction table based on the calculated correction coefficient;
performing shading correction using a predetermined light correction table corrected for the predetermined light image data;
Image reading device. A visible light correction table for correcting image data obtained by photographing in a visible light environment and a predetermined light correction table for correcting predetermined light image data obtained by photographing in a predetermined light environment. Calculate the correction coefficient based on
correcting the predetermined light correction table based on the calculated correction coefficient;
Image processing method.

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