# US 12,118,701 B2 · Method and system to characterize and monitor the sharpness of a digital imaging system

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- Number: US 12,118,701 B2
- Document ID: US12118701B2
- Status: Granted
- Kind: B2
- Application number: 17/421,981
- Filed: 2020-01-08
- Published: 2022-04-14
- Granted: 2024-10-15
- Earliest claimed: 2019-01-09
- Assignees: Agfa NV
- Applicants: Agfa NV
- Inventors: Marc Cresens
- Web page: https://patentgrep.com/patent/US12118701B2

## CPC

- G06T 7/0002: {Inspection of images, e.g. flaw detection}
- G01N 23/04: and forming images of the material
- G01N 23/083: the radiation being X-rays
- G06T 5/73: Deblurring; Sharpening
- G06T 7/97: {Determining parameters from multiple pictures (depth or shape recovery from multiple images G06T7/55; stereo camera calibration G06T7/85)}
- G01N 2223/04: and measuring absorption
- G01N 2223/40: Imaging
- G06T 2207/10116: X-ray image
- G06T 2207/20032: Median filtering
- G06T 2207/30168: Image quality inspection
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

The invention is related to a method for automatic selection and pre-processing of digital images that comprise the necessary amount of Transfer function modulated quantum-noise to apply a mathematical sharpness calculation method for calculation of a sharpness parameter of the digital imaging system. Suitable images for the method are selected from the pool of available images acquired by the digital imaging system during daily operation.

## Claims

### Claim 1

A method to determine the sharpness of a digital imaging system, comprising the steps of:
receiving at least one digital image that is acquired on said digital imaging system as input, said digital image comprising transfer function modulated quantum-noise,
selecting from said digital images at least one selected image I[X,Y] that comprises a contiguous and substantially equally exposed image area,
determining at least one ROI in said selected image I[X,Y] that comprises a contiguous and homogeneously exposed image area,
assigning said ROI as a spatial sample area R[x′,y′] in a calculation method to determine a point spread function PSFxy of said digital image detector system, comprising the steps of:
acquiring a set of image pixel values comprising transfer function modulated quantum noise in a spatial sample area R[x′,y′] of a digital image I[X,Y] that is substantially equally exposed,
determining a peripheral sensing kernel ki×j wherein the pixel values matrix k[x,y] is centred on a central pixel,
calculating for each local image pixel L(x,y) in said sample area R[x′,y′]:
a pixel deviation ΔL between a pixel value at pixel L(x,y) and its background value BL, wherein BL is defined as the median or mean value of all values in a background region centred on said local pixel L(x,y), and
a median or mean pixel deviation ΔNd of all background normalized neighbouring pixels values Nd(1→n)=Nd1, Nd2, . . . , Ndn that are located at the same distance d from said local image pixel L(x,y) and that are normalized against their respective background value BNd(i), wherein BNd(i) is defined as the median value of all pixel values in a background region BNd(i) centred on said neighbouring pixels Nd(i),
calculating an autocorrelation peak value by autocorrelating ΔL for all local pixels L(x,y) in the sample area R[x′,y′], as
AutoCorrelationPeak(R[x′,y′])=ΣΣx=0,y=0R[x′,y′]ΔL2
calculating PSFxy as
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for all values of d from a central pixel as defined in peripheral sensing kernel ki×j, where Correlation(ΔL,ΔNd) is obtained by correlating ΔL with ΔNd for a distance d from local pixel L(x,y), and by summing the results over all pixels in the sample area R[x′,y′],
Correlation(ΔL,ΔNd)=ΣΣx=0,y=0R[x′,y′]ΔL·ΔNd.

### Claim 2 (depends on 1)

The method according to claim 1, wherein said ROI in said selected image I[X,Y] was contiguous and directly exposed by an X-ray source.

### Claim 3 (depends on 2)

The method according to claim 2, wherein said point spread function PSFxy is converted into a sharpness parameter, such as an MTF function.

### Claim 4 (depends on 3)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 3.

### Claim 5 (depends on 3)

A computer readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 3.

### Claim 6 (depends on 2)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 2.

### Claim 7 (depends on 2)

A computer readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 2.

### Claim 8 (depends on 1)

The method according to claim 1, wherein all exposure values of all pixels in said ROI in said selected image I[X,Y] exceed a predetermined threshold value.

### Claim 9 (depends on 8)

The method according to claim 8, wherein said point spread function PSFxy is converted into a sharpness parameter, such as an MTF function.

### Claim 10 (depends on 9)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 9.

### Claim 11 (depends on 9)

A computer readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 9.

### Claim 12 (depends on 8)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 8.

### Claim 13 (depends on 8)

A computer readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 8.

### Claim 14 (depends on 1)

The method according to claim 1, wherein said point spread function PSFxy is converted into a sharpness parameter, such as an MTF function.

### Claim 15 (depends on 14)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 14.

### Claim 16 (depends on 14)

A computer readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 14.

### Claim 17 (depends on 1)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 1.

### Claim 18 (depends on 1)

A computer readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of claim 1.