Patent ID: 11915402
Assignee: AGFA NV
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. A method to determine a point spread function PSFxy of a 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] wherein no structural objects are present that cause image signal variations against the recorded background of more than 1%,
determine 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 val(BL), wherein val(BL) is defined as the median or mean value of all values in a background region BL centred on said local pixel L(x, y), and
a median or mean pixel deviation ΔNd of all background normalized neighbouring pixels values val(Nd(1→n))=val(Nd1), val(Nd2), . . . , val(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 val(BNd(i)), wherein val(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, PSF
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      Correlation
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        ), for all values of distance 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.