Patent ID: 7376282
Filing Date: 2008-05-20
Classification: G06T

Abstract:
1. Method for descreening a digital image comprising: (a) selecting a cut-off frequency and designing therefrom a one-dimensional separable low pass filter (LP), one-dimensional separable low pass filter LP being a row vector having entries [Z (b) obtaining a two-dimensional separable filter (LPP) by performing the operation: LP* X LP, LP* being a column vector having the same entries as one-dimensional separable low pass filter LP, two-dimensional separable filter LPP having dimensions given by: {2n+1, 2n+1}, n is integer; (c) generating a two-dimensional contour plot for the two-dimensional filter LPP; (d) designing a one-dimensional separable high pass filter (LLP), one-dimensional separable high pass filter HP being a row vector having entries [Y (e) obtaining a two-dimensional separable filter (HPP) by performing the operation: LLP* X LLP, LLP* being a column vector having the same entries as one-dimensional separable high pass filter LLP, two-dimensional separable filter HPP having dimensions: {2m+1,2m+1}, m is integer; (f) generating a two-dimensional contour plot for the two-dimensional filter HPP; (g) generating a two-dimensional filter (ONE) when the two-dimensional contour plot for the two-dimensional separable filter LPP overlaps the two-dimensional contour plot for the two-dimensional separable filter HPP, two-dimensional filter ONE having the same dimensions of two-dimensional separable filter HPP with the only non-zero entry of value 1 being located at the center of two-dimensional filter ONE; (h) subtracting two-dimensional separable filter HPP from two-dimensional filter ONE to create matrix (HPPinv); (i) convolving two-dimensional separable filter LPP with matrix HPPinv to obtain non-separable filter DSCRN having dimensions: {2m+2n+1,2m+2n+1}; (j) generating a two-dimensional contour plot for non-separable filter DSCRN; and (k) selecting two-dimensional separable filter LLP and two-dimensional separable filter HHP when the two-dimensional contour plot for non-separable filter DSCRN is an approximation to a desired circular symmetry; (l) repeating (a)-(j) when the two-dimensional contour plot for non-separable filter DSCRN is not an approximation to a desired circular symmetry; (m) electronically applying the selected two-dimensional separable filter LLP to a digital image to produce a first filtered image; (n) electronically applying the selected two-dimensional separable filter HHP to a digital image to produce a second filtered image; and (o) subtracting the second filtered image from the first filtered image to, generate a descreened digital image.