Patent ID: 6542629
Filing Date: 2003-04-01
Classification: H04N

Abstract:
A method for determining whether an image area contains a security mark,comprising:scanning the image area to produce original pixels in L,a,b color space; filtering the b-component of the scanned image area to attenuate any overlaid lines and to produce smoothed b pixels by computing an average b pixel value; determining a maximum pixel density and a minimum pixel density of the smoothed b pixels in the scanned image area; and calculating the difference between the maximum pixel density and the minimum pixel density, wherein if the difference is greater than a threshold value, a security mark may be present in the image area; wherein the average b pixel value is computed in a x by y pixel sub-area of the scanned image area according to the relationship: bij(avg)=Â¼(biâˆ’l,jl+biâˆ’lj+bijâˆ’l+bi,j), where bij(avg) is the smoothed b(avg) component of the ith scan line and jth pixel.