Patent ID: 7239430

Claim:
A method of processing image data to determine the frequency a binary halftone, the method comprising: receiving a block of pixels; applying a function to the block of pixels, the function being given by A ′ ⁡ ( kx , ky ) = ∑ x = 1 , y = 1 Nx , Ny ⁢ ⁢ P ⁡ ( x , y ) ⋀ P ⁡ ( x + kx , y + ky ) where P(x,y) represents a pixel intensity function at pixel position x,y in the image data, x and y define a selected pixel position, and kx and ky are selected shifts in pixel position applied to the pixel intensity function, and Nx and Ny define the pixel range over which the function is evaluated; identifying locations of local minimums in A′(kx,ky); and determining a halftone frequency f based upon locations of the local minimums.