Patent ID: 8564712

Claim:
An apparatus for determining blur difference between captured images at different focus positions, comprising: a processor configured for processing images; and programming executable on said processor for determining blur difference between at least a first focus position in a first image and a second focus position in a second image by performing steps comprising: modeling blur change as a point spread function from the first focus position to the second focus position; approximating said point spread function as a series of convolutions; performing a first portion of said series of convolutions in response to using a first kernel having a first variance; and performing the remaining convolutions of said series of convolutions in response to using at least a second kernel having at least a second variance which is smaller than said first kernel variance to determine blur difference between said first image and said second image; wherein utilizing a combination of said first kernel and said second kernel during convolutions provides an accuracy of blur difference determination of said second kernel with a computational cost approaching performing convolutions with said first kernel when determining blur difference between said first image and said second image.