A method and application specific integrated circuit for determining focus for an image capture system using scene content within an image, including the steps of: acquiring, from the image, image data having different focus positions; dividing the image data into sub-images; calculating a sub-image sharpness value for each sub-image; calculating an image sharpness value for each focus position using the sub-image sharpness values; plotting the sharpness values versus the focus position; fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and determining the focus of the image capture system from a point on the curve.