The method of determining a focus measure from an image includes detecting one or more edges in the image by processing the image with one or more first order edge detection kernels adapted to reject edge phasing effects. A first measure of the strength of each of the edges, and the contrast of each of the edges may be determined. The method may include normalizing the first measure of the strength of each of the edges by the contrast of each of the edges to obtain a second measure of the strength of each of the edges, and resealing the second measure of the strength of each of the edges. The method may also include selecting one or more of the edges from the image in accordance with the second measure of their strengths, and calculating the focus measure from the second measure of the strengths of the selected edges.