1. A method of determining a depth value of a fine structure pixel in a first image of a scene using a second image of the scene, the method comprising: determining a gradient orientation for each of a plurality of fine structure pixels in the first image; generating difference images from the second image and a series of blurred images formed from said first image, each said difference image corresponding to one of a plurality of depth values; smoothing each of the difference images, in accordance with the determined gradient orientations, to generate smoothed difference images having increased coherency of fine structure; selecting, for each of a plurality of fine structure pixels in the first image, one of said smoothed difference images; and determining the depth value of the fine structure pixel corresponding to the selected smoothed difference image.