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; generating smoothed difference images by applying oriented smoothing to each of the difference images with an angle of the oriented smoothing being determined according to the determined gradient orientation, the smoothed difference images having increased coherency of fine structure; selecting, for each of the plurality of fine structure pixels in the first image, one of the generated smoothed difference images having a minimum smoothed blur difference value at a corresponding pixel of the generated smoothed difference image; and determining the depth value of the fine structure pixel corresponding to the selected smoothed difference image.