Dry-cured Iberian pig products are some of the most valuables meat products in Spain. Visually discernible features of fat and lean, such as marbling, have an effect on the acceptability of these products. Marbling properties include the amount and spatial distribution of intramuscular fat streaks. Thresholding techniques are the simplest and most widely used for image segmentation, but pay no attention to all spatial information on the images. In this paper we propose another method to evaluate fat level in loin and make a three-dimensional visualization with only the isolated fat in order to give knowledge about fat distribution, and about width of fat streaks, helping the experts in food science to analyze marbling. In order for fat isolation we apply a method based on a pyramidal decomposition of images combined with region-growing techniques. 3D reconstruction is obtained by marching cubes algorithm.