1. A method for determining a bedding surface from an azimuthal image made from a signal provided by a logging tool placed in a cylindrical wellbore, said method comprising: determining, using a computer and based on minimum variance, a best sine wave in the image at each of a plurality of selected depths; computing contrast at each selected depth along the best sine wave in the image; and locating one or more bedding surface boundaries at one or more depths with highest contrasts.