Ultrasound is an important way of physical examination nowadays. Many literatures tried to find a quantified standard for diagnosing ultrasonic images; however, they neglected the effect of scan-conversion on image textures. This paper provides a preprocessing method, which practically conforms to the ultrasound image formats, and then compares the effect of the preprocessing method. Several images of sponges were used to evaluate the effect of the preprocessing because of their nearly homogeneous texture. It was found that the spread of standard deviations of the extracted features got narrower, at best 4 times, with preprocessing than that without preprocessing. The back-scan conversion is indispensable for the analysis of ultrasound images using features sensitive to depth and orientation.