Discussion of medical x-ray picture normalization

There is great significance in comparing medical x-ray pictures, which are taken in different periods. For the orthopaedics surgeon comparing the density of bone is one important way of clinical diagnosis. Some persons think that if these orthopaedics pictures are processed by histogram normalization their gray level and pseudo color can be compared directly. But for one picture we know that the gray distribution is different between the original picture and the processed picture. Comparing these pictures is not authentic. In this paper we discuss that subject and describe the basis of histogram normalization. The distribution on original x-ray pictures and processed pictures is provided. The methods to compare different pictures are mentioned.