Keywords: 
• sediment core /
• Xray radiograph /
• gray value /
• grainsize /
• influencing factor

Abstract: Xray radiograph of sedimentary core contains much information, including sedimentary texture, density, structure, etc. We can quickly extract the information of climate and environment changes from sedimentary core by using digital image processing method, witch may be a powerful research tools to exploring highresolution sedimentary records and palaeoenvironment evolution. Based on the matlab software platform, we obtained the Xray images of the sediment core taken from the subaqueous Yangtze River delta and changed them into digital gray images then for extracting their gray values. Combined with the sediment properties in the core such as grain size parameters, influencing factors of the digital gray values were discussed. The results indicate that the gray values of sediment core are influenced comprehensively by sediment composition, texture and structure, with being dominantly influenced by sediment grainsize. There is a good linear relationship between mean grainsize and gray value. Furthermore, there is a positive correlation between sand, silt and gray value. In contrary, it is of a good negative relationship between clay and gray value. Generally, the Xray image gray value of sediment core may be an ideal proxy of comprehensive sedimentary records.