**3.3 Image display and image enhancement**

The rasterized geochemical image (**Figure 7**) may be carried out by image enhancement. For example, if expanding or changing the value field range of gray scale, or changing the distributional pattern of gray value, the sharpness of image may be enhanced. Some methods, e.g., direct gray transformation, histogram equalization, etc. may be adopted. And in order to make the edge of the image bright and clear, the image filtering method could be used. The image formed from geochemical data can constitute the ternary RGB image, e.g., the formed K2O-Na2O-SiO2 image (**Figure 8**); it is known that K-Na-Si ingredient can be used to judge the composition of rocks.
