Image fractal dimension is a useful measure which can be used to characterize features of images. In this paper

three new methods—gray scale surface fractal

curse fractal

pixel fractal to estimate the fractal dimension of thermal image are proposed. The practices indicate that gray scale surface fractal can open out the unitary fractal character of thermal image

curse fractal can contrast and research the thermal radiation character of typical area and pixel fractal can give a quantitative description of variety grades of thermal radiation. After the researching of general fractal theory

the related characters of those methods are discussed. As an example

Shanghai City thermal image is given and the signification of experimental result is analyzed lastly.