To solve problems such as uneven illumination and fuzzy details of rock surface edge are shown in digital borehole images

an adaptive image enhancement algorithm is proposed. Firstly

homomorphic filtering is used to original image. Then

the original image and the filtered image are decomposed by Curvelet transform while the coefficient histogram matching algorithm is used for the low frequency subband of the two. The histogram of the former is matched with the latter to improve effect of illumination unevenness. Next

the high-frequency subband is filtered by an adaptive threshold and is enhanced with an adaptive enhancement function. Finally

the enhanced image is reconstructed by Curvelet inverse transform. The experimental results show that the illumination unevenness is improved effectively and the edge information is enhanced obviously. Certain advantages compared with other algorithms are shown in both subjective and objective evaluation indices.