In this paper, a new image enhancement approach is proposed, which has the ability to improve the gridding results in DNA microarray analysis. The proposed approach is implemented as a conditional sub-block bi-histogram equalization (CSBE). This is accomplished by first, decomposing an input image into a number of m x n sub-blocks. Second, the threshold of each sub-block is determined independently. Third, the sub-block is divided into two sub-images based on the threshold. Fourth, only pixels having value greater than the threshold are histogram equalized, and the two sub-images are then recombined. The proposed method is tested on various DNA microarray images, giving excellent results, compared to existing methods.