Fast centre-surround contrast modification

A new algorithm for fast contrast modification of standard dynamic range (SDR) images (8 bits/ channel) is presented. Its thrust is to enhance the contrast in the under-/over-exposed regions of SDR images, caused by the low dynamic range of the capturing device. It is motivated by the attributes of the shunting centre-surround cells of the human visual system. The main advantage of the proposed algorithm is its O(N) complexity which results in very fast execution, even when executed on a conventional personal computer (0.2 s/frame for a 640 x 480 pixel resolution on a 3 GHz Pentium 4). Thus, it moderately increases the computational burden if it is used as a pre-processing stage for other image processing algorithms. The proposed method is compared with other established algorithms, which can enhance the contrast in the under-/over-exposed regions of SDR images: the multi-scale Retinex with colour rendition, the McCann Retinex (McCann99), the rational mapping function and the automatic colour equalisation. The results obtained by this comparison indicate that the proposed algorithm exhibits at least comparable results in contrast modification tasks to the other algorithms, in significantly reduced execution times.