Constant time O(1) contextual and variational contrast enhancement with integral histogram

This paper proposes an efficient method for contrast enhancement using various inter-pixel contextual information. In order to make full use of the contextual and variational information, a two-dimensional (2D) histogram of the input image must be generated using mutual relationship between each pixel and the corresponding neighbourhoods, while the additional execution time is consumed due to the joint spatial and range filtering. In order to solve this problem, a constant time O(1) 2D target histogram (CTTH) method based on the characteristic of integral histogram is proposed to generate 2D histogram for contrast enhancement. Constant time means that the execution time of the joint spatial procedure remains same even if the mask size becomes very large. Experimental results demonstrate the efficiency of the proposed method by the arithmetic evaluation and a report of time consumption.