Tone-preserving contrast enhancement in images using rational tone mapping and constrained optimization

In this paper, we propose tone-preserving contrast enhancement in images using rational tone mapping and constrained optimization. We first perform spike-removed histogram equalization (SRHE) for contrast enhancement to avoid over-enhancement caused by the conventional HE. We conduct rational tone mapping (RTM) with low-complexity to preserve the original tone continuity. Then, we formulate a constrained optimization problem consisting of the contrast enhancement and tone-preserving terms. By minimizing the objective function, we find the best trade-off between the two conflicting terms. Experimental results demonstrate that the proposed method enhances contrast in images while successfully preserving details, and outperforms state-of-the-art ones in both subjective and objective assessments.