Enhancement of Low Light Level Images with Regression Methods

The enhancement of Low Light Level Images (LLLIs) is challenging, due to their poor brightness and low contrast. Traditional enhancement methods fail to perform satisfactorily when applying to LLLIs. In this paper, we formulate the LLLI enhancement as a regression problem: the regressor maps patches of input image to enhanced patches, and the regression function is estimated by learning from sample images. We implemented two efficient regression methods based on piece-wise linear regression: locally linear regression and random forest (RF). Meanwhile, we designed a new split function considering reconstruction error for random forest method. Experimental results on an open dataset and practical LLLIs demonstrate the effectiveness of our methods. The RF regression method performs superiorly in both enhancement quality and computation efficiency.