High dynamic range image compression based on the multi-peak S-shaped tone curve.

Tone mapping methods aim to compress the high dynamic range (HDR) images so that they can be displayed on common devices. The tone curve plays a key role in many tone mapping methods, which can directly adjust the range of the HDR image. The S-shaped tone curves can produce impressive performances due to their flexibility. However, the conventional S-shaped tone curve in tone mapping methods is single and had the problem of excessive compressing of the dense grayscale areas, resulting in the loss of details in this area, and insufficient compressing of the sparse grayscale areas, resulting in low contrast of tone mapped image. This paper proposes a multi-peak S-shaped (MPS) tone curve to address these problems. Specifically, the grayscale interval of the HDR image is divided according to the significant peak and valley distribution of the grayscale histogram, and each interval is tone mapped by an S-shaped tone curve. We further propose an adaptive S-shaped tone curve based on the luminance adaptation mechanism of the human visual system, which can effectively reduce the compression in the dense grayscale areas and increase the compression in the sparse grayscale areas, preserving details while improving the contrast of tone mapped images. Experiments show that our MPS tone curve replaces the single S-shaped tone curve in relevant methods for better performance and outperforms the state-of-the-art tone mapping methods.