1. Field of the Invention
The present invention generally relates to an auto-contrast enhancement system, and more particularly to a human visual system (HVS)-based auto-contrast enhancement system with side-effect suppression.
2. Description of Related Art
Image enhancement is widely applied to refine images with low contrast or images captured in non-ideal lighting conditions. Traditional contrast enhancement algorithms usually suffer from over-enhancement, which makes images look unnatural and amplifies noise.
Histogram enhancement (HE) is the most common method for improving contrast enhancement. With HE, the intensities of an image are distributed more uniformly to achieve better contrast. The overall complexity of HE-based algorithms is low compared to that of other methods. However, HE can easily induce over-enhancement, noise amplification, fine detail loss, or making the image look unnatural.
Moreover, human eyes cannot easily distinguish the intensity variation in a saturated region. The saturation region is generally regarded as a smooth region that contains no texture information. However, slight intensity variation and random distributed hue are frequently hidden inside the saturation region. If contrast enhancement is applied directly, noise amplification will be strong in this region.
Therefore, a proper enhancement level and side-effect reduction methods are crucial in a contrast enhancement system.