A new shadow removal method using color-lines

Abstract

In this paper, we present a novel method for single-image shadow removal. From the observation of images with shadow, we find that the pixels from the object with same material will form a line in the RGB color space as illumination changes. Besides, we find these lines do not cross with the origin due to the effect of ambient light. Thus, we establish an offset correction relationship to remove the effect of ambient light. Then we derive a linear shadow image model to perform color-line identification. With the linear model, our shadow removal method is proposed as following. First, perform color-line clustering and illumination estimation. Second, use an on-the-fly learning method to detect umbra and penumbra. Third, estimate the shadow scale by the statistics of shadow-free regions. Finally, refine the shadow scale by illumination optimization. Our method is simple and effective for producing high-quality shadow-free images and has the ability for processing scenes with rich texture types and non-uniform shadows.