Single Image Shadow Detection via Complementary Mechanism

In this paper, we present a novel shadow detection framework by investigating the mutual complementary mechanisms contained in this specific task. Our method is based on a key observation: in a single shadow image, shadow regions and non-shadow counterparts are complementary to each other in nature, thus a better estimation on one side leads to an improved estimation on the other, and vice versa. Motivated by this observation, we first leverage two parallel interactive branches to jointly produce shadow and non-shadow masks. The interaction between two parallel branches is to retain the deactivated intermediate features of one branch by introducing the negative activation technique, which could serve as complementary features to the other branch. Besides, we also apply identity reconstruction loss as complementary training guidance at the image level. Finally, we design two discriminative losses to satisfy the complementary requirements of shadow detection, i.e., neither missing any shadow regions nor falsely detecting non-shadow regions. By fully exploring and exploiting the complementary mechanism of shadow detection, our method can confidently predict more accurate shadow detection results. Extensive experiments on the three widely-used benchmarks demonstrate our proposed method achieves superior shadow detection performance against state-of-the-art methods with a relatively low computational cost.