Ranking-Based Salient Object Detection and Depth Prediction for Shallow Depth-of-Field

Shallow depth-of-field (DoF), focusing on the region of interest by blurring out the rest of the image, is challenging in computer vision and computational photography. It can be achieved either by adjusting the parameters (e.g., aperture and focal length) of a single-lens reflex camera or computational techniques. In this paper, we investigate the latter one, i.e., explore a computational method to render shallow DoF. The previous methods either rely on portrait segmentation or stereo sensing, which can only be applied to portrait photos and require stereo inputs. To address these issues, we study the problem of rendering shallow DoF from an arbitrary image. In particular, we propose a method that consists of a salient object detection (SOD) module, a monocular depth prediction (MDP) module, and a DoF rendering module. The SOD module determines the focal plane, while the MDP module controls the blur degree. Specifically, we introduce a label-guided ranking loss for both salient object detection and depth prediction. For salient object detection, the label-guided ranking loss comprises two terms: (i) heterogeneous ranking loss that encourages the sampled salient pixels to be different from background pixels; (ii) homogeneous ranking loss penalizes the inconsistency of salient pixels or background pixels. For depth prediction, the label-guided ranking loss mainly relies on multilevel structural information, i.e., from low-level edge maps to high-level object instance masks. In addition, we introduce a SOD and depth-aware blur rendering method to generate shallow DoF images. Comprehensive experiments demonstrate the effectiveness of our proposed method.