Unsupervised depth estimation from a single image is a very attractive technique with several implications in robotic, autonomous navigation, augmented reality and so on. This topic represents a very challenging task and the advent of deep learning enabled to tackle this problem with excellent results. However, these architectures are extremely deep and complex. Thus, real-time performance can be achieved only by leveraging power-hungry GPUs that do not allow to infer depth maps in application fields characterized by low-power constraints. To tackle this issue, in this paper we propose a novel architecture capable to quickly infer an accurate depth map on a CPU, even of an embedded system, using a pyramid of features extracted from a single input image. Similarly to state-of-the-art, we train our network in an unsupervised manner casting depth estimation as an image reconstruction problem. Extensive experimental results on the KITTI dataset show that compared to the top performing approach our network has similar accuracy but a much lower complexity (about 6 of parameters) enabling to infer a depth map for a KITTI image in about 1.7 s on the Raspberry Pi 3 and at more than 8 Hz on a standard CPU. Moreover, by trading accuracy for efficiency, our network allows to infer maps at about 2 Hz and 40 Hz respectively, still being more accurate than most state-of-the-art slower methods. To the best of our knowledge, it is the first method enabling such performance on CPUs paving the way for effective deployment of unsupervised monocular depth estimation even on embedded systems.
Although depth estimation from images has a long history in computer vision @cite_28 , methods using a single image are much more recent and mostly based on machine learning techniques. These works and other efficient end-to-end approaches for dense prediction tasks such as optical flow are relevant to our work.
@cite_28
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Depth estimation from a single image is a fundamental problem in computer vision. In this paper, we propose a simple yet effective convolutional spatial propagation network (CSPN) to learn the affinity matrix for depth prediction. Specifically, we adopt an efficient linear propagation model, where the propagation is performed with a manner of recurrent convolutional operation, and the affinity among neighboring pixels is learned through a deep convolutional neural network (CNN). We apply the designed CSPN to two depth estimation tasks given a single image: (1) Refine the depth output from existing state-of-the-art (SOTA) methods; (2) Convert sparse depth samples to a dense depth map by embedding the depth samples within the propagation procedure. The second task is inspired by the availability of LiDAR that provides sparse but accurate depth measurements. We experimented the proposed CSPN over the popular NYU v2 [1] and KITTI [2] datasets, where we show that our proposed approach improves not only quality (e.g., 30 more reduction in depth error), but also speed (e.g., 2 to 5 ( ) faster) of depth maps than previous SOTA methods. The codes of CSPN are available at: https: github.com XinJCheng CSPN. Computational depth estimation is a central task in computer vision and graphics. A large variety of strategies have been introduced in the past relying on viewpoint variations, defocus changes and general aperture codes. However, the tradeoffs between such designs are not well understood. Depth estimation from computational camera measurements is a highly non-linear process and therefore most research attempts to evaluate depth estimation strategies rely on numerical simulations. Previous attempts to design computational cameras with good depth discrimination optimized highly non-linear and nonconvex scores, and hence it is not clear if the constructed designs are optimal. In this paper we address the problem of depth discrimination from J images captured using J arbitrary codes placed within one fixed lens aperture. We analyze the desired properties of discriminative codes under a geometric optics model and propose an upper bound on the best possible discrimination. We show that under a multiplicative noise model, the half ring codes discovered by [1] are near-optimal. When a large number of images are allowed, a multiaperture camera [2] dividing the aperture into multiple annular rings provides near-optimal discrimination. In contrast, the plenoptic camera of [5] which divides the aperture into compact support circles can achieve at most 50 of the optimal discrimination bound. Estimating depth from a single image is a very challenging and exciting topic in computer vision with implications in several application domains. Recently proposed deep learning approaches achieve outstanding results by tackling it as an image reconstruction task and exploiting geometry constraints (e.g., epipolar geometry) to obtain supervisory signals for training. Inspired by these works and compelling results achieved by Generative Adversarial Network (GAN) on image reconstruction and generation tasks, in this paper we propose to cast unsupervised monocular depth estimation within a GAN paradigm. The generator network learns to infer depth from the reference image to generate a warped target image. At training time, the discriminator network learns to distinguish between fake images generated by the generator and target frames acquired with a stereo rig. To the best of our knowledge, our proposal is the first successful attempt to tackle monocular depth estimation with a GAN paradigm and the extensive evaluation on CityScapes and KITTI datasets confirm that it enables to improve traditional approaches. Additionally, we highlight a major issue with data deployed by a standard evaluation protocol widely used in this field and fix this problem using a more reliable dataset recently made available by the KITTI evaluation benchmark. In this paper we address three different computer vision tasks using a single basic architecture: depth prediction, surface normal estimation, and semantic labeling. We use a multiscale convolutional network that is able to adapt easily to each task using only small modifications, regressing from the input image to the output map directly. Our method progressively refines predictions using a sequence of scales, and captures many image details without any superpixels or low-level segmentation. We achieve state-of-the-art performance on benchmarks for all three tasks.