In this letter, we propose a map-less visual navigation system for biped humanoid robots, which extracts information from color images to derive motion commands using deep reinforcement learning (DRL). The map-less visual navigation policy is trained using the Deep Deterministic Policy Gradients (DDPG) algorithm, which corresponds to an actor-critic DRL algorithm. The algorithm is implemented using two separate networks, one for the actor and one for the critic, but with similar structures. In addition to convolutional and fully connected layers, Long Short-Term Memory (LSTM) layers are included to address the limited observability present in the problem. As a proof of concept, we consider the case of robotic soccer using humanoid NAO V5 robots, which have reduced computational capabilities, and low-cost Red - Green - Blue (RGB) cameras as main sensors. The use of DRL allowed to obtain a complex and high performant policy from scratch, without any prior knowledge of the domain, or the dynamics involved. The visual navigation policy is trained in a robotic simulator and then successfully transferred to a physical robot, where it is able to run in 20 ms, allowing its use in real-time applications.

The aim of this work is to carry out a comparative study of face recognition methods that are suitable to work in unconstrained environments. The analyzed methods are selected by considering their performance in former comparative studies, in addition to be real-time, to require just one image per person, and to be fully online. In the study two local-matching methods, histograms of LBP features and Gabor Jet descriptors, one holistic method, generalized PCA, and two image-matching methods, SIFT-based and ERCF-based, are analyzed. The methods are compared using the FERET, LFW, UCHFaceHRI, and FRGC databases, which allows evaluating them in real-world conditions that include variations in scale, pose, lighting, focus, resolution, facial expression, accessories, makeup, occlusions, background and photographic quality. Main conclusions of this study are: there is a large dependence of the methods on the amount of face and background information that is included in the face's images, and the performance of all methods decreases largely with outdoor-illumination. The analyzed methods are robust to inaccurate alignment, face occlusions, and variations in expressions, to a large degree. LBP-based methods are an excellent election if we need real-time operation as well as high recognition rates.