Patrick Snape

Mnemonic Descent Method: A Recurrent Process Applied for End-to-End Face Alignment

Cascaded regression has recently become the method of choice for solving non-linear least squares problems such as deformable image alignment. Given a sizeable training set, cascaded regression learns a set of generic rules that are sequentially applied to minimise the least squares problem. Despite the success of cascaded regression for problems such as face alignment and head pose estimation, there are several shortcomings arising in the strategies proposed thus far. Specifically, (a) the regressors are learnt independently, (b) the descent directions may cancel one another out and (c) handcrafted features (e.g., HoGs, SIFT etc.) are mainly used to drive the cascade, which may be sub-optimal for the task at hand. In this paper, we propose a combined and jointly trained convolutional recurrent neural network architecture that allows the training of an end-to-end to system that attempts to alleviate the aforementioned drawbacks. The recurrent module facilitates the joint optimisation of the regressors by assuming the cascades form a nonlinear dynamical system, in effect fully utilising the information between all cascade levels by introducing a memory unit that shares information across all levels. The convolutional module allows the network to extract features that are specialised for the task at hand and are experimentally shown to outperform hand-crafted features. We show that the application of the proposed architecture for the problem of face alignment results in a strong improvement over the current state-of-the-art.

Menpo: A Comprehensive Platform for Parametric Image Alignment and Visual Deformable Models

The Menpo Project, hosted at http://www.menpo.io, is a BSD-licensed software platform providing a complete and comprehensive solution for annotating, building, fitting and evaluating deformable visual models from image data. Menpo is a powerful and flexible cross-platform framework written in Python that works on Linux, OS X and Windows. Menpo has been designed to allow for easy adaptation of Lucas-Kanade (LK) parametric image alignment techniques, and goes a step further in providing all the necessary tools for building and fitting state-of-the-art deformable models such as Active Appearance Models (AAMs), Constrained Local Models (CLMs) and regression-based methods (such as the Supervised Descent Method (SDM)). These methods are extensively used for facial point localisation although they can be applied to many other deformable objects. Menpo makes it easy to understand and evaluate these complex algorithms, providing tools for visualisation, analysis, and performance assessment. A key challenge in building deformable models is data annotation; Menpo expedites this process by providing a simple web-based annotation tool hosted at http://www.landmarker.io. The Menpo Project is thoroughly documented and provides extensive examples for all of its features. We believe the project is ideal for researchers, practitioners and students alike.

Offline Deformable Face Tracking in Arbitrary Videos

Generic face detection and facial landmark localization in static imagery are among the most mature and well-studied problems in machine learning and computer vision. Currently, the top performing face detectors achieve a true positive rate of around 75-80% whilst maintaining low false positive rates. Furthermore, the top performing facial landmark localization algorithms obtain low point-to-point errors for more than 70% of commonly benchmarked images captured under unconstrained conditions. The task of facial landmark tracking in videos, however, has attracted much less attention. Generally, a tracking-by-detection framework is applied, where face detection and landmark localization are employed in every frame in order to avoid drifting. Thus, this solution is equivalent to landmark detection in static imagery. Empirically, a straightforward application of such a framework cannot achieve higher performance, on average, than the one reported for static imagery. In this paper, we show for the first time, to the best of our knowledge, that the results of generic face detection and landmark localization can be used to recursively train powerful and accurate person-specific face detectors and landmark localization methods for offline deformable tracking. The proposed pipeline can track landmarks in very challenging long-term sequences captured under arbitrary conditions. The pipeline was used as a semi-automatic tool to annotate the majority of the videos of the 300-VW Challenge.

DenseReg: Fully Convolutional Dense Shape Regression In-the-Wild

In this paper we propose to learn a mapping from image pixels into a dense template grid through a fully convolutional network. We formulate this task as a regression problem and train our network by leveraging upon manually annotated facial landmarks in-the-wild. We use such landmarks to establish a dense correspondence field between a three-dimensional object template and the input image, which then serves as the ground-truth for training our regression system. We show that we can combine ideas from semantic segmentation with regression networks, yielding a highly-accurate quantized regression architecture. Our system, called DenseReg, allows us to estimate dense image-to-template correspondences in a fully convolutional manner. As such our network can provide useful correspondence information as a stand-alone system, while when used as an initialization for Statistical Deformable Models we obtain landmark localization results that largely outperform the current state-of-the-art on the challenging 300W benchmark. We thoroughly evaluate our method on a host of facial analysis tasks, and demonstrate its use for other correspondence estimation tasks, such as the human body and the human ear. DenseReg code is made available at http://alpguler.com/DenseReg.html along with supplementary materials.

Face Flow

In this paper, we propose a method for the robust and efficient computation of multi-frame optical flow in an expressive sequence of facial images. We formulate a novel energy minimisation problem for establishing dense correspondences between a neutral template and every frame of a sequence. We exploit the highly correlated nature of human expressions by representing dense facial motion using a deformation basis. Furthermore, we exploit the even higher correlation between deformations in a given input sequence by imposing a low-rank prior on the coefficients of the deformation basis, yielding temporally consistent optical flow. Our proposed model-based formulation, in conjunction with the inverse compositional strategy and low-rank matrix optimisation that we adopt, leads to a highly efficient algorithm for calculating facial flow. As experimental evaluation, we show quantitative experiments on a challenging novel benchmark of face sequences, with dense ground truth optical flow provided by motion capture data. We also provide qualitative results on a real sequence displaying fast motion and occlusions. Extensive quantitative and qualitative comparisons demonstrate that the proposed method outperforms state-of-the-art optical flow and dense non-rigid registration techniques, whilst running an order of magnitude faster.

Automatic construction Of robust spherical harmonic subspaces

In this paper we propose a method to automatically recover a class specific low dimensional spherical harmonic basis from a set of in-the-wild facial images. We combine existing techniques for uncalibrated photometric stereo and low rank matrix decompositions in order to robustly recover a combined model of shape and identity. We build this basis without aid from a 3D model and show how it can be combined with recent efficient sparse facial feature localisation techniques to recover dense 3D facial shape. Unlike previous works in the area, our method is very efficient and is an order of magnitude faster to train, taking only a few minutes to build a model with over 2000 images. Furthermore, it can be used for real-time recovery of facial shape.

Face Normals "In-the-Wild" Using Fully Convolutional Networks

In this work we pursue a data-driven approach to the problem of estimating surface normals from a single intensity image, focusing in particular on human faces. We introduce new methods to exploit the currently available facial databases for dataset construction and tailor a deep convolutional neural network to the task of estimating facial surface normals in-the-wild. We train a fully convolutional network that can accurately recover facial normals from images including a challenging variety of expressions and facial poses. We compare against state-of-the-art face Shape-from-Shading and 3D reconstruction techniques and show that the proposed network can recover substantially more accurate and realistic normals. Furthermore, in contrast to other existing face-specific surface recovery methods, we do not require the solving of an explicit alignment step due to the fully convolutional nature of our network.

Adaptive cascaded regression

The two predominant families of deformable models for the task of face alignment are: (i) discriminative cascaded regression models, and (ii) generative models optimised with Gauss-Newton. Although these approaches have been found to work well in practise, they each suffer from convergence issues. Cascaded regression has no theoretical guarantee of convergence to a local minimum and thus may fail to recover the fine details of the object. Gauss-Newton optimisation is not robust to initialisations that are far from the optimal solution. In this paper, we propose the first, to the best of our knowledge, attempt to combine the best of these two worlds under a unified model and report state-of-the-art performance on the most recent facial benchmark challenge.

Kernel-PCA Analysis of Surface Normals for Shape-from-Shading

We propose a kernel-based framework for computing components from a set of surface normals. This framework allows us to easily demonstrate that component analysis can be performed directly upon normals. We link previously proposed mapping functions, the azimuthal equidistant projection (AEP) and principal geodesic analysis (PGA), to our kernel-based framework. We also propose a new mapping function based upon the cosine distance between normals. We demonstrate the robustness of our proposed kernel when trained with noisy training sets. We also compare our kernels within an existing shape-from-shading (SFS) algorithm. Our spherical representation of normals, when combined with the robust properties of cosine kernel, produces a very robust subspace analysis technique. In particular, our results within SFS show a substantial qualitative and quantitative improvement over existing techniques.

Disentangling the Modes of Variation in Unlabelled Data

Statistical methods are of paramount importance in discovering the modes of variation in visual data. The Principal Component Analysis (PCA) is probably the most prominent method for extracting a single mode of variation in the data. However, in practice, several factors contribute to the appearance of visual objects including pose, illumination, and deformation, to mention a few. To extract these modes of variations from visual data, several supervised methods, such as the TensorFaces relying on multilinear (tensor) decomposition have been developed. The main drawbacks of such methods is that they require both labels regarding the modes of variations and the same number of samples under all modes of variations (e.g., the same face under different expressions, poses etc.). Therefore, their applicability is limited to well-organised data, usually captured in well-controlled conditions. In this paper, we propose a novel general multilinear matrix decomposition method that discovers the multilinear structure of possibly incomplete sets of visual data in unsupervised setting (i.e., without the presence of labels). We also propose extensions of the method with sparsity and low-rank constraints in order to handle noisy data, captured in unconstrained conditions. Besides that, a graph-regularised variant of the method is also developed in order to exploit available geometric or label information for some modes of variations. We demonstrate the applicability of the proposed method in several computer vision tasks, including Shape from Shading (SfS) (in the wild and with occlusion removal), expression transfer, and estimation of surface normals from images captured in the wild.