Alexandra Branzan Albu

Towards view-invariant gait modeling: Computing view-normalized body part trajectories

This paper proposes an approach to compute view-normalized body part trajectories of pedestrians walking on potentially non-linear paths. The proposed approach finds applications in gait modeling, gait biometrics, and in medical gait analysis. Our approach uses the 2D trajectories of both feet and the head extracted from the tracked silhouettes. On that basis, it computes the apparent walking (sagittal) planes for each detected gait half-cycle. A homography transformation is then computed for each walking plane to make it appear as if walking was observed from a fronto-parallel view. Finally, each homography is applied to head and feet trajectories over each corresponding gait half-cycle. View normalization makes head and feet trajectories appear as if seen from a fronto-parallel viewpoint, which is assumed to be optimal for gait modeling purposes. The proposed approach is fully automatic as it requires neither manual initialization nor camera calibration. An extensive experimental evaluation of the proposed approach confirms the validity of the normalization process.

Computing and evaluating view-normalized body part trajectories

This paper proposes an approach to compute and evaluate view-normalized body part trajectories of pedestrians from monocular video sequences. The proposed approach uses the 2D trajectories of both feet and of the head extracted from the tracked silhouettes. On that basis, it segments the walking trajectory into piecewise linear segments. Finally, a normalization process is applied to head and feet trajectories over each obtained straight walking segment. View normalization makes head and feet trajectories appear as if seen from a fronto-parallel viewpoint. The latter is assumed to be optimal for gait modeling and identification purposes. The proposed approach is fully automatic as it requires neither manual initialization nor camera calibration. An extensive experimental evaluation of the proposed approach confirms the validity of the normalization process.

A computer vision-based system for real-time detection of sleep onset in fatigued drivers

This paper proposes a novel approach for the real-time detection of sleep onset in fatigued drivers. Sleep onset is the most critical consequence of fatigued driving, as shown by statistics of fatigue-related crashes. Therefore, unlike previous related work, we separate the issue of sleep onset from the global analysis of the physiological state of fatigue. This allows us for formulating our approach as an event-detection problem. Real-time performance is achieved by focusing on a single visual cue (i.e. eye-state), and by a custom-designed template-matching algorithm for on-line eye-state detection.

Body tracking in human walk from monocular video sequences

This paper proposes a method to automatically track human body parts in the context of gait modelisation and recognition. The proposed approach is based on a five points human model (head, hands, and feet) where the points are detected and tracked independently. Tracking is fully automatic (no manual initialization of the five points) since it will be used in a real-time surveillance system. Feet are detected in each frame by first finding the space between the legs in the human silhouette. The issue of feet self-occlusion is handled using optical flow and motion correspondence. Skin color segmentation is used to find hands in each frame and tracking is achieved by using a bounding box overlap algorithm. The head is defined as the mass center of a region of the upper silhouette.

Trajectories normalization for viewpoint invariant gait recognition

This paper proposes a method to obtain fronto-parallel (side-view) body part trajectories for a walk observed from an arbitrary view. The method is based on homography transformations computed for each gait half-cycle detected in the walk. Each homography maps the body part trajectories to a simulated side view of the walk. The proposed method is stable as the resulting normalized trajectories are not influenced by missing or omitted parts of the raw trajectories. Experiments confirm that normalized trajectories are in agreement with the ones that would be obtained from a side view.

A Morphology-Based Approach for Interslice Interpolation of Anatomical Slices From Volumetric Images

This paper proposes a new morphology-based approach for the interslice interpolation of current transformer (CT) and MRI datasets composed of parallel slices. Our approach is object based and accepts as input data binary slices belonging to the same anatomical structure. Such slices may contain one or more regions, since topological changes between two adjacent slices may occur. Our approach handles explicitly interslice topology changes by decomposing a many-to-many correspondence into three fundamental cases: one-to-one, one-to-many, and zero-to-one correspondences. The proposed interpolation process is iterative. One iteration of this process computes a transition sequence between a pair of corresponding input slices, and selects the element located at equal distance from the input slices. This algorithmic design yields a gradual, smooth change of shape between the input slices. Therefore, the main contribution of our approach is its ability to interpolate between two anatomic shapes by creating a smooth, gradual change of shape, and without generating over-smoothed interpolated shapes.

Texture sparseness for pixel classification of business document images

Contemporary business documents contain diverse, multi-layered mixtures of textual, graphical, and pictorial elements. Existing methods for document segmentation and classification do not handle well the complexity and variety of contents, geometric layout, and elemental shapes. This paper proposes a novel document image classification approach that distributes individual pixels into four fundamental classes (text, image, graphics, and background) through support vector machines. This approach uses a novel low-dimensional feature descriptor based on textural properties. The proposed feature vector is constructed by considering the sparseness of the document image responses to a filter bank on a multi-resolution and contextual basis. Qualitative and quantitative evaluations on business document images show the benefits of adopting a contextual and multi-resolution approach. The proposed approach achieves excellent results; it is able to handle varied contents and complex document layouts, without imposing any constraint or making assumptions about the shape and spatial arrangement of document elements.

Analysis of Irregularities in Human Actions with Volumetric Motion History Images

This paper describes a new 3D motion representation, the Volumetric Motion History Image (VMHI), to be used for the analysis of irregularities in human actions. Such irregularities may occur either in speed or orientation and are strong indicators of the balance abilities and of the confidence level of the subject performing the activity. The proposed VMHI representation overcomes limits of the standard MHI related to motion self-occlusion and speed and is therefore suitable for the visualization and quantification of abnormal motion. This work focuses on the analysis of sway, which is the most common motion irregularity in the studied set of human actions. The sway is visualized and quantified via a user interface using a measure of spatiotemporal surface smoothness, namely the deviation vector. Experimental results show that the deviation vector is a reliable measure for quantifying the deviation of abnormal motion from its corresponding normal motion.

Work in progress - problem-based learning in digital signal processing

Learning core concepts in signal processing courses is difficult for undergraduate students in electrical engineering. In our opinion, this difficulty comes from the gap between understanding the mathematical formalism of such concepts and being able to make sense of them in a practical way.

Towards an Intelligent Bed Sensor: Non-intrusive Monitoring of Sleep Irregularities with Computer Vision Techniques

This paper proposes a novel approach for monitoring sleep using pressure data. The goal of sleep monitoring is to detect and log events of normal breathing, sleep apnea and body motion. The proposed approach is based on translating the signal data to the image domain by computing a sequence of inter-frame similarity matrices from pressure maps acquired with a mattress of pressure sensors. Periodicity analysis was performed on similarity matrices via a new algorithm based on segmentation of elementary patterns using the watershed transform, followed by aggregation of quasi-rectangular patterns into breathing cycles. Once breathing events are detected, all remaining elementary patterns aligned on the main diagonal are considered as belonging to either apnea or motion events. The discrimination between these two events is based on detecting movement times from a statistical analysis of pressure data. Experimental results confirm the validity of our approach.