Pratim Ghosh

Efficient and Robust Detection of Duplicate Videos in a Large Database

We present an efficient and accurate method for duplicate video detection in a large database using video fingerprints. We have empirically chosen the color layout descriptor, a compact and robust frame-based descriptor, to create fingerprints which are further encoded by vector quantization (VQ). We propose a new nonmetric distance measure to find the similarity between the query and a database video fingerprint and experimentally show its superior performance over other distance measures for accurate duplicate detection. Efficient search cannot be performed for high-dimensional data using a nonmetric distance measure with existing indexing techniques. Therefore, we develop novel search algorithms based on precomputed distances and new dataset pruning techniques yielding practical retrieval times. We perform experiments with a database of 38 000 videos, worth 1600 h of content. For individual queries with an average duration of 60 s (about 50% of the average database video length), the duplicate video is retrieved in 0.032 s, on Intel Xeon with CPU 2.33 GHz, with a very high accuracy of 97.5%.

A Nonconservative Flow Field for Robust Variational Image Segmentation

We introduce a robust image segmentation method based on a variational formulation using edge flow vectors. We demonstrate the nonconservative nature of this flow field, a feature that helps in a better segmentation of objects with concavities. A multiscale version of this method is developed and is shown to improve the localization of the object boundaries. We compare and contrast the proposed method with well known state-of-the-art methods. Detailed experimental results are provided on both synthetic and natural images that demonstrate that the proposed approach is quite competitive.

Robust dynamical model for simultaneous registration and segmentation in a variational framework: A Bayesian approach

We introduce a dynamical model for simultaneous registration and segmentation in a variational framework for image sequences, where the dynamics is incorporated using a Bayesian formulation. A linear stochastic equation relating the tracked object (or a region of interest) is first derived under the assumption that the successive images in the sequence are related by a dense and possibly non-linear displacement field. This derivation allows for the use of a computationally efficient and recursive implementation of the Bayesian formulation in this framework. The contour of the tracked object returned by the dynamical model is not only close to the previously detected shape but is also consistent with the temporal statistics of the tracked object. The performance of the proposed approach is evaluated on real image sequences. It is shown that, with respect to a variety of error metrics such as F-measure, mean absolute deviation and Hausdorff distance, the proposed approach outperforms the state-of-the art approach without the dynamical model.

Robust Simultaneous Registration and Segmentation with Sparse Error Reconstruction

We introduce a fast and efficient variational framework for Simultaneous Registration and Segmentation (SRS) applicable to a wide variety of image sequences. We demonstrate that a dense correspondence map (between consecutive frames) can be reconstructed correctly even in the presence of partial occlusion, shading, and reflections. The errors are efficiently handled by exploiting their sparse nature. In addition, the segmentation functional is reformulated using a dual Rudin-Osher-Fatemi (ROF) model for fast implementation. Moreover, nonparametric shape prior terms that are suited for this dual-ROF model are proposed. The efficacy of the proposed method is validated with extensive experiments on both indoor, outdoor natural and biological image sequences, demonstrating the higher accuracy and efficiency compared to various state-of-the-art methods.

Robust depth estimation for efficient 3D face reconstruction

This paper proposes a learning based framework for efficient 3D face reconstruction. We transfer the 3D reconstruction into a statistical learning problem of finding appropriate mapping between texture and depth subspaces. Instead of using grayscales to directly estimate the depth, we use local binary pattern (LBP) to further encode the face texture, providing robustness for depth estimation under different illumination conditions. Then the high dimension learning problem between face subspaces is tackled by the kernel partial least squares (PLS) regression. The experimental results show that the proposed method can reconstruct 3D face from single frontal image efficiently and robustly.

An automatic feature based model for cell segmentation from confocal microscopy volumes

We present a model for the automated segmentation of cells from confocal microscopy volumes of biological samples. The segmentation task for these images is exceptionally challenging due to weak boundaries and varying intensity during the imaging process. To tackle this, a two step pruning process based on the Fast Marching Method is first applied to obtain an over-segmented image. This is followed by a merging step based on an effective feature representation. The algorithm is applied on two different datasets: one from the ascidian Ciona and the other from the plant Arabidopsis. The presented 3D segmentation algorithm shows promising results on these datasets.

Generalized simultaneous registration and segmentation

Simultaneous registration and segmentation (SRS) provides a powerful framework for tracking an object of interest in an image sequence. The state-of-the-art SRS-based tracking methods assume that the illumination is maintained constant across consecutive frames. However, this assumption does not hold in many natural image sequences due to dynamic light source and shadows. We propose a generalized model for SRS-based tracking in this paper to account for non-uniform additive illumination changes. More specifically, we introduce two new terms in the SRS energy functional which address the above mentioned problem. The first term couples the shape-based cue and intensity-based cue to establish a correspondence between them. The second term compensates for the illumination change which is complementary to the first term. We demonstrate that the proposed SRS energy functional yields superior performance over the state-of-the-art SRS-based methods for various indoor and outdoor image sequences.

Retina Layer Segmentation and Spatial Alignment of Antibody Expression Levels

The expression levels of rod opsin and glial fibrillary acidic protein (GFAP) capture important structural changes in the retina during injury and recovery. Quantitatively measuring these expression levels in confocal micrographs requires identifying the retinal layer boundaries and spatially corresponding the layers across different images. In this paper, a method to segment the retinal layers using a parametric active contour model is presented. Then spatially aligned expression levels across different images are determined by thresholding the solution to a Dirichlet boundary value problem. Our analysis provides quantitative metrics of retinal restructuring that are needed for improving retinal therapies after injury.

A linear program formulation for the segmentation of Ciona membrane volumes.

We address the problem of cell segmentation in confocal microscopy membrane volumes of the ascidian Ciona used in the study of morphogenesis. The primary challenges are non-uniform and patchy membrane staining and faint spurious boundaries from other organelles (e.g. nuclei). Traditional segmentation methods incorrectly attach to faint boundaries producing spurious edges. To address this problem, we propose a linear optimization framework for the joint correction of multiple over-segmentations obtained from different methods. The main idea motivating this approach is that multiple over-segmentations, resulting from a pool of methods with various parameters, are likely to agree on the correct segment boundaries, while spurious boundaries are methodor parameter-dependent. The challenge is to make an optimized decision on selecting the correct boundaries while discarding the spurious ones. The proposed unsupervised method achieves better performance than state of the art methods for cell segmentation from membrane images.

Object Tracking with Ratio Cycles Using Shape and Appearance Cues

We present a method for object tracking over time sequence imagery. The image plane is represented with a 4-connected planar graph where vertices are associated with pixels. On each image, the outer contour of the object is localized by finding the optimal cycle in the graph such that a cost function based on temporal, appearance and shape priors is minimized. Our contribution is the particle filtering-based framework to integrate the shape cue with the temporal and appearance cues. We demonstrate that incorporating the shape prior yields promising performance improvement over temporal and appearance priors on various object tracking scenarios.