International audience

This article presents a 3D approach in plant growth monitoring and deals with the tracking of leaves of sunflower plants. Our aim is to compute time-series of individual leaf area, under water stress and control conditions. These data will then be used by biologists to study the drought resistance of various sunflower species. Our method to track the leaves in 3D has been evaluated on a set of 132 point clouds obtained via classical structure-from-motion techniques and multi-view stereo software. These 3D acquisitions have been performed on 12 sunflower plants (6 water-stressed, 6 well-watered) during a period of one month (11 measurement dates per sunflower plant). This method gives promising results for both conditions (water-stressed and well-watered), for different species and is able to follow the growth of the plants, as well as to detect new leaf emergence and leaf decay.

Perceptual systems deployed in embedded intelligent systems are handicapped with limited computation resources. As a result, they require explicit computation time consideration during design time. In this paper, we investigate the impact a visual person detector explicitly optimized to minimize computational time has on an exemplar robotic application - navigation in human shared environments. The experimental results attest the improved perceptual frame rate leads to significant improvements in vision system performance and robotic mission success rate.

In this paper, we investigate the notion of incorporating feature computation time (CT) measures during feature selection in a boosted cascade people detector utilizing heterogeneous pool of features. We present various approaches based on pareto-front analysis, CT weighted adaboost, and Binary Integer Programming (BIP) with comparative evaluations. The novel feature selection method proposed based on BIP — the main contribution — mines heterogeneous features taking both detection performance and CT explicitly into consideration. The results demonstrate that the detector using this feature selection scheme exhibits low miss rates (MRs) with significant boost in frame rate. For example, it achieves a [Formula: see text] less MR at [Formula: see text] FPPW compared to Dalal and Triggs HOG detector with a [Formula: see text]x speed improvement. The presented extensive experimental results clearly highlight the improvements the proposed framework brings to the table.

In this paper we present a novel people detector that employs discrete optimization for feature selection. Specifically, we use binary integer programming to mine heterogeneous features taking both detection performance and computation time explicitly into consideration. The final trained detector exhibits low Miss Rates with significant boost in frame rate. For example, it achieves a 2.6% less Miss Rate at 10-4 FPPW compared to Dalal and Triggs HOG detector with a 9.22x speed improvement.

In this paper, we present a fast Histogram of Oriented Gradients (HOG) based person detector. The detector adopts a cascade of rejectors framework by selecting discriminant features via a new proposed feature selection framework based on Binary Integer Programming. The mathematical programming explicitly formulates an optimization problem to select discriminant features taking detection performance and computation time into account. The learning of the cascade classifier and its detection capability are validated using a proprietary dataset acquired using the Ladybug2 spherical camera and the public INRIA person detection dataset. The final detector achieves a comparable detection performance as Dalal and Triggs [2] detector while achieving on average more than 2.5×-8× speed up depending on the training dataset.

In this paper, a boosted cascade person detection framework with heterogeneous pool of features is presented. The framework unveils a new feature selection scheme based on Pareto-Front analysis and AdaBoost. At each cascade node, Pareto-Front analysis is used to select dominant features thereby reducing the total number of features to a size easily manageable by AdaBoost. The final detector achieves a very low Miss Rate of 0.07 at 10-4 False Positives Per Window on the INRIA public dataset.

This paper proposes a novel approach that allows region-based active contour energy to be re-expressed combining local and global information. The basic idea of this technique consists in extracting image statistics locally from the heterogeneous region (foreground or background) and globally from the other region at each point along the curve. By exploiting benefits of both local-based and global-based statistics, this technique proves to be robust against heterogeneity and noise and shows low sensitivity to curve initialization. Experimental results for synthetic and real images reveal significant improvement compared to conventional methods.

This paper deals with motion estimation and segmentation in video sequences. Some methods of motion computation between two consecutive frames of a video sequence are based on the minimization of the square error of the prediction error. More robust estimators such as absolute value or M-estimators were proposed but these estimators loose their efficiency when the data do not have parametric distributions. We relax the parametric assumption on the prediction error distribution and propose to use a nonparametric estimator for the motion estimation : the entropy of the prediction error. We use the same criterion to perform a spatio-temporal segmentation of the sequence using an active contour algorithm. Segmentation and tracking tests on a textured synthetic and a real sequence, compared to a standard method in motion segmentation, tends to show that our method is more stable and accurate.

In this paper we address the problem of video segmentation. We propose a new method which combines an active contour and a watershed presegmentation. We first apply active contours to track moving objects with a basic motion criterion. Then, we eliminate the variation due to motion on the object boundaries by attracting the curve to the nearest boundaries of a watershed oversegmentation. We constrain the curve length to smooth the propagation driven by the distance to the watershed boundaries. The proposed method improves active contour segmentation and gives smoother results than watershed segmentation

The paper deals with video and image segmentation using region based active contours. We consider the problem of segmentation through the minimization of a new criterion based on information theory. We first propose to derive a general criterion based on the probability density function using the notion of shape gradient. This general derivation is then applied to criteria based on information theory, such as the entropy or the conditional entropy for the segmentation of sequences of images. We present experimental results on grayscale images and color videos showing the accuracy of the proposed method.