In this paper, we propose an original framework for an intuitive tuning of parameters in image and video segmentation algorithms. The proposed framework is very flexible and generic and does not depend on a specific segmentation algorithm, a particular evaluation metric, or a specific optimization approach, which are the three main components of its block diagram. This framework requires a manual segmentation input provided by a human operator as he/she would have performed intuitively. This input allows the framework to search for the optimal set of parameters which will provide results similar to those obtained by manual segmentation. On one hand, this allows researchers and designers to quickly and automatically find the best parameters in the segmentation algorithms they have developed. It helps them to better understand the degree of importance of each parameter's value on the final segmentation result. It also identifies the potential of the segmentation algorithm under study in terms of best possible performance level. On the other hand, users and
operators of systems with segmentation components, can efficiently
identify the optimal sets of parameters for different classes of images or video sequences. In a large extent, this optimization can be
performed without a deep understanding of the underlying algorithm,
which would facilitate the exploitations and optimizations in real
applications by non-experts in segmentation. A specific implementation
of the proposed framework was obtained by adopting a video segmentation algorithm invariant to shadows as segmentation component, a full reference segmentation quality metric based on a perceptually motivated spatial context, as the evaluation component, and a down-hill simplex method, as optimization component. Simulation results on various test sequences, covering a representative set of indoor and ourdoor video, show that optimal set of parameters can be obtained efficiently and largely improve the results obtained when compared to a simple implementation of the same segmentation algorithm with ad-hoc parameter setting strategy.
Shadow segmentation is a critical issue for systems aiming at
extracting, tracking or recognizing objects in a given scene. Shadows
can in fact modify the shape and colour of objects and therefore
affect scene analysis and interpretation systems in many applications,
such as video database search and retrieval, as well as video analysis
in applications such as video surveillance. We present a shadow
segmentation algorithm which includes two stages. The first stage
extracts moving cast shadows in each frame of the sequence. The second
stage tracks the extracted shadows in the subsequent frames. Tentative
moving shadow regions are first identified based on spectral and
geometrical properties of shadows. In order to confirm this tentative
identification, shadow regions are then tracked over time. This second
stage aims at exploiting the prior knowledge of a shadow detected in
previous frames by evaluating its temporal behaviour. Shadow tracking
is a difficult task, since colour, texture, and motion features in
shadow regions cannot be used for solving the correspondence
problem. Colour and texture change according to changes in the
background's characteristics. The measurement of motion cannot be
reliably computed for shadows. Therefore shadows may be described only
by a limited amount of information. The proposed tracking algorithm
makes use of this information and provides a reliability estimation of
shadow recognition results of the first stage over time. This temporal
analysis eliminates the possible ambiguities of the first stage and
improves the efficiency of the overall shadow detection algorithm. The
benefit of the proposed shadow segmentation and tracking algorithm is
evaluated on both indoor and outdoor scenes. The obtained results are
validated based on subjective as well as objective comparisons.
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