OpenRaiser/Intern-Atlas huggingface dataset:
Interactive image matting for multiple layers
Authors: Dheeraj Singaraju, René Vidal
Venue: CVPR
Year: 2008

Image matting deals with finding the probability that each pixel in an image belongs to a user specified dasiaobjectpsila or to the remaining dasiabackgroundpsila. Most existing methods estimate the mattes for two groups only. Moreover, most of these methods estimate the mattes with a particular bias towards the object and hence the resulting mattes do not sum up to 1 across the different groups. In this work, we propose a general framework to estimate the alpha mattes for multiple image layers. The mattes are estimated as the solution to the Dirichlet problem on a combinatorial graph with boundary conditions. We consider the constrained optimization problem that enforces the alpha mattes to take values in [0; 1] and sum up to 1 at each pixel. We also analyze the properties of the solution obtained by relaxing either of the two constraints. Experiments demonstrate that our proposed method can be used to extract accurate mattes of multiple objects with little user interaction.
Order consistent change detection via fast statistical significance testing
Authors: Maneesh Singh 0001, Vasu Parameswaran, Visvanathan Ramesh
Venue: CVPR
Year: 2008

Robustness to illumination variations is a key requirement for the problem of change detection which in turn is a fundamental building block for many visual surveillance applications. The use of ordinal measures is a powerful way of filtering out illumination dependency in representing appearance, and several such measures have been proposed in the past for change detection. By design, these measures are invariant to unknown monotonic transformations that may be caused due to global illumination changes or automatic camera gain. However, previous work has left theoretical and practical gaps that limit their full potential from being realized. For instance, random noise has not been given a principled treatment. In this paper, we formulate the change detection problem in terms of order consistency and show that in the presence of noise with known statistical properties, significance tests for order consistency yield much better results than the state of the art. Since ordinal measures require a reordering of patches, they are usually expensive in practice (O(n*log n) at best). We improve upon this by connecting the problem to monotonic regression, and applying a fast algorithm from the corresponding literature. We also show that good trade offs between speed and accuracy can be made by quantization to achieve accurate and very fast matching algorithms in practice. We demonstrate superior performance on statistical simulations as well as real image sequences.
Histogram-based search: A comparative study
Authors: Mikhail Sizintsev, Konstantinos G. Derpanis, Andrew Hogue
Venue: CVPR
Year: 2008

Histograms represent a popular means for feature representation. This paper is concerned with the problem of exhaustive histogram-based image search. Several standard histogram construction methods are explored, including the conventional approach, Huangpsilas method, and the state-of-the-art integral histogram. In addition, we present a novel multiscale histogram-based search algorithm, termed the distributive histogram, that can be evaluated exhaustively in a fast and memory efficient manner. An extensive systematic empirical evaluation is presented that explores the computational and storage consequences of altering the search image and histogram bin sizes. Experiments reveal up to an eight-fold decrease in computation time and hundreds- to thousands-fold decrease of memory use of the proposed distributive histogram in comparison to the integral histogram. Finally, we conclude with a discussion on the relative merits between the various approaches considered in the paper.
Skeletal graphs for efficient structure from motion
Authors: Noah Snavely, Steven M. Seitz, Richard Szeliski
Venue: CVPR
Year: 2008

We address the problem of efficient structure from motion for large, unordered, highly redundant, and irregularly sampled photo collections, such as those found on Internet photo-sharing sites. Our approach computes a small skeletal subset of images, reconstructs the skeletal set, and adds the remaining images using pose estimation. Our technique drastically reduces the number of parameters that are considered, resulting in dramatic speedups, while provably approximating the covariance of the full set of parameters. To compute a skeletal image set, we first estimate the accuracy of two-frame reconstructions between pairs of overlapping images, then use a graph algorithm to select a subset of images that, when reconstructed, approximates the accuracy of the full set. A final bundle adjustment can then optionally be used to restore any loss of accuracy.
Learning the viewpoint manifold for action recognition
Authors: Richard Souvenir, Justin Babbs
Venue: CVPR
Year: 2008

Researchers are increasingly interested in providing video-based, view-invariant action recognition for human motion. Addressing this problem will lead to more accurate modeling and analysis of the type of unconstrained video commonly collected in the areas of athletics and medicine. Previous viewpoint-invariant methods use multiple cameras in both the training and testing phases of action recognition or require storing many examples of a single action from multiple viewpoints. In this paper, we present a framework for learning a compact representation of primitive actions (e.g., walk, punch, kick, sit) that can be used for video obtained from a single camera for simultaneous action recognition and viewpoint estimation. Using our method, which models the low-dimensional structure of these actions relative to viewpoint, we show recognition rates on a publicly available data set previously only achieved using multiple simultaneous views.
Cell motion analysis without explicit tracking
Authors: Richard Souvenir, Jerrod P. Kraftchick, Sangho Lee, Mark G. Clemens, Min C. Shin
Venue: CVPR
Year: 2008

Automated cell tracking using in vivo imagery is difficult, in general, due to the noise inherent in the imaging process, occlusions, varied cell appearance over time, motion of other tissue (distractors), and cells traveling in and out of the image plane. For certain types of cells these problems are exacerbated due to erratic motion patterns. In this paper, we introduce the Radial Flow Transform, which provides motion estimates for objects of interest in a scene without explicitly tracking each object. The transform is robust to misdetected objects, temporally-disjoint motion events, and can represent multiple directions of flow at a single location. We provide operations to convert to and from a vector field representation. This allows for intuitive reasoning about the motion patterns in a scene. We demonstrate results on synthetic data and in vivo microscopy video of a mouse liver.
Towards unsupervised whole-object segmentation: Combining automated matting with boundary detection
Authors: Andrew N. Stein, Thomas S. Stepleton, Martial Hebert
Venue: CVPR
Year: 2008

We propose a novel step toward the unsupervised segmentation of whole objects by combining ldquohintsrdquo of partial scene segmentation offered by multiple soft, binary mattes. These mattes are implied by a set of hypothesized object boundary fragments in the scene. Rather than trying to find or define a single ldquobestrdquo segmentation, we generate multiple segmentations of an image. This reflects contemporary methods for unsupervised object discovery from groups of images, and it allows us to define intuitive evaluation metrics for our sets of segmentations based on the accurate and parsimonious delineation of scene objects. Our proposed approach builds on recent advances in spectral clustering, image matting, and boundary detection. It is demonstrated qualitatively and quantitatively on a dataset of scenes and is suitable for current work in unsupervised object discovery without top-down knowledge.
Robust unambiguous parametrization of the essential manifold
Authors: Raghav Subbarao, Yakup Genc, Peter Meer
Venue: CVPR
Year: 2008

Analytic manifolds were recently used for motion averaging, segmentation and robust estimation. Here we consider the epipolar constraint for calibrated cameras, which is the most general motion model for calibrated cameras and is encoded by the essential matrix. The set of all essential matrices forms the essential manifold. We provide a theoretical characterization of the geometry of the essential manifold and develop a parametrization which associates each essential matrix with a unique point on the manifold. Our work provides a more complete theoretical analysis of the essential manifold than previous work in this direction. We show the results of using this parametrization with real data sets, while previous work concentrated on theoretical analysis with synthetic data.
On handling uncertainty in the fundamental matrix for scene and motion adaptive pose recovery
Authors: Sreenivas R. Sukumar 0001, Hamparsum Bozdogan, David L. Page, Andreas F. Koschan, Mongi A. Abidi
Venue: CVPR
Year: 2008

The estimation of the fundamental matrix is the key step in feature-based camera ego-motion estimation for applications in scene modeling and vehicle navigation. In this paper, we present a new method of analyzing and further reducing the risk in the fundamental matrix due to the choice of a particular feature detector, the choice of the matching algorithm, the motion model, iterative hypothesis generation and verification paradigms. Our scheme makes use of model-selection theory to guide the switch to optimal methods for fundamental matrix estimation within the hypothesis-and-test architecture. We demonstrate our proposed method for vision-based robot localization in large-scale environments where the environment is constantly changing and navigation within the environment is unpredictable.
Image super-resolution using gradient profile prior
Authors: Jian Sun 0009, Zongben Xu, Heung-Yeung Shum
Venue: CVPR
Year: 2008

In this paper, we propose an image super-resolution approach using a novel generic image prior - gradient profile prior, which is a parametric prior describing the shape and the sharpness of the image gradients. Using the gradient profile prior learned from a large number of natural images, we can provide a constraint on image gradients when we estimate a hi-resolution image from a low-resolution image. With this simple but very effective prior, we are able to produce state-of-the-art results. The reconstructed hi-resolution image is sharp while has rare ringing or jaggy artifacts.
Stereo reconstruction with mixed pixels using adaptive over-segmentation
Authors: Yuichi Taguchi, Bennett Wilburn, C. Lawrence Zitnick
Venue: CVPR
Year: 2008

We present an over-segmentation based, dense stereo algorithm that jointly estimates segmentation and depth. For mixed pixels on segment boundaries, the algorithm computes foreground opacity (alpha), as well as color and depth for the foreground and background. We model the scene as a collection of fronto-parallel planar segments in a reference view, and use a generative model for image formation that handles mixed pixels at segment boundaries. Our method iteratively updates the segmentation based on color, depth and shape constraints using MAP estimation. Given a segmentation, the depth estimates are updated using belief propagation. We show that our method is competitive with the state-of-the-art based on the new Middlebury stereo evaluation, and that it overcomes limitations of traditional segmentation based methods while properly handling mixed pixels. Z-keying results show the advantages of combining opacity and depth estimation.
Image/video deblurring using a hybrid camera
Authors: Yu-Wing Tai, Hao Du 0004, Michael S. Brown, Stephen Lin 0001
Venue: CVPR
Year: 2008

We propose a novel approach to reduce spatially varying motion blur using a hybrid camera system that simultaneously captures high-resolution video at a low-frame rate together with low-resolution video at a high-frame rate. Our work is inspired by Ben-Ezra and Nayar who introduced the hybrid camera idea for correcting global motion blur for a single still image. We broaden the scope of the problem to address spatially varying blur as well as video imagery. We also reformulate the correction process to use more information available in the hybrid camera system, as well as iteratively refine spatially varying motion extracted from the low-resolution high-speed camera. We demonstrate that our approach achieves superior results over existing work and can be extended to deblurring of moving objects.
Locally adaptive learning for translation-variant MRF image priors
Authors: Masayuki Tanaka 0001, Masatoshi Okutomi
Venue: CVPR
Year: 2008

Markov random field (MRF) models are a powerful tool in machine vision applications. However, learning the model parameters is still a challenging problem and a burdensome task. The main contribution of this paper is to propose a locally adaptive learning framework. The proposed learning framework is simple and effective learning framework for translation-variant MRF models. The key idea is to use neighboring patches as a locally adaptive training set. We use multivariate Gaussian MRF models for local image prior models. Although the Gaussian MRF models are too simple for whole natural image priors, the locally adaptive framework enables to express the prior distributions of the every observed image. These locally adaptive learning framework and the multivariate Gaussian translation-variant MRF models simplify the learning procedures. This paper also includes other two contributions; a novel iteration framework by updating the prior information, and a simple and intuitive derivation of the well-known bilateral filter. Experimental results of denoising applications demonstrate that the denoising based on the proposed locally adaptive learning framework outperforms existing high-performance denoising algorithms.
The Logistic Random Field - A convenient graphical model for learning parameters for MRF-based labeling
Authors: Marshall F. Tappen, Kegan G. G. Samuel, Craig V. Dean, David M. Lyle
Venue: CVPR
Year: 2008

Graphical models are fundamental tools for modeling images and other applications. In this paper, we propose the logistic random field (LRF) model for representing a discrete-valued graphical model. The LRF model is based on an underlying quadratic model and a logistic function. The chief advantages of the LRF are its convenience and flexibility. The quadratic model makes inference easy to implement using standard numerical linear algebra routines. This quadratic model also allows the log-likelihood of the training data to be differentiated with respect to any parameter in the model, enhancing the flexibility of the LRF model. To demonstrate the usefulness of this model we use it to learn how to segment objects, specifically roads, horses, and cows. In addition, we demonstrate the flexibility of the LRF model by incorporating super-pixels. We then show that the LRF segmentation model produces segmentations that are competitive with recently published results.
Branch-and-bound hypothesis selection for two-view multiple structure and motion segmentation
Authors: Ninad Thakoor, Jean Gao
Venue: CVPR
Year: 2008

An efficient and robust framework for two-view multiple structure and motion segmentation is proposed. To handle this otherwise recursive problem, hypotheses for the models are generated by local sampling. Once these hypotheses are available, a model selection problem is formulated which takes into account the hypotheses likelihoods and model complexity. An explicit model for outliers is also added for robust model selection. The model selection criterion is optimized through branch-and-bound technique of combinatorial optimization which guaranties optimality over current set of hypotheses by efficient search of solution space.
Pose primitive based human action recognition in videos or still images
Authors: Christian Thurau, Václav Hlavác
Venue: CVPR
Year: 2008

This paper presents a method for recognizing human actions based on pose primitives. In learning mode, the parameters representing poses and activities are estimated from videos. In run mode, the method can be used both for videos or still images. For recognizing pose primitives, we extend a Histogram of Oriented Gradient (HOG) based descriptor to better cope with articulated poses and cluttered background. Action classes are represented by histograms of poses primitives. For sequences, we incorporate the local temporal context by means of n-gram expressions. Action recognition is based on a simple histogram comparison. Unlike the mainstream video surveillance approaches, the proposed method does not rely on background subtraction or dynamic features and thus allows for action recognition in still images.
Learning subcategory relevances for category recognition
Authors: Sinisa Todorovic, Narendra Ahuja
Venue: CVPR
Year: 2008

A real-world object category can be viewed as a characteristic configuration of its parts, that are themselves simpler, smaller (sub)categories. Recognition of a category can therefore be made easier by detecting its constituent subcategories and combing these detection results. Given a set of training images, each labeled by an object category contained in it, we present an approach to learning: (1) Taxonomy defined by recursive sharing of subcategories by multiple image categories; (2) Subcategory relevance as the degree of evidence a subcategory offers for the presence of its parent; (3) Likelihood that the image contains a subcategory; and (4) Prior that a subcategory occurs. The images are represented as points in a feature space spanned by confidences in the occurrences of the subcategories. The subcategory relevances are estimated as weights, necessary to rescale the corresponding axes of the feature space so that the images with the same label are closer to each other than to those with different labels. When a new image is encountered, the learned taxonomy, relevances, likelihoods, and priors are used by a linear classifier to categorize the image. On the challenging Caltech-256 dataset, the proposed approach significantly outperforms the best categorizations reported. This result is significant in that it not only demonstrates the advantages of exploiting subcategory taxonomy for recognition, but also suggests that a feature space spanned by part properties, instead of direct object properties, allows for linear separation of image classes.
Learning Bayesian Networks with qualitative constraints
Authors: Yan Tong, Qiang Ji
Venue: CVPR
Year: 2008

Graphical models such as Bayesian Networks (BNs) are being increasingly applied to various computer vision problems. One bottleneck in using BN is that learning the BN model parameters often requires a large amount of reliable and representative training data, which proves to be difficult to acquire for many computer vision tasks. On the other hand, there is often available qualitative prior knowledge about the model. Such knowledge comes either from domain experts based on their experience or from various physical or geometric constraints that govern the objects we try to model. Unlike the quantitative prior, the qualitative prior is often ignored due to the difficulty of incorporating them into the model learning process. In this paper, we introduce a closed-form solution to systematically combine the limited training data with some generic qualitative knowledge for BN parameter learning. To validate our method, we compare it with the Maximum Likelihood (ML) estimation method under sparse data and with the Expectation Maximization (EM) algorithm under incomplete data respectively. To further demonstrate its applications for computer vision, we apply it to learn a BN model for facial Action Unit (AU) recognition from real image data. The experimental results show that with simple and generic qualitative constraints and using only a small amount of training data, our method can robustly and accurately estimate the BN model parameters.
Measuring camera translation by the dominant apical angle
Authors: Akihiko Torii, Michal Havlena, Tomás Pajdla, Bastian Leibe
Venue: CVPR
Year: 2008

This paper provides a technique for measuring camera translation relatively w.r.t. the scene from two images. We demonstrate that the amount of the translation can be reliably measured for general as well as planar scenes by the most frequent apical angle, the angle under which the camera centers are seen from the perspective of the reconstructed scene points. Simulated experiments show that the dominant apical angle is a linear function of the length of the true camera translation. In a real experiment, we demonstrate that by skipping image pairs with too small motion, we can reliably initialize structure from motion, compute accurate camera trajectory in order to rectify images and use the ground plane constraint in recognition of pedestrians in a hand-held video sequence.
Parameterized Kernel Principal Component Analysis: Theory and applications to supervised and unsupervised image alignment
Authors: Fernando De la Torre, Minh Hoai Nguyen
Venue: CVPR
Year: 2008

Parameterized Appearance Models (PAMs) (e.g. eigen-tracking, active appearance models, morphable models) use Principal Component Analysis (PCA) to model the shape and appearance of objects in images. Given a new image with an unknown appearance/shape configuration, PAMs can detect and track the object by optimizing the model’s parameters that best match the image. While PAMs have numerous advantages for image registration relative to alternative approaches, they suffer from two major limitations: First, PCA cannot model non-linear structure in the data. Second, learning PAMs requires precise manually labeled training data. This paper proposes Parameterized Kernel Principal Component Analysis (PKPCA), an extension of PAMs that uses Kernel PCA (KPCA) for learning a non-linear appearance model invariant to rigid and/or non-rigid deformations. We demonstrate improved performance in supervised and unsupervised image registration, and present a novel application to improve the quality of manual landmarks in faces. In addition, we suggest a clean and effective matrix formulation for PKPCA.
An importance sampling approach to learning structural representations of shape
Authors: Andrea Torsello
Venue: CVPR
Year: 2008

This paper addresses the problem of learning archetypal structural models from examples. This is done by providing a generative model for graphs where the distribution of observed nodes and edges is governed by a set of independent Bernoulli trials with parameters to be estimated, however, the correspondences between sample node and model nodes is not known and must be estimated from local structure. The parameters are estimated maximizing the likelihood of the observed graphs, marginalizing it over all possible node correspondences. This is done adopting an importance sampling approach to limit the exponential explosion of the set of correspondences. The approach is used to summarize the variation in two different structural abstraction of shape: Delaunay graph over a set of image features and shock graphs. The experiments show that the approach can be used to recognize structures belonging to a same class.