Results 1 
9 of
9
Probabilistic parsing using left corner language models
 In Proc. of the 5th Intl. Workshop on Parsing
, 1997
"... We introduce a novel parser based on a probabilistic version of a leftcorner parser. The leftcorner strategy is attractive because rule probabilities can be conditioned on both topdown goals and bottomup derivations. We develop the underlying theory and explain how a grammar can be induced from ..."
Abstract

Cited by 35 (2 self)
 Add to MetaCart
We introduce a novel parser based on a probabilistic version of a leftcorner parser. The leftcorner strategy is attractive because rule probabilities can be conditioned on both topdown goals and bottomup derivations. We develop the underlying theory and explain how a grammar can be induced from analyzed data. We show that the leftcorner approach provides an advantage over simple topdown probabilistic contextfree grammars in parsing the Wall Street Journal using a grammar induced from the Penn Treebank. We also conclude that the Penn Treebank provides a fairly weak testbed due to the flatness of its bracketings and to the obvious overgeneration and undergeneration of its induced grammar.
Spatial random tree grammars for modeling hierarchal structure in images with . . .
 IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE
, 2004
"... We present a novel probabilistic model for the hierarchical structure of an image and its regions. We call this model spatial random tree grammars (SRTGs). We develop algorithms for the exact computation of likelihood and maximum a posteriori (MAP) estimates and the exact expectationmaximization ( ..."
Abstract

Cited by 18 (2 self)
 Add to MetaCart
We present a novel probabilistic model for the hierarchical structure of an image and its regions. We call this model spatial random tree grammars (SRTGs). We develop algorithms for the exact computation of likelihood and maximum a posteriori (MAP) estimates and the exact expectationmaximization (EM) updates for modelparameter estimation. We collectively call these algorithms the centersurround algorithm. We use the centersurround algorithm to automatically estimate the maximum likelihood (ML) parameters of SRTGs and classify images based on their likelihood and based on the MAP estimate of the associated hierarchical structure. We apply our method to the task of classifying natural images and demonstrate that the addition of hierarchical structure significantly improves upon the performance of a baseline model that lacks such structure.
Hierarchical stochastic image grammars for classification and segmentation
 IEEE Trans. Image Processing
, 2006
"... Abstract—We develop a new class of hierarchical stochastic image models called spatial random trees (SRTs) which admit polynomialcomplexity exact inference algorithms. Our framework of multitree dictionaries is the starting point for this construction. SRTs are stochastic hidden tree models whose l ..."
Abstract

Cited by 16 (3 self)
 Add to MetaCart
Abstract—We develop a new class of hierarchical stochastic image models called spatial random trees (SRTs) which admit polynomialcomplexity exact inference algorithms. Our framework of multitree dictionaries is the starting point for this construction. SRTs are stochastic hidden tree models whose leaves are associated with image data. The states at the tree nodes are random variables, and, in addition, the structure of the tree is random and is generated by a probabilistic grammar. We describe an efficient recursive algorithm for obtaining the maximum a posteriori estimate of both the tree structure and the tree states given an image. We also develop an efficient procedure for performing one iteration of the expectationmaximization algorithm and use it to estimate the model parameters from a set of training images. We address other inference problems arising in applications such as maximization of posterior marginals and hypothesis testing. Our models and algorithms are illustrated through several image classification and segmentation experiments, ranging from the segmentation of synthetic images to the classification of natural photographs and the segmentation of scanned documents. In each case, we show that our method substantially improves accuracy over a variety of existing methods. Index Terms—Dictionary, estimation, grammar, hierarchical model, image classification, probabilistic contextfree grammar, segmentation, statistical image model, stochastic contextfree grammar, tree model. I.
Parameter Estimation For Spatial Random Trees Using the EM Algorithm
 In Proc. ICIP
, 2003
"... A new class of multiscale multidimensional stochastic processes called spatial random trees was recently introduced in [9]. The model is based on multiscale stochastic trees with stochastic structure as well as stochastic states. In this work, we describe a method for estimating the parameters of th ..."
Abstract

Cited by 11 (5 self)
 Add to MetaCart
A new class of multiscale multidimensional stochastic processes called spatial random trees was recently introduced in [9]. The model is based on multiscale stochastic trees with stochastic structure as well as stochastic states. In this work, we describe a method for estimating the parameters of the process.
Modeling and Estimation of Spatial Random Trees with Application to Image Classification
 In Proc. ICASSP, Hong Kong
, 2003
"... A new class of multiscale multidimensional stochastic processes called spatial random trees is introduced. The model is based on multiscale stochastic trees with stochastic structure as well as stochastic states. Procedures are developed for exact likelihood calculation, MAP estimation of the proces ..."
Abstract

Cited by 9 (7 self)
 Add to MetaCart
A new class of multiscale multidimensional stochastic processes called spatial random trees is introduced. The model is based on multiscale stochastic trees with stochastic structure as well as stochastic states. Procedures are developed for exact likelihood calculation, MAP estimation of the process, and estimation of the parameters of the process. The new framework is illustrated through a simple binary image classification problem.
Spatial Random Trees and the CenterSurround Algorithm
 Purdue University, School of Electrical and Computer Engineering
, 2003
"... A new class of multiscale stochastic processes called spatial random trees (SRTs) is introduced and studied. As with previous multiscale stochastic processes, SRTs model multidimensional signals using random processes on trees. Our key innovation, however, is that the tree structure itself is rand ..."
Abstract

Cited by 6 (5 self)
 Add to MetaCart
A new class of multiscale stochastic processes called spatial random trees (SRTs) is introduced and studied. As with previous multiscale stochastic processes, SRTs model multidimensional signals using random processes on trees. Our key innovation, however, is that the tree structure itself is random and is generated by a probabilistic contextfree grammar (PCFG) [26]. While PCFGs have been used to model 1D signals, the generalization to multiple dimensions is not direct because the leaves of a tree generated by a PCFG cannot be naturally mapped to a multidimensional lattice. We solve this problem by defining a new class of PCFGs which can produce trees whose leaves are naturally arranged in a multidimensional lattice. We call such trees admissible and show that each of them generates a unique multidimensional signal. Based on this framework, procedures are developed for likelihood calculation, MAP estimation of the processes, and parameter estimation. The new framework is illustrated through simple detection problems.
Simulation Of A Multitype GaltonWatson Chain
"... We investigate the behaviour of a class of multitype GaltonWatson chains modelling the development of a genetic population. An algorithm for the computer generation of their trajectories is described and details concerning its implementation are given. We analyze through a simulation study the d ..."
Abstract
 Add to MetaCart
We investigate the behaviour of a class of multitype GaltonWatson chains modelling the development of a genetic population. An algorithm for the computer generation of their trajectories is described and details concerning its implementation are given. We analyze through a simulation study the dependence of the extinction time of several populations on the initial gene frequencies and on the individual relative fertilities.
Hierarchal Perceptual Organization with the CenterSurround Algorithm
, 2003
"... We present a method for imposing hierarchal structure on segmented images using probabilistic contextfree grammars (PCFGs). The notion of PCFG, which has been used in the past to characterize 1D word strings, is extended to characterize 2D images as well. The insideoutside algorithm is then extend ..."
Abstract
 Add to MetaCart
We present a method for imposing hierarchal structure on segmented images using probabilistic contextfree grammars (PCFGs). The notion of PCFG, which has been used in the past to characterize 1D word strings, is extended to characterize 2D images as well. The insideoutside algorithm is then extended to support training, classification, and parsing on images with these extended PCFGs. The soundness and efficiency of these extensions rely on a novel notion of constituency that constrains the allowable ways to partition a parent segment into child subsegments during parsing. We successfully apply our method to the task of classifying natural images and also show that our method can learn the common hierarchal structure in such images, in an unsupervised fashion, from unlabeled training data.
Spatial random tree grammars for modeling . . .
, 2007
"... We present a novel probabilistic model for the hierarchical structure of an image and its regions. We call this model spatial random tree grammars (SRTGs). We develop algorithms for the exact computation of likelihood and maximum a posteriori (MAP) estimates and the exact expectationmaximization (E ..."
Abstract
 Add to MetaCart
We present a novel probabilistic model for the hierarchical structure of an image and its regions. We call this model spatial random tree grammars (SRTGs). We develop algorithms for the exact computation of likelihood and maximum a posteriori (MAP) estimates and the exact expectationmaximization (EM) updates for modelparameter estimation. We collectively call these algorithms the centersurround algorithm. We use the centersurround algorithm to automatically estimate the maximum likelihood (ML) parameters of SRTGs and classify images based on their likelihood and based on the MAP estimate of the associated hierarchical structure. We apply our method to the task of classifying natural images and demonstrate that the addition of hierarchical structure significantly improves upon the performance of a baseline model that lacks such structure.