A Meta-Top-Down Method for Large-Scale Hierarchical Classification

A Meta-Top-Down Method for Large-Scale

Hierarchical Classification

ABSTRACT

With an increasing number of images that are available in social media, image annotation has emerged as an important research topic due to its application in image matching and retrieval. Most studies cast image annotation into a multi-label classification problem. The main shortcoming of this approach is that it requires a large number of training images with clean and complete annotations in order to learn a reliable model for tag prediction. We address this limitation by developing a novel approach that combines the strength of tag ranking with the power of matrix recovery. Instead of having to make a binary decision for each tag, our approach ranks tags in the descending order of their relevance to the given image, significantly simplifying the problem. In addition, the proposed method aggregates the prediction models for different tags into a matrix, and casts tag ranking into a matrix recovery problem. It introduces the matrix trace norm to explicitly control the model complexity so that a reliable prediction model can be learned for tag ranking even when the tag space is large and the number of training images is limited. Experiments on multiple well-known image datasets demonstrate the effectiveness of the proposed framework for tag ranking compared to the state-ofthe- art approaches for image annotation and tag ranking.

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EXISTING SYSTEM

cast image annotation into a multi-label classification problem. The main shortcoming of this approach is that it requires a large number of training images with clean and complete annotations in order to learn a reliable model for tag prediction. We address this limitation by developing a novel approach that combines the strength of tag ranking with the power of matrix recovery. Instead of having to make a binary decision for each tag, our approach ranks tags in the descending order of their relevance to the given image, significantly simplifying the problem

PROPOSED SYSTEM:

the proposed method aggregates the prediction models for different tags into a matrix, and casts tag ranking into a matrix recovery problem. It introduces the matrix trace norm to explicitly control the model complexity so that a reliable prediction model can be learned for tag ranking even when the tag space is large and the number of training images is limited. Experiments on multiple well-known image datasets demonstrate the effectiveness of the proposed framework for tag ranking compared to the state-ofthe- art approaches for image annotation and tag ranking.

MODULE DESCRIPTION:

Automatic image annotation.

Tag ranking.

Low-rank.

Matrix recovery.

Trace norm.

Automatic image Annotation.

Automatic image annotation aims to find a subset of keywords/ tags that describes the visual content of an image. It plays an important role in bridging the semantic gap between low-level features and high-level semantic content of images. Most automatic image annotation algorithms can be classified into three categories generative models that model the joint distribution between tags and visual features, discriminative models that view image annotation as a classification problem, and search based approaches. Below, we will briefly review approaches in each category. Both mixture models and topic models, two well known approaches in generative model, have been successfully applied to automatic image annotation. In a Gaussian mixture model is used to model the dependence between keywords and visual features. In kernel density estimation is applied to model the distribution of visual features and to estimate the conditional probability of keyword assignments given the visual features. Topic models annotate images as samples from a specific mixture of topics, which each topic is a joint distribution between image features and annotation keywords. Various topic models have been developed for image annotation, including probabilistic latent semantic analysis (pLSA) ,latent Dirichlet allocation and hierarchical Dirichlet processes . Since a large number of training examples are needed for estimating the joint probability distribution over both features and keywords, the generative models are unable to handle the challenge of large tag space with limited number of training images

Discriminative models , views image annotation as a multi-class classification problem, and learns one binary classification model for either one or multiple tags. A 2D multiresolution hidded Markov model (MHMM) is proposed to model the relationship between tags and visual content .A structured max-margin algorithm is developed in to exploit the dependence among tags. One problem with discriminative approaches for image annotation is imbalanced data distribution because each binary classifier is designed to distinguish image of one class from images of the other classes. It becomes more severe when the number of classes/tags is large .Another limitation of these approaches is that they are unable to capture the correlation among classes, which is known to be important in multi-label learning. To overcome

Tag ranking.

Tag ranking aims to learn a ranking function that puts relevant tags in front of the irrelevant ones. In the simplest form, it learns a scoring function that assigns larger values to the relevant tags than to those irrelevant ones. In , the authors develop a classification framework for tag ranking that computes tag scores for a test image based on the neighbor voting. It was extended in [46] to the case where each image is represented by multiple sets of visual features. Liu et al.  utilizes the Kernel Density Estimation (KDE) to calculate relevance scores for different tags, and performs a randomwalk to further improve the performance of tag ranking by exploring the correlation between tags. Similarly, Tang et al.  proposed a two-stage graph-based relevance propagation approach. In , a two-view tag weighting method is proposed to effectively exploit both the correlation among tags and the dependence between visual features and tags. In , a max-margin riffled independence model is developed for tag ranking. As mentioned in the introduction section, most of the existing algorithms for tag ranking tend to perform poorly when the tag space is large and the number of training images is limited.

Low-rank.

In mathematics, low-rankapproximation is a minimization problem, in which the cost function measures the fit between a given matrix (the data) and an approximating matrix (the optimization variable), subject to a constraint that the approximating matrix has reduced rank. The problem is used for mathematical modeling and data compression. The rank constraint is related to a constraint on the complexity of a model that fits the data. In applications, often there are other constraints on the approximating matrix apart from the rank constraint, e.g., non-negativity and Hankel structure.

We study the rank, trace-norm and max-norm as complexity measures of matrices, focusing on the problem of fitting a matrix with matrices having low complexity. We present generalization error bounds for predicting unobserved entries that are based on these measures. We also consider the possible relations between these measures. We show gaps between them, and bounds on the extent of such gaps.

Matrix recovery.

A common modeling assumption in many engineering applications is that the underlying data lies (approximately) on a low-dimensional linear subspace. This property has been widely exploited by classical Principal Component Analysis (PCA) to achieve dimensionality reduction. However, real-life data is often corrupted with large errors or can even be incomplete. Although classical PCA is effective against the presence of small Gaussian noise in the data, it is highly sensitive to even sparse errors of very high magnitude.  We propose powerful tools that exactly and efficiently correct large errors in such structured data. The basic idea is to formulate the problem as a matrix rank minimization problem  and solve it efficiently by nuclear-norm minimization. Our algorithms achieve state-of-the-art performance in low-rank matrix recovery with theoretical guarantees. Please browse the links to the left for more information. The introduction section provides a brief overview of the low-rank matrix recovery problem and introduces state-of-the-art algorithms to solve. Please refer to our papers in the references section for complete technical details, and to the sample code section for MATLAB packages. The applications section showcases engineering problems where our techniques have been used to achieve state-of-the-art performance.

Trace norm.

Trace-norm and max-norm as complexity measures of matrices, focusing on the problem of fitting a matrix with matrices having low complexity. We present generalization error bounds for predicting unobserved entries that are based on these measures. We also consider the possible relations between these measures

Accelerated Gradient Algorithm

Gradient descent is a first-order optimization algorithm. To find a local minimum of a function using gradient descent, one takes steps proportional to the negative of the gradient (or of the approximate gradient) of the function at the current point. If instead one takes steps proportional to the positive of the gradient, one approaches a local maximum of that function; the procedure is then known as gradient ascent.

Gradient descent is also known as steepest descent, or the method of steepest descent. When known as the latter, gradient descent should not be confused with the method of steepest descent for approximating integrals.

 System Configuration:

HARDWARE REQUIREMENTS:

         Hardware                             -     Pentium

         Speed                                   -     1.1 GHz

         RAM                                   -    1GB

         Hard Disk                           -    20 GB

         Floppy Drive                       -    1.44 MB

         Key Board                          -    Standard Windows Keyboard

         Mouse                                 -    Two or Three Button Mouse

         Monitor                               -    SVGA

SOFTWARE REQUIREMENTS:

          Operating System                 : Windows

          Technology                           : Java and J2EE

          Web Technologies                : Html, JavaScript, CSS

           IDE                                       : My Eclipse

           Web Server                           : Tomcat

           Tool kit                                     : Android Phone

           Database                                    : My SQL

           Java Version                           : J2SDK1.5                 

                

CONCLUSION

Extensive experiments on image annotation and tag ranking have demonstrated that the proposed method significantly outperforms several state-of-the-art methods for image annotation especially when the number of training images is limited and when many of the assigned image tags are missing. In the future, we plan to apply the proposed framework to the image annotation problem when image tags are acquired by crowdsouring that tend to be noisy and incomplete.

In addition, the proposed method aggregates the prediction models for different tags into a matrix, and casts tag ranking into a matrix recovery problem. It introduces the matrix trace norm to explicitly control the model complexity so that a reliable prediction model can be learned for tag ranking even when the tag space is large and the number of training images is limited. Experiments on multiple well-known image datasets demonstrate the effectiveness of the proposed framework for tag ranking compared to the state-ofthe- art approaches for image annotation and tag ranking.