Elsevier

Pattern Recognition

Volume 40, Issue 5, May 2007, Pages 1466-1473
Pattern Recognition

Extension of higher order local autocorrelation features

https://doi.org/10.1016/j.patcog.2006.10.006Get rights and content

Abstract

This study investigates effective image features that are widely applicable in image analysis. We specifically address higher order local autocorrelation (HLAC) features, which are used in various applications. The original HLAC features are restricted up to the second order and are represented by 25 mask patterns. We increase their orders up to eight and extract the extended HLAC features using 223 mask patterns. Furthermore, we create large mask patterns and construct multi-resolution features to support large displacement regions. In texture classification and face recognition, the proposed method outperformed Gaussian Markov random fields, Gabor features, and local binary pattern operator.

Introduction

Computer image analysis has been investigated actively for many years. To date, it has produced widespread practical applications. Recent great advances in computer technology are further expanding its fields of application. That trend increases the fundamental need for basic image features that are applicable to various tasks. Many basic features such as gray-level histograms, Fourier features and Gabor features have been proposed. Among them, we specifically address higher order local autocorrelation (HLAC) features [1] because they offer many advantages.

One advantage of HLAC features is their wide availability for image analysis. They have demonstrated good performance in face recognition [2], [3], natural object recognition [4], gesture recognition [5], etc. Another advantage that they offer is feature representation using mask patterns. Various mask patterns are easily producible without limitations imposed in terms of specific directions or symmetric distributions. Using them, we can characterize complex distributions of image intensities. The use of mask patterns for feature calculation is suitable for digital image processing (no need of additional calculation such as interpolation). Their use allows simple and fast calculation of HLAC features. Furthermore, they are suitable for hardware implementation. A vision chip that calculates HLAC features has been built. It allows even faster processing [6]. These properties are all desirable for practical applications.

The original HLAC features are restricted up to the second order and are represented by 25 mask patterns. We increase their orders up to eight and represent the extended HLAC features using 223 mask patterns. Each feature value corresponds to the power spectrum of the mask pattern. Therefore, the use of many mask patterns allows detailed characterization of an image. We also use large mask patterns to enlarge the support regions. Using different mask sizes together, we can construct multi-resolution HLAC features.

We evaluate the performance of the proposed method through several texture classifications using images of different sizes, scaled images, and rotated images. Results obtained in the area of texture classification will suggest their availability in other applications such as medical image analysis, remote sensing, and segmentation of scene images. To examine their applicability to an object with shape, we also conduct face recognition. The performance of the proposed method is compared with that obtained using other popular methods: Gaussian Markov random fields (GMRF) [7], Gabor features [8], and local binary pattern (LBP) operator [9].

Section snippets

Conventional HLAC features

The Nth-order autocorrelation functions, extensions of autocorrelation functions, are defined asx(a1,a2,,aN)=f(r)f(r+a1)f(r+aN)dr,where f(r) denotes the intensity at the observing pixel r, and a1,a2,,aN are N displacements. HLAC features are primitive image features based on Eq. (1) [1]. Their orders and displacements are arbitrary. However, high-order features with a large displacement region become extremely numerous. Hence, the original HLAC features are restricted up to the second order

Texture classification

We conducted five tests of gray-scale texture classification to evaluate the performance of the proposed method. The “Outex database” [11] was used. It is an empirical evaluation framework for texture analysis that contains widely various texture images and precisely specified classification problems. Table 1 presents a description of the experimental data. In each Test, the performance was evaluated by classifying the test samples that have no overlap with the training samples.

We compared our

Face recognition: AT&T database

In the experiments described above, we applied the proposed method to texture classifications in which the images were characterized based on homogeneous properties. Subsequently, as described in this section, we applied it to face recognition to show that the proposed method is also effective for objects with shape. The conventional second-order HLAC features have demonstrated good performance in face recognition [2], [3]. For that reason, the extended method is also expected to perform well.

Conclusions

We proposed an extension of the HLAC features, which are widely available in image analysis. We increased their orders up to eight and represented the extended HLAC features with 223 mask patterns. By this extension, the image is characterized more closely than conventional second-order features. We also constructed multi-resolution HLAC features that contain both high-frequency and low-frequency information. In texture classification and face recognition, the proposed method demonstrated its

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