Elsevier

Pattern Recognition

Volume 43, Issue 1, January 2010, Pages 58-68
Pattern Recognition

Novel moment invariants for improved classification performance in computer vision applications

https://doi.org/10.1016/j.patcog.2009.05.008Get rights and content

Abstract

A novel set of moment invariants based on the Krawtchouk moments are introduced in this paper. These moment invariants are computed over a finite number of image intensity slices, extracted by applying an innovative image representation scheme, the image slice representation (ISR) method. Based on this technique an image is decomposed to a several non-overlapped intensity slices, which can be considered as binary slices of certain intensity. This image representation gives the advantage to accelerate the computation of image's moments since the image can be described in a number of homogenous rectangular blocks, which permits the simplification of the computation formulas. The moments computed over the extracted slices seem to be more efficient than the corresponding moments of the same order that describe the whole image, in recognizing the pattern under processing. The proposed moment invariants are exhaustively tested in several well known computer vision datasets, regarding their rotation, scaling and translation (RST) invariant recognition performance, by resulting to remarkable outcomes.

Introduction

Image moments have attracted the attention of the engineering scientific community for several decades, as a powerful tool to describe the content of an image. They have been used in many research fields of the engineering life, such as image processing [1], [2], [3], [4], pattern recognition and machine vision [5], [6], with considerable results. The first introduction of image moments for classification purposes was performed by Hu [7], by introducing the concept of moment invariants for invariant pattern recognition applications. By using the geometrical, central and normalized image moments, Hu [1] proposed seven measurements invariant to any translation, scaling and rotation transformation of the image be processed, called moment invariants. These moment invariants are successfully used as image descriptors in many pattern recognition applications [8], [9].

Since the first introduction of moment invariants in classification problems, many attempts to develop improved moment invariants with superior classification performance have occurred lately [10], [11], [12], [13]. However, these types of moment invariants suffer from high information redundancy, by making them less efficient in difficult problems where more discriminative information needs to be captured. This fact motivated scientists to develop the orthogonal moments, which use as kernel functions polynomials that constitute an orthogonal basis. This property of orthogonality, gives to the corresponding moments the feature of minimum information redundancy, meaning that different moment orders describe different image part. Such moment families are the Legendre [1], Zernike [6], Pseudo-Zernike [1], Fourier–Mellin [14], Tchebichef [15], Krawtchouk [3] moments. These moments can be used as image descriptors after an appropriate normalization procedure in order to achieve translation, scale and rotation invariances.

Among the above orthogonal moment families the Krawtchouk moments exhibit significant properties in comparison with the other ones, due to their high noise robustness and local behaviour and have been selected as the base on which the proposed methodology is applied.

In this paper, a novel methodology that generates moment invariants from a set of Krawtchouk moment invariants (KMIs), which improves the overall classification performance in difficult pattern recognition applications, is presented and analysed in detail.

The proposed methodology is based on a new image representation technique introduced by the authors in [19], which gives more degrees of freedom to the computation of moment invariants. By applying the image slice representation (ISR) technique an image can be decomposed to a finite number of intensity slices, and the computation of the total image moments can be reduced to the computation of the corresponding moment of each image's slices. The resulted moments of each slice, can be considered as the components of the original moment in the intensity domain.

The performance of the newly proposed moment invariants, which are called slice moment invariants (SMIs), are investigated in detail through appropriate experiments to several well known benchmark pattern recognition problems. The experiments show that the conventional KMIs can effectively be replaced by a new set of moment invariants since they perform better in recognizing patterns.

The paper is organized as follows: Section 2 describes the Krawtchouk moment invariants and the way they can be derived. The proposed surrogate moment invariants are introduced in Section 3, while a detailed experimental study demonstrates the efficiency of the novel invariants, in terms of classification performance, in Section 4. Finally, the main conclusions are summarized and discussed in Section 5.

Section snippets

Krawtchouk moment invariants

Krawtchouk orthogonal moments constitute a high discriminative moment family in the discrete domain introduced in image analysis by Yap et al. [3]. These moments are making use of the discrete Krawtchouk polynomials, having the following form, Kn(x;p,N)=2F1(-n,-x;-N;1p)=k=0Nak,n,pxkwhere x,n=0,1,2,…,N, N>0, p(0,1) and 2F1 is the hypergeometric function.

The computation of the Krawtchouk polynomials by using Eq. (1), presents numerical fluctuations and therefore a more stable version of them,

Slice moment invariants

The computation of KMIs by using Eqs. (9), (10), (11), (12), (13), (14) seems to be a time consuming task because of the appearance of quite complicated quantities and repetitive calculations. Additionally, the recursive formulas Eqs. (6), (7), (8) cannot be applied, since the description of KMIs through the GMIs eliminates the occurrence of the original Krawtchouk polynomials that can be quickly computed recursively. The overall overhead in computing the KMIs increases significantly when

Experimental study

In order to investigate the discrimination performance of the proposed moment invariants, four classification problems were arranged. The COIL-20 [21], 53_obj [22] computer vision and the ORL [23] ,Yale [24] face datasets, their main properties are shown in Table 1, were selected as benchmarks for studying the classification capabilities of the SMIs in comparison with the corresponding conventional ones.

Conclusion

A new methodology for the generation of high discriminant moment invariants based on the ISR representation was introduced in the previous sections. The proposed moment invariants are computed as parts of the original moment invariants and they present zero information redundancy since they describe non-overlapping information of the image in process. Despite their high classification capabilities the proposed invariants eliminate the need for high order moment invariant computations, a process

About the Author—GEORGE A. PAPAKOSTAS received the Diploma in Electrical and Computer Engineering in 1999 and the M.Sc. and Ph.D. Degree in Electrical and Computer Engineering (topic in Feature Extraction and Pattern Recognition) in 2002 and 2007, respectively, from Democritus University of Thrace (DUTH), Greece. He is the author of 30 publications in international scientific journals and conferences. His research interests are focused in the field of pattern recognition, neural networks,

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    About the Author—GEORGE A. PAPAKOSTAS received the Diploma in Electrical and Computer Engineering in 1999 and the M.Sc. and Ph.D. Degree in Electrical and Computer Engineering (topic in Feature Extraction and Pattern Recognition) in 2002 and 2007, respectively, from Democritus University of Thrace (DUTH), Greece. He is the author of 30 publications in international scientific journals and conferences. His research interests are focused in the field of pattern recognition, neural networks, feature extraction, optimisation, signal and mage processing.

    About the Author—KARAKASSIS EVAGGELOS received the Diploma in Production Management Engineering. He is currently pursuing the Ph.D. degree in the Department of Production Management Engineering, Democritius University of Thrace, Greece. His research interest includes robotics, image processing, computational intelligence.

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