Abstract

A large variety of well-known scale-invariant texture recognition methods is tested with respect to their scale invariance. The scale invariance of these methods is estimated by comparing the results of two test setups. In the first test setup, the images of the training and evaluation set are acquired under same scale conditions and in the second test setup, the images in the evaluation set are gathered under different scale conditions than those of the training set. For the first test setup, scale invariance is not needed, whereas for the second test setup, scale invariance is obviously crucial. The difference between the results of these two test setups indicates the scale invariance of a method (the higher the scale invariance the lower the difference). The scale invariance of the methods is additionally estimated by analyzing the similarity of the feature vectors of images and their scaled versions. Additionally to the scale invariance, we also test eventual viewpoint and illumination invariance of the methods. As texture databases for our tests we use the KTH-TIPS database and the CUReT database. Results imply that many of the considered methods are not as scale-invariant as expected.

Highlights

  • Texture analysis is one of the fundamental issues in image processing and pattern recognition

  • In the first test setup, the images of the training and evaluation set are acquired under same scale conditions and in the second test setup, the images in the evaluation set are gathered under different scale conditions than those of the training set

  • In this paper we focus on general texture recognition and will analyze the scale invariance of the original proposed methods using well known public texture databases

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Summary

Introduction

Texture analysis is one of the fundamental issues in image processing and pattern recognition. Our results with respect to the scale, viewpoint and illumination invariance of the features could be helpful in many practical applications of the employed features like, e.g. face and facial expression recognition [16, 31], object recognition [3], medical image analysis [12], et cetera. The contributions of this manuscript are as follows:. We define a texture descriptor as being scale-invariant, if the distances between the feature vectors of images from a single texture class compared to the distances between feature vectors of different texture classes are not influenced by the fact whether the images are all gathered under one or under different scale conditions

Scale-invariant texture descriptors
Scale-invariant wavelet-based methods
The slide matching approach
The dominant scale approach
Scale-invariant methods based on fractal analysis
The multi-fractal spectrum
Fractal analysis using filter banks
Fractal dimensions for orientation histograms
Other approaches
SIFT features
Pulse-coupled neural networks based methods
Multiscale blob features
Scale-dependent methods
Experimental setup
The CUReT database
Method
The KTH-TIPS database
Discussion
Analyzing the misclassifications caused by scaling
Analyzing the methods scale invariance
Analyzing the methods viewpoint and scale invariance
Analyzing the methods illumination and scale invariance
Comparing the RoS with the kNN-classifier
A comparison of the rank based measures
The summation of the findings using rank-based measures
Analyzing the impact of the databases on the tested scale invariance
The different number of image samples per class
The different extent of scale changes
The different image scales
Summing up the impacts of the databases on the tested scale invariance
Conclusion
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