CW-SSIM based image classification

Complex wavelet structural similarity (CW-SSIM) index has been proposed as a promising image similarity measure that is robust to small geometric distortions such as translation, scaling and rotation of images, but how to make the best use of it in image classification problems has not been deeply investigated. In this paper, we propose a novel “feature-extraction free” image classification algorithm based on CW-SSIM and use handwritten digit recognition as an example to demonstrate it. First, a CW-SSIM based unsupervised clustering method is used to divide the training images into clusters and to pick a representative image for each cluster. A supervised learning method based on support vector machines is then employed to maximize the classification accuracy based on CW-SSIM values between an input image and the representative images. Our experiments show that such a conceptually simple image classification method, which does not involve any registration, intensity normalization or sophisticated feature extraction processes, and does not rely on any modeling of the image patterns or distortion processes, achieves competitive performance with reduced computational complexity.