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Machine Learning Summer School 2005 - Canberra
Pascal

Kernel Methods for Higher Order Image Statistics

author: Matthias O. Franz, Max Planck Institute for Biological Cybernetics

Description

The conditions under which natural vision systems evolved show statistical regularities determined both by the environment and by the actions of the organism. Many aspects of biological vision can be understood as evolutionary adaptations to these regularities. This is demonstrated by the recent sucess in explaining properties of retinal and cortical neurons from the statistics of natural images. At the same time, we observe an increasing interest in statistical modeling techniques in the computer vision community. Here, the motivation comes from the need for powerful image models in image processing tasks such as super-resolution or denoising. In the literature, the statistical analysis of natural images has mainly been done with linear techniques such as Principal Component Analysis (PCA) or Fourier analysis. These techniques capture only the second-order statistics of an image ensemble. A large part of the interesting image structure, however, is contained in the higher-order statistics. Unfortunately, the estimation of these statistics involves a huge number of terms which makes their explicit computation for images infeasible in practice. Kernel methods provide an implicit access to higher-order statistics that avoids this combinatorial explosion. In the course, we start with an overview of existing approaches to image statistics. The need to go beyond the usual linear, second-order techniques will lead us to the classical higher-order statistics such as Wiener series, higher-order cumulants and spectra. We will see that the exponential number of terms involved in these statistics prevents them from being applied to images. This motivates the introduction of kernel techniques. Here, we will discuss two approaches: 1. The Wiener series can be estimated implicitly via polynomial kernel regression. We will use this technique to decompose an image into components that are characterized by pixel interactions of a given order. 2. Kernel PCA of image patches provides a powerful image model that takes higher-order statistics into account. We will show applications of this model to various image processing tasks.

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Slides
0:00 Kernel methods for higher-order image statistics
2:10 Global Overview
3:18 Lecture 1: Statistics of natural images in the literature
4:40 Why are image statistics important?
7:09 Why are image statistics important? (2)
8:36 Single frame superresolution (Freeman et al., 2000)
11:58 Texture synthesis example (Efros & Freeman, 2001)
12:58 Texture synthesis example II (Efros & Freeman, 2001)
14:29 Region lling and object removal (Criminisi et al., 2004)
15:06 Region lling and object removal II (Criminisi et al., 2004)
15:34 First-order image statistics and contrast coding
17:48 Maximizing entropy by histogram equalization
24:52 LMC response curve is matched to CDF
27:54 Second order image statistics
30:25 Second order pixel correlations
31:57 1/f spectra of natural images [Field, 1987]
33:19 Redundancy reduction by predictive coding
40:03 Why are 2nd-order statistics not enough? (1)
42:41 Why are 2nd-order statistics not enough? (2)
43:30 Why are 2nd-order statistics not enough? (3) - Kurtosis
46:20 Higher order image statistics and sparse cortical coding
50:47 Independent components of images and receptive elds in V1
54:08 Conclusions

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Comment1 sayuri, July 3, 2008 at 7:41 a.m.:

thankyou!!


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