Chapter 1
Introduction
1.1 What this Book Is All About
The purpose of this book is to present a general theory of early vision and image
processing. The theory is normative, i.e. it says what is the optimal way of doing
these things. It is based on construction of statistical models of images combined
with Bayesian inference. Bayesian inference shows how we can use prior infor-
mation on the structure of typical images to greatly improve image analysis, and
statistical models are used for learning and storing that prior information.
The theory predicts what kind of features should be computed from the incoming
visual stimuli in the visual cortex. The predictions on the primary visual cortex
have been largely confirmed by experiments in visual neuroscience. The theory also
predicts something about what should happen in higher areas such as V2, which
gives new hints for people doing neuroscientific experiments.
Also, the theory can be applied on engineering problems to develop more ef-
ficient methods for de-noising, synthesis, reconstruction, compression, and other
tasks of image analysis, although we do not go into the details of such applications
in this book.
The statistical models presented in this book are quite different from classic sta-
tistical models. In fact, they are so sophisticated that many of them have been devel-
oped only during the last 10 years, so they are interesting in their own right. The key
point in these models is the non-Gaussianity (non-normality) inherent in image data.
The basic model presented is independent component analysis, but that is merely a
starting point for more sophisticated models.
A preview of what kind of properties these models learn is in Fig. 1.1.The
figure shows a number of linear features learned from natural images by a statis-
tical model. Chapters 5–7 will already consider models which learn such linear
features. In addition to the features themselves, the results in Fig. 1.1 show an-
other visually striking phenomenon, which is their spatial arrangement, or topog-
raphy. The results in the figure actually come from a model called Topographic
ICA, which is explained in Chap. 11. The spatial arrangement is also related to
computation of non-linear, invariant features, which is the topic of Chap. 10. Thus,
the result in this figure combines several of the results we develop in this book.
All of these properties are similar to those observed in the visual system of the
brain.
In the rest of this Introduction, we present the basic problem of image analysis,
and an overview of the various ideas discussed in more detail in this book.
A. Hyvärinen, J. Hurri, P.O. Hoyer, Natural Image Statistics,
Computational Imaging and Vision 39,
© Springer-Verlag London Limited 2009
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