The problem of separating a non-rectangular foreground image from a background image is a classical problem in image processing and analysis, known as matting or keying. A common example is a film frame where an actor is extracted from the background to later be placed on a different background. Compositing of these objects against a new background is one of the most common operations in the creation of visual effects. When the original background is of non-constant color the matting becomes an under determined problem, for which a unique solution cannot be found. This thesis describes a framework for computing mattes from images with backgrounds of non-constant color, using Bayesian statistics.

Departing from Fred Dretske?s groundbreaking article, this essay explore the epistemic closure principle: the principle that states that knowledge is closed under known implication. It also explores the relationship to skepticism, various attempts to challenge and defend the principle, as well as developing a new perspective where the skeptical premise is seen as an a priori justified tautology that can be overriden by A posteriori experience. I argue that Dretske?s illuminating example makes it clear that there is an unescapable choice between either rejecting a skeptical premise ? however intuitive it may seem ? or inextricably having to admit a skeptical conclusion. .

The paper contains comment, clarification and criticism, even constructive criticism, of some theses that have been put forward by Laurence Bonjour in his In Defense of Pure Reason.It presents a concept of experience that deals with the relation between cognizer and object of experience that has a great similarity to that of Bonjour. Through analysis it is shown that the concept of a priori entails that Bonjour has two concepts of a priori, a narrow and a broad one. The narrow one is, in my own words: According to moderate rationalism a proposition p is a priori justified if and only if you apprehend that p must be true in every possible world. This doesn?t mean that Bonjour doesn?t believe in an epistemological, metaphysical and semantic realm.