How does Scala's (2.8) Manifest work?

I have some Scala code that makes fairly heavy use of generics, and I have gleaned from the docs that using a manifest in the parametrization constraints can help me work around the type erasure issues (e.g. I want to instantiate a new object of the generic type). Only, I'd like to understand more about how this works. It almost feels like some sort of hashmap that's getting an entry for every invocation site... Can anyone here elaborate?

class Image[T <: Pixel[T] : Manifest](fun() => T, size: Array[Int], data: Array[T]) {
    def this(fun: () => T, size: Array[T]) {
        this(fun, size, new Array[T](size(0) * size(1));
    }
}

This is something that doesn't seem to be covered in any of the documentation that I found on the site, and on Google I mostly get older posts that have very different syntax, and since 2.8 seems to have a lot of things changed, I'm not sure those are still accurate.