Wavelets and Reflection image question

Started by March 25, 2008
Hi all,

I've recently begun trying to understand the fundamentals of
lossy image compression via transforms such as DCT and Wavelets
(CDF9/7).

In a paper I was reading it suggested that prior to applying a
forward transform that a "reflection image" of the original image
be created.

This involves flipping the image vertically and horizontally and
copy those flipped variants above, below and to the left and right
hand-side, ending up with a larger image that is 3xwidth and 3xheight
of the original. then applying the forward transform and then the
inverse transform leads to a much higher PSNR than when the image
itself is forward then inverse transformed.

My questions are:

1. What is this method called? as I can't find anything else in the
literature I have that comments about this


2. Why does it provide a better result? is this some kind of Gibbs
effect on the border areas? I find that a great deal of the nose
when only using the original image comes from around the borders.



Any help would be greatly appreciated,


Rgds,

Jerzie