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