[vorbis-dev] 2d wavelet transforms

Segher Boessenkool segher at wanadoo.nl
Sat Dec 30 11:32:26 PST 2000

> So, which on is the mathmatically correct one?

It doesn't matter, as long as your inverse transform expects
the same ordering. Use the one that compresses better
(I think that would be the second one).

> Oh, and another question I just remembered: audio signals
> are signed, because they're representations of the movement
> of the microphone. Video data does not have that, but the
> wavelet transform does expect signed data (or doesn't it?

You can view unsigned data as signed data, that "just happens"
to be all positive :-)

> Haar works on unsigned data but what about Daubechies and
> other wavelets?). So how do I convert? Simply subtracting
> 128 from each sample (ie casting to signed int) seems wrong.

If think you'll get better results if you transform the pixel
luminances to log doamin first (take a dB or something).

> Hope I didn't steal too much time from your efforts of
> getting it to work on Solaris :)

...or to work _at all_, in my case ;-)
(Just found out that a 10^48 big codebook is a no-no).



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