[x264-devel] Re: [patch] SSE2 pixel routines

[Alexander Izvorski]

On 7/25/05, Loren Merritt <lorenm at u.washington.edu> wrote:
> On Fri, 22 Jul 2005, Alexander Izvorski wrote:
> > Why is the result of satd divided by two?!  That throws away one bit
> > of precision which would have a small but noticeable impact on PSNR.
> > (see the "shr     eax,1" in MMX_SUM_MM).
> 
> It allows SAD and SATD to use the same lambda table. Now, I'm not sure
> that the difference is exactly a factor of 2, so maybe they should be
> separate.
> For that matter, the current lack of precision in lambda should make much
> more difference than 1 bit in satd.

Can you explain that a bit?  Why is lambda table not precise?  How can
we make it more precise?  Why is the difference assumed to be
approximately a factor of two?

Regards,
-Alex Izvorski

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