[XviD-devel] Shift Histograms

[Michael Militzer]

Hi,

Xvid's RGB <-> YUV conversions have been designed to be fast. It is known
that they aren't precise (especially the MMX versions). So if you measure
a ~1% deviation this may not be a big surprise.

The implementation in C should be more precise. So for a test you may want
to disable MMX/SSE optimizations in the xvid GUI and check whether the
C-code provides better results.

In general especially the YUV -> RGB conversions have been included into
xvid at a time when graphics cards with YUV overlay support were not the
norm and when low-end PC processors still had a hard time to decode PAL
resolution video in realtime. So the primary goal was to make the
conversions fast to enable fluent playback...

Regards,
Michael


Quoting A Uio <a.xvid at uio9.org>:

> Howdy,
>
> I think I may have found a bug in Xvid's RGB/YUV conversions. I've been
> posting about it at
>
> http://forum.doom9.org/showthread.php?p=1281193
>
> Despite what responders have posted, I'm fairly sure its not a PC/Video
> levels or 601/709 issue.  No one took me up on my request to replicate the
> tests on their systems, so it is always could just be something wrong with
> my system.
>
> Hope this is helpful!
>
> Regards,
> A
>
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>