Re: Shift Histograms

Thank for your reply!  That makes total sense.

Do you know if this bias is well known?  Has anyone besides me ever tested 
this?  Random variations of plus or minus 1% for individual pixels is no big 
deal, but having the whole image get 1% darker is.  It seems a shame to have 
such a cool codec as Xvid be so accurate when given Yv12 source, and then 
have it become so inaccurate if handed RGB.  Obviously I can choose to feed 
it only YV12, but I'm guessing less tech savvy users would get confused 
about this.

Regards,
Andrew



--------------------------------------------------
From: "Michael Militzer" <[email protected]>
Sent: Monday, May 11, 2009 2:01 AM
To: <[email protected]>
Subject: Re: [XviD-devel] Shift Histograms

> 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 <[email protected]>:
>
>> 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
>>
>> _______________________________________________
>> Xvid-devel mailing list
>> [email protected]
>> http://list.xvid.org/mailman/listinfo/xvid-devel
>>
>>
>
>
>
>
>
>
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