[opendtv] Re: FW: Re: negative RGB (bit depths)
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 17 Jan 2005 20:26:05 -0500
Yep, if you go back a bit that's sort of what started this discussion.
I was wondering if 10-12 bits would be mostly the same as 8 in the usual
cases where bit rate control would force it to be quantized to more or
less that amount anyway, but better when you have excess bits to code
transparency.
However it appears that 10-12 bits performed even better than I
expected, possibly for the reasons Craig explained. But maybe also for
CBR because more bits could then sometimes be used on the easy-to-code
still scenes, improving average PSNR with the extra depth.
Generally it's convinced me that the extra depth is probably a good
thing when you can do it.
Is there any problem decoding 12 bit material with 8 bit decoders?
- Tom
Ron Economos wrote:
> I read the paper last night. Pretty interesting, but given that
> the PSNR values where 8 bit diverged from 10/12 bit were
> all above 45 to 50 dB, I wonder if this discovery is just a
> novelty. From my measurements of HD MPEG-2 PSNR,
> 45 dB or greater PSNR is perceptually identical to the
> original (unless you're from the planet Krypton), so it
> doesn't seem useful to code at these bitrates (where the
> effect takes place) even for Digital Cinema.
>
> Ron
>
> Tom Barry wrote:
>
>
>>Tom McMahon was kind enough to send me the paper mentioned below, even
>>though the list bounces attached .doc files.
>>
>>That paper does seem to suggest that feeding the AVC encoder more bit
>>depth will almost always result in a higher (at least non-lower) PSNR
>>for the same specified output bit rate.
>>
>>Or generally, a lower output bit rate to keep the same fixed output
>>quality level when you input as 10 or 12 bits instead of 8.
>>
>>I'm just guessing this is because rate control will quantize down to
>> a smaller number of bits / pixel anyway where needed. And for
>>properly filtered material this may avoid some aliasing that would
>>otherwise be created by the truncation to a lower bit depth in integer
>>processing before reaching the encoder.
>>
>>But, whatever the reason, this is very good news for folks with > 8 bit
>>encoders, which we all should go get immediately. I'm going to
>>prematurely take this to mean we should ALWAYS be using 12 bits
>>everywhere, and let the encoders make the choice based upon desired
>>output bit rate and our quality trade-offs. Very cool.
>>
>>- Tom
>>
>>
>>
>
>
>
>
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