[theora-dev] YUV clamped or unclamped ?

[salsaman]

Ah OK, thanks for clarifying. So a chroma value of 241 - 255 should just be
treated as 240 then.


Regards,
Salsaman.

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https://www.ohloh.net/accounts/salsaman



On Wed, Apr 14, 2010 at 9:36 PM, Timothy B. Terriberry <
tterribe at email.unc.edu> wrote:

> salsaman wrote:
> > Hi,
> > can somebody confirm whether theora uses clamped (16 - 235, 16 - 240) or
> > unclamped (0 - 255) YUV ?
>
> The specification clearly states that the former is to be used (see
> Section 4.3). However, there is nothing internal to the codec that
> enforces this.
>
> > My tests are showing that Y is always in the range 16 - 235 but the U
> > and V channels occasionally go above 240.
>
> The codec itself will not clamp things to these ranges, so the whole
> "lossy compression" thing can occasionally produce values slightly
> outside of them. This is normal.
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