[x264-devel] I444 support

[List, Peter]

> hello list
> 
> i'm working on a system to archive old media digitally, and i want to
> do that with as little data loss as possible.
> 
> as h.264 offers very good compression ratios and can operate in a no-
> quantisation mode (qp=0), i want to use that, if possible.

Yes, x264 offers very good quality/compression ratio, in particular at
high compression rates. I would not be so sure this is still true with
VERY LOW compression like with qp-values of around 0. I don't know, but
you might very well get a data expansion (even more so with 4:4:4). 
Also, at very low compression rates (high data rates) the gain from
temporal prediction (motion compensation) can be very small. So,
consider to use a pure INTRA compression scheme like JPEG2000. For
instance the Kakadu JPEG200 encoder already includes 4:4:4 RGB
compression. 
Finally, of cause I don't know what exactly you try to archive. But, if
the material is old and/or analog or if your film scanner (for analog
sources) only has a limited quality, it will definitely not be worth
archiving at very high data rates. In that case you would just waist
expensive storage room to archive a lot of noise... 
Regads
Peter

> but there is another bottleneck besides quantisation: the colorspace
> compression.luckily, the h.264 specification describes support for
4:4:4 
> (no chroma subsampling) in the fidelity range extensions -
unfortunately
> x264 does not (yet) support this. In fact, i've been looking for a
> suitable codec that can do rgb24 or yuv4:4:4 for quite some time.
> 
> how hard would it be to add this missing feature? does the current
> implementation rely on a subsampled colorspace? and where should i
> start if i want to implement it myself?
> 
> thanks
> gregor