Out of curiosity how much is the data "damaged" by a conversion from
4:1:1 to RGB and from there to 4:2:0?
Or really how much more damage than is already done going from 4:1:1
to 4:2:0, which really results in the (quality) equivalent of 4:1:0
(if such a beast exists).
The decimation and interpolation errors that result from 4:1:1 ->
4:4:4 (RGB) -> 4:2:0 can be made as small as you like in theory - just
use larger filters (kernels). Of course, many of the available
conversion tools don't allow very sophisticated filtering, and large
filters take a while to compute. In particular the decimation
(subsampling) stage is the critical one.
As for colorspace-conversion damage, I presume this depends on the
nature of the input. The full R'G'B' colorspace maps into YCbCr, but
even ignoring quantization it's not always invertible. It's easy
enough to check for clipping in the inverse map, though (although I
don't know of any programs that do). If the actual source of the video
was an RGB source - say a typical CCD-based video camera, then maybe
you're OK. My own camera does actually produce Y values above 235, in
which case you would have to scale it down to avoid clipping.
I have used yuvcorrect in RGB mode on occasion, and I can't say I've
identified any obvious artifacts due to the conversion. Certainly the
CCD noise dominates any extra quantization noise.
A cheap and dirty measurement would be to measure the mean-square/avg/peak
error between 4:1:1->4:2:0 frames and 4:1:1->RGB->4:2:0. Or just look
at them side by side.
The normal path is to go from DV (411) to 420 directly but I'm
eye'ing some of the NetPBM filters (seems that most/many of the good
filters want PPM data).
In particular the 'pnmnlfilt' program sounds intriguing, it offers:
'Alpha trimmed mean filter', 'Optimal estimation smoothing' and
'Edge enhancement'. All the types of things we might want to do or
at least try.
Do they do pipes? Horrible to think of splitting into frame images...
Dan
-------------------------------------------------------
This SF.net email is sponsored by:
The Definitive IT and Networking Event. Be There!
NetWorld+Interop Las Vegas 2003 -- Register today!
http://ads.sourceforge.net/cgi-bin/redirect.pl?keyn0001en
_______________________________________________
Mjpeg-users mailing list
[EMAIL PROTECTED]
https://lists.sourceforge.net/lists/listinfo/mjpeg-users
