Hey,
I have a bttv-compatible card (BT878) and I was noticing that my
images are too 'bright'. I quickly discovered this is because the BT878
samples the luma channel in the range 16-253 instead of the normal
16-235 specified by Rec. 601.
There are, of course, a couple of nasty implications of this:
1. All images from the bttv driver must be converted to a correct
excursion before they can be used by other tools, such as MPEG
encoders, display on an XVideo surface, etc.
2. Cards which output correct Y'CbCr images will have to somehow
be distinguishable from these crappy bttv image maps through the
API.
Thoughts? Is this described somewhere that I don't know about? It
would be nice if the header file or documentation mentioned this, at
least ...
It would also be nice if the data types used in video4linux reflected
what the values meant. What I mean is, VIDEO_PALETTE_YUV422 is actually
(or should actually be) Y'CbCr at 4:2:2 sampling, and not actual Y, U,
or V values. See http://www.inforamp.net/~poynton/ for his colour FAQ.
--
Billy Biggs bbiggs@xxxxxxxxxxxx
http://www.billybiggs.com/ wbiggs@xxxxxxxxxxxx
Attachment:
pgptPMiWdHYeN.pgp
Description: PGP signature
