I read on http://mythtv.org/pipermail/mythtv-users/2004-March/037866.html
that it's a good idea to use v4lctl -c /dev/video0 setattr 'chroma agc'
on to really improve colour quality.
Since that posting I finally got around to doing the obvious
and set it as an option parameter when loading the module:
options bttvchroma_agc=1 combfilter=2
The combfilter is a very good thing also as it gets rid of the
multicolored flickering around high contrast edges. I read
somewhere about how the combfilter options work and that 2
did a better job. Seems to work well.
Interesting thing on the combfiler. From what I can tell (briefly
looking through the code), it's mostly a post-processing hack. The
bt87[89] chip does *not* have a hardware comb filter on the luma channel,
and thus relies on either a lowpass or a chroma notch. At least that's
what the datasheet says... :)
Basically that means that while you can post-process a phony up a
comb-filter to get rid of some color artifacts, you still lose all
luminance bandwidth at the chip level. That's why the BT8x8 chips have
excruciatingly low resolution (352x480 at *best*). The best they do is
lowpass the luma to keep out the chroma... and that knee is at best 3MHz.
At 80 lines per MHz, that's 240 * 4/3 = 320, so 352x480 is being a bit
generous. With S-vid you can do better since it bypasses the Y/C demod.
Just thought some people might light to know... :)
-Cory
*
* Cory Papenfuss*
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*
___
mythtv-users mailing list
[EMAIL PROTECTED]
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
