Good to know I'm not the only one that's considered the capture
quality to be sub-par. Of course, my issue has been all along on the
-250's capture resolution. If you look through my posts from over a year
ago, I looked into it quite a bit. If you're looking for a way to
objectively determine resolution, I put together a test clip DVD image
from stuff I found on the 'net. In particular, the EIA1596 B&W test
pattern is good to determing lines of resolution. A DVD-burnable image
for NTSC (and an untested PAL) is here:
http://www.ee.vt.edu/~mythtv/mythtvstuff/
That's exactly why I got a 150; I was under the impression that the comb
filter would be better and I'd get better quality. I have not found that to
be the case though. The filters are enabled by default and I've spent a ton
of time trying to tweak them to get the picture better. I usually use the
composite input and a DVD source to rule out tuner problems. You can try
playing with them yourself, the relevant registers are:
COMB_NOTCH_MODE=0-3
LCOMB_2LN_EN=0/1
LCOMB_3LN_EN=0/1
CCOMB_2LN_EN=0/1
LCOMB_3LN_EN=0/1
LCOMB_ERR_LIMIT=0-255
CCOMB_ERR_LIMIT=0-255
COMB_PHASE_LIMIT=0-255
I also like the results of enabling the sharpness enhancer (which is on on
250/350s)
PEAK_EN=0/1
PEAK_SEL=0-2
I've got a buddy with a PVR-500. AIUI, that's two 150's on the
same board, so this should be applicable to that, too, right?
I encourage you to play with the comb filters and see if you can improve
the picture quality. I've spent hours on it already and haven't really come
up with much. Here's my baseline:
http://capnbry.net/~bmayland/fi/pvr150/pvr150-250.jpg
I'm pretty sure the fuzzyness in the 150's shot is because the
CCOMB_ERR_LIMIT was exceeded and it had dropped back to notch. The notch
filter blurs things badly (try setting the err limit to 0 to see). There's
also a ton of errors in the vertical lines on the sci-fi logo which look
horrible even in motion.
At least you're seeing some effect. Most stuff I played with
(like the DNR settings) didn't seem to do much unless turned way up. And
of course, then it just made things worse.
The notch filter truly is horrible. It limits resolution to
effectively 352x480-ish. Lower than VHS IMO. That's the biggest reason
not to use bttv-based cards for a mythbox. I do find it good comic
relief to hear of people having CPU performance problems capturing 720x480
MPEG4 from a bt878 card, though... :)
-Cory
--
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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