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fisix
26th November 2001, 01:37
i have a wintv pvr pci, 1GHz p3, and i use virtualdub to capture to huffyuv, then later encode using nandub to 2pass divx. the signal i get is from the tuner input, not the svideo input.

my problem, specifically, is that i lose the contrast between the southpark kids faces and thier eyes. the faces are almost white, and the eyes are white. i've tried adjusting the contrast and brightness as is explained on cart's (Luke's Video) website, and i seem to get a nice flat histogram, but even just viewing the capture file before i encode, the faces bleed into the eyes.

i'm currently trying to adjust the brightness and contrast to get something a little better (by mainly lowering both), but i was wondering if anyone else might have some suggestions/similar problems.



-fisix

Cart
26th November 2001, 03:48
Yeah, it can be hard to obtain good detail in the extreme white areas. You're probably going to want to decrease the contrast a bit.

If the PVR uses at BT878 chipset, you can try tweaking the luma range or forcing the "over-white" whites into the legal YUV range. See this nice post by Avery Lee for further information:
http://arstechnica.infopop.net/OpenTopic/page?a=tpc&s=50009562&f=67909965&m=6110948513&r=4910959513#4910959513

-Cart
http://www.geocities.com/lukesvideo/index.html

fisix
26th November 2001, 05:31
that's a good post. i ignored the special bt878 stuff because i thought it was only for weird capture sizes. i'll post up again after i've played a bit.

-fisix

fisix
26th November 2001, 23:34
thanks again, cart.

i did half of what avery lee suggested, by enabling full luma range and setting the white up and down to full left. it was pretty amazing what i had been missing. i spent about an hour looking at the difference between what was on my tv and what i got on screen with the wintv card and i finally see how someone could spend $1000's more on something better. in a cartoon scene with a white background and a light green lower half (cartoon grass), on the wintv i got a thin line separating 2 white fields (green bleached out to white). with the suggested tweak, i get a green thats there (yay!) but it looks kinda brownish green (boo). playing with the saturation and tint didn't seem to help at all.

i also tried something called AGC (automatic gain control?) crush in the bt878 tweak page, and it seemed to also help a bit, but i couldn't get the box to stay checked reliably. using the 'squish luma range' check in the regular virdub video menu did nothing..

any ideas on what the other sliders and check boxes do? they seem to only work in certain combinations, and i couldn't get the 're-something' button to affect anything.

anyway, i now have all the contrast range back (their eyes are back), but the colors are either dim or wrong, and tint and saturation only seem to make the wrong colors more evident. any ideas or help?

correct me if i'm wrong, but here's what i think is happening. WITHOUT the tweaks avery lee suggested, i think i'm getting the right colors, but anything above some specific color level (source), say 0.9 (white = 1.0 at the top, black = 0.0 at the bottom) is pinched into a small range near white(output). so everything from 0.9 to 1.0 (source) gets mushed into 0.98 to 0.1(output). when i use the tweak avery suggested, everything gets multiplicatively slid down the color scale (output), and so i get wrong colors, but 0.98 to 1.0 gets expanded back to 0.9 to 1.0 (or so). so, maybe what has happened is that Hauppage saw they had a color problem and they fixed the lower colors by hacking something that shifted the colors up somewhere in their pipeline of amps and ADC's, but the shift ended up compressing much of the high color levels into a short range. or maybe i've lost one of the counters in the high range.. i suppose i could get out an oscilliscope... bleaugh. or maybe something in the drivers for the yuy2 data stream is doing something funny. i'm trying to think what would cause a compression like that. hm. maybe my own video card has the video overlay gamma set too high. fiik.

willing to ponder? maybe if i used the svideo input and saw if there was a difference... that might at least keep the integrated tuner out of the list of possible problems. agg.

-fisix

Cart
29th November 2001, 06:43
Eh, even I don't put that much effort into tweaking the ol' WinTV. The card wasn't made for professional-quality adjustable captures, so it's hard to make things look better than average.

The "reassert" button reapplies the chosen settings to the BT878 chipset. This is necessary because the WinTV drivers reset your tweaks at every chance they get.

I really can't tell you much beyond what you already know about the tweaker. (I don't use it myself.) As for your color problems, perhaps a trusty levels filters could improve the situation?

-Cart
http://www.geocities.com/lukesvideo/index.html

fisix
6th December 2001, 05:35
which filter is a good levels filter? is something like that included in the flaxen filter set?

-fisix

Cart
21st December 2001, 23:34
VirtualDub includes a levels filter. You can also check out Donald Graft's filters:
http://sauron.mordor.net/dgraft/

-Cart
http://www.geocities.com/lukesvideo/index.html