[mythtv-users] nVidia GF4 mx440 tv-out optimization
blacklion at blacklion.org
blacklion at blacklion.org
Mon Mar 29 22:21:48 EST 2004
Thanks for the great response. I tried the v4lctl command and I don't
see the "chroma agc" settings you were talking about, so I guess I have
some kernel work to do.
Also, you mentioned a couple of filters, "adjust" and "kerneldeint".
I'm not familiar with filters on Myth. Are these filters included with
Myth? If so, is there some documentation on them? I couldn't seem to
find any in the normal documentation.
On Sun, 2004-03-28 at 14:50, Bruce Markey wrote:
> blacklion at blacklion.org wrote:
> > I've actually seen this same problem. I have a Chaintech 7NIF2 board
> > with the GF4 MX 440 S-Video out. The desktop looks terrible, as
> > expected. However, when I have the frontend running, I can see the
> > horizontal refresh flicker. I have this hooked up to a Sony 27-inch
> > TV. The TV has 3 A/V inputs. Only one of the inputs has an S-Video
> > connector. I have my HorizSync set to 30 - 50 and my VertRefresh set to
> > 60. I don't see this flicker when watching Live TV or videos. I
> > haven't put in any images yet so I'm not sure how they look. It's only
> > on the menu screens that I see a flicker.
> Flicker has to do with how TVs work and how eyes work. Several
> environmental factors can effect how much you perceive flicker
> but one general thing is to reduce the maximum brightness (by
> lowering "contrast" for most sets, go figure ;-).
> > On another note, I haven't been impressed so far with the Live TV
> > picture. I'm sure there is more configuration that I could do. I just
> > need some direction. Here are the two problems I'm seeing:
> Nor had I (rickin', sniggle frit...) and have experimented with
> a lot of things for over a year. Now with the "adjust" filter
> and lots of tweaking I finally have a picture that reproduces
> the color palette nearly identical to a direct feed into the
> TV set.
> > 1. Light colors and whites have hardly any detail at all. They are just
> > so bright that all the detail is just washed out.
> Bingo! This is the biggest problem for picture "quality" and
> there is no tweak to the resolution or compression or deinterlace
> that will fix the colors(!). There are actually a couple related
> issues with luma and chroma that need to be adjusted.
> Before going into these adjustments, it is very helpful to use AGC
> if possible. The "v4l2" interface for bttv includes an option to
> set Automatic Gain Control. Some card have too high saturation and
> others too low by default. AGC normalizes the chroma level which will
> prevent distortions when trying to compensate further down the line.
> $ v4lctl -c /dev/video0 list
> attribute | type | current | default | comment
> norm | choice | NTSC | PAL | PAL NTSC SECAM PAL-Nc PAL-M PAL-N NTSC-JP PAL-60
> input | choice | Televis | Televis | Television Composite1 S-Video
> audio mode | choice | lang1 | mono | mono stereo lang1 lang2
> bright | int | 34000 | 32768 | range is 0 => 65535
> contrast | int | 23200 | 32768 | range is 0 => 65535
> color | int | 32000 | 32768 | range is 0 => 65535
> hue | int | 32768 | 32768 | range is 0 => 65535
> mute | bool | off | off |
> chroma agc | bool | on | off |
> combfilter | bool | off | off |
> automute | bool | on | off |
> luma decim | bool | off | off |
> agc crush | bool | on | off |
> vcr hack | bool | off | off |
> whitecrush | int | 207 | 207 | range is 0 => 255
> whitecrush | int | 127 | 127 | range is 0 => 255
> If you don't see some of the attributes like "chroma agc" then
> your kernel doesn't have v4l2 support. You can go the bytesex.org
> to get the v4l2 patches for your kernel version.
> If you do have v4l2, this will turn on the AGC mode:
> $ v4lctl -c /dev/video0 setattr 'chroma agc' on
> The problems with the image from bttv are that there is a known
> bug in the values for the luma range and also the chroma range
> doesn't align properly with the luma.
> The luma bug causes anything near white to be fully white. Clouds
> in the sky, for example, are white blobs with no detail. The quick
> hack is the cut the v4l contrast to avoid high luma altogether.
> However, the better solution is to use the "adjust" filter written
> by Andrew Mahone. This remaps any value from the chip to fall
> within the normal range.
> The other problem is that the chroma range is misadjusted so that
> colors in bright areas are weak and pale compared to colors in
> darker areas. If you turn up the saturation to the point where
> dark red is beating and bleeding, bright red is still pinkish and
> pale as if white paint was mixed in. The overall effect is that
> video looks like "old film" as someone once described it. Things
> don't look dense but just sort of washed out.
> This can also be fixed with the "adjust" filter. By narrowing the
> chroma input range to the filter, the chroma range is stretched
> into the higher luma (bright) range. If saturation is the color
> width, this would be the color height =). More color at bright
> levels means that things look more solid, dense, vivid, lifelike,
> and more bright color without dark colors bleeding.
> With these adjustments, video looks like live video rather than
> that dingy film look.
> mysql -u mythtv -pmythtv -hyourhost mythconverg
> mysql> update channel set contrast=23200,brightness=34000,colour=32000,hue=32768;
> mysql> update channel set videofilters='adjust=18:237:1.0:35:220:1.0';
> PVR-X50 cards do have a better picture than bttv cards by default
> so it is 'common knowledge' that PVR cards are somehow superior
> in the quality of the capture hardware (even though they use the
> same capture chip =). However, with these adjustments, I see a much
> better, more vivid picture from my bttv cards than I can possibly
> get from any adjustments with my PVR-250.
> BTW, to return safely to the crappy defaults:
> mysql> update channel set contrast=32758,brightness=32768,colour=32768,hue=32768;
> mysql> update channel set videofilters='';
> > 2. I'm not sure what to call it,
> Call it "interlace artifacts" ;-)
> > but I see a lot of "jitter" or
> > horizontal lines during fast moving scenes on TV. I've activated the
> > "Jitter reduction" option in the TV settings, but that doesn't seem to
> > help.
> The horizontal lines are the result of TV being interlaced and
> every other line is a half of a frame later in time than the other
> half of the lines. The only way a TV picture can ever look right
> is if there is a true one-to-one alignment with the scanlines on
> the screen. With X running (at some resolution) in an underscaned
> area on the screen, that's not going to happen.
> There are way to blur the horizontal line called "deinterlacing".
> Go to TV Settings->Playback, first page. You could simply check
> "Deinterlace playback", however, you will get better results if
> you leave it unchecked and enter "kerneldeint" in the Custon
> Filters test box.
> "Jitter reduction" has to do with evening out the timing of the
> frame drawing and will reduce the choppy movement seen in news
> tickers. This has nothing to do with horizontal lines despite what
> you may have heard elsewhere ;-).
> -- bjm
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