Optimizing for TV-Out over composite (RCA)

[bilu]

@ TV experts,

I've been watching a lot of green and orange artifacts on dark areas over composite signal. It doesn't happen when watching on a monitor or with a scan converter through SCART RGB output.

It's not a CCIR-601 problem: I'm using Limiter() and verified with ColourYUV(analize=true), also tried ColorYUV(levels="PC->TV") and ColorYUV(opt="coring"), but the artifacts still happen.

I think it could be related to the composite signal limitations, and started to investigate. Found this link (http://www.cybertheater.com/Tech_Reports/Comb_Filter_Tut/guide_comb_filters.html)
on comb filters and I was thinking if it was possible to make a filter that could "optimize" the image for better viewing over composite signal. :rolleyes:

I already have a scan converter (Trust Televiewer) that grabs VGA and converts to RGB-Video through SCART.

But I can't change the refresh from 60Hz when it is connected (despite Trust has confirmed it supports 72Hz and 75Hz that I need for the Reclock filter :( ).

That's why I would prefer to use composite, if I could somewhat get rid of that colour artifacts with your help...
:p

Thanks in advance,

Bilu

[sh0dan]

Do you have a sample clip?

[bilu]

Hi Sh0dan,

I can post a capture with my Pinnacle PCTV from composite input tonight.
But it seems to be happening with every dark scene.

One of the tests was made with Chapter 15 from Gladiator, first 500 frames. On ColorYUV(analize=true) I get something like:

Y min= 30 ; Y max=220
U min= 125 ; U max=135
V min= 125 ; V max=135

The result I get on the PCTV is the same as on TV.
Using the scan converter with SCART RGB output has no problem but I get the same artifacts if I use composite output.
The other composite output is from my Compaq Armada M700, ATI Rage Mobility P/M. Both outputs get the same sort of artifacts.

From the link I posted at the beginning of the thread it seems that you can get artifacts on composite signal due to overlapping luma/chroma signalling, but it seemed to be possible to avoid this overlapping. :confused:

Bilu

[sh0dan]

My best guess would be that it is caused by hardware. If the clip is alright on the monitor, and you're able to get the proper output in some cases. Maybe you should try and switch between YV12 and YUY2 output, as it could be the hardware/driver is wrongly interpreting the data.

The values you post are quite valid. Green is caused by both UV values being "too low", and orange output happends if both UV are too high. It sould be a chroma precision issue.

Have you tried:

MergeChroma(Blur(1.3).Blur(1.3)) to smooth out chroma slightly?

But a small testsample would help to identify if there is anything wrong with the video.

[bilu]

Important reading:

Guide to Comb Filters:
Y/C SeparationThe Composite Video Signal

This is a very brief and simplified description of the composite video signal format. There is more information about composite video signals in the accompanying article, Video Signal Formats.

A composite video signal is the sum of a luminance (brightness) signal and a chrominance (color) signal. In video terminology they are referred to as the Y and C signals respectively. The C signal is a specially modulated combination of two other intermediate signals called I & Q, which in turn were created from the original Red, Green, and Blue (RGB) outputs of a video camera or film scanner.

Television signals can be transmitted over the air, or on cable systems, by modulating an RF (Radio Frequency) carrier signal with audio and composite video signals. The composite video and narrow bandwidth audio signals are easily separated upon reception because they don't overlap in the frequency spectrum. In order to minimize the bandwidth used by the composite video signal, the frequency ranges of the Y & C signals are designed to overlap. This permits more TV channels to be broadcast within the total frequency spectrum available to broadcast television.

The problem created by overlapping the Y & C signal's frequency spectra is that it is very hard to separate them completely. The original designers of the U.S. NTSC television standard (in 1953) recognized this limitation, but believed it was a good tradeoff to preserve frequency space and to provide compatibility with the existing black and white TV system.

They very cleverly standardized on a system which interleaved the Y and C frequencies where their spectra overlapped. The Y and C signal energy clusters around specific frequencies related to the horizontal scan rate, fitting together like the teeth of two combs. The signals alternate in frequency between Y clusters and C clusters.

During movement of certain images and patterns, the frequency clusters can become smeared and widen out. In some cases the Y & C clusters will overlap and become very difficult to separate. But the interleaving works quite well for most video images.

The original designers of the NTSC system probably expected technology to provide an economical means to effectively separate the Y/C signals much sooner than it actually happened. Comb filters, the preferred solution, date back to much earlier than the 1953 standards, but they were too expensive to use.

Video Signal Formats - What is Y/C Frequency Interleaving?

Real video images generate highly complex frequency spectra. Several types of simple analog comb filters are used in TV monitors for Y/C separation. Unfortunately, they can not eliminate the cross-color and cross-luminance artifacts associated with complex real-world video images. Advanced digital 2-D and 3-D adaptive comb filters are now used in premium and moderately expensive video products. Although still imperfect, they provide major picture improvements over the older technology.

A filter to avoid the "frequency clusters" problem could be an interesting challenge! ;)

Best regards,
Bilu

[bilu]

@Sh0dan,

I don't think it is the hardware. It affects:

PCTV and television input;
Laptop and scan converter output;

The scan converter is connected to the VGA port and displays the correct colors over RGB SCART, but not over composite.

But it could be that both the scan converter and the laptop share the same problem... :confused:

And I got orange and green artifacts on the same frames, with the values I posted before.

Still I'll post a clip tonight, together with screenshots from the capture on PCTV.

Bilu

[frank]

Compare with a DVD playing from PC.
Do you get the same issues?

Cross-colour and cross-luminance effects have something to do with analog frequency spectrum and colour sub-carrier.

They are produced in the video modulator stage (and decoders), and don't exist in the clear RGB/YUV world.
Digital comb filters are placed in PAL decoders, Y-amplifiers.

I bet you have a hardware problem.
Or a driver problem of your PCTV card.

[bilu]

Compare with a DVD playing from PC.
Do you get the same issues?
I think I've seen them but I haven't watched a dark scene on DVD for a while. I'll check that tonight.

Cross-colour and cross-luminance effects have something to do with analog frequency spectrum and colour sub-carrier.

They are produced in the video modulator stage (and decoders), and don't exist in the clear RGB/YUV world.
Digital comb filters are placed in PAL decoders, Y-amplifiers.
I think it would be possible to minimize those "frequency clusters" that give a hard time on Y/C separation to comb filters.

I bet you have a hardware problem.
Or a driver problem of your PCTV card.
The PCTV card has the same kind of input problem as the TV itself.
Tonight I'll post a sample video, screenshots from the capture and the results on playing the original DVD.

Best regards,
Bilu

[bilu]

Hi,

Just to say I get much better image forcing RGB32 output on FFDShow.
It gets much better on every movie!!! :D

It may be related to hardware/drivers: both on my Geforce 2 MX400 and the laptop's ATI Rage Mobility image is much darker with RGB32 than with YV12 - tried forcing RGB32 on Koepi's XVID 08/03/2003, FFdshow 03/01/2003 and AVisynth 2.51 . FFDshow looks much better than XVID with forced colorspace.

Best regards,
Bilu

[bilu]

I would like to ask a moderator to move this thread since it has become playback related.

Please do not close it because I'm not finished yet. ;)


Best regards,
Bilu

[Guest]

Move it where?

[bilu]

Hmmm... I just realized that there are lots of posts on this subject, but not on a specific forum. Sometime issues are related to drivers, others to decoders, and others to hardware.

I think this topic deserves a section for itself, will post this as suggestion to Doom9.


Bilu

[bilu]

Since I've started this thread here, I'll continue it :)

My XVID encodes look better than my DVDs now over composite.

The key is not using RGB32 (changed my mind here) but FFDshow postprocessing:

Noise, Mplayer Uniform, Luma stregth 10, Chroma strenght 15

It corrects all the greenish artifacts that I could see over composite but not on the monitor! :D

Just need to find a way to use FFDshow postprocessing on DVDs also... :sly:


Best regards,
Bilu

[sh0dan]

In principle enabling "Raw Video" as input should make this possible.

[bilu]

Found this very good article on playback with Zoom Player, FFDshow and others:

http://www.inmatrix.com/articles/mediasetup.shtml

Bilu

[^^-+I4004+-^^]

bilu you have found a deeper knowledge;
mpeg4 has blocks (both in luma and chroma)
they are visible to you....
adding noise removes them
ffdshow is excellent...
any more good news out there?
(hehe)

ok,but seriously...first thin gto do on watching
with tv-out is to fine tune
1-tvout program (it's better if you have tvtool)
2-ffdshow

cranking that brightness and contrast
makes blocks visible,doesn't it?
dark areas are dark,correct?
that means they have no light..
if they have no light,you can't see
any blocks....
check the brightness/contrast seting and try again...
(although obviously...too low bitrate produces blocks too...
that ones are hard to get rid of with mere brightness...)

after this,you have solution of adding noise with
ffdshow...that's a good one too....

blocks?
what blocks?
what color artifacts?
matter of tweaking,and should be tried first...
(perhaps even without asking on forums...?)

[bilu]

Yeah, some deeper knowledge ;) hehe

I don't know any TV-tool for Windows that works on my ATI Rage Mobility P/M. I'm using a laptop, Compaq Armada M700. The only tool I've heard of was GATOS, but that's for Linux :rolleyes:

I've tuned a preset on my TV just for this and it looks fine now.
But FFDShow noise made the biggest difference.

Bilu

[SundanceKid]

Have you already tried this tool?
http://tvtool.info/

[bilu]

That's for Nvidias, not ATI.

[Aktan]

ATI's driver doesn't have the option?

[bilu]

What options? They have sharpness, brightness and contrast settings.