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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 16 Mar 2014, 18:18 
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Played around with filtering yesterday - I figured out why VE was so tough. Basically the fourth harmonic signals are visible - I'm able to filter out the AC3 signal at 11.x mhz, but the left channel signal still shows. That said, I've reduced the interference and improved the color SN a lot.

My PSNR calculations show that I'm getting >=44.5db on pause frames now, a good bit of that's unavoidable due to spindle speed and time base correction.

I've also been looking at multiburst, there's a bit of a tradeoff with my primitive de-emphasis/equalization code because while it does the job, it's not working quite right yet. So that's the next thing to tackle, then 3D comb filtering and noise reduction, which is my only chance for getting rid of crosstalk and that left channel noise...

So I'm still plugging away, and I've got VE looking decent if not perfect now:

Image
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 17 Mar 2014, 12:36 
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Good job! Happy to know you are still working hard on this, and hope you will release an executable Windows software, as Python is not my kind of things... :D
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 25 Mar 2014, 21:52 
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Very nice!

Cant wait to see how you tackle the comb problem!

Keep up the good work.
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 26 Mar 2014, 20:31 
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Thanks! My latest checked in code gets a 48db PSNR between captured paused frames. I've also got code that can convert composite captures using my capture card into what my TBC and comb filter expect. I'm not sure how Pioneer measured (if they actually did at all) SNR, it seems a bit arbitrary. (I was going to put numbers here, but remembered I was analyzing at 8fsc/1488 lines, deflating the #'s...)

My next step is to attempt to cancel out the audio channel interference (I do this for the chroma carrier) - if I succeed in that I can adjust the filtering a bit more, and the composite-level decoding might compare decently with good players.

Then I'll look at 3D comb filtering and adaptive noise reduction. That's a bit off, but the results should be quite rewarding. The adaptive NR would probably clean up some of the audio channel issues, but since this is about doing things The Hard Way, I want to get clean composite output from my decoder :)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 26 Mar 2014, 20:34 
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Great news!!!
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 16 Apr 2014, 08:24 
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Still looking at the de-emphasis filtering... it's something that needs to be implemented well to avoid ringing/ghosting while maintaining good frequency response. So I don't have anything great to report right now, but I'm working in a few different areas. This is a hobby/learning project, afterall, and when it comes to these things it really is about the journey.

- Found Greg Berchin's FDLS filter design code. This has given me good results for de-emphasis, but... it's not open source code (and I'm not even sure I can legally use the output from his sample program), and nobody has re-implemented it as he suggested yet. I guess that means it's up to me. :)

- I have a nice VGA signal amp/splitter with adjustable gain that I use for capturing RF from the player. I can't get another one or point other people to it, as the seller's stock was returned as defective. (It worked for my uses, though...) The common Monoprice unit only has unity gain, which is less than ideal.

- I looked at tapping the pre-TBC signal off my Denon D503-clone to run it through my decoders - and see if the TBC in one of my Panasonic DVD recorders can deal with it- but the Monoprice unit has too much impedence. So to handle the two issues, I've got some AD811 chips on order and I'm hoping to breadboard a couple of amp circuits this weekend. If I can get that to work well, I might make an AD811 breakout board at OSH Park, if there isn't one already.

- Regardless I'll do some captures off the D503 this weekend, since it is better aligned than either of my V2800's (I can't get a service manual for it at a reasonable price anywhere. Sears has some, but for $70. eek.)

- THX Wow has some nice clean test signals. It's definitely a good part of the toolbox, behind the Pioneer disk and about equal to VE overall.

So things are plugging along, and I'll have some useful side-products soon that might be actually useful for practical things. :thumbup:
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 27 Apr 2014, 19:13 
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I got a Python version of Berchin's FDLS algorithm working and replaced a couple of my filters with it. Pretty soon I'll post it on github as it's own project, and maybe it'll wind up in SciPy's signal processing library someday. It really is quite nice :thumbup:

Also making some headway on 3D comb filtering, but it's not nearly finished/refined yet, and most importantly it looks pretty bad on real footage. But on the plus side you can see I've got 400 lines of resolution with the new filters :)

http://i.imgur.com/H9fyQXz.jpg

This was captured off my Denon 503-clone, which is a little bit cleaner than my crosstalk-y V2800. I need to sacrifice another VGA cable to add an RF tap to my 3080 and probably my V2200. Since they probably both use the 1987 pickup design (hifi engine has the 3070 service guide), I suspect they'll be closer in quality than one would otherwise expect.
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 27 Apr 2014, 20:29 
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You have reached a very good resolution, good job!
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 27 Apr 2014, 21:38 
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Wow, just wow!

I look forward to trying this out on a tapebased media at some point!
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 27 Apr 2014, 23:13 
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Thanks!

(edit: Yup, it's going to take a while for me to get a good 3D comb filter. There are definitely some new gotcha's and my earlier 1D/2D design doesn't really fit)

A lot of the technology is adaptable to tape-based media, but it's a bit different in practice as color is separated from the luma*. Glimmie over on AVS pointed me to a paper done by people who have actually done this for Betacam. It's not open source, and the capture device is probably not affordable. I might look at VHS eventually, but I also might take up an entirely different hobby project after this. I like projects like this where I have to learn more about a lot of things to get results :thumbup:

Also the excessive background noise mostly appears to occur on VE and other late Kuraray titles... they're definitely gaining sharpness at the expense of noise. The Pioneer service disk only gets to about 350-360 horizontal lines, the sweep pattern blurs out before 5mhz on every setup I've looked at. Also in both cases there is attenuation in multiburst pictures that I don't see in the version embedded in the vertical interval test signals.

But it shouldn't be too hard to implement modest NR to clean up the signal. The earlier deemphasis routine I used basically did NR, but it reduced the frequency response too much.

(* - a lot of LD's evolution over the years is because it wasn't - improved encoding techniques such as SuperNTSC improved LD quality quite a bit.)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 28 Apr 2014, 20:41 
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Could you please point me to that paper?
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 28 Apr 2014, 21:29 
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"Asset values increased – new technologies for the automatic transfer and digital preservation of analogue
video-cassettes J. Burghardt, J. Houpert and T. Mayer"

http://www.theiet.org/communities/multi ... m?type=pdf
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 14 May 2014, 14:31 
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Thanks!

I contacted them and their partner cubetec last year, they will have a product coming in one or more years. It will cost 30.000 euros for the device(one device needed per format with only betacamSP being done first) Then another 30.000 euros for the software decode station. So quite expensive. I am still looking into a diy solution and also maybe some funding from the norwegian goverment to make a pilot project.
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 15 May 2014, 06:00 
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Wow. i figured it would be a few thousand dollars, not 60K euro!

If you're up for dealing with lower level Linux stuff, I can give you some pointers on how to set up a capture. The CX2388x PCI (non-E) boards I use are very cheap, at least here, and I'm playing around with different second-hand amplifiers, etc. I need to find/build one around say the AD811 chip - first I need a good dual-rail supply for it, though. For now I can use my amp which has better gain adjustments.

Something like the USRP2 would do a better job, but that's about $600 or so and I don't have that kinda money right now...
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 15 May 2014, 20:34 
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Well they do mostly installations for massive industrialised ingestion. The rest of their systems are priced similarly. But for normal smallsized projects and individuals its completely out of reach. I wonder if they have killer software or if its just ok. I have tried to get images from them comparing thr RFdirect method with regular digitisation but I have not seen any. I have some press material and such if you interested and their patent is easy to find. http://www.sumobrain.com/patents/wipo/C ... 6908A2.pdf

For me the novelty with this approach is that when capturing the full RF you get what is really on the tape and if software improves in the future you can extract more material in better quality. These old tapes are slowly dying and this method would potentially save them, it makes it possible to ingest in the best possible way right now, before the tapes deteriorate completely.
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 30 May 2014, 22:09 
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Have you had any progress? I am really looking forward to trying this out when I find the time.

Keep on keepin on.
  
 
 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 31 May 2014, 07:28 
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No progress yet, but thanks :)

(I'm on vacation right now, and haven't felt like coding much of anything)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 13 Jul 2014, 08:41 
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Dusted this off about a week ago and made some progress - I implemented a Hilbert transform for FM demodulation in my Python version, then removed all scalar code and got slightly better and about 70% faster results than the C version. The nice thing about working in Python is that one can iterate a lot faster, and I was able to fine tune things a bit.

One of my tests is decoding a still frame several times and comparing the PSNR of the results. Interestingly, the current code when decoding frame 40735 on side B (a test black frame) of THX Wow! gets the exact same results for each captured frame once the frame transition bit is cropped - because of the intrinsic signal noise and motor speed variation, the TBC has to be working perfectly for that to happen. The same comparison with a frame of VE gets 49dB (between one frame and the average) and the Pioneer ref disk only got 46, probably because the V2800's spindle is less accurate with the smaller disc.

White SNR is about 40db with current settings, which is less impressive but OK given the lack of NR that most players do have.

At this point the comb filtering needs the most work - on some scenes/frames, it looks fine, but going from color to color is rough.

(test pics will be edited into this post soon)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 13 Jul 2014, 20:09 
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Hilbert transforms? You fool! You'll crack open the Universe and plunge us all into De Sitter space!
(Actually an objection I saw someone on the Internet make once. Apparently this fellow was unaware that De Sitter space is a pure mathematical construct, & it's not going to leak into our reality no matter how hard we crunch numbers with our numbercrunchermachines.)
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 Post subject: Re: (WIP) Laserdisc software image decoder from raw signal
PostPosted: 13 Jul 2014, 20:57 
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LOL :)
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