Very curious issue with DV

farss wrote on 12/10/2003, 4:01 AM
I don't think this is any way VVs fault, I suspect it's an issue with the nature of DV but I'm damned if I can explain it.
Today I transferred quite a bit of 8mm film using my new ADVC-300. Worked beautifully. I felt so inspired just for kicks I went and did some color correction following BBs tutorial on removing color casts. Wow what a difference, bride is now wearing white, not yellow and the roses are yellow not green. So I had a go at another clip for the same client.
The film was in much worse condition, some of it just cannot be corrected, it seems sometimes due to bad processing or storage one or more of the dye layers just disappears. It was also very dark and grainy. Boosting up the gain and apply whatever CC would help mostly it looks OK apart from the grain and noise.

Now comes the wierd part. I was monitoring extrenally via the ADVC-300 and I started to notice some horrendous artifacts, much like serious venetian blinds that are shifted about 5% of image to the left on any vertical during motion. Damn I thought something wierd in the D/A, it wasn't on the PC monitor so I just ignored it. I did try prerendering it just in case but it was still on the external monitor but not on the internak.

Anyway job is late so I pressed on, making a note to better check out the ADVC-300. Encoded to mpeg for DVDA and then lost a few hours having DVDA dramas. Finally burnt DVD and had a look how my CC turned out. First clip of wedding looks truly great, went to the really dodgy clip and horror of horrors there are the venetian blinds.

So back to VV. If I disable the CC problem is there but not as bad, if I enable Reduce Interlace Flicker on the clip properties, problem goes away, if I apply slight gaussian blur problem goes away. So I can find lots of ways to fix it but none of them make any sense. These artifacts are way too big to have anything to do with interlace. The only factor is the amount of noise i.e total number of pixels changing from frame to frame. The CC has bought the noise from the CCDs and the film grain up a lot, the blur would reduce it.
As I don't know just what reduce Interlace Flicker does I cannot comment on that. It almost looks like there is just too much happening for the DV codec to cope with BUT DV encoding isn't temporal.

Obviously I've fixed the problem but I'd sure ike to know why what I'e done fixed it. I might add the actual source is at 18 fps with some very dodgy pulldown to PAL at 25fps but that has never caused a problem before, all the other reels on the same timeline are fine.

Comments

jamcas wrote on 12/10/2003, 4:25 AM
Hey Farss,

Do you have a website or contact number I could reach you on ?

im interested to convert some 8mm film to DV

regards
Jc
farss wrote on 12/10/2003, 4:50 AM
farssAToptusnetDOTcomDOTau
johnmeyer wrote on 12/10/2003, 2:24 PM
What are you using to project the 8mm film? I use the Workprinter, which captures one frame at a time. The result is one frame of film onto one frame of video. Because of the stop-motion nature of this capture technique, the video is actually progressive. If you've used this method, and are telling Vegas that the video is interlaced, this could be part of the problem. There are also issues with how Vegas handles the "pulldown" if you choosed to have Vegas slow down the footage (since it is 15, 18, or 24 fps, you have to slow it down so it looks right when played back at 29.97 -NTSC or 25 fps - PAL).

If you captured the footage by pointing the camera at a projector, this introduces all sorts of artifacts that could be what you are seeing.
jaegersing wrote on 12/10/2003, 4:33 PM
I saw exactly this effect recently. It was due to the clip and project resoilution settings being slightly different. For example, a clip of 328x248 in a project of 320x240 (or something like that). I think the resampling in Vegas is what is producing the venetian blind effect. A close (but not exact) multiple of the resolution also produces this (like 328x248 in a 640x480 project).

I solved it by applying a crop to the affect clips, and basically forcing off the resample. I suggest you check the clip properties and project properties and see if there is any mismatch. Another possibility is that you have applied a fixed zoom factor somewhere (in track motion or event crop) that causes a similar resampling to take place.

(If you're wondering where I got such strange clip sizes, it was some screen captures from Hypercam where I hadn't set the capture window size carefully.)

Richard Hunter
Vince Denali wrote on 12/10/2003, 6:15 PM
> BBs tutorial on removing color casts

I tried searching for BB and "color cast", but was unable to find this tutorial.
Would you please tell me more?

Thanks !
farss wrote on 12/10/2003, 7:41 PM
John,
I use Elmo telecine so it is 50i but but wierd "pulldown". All other clips are fine.
I'd love to have a Printworker, or at least clients who'd pay what it costs to put in that amount of effort. I from to time come accross work done by the competition and my stuff is miles in front. I might have a chance at getting a real telecine with a super 8 gate but apart from the space, the compressed air feed and the cost of tubes for what I can get clients to pay I doubt it'd cover the cost of power and air conditioning to run the thing.

jaegersing,
You've hit it in one. The other thing I'd forgotten about was I'd slightly downsized the frame to keep all the action in the safe area. The telecine masks off just a little and most TV just a little more. Usually I don't worry about this but this was a 'movie' as in something acted out and I wanted to keep as much of it for the client as I could (just for Xmas!)

sting:

http://www.wideopenwest.com/%7Ewvg/tutorial-menu.htm