32 bit and banding problem

Philuk wrote on 2/28/2009, 1:10 PM
Hi,

I’m coming to the end of an edit which was shot on Digibeta and feed into Vegas via a J30 with the Black Magic SDI board at 10 bit. All’s going well until I start to author to DVD. I’m rendering with 32 bit floating point at 10 bit in Vegas, but I’m getting banding in the final DVD, also the blacks look crushed. (I’ve followed a few postings about this subject; Farss (Bob) raised the issue along with explanation from Glenn, which left me completely baffled!)

Basically is there a simple work around I can apply to resolve both problems?

Do I use 2.2 or 1 gamma? Do I render in 8 bit or 32 to get the best out of the pictures? And why do England keep losing at rugby?

Thanks for replying


Phil

Comments

farss wrote on 2/28/2009, 5:49 PM
32bit may give you a bit more to play with if you're doing heavy CC. Use 2.22 gamma, apply ComputerRGB to StudioRGB conversion on the video buss master. The color correction FX has a preset for this. Note that the level meters are wrong in 32bit unless you apply the ComputerRGB to StudioRGB conversion.

Check your final output on a CRT. I've had major issues with Vegas and DigiBeta material with Vegas mixing up field order almost at random. Sorry to have to admit that I've pretty much given up on Vegas for this kind of work. This field order problem has been around for a long, long time. It's possible that for some obscure reason it's only a problem in PAL as others don't seem to be having this issue.

I plan to deliver some DVDs that clearly show the field order problem to the SCS guys at NAB.

Bob.
GlennChan wrote on 2/28/2009, 8:26 PM
Maybe it's your DVD encoder? DVD is an 8-bit format, but the encoder may reduce the bit depth further than that for compression purposes?

2- Are you rendering to the main concept mpeg2 encoder / the one that comes with Vegas?

3- How are you monitoring?
Philuk wrote on 3/1/2009, 1:42 PM
Thanks both for replying.

Bob: Thank you for the work around I’ll have a tinker and let you know. Yes I agree it’s a shame this is problem for Digi and/or PAL. This is my first project using Digi at 10 bit and wasn’t expecting to have this see this. I’ve been an avid (no pun intended) fan of Vegas since it’s early days. Problems like this really make it look poor if you want to use it for broadcast work, when really it should be outstripping the other NLE’s considering it’s breadth.

To give you an idea of what I’ve tried. The project is set at 32bit floating, I’ve tried both 1 and 2.2 gamma, resolution set at ‘best’ and I set it to ‘blended fields’.

Glen: I’ve then rendered using Main concept Mpeg 2, DVD Architect Pal widescreen. I’ve then added 2 pass VBR I’ve tried a selection of different bit rates from 8 to 10 bit all come out the same.

I’ve just noticed that the default in Main Concepts is to turn on the ‘Allow field-based motion compression’, which I hope isn’t the problem. I’ve also changed the field order around to see if that helps.

The image on my computer monitor looks fine, although they’re not the best in town, it seems the problem starts when I produce a DVD and play back onto my domestic CRT TV. What I seem to get is fine banding, which shows up more in the highlights. There also seems to be jagged edges when you have a face lit against a dark background.

I’ve got a couple of different monitors, the one coming out of the Black magic into a Panasonic 17” - BT –LH17 which takes SDI, ironically looks fine, as I said it’s only when I record to DVD using Architect Pro, do the problems start.

I’m going to try Bob’s work around and will also try a render at 8 bit rather than 32 bfp and will get back to you.


Phil
farss wrote on 3/1/2009, 10:03 PM
I think you have two problems.

1) Your levels are wrong. In 32 bit 2.22 Vegas outputs the YUV codec at ComputerRGB. i.e. levels go from 0 to 255. If you encode this to mpeg-2 and make that into a DVD the player will clamp blacks at 0 IRE on the composite output and your blacks ill indeed be crushed. Applying the correct transform will get your levels back to where they should be.

2) Banding. This banding sounds more like interlace artifacts that color banding but I'd suggest getting your levels correct before worrying about this. Color banding is seen in large flat areas of color usually.

Bob.
Philuk wrote on 3/2/2009, 1:36 AM
Also spotted another quirk of 32bfp, the velocity envelope doesn't work.

I've squeezed a shot with control and drag them placed an VE over that. The shot contains some people who are taking a flash lit photo. I've freeze framed from the flash using the VE to when the flash illuminates them, when it gets to Architect the shot continues without the freeze....!

This is a bit of a pain as the client was really pleased with that shot, any ideas about solving it without?

By the way the work around worked a treat, although the interlaced banding/ artifact still looks pretty poor. I've trailed though the forum but can't seem to find any reference to solve this also.

Phil
farss wrote on 3/2/2009, 2:07 AM
"This is a bit of a pain as the client was really pleased with that shot, any ideas about solving it without?"

Velocity envelopes are darn confusing, I suspect your problem might not have anything to do with 32bit but just to be sure I'd do that in a seperate little project, render that out to a Sony YUV AVI and cut that into your main project. I make a point of doing the tricky bits by themsleves, that way it's easier to isolate problems.

"although the interlaced banding/ artifact still looks pretty poor"

I'm lost on this one. Is your source, your project and what you're rendering to all 720x576?
Can you post a screenshot of the problem or email one to me, address is in my user profile?

Bob.