HDV & 32 bit - how to ensuring correct levels?

TLF wrote on 2/3/2008, 1:40 AM
I'm working with HDV from the Canon, and need to prpare it for broadcast in HD (1080i). I've been asked to provide it in DVCPro HD, but vegas does not export to this format, so it has been agreed I can provide it in HDV.

Because the final video will contain plenty of crossfades, I've decided that working in 32 bit will give me the best quality possible.

However, from reading Glen Chan's information, I'm not sure if 32 bit will give the best quality.

As I understand it, when converting to 32 bit, Vegas incorrectly decodes HDV to Computer RGB which will "stretch" the colours. So, if I work in 32 bit, when I export, will Vegas correct recode to Studio RGB or will the video remain in Computer RGB?

Glen suggests applying the Computer RGB to Studio RGB filter to the 32 bit video - will this impact upon the output?

I have considered using Premiere Pro CS3 which I believe can work with Y'CrCb without converting to Studio RGB (unlike Vegas) and it exports to DVCPro HD, but it's such a cumbersome beast, and I don't have the time to learn a new workflow. Besides, Vegas's crossfades are easier to work with, and the fade types are invaluable for the type of video I am producing.

Any advice or clarifications would be extremely helpful.

Comments

GlennChan wrote on 2/3/2008, 11:36 AM
As I understand it, when converting to 32 bit, Vegas incorrectly decodes HDV to Computer RGB which will "stretch" the colours.
It's not incorrect.

In your situation, do this:

Option A: Work in 32-bit
When working in 32-bit, you should (in almost all cases) convert everything to computer RGB levels and choose to work with computer RGB levels. All your HDV material will decode to computer RGB, so that is fine.

When you render to HDV, the HDV codec (in 32-bit) wants to see computer RGB levels.

So essentially you don't need to do any levels conversions.


Option B: Work in a 8-bit project (because it is faster; if you have tight deadlines, this might be better)
HDV will decode to studio RGB levels, and when encoding to HDV you should feed the encoder studio RGB levels. I would keep everything in the project as studio RGB levels. If you bring in any still images, you should apply a "computer RGB to studio RGB" color corrector preset on them.

Whenever you do a crossfade to black, make sure you are crossfading to 16 16 16 RGB. So use the solid color generator, and lay a track of 16 16 16 RGB over the length of your entire project. Put that on the bottom-most track.

Use the SMLuminance plug-in if you want linear light cross dissolves.



No (in a 32-bit project with 2.222 compositing gamma).

In a 8-bit project, there will be some minor rounding error. (In practice I don't think you'd ever worry about this.)
TLF wrote on 2/3/2008, 12:19 PM
Hello Glenn, thank you for the response.

So, I don't have to worry about a thing? Great, especially as I am not working to deadlines (yet).

Just load the footage, switch to 32 bit, and work as normal...

Thank you.
GlennChan wrote on 2/3/2008, 1:20 PM
Yes.

The only exception is if you have to bring in particular formats like DV or cineform (it's laid out in the table on the article on my website). Any clip that uses a codec that decodes to studio RGB will need to be converted to computer RGB.
TLF wrote on 2/3/2008, 11:21 PM
I ran a couple of tests last night, and could see no difference in exported media where one was edited in 8 bit and the other in 32 bit. Only cross fades were applied.

Would I be right in concluding, therefore, that none of the video levels crossed the boundary that would allow them to benefit from 32 bit processing? (I had chosen clips where there were a lot of bright areas, hoping that the cross fades would cause blow outs and clipping).

On another note, HDV from the canon HV20 records super whites (levels above 235). doesn't converting to Computer RGB clip those super white values?

thanks you.
GlennChan wrote on 2/4/2008, 11:43 AM
On another note, HDV from the canon HV20 records super whites (levels above 235). doesn't converting to Computer RGB clip those super white values?
Yes. The superwhite values are kind of illegal to begin with.

If you want, you can map the superwhites into legal range.
MH_Stevens wrote on 2/4/2008, 11:47 AM
Glenn: As you know from another thread the EX1 gives super blacks and super whites, so I ask how do you "map .... into legal range"? Is there an automatic way other than using Sony color curves or the like?
GlennChan wrote on 2/4/2008, 12:32 PM
I'd probably use the levels filter. Change output end to bring the superwhites in. Add the Levels filter, change output end to 0.916. [This applies only to 32-bit projects, for HDV or MPEG2 footage.]

2- I haven't played with EX1 footage myself.

The superblacks might be due to noise (e.g. compression noise, sensor noise). It might be that the correct thing to do is to do nothing (?).
TLF wrote on 2/4/2008, 11:29 PM
That's much better.

I could see some superwhites in the 8 bit project, but these were clipped in 32 bit. Apply the levels filter (at track level) did the trick. At the same time, removed they grey overcast that SD has.

Thank you very much Glenn!