Importing Cineform into Virtualdub, 601, 709, RGB issues

[Pat Reddy]

I often do some color and levels correction in Vegas, render to Cineform intermediate files, import into Virtualdub for deshaking, and then render back to Cineform intermediate files (using Neo HDV). One thing I have never been clear about is the best settings for preserving image quality in this process. Specifically I have questions about which settings to use on the Cineform video for windows control panel and Virtualdubs color settings (24 bit for import and export?, autoselect ?, etc.).

I know Cineform files are computer RGB, 32 bit, and that Virtualdub may have a bug that makes it see these as 24 bit. In Douglas Spotted Eagle's book "HDV What You Need to Know" he mentions that Virtualdub uses the 601 color space and that this can cause problems. This book was written 4 years ago, and so things may be different now, or are they? Any info on all this would be greatly appreciated.

Pat

[Bill Ravens]

I think you're confusing Vegas' somewhat questionable use of the floating point math known as "32 bit" with the bit depth of Cineform files. CFHD is 10-bit, meaning over 1 billion colors in the space, as opposed to 8 bit which is over 16 million. The fact that Vegas "allows" 10 bit when you select 32 bit floating point processing is a behavior I've yet to understand.

[Pat Reddy]

I certainly do confuse those two all the time, but in this case I don't think I am. Virtualdub's color settings have 24 bit and 32 bit options, and Dave of Cineform has talked about these issues with respect to Cineform in Virtualdub, but I still don't have the full picture.

Pat

[David Newman]

24-bit and 32-bit have the same precision in RGB space, as one mode has an alpha channel (both formats are 8-bits per channel.) Also RGB decodes don't have 601 vs 709 issues, that is a YUV only issue.

[Bill Ravens]

wow! never made that connection in my muddled thinking.Thanx, David...I get it!!!

[Pat Reddy]

Thanks, David. I still have two questions for you. When I load a cineform avi into Virtualdub and go to set the compression settings, I select Cineform and then I can select the configure window which launches the Cineform Video fo Windows control panel. Do I check the two "709" boxes, the Use Video systems RGB boxes, all of them, none of them or what to ensure the best quality results for later avi file use back in Vegas? On the color depth settings, do I select "autoselect" for decompression and output, 32 bit for each, 24 bit for each, or something else if I want to ensure the greatest preservation of quality while the clip is in Virtualdub and subsequently saved as an avi for later use in Vegas?

Thanks,

Pat

[David Newman]

If you are doing 4:2:2 YUV encode from an RGB source (VirtualDub), the 709 switch sets the encoding method. Use 709 for everything bigger than SD.

[Pat Reddy]

So select both boxes on the 709 line of the VFW control. Then do I select "4:2:2 (YCbCr UYVY)" under color depth in Virtualdub for both decompression and output format?

Thanks,

Pat

[David Newman]

No, keep VirtualDub in RGB.

[Pat Reddy]

And you said it didn't matter whether it was 24 or 32 bit?

Pat

[David Newman]

It doesn't matter unless you have an alpha channel (which VirtualDub doesn't support anyway.)

[Pat Reddy]

Thanks so much David. I have been trying to figure this stuff out for a few weeks. The world of color in video is rocket science to me.

Thanks again!

Pat