Avid/Final Cut Pro levels issue.

[Matt Gottshalk]

From a client of mine who specializes in compression:


"We've been trying to figure something out, and are blocked on solving
it. it hit me that you may know the solution.

we have a customer with Avid Media Composer, and they're playing out
an Avid DVCPRO50 source over SDI to a waveform monitor. as a YPbPr
source, they're seeing black level of 0mV and white level of 700mV,
and color spectrum is correct.

if we take that source (QT reference file) and flatten it to .mov, and
play it out with Final Cut Pro (over SDI) to the same workform
monitor, the black levels are high (by 50mV) and color range is
broadened in spectrum and high by 20mV. (according the customer
reports)

we're trying to use the flattened file as a source for transcoding,
but there's some interaction between Avid and QT that we're not
understanding, because our transcoded version still has higher black
levels than the source.

i appreciate any time you have to think about this. our video editor
checked gamma levels and other filters, and couldn't solve what the
difference was. even the solution our Avid contact gave us didn't
work..."

Any ideas?

I thought it was the dreaded Gamma shift from PC to Mac but now I'm not sure

 

[xmephestox]

FCP natively causes a gamma shift on your footage. there is no way around it. my only workaround would be to try to eyeball it and try to crush things down further out of avid so it evens out in FCP, or recorrect it in fcp to adjust for the gamma shift.

 

[grinner]

You'll also se a shift in reference file exports from Avid.
You can verify this by exporting a quick clip to AE, rendering it to your favorite codec and importing it back to Avid. Blacks are up considerably. I actually have a color effect saved to fix this as it's just become part of the workflow.
If I'm not mastering back to tape, I always crush the blacks a bit to make up for the export.

 

[MichaelP]

Export out from Avid as RGB and not 601. Avid will take the 16-235 to 0-255 where final cut, compressor, etc, apps will lift the blacks backs and lower to 16. Don't know what it does on the whites.

Michael