Question Video levels on file vs. tape

Former user wrote on 9/24/2007, 10:39 AM
I had a curious thing happen when using Final Cut and Vegas to edit a project and I wanted to see if someone could maybe explain what happened.

I captured some old VHS through my Canopus AVDC110 convertor to Final Cut. I edited, and then printed to digital 8 tape. I then captured the D8 tape in Vegas to make a DVD. During print to tape, some glitches appeared so I used the Final Cut timeline and just rendered those segments to a QuickTime DV codec file.

The video I captured from tape in Vegas had the expected 100ire whites and 0 blacks for DV. But the QT DV file, when imported came in with brighter whites and lower blacks. I was always under the impression that the print to tape would be identical as the render to file since I was not changing the file format of the video itself.

Anyone know why the levels between the tape and the rendered QT would be different? The rendered QT matched the original video on the timeline when re-imported to Final Cut. Is it maybe because the way Windows/Vegas handles the QT codec?

Thanks,
Dave T2

Comments

rs170a wrote on 9/24/2007, 1:18 PM
I stand to be corrected but I believe that FCP uses the full 0-255 range while Vegas only uses 16-235 which would account for the different levels.

Mike
Former user wrote on 9/24/2007, 1:40 PM
Mike,

Thanks, that is what appears to be the situation, but I find it curious that FC laid the video to tape at the 16-235 level, but made the file at the 0-255. Unless Vegas is adjusting the levels during capture?

Dave T2
GlennChan wrote on 9/24/2007, 2:37 PM
FCP records the values to a 16-235 Y'CbCr range. The Y'CbCr conversion to R'G'B' is determined by the codec you use.

In Vegas, the 16-235 Y'CbCr values map to 0-255 R'G'B' when decoding via Quicktime via Quicktime/Apple's DV codec.

Where if you have a DV AVI file, it decodes via Video for Windows using Vegas' DV codec. Vegas' codec will map the 16-235 range to 16-235 R'G'B'.
Former user wrote on 9/24/2007, 4:41 PM
GlennChan,

Thanks, that makes it clearer.

Dave T2