So in your experience if you were working with say Arri LogC and put the LogC to Rec 709 LUT on an upper track then color corrected everything you could then take the same sequence and put a LogC to 20/20 LUT in place of the LogC to Rec 709 LUT and the levels would be correct for 20/20 space?
I just can't let go of the fact that if I alter the image levels prior to processing them through the LUT I'm altering the very nature of the math transform math. Perhaps this isn't as significant as I think it is?
Also most of my work involves a variety of sources from different cameras with some log and some not. In those cases it would be impossible to choose one output LUT.
Here's my overly simplistic analogy. Back in the day of audio cassettes there was Dolby B. It emphasized the high end where tape hiss lives and made for a trebley sound on playback without the Dolby B decoder. Once the decoder knocked the high end back down things sounded normal. Now if I started messing with the EQ playback before it hit the Dolby B decoder I would surely be changing the sound from what was originally intended. Perhaps it wouldn't matter all that much but I feel the LUT/Log math is more complicated so the results of preprocessing before LUTing might have some odd and unintended consequences. Maybe these aren't visible but after seeing what camera bars look like with and without the VLog LUT applied from a Panny camera I think there is some potential for odd quadrature like distortions when adjusting the levels pre LUT.
---In Avid-L2@yahoogroups.com, <jay_mahavier@...> wrote :
On Nov 8, 2016, at 3:57 PM, John Moore bigfish@... [Editing-List] <Editing-List@yahoogroups.com> wrote:Working on a 4K show shot with Panasonic Varicam 35 in Panny Vlog mode. We apply the Panny Vlog to Rec 709 LUT from the Panny website and then a Full Range to Legal Scaler to the source clips. This gives me a decent starting point. Then I color correct in Symphony. Everything is fine and I deliver a 10 bit DPX legal level of the finished show.For archive purposes, which seems to mean future proofing, we deliver a textless and also an ungraded master. The ungraded master in theory is supposed to have the "Output LUT" removed but the grading remains. The problem is if I just remove the LUT color adapters and leave the symphony color correction the resulting file doesn't look right if the Vlog and scaler LUTs are readded. This all makes sense to me as the processing order is important. If the LUTs aren't processed first the resulting color correction is vastly different. I understand why this is but it seems problematic to start creating color correction LUT effects to use on upper tracks so that I in essence do the symphony color correction before the footage is LUT processed.The idea behind shoot in Log be it Panny Vlog or Arri LogC etc is the image date gets remapped by a math transform to new values that will fit into the dynamic range of the codec used. Later the values and be "unmapped" back to an image that represents what they were looking at in the field. If I start color correcting the image before it hits the LUT processing I'm messing with the math transform math. Given the complexity of the math involved, which favors image detail in the more visible areas and also may be doing different things to the various YUV channel data, I would think adjusting the levels before the unmapping takes place is breaking the math and could lead to some very strange results.I've done tests with my existing workflow and if I turn the LUTs into Color Correction LUT effects I have to create a color correction effect based on the symphony color correction and apply that above the LUT Color Correction effects to achieve the same image levels I have in my normal sequence.Bottom line it just seems wrong to me to apply image color correction before applying the LUTs as it breaks the math involved in the Log/Lut relationship. Does that seem like a viable concern?John Moore Barking Trout Productions Studio City, CA bigfish@...
Posted by: bigfish@pacbell.net
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