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VFX shots. Grade before or after?
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[MichaelMaier] “Are you talking about the Super HIgh Band AVR-3 quad videotape days”
1980-1986. But the same limitations still hold true with some of today’s lossy DV codecs, which tend to fall apart even faster. ProRes and DNxHD have made enormous strides, though, and 8-10 generations, which aren’t really re-compressions, really do hold up well. I really do disagree with attempting to flip back and forth, though, between RGB and Y’CbCr with so-called “Uncompressed” codecs and TIFF/DPX sequential files. Its not penalty-free, considering the re-matrixing and 4:2:2 processing that necessarily have to happen.
jPo
“I always pass on free advice — its never of any use to me” Oscar Wilde.
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[Joseph Owens] “ProRes and DNxHD have made enormous strides, though, and 8-10 generations, which aren’t really re-compressions, really do hold up well.”
What would you consider really re-compressions or not?
[Joseph Owens] “I really do disagree with attempting to flip back and forth, though, between RGB and Y’CbCr with so-called “Uncompressed” codecs and TIFF/DPX sequential files. Its not penalty-free, considering the re-matrixing and 4:2:2 processing that necessarily have to happen.”
Totally agree here. I think once you go RGB(DPX) you should stay there.
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Its just my internal guideline, and pretty sure that there will be general disagreement.
A recompression for me is a transcode from one codec to another — even within the same family, where a color-encoding, bit rate, or intra-framing recalculation occurs. To a certain extent, not even the render from a grade application, unless you are changing codec, really qualifies as a full recompression, more like a fractional “generation”. All you are really doing is re-assigning the HSL or RGB values of single pixels, and this doesn’t really change its relationship to its surrounding value fields (slots in the pixel array) at least in a lossless codec. Things do change, however, when you start merging and blending external picture elements — blurs, sharpening, mattes, noise, grain… and again if you start geometric manipulation. That’s a different set of rules.
I don’t necessarily count an export from an edited timeline — for example, all-ProRes-422 clips on a ProRes-422 timeline to create a single ProRes-422 Quicktime to be a full recompression. For me, it is fundamentally a simple re-ordering of the frames. However, there are codecs that exhibit losses quickly because they recalculate values based on long-GOP i-b-p economics, or chroma subsampling. Non-square resolutions also raise more than the usual amount of suspicion as to whether you are getting back exactly what you put in.
When you simply copy a digital file from one directory to another… that’s obviously not a compression generation. If you were to change a few of the pixel values inside a frame… but you don’t change the codec, that’s not really a recompression, either. If you pull a subclip or merge clips, unless the codec depends on the field sequence order for its bit reduction scheme, that’s all thats going to change, not the content or values of the intra frames themselves.
Thats my model, anyway.
Love to hear other opinions.
jPo
“I always pass on free advice — its never of any use to me” Oscar Wilde.
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In a completely non pro situation, which is mine and my partners, we both do the shoot, one directs the other is on camera. My work station is a current imac running Davinci which handles RAW DNG’s, I send him the proxies to edit in Adobe on Windows. He sends me the XML I do the grade then I send him the final grade. He then replaces the proxies on the timeline with the Graded files and adds VFX and finishes.
So a basic edit seems to work best as Adobe and Davinci deal with complex transitions differently.
Transitions, stabilisation and VFX seem to be best done after the grade and before the final render.
Hopefully this helps any others in a similar situ, or gives me exposure to be shown a better way which I’m always willing to learn.
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I agree. As a VFX Artist/Supervisor and once in a while Colorist, I find the tech grade to be very helpful. If the timeline allows for showing also what the final grade will look like, great. I often find that not to be the case.
It doesn’t mean that VFX Artists shouldn’t check their work. However. There’s so much we can do in Grading that is non-physical, which would mean a lot of additional work to try to match with very different tools.
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markus manninen -
>>There is nothing proprietary in FilmLight’s approach…
Well, no, not if you’re referring to the use of standard XML tags. But the approach is completely proprietary in the sense that the file cannot be properly interpreted and the values properly applied without the use of a Baselight or a Filmlight Baselight Editions plugin.
I think what’s being overlooked in this discussion is that the use of ACES virtually ensures that the data being presented to the VFX artist is already in scene referred, linear light space. That is usually preferred in compositing because it behaves in a similar way to real world physics, modeling the properties of “real” light. It also operates in a floating point space, ensuring that no clipping takes place through the various compositing operations. ACES is by design very VFX friendly.
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Before. Pretty much 95%
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We work mostly with commercials and this is how we do it too. We do a tech grade first where all shots are nicely balanced. This will be a “safe” grade that leans towards the final look already.
After all vfx work is done, we do a final grade. Step one is to make sure everything blends seamlessly. We use external mattes. After everything looks good and “correct”, we have more freedom to play with the look and take it whatever direction the director wants to go.
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But don’t you need as much latitude in the plates as you can get ?
A tech grade will goto Rec709 plus its a recompress – unless your going log out with a LUT ?
So you’ll be comping on possibly Log-c > Rec709 > Lin > :-/
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