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Colorspace question

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Eugene Lehnert

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I have been searching the forums and found some answers to my questions. I am creating DPX sequences for VFX work that will be color graded in the Baselight. I have been using RedSpace2 and RedGamma2 and have told the VFX people to use the rec709 gamma curve. Typically in the past I have finished in rec709 but now it looks like this film could go to a DCP. VFX people in the past have requested 10-bit linear files and I have worked in Video in the Baselight for an HD finish. Do I gain anything by using Log when the final result will not go to film? We now have a Dolby monitor and I'm assuming I should be using RedLogFilm on this job? Is it ok to use RedSpace2 and RedGamma2 for the VFX work?
 
My understanding

My understanding

My understanding is that a log function is used to capture information from film because film behaves like a log function. But the RED camera is not film so it responds to light in a linear function. I also was under the impression that VFX software linearizes Log footage because the math inside of VFX software works with linear data then at the end the Log function would be added back to the footage. Do I understand this correctly? Which is why I have been sending VFX houses 10-bit DPX files in the past. If anyone wants to ring it I would appreciate it.
 
It's all very confusing. If you look through Graeme's posts in the forum, you'll see he often chimes in to resolve inconsistencies in the use of the terms log, lin and linear for this very reason.

EDIT: I deleted my confusing crap since I was using log and linear wrong as well :/
 
it's okay to use anything that works. however, i'd recommend redLogFilm and think about using EXR's over DPX. otherwise, see if they don't just want the r3d files.
 
Ok - use either REDlogFilm or EXR for the output to send to VFX. Nothing else is correct. For RLF make sure contrast, shadow, user curve etc. etc. are all nulled out. Only things that should be "set" are white balance with kelvin and tint and ISO / FLUT.

In Nuke (or whatever) you can linearize the RLF to linear light with a standard Log2Lin node or "cineon" interpretation.

Similarly when the compositing is done, you can output back back RLF by using the lin2log node.

Using REDcolor2 is correct.

Graeme
 
RedGamma2

RedGamma2

Thanks. Using RedGamma2 would used when working with the rec709 color space then? Making ProRes HD files etc?
 
RG2/RC2 is useful when going out to a REC709 monitor or file for display on one. Before long you'll be moving to use REDGamma3/REDColor3 for this purpose though.

Graeme
 
So the ones who prefer/work on RLF/RC2 have nothing to look forward as far as RG3?

Don't get me wrong, I am SUPER happy with RLF, and I am sure RC3 will strike the right balance from all the previous stabs at color science.
 
I think even if you use RLF you'll like it with RC3.

Graeme
 
Graeme Nattress said:
Ok - use either REDlogFilm or EXR for the output to send to VFX. Nothing else is correct. For RLF make sure contrast, shadow, user curve etc. etc. are all nulled out. Only things that should be "set" are white balance with kelvin and tint and ISO / FLUT.
Click to expand...

When exporting from RSX:

Is it safe to assume that when REDlogFilm is chosen, but you export as EXR, the file is written linear with REDgamma2? (The outputs seem to match once the log file is converted to linear in Nuke.)

Another thing that I noticed is that if REDgamma2 is chosen but you export a DPX, the file is converted to LOG, but not the same as REDlogFilm. What type of log gamma is used?

Note: DPX is typically a 10bit format that requires a log gamma curve to preserve the data. EXR is typically a 16bit half float, or 32bit float format with a linear gamma. This is why RSX is auto correcting the gamma curve upon export.
 
WHen you export an EXR the result is always linear light - there is no gamma curve applied. Mid grey is always placed at 0.18 and pure lens-cap black at 0.0

DPX doesn't convert to log - it just uses whatever gamma type you select.

Graeme
 
Graeme Nattress said:
WHen you export an EXR the result is always linear light - there is no gamma curve applied. Mid grey is always placed at 0.18 and pure lens-cap black at 0.0

DPX doesn't convert to log - it just uses whatever gamma type you select.

Graeme
Click to expand...


I got it. So when exporting to EXR the gamma setting is essentially ignored. When exporting DPX, it is not ignored and REDlogFilm is recommended.
 
Is RedlogFilm is a different type of log format than you would get from a film scan? When I use the Log2Lin node in Shake I do not see the correct image unless I adjust the black and white points.
 
RLF is exactly what you'd expect from a film scan. The log format adheres strictly to spec: gamma= 0.6, black point = 95, white point = 685. Nuke displays thing correctly. If I use the Truelight node in Shake, that will make the log image look very much like my redgamma2/3 output, which pretty much means the log is right. WHen you do log2lin in shake, it appears to be getting it right - slap a gamma 2.2 node on after linearization and all looks normal.

Graeme
 
I see. Nuke has the rec709 lut built into the viewer and Shake does not. Thanks for the help, it's slowly making more sense. Did you ever publish information about colorspaces and gamma curves online? I feel you wrote an article discussing how and why it worked. I maybe recollecting information I've come across in forums.
 
Hey guys,

very interesting thread. I have a question and would love for Graeme to chime in:

for our VFX workflow we start in Adobe After Effects with the original R3D files. We then do all of our retouching work in AE and export for final color grading in Resolve 10. This has been our workflow so far:

1) import R3D files into AE project (set to 32bit)
2) Interepret R3D files to remove all custom curves and set color space to REDcolor3 and REDlogFilm
3) Retouch shots with a RedlogFilm to Redgamma3 preview LUT on a guide layer
4) Export final shots without the preview LUT to ProRes 4444.
5) Import the "milky" log files into Resolve and grade (sometimes using the RedlogFilm to Redgamma3 LUT as a starting point)

Now I have been told that exporting to ProRes 4444 is not a good idea and that we should export to EXR instead. If we do this would we still follow steps 1 - 3 and then just export to EXR in step 4? I have tried that and the resulting EXR files look very dark when importing into Resolve. Throwing a linear -> REC709 LUT on them make them look almost the same as the looked in RedlogFilm in AE but not 100% the same. Or do we need to select a different gamma curve in step 2 if we plan on exporting to EXR?

If I understood correctly RedcineX will simply ignore the gamma settings when exporting to EXR but I don't think Adobe After Effects does the same since we had manually set the gamma to RedlogFilm?

Would really appreciate some input as we are not sure what the best workflow is to export VFX shots from After Effects for grading in Resolve.
 
Just a note that you shouldn't be monitoring with the REC709 LUT on your monitor unless your monitor is calibrated to REC709 instead of sRGB. You should be working in a lin-> sRGB or whatever your monitor's LUT is and then outputting to rec709 at the end of your chain if that's what you'll be displaying on. I see this mistake a lot where they use an sRGB monitor but apply a REC709 LUT and then are surprised when everything looks different on a TV. For example imagine for a moment that your sRGB monitor had a white point of 1.0 and a black point of 0.0. Now imagine hypothetically that REC709 had a black point of 0.1 and a white point of 0.9. The image would be considerably more contrasty than it would look on a hypothetical rec709 display which expands the 0.1 -> 0.9 range to black -> white. Seeing this excessively contrasty image people usually drop the contrast of the base linear image (which just has a rec709 LUT enabled) and then when it's viewed on a rec709 monitor the corrections they applied to make it look "good" on a computer display cause it to wash out.
 
Gavin Greenwalt said:
Just a note that you shouldn't be monitoring with the REC709 LUT on your monitor unless your monitor is calibrated to REC709 instead of sRGB. You should be working in a lin-> sRGB or whatever your monitor's LUT is and then outputting to rec709 at the end of your chain if that's what you'll be displaying on. I see this mistake a lot where they use an sRGB monitor but apply a REC709 LUT and then are surprised when everything looks different on a TV. For example imagine for a moment that your sRGB monitor had a white point of 1.0 and a black point of 0.0. Now imagine hypothetically that REC709 had a black point of 0.1 and a white point of 0.9. The image would be considerably more contrasty than it would look on a hypothetical rec709 display which expands the 0.1 -> 0.9 range to black -> white. Seeing this excessively contrasty image people usually drop the contrast of the base linear image (which just has a rec709 LUT enabled) and then when it's viewed on a rec709 monitor the corrections they applied to make it look "good" on a computer display cause it to wash out.
Click to expand...

We have a Flanders scientific grading monitor connected the the 6gb/s SDI out of a Decklink Studio 4k. So not sure what the right display LUT would be, actually.

However, i use placed the input LUT on the EXR files because I was trying to get the log image that they contain to show up as log again. Didn't really have anything to do with output luts. I was simply trying to tell resolve that "hey, this EXR contains RedlogFilm data and I'd like you to display it as such".
 
I'd not use EXR for log data. I don't see the need / point of that. Use DPX or TIFF.

Graeme
 
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