Colorspace question

[Eugene Lehnert]

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?

[Eugene Lehnert]

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.

[Jake Bastian]

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 :/

[paulherrin]

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.

[Graeme Nattress]

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

[Eugene Lehnert]

Thanks. Using RedGamma2 would used when working with the rec709 color space then? Making ProRes HD files etc?

[Graeme Nattress]

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

[Frank Cueto]

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.

[Graeme Nattress]

I think even if you use RLF you'll like it with RC3.

Graeme

[Justin Johnson]

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.

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.