QUESTION: We have shot a movie on RED and are adding some VFX to the shots in After effects. I've read I have to interprete my Raw footage to log, right? To sell the composite effect, the added effects have to have the same log-look my material has now, right? Do I need a color profile? What about this checkbox at the DPX-settings "logarithmic conversion"? What is this about?

With Red or film footage it is preferable to work in 32 bit linear for all compositing. You *do not* want to work in "LOG" space.

You will only convert to LOG DPX sequence if that is what the DI house wants - but that is an export issue, not a working space issue.

FIRST: let's clear up a misconception - what is "LOG" space really? It is actually a LINEAR encoding of FILM DENSITY - but guess what? Film density is log - therefore, we are used to talking about film footage in 10 bit DPX as "log"., or put another way, the gamma curve is "log" - interestingly, the gamma curve for regular video is actually quite similar to log - and it is technically incorrect to call regular video with a gamma curve "linear".

"Lin" or Linear means a "straight line", also known as "Gamma 1.0". "Vid" or Video typically means with a particular gamma curve applied - and that gamma curve will vary depending on the color space used.

Stu discusses this at length:

http://prolost.com/blog/2009/9/30/passing-the-linear-torch.html

http://www.fxguide.com/featured/After_Effects_32-bit_Workflow_In-Depth/

But to sum:

Vid: Implies a gamma encoded image file.

Lin: implies an image file with no gamma (aka Gamma 1.0)

Log: Implies an image file encoded with film densities, i.e. a gamma that evaluates as film densities.

Your workflow:

So what you want to do is bring in your RED footage to an AE project that is set to 32-bit linear, and pick a colorspace for working - in most cases I suggest sRGB when working in linear space, though there are reasons to work in a larger space at times, in *most cases*, a working space of Linear (gamma 1.0) sRGB is preferable, particularly if you are going to end up in Rec709 (HD) space. 

If you are going to output to film or to Digital Cinema, a case can be made for working in a larger space like Adobe 98 or DCI/P3 (particularly if you have a true wide gamut display that is properly calibrated). I do suggest that you avoid working in any of the really large spaces like "ProPhoto" however.

When you do your compositing in AE (or Nuke) using linear space, then when you ADD, you will be adding images the same way that lights add in real life (that is, real light is linear).

Set your comps to *Use Display Color Management" Under the "VIEW" menu.

When you EXPORT, you can use the Cineon converter method, or use the "Universal FIlm Profile". You should discuss with your DI house what specs they want for the show. If you use the Cineon converter method, one common setting when *coming from a linearized workspace* is:

 

"Gamma 1.0" is the same as saying "Linear working space".

The "Log Convert" checkbox will then convert to log space.

Use your working space for your color profile in most cases here.

If you use the "Universal Film Profile", it takes care of the Cineon/log conversion for you.

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