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 might convert your final product to a LOG DPX sequence if that is what the DI house wants - but that is an export issue, not a working space issue.

IS THIS THE SAME LOG WE SAW BEFORE?

Let's clear up some misconceptions - 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 scanned into 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".

As an example, sRGB is encoded with a gamma curve of 0.45, which unwinds for display by applying a curve of 2.2. Rec709 is encoded with a 0.45 curve the sits on top of a linearized offset region near the blacks, and results in an "equivalent" gamma of about 1.9 - 2.0. It unwinds by applying a gamma of 2.4, which creates a net gamma increase of 1.2

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

Stu Maschwitz 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/

In Summary:

Vid: (video) Implies a gamma encoded image file.

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

Log: (logarithmic) Implies an image file encoded with negative film densities, i.e. a gamma that evaluates as film density.

Your workflow for RED:

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 the working color primaries - in most cases I suggest sRGB primaries*** when working in linear space, though there are reasons to work in a larger space at times.

A working space of Linear (gamma 1.0) sRGB is preferable if you are going to end up in Rec709 (HD) space, or for a Web based video. If you are going theatrical or film, then a linearized space with DCI P3 color primaries might be best, or the primaries your DI house specifies.

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" as the primaries for ProPhoto are so far apart, some of them are negative, and this causes a number of workflow problems.

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

Set your comps to *Use Display Color Management" Under the "VIEW" menu, this converts the linear space on the fly into your display monitor's space. It is best to have this monitor well calibrated and profiled.

When you EXPORT your final effect, you can use the Cineon converter method shown below, use the "Universal FIlm Profile"****, or use another appropriate transfer curve using either an ICC profile, a LUT, or the OpenColorIO plugin — this should be discussed with your DI house to conform with what they need for the show. 

TIP: The first frame of your image sequence (frame 0) should always be a slate, and that slate should clearly state what specific curve and colorspace you are using!

If you use the Cineon converter method, to create "Standard Cineon LOG" a 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.

 

Footnotes:

** There was a time in the 1990s when some compositing platforms would do their operations in LOG space. But today, the preferred space for compositing is a linearized colorspace, with a gamma of 1.0

*** It's useful to note that sRGB and Rec709 use the same exact color primaries and white point, so there is no difference when you linearize either sRGB or Rec709. 

**** We no longer recommend the Universal Film Profile, and instead we suggest using the OpenColor plug in, placed on an adjustment layer at the top of your comp stack, to convert to the appropriate transfer curve. Then set the output module to "Preserve RGB", (do not apply a color space in the output module.)

This article was originally written circa 2012, but was revised July 2018

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