• Adobe After Effects Expressions

  Expression for Alexa footage. Example expression included.

  Posted by Simon Björk on September 12, 2011 at 11:10 am

  At the moment there isn’t a simple way to do a logC to linear color conversion of Arri Alexa footage in After Effects. The LUTs provided by Arri doesn’t seem to work for this. In Nuke, you just use a simple curve created be this expression:

  AlexaV3LogC =

  (x > 0.1496582 ? pow(10.0, (x – 0.385537) / 0.2471896) : x / 0.9661776 – 0.04378604) * 0.18 – 0.00937677

  As I’m no expert on these type of expressions, I’m unsure how to convert it to use with a levels or a curve effect in AE. All I know is that it’s a if/else statement where ? is “then” and the : means “else”.

  Anyone?

  Dan Ebberts replied 14 years, 10 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Dan Ebberts

  September 12, 2011 at 3:21 pm

  I don’t know that much about LUTs, but is that formula for a pixel-by-pixel manipulation of luminance? If so, I would think you could do it with a PixelBender effect. Convert RGB to HSL, run luminance through the formula, then HSL to RGB. Something like that.

  Dan
• 

  Simon Björk

  September 14, 2011 at 8:11 am

  Thanks for your reply Dan, I will try to do some more research on the subject. Out of curiosity, how come you don’t think it’s possible with expressions?
• 

  Dan Ebberts

  September 14, 2011 at 5:57 pm

  My assumption is that it needs pixel-by-pixel processing, which you can’t do (at least in a practical way) with expressions. Of course, I could be completely wrong. I mean, can you manually set up a Levels effect to do this conversion? I guess if you could, you could just save that as a preset.

  Dan

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