Working with LUT

Is there a way to use a file lut (alexa lut in my case), make the comp with it, then reverse the lut to make it same as raw footage? Like cineonlog (log to lin then lin to log)?

LUT's aren't generally invertable. Further, you don't want to composite in a post-LUT space. Just stay linear, as the raw already should be.

Thank you Chad I will do as you say. Will use the lut only for viewing and work directly on raw footage.
I didn't know that the log like low contrast raw footage is actually linear.

If the input is raw, it's linear. If it claims to be raw, it can be anything.

Linear will be lower contrast in the shadows, but higher contrast in the highlights, but without a chart or light meter readings it's hard to know for sure. But if you assume the input is being honest, then it is linear.

but if he speaks about arri raw from alexa camera isnt it in LogC?

but if he speaks about arri raw from alexa camera isnt it in LogC?

Depends. Fusion's arri raw format loader lets you do logC, linear, DCI-P3, and rec.709. You'll want it to be linear inside Fusion, but it's something you need to check and not accept blindly.

but if he speaks about arri raw from alexa camera isnt it in LogC?

Depends. Fusion's arri raw format loader lets you do logC, linear, DCI-P3, and rec.709. You'll want it to be linear inside Fusion, but it's something you need to check and not accept blindly.

I've downloaded a couple of luts from arri website (lut generator) and they are working as expected. I think raw footage is logC.

Shouldn't the LUT/codec/colorspace/DigitalVoodo/.... applied to the footage show up in the metadata of the file?

Shouldn't the LUT/codec/colorspace/DigitalVoodo/.... applied to the footage show up in the metadata of the file?

Let me rephrase my question:

What is the best way to load alexa logC prores and raw footage, make a comp and render as it is (logC)?

Well...
The math behind pretty much any compositing tools on this planet is linear.
(As in "There is no logarhythmic Blur")
So processing the comp in log is wrong, the footage needs to be linearized first.

Which is were the metadata might come in handy.
If it tells which setting has been used on the shoot, you can grab the corresponding LUT off ARRI's Homepage.
Add a FileLUT after the Loader, load the LUT and you should be fine to go comping.

Now, not all LUTs can be inverted. That's just the nature of the beast.
*If* there was a corresponding LIN->LOG LUT available,
you could add another FileLUT directly before your saver,
converting the footage back to log.

What do you think about using Cineon Log, manual adjusting it to a reasonable gama, black and white level?
I mean Log to Lin before the comp and Lin to Log at the end?