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Hello I have a project recorded in Alexa Arriraw (12 bits) to grade in Davinci Resolve. What is the benefit or "sin" of using for example the 3D lut of Arri. Using lut did I lose quality of the material limiting the process of color correction? Another doubt if you use, I must use 3D output or 3D input.

Edited by Marcelo Cosme
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You can apply the Log to Rec709 3D LUT from Arri on a node to stretch the contrast instead of doing it manually. You can use that as a base before balancing and doing initial corrections. 

Using a LUT can clip both your blacks and whites, but you can create a node prior to the LUT correction to be able to control that. 

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6 minutes ago, Emily Haine said:

You can apply the Log to Rec709 3D LUT from Arri on a node to stretch the contrast instead of doing it manually. You can use that as a base before balancing and doing initial corrections. 

Using a LUT can clip both your blacks and whites, but you can create a node prior to the LUT correction to be able to control that. 

Thanks Emily!

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17 hours ago, dermot.shane said:

some LUTs have applaingly bad maths,

i drop any LUT over a grey scale ramp and look for math errors before using, usualy i re-create in the software to avoid said errors, as they usualy contain math errors.

Good idea man! How do you do those tests using grayscale ramp, can you explain?

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Don't forget about colorspace.
RGB curve - isn't the only thing what Log to Rec709 LUTs do. You still have to use RGB matrix (not an RGB mixer in resolve) to "remap" primaries (Alexa Wide Gamut for example) from one colorspace to another. Davinci Resolve 14 has OFX plugin for that.

Edited by Anton Meleshkevich
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I guess, I don't know.
Why don't you like "RGB curve"? It describes it's way of affecting colors.

It can be used for contrast, for gamma conversion, for inverting colors, for creating false color effect, etc.
So it isn't just a contrast curve, or a gamma curve.

Edited by Anton Meleshkevich
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7 hours ago, Nicolas Hanson said:

RGB+Y curve maybe. Why is it called a gamma curve when it's possible to adjust lift and gain as well?

Tone curve would likely be best generalized description. There's definitely some confusion around terminology here

Gamma is really broken down into 3 parts.

Input — OS/Correction/Intermediate — Output

There's an applet here where you can visualize it, as well as some better explanation of gamma correction: https://sites.google.com/site/marclevoylectures/applets/gamma-correction

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My personal preference is to use gamma to describe pure exponent functions. Unless talking about "Film Gamma" 

So 1.0, 2.2, 2.4, 2.6 etc. Or linear gamma (1.0), Rec.709 Display (2.4), .DCI-P3(2.6)

Then I reserve tone curve for more complex things, like camera curves, transfer functions, etc.

sRGB isn't a pure 2.2 function, so I don't say the gamma of sRGB., but rather the tonal response curve or transfer function of sRGB. 

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