Marcelo Cosme January 12, 2018 Share January 12, 2018 (edited) 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 January 12, 2018 by Marcelo Cosme Link to comment Share on other sites
Emily Haine January 13, 2018 Share January 13, 2018 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. 1 Link to comment Share on other sites
Marcelo Cosme January 13, 2018 Author Share January 13, 2018 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! Link to comment Share on other sites
dermot.shane January 13, 2018 Share January 13, 2018 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. 3 Link to comment Share on other sites
Marcelo Cosme January 13, 2018 Author Share January 13, 2018 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? Link to comment Share on other sites
Mike Leisegang January 13, 2018 Share January 13, 2018 Wise suggestion. 1 Link to comment Share on other sites
Anton Meleshkevich January 28, 2018 Share January 28, 2018 (edited) 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 October 8, 2019 by Anton Meleshkevich 2 Link to comment Share on other sites
Nicolas Hanson January 28, 2018 Share January 28, 2018 What is the difference between gamma curve and tonal curve? Link to comment Share on other sites
Anton Meleshkevich January 28, 2018 Share January 28, 2018 Just now, Nicolas Hanson said: What is the difference between gamma curve and tonal curve? I mean the same: RGB curve that converts log to Rec709 gamma. I should edit my post, I think. Link to comment Share on other sites
Nicolas Hanson January 28, 2018 Share January 28, 2018 Do you know what is the correct term for the LUT curve? Link to comment Share on other sites
Anton Meleshkevich January 28, 2018 Share January 28, 2018 (edited) 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 January 28, 2018 by Anton Meleshkevich 1 Link to comment Share on other sites
Nicolas Hanson February 1, 2018 Share February 1, 2018 RGB+Y curve maybe. Why is it called a gamma curve when it's possible to adjust lift and gain as well? Link to comment Share on other sites
cameronrad February 2, 2018 Share February 2, 2018 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 1 Link to comment Share on other sites
Nicolas Hanson February 2, 2018 Share February 2, 2018 Thank you! The illustrations on the link show the exact same thing, a modified curve. My point is that if a gamma correction simply is a modified tone curve, I can't really see the difference in either calling it a tone curve or gamma curve. Link to comment Share on other sites
cameronrad February 2, 2018 Share February 2, 2018 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. 1 Link to comment Share on other sites
