Park Edwards
Veteran
Just as the title says. Not sure what the heck LUT are. I have an idea, but would like if someone can explain it on an elementary level.
Can someone explain LUT like I'm five?
- Thread starter Park Edwards
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j1clark@ucsd.edu
Veteran
Look Up Table. A simple method to translate one set of values into some other set of values.
A simple Fahrenheit to Celsius 'Look Up Table'..
Fahrenheit Celsius
32 0
50 10
86 30
104 40
So to 'look up what 86 degrees Fahrenheit is in terms of Celsius... scan down to 86 -> 30.... look ma no formula to calculate... and in the olden days this was much faster than calculating out things that had multiply operations which use to be very expensive in ancient computer hardware...
There's a way of simplifying this for hardware implementation... but that's the 'principle'...
sonofaresiii
Well-known member
Okay. So I'm going to grade a movie. We know we're printing this movie to film, and the actual film is going to make the movie look more contrasty by X amount. Since I know exactly how much more contrasty it's going to look when I print the film, I digitally add X amount of contrast before I grade-- that way when I look at it on my computer, I know exactly what it's going to look like when I print it to film.
I save the value X as a sort of filter I can add anytime I know I'm going to be printing to this film. That becomes my "look-up table." So, you can say I apply the LUT.
Or here's another thing I've seen:
I'm a DP, and I've decided it's best to shoot this scene very flat. It looks terrible flat, very desaturated and everything, but I know it's going to look great after the grade. But my producer comes over and starts yelling at me: "What the fsck you idiot, this looks terrible! Make it look good!" "No, it's fine, it's going to be done in post." "I don't want to fix it in post! It's your job to make it look good and it looks like crap!" "Alright, fine, whatever." I artificially add a temp filter that adds back the saturation and the contrast, something similar to what the final product will look like. It's not *actually* on the footage, since I'm still shooting flat, but it can be easily removed and makes it LOOK something closer to the final product. Now our producer sees it and says "oh, wow, you really fixed that footage! Good job, just don't let it happen again!" That filter I've applied can be thought of as a LUT.
Okay, I've got one more for ya (and yep, I've seen or heard of LUTs being used in all these circumstances, whether it was wise or the best choice or whatever is up to you to decide... this is just what I've seen/heard).
Say I'm shooting a tv show. I was too busy to get to the grade of the first episode, and the guy grading it totally bombed it. Completely not what I had in mind, he did his own thing and it totally ruined what I was going for. So I'm going to sit down on set, talk to my DIT, and we'll come up with a temporary feel... say, very saturated, very sharp, very warm-- for the footage I shot. We'll save those settings as a LUT and send it to the guy doing the actual grade. Now he looks at it, goes "Ohhhh THAT'S what he was going for," and can remove the LUT and do a proper grade with my "notes" in mind.
As others have said, it's a way to look up values for a result in mind, without changing the actual footage. Just that the values we have are represented visually.
edit: and apparently there's always arguments over what actually is a LUT and what isn't, and whether the term is misused or not... whatever. Call it what you will, everyone has their own terminology like everything else in the industry, but that's the basic idea.
I save the value X as a sort of filter I can add anytime I know I'm going to be printing to this film. That becomes my "look-up table." So, you can say I apply the LUT.
Or here's another thing I've seen:
I'm a DP, and I've decided it's best to shoot this scene very flat. It looks terrible flat, very desaturated and everything, but I know it's going to look great after the grade. But my producer comes over and starts yelling at me: "What the fsck you idiot, this looks terrible! Make it look good!" "No, it's fine, it's going to be done in post." "I don't want to fix it in post! It's your job to make it look good and it looks like crap!" "Alright, fine, whatever." I artificially add a temp filter that adds back the saturation and the contrast, something similar to what the final product will look like. It's not *actually* on the footage, since I'm still shooting flat, but it can be easily removed and makes it LOOK something closer to the final product. Now our producer sees it and says "oh, wow, you really fixed that footage! Good job, just don't let it happen again!" That filter I've applied can be thought of as a LUT.
Okay, I've got one more for ya (and yep, I've seen or heard of LUTs being used in all these circumstances, whether it was wise or the best choice or whatever is up to you to decide... this is just what I've seen/heard).
Say I'm shooting a tv show. I was too busy to get to the grade of the first episode, and the guy grading it totally bombed it. Completely not what I had in mind, he did his own thing and it totally ruined what I was going for. So I'm going to sit down on set, talk to my DIT, and we'll come up with a temporary feel... say, very saturated, very sharp, very warm-- for the footage I shot. We'll save those settings as a LUT and send it to the guy doing the actual grade. Now he looks at it, goes "Ohhhh THAT'S what he was going for," and can remove the LUT and do a proper grade with my "notes" in mind.
As others have said, it's a way to look up values for a result in mind, without changing the actual footage. Just that the values we have are represented visually.
edit: and apparently there's always arguments over what actually is a LUT and what isn't, and whether the term is misused or not... whatever. Call it what you will, everyone has their own terminology like everything else in the industry, but that's the basic idea.
Gabel
Well-known member
Great examples!
Another is that a camera will shoot very flat (like a RED, Alexa or BMC) but you don't want to light for that. Then you would use a LUT in camera that you would light for, but the let material going out be flat.
Or say you've shot with a RAW camera and you want to transcode the material for editing. Then you might do a quick color correction, adding some contrast and saturation to the material, so it's nicer to look at during the grade.
Another is that a camera will shoot very flat (like a RED, Alexa or BMC) but you don't want to light for that. Then you would use a LUT in camera that you would light for, but the let material going out be flat.
Or say you've shot with a RAW camera and you want to transcode the material for editing. Then you might do a quick color correction, adding some contrast and saturation to the material, so it's nicer to look at during the grade.
j1clark@ucsd.edu
Veteran
Well, I can't talk to you as a 5 year old... Think of the Look Up Table (LUT) as a 'translation' mechanism. The Raw (or whatever) data can be translated without affecting the original copy by passing the data through the LUT. The example I gave is a 'linear' LUT, Fahrenheit to Celsius. However, you can create translation curves that 'increase contrast', 'roll off high values', etc. Most displays need some sort of 'adjustment' or 'compensation'. When you calibrate your screen you create a LUT to take the data in the file and display it 'correctly'. You don't change the data in the file, you change what the translation table is for your display.