Ceci est une ancienne révision du document !
If you have been following our Darktable tutorials, you will know we are working with the latest version, not the version that is bundled in the Ubuntu Software centre. Disclaimer: In no way am I an expert in photo manipulation, I just know a guy who had a dog that gave me some fleas. I thought I may help you scratch an itch also. As promised, this issue we look into the wonderful world of LUTs. This is what we currently have (pre Darktable 2.6) : https://www.darktable.org/2016/05/color-manipulation-with-the-colour-checker-lut-module/
But, in the newer versions (Darktable 2.7+), we have LUT 3D. But what is it you may ask? Well LUT is short for Look-Up Table. Why do we need it? LUTs allow us to change color spaces. That said, technically, you have more than one LUT type. We have the Technical / Scientific LUT for precise color shifts, and we have Creative / Artistic LUTs that you see in something like Snapseed on your phone. Now you will read that LUTs are mathematically precise, but that holds true only for the first type. Think of the two as serious and fun; you just have to decide where your work space is. It’s also not a ‘one size fits all’ scenario, that is why there are so many. Because it is a mathematical formula, it gets applied to your exposure ‘x’ so the result where ‘x’ changes, it changes the outcome. There are a lot of variables, so you will need to put some effort in.
So what is a 3D Lut? Well think of it as an array in 3 dimensions. Read more here: https://www.darktable.org/2019/05/New%20module-lut3d/ Again, I am no expert, but people are visual creatures and sometimes we need to picture something to understand it. Not all of us need to be experts in everything, and that is OK, you just need to know enough to enjoy something.
To understand LUTs, let’s look at their origins. LUTs started because of the need to match the output of different cameras. Though it is still used for this, it has become so much more. Think of LUTs as a quick way to apply a color preset, like Snapseed on your phone does. That said, it is not a complete automation, as you still need to denoise or sharpen manually. LUTs apply to colors. There are basically two types us n00bs need to be aware of – the type they use in film production (CUBE FILES), and the type we use in digital photography (HALDCLUT FILES). So be sure you download the correct one, though you *can use the cube files, the latter is preferred. Should you see 3DL files or MGA-files; these are LUTs too, but just be aware that not all types of LUT files are supported by every photo manipulation application. If you have used RawTherapee or Photoflow, you will know which you need. All well and good, but where can you get LUTs? Here is a starting point: https://freshluts.com/, or we can borrow from RawTherapee: http://rawtherapee.com/shared/HaldCLUT.zip
If you have metered internet, know that some of these preset packages can be quite large. Once you have some LUTs, you need to set the path. In Darktable, open the settings, go to the core settings tab and scroll all the way down. Choose your LUT root folder as per the image: Add the 3D LUT module to your module arsenal. With the new search bar it is as easy as typing ‘3D’ if you do not see it. Click the little folder to open the path you set previously. If this does not work, go back and set the path again. Make sure the file types are set to *your LUT type at the bottom of the new window that opened. (Remember CUBE and HALDCLUT files?). You should then be presented with your presets. Double-clicking any of them will apply it to your picture. The only issue here is that if you have lots of LUTs, you will need to click on that mini folder again to open your list, and double-click each one in succession. There is, unfortunately, no quick way to run through them that I know of. If there is, or if you know of a faster way, please let us know.
LUTs are applied at 100% opacity. You can change that. Feel free to play around with that as it can create some interesting effects. How do you do this, you may ask? Well, next to the big X is an O that you click. (No, we are not playing Tic Tac Toe). If you hover your mouse pointer over this, you will see a tooltip that says “uniformly”. Applying a LUT is not the be-all and end-all of your color correction. You can still go and adjust every aspect of the applied LUT with the other modules. Think of it as a cheat, to get you 90% of the way there (color correction). The differences between some LUTs are very subtle. Do not be afraid to take snapshots to compare them. There is no great skill required to use LUTs. Open one of your LUTs in your file manager and view it with mousepad or leafpad or gedit (whatever your choice of notepad application is), and you will see that a LUT is just text. Lots and lots of numbers.
I say this, as there are lots of free LUTs available on the internet, but you do not want a binary. Always make sure that the so-called LUT you just downloaded is actually a simple text file with numbers like these. Malware on Linux is a thing. Rather be safe than sorry. Though I have seen .EXE-files parading as LUTs, know that a LUT file is simply a lookup table that changes color values. Delete the binaries and find your LUTs elsewhere. Generally, LUTs will work on your Windows and MAC computers too, as they are text. Now, about our two types of LUTs I mentioned in the beginning. The Technical LUT will make a drab picture look like it should, or bring life to it. The Artistic LUT is one you add to an already good looking picture to give it style or flair. Be aware of how you use each one. Happy editing and should you have any questions or corrections, yes everyone makes mistakes, email us at: misc@fullcirclemagazine.org