AND WHY YOU SHOULD NOT USE THEM
What is a LUT?
A LUT, a lookup table, transforms tone and color based upon settings chosen by the creator of the LUT. A LUT transforms incoming RGB data to your desired output values. Originally, LUTs were designed for practical purposes. A “Viewing LUT” would allow you to make log footage look like rec709 footage, so you had a better representation of what your final film would look like. “Calibrations LUTs” are used to calibrate monitor displays. There are “film emulation LUTs” that mimic the look of stock film. More recently, LUTs have been employed for creative purposes. (Creative LUTs).
In order for a LUT to be 100% precise the input has to match the conditions in which the LUT was created, likewise the output has to match 100% as well. You have to know exactly what your input device and output device will be. This is why LUTs are mainly used in-house at post-production houses or colorists working on their own stations.
If you’re using someone else’s LUTs you cannot be 100% sure what equipment they were using, and you also don’t know how they created this LUT.
HOW TO FIND OUT IF
A “CREATIVE LUT” IS BAD
It can be difficult to objectively judge the quality of a LUT being provided when applied to real footage. Here are two simple methods that help you to analyze a LUT.
1. Grayscale / Waveform test
A simple way is to place a grayscale image into your timeline and apply the LUT to it. In this example, you can already see heavy banding issues on the grayscale image itself, which is partly a result by “Trilinear” interpolation in DaVinci Resolve. If you check the Waveform on the scopes, it reveals that the blacks doesn’t go down to zero. In the highlights, the RGB values are “split”. A professional Kodak 2383 D55 LUT also does not hit zero and the RGB highlight values are split, too, but in a more elegant way. A grayscale test is just the first method you should check with a LUT to understand where the RGB values are going.
2. Gradient / CIE chromaticity test
For this test, we apply a “Four Color Gradient” to our timeline. It is pretty clear when you look at the gradient itself that you might run into artifacts, banding and noise issues. When we look at the ” CIE chromaticity” in our scopes, we see huge dark gaps between the colors.
For your information, these tested LUTs come from very popular, successful, and expensive LUT packages. The companies behind it call themselves “Leading Developer”, “Industry standard” and write sentences like: “Trusted and used by professional” on their websites and name customers like: Netflix, Sony and Universal, Nike, Adidas, on their pages. But none of the LUTs I’ve tested so far are “professional”. Quite the opposite.
3. Test Charts
A third method of testing and analyzing LUTs is through test charts. I did a couple. FREE to download. CLICK HERE.
A “CLEAN” LUT
“Rec709 Kodak 2383 D65” LUT by Blackmagic
Rec709 Kodak 2383 D65 LUT by Blackmagic
Rec709 Kodak 2383 D65 LUT by Blackmagic
With this blog-post, I just want to show you a quick demonstration how to check LUTs easily with the tools inside DaVinci Resolve and sharpen your vision on LUTs.
Let’s summarize the most important points:
- A LUT is always a “black box” / “mystery box”. You can not look inside a LUT and see how the LUT was build. You cannot “deconstruct” the elements.
- Use trustworthy LUTs only. It is always better to recreate a Look as a PowerGrade or hire a true LUT Developer for your project. But be careful rebuilding LUTs. If you push tools like the ColorWarper too far, your image will might break, too.
- Benefits of a PowerGrade: PowerGrades are instructional, since you can take them apart, figure out why and how they work, and you can reshape them for your specific project.
- In my latest “Soft 2 Strip” Project you can see the strength of a Power Grade which I build around a Kodak 2383 LUT. This is a good example of how PowerGrades and a clean LUT work perfectly together.
For more information on the topic “How to test LUTs“ I highly recommend this article by Jason Bowdach (PixelTools) for Mixing Lights:
Evaluating LUTs with a Stress Test:
One last statement:
Creative LUTs don’t have to be bad. There are some LUTs out there that are pretty good. And like the Kodak 2383 it is nearly impossible to rebuild those LUTS with native Tools Inside DaVinci Resolve.
LUTs are not bad. LUTs (even Creative LUTs) can be a very helpful tool by achieving a certain Look. Just test those LUTs using Test Charts and make sure that they will not “break” your image.
Click here to Download some Test Charts.
WORKING WITH LUTS
TRILINEAR / TETRAHEDRAL
There are two ways LUTs are interpolated in DaVinci Resolve. By default, it is set to “Trilinear”. It is better to switch to “Tetrahedral”. It takes a bit more processing power but it will give you much better, cleaner results.