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ARRI | Unicolor vs 3D LUT | Differences


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I already made a topic last year about Rec709 -> sRGB and color transform regarding Unicolor.



Now I am working on a TVC shot on a Alexa in LogC and if I transform Arri LogC to Rec 709 I get a super contrasty result with the Unicolor.






Versus using a 3D LUT provided by ARRI.





My question is why is there such a big difference in the transformation?
I really like to use the Unicolor since it is not LUT based, but that is only possible if it got the transformations right.

(or am I doing something wrong here?)


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Hi Jan!

Indeed, as Yoav said, Unicolor makes color transformation based on sheer mathematical operations. It lacks tone mapping and that can lead to over exposed images. The way to tackle this is simply by manually setting the signal somewhere where you feel it should be according to your image and signal response. In other words, by manually adjusting the tone mapping. 

Also, you can use the ACES ODT. ACES color science has an amazingly well crafted tone mapping that creates a pleasing tone which was created after multiple case studies and screen audience tests.  However, color tools in ACES will not respond to the signal the same way that you are used to on a regular rec709 signal.  

Both approaches, as well as the the use of a LUT crafted by the manufacturer are perfectly okay and respectful to the color science of the camera you use. Depending on the project and your needs, you can decide which suits you the best ?




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Hey Yoav, the Aces ODT works quite ok, good to know there is no tone mapping applied by the unicolor

I did some extra research on this subject and compared 'OpenColorIO' with the ARRI Rec 709 LUT and came to the conclusion it does the same transformation compared to 'ACES ODT' within Mistika which is super nice for a reliable workflow.

Still the 'ACES ODT' and 'OCIO' are a bit to contrasty and oversaturated compared to the LUT provided by ARRI especially in the highlights.





ARRI Rec709 vs Mistika ACES ODT 








Log C GRADED.jpg

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Thanks a lot for sharing this. The changes are very nuanced, but still those are elements to take into account seriously when dealing with a project. 

On 8/28/2020 at 2:35 PM, JanMaarten said:

Still the 'ACES ODT' and 'OCIO' are a bit to contrasty and oversaturated compared to the LUT provided by ARRI especially in the highlights.


Also we have to bear in mind that the LUT provided by ARRI is backed up by the color science of the manufacturer itself. So, unlike a lot of LUTs that can be downloaded on the internet, this is for sure one that can be trusted. 

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