Read the Readme, Dumb~Me...

Important Note to Self: Read the ReadMe file!!!

I've experienced a couple challenges recently when trying Fuji film simulations in RawTherapee. Things just weren't working out as expected.

For instance, when downloading cinema oriented Fuji-look-alike LUTs I learned to be very careful to find out if the LUT collection was made for S-Log input.  Why?  S-Log on the video side produces a very flat file for a very specific set of reasons that have nothing to do with stills photography.  And I'm not sure how to create an S-Log image starting from a stills RAW.

No matter how hard I tried, applying a S-Log LUT to a stills image seriously distorts the colors and contrast.  What drives me crazy is that none of the cine LUTs I tried come with a ReadMe file that might explain any of this.  Apparently I'm not one of the "cool kids" who can figure this out before downloading and attempting something.  So to make my life easier I've learned to avoid cine LUTs in general.

Further narrowing my search a little to camera profiles and LUTs developed for stills work I have belatedly learned that some of these files were specifically designed for use with "linear" camera profiles in RentWare.  The devil is in the details.  This is very important as some camera profiles and LUTs both add not only the color grading/film simulation, but they're also managing the initial tone curve as well.  

Once I understood that some LUTs require a "linear" camera profile starting point I was able to achieve the film simulation I was looking for.  It's correct to the point I doubt anyone would be able to tell which camera was used with the Fuji film simulation.  

When working in RawTherapee I create a "linear" camera profile by simply de-selecting "Tone Curve" in the Color Management module.  There is no need to load a specially made for RentWare "linear" camera profile into RawTherapee.

One more step is required.  To ensure the camera profiles color grading function does not influence the film simulation result I simply  de-select "Look Table" in the Color Management module as well.  

Here's a quick look at how de-selecting these two components in Color Management compare to the RawTherapee default color managed state -

 

 

Resources -

An excellent look at how Fuji film simulations modify colors - 

https://www.imaging-resource.com/news/2020/08/18/fujifilm-film-simulations-definitive-guide 

Individual Cluts can be downloaded off this site.  I've found that I can load a RAW image into RawTherapee, deselect "Tone Cuve" and "Look Table" in the Color Management module, and then apply these film simulations without further image manipulation (as in the above image).

Another Fuji HaldCLut package - 

https://blog.sowerby.me/fuji-film-simulation-profiles/

Note: When using these HaldCluts I've found I need to lighten the tones while keeping the Color Management "linear."  I do this by modifying "Exposure" or by sliding the top end of the tone curve to the left using "Luminosity."  Doing these things allows me to match the output of the above Clut collection.