Film emulation/simulation

Processing
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Hello,

There are many sites (free as well as commercial) offering LUTs for imitating classic film look. Some are generic, while others claim to closely resemble specific film emulsions.
I have always been puzzled about what input such LUTs require. Do you apply them on scene-referred, linear input? (I know that @t3mujin provides complete darktable styles using channel mixer and tone curve, as well as LUTS.) If not, how do you prepare your raw files before applying a LUT or style?
(I understand that when someone is just looking for an artistic effect, accuracy does not matter, as long as the outcome is pleasing. I’m just curious about the background of this technique, and how one is supposed to use them to closely approximate some specific film stock.)

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different LUTs, different input reqirements.

I believe the film simulation HaldCLUT pack from Rawatherapee expects sRGB images, so you’ll probably get the best results if you apply that after filmic/base curve.

a lot of the free LUTs out there are from video land however and generally expect some sort of log gamma in Rec709. If you want to use these in darktable you can by using two lut3D modules, one to transform into a log space, which works quite well infront of color balance, followed by the “look” LUT further along.

basically all my responses to Play RAWs have been me experimenting with this technique if you want to have a look at my posting history. The .xmp files won’t be of tremendous use without the LUTs but I can tell you all about the approach if you’re interested.

I was actually thinking about doing a post on it just to share the approach and give people.the opportunity to.tell me why its a dumb idea lol.

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Yes, in principle every LUT needs to specify it’s input colorspace and ‘gamma’ and it’s output colorspace and ‘gamma’.

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Hi Dave & Bob,
Thanks for the feedback.

Simply specifying the input a colour space does not say anything about what kinds of curves are to be applied (if any), right? That is, simply knowing that a png LUT needs sRGB input does not say anything about mapping my scene-referred, linear image into sRGB. It is exactly the

you’ll probably get the best results if you apply that after filmic/base curve

part that I’m asking about. One can choose between lots of base curves or create their own; similarly, filmic has quite a few options to tweak. Surely there are some that give results that are closer to what could be achieved by photographing the same scene with same exposure settings using the film stock that the film emulation package (whether a LUT or a bunch of modules) intends to emulate.

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I think you can also use unbreak profile I saw someone use it some time ago in a discussion about LUTs I am just not exactly sure of the correct application of it ie spot in pipeline etc

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Some examples, using the same LUT (@sacredbirdman’s Astia):
Filmic, with a ‘straight curve’ (so logarithmic, unless I’m mistaken):

2020-05-31_19-13-33_P1030280
2020-05-31_19-13-33_P10302803791×2535 3.55 MB

Same, with chroma preservation turned off:
2020-05-31_19-13-33_P1030280_01
2020-05-31_19-13-33_P1030280_013791×2535 3.88 MB

Without filmic:
2020-05-31_19-13-33_P1030280_02
2020-05-31_19-13-33_P1030280_023791×2535 3.52 MB

WIth ‘Leica-like’ base curve, exposure adjusted so that the grass has similar brightness:
2020-05-31_19-13-33_P1030280_03
2020-05-31_19-13-33_P1030280_033791×2535 3.44 MB

Then @t3mujin’s Astia style, finally his Astia LUT, which he says is created from the style. Clearly, these require some kind of (base?) curve, as when applied to a pristine photo, they look like this – and quite different from each-other:

2020-05-31_19-13-33_P1030280_04
2020-05-31_19-13-33_P1030280_043791×2535 3.04 MB

2020-05-31_19-13-33_P1030280_05
2020-05-31_19-13-33_P1030280_053791×2535 3.03 MB

I can just go and pick whichever I like, of course; but here, I’m asking about the intended use. Maybe @sacredbirdman can answer how he developed the LUT and what the intended usage is? But then is that applicable to other LUTs?

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@kofa If you take a look on the Usage section on t3mujinpack:

The presets aren’t meant to be a single step solution, specially for RAW images, but a step in a workflow that slightly changes the color and exposure look and feel. The simplified version of that workflow would be something like this:

Basic processing (exposure, white balance, etc.)
Apply the preset
Further processing, including additional adjustments in exposure or tone curves

Right now in my workflow, regardless of the way I process the photos, that style is the very last step to be applied to the photo. Those LUTs are an alternate way to use the styles, even outside DT, but were generated based on that workflow.

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Yes, thanks for the reminder. I think we have discussed that previously.

In general, I wonder how one develops these presets/styles/LUTs.

If I understand correctly, @sacredbirdman wrote a custom tool that used photos processed using a Fuji camera to create the LUT. His LUT provides strong contrast without other curves, though he does recommend tone EQ for exposure adjustments (see Fujifilm X-H1 Astia HaldCLUT). @Jean-Paul_GAUCHE had applied a similar approach (processing identity HaldCLUT using Fuji’s software, see Fujifilm X-H1 Astia HaldCLUT - #5 by Jean-Paul_GAUCHE).

I think @patdavid’s presets (https://patdavid.net/2013/08/film-emulation-presets-in-gmic-gimp/ and https://patdavid.net/2015/03/film-emulation-in-rawtherapee/) also assume some pre-processing. This is his Astia 100F, with the ‘straight Filmic’ treatment:

2020-05-31_19-13-33_P1030280_06
2020-05-31_19-13-33_P1030280_063791×2535 3.13 MB

So can we say that the LUTs listed above can be divided into two groups:

  • one derived in a fully digital way, imitating a manufacturer’s processing, including contrast as well as colours;
  • the other group is more hand-crafted, requires additional curves, applies more subtle contrast changes, and is more concerned about colours?

I don’t know what other, commercially available LUTs claim to achieve (I mean whether their creators actually went and shot scenes on film and with a digital camera and then tried to reproduce the look on previously processed files (curves etc, or straight out-of-camera JPG) or minimally adjusted raw files).

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I developed the LUTs by taking ~100 photos, developed them in Darktable without any adjustments (so, base curve etc. off) and used a tool I made to calculate a LUT that would closely imitate Astia JPGs that my X-H1 made. So, it also imitates the contrast curve (this could of course be somewhat straightened with additional calculations). My intention was to get the Fuji look fast and easy as a starting point because I often have somewhat large number of images to edit and a time limit.

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Thank you for the detailed description.

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Usually the Luts are grouped as being designed to work on tonal adjustments or for color grading although of course there will be some cross over. I found this to be a good overview when I went looking a while back. I have a lut that preserves highlights and one that is designed to recover shadows and others that affect tone. Lutify.me | Using LUTs? Here is What You Need to Know

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Did you ever develop that tool or share it. I recall you suggesting it was a bit rough so you wanted to refine it??

@kofa Funny with these things. I was playing around and trying to understand the Color LUT module a while back. It opens with the values of a CC24 colorchecker but as a no-op on the image. I just for fun was playing around and thought I would set each patch to absolute and enter the LAB values for my color checker the Spyderchecker24. This is not a correct use or any type of calibration but I saved it as a preset because I found a nice little bump to contrast and color. It may be unique to my set up but you should try it and see what happens. Again no technical correctness to this just me messing around…Spyderchecker.dtstyle (2.2 KB)

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broadly speaking there are two categories, technical LUTs and creative LUTs. I would probably call all the examples you looked at creative LUTs, just because they haven’t necessarily been made with the same rigour as a print film emulation (PFE) LUT from the film industry.

which leads us to technical LUTs, of which there are kind of two main categories as well, LUTs that go at the beginning of the image pipe and LUTs that are the final step in the pipe.

the PFE LUT is an example of the latter, they came about in the early days of digital intermediates, where movies were captured on film, scanned digitally for editing, VFX, colour work, etc, then printed back to film for distribution. So as we know, film will always have some effect on the colours and contrast of whatever’s being captured, and the role of the PFE is to accurately represent this transform. The colourist can apply the LUT in their final node, adjust the image seeing what it will look like once its printed to film, then can turn it off before they send it off to be printed.

now with digtal distribution it has evolved into more of an artistic tool. Digital projection doesn’t impart the same sort colouration, so in some cases people will still use a PFE LUT and just leave it on. In this case of course there are no rules as its only serving as a look, so you can use the PFE LUT earlier in the pipe if you want.

the other LUTs that go up front are typically for transorming large gamut colourspaces with log gamma (cineon was the classic curve for digitizing film, and most digital camera manufacturers have their own) into a Rec709 or Rec2020 colour space to make sure all your values are legal while preserving colours accurately.

then most of the LUTs leftover are creative LUTs, and in most cases there’s no telling what they’re trying to do, with at least one notable exception: often a director, cinematographer and colourist will try to develop the look of a production quite early on, and using test footage they will create the look they’re going for and use that as a monitor LUT on set. Because you’re likely shooting log or RAW, and will need a standard conversion LUT to get a more legiable image anyway, the idea is to replace this with a viewing LUT to give you a better impression of the final look you’re going for. Sometimes people will even bake in exposure compensation and things like that as well.

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Have fun!
Claes in Lund, Sweden

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