In Color Calibration I find several presets (Fuji Acros, Ilford, etc.) that are convenient to test/use in converting an image to B&W. Once converted I can then apply Contrast Equalizer, Tone Equalizer, etc.
In LUT 3D, I can use the ‘haldcluts’ set of LUTS and thereby avail a larger set of presets. The list of LUTS are beyond what I can imagine I need or would use!
For B&W conversion:
Were I to use a B&W LUT in LUT 3D, what benefit would I get or forego from use of Color Calibration for any reason? [I’d imagine not but want to make sure I’m not missing something.]
Vice versa: if I use a B&W film preset via Color Calibration, what benefit would I get or forego from using LUT 3D?
It works well for me to use Contrast Equalizer and Tone Equalizer after I, say, apply Fuji Acros in Color Calibration. Are there any pros/cons of doing the same after use of LUTS via LUT 3D?
The color calibration method will give you lits of flexability. It just sets the module sliders to specific values. You can continue to tweak those values and any other sliders in the module until you’re content.
The LUT is less flexible, you apply it, and that is more or less it. The LUT looks the way it looks.
If you’re obtaining results you’re happy with from a specific module order then keep doing it. The other modules you mention work in LAB space and are prone to artifacts if you push them too hard.
Ok, Color Calibration offers a smaller set of film emulation presets and then provides lots of flexibility: applying a preset sets the sliders to specific vales that I can then tweak until I’m content. LUT 3D offers a much larger set of film emulation presets but I cannot tweak them any after application.
What are the pros/cons of my applying a LUT via LUT 3D first, and then activating Color Calibration and tweaking the sliders (from the values set by the specific LUT)?
To emphasize a key concern: I’d be tweaking, not pushing, the sliders in Color Calibration. Similarly, in Contrast Eq and Tone Eq I’d be applying a preset (e.g., bloom, sharpen, medium or soft contrast…) but not pushing the modules.
I misunderstood. I thought the Color Calibration module, activated after a LUT was applied in LUT 3D, would pick up and reflect in its sliders the change in the image produced by the LUT and I can then tweak the sliders from there on. I now see it doesn’t work that way, the two modules are unrelated and independent, and I can use the film emulating presets in either LUT 3D or Color Calibration modules.
Aurélien (the developer of color calibration claimed that he set up the channel mixer parameters based on actual film stock documentation. See the code starting at
One major difference to keep in mind: the LUTs are designed and work in the display-referred part of the pipeline - after filmic/sigmoid.
Another thing: LUTs can be large and much more precise in terms of specific color tweaks than profiles and can even be totally non-linear. That’s how a Look Up Table works. It takes an input value and just delivers the corresponding output value. This makes them a fast one-stop-shop because they can contain multiple “adjustments” all in one.
They can have color shifts, inversions and all kinds of funny effects you can not replicate with parametric tools like color calibration. But for their full potential they also need to work with a clearly defined basis or their transformations can have strange side-effects.
Yes, I understand LUTS come with a big “caveat emptor” sign that flashes red.
My use of darktable is very narrow and constrained: to convert pics I take of people into B&W. Toward that the primary modules I relied on were Color Balance RGB (presets to make colors vivid or for natural skin tone) followed by Color Calibration (where I use a B&W film emulation preset–e.g., Fuji Acros, Ilford Delta) followed by (occasionally) Contrast Equalizer followed by (almost always) Tone Equalizer.
I’m finding I have more options with emulating B&W films with LUT 3D.
My understanding is my use of LUT 3D in that way would mean there is no need for Color Bal RGB and Color Calibration (in the sequence outlined above) and I can use Contrast and Tone Equalizers (again, as in the sequence above).
You are probably not generally mistaken, but only you can decide what you really need. The two color modules are capable of modifying saturation and brilliance, which both effect the light/dark tone of the color.
If you wanted to make all red parts of the image darker, you could do that with either of the color modules, and that’d give you a different b/w rendering.
That’s actually one of the great things about dt - you have a myriad of ways to do things, and can chose what works best. Yes, there are ways which are ‘better’ or more technically correct, but you’re still free to chose.