Haha, yeah, like international research team sponsored by large industry partner monumental! Could be an interesting PhD position though 
There’s a solution for this with argyllcms & darktable.
See pcode — Darktable Camera Color Profiling
But it’s more easy is just use new colorcalibration enhancement to take the calibration from a color checker target in upcoming 3.6
I don’t have lumariver only the commandline dcamprof but as for DT the proper way to generate the tiff for color profile programs is generally as outlined here…GitHub - pmjdebruijn/colormatch: ColorMatch The key is the input and output profile should be the same. This way DT does a direct pass thru and gives you a tiff with no color corrections.
Actually Pascals script using argyllcms and using a jpg/raw pair does a nice job of matching the two if that is something people want to try. I haven’t gotten around to comparing a custom icc with Aureliens correction in color calibration yet…maybe doing both would really nail the color so do a custom icc and then further tweak it with color calibration …
I think you could actually double up. So you could make that custom profile and use that and then you could add the color calibration which in the end is like a set of channel mixer tweaks to try to match the color better . At least you could try a couple of time to see if it was worth it?? But I think we are hijacking the topic a bit…
It’s what I use to make LUT ICC camera profiles from spectral measurements.
Note that in darktable 3.6, the colour calibration module will support improving colours using a Color Checker.
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I think he asked about it already above but was just not sure if it was any good…
It would be interesting to use the evaluation features and compare the standard profile vs custom and see what sort of a deltaE difference there was between them using the color correction profile assessment
The story of hot lightsabers and why even monochromatic lasers should desaturate at high brightness levels.
Why do lightsabers in both the old and the new movies look super bright and highly energetic even on both prints and low dynamic range screens?
First an example from one of the classics:
And one from the third trilogy
Compare that with this disaster
Why is this last one so bad compared to the two from the movies? Whoever made them thought that the actual blade should be in bright saturated displayable colors while the movie frames are essentially white. This is quite understandable, just study you local traffic lights next time you are out for a strool at night. They do not desaturate at all to our human eyes but they still look bright. But it somehow does not work for images and paintings. Have a look at this classical lightsaber VFX tutorial: VIDEO COPILOT | After Effects Tutorials, Plug-ins and Stock Footage for Post Production Professionals Andrew uses a white solid for the blade and a colored glow around to make it look bright, and it works, its white but we precive it as a self luminous colored lightsaber.
Here is a more modern version of the same tutorial where Ian Hubert takes advantage of the ACES-like desaturation of high brightness colors and adds a scene-referred glow to make it, well glow!
So why does this work so well? It’s called glare effect or grey glow illusion, making it possible to make reflective materials like a print appear emissive. Here is a classical test image and some papers to read if it is of interest:
The Glare Effect and the Perception of Luminosity
Gradient representations and the perception of luminosity
But how does this translate into image editing? Here is my take. A global scene to display transform should smoothly converge to pure white as the brightness goes up. It actually should not preserve saturation of highlights. The problem is that good lenses are designed to suppress glare like this which will causes bright light sources to just be white with no punch. I generated my own version for this using Blender, one with and without glare (known as bloom in Blender). A good lens will produce the second version without bloom which will look much worse than a lens with some imperfections! Import the exr add sigmoid with preserve hue and a bit of exposure tuning to reproduce the results.
With Bloom - “Bad lens”
glare triangle bloom.exr (21.7 MB)
Without Bloom “Good lens”
glare triangle.exr (1.1 MB)
The solid triangle in the above two images are the same, think about that for a second! A global tone mapper which only works on individual pixel values and takes the second image without bloom could and should never produce anything like the version with bloom. The correct result for a global tone mapper, be it sigmoid, filmic or something else, is instead just the white triangle. The bloom effect has to be either created manually when shooting by some filter / dirt or in post in a separate module.
I hope that some of you darktable users now shout, but the bloom module, we have the bloom module for this! And you absolutely should because that is the correct way of solving this in post! The only problem is that the results of that module is, weeeeeelll…, kind of disappointing. The reason? Simple, the module assumes a display referred workflow and needs an update to scene referred (operate on rgb ratios instead of L in Lab) for it to work as expected.
PS I cant stop laughing over how bad the darktable bloom module looks on this test image. DS
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Enjoy your long form posts. Hope D isn’t feeling particularly litigious. 
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The darktable user manual already states quite clearly that when working with a scene-referred workflow, the “bloom” module should be avoided, for the exact reason that it does blurs in Lab space:
https://darktable-org.github.io/dtdocs/overview/workflow/edit-scene-referred/
So, no need for litigation 
There is a new “diffusion” module based on heat transfer equations that is proposed, which works in linear scene-referred space, and it might be interesting to apply that module to this sort of problem.
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Once upon a time I made a more physically correct bloom module for darktable but it never made its way in…
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Blurs and blooms are interesting because bright or dark patterns can emerge where point blurs extend or meet, especially from corners or edge inflections. Even in the coloured triangle, to the eye, the bloom appears heavier on the bottom right corner and it doesn’t appear to extend beyond the corners.
I was referring to the Walt D Company. 
I have not caught up with the latest on this topic, but I do hope this gets included in upcoming versions. I’m on Windows, and I would have to wait for it to become included in the official release for Windows.
I love your way of thinking. And best wishes on your contributions to darktable.
I love darktable’s modularity, and the hope that we can have in future a choice of different scene referred to display referred transform options…
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The pull request is still tagged as controversial. In the meantime, you could try your hand at building a dt with the module. There is some guidance already in this thread. It will be trickier to accomplish on windows though.
My apologies to anyone who might consider this an “interruption” of the thread. my enquiry is directly related to the Sigmoid module, and I hope you agree - relevant.
I am highly interested in exploring the opportunities of your proposed Sigmoid module, for achieving a scene referred to display referred transform.
My constraint is I am on Windows 10, however am able to build for Windows 10, from sources. Details of how I achieve this, is on another thread, which has been split from my earlier enquiry on your thread.
https://discuss.pixls.us/t/building-darktable-on-windows-10/
What I will need, from you, with your kind assistance, are the following :
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How do I gain access to your “fork” of darktable which included the sigmoid module?
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Are there any changes I would need to make, to ensure an effective build on Windows?
Please don’t cross post. The forum clearly shows where the posts were split to:
Image
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At the top of this thread…
First I’d like to be sure I’m using the right version of sigmoid, cos I followed the process linked to below, adapted for Windows, to build what shows up as this darktable version
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With a sigmoid module that looks like this :
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I ask cos I do not see a “log-logistic” or “weilbull” option which was discussed or referred to here in the opening post of this thread. Have these options been deleted from the user interface? :
Will do in due course. If your request is still open… I have to ensure I have all the collateral, to support any opinions, so please give me a few more days. Discovered this thread only a short while ago.
Nice progress on building darktable!
That is indeed the correct version, the module has changed over the spring and will change some more soon. And another reminder, this module WILL brake a couple of more times as I still change the UI parameters from time to time.
The module now only supports log-logistic with skew as that generalizes better with less clutter. Looking forward to hear your feedback!
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