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07:07 | anuejn | polyrhythm: that is sad indeed :(
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07:08 | anuejn | but understandable since CDNG is such a monstrosity that it is basically impossible to implement all of it
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07:09 | anuejn | I see that resolve is a valuable tool but I also think that we can build a solution for somehow getting our magic into resolve ;)
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07:15 | anuejn | but yeah i am also looking forward to seeing your results :)
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07:16 | anuejn | also: do you have any idea if there is a public dataset on spectral reflectance of different realworld stuff (different skin tones, foliage, ...)?
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08:24 | vup | polyrhythm: right, but DNG does specify that the transformation matrices are supposed to bring the camera space into XYZ_D50
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08:24 | vup | (also I stopped being lazy and read the DNG spec myself, there is some pretty crazy stuff in there)
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08:24 | vup | (for example DNG 1.6.0.0 allows you to specify a custom illuminant by its spectral data
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08:26 | vup | oh also: does one not need to correct for the wavelength dependent absorption of the lens glass?
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08:44 | anuejn | I suppose
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08:44 | anuejn | there is even an ISO standart lens: https://colour.readthedocs.io/en/develop/generated/colour.SDS_LENSES.html
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08:45 | anuejn | though its spectrum is relatively boring
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08:46 | se6astian | hmm, as there are tons of different lenses and coating I cant imagine the camera needs to account for what those are doing...
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08:47 | anuejn | I mean it _could_ but in practice it shouldnt make much of a difference
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08:48 | anuejn | In the end I get the feeling that colour-science is more more about colour than about science ;)
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08:49 | polyrhythm | the general idea is that you try to do the calibration with a lens that doesn't have an obvious color cast. modern lenses definitely qualify, especially when put into controlled lighting and looking at a very matte surface like a color chart
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08:50 | polyrhythm | modern lenses are so good, you really have to try very hard to get them to exhibit any kind of obvious flaws. although in the case of e-mount lenses i'm not sure what is great. i'm used to PL-mount cinema stuff
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08:53 | polyrhythm | anuejn: the standaard x-rite color chart is a good spectral reference for basic diffuse reflectance of foliage, skin tones, etc.
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08:53 | polyrhythm | other than that, there's not a specific need in the games/film industry for amassing a spectral DB of material types (yet...!) because most production rendering is taking RGB values and rendering just with that, or in the very specific case of a few studios like weta, they upsample RGB to spectral. hardly anybody is going out in the world to measure spectral data and use that info directly.
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08:53 | polyrhythm | also because what we think is a relatively straightforward value is actually not really.
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08:53 | polyrhythm | for example, if you take a spectrometer and sample human skin, you'll come up with some crazy dark value, because human skin doesn't really diffuse much light, it scatters it below the surface.
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08:53 | polyrhythm | this is all a fancy way of saying that you first have to define what kind of spectral reflectance data is meaningful to you
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08:54 | anuejn | I see
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08:55 | polyrhythm | there's lots of stuff like this for RGB values tho https://physicallybased.info/
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08:56 | polyrhythm | which again is all witchcraft fakery for the most part, totally just taken from neutralized photographs rather than any kind of rigorous spectral measurement
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08:56 | polyrhythm | and in rec 709 primaries
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08:57 | anuejn | interesting
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08:58 | polyrhythm | for games we usually go out with a color chart and just photograph a bunch of materials with a polarizing filter, then we use the chart to color neutralize and the polarizer to try and get rid of specular influence
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08:58 | polyrhythm | it works pretty decent
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08:58 | anuejn | I was especially interested in data outside of the visible spectrum to get an idea about the effect of uv/ir cut filters
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08:58 | anuejn | but that is probably rather hard to get
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08:58 | polyrhythm | there's a device that can do it rather easily i think, and it's not too pricy, hang on
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08:59 | anuejn | Like, I would really like to get my hands on a hyperspectral-camera one day :D
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08:59 | anuejn | polyrhythm: sounds like a solid method
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09:01 | polyrhythm | https://www.nixsensor.com/nix-spectro/
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09:01 | polyrhythm | this thing, pretty badass
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09:01 | polyrhythm | i was evaluating it for use at a game studio
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09:02 | anuejn | honestly: to me that does not sound to interesting
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09:02 | anuejn | since it has only 31 channels
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09:02 | anuejn | and does it have a builtin light?
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09:03 | anuejn | ok it does
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09:03 | anuejn | thats nice
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09:03 | polyrhythm | yeah of course, it has a D50 illuminant if i recall correctly
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09:03 | polyrhythm | it actually has to position it at a certain angle to defeat specular interference, it's not a straight on thing
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09:03 | polyrhythm | and yes it buckets the spectral data, but that's still more than enough for most use cases that they're trying to tackle anyways
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09:04 | polyrhythm | at it's price point there's no competition
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09:04 | polyrhythm | the next step up is like an order of magnitude more expensive
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09:05 | anuejn | yeah all in all it seems like a pretty good package
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09:05 | anuejn | also that its portable is a big plus
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09:06 | polyrhythm | yeah, plus phone app blah blah. now: how it relates to making a better camera sensor characterization, ehh....not so sure. :) but a fun toy
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09:06 | polyrhythm | what we need is the opposite, which is a LED or something that can very accurately emit certain wavelengths of light so we can see what the sensor does with it
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09:07 | anuejn | or a spectrometer and a beamsplitter
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09:08 | anuejn | so that we can just calibrate out the insufficiencies of the light source
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09:08 | anuejn | (+ a prism of course)
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10:57 | vup | well more likely a diffraction grating
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10:57 | vup | the problem is the intensity calibration
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10:57 | vup | most cheap spectrometers are not (relative) intensity calibrated
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10:58 | vup | so for calibration you would still need a light source with a know spectrum
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11:06 | vup | which is again expensive: https://www.oceaninsight.com/products/light-sources/calibration-sources/radiometric-calibrated/
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11:06 | vup | https://www.princetoninstruments.com/products/technologies-family/intellical
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11:09 | anuejn | probably we could calibrate with some university equipment?
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11:09 | anuejn | either you or se6astian can access?
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11:18 | se6astian | not sure...
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11:23 | vup | anuejn: maybe / possibly
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22:52 | anuejn | there is some more color-science at https://github.com/anuejn/cmv12k_color_response/blob/main/color_matrices.ipynb
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22:52 | anuejn | this incooperates filters and minimization of the color measured in a perception-matched way
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22:53 | anuejn | the results are already quite good and probably as far as I want to go for now
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22:54 | anuejn | if you have more ideas on what I should try, feel free to throw them at me
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