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Author Topic: New profile making software: Lumariver Profile Designer  (Read 20561 times)

AlterEgo

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Re: New profile making software: Lumariver Profile Designer
« Reply #220 on: October 12, 2017, 01:24:26 PM »

It "works" with caveats.

works (not "works" !) with caveats that you need some measured (even not ideally) reference data from other cameras, yes ... for us hoi polloi who are using regular mass produced C&N&S&O&P cameras


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daicehawk

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Re: New profile making software: Lumariver Profile Designer
« Reply #221 on: October 12, 2017, 01:26:43 PM »

I apologize if this is old news - I just received an email regarding v 5.5 of BabelColor's Patch Tool.  The email notes that one of the new features is the "Spectrum Generator"

From: http://www.babelcolor.com/patchtool_spectrum_generator.htm

Any thoughts on the usefulness of this feature as it relates to using spectral data in Profile Editor?

Thanks,

kirk
One to many relationship. one XYZ can be a gazzillion of different spectra. I cannot see any use of this.
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Doug Gray

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Re: New profile making software: Lumariver Profile Designer
« Reply #222 on: October 12, 2017, 02:18:07 PM »

One to many relationship. one XYZ can be a gazzillion of different spectra. I cannot see any use of this.

Sure, and they're all metamers. But if you look at the spectra of existing pigments and combinations and decompose it, they collapse to a reasonable set of principal components that can, in linear combination, be quite a good match in most all cases.

However the XYZ triplet under one illuminant is certainly not very constraining so the synthesized spectrum is going to be fixed from the 3 principal components that best fit for that particular XYZ. One could just as easily publish a database of XYZ -> Spectra.

I can't imagine much application other than modeling metameric shifts under different illuminants when you don't have object spectra available but want to get some idea based on their large color database.

NOTE: I have re-corrected my first comment. Indeed, when only selecting 3 PCA components (single illuminant) the generated spectrums are the same whether or not the full patch spectrums or just the XYZ (or lab which is convertible to XYZ) is used.
« Last Edit: October 12, 2017, 03:24:39 PM by Doug Gray »
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Alexey.Danilchenko

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Re: New profile making software: Lumariver Profile Designer
« Reply #223 on: October 12, 2017, 04:18:32 PM »

Link or actual software product which does interface with a Spectrophotometer and does capture spectral data?
Have you actually read what the post and software was about (to which my post replied)?

The post was referring to spectrum generator from XYZ/LAB samples and was asking of using spectral data from that generator in profile editor. I did say it was not real spectral data since the generator does not measure any.

Is that any clearer now?
« Last Edit: October 12, 2017, 04:23:03 PM by Alexey.Danilchenko »
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Alexey.Danilchenko

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Re: New profile making software: Lumariver Profile Designer
« Reply #224 on: October 12, 2017, 04:40:09 PM »

works (not "works" !) with caveats that you need some measured (even not ideally) reference data from other cameras, yes ... for us hoi polloi who are using regular mass produced C&N&S&O&P cameras
Not in this sense - PCA will only give you results very similar to the chosen dataset. Anything that is substantially different will not be recovered correctly. It is only useful to analyze similar data
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GWGill

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Re: New profile making software: Lumariver Profile Designer
« Reply #225 on: October 12, 2017, 09:29:23 PM »

One to many relationship. one XYZ can be a gazzillion of different spectra. I cannot see any use of this.
The point is that what a camera interprets is unlikely to be any of "a  gazzillion of different spectra", instead it is likely to be a spectra that is available in the real world. Using this insight helps guide the trade-offs in creating a camera to standard observer transform.

As for PCA as a technique, the impression I get from reading a few papers on the subject is that it is not quite as good as using actual real world spectra. The problem is that reconstructing spectra from PCA doesn't necessarily result in spectra that you are likely to get from the real world. You can get the flavor of this problem from the realization that using unconstrained reconstruction will happily generate spectra with negative values.

[ Another approach I have read about recently that isn't based on real world spectra statistics, constructs the metamer set for each camera color, and uses the perceptual mean of the set volume as the representative standard observer color. One could tweak that approach to include real world statistics by weighting the mean according to real world metamer likelihood. ]
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Doug Gray

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Re: New profile making software: Lumariver Profile Designer
« Reply #226 on: October 13, 2017, 12:26:51 AM »

The problem is that reconstructing spectra from PCA doesn't necessarily result in spectra that you are likely to get from the real world. You can get the flavor of this problem from the realization that using unconstrained reconstruction will happily generate spectra with negative values.

I was wondering about how patchtool handles unrealizable colors in those circumstances. The choice is to come as close to the XYZ color as possible with a reflective surface from their dataset or return exact XYZ matches but with spectra allowed to be <0 or > 1.0.   So I checked it with Adobe RGB (255,0,0) which is not realizable by existing reflective surfaces. Sure enough, the PCA spectrum goes negative and well over 100% in places.
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Jack Hogan

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Re: New profile making software: Lumariver Profile Designer
« Reply #227 on: October 13, 2017, 10:53:37 AM »

With PCA as with many other machine learning techniques you are effectively fitting data and doing pattern recognition.  Results can be quite good if the training set is large enough and of good enough quality.  However you get 'plausible' results - not necessarily 'accurate' ones.  It depends what one is after.

Jack
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torger

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Re: New profile making software: Lumariver Profile Designer
« Reply #228 on: Today at 10:47:59 AM »

DCamProf also has a spectral generator since quite some time if someone wants to experiment.
 https://www.ludd.ltu.se/~torger/dcamprof.html#generated_spectra

It's more of an experimental feature and I didn't add it to Lumariver Profile Designer. What it is typically used for in DCamProf is when you make a profile based on real spectral measurements but you have some gaps, and then you can fill it out with generated spectra. As many have noted you can have infinite variations of a spectrum for one XYZ coordinate, so what DCamProf does is that it has various models using gaussian distributions to make as smooth spectra as possible for a given coordinate, the rationale being that making a profile based on such spectrum will make it more all-around than using peaky spectra. Regarding "impossible" colors the generator will then fail to make a spectrum.
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Doug Gray

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Re: New profile making software: Lumariver Profile Designer
« Reply #229 on: Today at 05:59:15 PM »

DCamProf also has a spectral generator since quite some time if someone wants to experiment.
 https://www.ludd.ltu.se/~torger/dcamprof.html#generated_spectra

It's more of an experimental feature and I didn't add it to Lumariver Profile Designer. What it is typically used for in DCamProf is when you make a profile based on real spectral measurements but you have some gaps, and then you can fill it out with generated spectra. As many have noted you can have infinite variations of a spectrum for one XYZ coordinate, so what DCamProf does is that it has various models using gaussian distributions to make as smooth spectra as possible for a given coordinate, the rationale being that making a profile based on such spectrum will make it more all-around than using peaky spectra. Regarding "impossible" colors the generator will then fail to make a spectrum.

Interesting Anders.

I've kicked around the notion if using PCA to find the dominant absorption curves of a printer then using that info to optimize the response of a camera's CFA. Possibly by taking to images, one with D50 ish light the other with Ill. A. One could even add various CFLs/LEDs with known spectra. This should provide enough info to generate 5 or more PCs to characterize a CFA reasonably well. And it should work especially well for colorimetric imaging of that printer's prints.  Know of any work done in that area?
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