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Different CMFs with Spectros

 
 
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Author erazortt
ZRO
#1 | Posted: 2 Nov 2024 09:05 
Out of interest, and for my education: Why is there the possiblity to change the CMF for CR250/CR300 spectros but not for all other spectros? I'm asking since my understaning would have been that all spectros should be able to be operated with any CMF, since the spectro retuns a spectrum which is then folded with the CMF to result in the tristimulus values. So I would have expected this setting to be available for all spectros. Or what is wrong with my understanding of the matter?

Author Steve

INF
Male
#2 | Posted: 2 Nov 2024 15:38 
That is down to the spectro manufacturers to provide such options.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author erazortt
ZRO
#3 | Posted: 2 Nov 2024 19:13 
I don't understand that. How could that be dependent on the spectrometer or its manufacturer. Again, what a spectrometer returns is "just" the pure spectrum. It does not have anything to do with a CMF. The CMF is calculated in software on top of that spectrum which then results in the xyz coordinates.
So if that is not true, then please educate me and tell me what a spectrometer returns and how the xyz is calculated from that.

Author Steve

INF
Male
#4 | Posted: 3 Nov 2024 08:49 
The spectos that offer different CMFs have them as an option within the probe itself. They are not performed post-processing within ColourSpace.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author erazortt
ZRO
#5 | Posted: 7 Nov 2024 20:13 
Ah ok I see. So, in view that more and more colorimeters are available with the CIE 170:2 2015 CMF instead of the CIE 1931 CMF would it be possible to add this option to ColourSpace?

Author Steve

INF
Male
#6 | Posted: 7 Nov 2024 20:40 
As said, if a spectro has different CMF capability, it can be added - if/when we update the integration.

With colorimeters, they will just adopt the CFM in use by the spectro when a Probe Match is performed.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author erazortt
ZRO
#7 | Posted: 7 Nov 2024 21:00 
Steve:
if a spectro has different CMF capability, it can be added

I really don't understand what you mean by that. A spectro has no CMF, and does not have anything related to a CMF. It just takes the spectrum and returns the spectrum to the software (aka Jeti LiVal, ColourSpace or whatever). The software uses whatever CMF it wants to produce the XYZ out of the spectrum.

Steve:
With colorimeters, they will just adopt the CFM in use by the spectro when a Probe Match is performed.

No, they dont. They have interal filters which are produced to match a predefined CMF (either CIE 1931 or CIE 170-2 2015). The CMF of a colorimeter cannot be changed, it is fixed, since it is given by the filters. Colormathing will not change the colorimeters CMF.

Author Steve

INF
Male
#8 | Posted: 7 Nov 2024 21:07 
I'll leave you to research all that.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author erazortt
ZRO
#9 | Posted: 7 Nov 2024 21:49 
Help! Could anybody please point out in which way my two answers to the two quotes in my last post are wrong? And please get as technical as necessary.

Author Steve

INF
Male
#10 | Posted: 8 Nov 2024 10:06 
Ok - I will provide some additional help.

CMFs can only be applied correctly/accurately to spectral data.
When taking calibration measurements XYZ (converted to Yxy for graphing) data is used, as can be seen in ColourSpace profiles.
You cannot accurately apply an alternative CMF to the measured XYZ data.

Some Spectros have the ability to use different CMFs within the probe, before the spectral measurement data is converted into XYZ.
We offer those settings for those spectros that have that capability.

And yes, while all tristimulus colourimeters have their CMF fixed by the filters used, when you probe match to a spectro that is using a different CMF you are matching to that CMF.
That is an 'approximation', but nevertheless it is matching the CMF as in use by the spectro.

It is this 'approximation' that some other calibration software provides as post-measurement CMF adjustments, for spectros and colourimeters.
It is not correct/accurate.
(The concept of the colour space target for different CMFs is a big part of this approximation. )

It is also a big part of why we developed the concept of Perceptual Colour Matching.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author wikihua
ZRO
#11 | Posted: 10 Nov 2024 14:38 
Steve:
CMFs can only be applied correctly/accurately to spectral data.
When taking calibration measurements XYZ (converted to Yxy for graphing) data is used, as can be seen in ColourSpace profiles.
You cannot accurately apply an alternative CMF to the measured XYZ data.

Hi Steve,

I've also been researching this topic, and I wanted to confirm my understanding based on your explanation. So, as you mentioned, most spectros (like the i1 Pro series) do measure spectral data initially. However, when they output the "data," it's already been converted to XYZ values using the CIE 1931 2° CMF within the device itself. This means they don't output raw spectral data, making it impossible to calculate XYZ values for other CMFs (like CIE 2012 10°), correct?

Author Steve

INF
Male
#12 | Posted: 10 Nov 2024 16:46 
If the probe only outputs Yxy/XYZ measurement data, you are correct.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author erazortt
ZRO
#13 | Posted: 11 Nov 2024 08:15 
Ok, now I understand! Thank you.

Author wikihua
ZRO
#14 | Posted: 11 Nov 2024 23:51 
Steve
Steve:
If the probe only outputs XYZ measurement data

Thanks for the reply Then does i1 pro2/3 only output XYZ? Is it able to also output spectral data?

Author Steve

INF
Male
#15 | Posted: 12 Nov 2024 12:09 
That's irrelevant, as ColourSpace doesn't (presently) use spectral data.

Steve
Steve Shaw
Mob Boss at Light Illusion

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