[argyllcms] Re: Fwd: Question about M1 measurements

  • From: Claas Bickeböller <lists@xxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 29 Aug 2014 08:34:06 +0200

Dear all,

as already stated the "corrections" (corrected is the wrong UV excitation of 
the instrument's light source compared to the desired reference illuminant) 
have to be illuminant dependent.

I tried to outline it here:
http://www.konicaminolta.eu/en/measuring-instruments/learning-centre/colour-measurement/colour/to-see-what-you-dont-see.html

In addition I wrote an article of possible ways to achieve M1 where I also 
clearly stated that M1 is perfect for viewing conditions that closely match D50.
For environments that have a UV content differing from D50 (like typical older 
"D50"-tubes or warehouse lighting), for a perfect correlation between 
measurements and visual appraisal, M1 is not the best choice.

http://www.konicaminolta.eu/en/measuring-instruments/learning-centre/colour-measurement/colour/iso13655-demystified.html

M0 is also not a good choice except the UV excitation of your instrument 
matches your viewing condition. But you can never know that unless you measured 
the light source of your particular instrument. Please note that M0 does _not_ 
mean tungsten. An instrument with a tungsten lamp as light source is M0, but M0 
covers all illuminations incl. M2 and M1 as the UV content is not defined and 
the demand for matching a CCT of 2856K is only a should.
For tungsten based M0 instruments also keep in mind that the UV content that is 
emitted from a tungsten lamp changes over time. So for all "FWA-compensations" 
that assume a certain UV content of a generalized instrument's light source it 
is not unlikely that they do not work correctly with your particular instrument.
Also all methods that try to derive the FWA content from a single UV excitation 
will fail for papers that 
a) use a lot of shading agents in combination with FWAs
b) do not show the typical strong "FWA-peak" as their "reflective  color" (so 
without FWA emission -> UV-Cut) is yellowish
c) maybe there are other circumstances where they fail

All these are the reasons why we (in our VFS) detect the amount of FWAs using 
two different UV-excitations and are also able to make use of what we call a 
"User-Illuminant".

M2 is a good choice if you are in a UV-free environment.

I hope that helps to clarify the "myth".

Best regards

Claas Bickeböller
Product Manager Graphic Arts
Konica Minolta Sensing


Am 26.08.2014 um 15:15 schrieb Roger Breton <graxx@xxxxxxxxxxxx>:

> So corrections are "illuminant-dependent" then?
> 
> / Roger
> 
> -----Original Message-----
> From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx] 
> On Behalf Of Graeme Gill
> Sent: 26 août 2014 09:08
> To: argyllcms@xxxxxxxxxxxxx
> Subject: [argyllcms] Re: Fwd: Question about M1 measurements
> 
> Roger Breton wrote:
> 
>> I have not looked at your code but do you use a "fixed" correction or a 
>> "dynamic"
>> correction in argyll FWA compensation?
> 
> Sorry Roger, it's hard to answer such a question. Every reading is different, 
> so by definition nothing is fixed.
> 
> If you're imagining something like a static shift in b*, then no - far from 
> it.
> It's a spectral correction model of the way the light interacts with the 
> media, including the FWA response.
> 
> Graeme Gill.
> 
> 
> 
> 


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