[argyllcms] Re: ColorMunki measurement drift

  • From: Sam Berry <samkberry@xxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 2 Oct 2010 14:44:33 +0100

Whilst I appreciate that there is a lot of care that goes into the
calibration of these instruments, and that I have no direct experience with
such a calibre of instrument, the uncertainty levels you refer to are surely
quoted measuring illuminant 'A'. I cannot find any spectroradiometer
specifications which give typical uncertainties when measuring typical
display spectra, but I would be very surprised to find that they are up to
such similarly high standards. In the absence of a published spec, it seems
unfair to assume. You may certainly have more practical experience that me,
however, but I doubt that many people have access to a lab with multiple
spectros.  I would hope that repeatability a good order of magnitude better
than shown by the colormunki here was attainable though.

Although I cannot find the spec of the Pr-704 online, the Pr-705's accuracy
is listed as +-0.0015x +-0.001y. According to my calculations, this results
in an error disc approximately 1.3deltaE in diameter, for a single
instrument measuring a continuous and known spectrum. I would be extremely
surprised to find different manufacturer's lab grade spectros agreeing
within 2deltaE of each other on a spectra such as an LED's, or perhaps a
CCFL such as in the NEC above. Only the single-instrument repeatability
specs are under 1DE. Am I mis-reading something?

Regards,
Sam Berry
www.satsumatree.co.uk



On 2 October 2010 12:42, Roger Breton <graxx@xxxxxxxxxxxx> wrote:

> The lamps these instruments are calibrated against are either PTB, NIST or
> NRC traceable, within their respective uncertainty budgets, which usually
> translate into fractions of delta Es. Still not good enough for you?
>
> Roger
>
> > -----Original Message-----
> > From: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-
> > bounce@xxxxxxxxxxxxx] On Behalf Of edmund ronald
> > Sent: 2 octobre 2010 04:50
> > To: argyllcms@xxxxxxxxxxxxx
> > Subject: [argyllcms] Re: ColorMunki measurement drift
> >
> > I am afraid there is not really "ONE" reference instrument at this time -
> > depending on whether you chose PhotoResearch or Minolta or something
> > else you will get different "references". The best one can really hope
> for
> is
> > that one manufacturer's instruments match between each other.
> >
> >  That's assuming they are good enough to measure the same at different
> > points in time.
> >
> > Edmund
> >
> > On Sat, Oct 2, 2010 at 3:53 AM, Roger Breton <graxx@xxxxxxxxxxxx> wrote:
> > > Among all the instruments I enumerated, the PR-704 can be a reference
> > > instrument – no offence / Roger
> > >
> > >
> > >
> > > From: argyllcms-bounce@xxxxxxxxxxxxx
> > > [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
> > > On Behalf Of János, Tóth F.
> > > Sent: 1 octobre 2010 21:02
> > >
> > > To: argyllcms@xxxxxxxxxxxxx
> > > Subject: [argyllcms] Re: ColorMunki measurement drift
> > >
> > >
> > >
> > > Well, I think we should compare each of those instruments to a much
> > > better reference instrument (or a reference light source), but not
> > > between each others. I think it can't tell anything. They will be
> > > closer to or further from the true but randomly, so you can't tell.
>
>
>
>
>

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