[argyllcms] Re: About Hi-Res spectral mode

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 26 Oct 2010 00:09:02 +0200

Am 25.10.2010 22:22, schrieb Graeme Gill:
> Whether that is of any significance, depends on your context. If it is
> of no consequence to you, then I guess purchasing an instrument with 1
> nm resolution is not on your agenda :-) [Note that I currently have no
> means of verifying whether the above differences represent an
> improvement in accuracy of not.]

Hi Graeme,

looking at your laser pointer spectral plots it seems that the FWHM of
the instrument's optical system is still the limiting factor [hard to
tell exactly from the diagram - but I'd guess about 20nm ? - assuming of
course that the laser is really monochromatic] The benefit of higher
sampling resolution is of course limited if the bandwidth cannot be
reduced as well. Theoretically the higher sampling resolution should
offer an opportunity do deconvolve to a smaller effective bandwidth, but
in practice a stronger deconvolution is limited either, by a too bad S/N
ratio. Certainly, as we see, high-res mode does reduce the effective
FWHM, but obviously it can't reduce the effective BW by the same factor
as the sampling resolution is increased. So I'd still expect a
noticeable improvement from an instrument which reports not just with
1nm resolution, but also *with 1nm FWHM*. According to the literature,
20nm BW is too much for accurate measurement of narrow-band light
spectra, the literature rather suggests to use a BW of 5nm or less (and
a corresponding resolution too, of course). To get a feeling for the
impact, it's quite easy to simulate how the effective spectrum locus
moves in chromaticity space, when monochrome spectra are "broadened" to
a triangle or Gaussian with say 5nm, 10nm, 20nm, etc. FWHM [see
http://tinyurl.com/ykrms2], and it should be easy as well to compute the
corresponding colorimetric errors.

Regards,
Gerhard


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