Re: ProfileMaker 5
Re: ProfileMaker 5
- Subject: Re: ProfileMaker 5
- From: Roger Breton <email@hidden>
- Date: Tue, 15 Aug 2006 13:37:42 -0400
Dear Mr. Myers,
> First, the illumination in the Spectrolino is a standard
> tungsten-halogen bulb, thus very deficient in the blue and violet
> spectral region.
Yes, that is to be expected. Can't change the nature of tunsgten filaments.
> The D65 filter changes the ratio of blue light in the
> illuminant, ostensibly to achieve a D65 simulated illuminant.
Ah!
> My
> sources at Gretag have stated that it does not really achieve a full
> D65 simulation,
How could it?
> but it gets close to a D50 simulated illuminant.
It'd be interesting to obtain from GretagMacbeth (now X-rite) the SPD of the
unfiltered lamp output vs that of the D65 filtration. Can't this be
measured, indirectly, if I have the T spectroscan and measure in
transmissive mode? Just a thought. I gather that what I'm really after is
the spectral transmission characteristics of the Lino D65 filter (it must
the same as in the SpectroEye?)....
> I have
> not had the time to confirm this with my own measurements but it does
> sound plausible.
Yes, it must be attenuating some of the yellow components of the light
source in order to mimic, relatively speaking, the "shape" of the D65
illuminant in the visible region.
> Second, many of the experiments I have made with regard to UV
> excitation and fluorescing subjects show that using the D65 filter
> causes much more excitation than the U filter.
Ah! This is worth investigating. Wonder why FOGRA not suggesting measurwing
with a D65 filter since they are so pushy for some kind of UV filtration in
the next ISO 5-3 standard (that's what I heard)?
> Try this for yourself
> with a FWA brightened paper measured with the D65 and U filters. Using
> the D65 filter produces a much more pronounced fluorescence.
I'll try it. Does an inkjet media with a b* of -4 value be sufficient to see
a difference in your experience? (Of course, on substrate with b* less than
1.0, measuring with the D65 or the U filter should not make much difference,
doesn't it?)
> Third, using the U filter would require the signals at the violet and
> blue ends of the spectrum to be heavily amplified,
You mean "if we'd want to simulate D65" strictly in hardware, with
electronics alone? No optics?
> increasing the noise
> in these signals. The Spectrolino automatically increases the
> integration time when the D65 filter is present to improve the signal
> to noise ratio, thus compensating for the reduced light transmission,
> resulting in a more even distribution of noise across the spectrum.
100% with you.
> By the way, the U filter is not merely an empty tube,
I'll be damned. Thank's for sharing this tidbit of info. Always thought that
that clear glass was spectrally flat.
> it contains a
> piece of clear glass. So optically it is effecting the instrument in a
> similar way to the other filters with regards to refraction and focus.
Ah. I get it.
> A small effect to be sure, but it shows the attention to detail of the
> Gretag engineers in their pursuit of good measurements.
Yes, and I hope this small attention to detail will not get lost in the
X-Rite shuffle...
> Robin Myers
Regards,
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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