[argyllcms] Re: has anyone tried ColorVision PrintFIX ?

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 12 Oct 2005 23:39:31 +0200

Graeme Gill schrieb:

Very possibly, but it's up to the manufacture as to what sort of light
source, and what sort of phosphor to use, so between the light and
the filters, it is possible to get it to work reasonably. When
you're using LEDs, it's pretty hard to avoid it being narrow band.

Graeme, sure, no doubt, that's pretty hard.

Btw, I found some old, archived experimetal results. A couple of years ago, I had attempted to reconstruct the spectral response of my old scanner (may god rest his soul) from spectral measurements of an IT 8.7/2 target. For the recovery I did make the assumption that the unknown CCFL light source can be modeled as weighted sum of the twelve fluorescent F<n> illuminants (with the weights being estimated as well), and I did impose non-negativity and smoothness constraints on the shapes of the sensor responses in order to obtain reasonable results (as you know, the recovery problem is very ill-conditioned and extremely sensitive to noise).

Estimated RGB sensor sensitivities (i.e. sensor+filters):
(36 bands @ 10nm)

Estimated overall response (flurescent light source+sensors+filters):
(36 bands @ 10nm)

Since I don't know the actual response, there was no way for me to verify the accuracy of the reconstruction. One problem is indeed, that different parameters used for the estimation (for instance different error/smoothness trade-offs) eventually result in noticeably different shapes of the estimated sensitivities. But I think, the results look at least reasonable, though they are surely not perfectly accurate.

As you can see, particularly the red and green responses seem to be relatively narrow-band too. Actually I do not have the impression, that the manufacturer did make any attempts to optimized lamp & filters in order to approximate a colorimetric response. If they are optimized at all, then likely rather for other objectives (e.g. for max. light ouput of the lamp to reduce SNR, etc.).

When I later got my Spectrocam, I also measured the spectrum of the scanner's CCFL lamp. Here is the measurement result:
(Spectrocam has 5nm interval, 20nm bandwidth)


Other related posts: