[argyllcms] Re: Calibrate a HCFR hardware

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 13 Jan 2008 15:47:33 +0100

Graeme Gill wrote:
>> As the final usage of that colorimeter is for projectors, do you
>> think I should make the calibration on a projector (as argyll does
>> not have a projector flag, I can use the LCD one, instead)?

I guess that the CRT/LCD switch could have other side effects too, like
syncing to the display's refresh rate (CRT) or omitting the
synchronization (LCD), and not just to select one of two different
calibration sets? Graeme, can you please tell, how this is implemented?
Btw, does the HCFR instrument actually sync to the dispay's refresh rate

> You will always get the best possible calibration for a particular
> display if calibrated using that display type.

...where limiting the "display types" to only two classes "CRT" and
"LCD" is already a significant trade-off, which may be still reasonable
for the various monitor colorimeters (like DTP94, i1 display, Spyder,
etc.), but which may not be reasonable for the sensors of the HCFR
instrument, whose spectral responses are far-off colorimetric (see
http://tinyurl.com/2s5fpo). These sensors may possibly rather require an
individual calibration for each different display or projector model (or
even for each individual display device), and not just a distinction
between "CRT" and "LCD".

Maybe dispcal and friends should support instrument specific options,
which are transparently passed through to the driver and interpreted
only by the driver? (and for the HCFR driver, a file with individual
calibration data to use could be such an option).

Btw (maybe a little bit OT), when I look at the TCS230 datasheet then
I'm wondering, whether the HCFR instrument is equipped with an IR filter
in front of the sensor chips? Otherwise the presence of IR may
significantly tamper the readings, since all four photo diodes have a
significant sensitivity at IR wavelengths up to 1100nm (IMO colorimeter
sensors should not respond to radiation outside the human visible
spectral band).

I'm also wondering, whether possibly the use of all 4 diodes (R, G, B
and clear) in conjunction with a 4x3 transformation matrix to XYZ (i.e.
treating it as a 4-band instrument) might be helpful to improve some
aspects of the gadget (e.g. same calibration valid for a larger set of
displays - this requires of course linear independence of the four
spectral photodiode responses, and just by looking at the diagram in the
datasheet I don't feel able to assess to which extent this is granted).


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