[argyllcms] Re: Camera Profiling Ideas [Was: Re: Re: A few questions + an idea for spyd2.c (this time even more useless than before!)]
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 13 Mar 2009 11:41:32 +1100
Andrew Mihal wrote:
On the topic of alternatives to reflective charts for profiling
cameras, how about taking a photograph of the solar spectrum through a
spectroscope? You can use the positions of the absorption lines to
register your image against the well-known solar spectrum and then
compare your image data against the expected intensity of each color.
This was actually crossing my mind recently. The main issues in using
this approach that occurred to me were:
* Wavelength calibration. Maybe this would be possible with sunlight,
but the actual spectrum of sunlight is not consistent - it varies markedly
with location, time of day, atmosphere. I was thinking an incandescent
lamp, since a standard (ie. non-quartz halogen) will have a roughly
consistent and known spectrum, but is has no absorption lines.
* Geometry. I would imagine that the geometry between the light source and
diffraction grating and camera will have a noticeable effect on the
resulting
spectrum. Using a spectroscope may bring this under more control, but
can you take a photo of a spectroscope image, since they seem to be based
on viewing by eye - see
<http://scientificsonline.com/product.asp_Q_pn_E_3082305>
and <http://scientificsonline.com/product.asp_Q_pn_E_3052521>.
* diffraction grating efficiency. Each diffraction grating will influence
the intensity at different wavelengths. To compensate for this, the
efficiency of the grating at each wavelength needs to be known.
Graeme Gill.
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