[argyllcms] Re: Camera Profiling Ideas [Was: Re: Re: A few questions + an idea for spyd2.c (this time even more useless than before!)]

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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