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.