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UltravioletPhotography

Camera Spectral sensitivity using MATLAB?


dabateman

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I came across this old site which looked at 28 cameras using a spectrometer. It seems they claim you can used their MATLAB script to calculated the spectral response of a camera using a simple color chart. Not sure if this would work as I don't have MATLAB. However if it does work between 400nm and 720nm, which is were they set their limits. I wonder if this could be expanded, for a full spectrum converted camera.

 

Here is the site link describing their research:

http://www.gujinwei.org/research/camspec/

 

Here is the site link to their MATLAB script:

http://www.gujinwei.org/research/camspec/db.html

 

I guess the MATLAB experts here can better address if this can be used for more broad spectrum determination. Since the color checker seems to have a near standard UV signature, it may be possible to drop the lower threshold at least into the UV range.

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I've actually read this paper before and it's intriguing (and something I've considered), but the method will NOT work with a color checker since it requires a set of colors varying with wavelength, and the standard color checkers do not vary much, so will yield poor results. The question I have is whether it can be adapted to work with a sparticle. The right way to approach this is not to try to use their script, which isn't designed for our part of the spectrum, it's to take the basic idea and redo it. The caveats are these:

1) we could only find the combined sensitivity of the sensor and the Bayer dyes at best

-1b) This method only yields relative numbers not absolute. They note this also.

2) the lens would need to be quartz, or else the lens absorption will affect the results. Alternatively a pinhole would suffice.

3) the filter absorption curve needs to be known with certainty (although probably using Schott glass filters with the provided Schott data would be good enough for an estimate).

4) the illumination needs to contain all the wavelengths of interest in high enough intensity to get good statistics. In other words, if you use sunshine the error bars will get really big at the short end of the spectrum.

 

Side note: the method is based off of Principle Component Analysis (PCA), which I've discussed in other contexts elsewhere on the board!

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