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What's the easiest and most affordable way for obtaining UV reflectance images?

Started Apr 24, 2021 | Questions thread
ProfHankD
ProfHankD Veteran Member • Posts: 9,147
Multispectral band extraction
1

petrochemist wrote:

UV imaging is neither easy or cheap.

You said it all there... but....

I'll just mention that decoding multispectral information can be cheaper and easier than you'd think. If you look at the spectral profiles for typical RGB Bayer filters, they're really not narrow-bandpass filters, yet we get decent RGB extracted from captures with them. Basically, as long as the filters being used have different levels of response to the bands you care about, being able to extract the bands is primarily a matter of calibration and a bit of math.

For example, if you have a filter that does almost nothing beyond blocking UV, relatively simple differencing with an unfiltered view can give a decent UV image. For NIR, even the spectral response differences of Bayer RGB can allow extraction of a noisy NIR channel. However, I don't think the Bayer RGB colors differ much in NUV.  There are cheap gel filters that differ significantly in NUV response -- see the samplers from Rosco ; each (designed for theatrical lighting) filter comes with a response curve going from 360-740nm in 20nm steps.

BTW, you'll want to do the band extraction math on a linear representation of the pixel values, which generally means raws -- the log encoding used in JPEGs makes add/subtract behave more like multiply/divide, which is not what you want.

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