I am trying to calculate the uv reflectance of an area of an insect in a black and white photo. There are a 98% and a 4% standard in the photo. As far as I’m aware I have to create a mspec photo to find the UV reflectance value. When I do this I use a ‘UV’ camera setting that I made so only red and blue channels are shown. So when I measure UV reflectance I get different mean uv reflectance values for the two channels, whereas I want one uv value from the image. How do I do this ?
There’s not really any such thing as a single “UV” channel in the camera. The three (RGB) sensors have different spectral sensitivities to light at different wavelengths, and they can all detect a bit of UV. As a rule the camera’s red channel will be most sensitive and see deepest into the UVA region. So if you don’t have visible and UV images then just process the photos as standard “visible-only” photographs, and just measure the red channel’s UV reflectance values. Remember that you need to define UV in this instance as the camera’s red-channel sensitivity to UV (which you might not know, and will depend on your lens/camera/filter combination).