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Old 14-04-2021, 12:50 PM

JA is offline
Join Date: Oct 2016
Location: Melbourne, Australia
Posts: 2,582
Originally Posted by Gordy View Post
I am just starting my mono journey along with Pixinsight. I noticed a lot of tutorials show how to use SCNR to remove the colour green from images. One site mentions that there is no green in space so it makes sense to reduce that colour much as possible in images.

If this is the case, then why bother to take images using a green filter (LRGB) in the first place? People still do so there must be a reason - does anyone know what that is?
You don't only need green to represent green objects, but also to help generate other colours and nuances of colours either by Bayer filter interpolation/processing in the case of a colour camera, or in creating a colour image from Red, green and blue filtered images from a monochrome sensor using software.
Leaving aside the complexities of demosaicing and interpolation in software or camera firmware, think about how, for instance ,white is generated on a colour sensor: Red+Green+Blue and some hocus pocus. This hopefully goes most of the way to an answer

Also take a look at the spectral response of the various channels from a colour camera sensor. Here are two examples: a Nikon D600 DSLR and a ZWO ASI071, most DSLRs and other colour cameras will show something similar.....
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Remebering that the Oxygen lines OIII are around 500 nanometers, take a look at the graphs and you see that the OIII lines are represented by both the Blue and Green channels, almost in equal proportion. Even with a monochrome sensor the Red, Green and Blue filters used would have comparable bandwidths to those shown above on the colour sensor array, as evidenced in the Astronomik L-RGB filter set data below...
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Last edited by JA; 14-04-2021 at 01:31 PM.
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