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Old 08-06-2016, 02:04 PM
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Atmos (Colin)
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Join Date: Aug 2011
Location: Melbourne
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If your SII actually looks okay without being combined then it is just a question of colour calibration. The SII when stretched can look pretty good but it is quite weak compared to the OIII and especially Ha. For instance, you may have an area with a pixel value of 3200 in red, 18000 green and 11000 in blue. It will appear a greenish colour, this is why a SHO when just combined looks largely green. The Ha signal is overwhelming.

The idea is that the SII (red) needs to be stretched far more to get the correct Hubble Palette. This is the reason for magenta stars, the red and blue get stretched more than the green for colour balance.
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