by Chris Peterson » Mon Oct 15, 2018 1:51 pm
BDanielMayfield wrote: ↑Mon Oct 15, 2018 10:22 am
My apologies to the astrophotographer, Andrew Klinger, for the disparaging tone of my (and today's) first post about this excellent APOD. Here is what he wrote about the filters used and the color processing:
Here is my completed image of the Eagle Nebula (M16) imaged with Sulphur, Hydrogen, and Oxygen narrowband filters. This false-color widefield image of the nebula represents the strong oxygen signal as cyan, hydrogen as yellow/orange, and the stronger sulphur signal as red. Naturally, this nebula is nearly all red in color, as hydrogen-alpha dominates the field. With selective filters and processing I have stretched the intensity of the Oiii and Sii to better represent where they lie in the nebula.
Among his peers (his fellow astrophotographers) there is nothing but well deserved praise for this work. Sorry Andrew.
There is a real problem with this kind of mapping, however. When each filter is assigned to a single output channel, we can separate them. Indeed, I often do this with interesting APOD images- look at the red, green, and blue channels separately to get a better idea of where the oxygen or hydrogen are. You can't always see that directly in the false color image because of the way the elements (and therefore the colors) mix. With a mapping like this, the different filter channels are mixed into pairs of output channels, which means the data is mixed in a way that prevents elements from being isolated. It can certainly make for an aesthetically pleasing image, but it is of much less scientific value.
[quote=BDanielMayfield post_id=286550 time=1539598947 user_id=139536]
My apologies to the astrophotographer, Andrew Klinger, for the disparaging tone of my (and today's) first post about this excellent APOD. Here is what he wrote about the filters used and the color processing:
[quote]Here is my completed image of the Eagle Nebula (M16) imaged with Sulphur, Hydrogen, and Oxygen narrowband filters. This false-color widefield image of the nebula represents the strong oxygen signal as cyan, hydrogen as yellow/orange, and the stronger sulphur signal as red. Naturally, this nebula is nearly all red in color, as hydrogen-alpha dominates the field. With selective filters and processing I have stretched the intensity of the Oiii and Sii to better represent where they lie in the nebula.[/quote]
Among his peers (his fellow astrophotographers) there is nothing but well deserved praise for this work. Sorry Andrew.
[/quote]
There is a real problem with this kind of mapping, however. When each filter is assigned to a single output channel, we can separate them. Indeed, I often do this with interesting APOD images- look at the red, green, and blue channels separately to get a better idea of where the oxygen or hydrogen are. You can't always see that directly in the false color image because of the way the elements (and therefore the colors) mix. With a mapping like this, the different filter channels are mixed into pairs of output channels, which means the data is mixed in a way that prevents elements from being isolated. It can certainly make for an aesthetically pleasing image, but it is of much less scientific value.