Philosophical musings on image processing...
There are just so many ways to process exactly the same data set that it is quite possible to produce a whole set of perfectly valid interpretations of the same data that end up almost unrecognizably different from each other on the basis of decisions made during processing. The tools get ever more powerful and the options wiider. We probably all just end up with our own predominant 'style'. Just interested here in exploring how much we vary , the main drivers for decision making and whether there is any mainstream concensus at all?
For my own part ..decision making is probably about 70% science (to the level that I think that I understand it) and about 30 % artistic effect. So for example ..
# I like to use the OOH palette alongside RGB stars for many HII regions because it is more 'naturalistic' - but nevertheless acknowledge that this is still an artifact because the nebulae are, in reality, too diffuse for the colours to be seen. I will stretch the OIII signal up for better effect and to make it obvious where it is --- but almost feel guilty taking this too far because it distorts the depiction of the relative ratios of HA and OIII light.
# I also like to use the SHO palette particularly on some type II nebula. Although certainly highly unfaithful in depicting the relative levels of NB emissions this palette can provide almost 3 D information on the nebula shape with the O3 usually locating the hotter core region and the SII some of the ionization edges (nearest the viewer) - so there is real scientific value as well as artistry in the depiction
However how far to take the stretching up of SII and OIII? It is easy - no decision to make - with some of the Wolf Rayet nebulae such as the Lion and the Crescent because the energies involved make the OIII relatively bright. But for some of the H II regions the ratio between the strength of the HA versus OIII or SII emissions is really quite extreme --- so it takes relatively a lot of imaging and time to get sufficient SNR using these two filters to even get enough signal to get much 'blue' and 'orange/ brown' into the image at all. Good 'current season' examples might be the Cave nebula and the Bubble nebula where there are striking SHO as well as many predominantly red images .
I can't help but think that with images seen side by side the totality can all seem misleading --- i.e. the same often predominantly brown/ orange/ blue depiction of a vast range of objects that are really very different but that as we depict them might appear to be constituted almost the same.
Obviously no right answers on any of this -- just interested to know what other folk think
TimH
There are just so many ways to process exactly the same data set that it is quite possible to produce a whole set of perfectly valid interpretations of the same data that end up almost unrecognizably different from each other on the basis of decisions made during processing. The tools get ever more powerful and the options wiider. We probably all just end up with our own predominant 'style'. Just interested here in exploring how much we vary , the main drivers for decision making and whether there is any mainstream concensus at all?
For my own part ..decision making is probably about 70% science (to the level that I think that I understand it) and about 30 % artistic effect. So for example ..
# I like to use the OOH palette alongside RGB stars for many HII regions because it is more 'naturalistic' - but nevertheless acknowledge that this is still an artifact because the nebulae are, in reality, too diffuse for the colours to be seen. I will stretch the OIII signal up for better effect and to make it obvious where it is --- but almost feel guilty taking this too far because it distorts the depiction of the relative ratios of HA and OIII light.
# I also like to use the SHO palette particularly on some type II nebula. Although certainly highly unfaithful in depicting the relative levels of NB emissions this palette can provide almost 3 D information on the nebula shape with the O3 usually locating the hotter core region and the SII some of the ionization edges (nearest the viewer) - so there is real scientific value as well as artistry in the depiction
However how far to take the stretching up of SII and OIII? It is easy - no decision to make - with some of the Wolf Rayet nebulae such as the Lion and the Crescent because the energies involved make the OIII relatively bright. But for some of the H II regions the ratio between the strength of the HA versus OIII or SII emissions is really quite extreme --- so it takes relatively a lot of imaging and time to get sufficient SNR using these two filters to even get enough signal to get much 'blue' and 'orange/ brown' into the image at all. Good 'current season' examples might be the Cave nebula and the Bubble nebula where there are striking SHO as well as many predominantly red images .
I can't help but think that with images seen side by side the totality can all seem misleading --- i.e. the same often predominantly brown/ orange/ blue depiction of a vast range of objects that are really very different but that as we depict them might appear to be constituted almost the same.
Obviously no right answers on any of this -- just interested to know what other folk think
TimH
