NEAIC: Tonal Mapping

J-P Metsainio is giving a talk on his techniques for using narrow-band imaging to produce very sharp high contrast color images.  The technique appears to be a very clever application of the idea of using lower resolution in the color channels and blurring the noise (to reduce grain).

The critical first step in his technique is to separate the image into a stellar and non-stellar component.  J-P uses Photoshop’s "dust and speck" removal tool, but the idea is to use the spatial information to find and remove stars.  This step is critical because it allows one to manipulate the high-noise component separately from the high-signal component.  Once the stars are removed, contrast stretching no longer causes the stars to "bloat."

Low-signal components, like his 20-minute OIII image, need to be blurred to reduce graininess.  What this amounts to is imaging at lower resolution.  What you’re really looking for is to reduce the resolution to match the amount of data you have.   Low-signal should be matched with low resolution.  You could simply use binning during the acquisition to accomplish much of this, but you would probably still have to do some smoothing.

Then end effect is that one can maintain sharp stars while smoothing the higher noise nebulosity.  And the images look great!

You can find more information on J-P’s web site at http://www.astroanarchy.blogspot.com/.