M 101 - Blue Halos Reduction
by Alejandro Tombolini
Introduction
Image of deadwing publicated in PixInsight forum - Blue halos - Main Notes: Starmask to protect the galaxy and MultiscalLinearTranform and Interchannel Curves to reduce halos. Date: September 2014.
Processing
The idea of this processing example is that you follow the process by downloading the image and the processes used, and apply them following the notes that each process has understanding the parameter used in each tool.
Note: Load process icons and find them in workspace 2 (ALT+2).
Looking at the channels separately, CTRL+SHIFT+R, CTRL+SHIFT+G, CTRL+SHIFT+B can be seen that the stars in blue channel are bigger than in the others.
Recomendation: See Frecuently used shortcuts in PixInsight.
The image has an uneven background, that's why you will have as first process in the list the DynamicBacgroundExtraction process.
A possible solution to reduce the stars in the blue channel is to decrease the intensity of that channel protecting the rest of the image. For that first will be needed a star mask.
Try first StarMask with dafault values and then move each of the parameters that were modify in the example observing the change in each case. Note how the mask is stretched and smoothed to better fit the halos to be removed.
Finally protecting the galaxy with starmask, it is possibie to reduce the halos using a ProcessContainer that include several aplication of MultiscalLineraTransform applied to the blue channel and finally InterchanelCurves applied to the new RGB image.
Note: You can extract the processes from ProcessContainer and apply them one by one.
The following gif shows the before and after of the image
See also this processing example about blue stars halos reduction.