Processing the Bubble Nebula

Back in September I took 3 hours of Hydrogen-Alpha (Ha) data of NGC 7635, the Bubble Nebula. I captured the image using Maxim DL and CCD Commander, calibrated and stacked it in CCDStack, and processed it in PixInsight.

In PixInsight, I found an interesting way to pull the details out of the image. Here is the full processing sequence:

Flipped the image with a vertical mirror transformation. Somehow, the bit order for 32-bit floating point in CCDStack does not agree with how PixInsight is reading it, so it needs to be flipped to start.
Cropped the image to eliminate the border areas where alignment left behind some artifacts. This is important for stretching the image later as there can be extreme values in the border artifacts that can show up as clipped data later when they are really just noise.
Created a Star Mask.
Stretched the image with the histogram tool and slightly with the curves tool to just the edge of the noise floor. This is my base non-linear image.
With a clone of that image, performed a series of HDRWavelet transforms, with the number of layers from 2 to 6. For each number of layers, I saved the transformed image and returned to the original non-linear image. This gave me a gallery of images with different scaled features highlighted.
I then created a PixelMath expression that averaged all of the images and allowed me to weight each image. The expression was as follows. I started out with the weighting factor even across the images. Mean( 1.0*Base_Image, 1.0*HDR_Image_Scale2, 1.0*HDR_Image_Scale3, 1.0*HDR_Image_Scale4, 1.0*HDR_Image_Scale5, 1.0*HDR_Image_Scale6 )
I then combined the image using a variety of weights. As it turned out, a pure average of the images gave what I feel is the best result, so the weighting factor did not come into play on this image.
After that it was only a very slight stretch in curves and some delicate noise reduction using ACDNR to produce the final image.

Here is the final image. Clicking on the image will open the image the gallery.

NGC 7635—The Bubble Nebula

Here are the six images that went into creating the final. The first image will link to an animation showing each of the images in sequence. Clicking on any image will open a larger version.

Animation showing all the images in sequence (Warning—Over 2mb)