Unexpectedly, the CCDStack (CCDS) deconvolution routines also smooth the background. With positive constraint, the effect varies with the number of iterations. The smoothing is most pronounced with 15 to 20 iterations. With the maximum entropy routine, the smoothing seems to be more variable.

This background smoothing can completely remove faint detail between galaxy spiral arms. The following process uses CCDS data rejection to control where the deconvolution is applied. The focus is on maximum entropy, but also works with positive constraint.

Open the convolution dialog window and select Maximum Entropy. The documentation says to set the maximum radius to 1 to 2 times the FWHM, as calculated by CCDS. The suggested number of iterations is 100 to 300. However, some images, such as this one, can benefit from thousands of iterations. Set the maximum ADU to the brightest areas of the galaxy. Limiting the maximum ADU shortens the calculation time.

Next, drag a selection rectangle covering only the main galaxy. This greatly speeds up the process.  Sometimes, it may be necessary to process the entire image.

Make sure the new, deconvolved, image is selected.

Open the Data Reject window and select "reject range".

For this image, the information window shows maximum values of about 118 thousand. To be safe, enter 120 thousand and click "apply to this".

All data in the image are rejected. Now we must uncover just the deconvolved areas we want to keep.

Select freehand draw.

Hold down the left mouse button and erase an area encompassing the galaxy.

Now we can use "reject range" to again reject the faint areas between the galaxy arms. Start with about 100, for the maximum value, and double it until you have gone too far. Then click "undo" and try increasingly smaller values, until the rejection looks about right.

The image still as three stars that need freehand rejection. The deconvolution process created serious ringing artifacts around the brighter stars. Select "freehand draw" and enter a small "pen diameter". Hold down the left mouse button and paint over the stars. Be careful with stars between galaxy arms. Start at the center and work outward to encompass the ringing.

Now we are ready to combine the two images. Set the weight for the original image to one and the deconvolved image to 10. Then do a mean combine. In the area of the galaxy, the combined image will have one part of the original and 10 parts of the deconvolved image. In the faint areas and the bright stars, the data are 100% from the original image.

Here is the final image. Placing your mouse cursor over the image toggles to the original.