Telescope Reviews: computer processing of film images

I'm creating this thread so that we can deal with image software and processing procedures special for film astrophoto.
What image processing software do you use?
How do you process your pictures?

OK, I will start. Currently I use this combination of programs:
Zoner - for most of the basic operations: curves, levels, resizing, channel mixing
Image Analyzer (my loved

) - A small freeware program, but contains a number of usefull features rare in other applications. Unfortunatelly it works internally only with 8-bit per color. This program has it's own forum, where you can ask it's developer and suggest new features.
Matlab - I use it for everything what I can't do with another software. It's usually a lot of work. In fact it is programming of own software.
DenoiseMyImage - A dedicated denoising freeware appplication. It's said to be one of the best.
Registar - A well known program for celestial image registration and stacking.
I don't like Photoshop (I'm the only one in the world?). Mainly because it's a gigantic software with only several functions usefull for me (which I can do with Zoner). I mind I can't understand the principle of it's functions (what I can in Image Analyzer).

I promissed to write my method for background subtraction in Image Analyzer. It works only for pictures without extended objects like the Milky Way or large nebulae. It in two main steps - extracting the bakground and proper subtraction. I will describe the process in the latest version of IA (1.32).
* Open the picture to be flattened and make a copy: File-Open, Edit-Copy & Edit-Paste
* Deletion of smaller stars: Operation-Morphological operations-Erosion. Repeat typically 2-4 times.
* Deletion of remaining stars, dark speckles and larger objects by clonning: Tool selection button-Clone. Set the appropiate size by the button aside.
* The image brightness decreased by the erosion. It can be restored by dilatation: Operation-Morphological operations-Dilatation. Reapeat to reach the original background brightness.
* Delete the renewed stars by clonning.
* Blur the background: Operations-Filters-Smooth & set the blurr radius. It must be the smallest possible to perserve all the background features but all the grain and star remnants must disappear. A good starting point is usually about 60.
* Now comes the background subtraction. It is done via the dialog: Operations-Pixel format conversion-Combine images-User expression. You need to select 'p1' as the backround image and 'p2' the original. Now is needed to enter the combining mathematical expression (no restrictions here!!). Who don't want to experiment or don't like maths simply copy this formula

(p2-0.95*p1)/(256-0.95*p1)*236+20

which gives usually a good result and IA will remember it for the future. If want to know more about this formula read further. This method has no "physical" foundation, but it works. The basic idea is to subtract the background but save the values of bright stellar centres at 255 and at the same time set the values at the bakground level to 0. The values in between are uniformly stretched to this range. It leads along to the basic formula (p2-p1)/(255-p1)*255. The problem is the program is worried about possible division by zero, so 255 has to be changed to 256. A fully subtracted image looks offten boring flat, that's why I subtract the background only partially. Sutracting of e.g. 95% of the background is implemented by replacing p1 by 0.95*p1. The next bug is the part of original's backround is lower than the smoothed backround so the resulting value is lower than zero and is truncated to 0. To prevent this, you need to add a constant e.g. 20 and multiply by 236(=256-20) instead of 256. So this is that magic formula.