Bits and pieces

This is something like what I should say in previous posts but I forgot to do it. If you are aligning stack using Hugin tools, align_image_stack is HDR tool and it can’t handle well significant number of images in stack or significant movement between images. Workaround here is venerable divide and conquer strategy. Divide images into groups of few and stack them group by group. Then at the end stack those between steps. If your exposures are uneven, stack first shorter ones and later add them to longer ones. Specifying stacking order instead of giving asterisk may help.
After every contrast stretching operation keep noise level under control. Best tool around is wavelet denoise which is part of gimp-tool-registry. Don’t overdo denoising you will lose details and sharpnes. Reasonable level is up to 1.25 with residual 0.10.
If you are into photography then adding following repositories may be interesting:

sudo add-apt-repository ppa:otto-kesselgulasch/gimp
sudo add-apt-repository ppa:pmjdebruijn/darktable-unstable
sudo add-apt-repository ppa:philip5/extra
sudo add-apt-repository ppa:hugin/hugin-builds

They usually contain name of package, except for Philip Johnsson PPA. That one is suggested because it contains Luminance HDR but it also contains about everything else, though others have newer version. When you want to install Luminance HDR specify luminance-hdr and not common qtpfsgui, for qtpfsgui you will get old version from official repo.
For entangle, program for tethered camera control, you download deb from:

http://mirrors.dotsrc.org/getdeb/ubuntu/pool/apps/e/entangle/

that is GetDeb mirror. Pick 32 or 64 bit depending what system you are running.  There are no exotic dependencies for entangle.

In order to increase capacity and avoid loss of data many picture processing tools internally are using 32 bit float per channel. That is perfectly alright, though I do not know for CCD which is digitizing picture into anything better than 16 bit integer per channel. Problem is that you can’t easily see those 32 bit float per channel TIFF images, no many viewers around for them. Popular image stacking program Deep Sky Stacker produces Autosave.tif in that format and you can’t see what it looks like - very irritating. Perfectly capable viewer for many image formats is G’MIC and it can handle 32 bit float per channel TIFF. Once you install it open terminal (command line) and cd to folder with Autosave.tif. Execute:

gmic Autosave.tif

and GUI with Autosave.tif will show up, moving cursor over image you will be able to see values for current pixel. Now if you want to convert those TIFF images for less capable viewers, you can achieve that also using G’MIC. For example channel values will be between 0 and 1, for Deep Sky Stacker. So if we want to convert that into 16 bit integer we simply multiply channel value to 2 on power of 16 minus 1, what is 65535. Naturally we are talking about unsigned integers. So magic formula to convert it to 16 bit TIFF is

gmic Autosave.tif -mul 65535 -c 0,65535 -type ushort -output auto16.tiff

Now we can use almost any viewer to see what it looks like.