Windows XP. PS3. (or GIMP). (or Irfanview).
OK, it’s easy for windows since you have things like Deep Sky Stacker (that’s just one, for instance). They have tutorials for using their software. If you don’t know how to navigate directories and the like from a DOS prompt or don’t want to do things the hard way, stick with one of these types of programs. All of the photos I’ve posted here have been done the hard way (because I’m a cheap bastard using Linux).
If you want to do it the hard way, which really helps in understanding what’s going on, there is a fairly minimal toolkit you need.
The GIMP for final minor adjustments only. Whenever GIMP gets GEGL fully implemented that will change. You could actually do the entire process in GIMP if it could work in a 16bit/channel color space. GIMP is 8-bit, and during processing that makes a huge (and immediately apparent) difference in the final image quality. All of the combining, noise subtraction and levels adjustments really need to be done in 16bit. So far I like RawTherapee for doing the visual adjustments, and it also know dark frames and flats (more on those later).
Since GIMP can’t handle the depth, you need a copy of Image Magick and align_image_stack. There may be others, but these are the ones I found and so I use them. Both are available for windows, the latter as a simple .exe file that runs from any directory after you place a reference to it in your PCs path. Both are command-line tools. You don’t need to see what’s going on while they work so it works fine.
OK, so now you need image data. Bear with me because some explanation is needed first. The reason you stack and how you stack comes about because what you’re trying to do is defeat the flaws of the imaging process; you want to be able to reject the data that’s in the way and reinforce the data about the object you want a picture of. So what’s in your way? Camera noise, light pollution and atmospheric turbulence are pretty obvious, but dust on your sensor and vignetting are things you also want to correct.
To correct the things that degrade your image data, you’re going to get images of them. Since you can’t get an image of your object without those interfering factors (wouldn’t that be easy), you come at it from behind. Start with noise, it’s the most obvious. There are 2 ways to deal with noise. One is stacking and taking an average of all of your images (that’s what we’re here for) and the other is to take pictures of the noise (dark frames) of the same duration, ISO and camera temperature. This is time-consuming, but really has to be done. So snap the lens cap on and let the camera take about 20 frames in the dark. If the temperature is expected to change a lot during your shoot, do 1/2 your lights, then your darks, then the rest of your lights. The more lights you can swing the better, 20+ starts to look smooth but 40 or more will really give you a smooth final.
OK, enough theory… here’s how you stack: Convert all of your raw files to 16 bit/channel TIFF files (of course you shot in RAW) and separate your darks from your lights into 2 folders, “darks” and “lights, of course. Use imagemagick to average all the darks together. In Linux the command looks like:
Quote:
convert -average *.tif darkframe.tif [/unquote]
Check the manual for the windows equivalent, it should be similar if not identical. Just open a run dialog, navigate to your folder of darks and type it in. WHen it’s finished, you will have a file named darkframe.tif that you will use to clean up your individual files
before you do anything else to them. Copy this file over to your lights folder.
Now you want to use imagemagick to subtract the dark frame from each of your lights; the resulting files will then be aligned and stacked. So navigate to your lights folder now and type:
composite -compose minus lightframe#.tif darkframe.tif correctedlightframe#.tif
Again, check the manual for the windows version of the command composite and how it’s options are structured. If you do this right, you’ll have files named so that wildcards work in the following steps.
/screeching halt.
Yaknow, I thought I had done this write-up before… here it is.
