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Tutorial:
AstroImageJ, how to align rggb files


AstroImageJ, astrophoto editing tool

  1. Introduction
  2. Download and Installation
  3. My own downloadable macros
  4. How to use "Masterflats from CR2 files" macro
  5. How to use "Calibrated object files from CR2 files" macro
  6. How to align rggb files*
  7. How to stack rggb object files

Align rggb files

Here is one method to align images in AIJ, there are others and maybe better alternatives. The plugin I use here has the name Image Stabilizer and are already built in.

Import files

First you have to open your earlier converted and demosaiced images. You shall open them as a virtual stack, it means that you have them on the hard drive when working with them to save RAM memory. Use the File>Import>Image Sequence command.

select image directory

Choose your directory where you have your images, click on the first file and open. Note; All color files are in this directory, blue, green1, green2 and red. And because we align all of them any chromatic problem with the optics will be reduced at the same time.

sequence options

Sequence options: Enable "Use virtual stack".


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open as a vstack

Now it's open, scroll through with the scrollbar (left above the histogram). If any image is of bad quality, through it away from virtual stack with Image>Stack>Delete Slice.

plugin image stabilizer

Now it's time to align, select Plugins>Image Stabilizer.

varning, keep on

A warning will come up, but it's ok, use Virtual Stack, click on OK.


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make directory align

You will be asked where to store the aligned images. Created a new directory, I normally use the name "align".

align setup

Default setup, but use the Affine method! It will do the more advanced align: shift, rotation and scale.

Virtual stack of aliged images

The align process will take a couple of minutes, you can follow how far it has come on the status line. When working with Virtual Stacks the changes to individual images will not be stored in RAM memory, when finished you have to open (import) the aligned images as a virtual stack. If you now scroll through them you will see that all of them have been aligned if the process was successful. It works for me even if the dithering method have been used when taking the images.

Aligend files in directory

The aligned files in the directory align.

Update:

Sometimes I have found that it could be difficult to align correctly with the Image Stabilizer. Often this happen when there are crowded star fields (wide angle lens) and big movements between sub images (example, big dithering, drift etc). Then I divide the align process in two steps. First I do a align with only a translation in x and y axis with only one reference point and only in whole pixel steps, no interpolation. For this first step I use the Align Image or Align Stack under astronomy plugins with aperture setting. Step two I do as normal with the Image Stabilizer on the aligned images from step one.


Next: Stack rggb object files

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