1.3. Sequences of Images in Astro ImageJ¶
1.3.1. Before you begin¶
You cannot open a sequence of imgaes in AstroImageJ until you have opened at least one FITS file...so start by opening the first image for this lab.
FITS is a format for storing data in a way that any computer platform can read if it has the right software installed. It is very widey used in astronomy in part because you can store both the data itself and information about the data, called meta-data, in the file. The meta-data is stored in the FITS header and the data was the image itself.
There are two very different sets of menus displayed in AstroImageJ depending on whether the toolbar or an image window are on top in the display.
1.3.2. Opening a sequence of images¶
The idea here is that you need to tell AstroImageJ two things:
- Which folder the images are in
- Which files from the folder you want to load into a sequence.
Make sure you have an image window on top.
From the file menu, select “Open image sequence in new window...”
Choose the folder containing the images you want to open in a stack.
To choose the images to put in the sequence you have a few options:
- Use them all; just click OK in the window Sequence Options
- Choose the starting and ending image by specifying the number of the starting image and the increment.
- Enter a phrase or number that is in the name of all of the images that you want to open. Note that CaSe mAtTers; if the file name contains the word ‘bias’, for example, but you put ‘Bias’ in the box in Sequence Options, AstroImageJ will find no images.
- Enter a more complex pattern that matches the names of the files you want to include.
Opening more than a few dozen images in a sequence may bring your computer to a grinding halt because by default AstroImageJ loads them all into the computer’s memory. If you select Use virtual stack you avoid that problem because AstroImageJ only reads in single images when it needs them. That slows down processing a bit, so for small numbers of images it is easier to not use a virtual stack.
220.127.116.11. Pattern matching examples¶
AstroImageJ allows you to enter fairly complex patterns to match file names. In those patterns some symbols have a special meaning:
- Use a period . represent any single character.
- Use an asterisk * to represent zero or more of whatever character came before it.
- Put characters in square brackets  to represent any one of the characters in the brackets.
For example, the patter .* will always match all files because the period matches any character and the asterisk indicates zero or more of those characters.
The pattern twi-.*bias.* would match all files whose name starts with twi-, has zero or more characters, then the word bias, followed by zero or more characteres.
The pattern flood-.*00[1-9]B_flt.fit matches any files whose name starts with flood-, followed by any of the numbers 001 through 009, then B_flt.fit
For each file name below explain why the name would or would not match the pattern twi-.*bias.*
Look at the list of the files in the folder for_gain. For each of the items below come up with a pattern that matches the right files. Check your patterns by starting to open an image sequence in AstroImageJ, selecting the folder for_gain, entering the pattern in the right place, and verifying that the correct number of files matches.
- All bias images that have “twi” in the name (should be 11 files)
- The images in the R band (R is in the file name) that also have “flood” in the name and are number 001 through 003 (should be 3 files).
- The images in the I band with “flood” in the name (10 items)
- The images in the I band with “flood” in the name whose number is odd (001, 003, etc) (should be 5 images)