FITS files

As explained in the section 'Downloading your data', astronomers use special types of files called FITS files. To be able to view your images in these files, specialist software is needed. Some of these are listed below.

What software?

There are many different software packages that can be used to create colour images with your LCO data - some are free, some have costs associated with them. We recommend SalsaJ as it is free, easy to use and can be used to also carry out further astronomical data analysis. However, if you wish to find a better package for making colour images, then we would suggest you download 'The Gimp' or Phototshop.

Online editing with JS9-4L

There are a growing number of online editing packages which you can use to do simple processing and analysis of images. One of these is JS9-4L, which is run by the MicroObservatory. Although it's not as good as software you can download, you can use it to make a quick colour image very easily. The instructions below will explain how to do this.

SalsaJ

Description: SalsaJ is a software package dedicated to image handling and analysis in the classroom. It is particularly adapted to professional astronomy images. It is written in Java and can be used on several platforms for which there is a Java environment. It is based on ImageJ, a free Java software created by Wayne Rasband (Reseach Service Branch, National Institute of Mental health, Bethesda, Maryland, USA).

Cost: Free

Salsa-J website: http://www.euhou.net/

Available from: EUHoU

Align RGB plugin:

As part of the SalsaJ development a plugin has been written for aligning 3 colour frames, when using SalsaJ with the Astronomical Imaging project. Once you have downloaded the plugin, unzip the file to get a file with the ending ".class". This must be put in the plugins folder of your SalsaJ directory. Then restart SalsaJ.

Download the plugin

Background information on astronomical image processing

To undertake full astronomical image processing you need to use FITS files. Software such as JS9 and SalsaJ makes use of FITS files, and are able to convert and save images in JPEG, PNG and many other formats. However, neither of these formats contain the same quality of information as the FITS file. In particular, only 256 brightness levels are available for each pixel in a JPEG, whereas FITS allows up to 65,535, but in the case of colour imaging, this is irrelevant.

At the start of every FITS file is a header section, which contains important information about the image, such as the number of pixels, the date the image was taken, the telescope it was taken with, the exposure time, and much more. Astronomical image processing software (such as the ones mentioned above) allows you to view the FITS header data. In order to convert FITS files into a more useful format such as JPEG, TIFF or PNG then they must be processed. This allows more flexibility in the number of applications you can use for imaging.

Viewing FITS Files

As previously stated, a JPEG file can hold up to 256 pixel values and a FITS file can hold up to 65535 values. A computer monitor can display a range of values that is greater than a JPEG but less than a FITS file. This means that your computer monitor can not display all the detail contained within a FITS file. So in order to display these files more effectively, we can alter the way they look on screen. We do this by stretching the pixel values in the FITS image and there are various methods and algorithms for doing this. By doing this you can remove the brightness of the sky background and make features more easily visible; consider the following example:

Sample data files for colour Imaging

Sample data files for colour imaging can be found by downloading the files below: