For an astronomer, an image is not necessarily a pretty picture. Indeed the information in each image usually goes far beyond what you can see at first look. Image processing is the technique by which an image can be transformed to reveal (or suppress) selected features, or to extract quantitative information in other forms.
There are three programs we use often in astronomy to acquire, analyze, and modify images:
SAOImage ds9 Aladin ImageJ or AstroImageJ
We may use these in different instances because they offer a different set of features. Aladin, for example is excellent for comparing images with one another and with astronomical data bases, and for making quick color images from several images through different filters. SAOImage ds9 is versatile for acquiring images and interacts in real time with our cameras. ImageJ, written and maintained for biomedical imaging, can be modified for special tasks, and is ideal when we are measuring the brightesses of stars.
In this activity we will use ImageJ because it provides for sensitive control of the colors in an image and preserves all of the information of the original data.