Quasar is the digital equivalent of the keen photographer's long-time favourite glass filter - the starburst. The traditional starburst filter consists of a clear glass plate with a series of fine lines cut into its surface; attached to the front of the camera's lens, this adds a star-shaped diffraction pattern to any bright highlights. Of course, this means that the starburst effect is created at the time the image is captured, and experience is needed to judge the final results.The stars can usually be rotated,by rotating the filter itself, but the number of points is fixed and the final colouring of the stars can't be controlled.
And good quality glass filters can be quite expensive, even more so when you consider that each filter can produce only one type of effect. With starburst filters, for example, if you want to be able to produce stars with either 6 points or 8 points, then you need to buy two filters.