Image Enhancement

Astronomical images often span a wide range of brightness, while important features contained in them span a very narrow range of brightness. Alternatively, interesting features could span a range of brightnesses too great for the limited range of a computer monitor (or printer). Thankfully, there are a number of techniques (usually classified as “point operations”) that can be used to bring out details in images that would otherwise not be seen because of their low contrast. These examples will demonstrate what does what. More than just producing “pretty pictures”, these techniques can be used to enhance details and show structures that, because of their low contrast, would otherwise be invisible. However, some of these techniques must be used with care because they change the information in the image. After an image is calibrated, the pixel values in the image are directly proportional to the amount of light that fell on the CCD. The operations used here will modify the data in a non-linear manner, rendering them useless for photometric purposes. Some techniques modify the spatial distribution of the data, reducing their astrometric validity. So when using these techniques, be sure to have a clear idea of what your final goal is.