Digital image sensors . Sampling and quantization. Shot and thermal noise. Quantization refers to finite number of gray levels or colors used to represent the signal at each pixel. Shot noise results from quantum effects of light sources, usually manifest at low light levels.
Thermal noise is a random variation in light emission due to thermal effects.
Simple Image metrics . Image processing software . Since up to a few years ago, only the Macintosh computer was easy to use for doing graphics work, NIH-Image was written for the Mac . In addition, the program has a strong bent toward image problems arising in microscopy. This excellent program has been maintained and augmented regularly, and is still available as a freeware program.