Digitalization and quantization are the processes that convert a continuous image irradiance as it is projected by an optical system onto the image plane into a matrix of digital numbers that can be stored and processed by a digital computer. This process is not unique to image processing. It occurs with any type of signals and is generally known as sampling. For scalar signals, e. g., a temperature record, a time series is formed. This time series is sampled at discrete temporal intervals. For images, a similar spatial sampling strategy has to be applied. Finally, image sequences require spatial and temporal sampling.