Overview of Image Processing

The current mode of image capture in remote sensing of the earth by aircraft or satellite based sensors is in digital form. The pixels correspond to localized spatial information while the quantization levels in each spectral band correspond to the quantized radiometric measurements. It is most logical to regard each image as a vector array, that is, the pixels are arranged on a rectangular grid but the value of the image at each pixel is a vector whose elements correspond to radiometric levels (also known as intensity values or digital numbers) of the different bands. The image formed for each band is a monochrome image and for this reason, we refer to the quantized values of such an image as gray levels. The images may be acquired in a few bands (i.e. multi-spectral image) or in hundreds of bands (i.e. hyperspectral image). Image processing operations for both multispectral and hyperspectral images can therefore be either scalar image oriented, that is, each band is processed separately as an independent image or vector image oriented, where the operations take into account the vector nature of each pixel. Image processing can take place at several different levels. At its most basic level, the processing enhances an image or highlights specific objects for the analyst to view. At higher levels, processing can take on the form of automatically detecting objects in the image and classifying them.