Multispectral Image Coding

Multispectral images are a particular class of images that require specialized coding algorithms. In multispectral images, the same spatial region is captured multiple times using different imaging modalities. These modalities often consist of measurements at different optical wavelengths (hence the name multispectral), but the same term is sometimes used when the separate image planes are captured from completely different imaging systems. Medical multispectral images, for example, may combine MRI, CT, and X-ray images into a single multilayer data set [10]. Multispectral images are three-dimensional data sets in which the third (spectral) dimension is qualitatively different from the other two. Because of this, a straightforward extension of two-dimensional image compression algorithms is generally not appropriate. Also, unlike most two-dimensional images, multispectral data sets are often not meant to be viewed by humans. Remotely sensed multispectral images, for example, often undergo electronic computer analysis. As a result, the quality of decompressed images may be judged by a different criterion than for two-dimensional images. The most common example of multispectral images are conventional RGB color images, which contain three spectral image planes. The image planes represent the red, green, and blue color channels, which all lie in the visible range of the optical band. These three spectral images can be combined to produce a full color image for viewing on a display. However, most printing systems use four colors, typically cyan, magenta, yellow and black (CMYK) to produce a continuous range of colors. More recently, many high fidelity printing systems have begun to use more than four colors to increase the printer gamut, or range of printable colors. This is particularly common in photographic printing systems.