Module hsi_major_mode

Hyperspectral image analysis mode.

Major mode for hyperspectral image viewing and analysis. Commonly used in remote sensing applications, hyperspectral images have many more layers than just red, green, and blue. You can think of them as a stack of grayscale images, one on top of the other, where each image in the stack is looking at the same field of view, but at a different wavelength of light.

Each image in the stack is called a band, and because each pixel at the same row and column in the band refers to the same spot on the ground, each pixel can be associated with a spectrum. Because there can be hundreds of bands in an image, the spectrum can be quite high resolution. Because of the large number of samples in the spectrum, the spectrum can be used to identify the material(s) in the pixel.

The Federation of American Scientists has a good tutorial about remote sensing at http://www.fas.org/irp/imint/docs/rst/index.html, and it includes sections about hyperspectral imagery.

There are many hyperspectral imagers; most are airborne or mounted on spacecraft. NASA's AVIRIS sensor (http://aviris.jpl.nasa.gov/) is very well known in the field of earth remote sensing. There is some free data at http://aviris.jpl.nasa.gov/html/aviris.freedata.html

A common image format is the ENVI format, which consists of two files: a data file in a raw format, and a header file that describes the format. Hyperspectral images are very large, typically on the order of hundreds of megabytes for a standard scene. This means that most of the time an image won't be read entirely into memory at once. This major mode is capable of viewing images larger than physical memory.