SAM – Spectral Angle Map

Spectral Angle Map – SAM – compares a reference region of an image with every other pixel in the image. The output image represents how closely the spectrum of each pixel in the image matches the spectrum of the reference region.

SAM has two inputs, an input image and a reference image. Both images must have the same spectral dimension, e. the same number of spectral bands. The reference image may be cropped to a very small region, or it may be the whole image and the crop window is specified in SAM’s arguments. If more than one window is specified in the “roi” (region of interest() window, then all of those regions are part of the reference. Under the “regions” option, one can choose to average all regions together to for one reference, or they can be used separately and each window produces an individual output.

If there is only one reference window in “roi”, then the output will have only one band. If multiple windows are specified and the choice is to use them separately, then the output will have one band per window.

The output pixel values will vary between 0 and pi. Each pixel is represented as a vector with as many dimensions as spectral bands. The value of each output pixel is the angle between the reference vector and the corresponding pixel vector. A value of 0 represents a pixel that has the same spectrum as the reference.