Pixel Purity Index (PPI) is used to find the most spectrally pure (extreme) pixels in multispectral and hyperspectral images.

data needed:

1.MNF image

to perform ppi:

select the bands with maximum eigen values these bands have information,eigen values near unity(1) have noise

steps to get PPI in ENVI 5.3 classic:

spectral->pixel purity index->[FAST ] New output bands

Extraction of the pure pixels from the hyperspectral imagery, PPI is being used.

MNF bands are the requirement for the PPI algorithm. It works on the provided threshold value and iterations. More threshold values provides the more number of pixels but with the higher value of threshold the purity may decrease.