1. A method of identifying endmember spectra values from a multispectral image comprising multispectral image data, where each multispectral data value is equal to a sum of mixing proportions of each endmember spectrum, said method including the steps of: processing the multispectral image data to obtain a multidimensional simplex having a number of vertices equal to the number of endmembers, the position of each vertex representing a spectrum of one of the endmembers, wherein processing of the data includes: providing starting estimates of each endmember spectrum for each image data value; estimating mixing proportions for each data value from estimates of the spectra of all the endmembers; estimating the spectrum of each endmember from the estimates of the mixing proportions of the spectra of all the endmembers for each image data value; and repeating the estimation of the mixing proportions and the estimation of the spectrum of each endmember until a stopping condition is met, wherein the stopping condition occurs when a relative change in a regularized residual sum of squares determined in the estimation steps attains a threshold, wherein the regularized residual sum of squares comprises a sum of residual sum of squares and a measure of the size of the simplex, the residual squares is reflective of a difference between the multispectral image data and a calculated value based on the estimated mixing proportions and estimated spectrum of each endmember.