The Spectral Analyst can be used to compare unknown spectra extracted from an image to a library of known material spectra. ENVI includes several spectral libraries of minerals, vegetation and man-made materials but that does not mean that any of the spectra will match what is extracted from your image. These are lab spectra taken in perfect conditions with no atmospheric effects and ranges from 0-100 reflectivity (0-1.0). You will need to make sure your extracted spectral signatures of unknown materials are also in the same reflectivity to compare them to these libraries. However, this tool is only an aid and it is necessary that the analyst understands the types of materials that should be present in their image and you need to be able to evaluate if the comparison to a spectral library are relevant in Spectral Analyst.

Sorry, I didn't understand your answer. I think that the signatures of unknown materials, that are extracted from the Spectral Hourglass Wizard, are on the same reflectivity, but i don't know how to compare them with the signatures from spectral library and how to get a result if it is necessary for example to change the mineral that I use from the spectral library...

The spectra you extract from the image will be in the same units as the image - is the image in reflectance of 0-1.0?
What spectral library are you using? One of ENVI's sample libraries or one of your own?
You can change out the spectrum by displaying it in a spectral profile, then from the Spectral Analyst. Select Options->Auto input from Z-Profile

Yes, I converted my image to the reflectance of 0 - 1.0 and before I implement the "Spectral Hourglass Wizard", I resample the spectral library. The spectral library that I use is the usgs \minerals_beckman_3075 of ENVI. The problem is that the results from "Spectral Hourglass Wizard" are too many and I don't know how to compare them with the minerals from the spectral libraries, in order to conclude to the minerals of the image.. Thank you very much for your help!

The results from the Spectral Hourglass wizard can create a spectral library output. Open this spectral library and display the spectra you wish to use in the Spectral Analyst. Then import that using the method I mentioned above.

That was very helpful! Thank you very much and sorry for the number of the questions, but I am new at the usage of ENVI.. I have one last question related to the Spectral analyst. Because of the fact that it indicates only zeros for the SFF, I changed the max value, at the step of the weighting of the methods. But I can's figure out if this is going to give me wrong results at the step of the scores of the Spectral Analyst..

SFF is useful when the material you are interested in has a unique absorption feature. This usually can only be detected if you have hyperspectral data to detect those unique features. It also can be necessary to use only the portion of the spectrum where the absorption feature is prevalent. So often I don't use SFF and leave its weight at 0 and I find SAM to be more robust.

Thank you very much for your answer! I' ll try it! :)