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ENVI

Select Background

Select Background

The Background Selection and Rejection panel represents step 3 in the workflow. Here, you can select as “background” the pixel spectra that were incorrectly identified as targets in a SAM analysis. The BandMax algorithm will attempt to identify the bands that are best able to distinguish your targets from these backgrounds. This process works best when using a small set of target and background spectra.

If you do not want to specify any backgrounds:

  1. Toggle Select Backgrounds to Reject? to No.
  2. Click Next. The Wizard skips to the Select SAM Mapping Parameters panel, which represents step 5 in the workflow.
  3. To specify backgrounds:
  4. Toggle Select Backgrounds to Reject? to Yes. The Select Background section appears in the right part of the panel. This section contains the same items as the Target Spectra section in step 2 of the workflow.
  5. Collect background spectra by importing them or by dragging-and-dropping them into the table. You must select at least one spectrum to continue in the Wizard. All of the spectra selected in this table are used as backgrounds when calculating the significant bands.

    When importing ROIs as backgrounds, keep in mind that the average calculated from each region is used as the background spectrum. Therefore, you should include each separate material as a separate ROI.

  6. To select a specific spectrum in the table, click its related row number column on the far left. A spectrum is not selected if you do not highlight the entire row. You cannot select a spectrum by clicking its Spectrum Name column. You can select multiple spectra using Shift or a Ctrl. Or, click Select All to select all the spectra in the table.
  7. Click Plot to display the selected spectra in a separate plot window.
  8. Click Delete to delete any selected spectra.
  9. Click Next in the Wizard. The Select Optimal Bands panel appears.

The BandMax algorithm examines your target and background spectra to determine which bands are most significant for distinguishing your targets from the specified background. The best results are usually achieved if one target is selected for each Wizard session. In this case, BandMax is able to choose a band subset that is optimized for that individual target.



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