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ENVI

Automated Band Selection

Automated Band Selection

From the Method drop-down list in the Dimensionality Reduction and Band Selection panel, select Automated band selection.

Note: The Automated band selection method is only available if you selected background signatures using the Background Signature Selection panel.

Use automated band selection to identify spectral bands that best differentiate target signatures from background signatures. You can use the BandMax or Advanced Signature Optimization algorithm to perform automated band selection. Select one of these methods from the Selection Method drop-down list.

See the following sections:

BandMax


When you select this option, a plot window opens with the target and background signatures displayed. The grey plot curve (usually low in value) represents Band Significance. The following is an example:

The red, horizontal line on the plot represents the threshold used to define which bands are significant (shaded blue on the plot) and which are not. You can change the threshold by clicking and dragging the threshold bar in the plot window, or by using the Band Significance Threshold slider in the Dimensionality Reduction and Band Selection panel.

Adjusting the Significant Bands slider also controls the threshold position by setting it to force a specific number of significant bands to be selected. The bands deemed significant are shaded blue in the plot window and listed in the Dimensionality Reduction and Band Selection panel.

You can fine-tune the band selection by clicking Edit Band Selection and selecting or unselecting specific bands in the list. If you change the threshold further after editing these values, the threshold changes will be lost.

Click Output Bands to ASCII to save a bad bands list to a text file.

Advanced Signature Optimization


The Advanced Signature Optimization method works differently than BandMax in that you evaluate each target/background signature pair separately. After selecting Advanced Signature Optimization from the Selection Method drop-down list, follow these steps to continue:

  1. Click Add. The Select Signature Pairs dialog appears.
  2. Select a target from the Target Signatures list.
  3. Select a background from the Background Signatures list.
  4. Click the arrow button to add the target/background pair to the New Signature Pairs list.
  5. Click OK when you are finished adding target/background pairs. You can define as many pairs as needed. When you define at least one pair, an ASO Bands plot appears. The grey plot curve (usually low in value) represents Band Significance.
  6. The red, horizontal line on the plot represents the threshold used to define which bands are significant (shaded green on the plot) and which are not.

    You can change the threshold by clicking and dragging the threshold bar in the plot window, or by using the Threshold slider in the Dimensionality Reduction and Band Selection panel.

    The bands deemed significant are shaded green in the plot window and listed in the Dimensionality Reduction and Band Selection panel.

  7. If you determine that certain target/background pairs are more important than others, you can skew the band significance plot for that pair relative to the others. First, select the desired pair in the Target/Background Signature Pairs list. Then, adjust the Target Priority (%) slider to change the scale factor applied to that pair's band significance plot.
  8. You can fine-tune the band selection by clicking Edit Band Selection and selecting or unselecting specific bands in the list. If you change the threshold further after editing these values, the threshold changes will be lost.
  9. Click Output Bands to ASCII to save a bad bands list to a text file.



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