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Creating an Alpha Band

All images encoded to MrSID Generation 4 have an alpha band.

1. Click Advanced in the Properties tab.
2. Click the Alpha tab.

3. Select the method that you want to use to create an alpha band.

   You can select one of the following methods:

   • Opaque. The Opaque method specifies that all pixels should be treated as valid image data. By default the Opaque method is selected.
   • Transparency Value (metadata). Using this method, GeoExpress queries the image metadata for the transparency values and treats all pixels with matching band color values as transparent.
   • Specify Value. You may specify transparency values for each band. GeoExpress treats as transparent all pixels whose band color values match the specified values. If you decide to specify a value for each band, you can use the color picker.

If your source image already has an alpha band, a Regenerate Alpha Band check box appears at the bottom of this tab so that you can discard the existing alpha band. By default, GeoExpress uses and preserves a source image's alpha band. This option might be used if your alpha band is corrupted or incorrect, in which case GeoExpress creates a new one.

Skip to Specifying a Compression Method.