The format used is RGBA (red, green, blue with a fourth Alpha channel for transparency). This is a standard image format and is supported by many GIS packages.
This one is best demonstrated with pictures. The GIS used is QGIS, but the general process is the same in ArcGIS.
|The Acacia PD data displayed using a log scale with the default colour scheme.
|The RGB export is in the exports menu, with all the other exports.
|The file selection is the usual process.
|And now in the GIS, the file is selected using the normal process. Note that the file name is updated like the GeoTIFF exports, but with _rgb appended to the main part of the name.
|Biodiverse knows nothing about coordinate systems, so it is up to the user to choose the correct one for their data.
|The default display has all the colours, but the background is black. To fix that you need to set the fourth band as the transparency layer.
|As per the previous image caption, choose band 4 as the transparency layer. The same general process is needed in ArcGIS (set the alpha channel to be band 4).
|And here is the data with some Open Street Map data in the background.
And as a bonus, the RGB GeoTIFFs can be exported at the same time as a standard GeoTIFF export using the "Generate RGB Rasters" option.
|As the tooltip states, the RGB files are only generated for indices that have been displayed, so you don't get huge numbers of exports if you have not displayed them.
If you want to try this out before version 3 is released then the 2.99_004 (or later) development release can be accessed through the downloads page at https://github.com/shawnlaffan/biodiverse/wiki/Downloads
For more details about Biodiverse, see http://shawnlaffan.github.io/biodiverse
To see what Biodiverse has been used for, see https://github.com/shawnlaffan/biodiverse/wiki/PublicationsList
You can also join the Biodiverse-users mailing list at http://groups.google.com/group/Biodiverse-users