A "Spectral Response Curve" provides a graph giving information about the map data (feature data) associated with a cluster. The "Legend Control" feature is used to modify the legend of classes; among other things, you may assign a color to a class, list the clusters contained in the class, empty a class of clusters, transfer an entire class into another one, create a "catch-all" class of remaining unclassified clusters, and hide selected classes from view in order to examine the image without their interference. A "Zoom" capability allows you to zoom in on the image; when the Update Mode is set to Button Press, clusters may be assigned to a class by "painting" on the zoom window rather than in the image.
Spectrum was specifically designed for images that have been pre-clustered, and therefore have additional information associated with them, this info being stored in the map data. This special info in the map data will include N rows of cluster centers (mean vectors), where each column of the info is associated with a special feature of interest that was extracted during the previously-used clustering algorithm. If you do NOT have pre-clustered data, spectrum can still be used to interactively classify the pixels in the image; however, if you do have pre-clustered images, there are additional features of spectrum that you may take advantage of:
\(bu
display of different map columns as Red, Green, or Blue.
\(bu
display of functions of map columns as Red, Green, or Blue
(note: not implemented as of Khoros 2.0 Beta).
\(bu
a 2D scatter plot where one map column provides the X coordinates, and another
map column provides the Y coordinates; unassigned cluster numbers appear in
white, while assigned cluster numbers appear in the same color as was specified
for their class in the legend.
\(bu
the same 2D scatter plot as above, but with specified functions of map columns
providing the X and Y coordinates.
Please see the manual section on I/O if you have additional information associated with the input image provided by a clustering algorithm; this section details the input format expected by spectrum for such information. In addition, this section also details the ascii Legend File that is used with spectrum.
Spectrum is covered in detail in Chapter 8 of the Envision Manual; the information given there will not be repeated here, so you are referred to that document.
% spectrum -i albq2.viff -l albq2.lgd