Convert Multi-band Raster Images Into Single Band Classified Rasters

During the process of classifying imagery in ENVI for use in ArcGIS, you might come across the problem of having your classified .tif image displayed only in RGB format with no attribute table in ArcMap. This format is not useful if you are trying to analyze the unique land cover classifications in your image, so in order to convert the image into a raster with an attribute table that enables you to use the classified renderer in ArcMap, use the following steps:

1. Using the identifier tool in ArcMap, find out which two (out of the three) bands in your image give you a unique signature for each land cover class when added together. For example, an area classified as cropland may have the following RGB values: R=255 G=255 B=0.  If the red and green bands added together give unique values for each class, then those two bands will be used in the next step.

2. In ArcCatalog, expand the raster image with three bands in order to be able to load in the bands separately. In this step you will only load in the two bands that when summed together give you a unique number for each land class in your classified image.

3. Once those two bands have been loaded into ArcMap, use the raster calculator tool to sum the two bands. Your output will be a single raster with unique numbers for each land cover class. This raster should contain an attribute table and should allow you to render the image as classified. 

4. (Optional) In order to display the unique classes with a different set of numbers, you can use the reclassify tool and change the land class numbers (the result of summing two bands together) to your desired new values.