I have created thousands of png tiles using arcgis and have merged groups of them into large jp2 files for serving via geoserver. I need to flatten these to a single band so that I can apply a colour map to achieve transparency.
Merge single band and multi band color images is similar but the suggested tool "Composite Bands tool in arctoolbox" only merges single band to 3 band. I need the reverse!
This is based on the following question Getting a constant background color for transparency
I have arcgis 10.1, qgis/gdal, erdas imagine and global mapper.