I have two color images (orthophotomaps). One is only 1-band with color map and second is with 3-bands.
How can I merge them with any FOSS tools or ArcGIS?
Have you looked at using the Composite Bands tool in arctoolbox?
Sorry for answering to myself. In case, if someone wonder how to mosaic color map image (1 band) with RGB image (3 bands). I figured, that simplest method will be to convert color map into RGB (possible in Arc with Copy Raster tool) and then mosaic them. Thanks.