Dear ENVI users ,    This time, I am challenged by mosiaking two  landsat (same bands) images (using georeferencing).  When I tried to masiak them, a wide gap of irregular shape (in the intersection of the two scenes, with black background colour) appears when attempted to overlap to each other. why is that?   Do you think there is something wrong with the datum/projection? Ofcourse, there was an error associated with UTM projection in one of the scene (UTM 54 N instead of 54 S).  I edited that already. However I am not able to fix the problem even using the help menu.   Also I would like to select my study area boundary from the virtual mosiak. It seems that ROI is not effective  in my study area because it is beyond the image display. Could it be possible to select in the scroll it self instead of selecting ROI in the image?   Regards     Yohannes