I've been georeferencing aerial photographs. The photos are not North-South oriented, so they look tipped, but when I rectify them ArcGIS adds black triangles to the four sides to make the data north-south oriented. Is there any way to eliminate these black triangles easily? Or prevent them? I can't see any option when rectifying that implies I can opt out.
Rasters are rectangular (in rectifying a rectangular set of pixels is set up and then values from your georeferenced image are interpreted to it) and so the areas with no colors are No Data and you are seeing those as black. When you symboloize these in ArcMap you can set the No Data to have no color and then they won't be seen.
If you don't want this at all, instead of rectifying your images, just update the georeferencing. Then the information on location, rotation, etc. as well as projection will all be stored in an associated file (world files and aux.xml files). It is also usually faster.