Using material maps, if any of the mapped-to materials are transparent, then the material to which the map is applied should have the transparent property set in the materials database. This is a version 3 artifact resulting from how the ray-tracing and mapping systems interact. To work correctly, version 4 of DIRSIG does not require that transparency be set on the mapped-from material.
The new polarization features of DIRSIG v4 do not support reflectance and texture maps.
Reflectance and texture maps are tied to the classic emissivity model (from DIRSIG v3). They will not work with the other emissivity models featured in DIRSIG v4.
PGM and ENVI images define their origin to be at the upper-left corner of the screen, while the worldspace has its origin at the center of the screen. The difference in these coordinate systems, together with the way the tiling algorithm works, causes the map to appear upside-down.
In DIRSIG v3, the work around was to simply insert an image of height Y at position (0,Y) rather than (0,0). With DIRSIG v4 there is now a flag, IMAGE_Y_FLIP, which does the extra flip automatically, so that the image can be inserted at (0,0). For backward compatibility, the DIRSIG v3 behavior is still the default.