  The origin of the soft gamma-ray (200 keV - 1 MeV) galactic ridge emission is
one of the long-standing mysteries in the field of high-energy astrophysics.
Population studies at lower energies have shown that emission from accreting
compact objects gradually recedes in this domain, leaving place to another
source of gamma-ray emission that is characterised by a hard power-law spectrum
extending from 100 keV up to 100 MeV The nature of this hard component has
remained so far elusive, partly due to the lack of sufficiently sensitive
imaging telescopes that would be able to unveil the spatial distribution of the
emission. The SPI telescope aboard INTEGRAL allows now for the first time the
simultaneous imaging of diffuse and point-like emission in the soft gamma-ray
regime. We present here all-sky images of the soft gamma-ray continuum emission
that clearly reveal the morphology of the different emission components. We
discuss the implications of our results on the nature of underlying emission
processes and we put our results in perspective of GLAST studies of diffuse
galactic continuum emission.
