  Direct photon emission in heavy-ion collisions is calculated within a
relativistic micro+macro hybrid model and compared to the microscopic transport
model UrQMD. In the hybrid approach, the high-density part of the evolution is
replaced by an ideal 3-dimensional hydrodynamic calculation. This allows to
examine the effects of viscosity and full local thermalization, in comparison
of the transport model to the ideal fluid-dynamics. We study the origin of
high-p_T photons as well as the impact of elementary high-sqrt(s) collisions.
We further explore the contribution of different production channels and
non-thermal radiation to the spectrum of direct photons. Detailed comparison to
the measurements by the WA98-collaboration are also undertaken.
