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Abstract

One of the basic difficulties with interactive walkthroughs is the high
quality rendering of object surfaces with non-diffuse light scattering
characteristics. Since full ray tracing at interactive rates is usually
impossible, we render a precomputed global illumination solution using
graphics hardware and use remaining computational power to correct the
appearance of non-diffuse objects on-the-fly. The question arises, how to
obtain the best image quality as perceived by a human observer within a
limited amount of time for each frame. We address this problem by
enforcing corrective computation for those non-diffuse objects that are
selected using a computational model of visual attention. We consider both
the saliency- and task-driven selection of those objects and benefit
from the fact that shading artifacts of ``unattended'' objects are likely
to remain unnoticed. We use a hierarchical image-space sampling scheme to
control ray tracing and splat the generated point samples. The resulting
image converges progressively to a ray traced solution if the viewing
parameters remain unchanged. Moreover, we use a sample cache to enhance
visual appearance if the time budget for correction has been too low for
some frame. We check the validity of the cached samples using a
novel criterion suited for non-diffuse surfaces and reproject valid
samples into the current view.