Usability of Digital Cameras for Verifying Physically Based ...

cuses on how a digital camera can be used in this sense and – probably even more
important – what subproblems cannot be solved and therefore have to be treated
differently.
1.2 Believable vs. Correct
Photorealistic image synthesis has made outstanding progress in the last decades.
While the pioneers of this field tried to achieve realism with comparatively simple
algorithms like raytracing and radiosity, a lot of sophisticated algorithms – such
as path or photon tracing, as well as numerous hybrid techniques – have been
developed since then.
Nowadays it is possible to render images that can hardly be distinguished from
photographs. Consider for instance the Alias website “Is it Fake or Foto” [Ali06b].
There you can attempt to guess the origin of ten images depicting various scenes,
some of them real and some of them rendered with Maya [Ali06a]. If you know
what you have to look for, it is indeed possible to choose the right answers, but at
first sight the renderings look believably real.
The results are convincing, but we cannot assume that the rendering algorithm
is implemented correctly as far as physical accuracy is concerned. However, for
many applications this is good enough. For movies, computer games and related
areas it is essential that the images look appealing and – above all – believable. It is
not necessary and sometimes even counterproductive that an image is a physically
correct representation of the light transport in a scene.
However, for physically based rendering (as the field has become to be known),
this is absolutely crucial. Its applications are much more restricted than the largely
artistic realm of ordinary, “just believable” rendering techniques; the effort in-
volved is far greater – e.g. because one has to use measured surface reflectance
data or complicated analytical models for the scene description – and the cre-
ativity of the user is severely restricted by the constraints of physical correctness
(e.g. the inability to fine-tune the lighting in the scene for artistic reasons on a
per-object basis as it is common practice with current commercial systems).
2