Perceptually Based Image Synthesis
The synthesis of realistic images can be facilitated
by employing an algorithm that makes image quality judgments
while the picture is being created instead of relying upon the user
of the software to make these evaluations once the image is complete.
In this way it is possible to find the artifacts in a picture as it
is being rendered and to invest additional effort on those areas.
By targeting the parts of the picture where problems are visible,
the overall time necessary to compute the image is reduced. It is
also possible to have the algorithm stop when the picture quality
has reached a predetermined level. This permits the use of radically
different rendering algorithms but still has these methods produce
an equivalent visual result.
During the last four years Gary Meyer's perceptually based research
effort has successfully applied a visual difference predictor (VDP)
to the synthesis of realistic images. A VDP is an image quality tool
that takes an original and a defective picture as input and produces
a map of the visual differences as output. While his research group
did not invent these VDP algorithms, they did implement two of the
most important examples, and they performed one of the first evaluative
comparisons of these programs (Li,
Meyer, and Klassen, 1998). Using the results of this analysis,
a computationally efficient version of the most effective VDP was
created, and it was extended to handle color. The simplified VDP was
inserted into a rendering program where it was used to control a Monte
Carlo ray tracing algorithm (Bolin
and Meyer, 1998 and 1999).
This was the first realistic image synthesis program that could take
into account contrast, visual acuity (both monochrome and color),
and masking as a picture was being created. It also provided a halting
test that was directly related to the perceptibility of artifacts
in an image. This work is the culmination of a perceptually based
research initiative that extends back several years (Meyer
and Liu, 1992; Bolin
and Meyer, 1995).
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