A new image processing technique
developed by Disney Research could make high dynamic range (HDR) video look
better when shown on consumer-quality displays.
The technique works by preserving
much of the rich visual detail while eliminating “ghosting” and other unwanted
visual artifacts.
The combination of HDR acquisition
and the new technique enables video effects such as showing the detail of an
actor’s face even as lighting shifts from shadow to direct sunlight and back to
shadow.
HDR is a means of capturing images
with a greater range of lighting and contrast – from dark shadows to bright
sunlight – than is possible with standard photography and that is closer to how
people perceive natural scenes.
But HDR currently outstrips the
dynamic range that most televisions and video monitors can display, so HDR
video must go through a process called tone mapping to adapt those images to
the limitations of displays.
A number of such techniques, or tone
mapping operators (TMO), exist, noted Tunc Aydin, an Associate Research
Scientist at Disney Research Zurich.
But though they reduce the dynamic
range of the video, they either lose some of the visual details or they
introduce unwanted effects, such as brightness flickering, or amplify camera
noise to create ghosting.
The local tone mapping method
developed by Aydin and his colleagues at Disney Research uses an approach taken
with many TMOs – decomposing the signal into a base and a detail layer.
In that way, the dynamic range of
the base layer can be reduced while preserving a great amount of detail and
fine scale contrast.
The main difference that the Disney
team introduced is using a temporal filter on the detail layer and a
spatiotemporal filter on the base layer.
They also developed a simple interface that enables a user to perform tone mapping interactively once the base and detail layers have been pre-computed.
They also developed a simple interface that enables a user to perform tone mapping interactively once the base and detail layers have been pre-computed.
Researchers found that the technique
was capable of tone mapping video sequences with complex motion and lighting
changes and was worked particularly well in low-light situations where camera
noise was high.
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