Exploring the Visual System's Orientation Mechanisms in the Perception of Spatial Aliasing and De-Contouring Applications

perceived image quality of image processing algorithms and display design, the
complexity of these visual models has been steadily increasing as progress is
made in basic visual science. Beginning in the early 1990's applied visual
models began to use not only a multiband approach in radial spatial frequency
(e.g., the Laplacian pyramid) but also in orientation. At this point, the
ability to predict the important effects of masking became more accurate. This
first part of this talk will provide a close look at the role of these
orientation bands in the application of image scaling, which must balance the
tradeoffs between sharpness, aliasing, and ringing, all acting in concert with
the masking caused by the signal itself. The second part of the talk
addresses bit-depth applications arising from current LCD TV technology.
Contone imagery usually has eight bits per pixel for each of the three
primaries in typical displays. However, there are often points in the imaging
pipeline that constrain this number for cost reasons. Conversely, higher
quality displays seek to achieve 9-10 bits/pixel/color, though there may be
system bottlenecks limited at 8. In both cases, a goal is to achieve a higher
perceived bit-depth quality than is afforded by the imaging system. The two
main artifacts caused by reduced bit-depth are contouring and loss of low
amplitude detail. Prevention of these distortions can be accomplished by
applying a dithering process before the bit-depth limitation. A technique for
achieving bit-depth extension via spatiotemporal dithering has been previously
been presented. In applications where it is only possible to affect the image
after the bit-depth losses have already occurred, it is impossible to
accurately restore the loss of low-amplitude detail. However, it is possible
to remove the false contours. Of the several approaches used to remove false
contours, we will discuss predictive cancellation and its dependence on the
spatial frequency localization and masking properties of the visual system.
We discuss the key visual properties that arose while investigating these two
applications, which include the optical transfer function (OTF) of the eye,
masking by noise, and contour integration.