Defining and Refining Frameless Rendering
Abstract
Frame1ess Rendering (FR) is a rendering paradigm which performs
stochastic temporal filtering by updating pixels in a random
order, based on most recent available input data, and displaying
them to the screen immediately (3]. It has inherent in its design,
visual artifacts that come across as "spatial scatter''. Due to the asynchronicity
of pixel updates, a noisy or "scattered" image is perceived
if the update rate is not fast enough.
We describe the fac1ors that influence the perceptual quality when
Frarneless Rendering is implemented such as object and viewpoint
velocities, pattern and object size, and pattern and object separation.
The factors are formalized mathematically with respect to
their impact on spatial scatter. Spatial scatter is defined formally as
a combination of velocity, density and gradient. We also attempt
to define Frameless Rendering in terms of a new graphics pipeline,
and more concretely in terms of strategies for pixel prioritization
and handling aging pixels.
We zoom in on three factors that influence the perceptual quality.
We compare scenes \with strong versus \weak temporal coherence,
high versus low frequency content, and high versus low pixel computation
rates.
If strong temporal coherence is maintained, a Frameless Rendering
sequence exhibits little image degradation. Cutaway scenes have
no coherence between two successive frames and offer a natural
dissolve. Weak temporal coherence is associated with decreased
image fidelity. Image sequences comprised of scenes with primarily
low frequency content exhibit very little image degradation when
compared to image sequences comprised of scenes with high frequencies.
Computation speeds of 30 M pixels/second, sampling
inputs at JOO Hz, give the smoothness of motion and visual fidelity
of a traditional 30 fps double-buffered animation. (See Section 7 for
an anomalous case.) Compute speeds of I to 4 M pixels/second
reduce latency and smooth motion seen in a comparable double buffered
animation.
We also show comparisons of Frameless Rendering with reduced
pixel resolution. In cases of strong temporal coherence, Frameless
Rendering exhibits relatively little image degradation in comparison
with the reduced pixel resolution alternative. On the other hand,
in cases of relatively weak temporal coherence, the lo\V resolution
image sequence exhibits relatively little image degradation when
compared with the Frameless Rendering.