( see video or shadertoy )
Fabrice
NEYRET -
Maverick team, LJK, at INRIA-Montbonnot
Joelle
THOLLOT -
Maverick team, LJK, at INRIA-Montbonnot
Romain
VERGNE - Maverick team, LJK, at INRIA-Montbonnot
Procedural textures such as Perlin noise are a convenient and
cheap way to provide natural looking random details. But animating
their parameters along time, or making them change continuously in
space, induces very visible and distracting artefacts that our eyes
interpret as secondary shapes and motions doing totally unexpected
things. A part is the way « the maths »
« solves » paradoxical requirements ( e.g.
« keep the same »and « zoom »),
and a part relates to what the human visible system is very sensitive
or very blind about.
E.g. : See various artifacts in
« Interpolation and blending tricks »
shadertoys
). In the video
and shadertoy
where we « zoom and keep the same » Perlin
noise, islands appear suddenly for B&W images… but no
longer if we allow just a little bit a bit of grey.
We propose
a very delimited study workbench, but the problem of temporal
coherency and parasitic secondary motions occurs in many situations
like paint-like rendering [1,2,3,4],
fluid particles [5],
advected textures [6,7],
and many times a user just innocently wanted to modulate a noise
parameter along a shape (cf shadertoys above).
Since clandestine secondary motion is already obvious in very basic cases such as infinite zoom in black and white Perlin noise, this allows to settle a convenient experimental bench to test the interactions between various algorithmic combinations, textural characteristics, and families of perceivable artifacts. A first step would be characterizing and organizing the families of artefacts, to somehow initiates a domain of artefactology :-) .
A part of the work will consist in experiments with the bench
above, testing the perceptual effect of various combinations and
tunings, possibly some light perception experiments,
but also trying to tell the relation between the effect (e.g.
secondary motion, parasitic wavelength) and the maths of the
model.
Beside the beginning of a general understanding of
the issue, we expect from this studies to get recommendations helping
to improve time coherency in various applicative algorithms: Which
kind of transformations are unperceived or extremely perceived, or
which range of parameters make them so. Plus possibly, to
suggest some slight changes or new variants in tools, normalizations,
and tunings to avoid the artifacts.
General culture in Computer Graphics and math
Practical experience of texture or shader or ink/paint procedural generation would be a plus;
Some base notions and motivations around visual perceptions would be a plus ;
A motivation about questionning questions and evaluating evaluations before doing brute math or programming ; i.e., understanding what’s going on really behind the scholar equation :-)