PROCAMS 2005 San Diego Futures Laboratory MCS ANL CI UC Pixel Aligned Warping for Multiprojector...
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Transcript of PROCAMS 2005 San Diego Futures Laboratory MCS ANL CI UC Pixel Aligned Warping for Multiprojector...
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Pixel Aligned Warpingfor
Multiprojector Tiled Displays
Mark Hereld and Rick StevensArgonne National Laboratory
Computation InstituteUniversity of Chicago
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Introduction
Warping image content into projector frame buffers is a fact of life
Driven by geometrical constraints Never driven by clarity constraint
except in that geometrical constraints are sometimes driven by alignment with nearby or overlapping projected content
What if content crispness is more important?
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
pfcutoff 2
1
Pixel Exploit
Nyquist and the pixelLone illuminated pixel contains high frequency
components well beyond Nyquist cutoffAnti-aliasing techniques are the standard
antidote when sharp features don’t fall on pixel boundaries
Often exploited to represent thin, crisp featuresGraphics: single pixel width horizontal and
vertical lines, and pointsText: sharp and sometimes small fonts
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Example
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Warped
)),(),,((),( yxfyxfvu vu
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Nearest Neighbor
Plate
Rift Line
)),(),,((),( yxfyxfROUNDvu vu
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Warped w/Rifts
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Detail
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Possible Approaches
Modified nearest neighbor: soften rift boundary Stretch rift lines to avoid cutting through important stuff Perturb warp according to local measure of steepness Minimize an energy function that includes terms
reflecting affinity of features for pixel boundaries and gives weight to keeping proximal features together
Crystallize pixel values around nucleation centers related to locations of high-contrast features in the image
Segment the image into unwarpable islands of content
X coordinate of pixel
plateplate
rift
dX
of
warp
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Possible Approaches
Modified nearest neighbor: soften rift boundary Stretch rift lines to avoid cutting through important stuff Perturb warp according to local measure of steepness Minimize an energy function that includes terms
reflecting affinity of features for pixel boundaries and gives weight to keeping proximal features together
Crystallize pixel values around nucleation centers related to locations of high-contrast features in the image
Segment the image into unwarpable islands of content
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Possible Approaches
Modified nearest neighbor: soften rift boundary Stretch rift lines to avoid cutting through important stuff Perturb warp according to local measure of steepness Minimize an energy function that includes terms
reflecting affinity of features for pixel boundaries and gives weight to keeping proximal features together
Crystallize pixel values around nucleation centers related to locations of high-contrast features in the image
Segment the image into unwarpable islands of content)]),(),,(([),(
)],(),,([)),(1(],[
yxfyxfROUNDyxCONSTRAST
yxfyxfyxCONTRASTvu
vu
vu
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Possible Approaches
Modified nearest neighbor: soften rift boundary Stretch rift lines to avoid cutting through important stuff Perturb warp according to local measure of steepness Minimize an energy function that includes terms
reflecting affinity of features for pixel boundaries and gives weight to keeping proximal features together
Crystallize pixel values around nucleation centers related to locations of high-contrast features in the image
Segment the image into unwarpable islands of content
x,y
u,v
f0u,f0v
Ci-1.Ci Ci
.Ci+1
k k k
feature blocking energy
target warp term
pixel mis-alignment
penalty
fu,fv
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Possible Approaches
Modified nearest neighbor: soften rift boundary Stretch rift lines to avoid cutting through important stuff Perturb warp according to local measure of steepness Minimize an energy function that includes terms
reflecting affinity of features for pixel boundaries and gives weight to keeping proximal features together
Crystallize pixel values around nucleation centers related to locations of high-contrast features in the image
Segment the image into unwarpable islands of content
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Possible Approaches
Modified nearest neighbor: soften rift boundary Stretch rift lines to avoid cutting through important stuff Perturb warp according to local measure of steepness Minimize an energy function that includes terms
reflecting affinity of features for pixel boundaries and gives weight to keeping proximal features together
Crystallize pixel values around nucleation centers related to locations of high-contrast features in the image
Segment the image into unwarpable islands of content
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Islands in the Ocean
Lock contiguous blocks of high contrast pixels, islands, to one another and to nearest plate
Warp everything else, the ocean, in the usual fashion
Don’t worry about possible artifacts around the edges of the islands, the beaches
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Algorithm Compute contrast of each pixel
w.r.t. 3x3 neighborhood Binarize Consolidate into islands
Morphological fill & open Pin island coordinates
to plate containing island centroid Warp ocean Transfer islands into warped ocean
cut-and-paste unwarped
9.0)(
)(
minmax
minmax II
II
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Example
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Contrast
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Labeled
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Labeled w/Rifts
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
PAW
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Warped
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Results
Interesting notion Simple algorithm
Islands in the Ocean
Very effectiveExcept when it’s
not• See “Weaknesses”
Large warpsRotationKeystone
Tiling introduces new problemsOverlap or
abutting
Large islandsCollisions
Strengths Weaknesses
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Future
Robust rules for handling pathological cases gracefully
Fast implementation compatible with hardware accelerators
Handle blending areas in tiled displays Awareness of horizontal and vertical features
allow lines to stretch or shrink but not kink
Apply to image scaling Particularly high res laptop display driving XGA
projector
PROCAMS 2005San Diego
Futures LaboratoryMCS ANL CI UC
Summary
Pixel edges are commonly exploited to represent sub-Nyquist features
Warping can degrade this crispness
Many approaches to pixel aligned warping that could preserve much of this crispness at the expense of geometrical accuracy
Islands in the Ocean is effective