Post on 21-Jan-2016
description
PERCEPTUAL STRATEGIES FOR MATERIAL IDENTIFICATION
Qasim Zaidi Rocco Robilotto
Byung-Geun Khang
SUNY College of Optometry
1 2 3 4
•Three of the objects are made of identical gray paper while one is made of a different shade.•Illumination on the right is half the illumination on the left.
What is the number of the odd object?
3 1 2 4
“3” is the number of the odd object!
What strategy did you follow?
•Brightness discrimination threshold from % side-correct•Lightness identification threshold from % object-correct
Method of constant-stimuli
PREDICTIONS FOR TWO MODELS
Results of Lightness Identification
Hypothesis: P(I|D)=1.0Rejected at p=0.01Chi-squared > 16.8
Note systematic asymmetry in lightness identification compared to brightness discrimination.
1 2 3 4
•Choose the object that is most different in brightness.•Disregard the material and the illumination difference.
Brightness is different from photometer luminance because of adaptation and lateral interactions.
Results of Brightness Dissimilarity
Note systematic asymmetry in curves is similar to lightness identification results.
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0.05
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Exp 1
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Exp 1
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p 2
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Lightness Identification (Exp 1)
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p 2
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Lightness Identification (Exp 1)
Bri
gh
tne
ss I
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nti
fica
tio
n (
Ex
p 2
)
ST SS
ST SS
Brightness Discrimination Thresholds (Reflectance units)
Lightness Identification and Brightness Dissimilarity Thresholds (Reflectance units)
Half Illum.
Full Illum.
M ea n Lum in anc eo f S tim u lus
B r igh tn es so f S tim u lus
ga in
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1
x
i
Adding adaptation to the photometer modelGain= k/(k+l)
0 x-0.5
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0.5
1
x 3x-0.5
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0.5
1
0.5x x
x 1.67x
0.83x
1.18x
(Fu
llIl
lum
.)(H
alf
Illu
m.)
No
rma
lize
dP
rop
ort
ion
of
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sp
on
se=
Tes
t
Test Reflectance
(a)
=
(b)
=0.5
(c)
=0.1
8
Lightness identification based on brightness dissimilarity responses of adaptation model
PERCEPTUAL STRATEGIES FOR LIGHTNESS IDENTIFICATION
•Under everyday conditions, observers consistently judge and remember surfaces as having a certain lightness or grayness.
•This phenomenology is not sufficient evidence that the visual system generically has access to the lightness of materials.
•For 3-D objects, we show conditions where lightness identification is limited solely by the limen of brightness discrimination, and other conditions where lightness identification is considerably worse.
•More importantly, we show that the same relative brightness based strategy reproduces both sets of results.
Differences between brightness and color information for material identification
Systematic changes in cone-coordinates
Algorithms for simultaneous identification for Lambertian and non-Lambertian 3-D objects
•Three of the filters are identical while one is different.•Illumination on the right is skylight, on the left is sunlight.
Which is the odd filter?
FILTER IDENTIFICATION ACROSS ILLUMINANTS
Identical filters will cause systematically different spectral changes in two spectrally different lights.
Given information about the filtered and unfiltered lights, can an observer identify two filters with identical spectral transmittances?
400 450 500 550 600 650 7000
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8NATURAL LIGHTS (Taylor & Kerr,1941)
WAVELENGTH(nm)
RE
LA
TIV
E R
AD
IAN
T E
NE
RG
Y-- sunlight
-- skylight
400 450 500 550 600 650 7000
0.1
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1COLOR FILTERS (Kodak CC50)
WAVELENGTH(nm)
TR
AN
SM
ITT
AN
CE
--- red --- green --- blue --- yellow --- magenta--- cyan
400 450 500 550 600 650 7000
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2
3
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8SUNLIGHT THROUGH SIX FILTERS
WAVELENGTH(nm)
RE
LA
TIV
E R
AD
IAN
T E
NE
RG
Y
--- red --- green --- blue --- yellow --- magenta--- cyan
400 450 500 550 600 650 7000
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2
3
4
5
6
7
8SKYLIGHT THROUGH SIX FILTERS
WAVELENGTH(nm)
RE
LA
TIV
E R
AD
IAN
T E
NE
RG
Y
--- red --- green --- blue --- yellow --- magenta--- cyan
0.5 0.55 0.6 0.65 0.7 0.75 0.80
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
rg
b
y
m
cr
g
b
y
m
c
L/(L+M)
S/(
L+
M) R G B Y M C
0
0.02
0.04 SUNLIGHT
FILTERS
SD
(L/(
L+
M))
R G B Y M C0
0.02
0.04 SKYLIGHT
FILTERS
SD
(L/(
L+
M))
R G B Y M C0
0.02
0.04 SUNLIGHT
FILTERSS
D(S
/(L
+M
)) R G B Y M C
0
0.02
0.04 SKYLIGHT
FILTERS
SD
(S/(
L+
M))
R G B Y M C0
5
10
SUNLIGHT
FILTERS
SD
(L+
M+
S)
R G B Y M C0
5
10
SKYLIGHT
FILTERS
SD
(L+
M+
S)
Means of Material Chromaticities
SDs of Material Chromaticities
36 EVERYDAY MATERIALS (VRHEL et al 1994)
•Changes in means are systematic across illuminants.
•Filters can increase or decrease the color variation.
•Three of the filters are identical while one is different.•Illumination on the right is skylight, on the left is sunlight.
Which is the odd filter?
0 0.2 0.4 0.6 0.8 10
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1PSYCHOMETRIC CURVES
DELTA (CYAN VERSUS RED)
PR
OP
OR
TIO
N C
OR
RE
CT
SIDE CORRECT & FILTER CORRECT CURVES
•Method of constant stimuli•DELTA is distance between standard and distractor.•6 standards x 5 tests x 2 daylights x 6 deltas x 10 reps
0 0.2 0.4 0.6 0.8 10
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1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
BK
0 0.2 0.4 0.6 0.8 10
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1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
JM
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1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
JG
0 0.2 0.4 0.6 0.8 10
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0.4
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1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
EK
IDENTIFICATION VS DISCRIMINATION
FILTERS
RESULTS
Identification thresholds were generally similar to discrimination thresholds and were significantly greater only in 5%, 10%, 13%, and 23% of 60 pairs for 4 observers.
Observers can identify filters across different illuminants almost as well as they can discriminate filters within the same illuminant.
MATERIAL IDENTIFICATION ACROSS ILLUMINANTS
X-junctions at the edges of the circular filters, in conjunction with the systematic changes in chromaticities of partially overlaid objects, promote a percept of transparency.
Are these results influenced by transparency. By rotating the image of the circular filtered regions by 180, we abolished the edge-based cues to transparency while leaving unchanged the figural and color contents inside and outside the filters.
•Three patches are from the same material while one is different.•Illumination on the right is skylight, on the left is sunlight.
Which is the odd material?
0 0.2 0.4 0.6 0.8 10
0.2
0.4
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0.8
1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
BK
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
JM
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
IDE
NT
IFIC
AT
ION
DISCRIMINATION
o Sunlight
+ Skylight
JG
IDENTIFICATION VS DISCRIMINATION
MATERIALS
0 0.2 0.4 0.6 0.8 10
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0.4
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0.8
1
T-J
UN
CT
ION
X-JUNCTION
o Sunlight
+ Skylight
BK
0 0.2 0.4 0.6 0.8 10
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T-J
UN
CT
ION
X-JUNCTION
o Sunlight
+ Skylight
JM
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T-J
UN
CT
ION
X-JUNCTION
o Sunlight
+ Skylight
JG
0 0.2 0.4 0.6 0.8 10
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T-J
UN
CT
ION
X-JUNCTION
o Sunlight
+ Skylight
BK
0 0.2 0.4 0.6 0.8 10
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T-J
UN
CT
ION
X-JUNCTION
o Sunlight
+ Skylight
JM
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T-J
UN
CT
ION
X-JUNCTION
o Sunlight
+ Skylight
JG
IDENTIFICATION THRESHOLDS
DISCRIMINATION THRESHOLDS
FILTERS VS MATERIALS
RESULTS
Disrupting the X-junctions and color relations at the edges of the filters did not appreciably affect discrimination or identification.
Systematic color changes at the edges of the filter and X-junction cues to filter transparency were not necessary for good discrimination or identification performance.
COLOR IDENTIFICATION ACROSS ILLUMINANTS
•Both experiments can be conceived as identification of a circular ensemble of materials across the two natural lights.
•Both experiments indicate that identification of ensembles of materials is almost as good as discrimination between ensembles of materials.
•The significant cues are the chromaticity shifts across illuminants.
0.6 0.7 0.80.6
0.7
0.8RED
SK
YL
IGH
T
0.6 0.7 0.80.6
0.7
0.8GREEN
SK
YL
IGH
T
0.6 0.7 0.80.6
0.7
0.8BLUE
SUNLIGHT
SK
YL
IGH
T
0.6 0.7 0.80.6
0.7
0.8
YELLOW
SK
YL
IGH
T
0.6 0.7 0.80.6
0.7
0.8MAGENTA
SK
YL
IGH
T
0.6 0.7 0.80.6
0.7
0.8CYAN
SK
YL
IGH
T0.6 0.7 0.8
0.6
0.7
0.8NOFILTER
SK
YL
IGH
T
L/(L+M)
0 .03 .060
.03
.06
RED SK
YL
IGH
T
0 .03 .060
.03
.06
GREEN SK
YL
IGH
T
0 .03 .060
.03
.06
BLUE
SUNLIGHT
SK
YL
IGH
T
0 .03 .060
.03
.06
YELLOW SK
YL
IGH
T
0 .03 .060
.03
.06
MAGENTA SK
YL
IGH
T
0 .03 .060
.03
.06
CYAN SK
YL
IGH
T
0 .03 .060
.03
.06
NOFILTERSK
YL
IGH
T
S/(L+M)
0 20 400
20
40
RED SK
YL
IGH
T0 20 40
0
20
40
GREEN SK
YL
IGH
T
0 20 400
20
40
BLUE
SUNLIGHT
SK
YL
IGH
T
0 20 400
20
40
YELLOW SK
YL
IGH
T
0 20 400
20
40
MAGENTA SK
YL
IGH
T
0 20 400
20
40
CYAN SK
YL
IGH
T
0 20 400
20
40
NOFILTERSK
YL
IGH
T
L+M+S
CORRELATED CHROMATICITY CHANGES
•L/(L+M) coordinates translate
•S/(L+M) coordinates scale
•Means can be used to estimate translation and scaling constants
•Simple algorithms can exploit the affine transforms for material identification
# Observers Standard Test # Observer Standard Test
X- T- (Sunlight) (Skylight) X- T- (Skylight) (Sunlight)
________________________________________________________________________
_____
2 1 RED BLUE 3 2 BLUE MAGENTA
2 2 BLUE MAGENTA 1 1 MAGENTA RED
2 3 MAGENTA BLUE 2 2 BLUE RED
2 0 RED MAGENTA 1 1 RED BLUE
0 1 YELLOW GREEN 0 3 RED MAGENTA
3 1 CYAN BLUE 1 2 GREEN YELLOW
1 1 BLUE YELLOW
PAIRS OF CONFUSED FILTERS
Are RED and BLUE confused because observers judge deviations from directions of color vectors better than lengths of color vectors?
Means of Material Chromaticities
•If the material statistics are constant, then color identification only requires comparing rank-orders of chromaticities.•If material statistics change, affine transforms will give correct identification, but rank orders will not.
Color identification across illuminants within the same scene
PERCEPTUAL STRATEGIES FOR COLOR IDENTIFICATION
Identification based on similarity of appearance is affected by adaptation.
Identification based on systematic shifts of
appearance is based on geometrical operations in perceptual color space.
Identification strategies rely on associative
invariants of the natural world.