Osvaldo da Pos, Cristina Rao Department of Applied Psychology University of Padua
COLOURS SEEN THROUGH TRANSPARENT OBJECTS
Goals Do colours seen through a translucent filter appear constant? In which conditions do they change more?
Participants 4 female observers, ~ 24 year old, with good colour vision
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
MONDRIAN (objects in the background)
Test – initially achromatic areas Reference – 9 colours
Garau
FILTERS • 16 filters (Y, R, B, G) • two chroma levels: C = 20, C = 60 (NCS) • two transparency levels: α = 0.10, α = 0.50 • Control condition: without filter
80 60 40
b* 20 0 -20 -40 -60
-40
-20
0
20
40
60
a*
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
computation of the reduction colours highly chromatic filter (60)
= 0.1 rather opaque
+ = 0.5 rather transparent
Metelli’s model 1974
reduction colour
little chromatic filter (20)
partitive mixture
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
procedure The 2 columns are binocularly fused and only one is perceived
the 2 images are binocularly fused: the filter is seen behind (as a non transparent background)
the 2 images are binocularly fused: the filter is seen in front
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
RESULTS s1
100 80 60 40 20 b* 0 -20 -40 -60 -80 -100
100 80 60 40 20 0 -20 -40 -60 -80 -100
-60 -40 -20
0
20
40 60
80 100
s3
-60 -40 -20 0
a*
20 40 60 80 100
Taverna -60 -40 -20
100 80 60 40 20 0 -20 -40 -60 -80 -100
100 80 60 40 20 b* 0 -20 -40 -60 -80 -100
s2
0
20 40 60
80 100
s4
controls: without filter in blue the colours of the Mondrian In yellow the adjusted colours -60 -40 -20
0
20
40
60
80 100
a*
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
100 80 60 40 20 b* 0 -20 -40 -60 -80 -100
s1
100 80 60 40 20 0 -20 -40 -60 -80 -100
-60 -40 -20 0
100 80 60
s2
-60 -40 -20
20 40 60 80 100
s3
100
0
20 40
Taverna
60 80 100
s4
80 60
40 20 b* 0 -20 -40
differences between subjects
40 20 0 -20 -40
-60 -80 -100
-60 -80 -60 -40 -20 0
a*
20 40 60 80 100
-100 -60 -40 -20
0
a*
20 40 60 80 100
in blue the colours of the Mondrian In yellow the adjusted colours In green the reduction colours
20 B 0.5 AIC | 2010 - da Pos, Rao Colours seen through transparent objects
less chromatic
more chromatic 60 R 0.1
20 R 0.1 100 80 60 40 20 b* 0 -20 -40 -60 -80 -100
100 80 60 40 20
-60 -40 -20 0
20 40 60 80 100
0 -20 -40 -60 -80 -100
Duso -60 -40 -20
0
20 40 60
80 100
100 80 60 40 20 0 -20 -40 -60 -80 -100
100 80 60 40 20 b* 0 -20 -40 -60 -80 -100 -60 -40 -20
0
a*
20 40 60 80 100
20 R 0.5
more opaque more transparent
-60 -40 -20 0
a*
20 40 60 80 100
in blue the colours of the Mondrian In yellow the adjusted colours In green the reduction colours
60 R 0.5
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
colour difference (CIECAM02-UCS)
filter / background interactions Y, G, B, R : colours of the filters 60
60
Y
50 40
40
30
30
20
20
10
10
0
0 0
60
G 1R 2
3B Y 4
P5
O 6
7 W8 Gr 9 Bk 10 11
40
30
30
20
20
10
10
0
0 1R
0
G 2
3B Y 4
P5
O 6
7 W8 Gr 9 Bk 10 11
Gr 10 Bk 11 1R 2G 3B 4Y 5P 6O 7 W 8 9
R
50
40
0
Duso
60
B
50
G
50
0
1R G 2
The colours of the mondrian which are better reproduced (with smaller difference) are those which correspond to the colour of the filter
3B Y 4
5P O 6
7 W8 Gr 9 Bk 10 11
colours of the Mondrians AIC | 2010 - da Pos, Rao Colours seen through transparent objects
60
Filters at low chroma allow colour matchings with less difference
50 40 30 20 10 0 0
1R 2 G
3B 4 Y
(t287 = 5.658 p = 0.00000004)
Van der Weyden
= 0.1 low transparency = 0.5 high transparency
5P 6 O 7 W8 Gr 9 Bk 10 11
colour difference
colour difference
C = 60 high chroma C = 20 low chroma
60 50
Different degrees of transparency do not significantly influence the colour matching
40 30 20 10 0 0
R 1
G 2
B3
Y4
P5 O6
W 7 Gr 8 Bk 9
10
n.s. AIC | 2010 - da Pos, Rao Colours seen through transparent objects
chroma effect as a function of the degree o transparency
C = 60 high chroma C = 20 low chroma colour difference
60 50 40
*
30
Memling
20
The filter chroma is relevant when the filter is very transparent
10 0 0.0
0.1 1.0
0.5 2.0
3.0
transparency
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
ΔE’ 20
ΔE’
60
p
t71
Rosso
27,25
44,13
0,0009
3,476
Giallo
29,66
40,43
0,0014
3,327
Verde
28,36
37,45
0,0068
2,786
Blu
25,69 30,00
0,1276
1,541
C = 60 high chroma C = 20 low chroma
as a function of the mondrian colours Photo Carnevali colour difference
colore filtro
chroma effect
60 50 40 30 20 10 0 0
1R 2G 3B 4Y 5P 6 9 Bk 10 11 O 7 W8 Gr
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
filter colour
ΔE’ 0.1
ΔE’ 0.5
p
t71
Rosso
33,67
37,72
0,4334
0,788
Giallo
31,92
38,18
0,0425
2,066
transparency effect as a function of the filter colour Photo Carnevali
Blu
35,49
36,25
30,32
19,44
0,0777
0,0000
1,790
4,678
= 0.1 low transparency = 0.5 high transparency
colour difference
Verde
50
*
40
*
30 20 10 0 0
1
R
2
Y
3
G
4
B
5
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
Conclusions •
When the objects behind the filter are completely covered, colour constancy is very poor
•
Colour constancy depends on: – the chroma of the filter • low chroma at high transparency – the colour of the filter • blue filter at high transparency – not on the transparency level (under our conditions)
•
Bizantynes Mosaics, Ravenna (Italy), VI cent.
Variability inter-observers was not much higher than variability intraobservers
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
THANK YOU
FOR YOUR KIND
ATTENTION!
Garau
AIC | 2010 - da Pos, Rao Colours seen through transparent objects
Garau