dapos

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