COLOURS SEEN THROUGH TRANSPARENT OBJECTS

Osvaldo da Pos, Cristina Rao

Department of Applied Psychology

University of Padua

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

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

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a*

b*

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

Garau

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

= 0.5

rather

transparent

= 0.1

rather

opaque

little

chromatic

filter (20)

highly

chromatic

filter (60) Metelli’s model

1974

+

partitive mixture

reduction

colour

computation of the reduction colours

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

pro

cedu

re

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

The 2 columns are

binocularly fused

and only one is

perceived

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AIC | 2010 - da Pos, Rao Colours seen through transparent objects

s4

controls:

without filter

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Taverna

RESULTS

in blue the colours of the Mondrian

In yellow the adjusted colours

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

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20 B 0.5

differences

between

subjects

Taverna

in blue the colours of the Mondrian

In yellow the adjusted colours

In green the reduction colours

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20 R 0.5

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20 R 0.1

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

b*

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more transparent

more opaqueDuso

less chromatic more chromatic

in blue the colours of the Mondrian

In yellow the adjusted colours

In green the reduction colours

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0 1 2 3 4 5 6 7 8 9 10 11 R G B Y P O W Gr Bk

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0 1 2 3 4 5 6 7 8 9 10 11 R G B Y P O W Gr Bk

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0 1 2 3 4 5 6 7 8 9 10 11 R G B Y P O W Gr Bk

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0 1 2 3 4 5 6 7 8 9 10 11 R G B Y P O W Gr Bk

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

colours of the Mondrians

colo

ur

diffe

rence

(CIE

CA

M02

-UC

S)

Y, G, B, R : colours of the filters

G

R

Y

B

Duso

filter / background interactions

The colours of the

mondrian which are better

reproduced (with smaller

difference) are those which

correspond to the colour of

the filter

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0 1 2 3 4 5 6 7 8 9 10 11 R G B Y P O W Gr Bk

(t287 = 5.658 p = 0.00000004)

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0 1 2 3 4 5 6 7 8 9 10 R G B Y P O W Gr Bk

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

= 0.1 low transparency

= 0.5 high transparency

C = 60 high chroma

C = 20 low chroma

Van der

Weyden

n.s.

co

lou

rd

iffe

ren

ce

co

lou

rd

iffe

ren

ce

Filters at low chroma allow

colour matchings with less

difference

Different degrees of

transparency do not

significantly influence

the colour matching

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0.0 1.0 2.0 3.0 0.1 0.5

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

Memling

co

lou

rd

iffe

ren

ce

C = 60 high chroma

C = 20 low chroma

transparency

The filter chroma is relevant

when the filter is very transparent

*

chroma effect

as a function

of the degree o

transparency

chroma

effect

as a function

of the

mondrian

colours

colore

filtro 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

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

Photo Carnevali

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0 1 2 3 4 5 6 7 8 9 10 11 R G B Y P O W Gr Bk

C = 60 high chroma

C = 20 low chroma

co

lou

rd

iffe

ren

ce

transparency

effect

as a function

of the filter

colour

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

Verde 35,49 30,32 0,0777 1,790

Blu 36,25 19,44 0,0000 4,678

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

Photo Carnevali

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0 1 2 3 4 5R Y G B

co

lou

rd

iffe

ren

ce

= 0.1 low transparency

= 0.5 high transparency

**

Conclusions

• When the objects behind the filterare completely covered,colour constancy is very poor

• Colour constancy depends on:– the chroma of the filter

• low chroma at hightransparency

– the colour of the filter• blue filter at high

transparency– not on the transparency level

(under our conditions)

• Variability inter-observers was notmuch higher than variability intra-observers

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

Bizantynes Mosaics,

Ravenna (Italy), VI cent.

AIC | 2010 - da Pos, Rao Colours seen through transparent objects

THANK YOU

FOR YOUR

KIND

ATTENTION!

Garau

Garau