'Color
Illusions' by Gianni A. Sarcone and Marie-Jo Waeber
Color
only starts to exist when our perception systems produce
the impression of ‘color’: light is perceived
on the retina as a stimulus and is processed into a perception
of color in our brain. In substance, colors are already
illusions in themselves...
olor
is energy… in fact it is an electromagnetic phenomenon,
which depends on the way that light is reflected on
the objects. Every object absorbs a part of the light
which hits it and deflects the rest towards our eyes:
this reflected light is interpreted by our brain as
a particular color. We shouldn’t, therefore,
be surprised to find that the word color comes from
the Latin root celare (i.e. 'that which covers,
conceals'). Color is then already an illusion per
se, a ghost that takes life only in our visual
system, when light stimulates the photo-receptors -
the antennae that pick up
luminous
signals – that fill in the background of our
eyes. The world surrounding us is sadly in reality
monochrome.
But there is also another trick: to the eye color is
measured partly on the basis of the frequency of light
that hits it but above all in relation to colors nearby.
A color is perceived to be brighter, for example, if
it is surrounded by a complementary color (two colors
are said to be complementary if the sum of their radiation
equals or gives white) or lighter if the background color
is darker. There is then a mechanism that enhances the
contrast of the outline of an object
relatively
to its background: it is called lateral inhibition,
because each photo-receptor tends to inhibit the response
of the one next to it. The result is that which appears
to be clear appears even to be more so and vice versa.
The same mechanism works for colors: when a photo-receptor
from one area of the retina becomes stimulated by a
color, those next to it become less sensitive to that
color. So, for example, the light blue of a small square
that you see on a blue background, appears to our eyes
clearer than it would do on a yellow background (because
yellow contains no blue).
Just
GREY
An
alignment of grey bars allows us to discover the effect
of color assimilation: the grey bars in
contact with blue acquire a similar tone, the same for
the part that touches the red color, giving the impression
of color gradation. However, the grey is always grey!
Color
afterimage effect
Make
sure your cursor is moved away from the image below. Stare
at the "+" in the middle of
the picture for 15 seconds. Without looking away from the "+",
move your cursor over the image.
Which
of the strips below, A or B, corresponds to the green
strip positioned on the red and green field? This
illusion is based on the effect of simultaneous
color contrast. See
answer
Visual
Weave
Known
as simultaneous brightness contrast the
perceptual phenomenon that appears to make a colored
area seem clearer when it is placed on a dark background,
as in the example opposite. It is evident that the
lenticular forms at the bottom are all equal. Note,
though, how they appear to be different when they
are placed on different backgrounds, light and dark.
The difference is accentuated when we add an interwoven
background.
This
phenomenon has puzzled scientists and philosophers
for two millennia, yet there is still no consensus
as to exactly why it happens. Interesting observations
and comments on this subject are provided by scientists Edward
Adelson (lightness induction) and Alexander
Logvinenko (lightness-shadow invariance).
The
article featured on this page is adapted from our
'Optical Illusions Chronicles' (Visione,
in Italian) in Focus
Giochi review, issues #5, #6,
and #7. If you enjoy optical illusions,
why not to subscribe to Focus
Giochi and receive them in your mailbox?
Although
they appear to be completely different, the tiles a, b and c,
in the picture above, are identical in form color
and tone. Again it is caused by the effect of simultaneous
brightness contrast.
Which
ball on the coffee table corresponds exactly with Ball
a) on the floor: Ball b) or ball c)? See
answer
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olor
is energy… in fact it is an electromagnetic phenomenon,
which depends on the way that light is reflected on
the objects. Every object absorbs a part of the light
which hits it and deflects the rest towards our eyes:
this reflected light is interpreted by our brain as
a particular color. We shouldn’t, therefore,
be surprised to find that the word color comes from
the Latin root celare (i.e. 'that which covers,
conceals'). Color is then already an illusion per
se, a ghost that takes life only in our visual
system, when light stimulates the 
Known
as simultaneous brightness contrast the
perceptual phenomenon that appears to make a colored
area seem clearer when it is placed on a dark background,
as in the example opposite. It is evident that the
lenticular forms at the bottom are all equal. Note,
though, how they appear to be different when they
are placed on different backgrounds, light and dark.
The difference is accentuated when we add an interwoven
background.
Italy
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