Author: Claudio Oleari
E-mail: claudio.oleari@fis.unipr.it
Movie: Light, Darkness and Colours
Movie Clip: From 02:54 To 04:10
Director: Henrik Bëtius, Marie Luise Lauridsen and Marie Luise Lefèvre
Film Studio: Magic hour films ApS
Advanced level
The film’s scene looks at the properties that belong to the colour-appearance and
adaptation phenomena, whose origin is still today object of investigation. Particularly,
Colour appearance considers colour psychophysics and visual perception taking into
account the spectral and geometrical properties of the light combined with the visual
situation and illuminating conditions.
The adaptation is a visual process that produces luminous and chromatic alterations
dependent on the visual situation, e.g. background illumination. In the visual
processing in the retina and in the brain, the interaction between contiguous pathways
activated by different luminous radiations produces luminous and chromatic
sensations altered with respect to that produced by a same luminous radiation in a
dark surround..
Colour appearance phenomena:
The colour sensation produced by a light depends not only on the light itself, but also
on the surround, background, size, shape and generally to the visual situation to which
the observer is adapted.
Typical phenomena related to the colour appearance are the simultaneous luminance
contrast and the simultaneous chromatic contrast. These phenomena are considered
by Goethe and produced in the shadow generated by the change of the colour of the
illuminating light.
Goethe was a pioneer showing these phenomena, whose nature is described by the
Ewald Hering’s theory of the colour opponencies. This theory considers the
opponencies red-green, yellow-blue and dark-light as perceptual cardinal directions in
the colour space produced by the perceptual ordering of the colours.
Adaptation:
Adaptation is a visual processing with change of sensitivity of eye to meet the needs
of vision. This processing is a compensation that follows chromatic change of the
visual stimulus (chromatic adaptation) and luminance change (luminance adaptation).
Typical adaptation is that following a change of illumination.
Contrast:
Contrast is the subjective assessment of the difference in appearance of two parts of a
field of view seen simultaneously or successively.
Simultaneous Luminance contrast:
Simultaneous luminance contrast occurs when, for example, one views two objectively
equal patches embedded in two objectively different surrounds, one lighter and the
other darker than the patches, a condition that causes the objectively equal patches to
appear darker in the lighter surround and lighter in the darker surround. This
phenomenon is also named brightness induction (Fig. 3).
This phenomenon is amplified when the surround luminance is very close the sample
luminance, producing a further phenomenon termed crispening effect (Fig. 4).
1
Figure 3. Two equal grey squares in two different backgrounds appear different. This
phenomenon is the brightness induction.
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Figure 4. Simultaneous luminance contrast and luminance crispening in achromatic
figure. Two phenomena are represented in this figure. Two exactly equal grey scales
are represented. The strips of left the side scale are on a uniform grey surround while
in the right side contiguous strips are mutually touching. The left side strips appear
uniform and the right side strips appear with a non uniform luminosity, that is higher
where a strip is touching a darker strip and is lower where is touching a lighter strep.
This phenomenon is the luminance contrast. Moreover the left side strips that are
darker than the surround appear darker and the left side strips that are lighter than the
surround appear lighter. This phenomenon is the luminance crispening. The arrow
separates the two sets of strips and indicates the apparent discontinuity in the grey
scale. Any variation of the surround luminance shifts this discontinuity line.
Figure 5. Simultaneous luminance contrast in chromatic figure. Two figures are
represented, constituted by equal coloured squares, that are ordered in equal hue
lines with decreasing lightness from lest to right. Black lines are separating the
coloured squares: in the upper figure the black lines separate the squares of different
lightness and in the lower part separate the squares with different hues. In the lower
figure, the contact between equal hue and different luminance squares induces a
luminance simultaneous contrast such that the squares appear non uniform, darker at
left a lighter at right. In the upper figure the contact between different hues produces
non visual effect and the squares appear uniform as physically they are. This does not
mean that chromatic interaction does not exist (see Chromatic induction).
Figure 6. On a scale of uniform grey strips, three almost equal yellow colour samples
are reproduced, separated in the upper part and contiguously in the lower part. The
separated samples appear as equal while the contiguous samples appear different
with evident luminance contrast. Moreover the yellow samples appear darker on
lighter stripes and lighter on darker stripes.
Simultaneous chromatic contrast or Chromatic induction:
Simultaneous chromatic contrast occurs when, for example, one views an objectively
grey patch embedded in an objectively red surround, a condition that causes the
objectively grey patch to appear greenish. And analogously the same objectively grey
patch embedded in an objectively green surround appears reddish. Analogously two
objectively equal yellowish patches embedded in two red and green surrounds appear
different.
Figure 7. Simultaneous chromatic contrast is considered on coloured squares (upper
part) and on achromatic squares (lower part) is considered. Two equal yellowish
squares are presented on green and red background and appear different.
Analogously two equal grey squares are presented on a reddish surround and on a
greenish surround, respectively, and appear different: the first one appears greenish
and the second one reddish.
Figure 8. Three equal and uniformly yellowish disks are presented on a ground with
colour ranging continuously from green to red. Luminance and chromatic contrasts are
both present and the disks appear different and no longer uniform.
Hue angle 180°
Hue angle 0°
L*
Cab*
Cab*
Figure 9. This figure represents two pages at constant and opponent hue angles, red
and green, of the CIELAB system (CIE 1931 standard observer and D75 illuminant).
The coloured squares are physically uniform and are those reproducible by a cathode
ray-tube monitor. The lightness L* increases from bottom to top and the chroma Cab*
increases starting from the achromatic central vertical line. The luminance
simultaneous contrast appears between contiguous samples with different lightness
while simultaneous chromatic contrast appears between contiguous colours with equal
lightness. This last phenomenon occurs in the hue-angle 0°, where the right side of
the red squares appear desaturate tingeing with the opponent green hue, and
analogously in the hue-angle 180°, where the left side of the green squares appear
desaturate tingeing with the opponent red hue. The central line constituted of grey
squares, appears tinge of the green hue in the right side and of red hue in the left.
This phenomenon does not regard the squares at the border.
Simultaneous saturation contrast or Induced saturation:
Simultaneous saturation contrast occurs when, for example, one sees two objectively
equal pink patches embedded in an objectively red surround and in an objectively
green surround, respectively, a condition that causes the objectively pink patch to
appear redder on the green background.
Figure 10. Two equal pink squares are presented on a red and on a green surround,
respectively. The square on the green background appears redder than the other
showing the simultaneous saturation contrast.
http://en.wikipedia.org/wiki/
www.colorcube.com/
http://colorusage.arc.nasa.gov/guidelines_lum_cont.php
www.ncbi.nlm.nih.gov
http://www.visualexpert.com/FAQ/Part1/cfaqPart1.html
http://www.uni-mannheim.de/fakul/psycho/irtel/cvd.html
http://webvision.med.utah.edu/