Color appearance of natural objects

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Color appearance of natural objects

• Thorsten Hansen, Sebastian Walter
• and Karl R. Gegenfurtner

Department of Psychology University of
Giessen Germany
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Stages of color vision

• cones 2. cone-opponent 3. higher-order
  4. color
• 
  mechanisms categories

retina retina/LGN
visual cortex
black white red green yellow blue orange pink gray
brown
S
M
L
3
Stadien der Farbverarbeitung
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Motivation
Previous studies have investigated the color
appearance of homogeneous disks in the
isoluminant plane of DKL color space (e.g., De
Valois et al. 1997, Webster Miyahara 2000, De
Valois et al. 2000). These studies investigated
hue scaling for the unique hues RED, GREEN,
YELLOW, and BLUE in DKL color space. These
studies have shown that the cardinal axes do not
coincide with the unique hues. In particular, the
S-(LM) axis varies from violet to
yellow-green. Stimuli were always homogenous
patches.
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Motivation
In contrast to standard disk stimuli, natural
objects are characterized by a distribution of
different chromatic hues.
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Motivation

• Here we investigated two question
• Does the presentation of colors at different
  luminance values alters the location of the
  unique hue?
• Does the use of natural objects with a
  distinctive object color (e.g., a banana)
  influence the color appearance ?

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DKL color space
Derrington Krauskopf Lennie
Cone-opponent color space two chromatic axes
(L-M and S-(LM)), one luminance axis (LM).
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DKL cone-opponent axes vs. Hering's opponent
colors
Ewald H. Hering 18341918
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Methods
Stimulus creation translate color distribution
of the objects in the isoluminant plane of DKL
space.
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banana space
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Methods
Observers rated the appearance of the unique hues
(RGYB) for stimuli at 36 equally spaced chromatic
direction in the isoluminant plane of DKL color
space.
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Cone contrast in DKL space
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Methods
Observers rated the appearance of the unique hues
(RGYB) on a scale from 0 to 8.
R B G Y
Stimuli at each color directions were shown twice
in randomized order in each block. Five blocks
were run for each observer, resulting in a total
of 10 hue scaling for each chromatic direction.
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Methods

• Natural fruit stimuli (banana, salad, carrot) are
  compared against
• colored disks of homogeneous color
• outline shapes of homogeneous color
• at 5 different luminance values.
• N3 naïve observers participated in the study,
  with normal color vision as assessed by Ishihara
  pseudoisochromatic plates.

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Results
Color appearance of a standard disk stimulus.
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Results Variation of brightness.
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Results Natural objects
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Results Single subject data
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Results Comparison with outline shapes
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Results Other fruit salad.
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Summary

• In agreement with earlier studies we found that
• The cardinal axes do not coincide with the unique
  hues
• This is true for stimuli at a large range of
  different brightness values.

?
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Summary
The effect is smaller for outline shapes compared
to real images with a variety of hues.
The present study complements other work of our
group using natural objects where we have
investigated color discrimination (VSS 2005, ECVP
2005) and color memory (ECVP 2004).
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Conclusion
The distribution of hues in natural objects
influences color appearance and needs to be taken
into account for a full characterization of color
appearance.