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The Effect of Warm and Cool Object Colors on Depth Ordering. ... There is a clear cyclic trend in scores from cool to warm for the darker backgrounds. ... – PowerPoint PPT presentation

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Title: Stimuli were presented on a 17 inch monitor in a dimly lit room, operating at 60 Hz with a resolutio


1
The Effect of Warm and Cool Object Colors on
Depth Ordering. Reynold J. Bailey, Cindy M.
Grimm, Christopher Davoli
Contact rjb1_at_cse.wustl.edu
Goal
Experiment Design
To explore the color-depth relationship for
realistic, colored objects with varying shading
and contours.
Stimuli
  • 7 colored teapots
  • 7 uniform colored patches

Motivation
The phenomenon of warmer colors (red end of
spectrum) appearing nearer in depth to viewers
than cooler colors (blue end of spectrum) has
been studied extensively by psychologists and
other vision researchers. These studies
typically asked human observers to view
physically equidistant, colored stimuli and
compare them for relative depth Sundet,
1978. The stimuli presented were rather simple
Seven colors were manually selected and equated
for luminance. Each of the resulting equiluminant
colors was applied to an image of a teapot. The
colors were scaled by the pixel luminance values
of the original teapot to create the stimuli used
in this study. This approach preserves the
shading and specular highlights of the original
teapot.
Results
A score that tells how many times a given teapot
is chosen as appearing nearer relative to all
other teapots is computed for each of the 4
backgrounds (shown below).
Participants
Scores for background
Scores for background
Scores for background
Scores for background
90
  • Straight colored lines.
  • Uniform color patches.
  • Point light sources.
  • Symmetrical objects with uniform shading.
  • Highly saturated colors.
  • 15 volunteers (4 females, 11 males, ages
    18-40).
  • Normal or corrected-to-normal vision
    (self-reported).
  • No color vision abnormalities (self-reported).

Score
0
Method
There is a clear cyclic trend in scores from cool
to warm for the darker backgrounds. This cyclic
relationship is lost as the background gets
brighter. The scores for the uniform color
patches follow similar trends.
Stimuli were presented on a 17 inch monitor (in a
dimly lit room), operating at 60 Hz with a
resolution of 1280 x 1024. Two objects of the
same type (teapot or color patch) were
presented for each trial. The objects were
displayed 1 inch apart on either side of an
imaginary central point on the screen. Each
object subtended an angle of approximately 5o of
the visual field. The background could be one of
four different uniform levels of gray, ranging
from black to white Participants were
instructed to decide which object appeared nearer
(based on their first impulse) and responded by
moving the mouse over their choice and clicking
on it. Between each trial, a blank screen was
displayed for a 2 seconds. This was done to
prevent total adaptation, thereby ensuring that
depth perception remained stable. Each
participant experienced every possible comparison
against every background for both data sets (an
object was never compared against
itself). Participants were given breaks after
every 7 minutes of testing. The presentation
order of the stimuli was randomized for each
participant.
Although such stimuli are useful in isolating and
studying depth cues in certain contexts, they
leave open the question of whether the human
visual system operates similarly for realistic
objects.
The figures below show the average probability or
responding nearer for each of the teapots and
color patches over the 4 possible backgrounds.
The trends for color patches reveal less
variability. This suggests that the more complex
an image is, the more an observer may try to
gather other depth cues from that image. For the
color patches, red, which has been established in
literature as appearing nearer, does indeed show
this pattern. The red patch was chosen reliably
more than all other patches. The red teapot,
however, was chosen reliably more than only three
teapots (cyan, green, and yellow). This
observation supports the theory that color is a
relatively weak depth cue and is not necessarily
the overriding depth cue in complex images.
Physiological Basis for Color as a Depth Cue
Theory 1 Chromatic aberration. Shorter
wavelengths of visible light are refracted more
than longer wavelengths. As a result, equidistant
sources of differing wavelengths cannot be
simultaneously focused onto the retina by eyes
optical system.
Theory 2 Color sensitive cones in the retina
exhibit a slight bias (higher responses) to
colors toward warm end of visible spectrum
Stockman 1999, 2000. This bias may be strong
enough to result in differences in perceived
depth between colors.
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