PsyC54 Lecture Jan. 18: Part IPsyC54 Lecture Jan. 18: Part I
Color and Motion in Color and Motion in
Shape-from-shadow PicturesShape-from-shadow Pictures
Humera Iqbal, John Kennedy & Juan Bai
Hering’s Umbra and PenumbraHering’s Umbra and Penumbra
Loose shadow Loose shadow perception when perception when penumbra is covered.penumbra is covered.
umbra
penumbraPenumbra
Umbra
WHY?WHY?
Shape-from-shadow perceptionShape-from-shadow perception
Number-of-Contours AccountNumber-of-Contours AccountContours of a line play a role in shape-from- Contours of a line play a role in shape-from- shadow perception and too many contours shadow perception and too many contours prevent shape from shadow perceptionprevent shape from shadow perception
Shape-from-shadow perceptionShape-from-shadow perception
Belongingness HypothesisBelongingness HypothesisDark-to-light shadow border has to belong Dark-to-light shadow border has to belong to both the shadowed and the illuminated to both the shadowed and the illuminated areas to allow perception of a continuous areas to allow perception of a continuous face bearing shadowface bearing shadow
Border-Polarity HypothesisFor shape-from-shadow perception the
luminosity of the shadowed region and the shadow border must be lower than the luminosity of the illuminated region
Shape-from-shadow perceptionShape-from-shadow perception
All Possible Visual BordersAll Possible Visual Borders
Static or Motion
Luminance or Spectral
Monocular or Binocular
Manipulate each possibility 2 x 2 x 2 = 8
All Possible Visual BordersAll Possible Visual Borders
Spectral Difference Spectral Difference (colored)(colored)
Luminance Difference Luminance Difference (B/W)(B/W)
Colored Colored stereo stereo moviesmovies
Colored Colored stereo stereo
illustrationsillustrations
B/W stereo B/W stereo moviemovie
B/W stereo B/W stereo illustrationsillustrations
Colored Colored motionmotion
Colored Colored paintingpainting
B/W B/W motionmotion
B/W B/W drawingsdrawings
MotionMotionStaticStaticMotionMotionStaticStatic
BinocularBinocular
MonocularMonocular
Number of ContoursNumber of Contours
John Kennedy (1993)John Kennedy (1993)
Too many contours, Too many contours, prevents shape-prevents shape-from-shadow from-shadow perceptionperception
In the black-line In the black-line image the line has image the line has two contours: from two contours: from grey-to-black and grey-to-black and from black-to-whitefrom black-to-white
Belongingness Hypothesis…Belongingness Hypothesis…
Monocular and Monocular and Binocular depth Binocular depth perceptionperception
Looking through a Looking through a stereoscope, Ss. stereoscope, Ss. May see the small May see the small dotted line only dotted line only belonging to belonging to shadowed region or shadowed region or illuminated regionilluminated region
Border-Polarity HypothesisBorder-Polarity Hypothesis
Luminosity of shadow Luminosity of shadow region and shadow region and shadow border must be lower border must be lower than the luminosity of than the luminosity of non-shadowed non-shadowed region.region.
(i.e. positive border (i.e. positive border polarity)polarity)
All Possible Visual BordersAll Possible Visual Borders
original table from Kennedy et al. (2003)
Experiment 1Experiment 1
In a static image, In a static image, changed the changed the luminosity of the luminosity of the shadowed region shadowed region while maintaining while maintaining the luminosity of the luminosity of the red shadow the red shadow borderborder
Experiment 1Experiment 1
Created nine images with border polarity changing Created nine images with border polarity changing gradually from positive to negative and region gradually from positive to negative and region polarity kept positive except for the last imagepolarity kept positive except for the last imageRed BorderRed Border Black ShadowBlack Shadow
Hue = 239Hue = 239 Hue = 0 Hue = 0
Saturation = 240Saturation = 240 Saturation = 0 Saturation = 0
Participants asked to rate each image on a scale Participants asked to rate each image on a scale from 1-to-10, where 10 was “easy to recognize from 1-to-10, where 10 was “easy to recognize the old person” 1 was “difficult to recognize”the old person” 1 was “difficult to recognize”
Experiment 1Experiment 1
Border polarity changed from positive to negativeBorder polarity changed from positive to negative
Experiment 1Experiment 1
ResultsResultsThe face was more evident in frame 1, but The face was more evident in frame 1, but started to become difficult by frame 5, and started to become difficult by frame 5, and was totally gone by frame 9…gradation effectwas totally gone by frame 9…gradation effect
ConclusionConclusionShape-from-shadow perception becomes Shape-from-shadow perception becomes difficult as luminosity of the shadowed region difficult as luminosity of the shadowed region becomes higher than the luminosity of the becomes higher than the luminosity of the shadow bordershadow border
Experiment 2Experiment 2
Using “Polka Dots” instead of solid regionUsing “Polka Dots” instead of solid region
Changed luminosity of the shadow border and Changed luminosity of the shadow border and shadow region by changing number of dots in a shadow region by changing number of dots in a square areasquare area
Created motion of the shadow border by Created motion of the shadow border by changing positions of the polka dotschanging positions of the polka dots
Experiment 2Experiment 2
11stst Test Test
Black-dot borderBlack-dot border
Black-dot shadow Black-dot shadow
Negative border polarityNegative border polarity
22ndnd Test Test
Black-dot borderBlack-dot border
Black-dot shadowBlack-dot shadow
Positive border polarityPositive border polarity
Experiment 2Experiment 2
33rdrd Test Test
Red-dot borderRed-dot border
Black-dot shadowBlack-dot shadow
Negative border polarityNegative border polarity
44thth Test Test
Red-dot borderRed-dot border
Black-dot shadow Black-dot shadow
Positive border polarityPositive border polarity
PredictionsPredictions
difficult easy