psyc54 lecture jan. 18: part i color and motion in shape-from-shadow pictures humera iqbal, john...

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


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


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


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)


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


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”


Border polarity changed from positive to negativeBorder polarity changed from positive to negative


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


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


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


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

psyc54 lecture jan. 18: part i color and motion in shape-from-shadow pictures humera iqbal, john...

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