Perceiving edge contrast

Keith A. May, Mark A. Georgeson

Research output: Contribution to conferenceOther

Abstract

We have shown previously that a template model for edge perception successfully predicts perceived blur for a variety of edge profiles (Georgeson, 2001 Journal of Vision 1 438a; Barbieri-Hesse and Georgeson, 2002 Perception 31 Supplement, 54). This study concerns the perceived contrast of edges. Our model spatially differentiates the luminance profile, half-wave rectifies this first derivative, and then differentiates again to create the edge's 'signature'. The spatial scale of the signature is evaluated by filtering it with a set of Gaussian derivative operators. This process finds the correlation between the signature and each operator kernel at each position. These kernels therefore act as templates, and the position and scale of the best-fitting template indicate the position and blur of the edge. Our previous finding, that reducing edge contrast reduces perceived blur, can be explained by replacing the half-wave rectifier with a smooth, biased rectifier function (May and Georgeson, 2003 Perception 32 388; May and Georgeson, 2003 Perception 32 Supplement, 46). With the half-wave rectifier, the peak template response R to a Gaussian edge with contrast C and scale s is given by: R=Cp-1/4s-3/2. Hence, edge contrast can be estimated from response magnitude and blur: C=Rp1/4s3/2. Use of this equation with the modified rectifier predicts that perceived contrast will decrease with increasing blur, particularly at low contrasts. Contrast-matching experiments supported this prediction. In addition, the model correctly predicts the perceived contrast of Gaussian edges modified either by spatial truncation or by the addition of a ramp.
Original languageEnglish
Publication statusUnpublished - 2004
EventMovements and moments in vision research. 8th Applied Vision Association Christmas Meeting - Aston University, Birmingham (UK)
Duration: 17 Dec 2003 → …

Other

OtherMovements and moments in vision research. 8th Applied Vision Association Christmas Meeting
CityAston University, Birmingham (UK)
Period17/12/03 → …

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Bibliographical note

Abstract published in Eighth Applied Vision Association Christmas Meeting, Perception, 33 (3), p.757, ISSN: 0001-4966.

Keywords

  • edge perception
  • perceived blur
  • edge profiles
  • perceived contrast of edges
  • luminance profile
  • half-wave
  • edge's 'signature'

Cite this

May, K. A., & Georgeson, M. A. (2004). Perceiving edge contrast. Movements and moments in vision research. 8th Applied Vision Association Christmas Meeting, Aston University, Birmingham (UK), .
May, Keith A. ; Georgeson, Mark A. / Perceiving edge contrast. Movements and moments in vision research. 8th Applied Vision Association Christmas Meeting, Aston University, Birmingham (UK), .
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}

May, KA & Georgeson, MA 2004, 'Perceiving edge contrast' Movements and moments in vision research. 8th Applied Vision Association Christmas Meeting, Aston University, Birmingham (UK), 17/12/03, .

Perceiving edge contrast. / May, Keith A.; Georgeson, Mark A.

2004. Movements and moments in vision research. 8th Applied Vision Association Christmas Meeting, Aston University, Birmingham (UK), .

Research output: Contribution to conferenceOther

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T1 - Perceiving edge contrast

AU - May, Keith A.

AU - Georgeson, Mark A.

N1 - Abstract published in Eighth Applied Vision Association Christmas Meeting, Perception, 33 (3), p.757, ISSN: 0001-4966.

PY - 2004

Y1 - 2004

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AB - We have shown previously that a template model for edge perception successfully predicts perceived blur for a variety of edge profiles (Georgeson, 2001 Journal of Vision 1 438a; Barbieri-Hesse and Georgeson, 2002 Perception 31 Supplement, 54). This study concerns the perceived contrast of edges. Our model spatially differentiates the luminance profile, half-wave rectifies this first derivative, and then differentiates again to create the edge's 'signature'. The spatial scale of the signature is evaluated by filtering it with a set of Gaussian derivative operators. This process finds the correlation between the signature and each operator kernel at each position. These kernels therefore act as templates, and the position and scale of the best-fitting template indicate the position and blur of the edge. Our previous finding, that reducing edge contrast reduces perceived blur, can be explained by replacing the half-wave rectifier with a smooth, biased rectifier function (May and Georgeson, 2003 Perception 32 388; May and Georgeson, 2003 Perception 32 Supplement, 46). With the half-wave rectifier, the peak template response R to a Gaussian edge with contrast C and scale s is given by: R=Cp-1/4s-3/2. Hence, edge contrast can be estimated from response magnitude and blur: C=Rp1/4s3/2. Use of this equation with the modified rectifier predicts that perceived contrast will decrease with increasing blur, particularly at low contrasts. Contrast-matching experiments supported this prediction. In addition, the model correctly predicts the perceived contrast of Gaussian edges modified either by spatial truncation or by the addition of a ramp.

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May KA, Georgeson MA. Perceiving edge contrast. 2004. Movements and moments in vision research. 8th Applied Vision Association Christmas Meeting, Aston University, Birmingham (UK), .