Stability of the color-opponent signals under changes of illuminant in natural scenes

P. G. Lovell*, D. J. Tolhurst, C. A. Párraga, R. Baddeley, U. Leonards, J. Troscianko, T. Troscianko

*Corresponding author for this work

Research output: Contribution to journalArticle

49 Citations (Scopus)

Abstract

Illumination varies greatly both across parts of a natural scene and as a function of time, whereas the spectral reflectance function of surfaces remains more stable and is of much greater relevance when searching for specific targets. This study investigates the functional properties of postreceptoral opponent-channel responses, in particular regarding their stability against spatial and temporal variation in illumination. We studied images of natural scenes obtained in UK and Uganda with digital cameras calibrated to produce estimated L-, M-, and S-cone responses of trichromatic primates (human) and birds (starling). For both primates and birds we calculated luminance and red-green opponent (RG) responses. We also calculated a primate blue-yellow-opponent (BY) response. The BY response varies with changes in illumination, both across time and across the image, rendering this factor less invariant. The RG response is much more stable than the BY response across such changes in illumination for primates, less so for birds. These differences between species are due to the greater separation of bird L and M cones in wavelength and the narrower bandwidth of the cone action spectra. This greater separation also produces a larger chromatic signal for a given change in spectral reflectance. Thus bird vision seems to suffer a greater degree of spatiotemporal "clutter" than primate vision, but also enhances differences between targets and background. Therefore, there may be a trade-off between the degree of chromatic clutter in a visual system versus the degree of chromatic difference between a target and its background. Primate and bird visual systems have found different solutions to this trade-off.

Original languageEnglish
Pages (from-to)2060-2071
Number of pages12
JournalJournal of the Optical Society of America A: Optics and Image Science, and Vision
Volume22
Issue number10
DOIs
Publication statusPublished - 1 Jan 2005
Externally publishedYes

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primates
Birds
birds
Color
color
Lighting
Cones
illumination
cones
spectral reflectance
clutter
Uganda
Digital cameras
digital cameras
Primates
luminance
Luminance
Bandwidth
Wavelength
bandwidth

Cite this

Lovell, P. G. ; Tolhurst, D. J. ; Párraga, C. A. ; Baddeley, R. ; Leonards, U. ; Troscianko, J. ; Troscianko, T. / Stability of the color-opponent signals under changes of illuminant in natural scenes. In: Journal of the Optical Society of America A: Optics and Image Science, and Vision. 2005 ; Vol. 22, No. 10. pp. 2060-2071.
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Stability of the color-opponent signals under changes of illuminant in natural scenes. / Lovell, P. G.; Tolhurst, D. J.; Párraga, C. A.; Baddeley, R.; Leonards, U.; Troscianko, J.; Troscianko, T.

In: Journal of the Optical Society of America A: Optics and Image Science, and Vision, Vol. 22, No. 10, 01.01.2005, p. 2060-2071.

Research output: Contribution to journalArticle

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T1 - Stability of the color-opponent signals under changes of illuminant in natural scenes

AU - Lovell, P. G.

AU - Tolhurst, D. J.

AU - Párraga, C. A.

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AU - Leonards, U.

AU - Troscianko, J.

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AB - Illumination varies greatly both across parts of a natural scene and as a function of time, whereas the spectral reflectance function of surfaces remains more stable and is of much greater relevance when searching for specific targets. This study investigates the functional properties of postreceptoral opponent-channel responses, in particular regarding their stability against spatial and temporal variation in illumination. We studied images of natural scenes obtained in UK and Uganda with digital cameras calibrated to produce estimated L-, M-, and S-cone responses of trichromatic primates (human) and birds (starling). For both primates and birds we calculated luminance and red-green opponent (RG) responses. We also calculated a primate blue-yellow-opponent (BY) response. The BY response varies with changes in illumination, both across time and across the image, rendering this factor less invariant. The RG response is much more stable than the BY response across such changes in illumination for primates, less so for birds. These differences between species are due to the greater separation of bird L and M cones in wavelength and the narrower bandwidth of the cone action spectra. This greater separation also produces a larger chromatic signal for a given change in spectral reflectance. Thus bird vision seems to suffer a greater degree of spatiotemporal "clutter" than primate vision, but also enhances differences between targets and background. Therefore, there may be a trade-off between the degree of chromatic clutter in a visual system versus the degree of chromatic difference between a target and its background. Primate and bird visual systems have found different solutions to this trade-off.

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