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Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 19, Iss. 5 — May. 1, 2002
  • pp: 840–848

Spectral invariance under daylight illumination changes

John A. Marchant and Christine M. Onyango  »View Author Affiliations


JOSA A, Vol. 19, Issue 5, pp. 840-848 (2002)
http://dx.doi.org/10.1364/JOSAA.19.000840


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Abstract

We develop a method for calculating invariant spectra of light reflected from surfaces under changing daylight illumination conditions. A necessary part of the method is representing the illuminant in a suitable form. We represent daylight by a function E(λ, T)=h(λ)exp[u(λ)f(T)], where λ is the wavelength, T is the color temperature, h(λ) and u(λ) are any functions of λ but not T, and f(T) is any function of T but not λ. We use an eigenvalue decomposition on the logarithm of the CIE daylight standard at various color temperatures to obtain the necessary functions and show that this gives an extremely good fit to CIE daylight over our experimental range. We obtain experimental data over the range 350–830 nm from a range of standard colored surfaces for 50 daylight conditions covering a wide range of illumination spectra. Despite a considerable variation in the spectra of the reflected light, we show only small variations when the transformation is used. We investigate the possible causes of the residual variation and conclude that using the above approximation to daylight is unlikely to be a major cause. Some variation is caused by local daylight conditions being different from the CIE standard and the rest by measurement and modeling errors.

© 2002 Optical Society of America

OCIS Codes
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(150.0150) Machine vision : Machine vision
(150.2950) Machine vision : Illumination
(330.1690) Vision, color, and visual optics : Color
(330.6180) Vision, color, and visual optics : Spectral discrimination

History
Original Manuscript: June 26, 2001
Revised Manuscript: October 12, 2001
Manuscript Accepted: October 15, 2001
Published: May 1, 2002

Citation
John A. Marchant and Christine M. Onyango, "Spectral invariance under daylight illumination changes," J. Opt. Soc. Am. A 19, 840-848 (2002)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-19-5-840

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