OSA's Digital Library

Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 17, Iss. 11 — Nov. 1, 2000
  • pp: 1952–1961

Shadow-invariant classification for scenes illuminated by daylight

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


JOSA A, Vol. 17, Issue 11, pp. 1952-1961 (2000)
http://dx.doi.org/10.1364/JOSAA.17.001952


View Full Text Article

Enhanced HTML    Acrobat PDF (288 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

A physics-based method for shadow compensation in scenes illuminated by daylight is proposed. If the daylight is represented by a simplified form of the blackbody law and the camera filters are of infinitely narrow bandwidth, the relationship between red/blue (rm) and green/blue (gm) ratios as the blackbody’s temperature changes is a simple power law where the exponent is independent of the surface reflectivity. When the CIE daylight model is used instead of the blackbody and finite bandwidths for the camera are assumed, it is shown that the power law still holds with a slight change to the exponent. This means that images can be transformed into a map of rm/gmA and then thresholded to yield a shadow-independent classification. Exponent A can be precalculated from the CIE daylight model and the camera filter characteristics. Results are shown for four outdoor images that contain sunny and shadowed parts with vegetation and background. It is shown that the gray-level distributions of the pixels in the transformed images are quite similar for a given component whether or not it is in shadow. The transformation leads to bimodal histograms from which thresholds can easily be selected to give good classifications.

© 2000 Optical Society of America

OCIS Codes
(100.0100) Image processing : Image processing
(150.2950) Machine vision : Illumination

History
Original Manuscript: November 23, 1999
Revised Manuscript: June 14, 2000
Manuscript Accepted: June 14, 2000
Published: November 1, 2000

Citation
John A. Marchant and Christine M. Onyango, "Shadow-invariant classification for scenes illuminated by daylight," J. Opt. Soc. Am. A 17, 1952-1961 (2000)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-17-11-1952

You do not have subscription access to this journal. Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

You do not have subscription access to this journal. Article level metrics are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited