Shadow-invariant classification for scenes illuminated by daylight
JOSA A, Vol. 17, Issue 11, pp. 1952-1961 (2000)
http://dx.doi.org/10.1364/JOSAA.17.001952
Acrobat PDF (288 KB)
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
[Optical Society of America ]
OCIS Codes
(100.0100) Image processing : Image processing
(150.2950) Machine vision : Illumination
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. 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
Related Journal Articles 
- Separating the chaff from the wheat: possible origins of the oblique effect (JOSAA)
- Multiresolution spot detection by means of entropy thresholding (JOSAA)
- Quantum limits in the measurement of very small displacements in optical images (OL)
- Image processing with the radial Hilbert transform: theory and experiments (OL)
- Feature-specific structured imaging (AO)
Related Conference Papers
- Post-Coronagraph Wavefront Sensing Using Pupil Imaging and Phase-Diversity
- Joint Estimation of Amplitude and Phase from Phase-Diversity Data
- Compressive Imaging Using Random Active Illumination
- Locating Illumination Sources from Lighting on Planar Surfaces in Paintings: An Application to Georges de la Tour and Caravaggio
- Estimation of Illuminance Flow over Anisotropic Surfaces for Arbitrary Viewpoints
« Previous Article | Next Article »
OSA is a member of 