Abstract

Shadow is an inseparable aspect of all natural scenes. When there are multiple light sources or multiple reflections several different shadows may overlap at the same location and create complicated patterns. Shadows are a potentially good source of information about a scene if the shadow regions can be properly identified and segmented. However, shadow region identification and segmentation is a difficult task and improperly identified shadows often interfere with machine vision tasks like object recognition and tracking. We propose here a new shadow separation and contrast enhancement method based on the polarization of light. Polarization information of the scene captured by our polarization-sensitive camera is shown to separate shadows from different light sources effectively. Such shadow separation is almost impossible to realize with conventional, polarization-insensitive imaging.

© 2006 Optical Society of America

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2004

S. Nadimi and B. Bhanu, "Physical models for moving shadow and object detection in video," IEEE Trans. Pattern Anal. Mach. Intell. 26,1079-1087 (2004).
[CrossRef]

E. Salvador, A. Cavallaro, and T. Ebrahimi, "Cast shadow segmentation using invariant color features," Comput. Vis. Image Understand. 95,238-259 (2004).
[CrossRef]

S.-S. Lin, K. M. Yemelyanov, E. N. Jr. Pugh, and N. Engheta, "Polarization Enhanced Visual Surveillance Techniques," in Proc. IEEE Int. Conf. on Networking, Sensing and Control (IEEE Syst. Man..Cybern.Society, Taipei, Taiwan, 2004),  1, pp. 216-221.
[CrossRef]

2003

K. M. Yemelyanov, S.-S. Lin, W. Q. Luis, E. N. Jr. Pugh, and N. Engheta, "Bio-inspired display of polarization information using selected visual cues," in Polarization Science and Remote Sensing, J. A. Shaw and J. S. Tyo eds.Proc. SPIE,  5158,71-84 (2003).
[CrossRef]

K. M. Yemelyanov, M. A. Lo, E. N. Jr. Pugh, and N. Engheta, "Display of polarization information by coherently moving dots," Opt. Express 11,1577-1584 (2003).
[CrossRef] [PubMed]

R. Cucchiara, C. Grana, M. Piccardi, and A. Prati, "Detecting moving objects, Ghosts, and shadows in video streams," IEEE Trans. Pattern Anal. Mach. Intell. 25,1337-1342 (2003).
[CrossRef]

T. Gevers and H. Stokman, "Classifying color edges in video into shadow-geometry, highlight, or material transitions," IEEE Trans. Multimedia 5,237-243 (2003).
[CrossRef]

A. Prati, I. Mikic, M. M. Trivedi, and R. Cucchiara, "Detecting Moving Shadows: Algorithms and Evaluation," IEEE Trans. Pattern Anal. Mach. Intell. 25,918-923 (2003).
[CrossRef]

I. Sato, Y. Sato, and K. Ikeuchi, "Illumination from shadows," IEEE Trans. Pattern Anal. Mach. Intell. 25,290-300 (2003).
[CrossRef]

2001

M. W. Powell, S. Sarkar, and D. Goldgof, "A simple strategy for calibrating the geometry of light sources," IEEE Trans. Pattern Anal. Mach. Intell. 23,1022-1027 (2001).
[CrossRef]

2000

1999

J. Stauder, R. Melch, and J. Ostermann, "Detection of moving cast shadows for object segmentation," IEEE Trans. Multimedia 1,65-77 (1999).
[CrossRef]

1998

1996

1995

M. P. Rowe, E. N. Jr. Pugh, and N. Engheta, "Polarization-difference imaging: a biologically inspired technique for observation through scattering media," Opt. Lett. 20,608-610 (1995).
[CrossRef] [PubMed]

G. Horváth, "Reflection polarization patterns at flat water surfaces and their relevance for insect polarization vision," J. Theor. Biol. 175,27-37 (1995).
[CrossRef] [PubMed]

1994

C. Jiang and M. O. Ward, "Shadow segmentation and classification in a constrained environment," CVGIP: Image Understanding 59,213-225 (1994).
[CrossRef]

1993

D. Koller, K. Danilidis, and H.-H. Nagel, "Model-based object tracking in monocular image sequences of road traffic scenes," Int. J. Comput. Vis. 10,257-281 (1993).
[CrossRef]

1991

Y. Liow and T. Pavlidis, "Use of shadows for extracting buildings in aerial images," Comput. Vis. Graph. Image Process. 49,242-277 (1991).
[CrossRef]

C. Wang, L. Huang, and A. Rosenfeld, "Detecting clouds and cloud shadows on aerial photographs," Pattern. Recogn. Lett. 12,55-64 (1991).
[CrossRef]

1989

R. Irvin and D. Mckeown, "Methods for exploiting the relationship between buildings and their shadows in aerial imagery," IEEE Trans. on Syst. Man.Cybern. 19,1564-1575 (1989).
[CrossRef]

1986

1983

R. Schwind, "Zonation of the optical environment and zonation in the rhabdom structure within the eye of the backswimmer, Notenecta glauca," Cell and Tissue Research 232,53-63 (1983).
[CrossRef] [PubMed]

1982

1979

M. Nagao, T. Matsutyama, and Y. Ikeda, "Region extraction and shape analysis in aerial photographs," Comput. Vis. Graph. Image Process. 10,195-223 (1979).
[CrossRef]

1976

R. Wehner, "Polarized-light navigation by insects," Scientific American 235,106-114 (1976).
[CrossRef] [PubMed]

1949

K. Frisch, "Die polarisation des himmelslichtes als orientierender faktor bei den tanzen der bienen," Experientia 5,142-148 (1949).
[CrossRef] [PubMed]

Bhanu, B.

S. Nadimi and B. Bhanu, "Physical models for moving shadow and object detection in video," IEEE Trans. Pattern Anal. Mach. Intell. 26,1079-1087 (2004).
[CrossRef]

Cavallaro, A.

E. Salvador, A. Cavallaro, and T. Ebrahimi, "Cast shadow segmentation using invariant color features," Comput. Vis. Image Understand. 95,238-259 (2004).
[CrossRef]

Cucchiara, R.

A. Prati, I. Mikic, M. M. Trivedi, and R. Cucchiara, "Detecting Moving Shadows: Algorithms and Evaluation," IEEE Trans. Pattern Anal. Mach. Intell. 25,918-923 (2003).
[CrossRef]

R. Cucchiara, C. Grana, M. Piccardi, and A. Prati, "Detecting moving objects, Ghosts, and shadows in video streams," IEEE Trans. Pattern Anal. Mach. Intell. 25,1337-1342 (2003).
[CrossRef]

Danilidis, K.

D. Koller, K. Danilidis, and H.-H. Nagel, "Model-based object tracking in monocular image sequences of road traffic scenes," Int. J. Comput. Vis. 10,257-281 (1993).
[CrossRef]

Ebrahimi, T.

E. Salvador, A. Cavallaro, and T. Ebrahimi, "Cast shadow segmentation using invariant color features," Comput. Vis. Image Understand. 95,238-259 (2004).
[CrossRef]

Frisch, K.

K. Frisch, "Die polarisation des himmelslichtes als orientierender faktor bei den tanzen der bienen," Experientia 5,142-148 (1949).
[CrossRef] [PubMed]

Gershon, R.

Gevers, T.

T. Gevers and H. Stokman, "Classifying color edges in video into shadow-geometry, highlight, or material transitions," IEEE Trans. Multimedia 5,237-243 (2003).
[CrossRef]

Goldgof, D.

M. W. Powell, S. Sarkar, and D. Goldgof, "A simple strategy for calibrating the geometry of light sources," IEEE Trans. Pattern Anal. Mach. Intell. 23,1022-1027 (2001).
[CrossRef]

Grana, C.

R. Cucchiara, C. Grana, M. Piccardi, and A. Prati, "Detecting moving objects, Ghosts, and shadows in video streams," IEEE Trans. Pattern Anal. Mach. Intell. 25,1337-1342 (2003).
[CrossRef]

Horváth, G.

G. Horváth, "Reflection polarization patterns at flat water surfaces and their relevance for insect polarization vision," J. Theor. Biol. 175,27-37 (1995).
[CrossRef] [PubMed]

Huang, L.

C. Wang, L. Huang, and A. Rosenfeld, "Detecting clouds and cloud shadows on aerial photographs," Pattern. Recogn. Lett. 12,55-64 (1991).
[CrossRef]

Ikeda, Y.

M. Nagao, T. Matsutyama, and Y. Ikeda, "Region extraction and shape analysis in aerial photographs," Comput. Vis. Graph. Image Process. 10,195-223 (1979).
[CrossRef]

Ikeuchi, K.

I. Sato, Y. Sato, and K. Ikeuchi, "Illumination from shadows," IEEE Trans. Pattern Anal. Mach. Intell. 25,290-300 (2003).
[CrossRef]

Irvin, R.

R. Irvin and D. Mckeown, "Methods for exploiting the relationship between buildings and their shadows in aerial imagery," IEEE Trans. on Syst. Man.Cybern. 19,1564-1575 (1989).
[CrossRef]

Jepson, A. D.

Jiang, C.

C. Jiang and M. O. Ward, "Shadow segmentation and classification in a constrained environment," CVGIP: Image Understanding 59,213-225 (1994).
[CrossRef]

Jr, E. N.

S.-S. Lin, K. M. Yemelyanov, E. N. Jr. Pugh, and N. Engheta, "Polarization Enhanced Visual Surveillance Techniques," in Proc. IEEE Int. Conf. on Networking, Sensing and Control (IEEE Syst. Man..Cybern.Society, Taipei, Taiwan, 2004),  1, pp. 216-221.
[CrossRef]

K. M. Yemelyanov, S.-S. Lin, W. Q. Luis, E. N. Jr. Pugh, and N. Engheta, "Bio-inspired display of polarization information using selected visual cues," in Polarization Science and Remote Sensing, J. A. Shaw and J. S. Tyo eds.Proc. SPIE,  5158,71-84 (2003).
[CrossRef]

K. M. Yemelyanov, M. A. Lo, E. N. Jr. Pugh, and N. Engheta, "Display of polarization information by coherently moving dots," Opt. Express 11,1577-1584 (2003).
[CrossRef] [PubMed]

J. S. Tyo, E. N. Jr. Pugh, and N. Engheta, "Colorimetric representation for use with polarization-difference imaging of objects in scattering media," J. Opt. Soc. Am. A 15,367-374 (1998).
[CrossRef]

J. S. Tyo, M. P. Rowe, E. N. Jr. Pugh, and N. Engheta, "Target detection in optically scatter media by polarization-difference imaging," Appl. Opt. 35,1855-1870 (1996).
[CrossRef] [PubMed]

M. P. Rowe, E. N. Jr. Pugh, and N. Engheta, "Polarization-difference imaging: a biologically inspired technique for observation through scattering media," Opt. Lett. 20,608-610 (1995).
[CrossRef] [PubMed]

K. M. Yemelyanov, S.-S. Lin, E. N. Jr. Pugh, and N. Engheta, "Adaptive Algorithms for 2-channel polarization sensing under various polarization statistics with non-uniform distributions," Appl. Opt. (to be published).
[PubMed]

S.-S. Lin, K. M. Yemelyanov, E. N. Jr. Pugh, and N. Engheta, "Polarization- and specular-reflection-based, non-contact latent fingerprint imaging and lifting," J. Opt. Soc. Am. A (to be published).

Koller, D.

D. Koller, K. Danilidis, and H.-H. Nagel, "Model-based object tracking in monocular image sequences of road traffic scenes," Int. J. Comput. Vis. 10,257-281 (1993).
[CrossRef]

Lin, S.-S.

S.-S. Lin, K. M. Yemelyanov, E. N. Jr. Pugh, and N. Engheta, "Polarization Enhanced Visual Surveillance Techniques," in Proc. IEEE Int. Conf. on Networking, Sensing and Control (IEEE Syst. Man..Cybern.Society, Taipei, Taiwan, 2004),  1, pp. 216-221.
[CrossRef]

K. M. Yemelyanov, S.-S. Lin, W. Q. Luis, E. N. Jr. Pugh, and N. Engheta, "Bio-inspired display of polarization information using selected visual cues," in Polarization Science and Remote Sensing, J. A. Shaw and J. S. Tyo eds.Proc. SPIE,  5158,71-84 (2003).
[CrossRef]

K. M. Yemelyanov, S.-S. Lin, E. N. Jr. Pugh, and N. Engheta, "Adaptive Algorithms for 2-channel polarization sensing under various polarization statistics with non-uniform distributions," Appl. Opt. (to be published).
[PubMed]

S.-S. Lin, K. M. Yemelyanov, E. N. Jr. Pugh, and N. Engheta, "Polarization- and specular-reflection-based, non-contact latent fingerprint imaging and lifting," J. Opt. Soc. Am. A (to be published).

Liow, Y.

Y. Liow and T. Pavlidis, "Use of shadows for extracting buildings in aerial images," Comput. Vis. Graph. Image Process. 49,242-277 (1991).
[CrossRef]

Lo, M. A.

Luis, W. Q.

K. M. Yemelyanov, S.-S. Lin, W. Q. Luis, E. N. Jr. Pugh, and N. Engheta, "Bio-inspired display of polarization information using selected visual cues," in Polarization Science and Remote Sensing, J. A. Shaw and J. S. Tyo eds.Proc. SPIE,  5158,71-84 (2003).
[CrossRef]

Marchant, J. A.

Matsutyama, T.

M. Nagao, T. Matsutyama, and Y. Ikeda, "Region extraction and shape analysis in aerial photographs," Comput. Vis. Graph. Image Process. 10,195-223 (1979).
[CrossRef]

Mckeown, D.

R. Irvin and D. Mckeown, "Methods for exploiting the relationship between buildings and their shadows in aerial imagery," IEEE Trans. on Syst. Man.Cybern. 19,1564-1575 (1989).
[CrossRef]

Melch, R.

J. Stauder, R. Melch, and J. Ostermann, "Detection of moving cast shadows for object segmentation," IEEE Trans. Multimedia 1,65-77 (1999).
[CrossRef]

Mikic, I.

A. Prati, I. Mikic, M. M. Trivedi, and R. Cucchiara, "Detecting Moving Shadows: Algorithms and Evaluation," IEEE Trans. Pattern Anal. Mach. Intell. 25,918-923 (2003).
[CrossRef]

Nadimi, S.

S. Nadimi and B. Bhanu, "Physical models for moving shadow and object detection in video," IEEE Trans. Pattern Anal. Mach. Intell. 26,1079-1087 (2004).
[CrossRef]

Nagao, M.

M. Nagao, T. Matsutyama, and Y. Ikeda, "Region extraction and shape analysis in aerial photographs," Comput. Vis. Graph. Image Process. 10,195-223 (1979).
[CrossRef]

Nagel, H.-H.

D. Koller, K. Danilidis, and H.-H. Nagel, "Model-based object tracking in monocular image sequences of road traffic scenes," Int. J. Comput. Vis. 10,257-281 (1993).
[CrossRef]

Onyango, C. M.

Ostermann, J.

J. Stauder, R. Melch, and J. Ostermann, "Detection of moving cast shadows for object segmentation," IEEE Trans. Multimedia 1,65-77 (1999).
[CrossRef]

Pavlidis, T.

Y. Liow and T. Pavlidis, "Use of shadows for extracting buildings in aerial images," Comput. Vis. Graph. Image Process. 49,242-277 (1991).
[CrossRef]

Pentland, A. P.

Piccardi, M.

R. Cucchiara, C. Grana, M. Piccardi, and A. Prati, "Detecting moving objects, Ghosts, and shadows in video streams," IEEE Trans. Pattern Anal. Mach. Intell. 25,1337-1342 (2003).
[CrossRef]

Powell, M. W.

M. W. Powell, S. Sarkar, and D. Goldgof, "A simple strategy for calibrating the geometry of light sources," IEEE Trans. Pattern Anal. Mach. Intell. 23,1022-1027 (2001).
[CrossRef]

Prati, A.

R. Cucchiara, C. Grana, M. Piccardi, and A. Prati, "Detecting moving objects, Ghosts, and shadows in video streams," IEEE Trans. Pattern Anal. Mach. Intell. 25,1337-1342 (2003).
[CrossRef]

A. Prati, I. Mikic, M. M. Trivedi, and R. Cucchiara, "Detecting Moving Shadows: Algorithms and Evaluation," IEEE Trans. Pattern Anal. Mach. Intell. 25,918-923 (2003).
[CrossRef]

Rosenfeld, A.

C. Wang, L. Huang, and A. Rosenfeld, "Detecting clouds and cloud shadows on aerial photographs," Pattern. Recogn. Lett. 12,55-64 (1991).
[CrossRef]

Rowe, M. P.

Salvador, E.

E. Salvador, A. Cavallaro, and T. Ebrahimi, "Cast shadow segmentation using invariant color features," Comput. Vis. Image Understand. 95,238-259 (2004).
[CrossRef]

Sarkar, S.

M. W. Powell, S. Sarkar, and D. Goldgof, "A simple strategy for calibrating the geometry of light sources," IEEE Trans. Pattern Anal. Mach. Intell. 23,1022-1027 (2001).
[CrossRef]

Sato, I.

I. Sato, Y. Sato, and K. Ikeuchi, "Illumination from shadows," IEEE Trans. Pattern Anal. Mach. Intell. 25,290-300 (2003).
[CrossRef]

Sato, Y.

I. Sato, Y. Sato, and K. Ikeuchi, "Illumination from shadows," IEEE Trans. Pattern Anal. Mach. Intell. 25,290-300 (2003).
[CrossRef]

Schwind, R.

R. Schwind, "Zonation of the optical environment and zonation in the rhabdom structure within the eye of the backswimmer, Notenecta glauca," Cell and Tissue Research 232,53-63 (1983).
[CrossRef] [PubMed]

Stauder, J.

J. Stauder, R. Melch, and J. Ostermann, "Detection of moving cast shadows for object segmentation," IEEE Trans. Multimedia 1,65-77 (1999).
[CrossRef]

Stokman, H.

T. Gevers and H. Stokman, "Classifying color edges in video into shadow-geometry, highlight, or material transitions," IEEE Trans. Multimedia 5,237-243 (2003).
[CrossRef]

Trivedi, M. M.

A. Prati, I. Mikic, M. M. Trivedi, and R. Cucchiara, "Detecting Moving Shadows: Algorithms and Evaluation," IEEE Trans. Pattern Anal. Mach. Intell. 25,918-923 (2003).
[CrossRef]

Tsotsos, J. K.

Tyo, J. S.

Wang, C.

C. Wang, L. Huang, and A. Rosenfeld, "Detecting clouds and cloud shadows on aerial photographs," Pattern. Recogn. Lett. 12,55-64 (1991).
[CrossRef]

Ward, M. O.

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Figures (6)

Fig. 1.
Fig. 1.

(a) General macroscopic reflection model (b) Polarization of light resulting from specular reflection from a dielectric surface.

Fig. 2.
Fig. 2.

Left: “Intensity-only” image of an outdoor scene with light and shadow. Right: “Degree-of-polarization” image of the same scene; this image plots the quantity p = IA/IU [see Eq. (2)], extracted for each image pixel. Hidden patterns of shadows within shadows are clearly visible in high contrast. The glass-walled building is shown in Fig. 4. The yellow circle points out the same sewage drain cover that is visible in all related pictures up to Fig. 4 except Fig. 4 Left to help orientation.

Fig. 3.
Fig. 3.

Images in Fig. 2 are contrast-enhanced by linear intensity range stretch followed by gamma correction of 0.5 to show the details in the dark area. Left: intensity image. Right: degree of polarization image. It is clear that the pattern revealed in the polarization image is not present in the intensity image even after contrast enhancement. The yellow circle points out the same sewage drain cover that is visible in all related pictures up to Fig. 4 except Fig. 4 Left to help orientation.

Fig. 4.
Fig. 4.

(Pictures shown in this figure are all regular intensity images with no polarization information) Left: the glass-wall building showing big glass rectangles and frames. Right: A picture of the same walk way as in Fig. 2 and Fig. 3 taken another day when the direct sun light is blocked due to nearby construction scaffolding. The shadow pattern cast on the walk way by the glass-wall and frames is visible. The yellow circle in the Right picture points out the same sewer drain cover as seen in Fig. 2 and Fig. 3. The left and right pictures in this figure can be related by the same glass door bracketed by the overlaid green rectangle. Note that pictures in Fig. 4 are taken with the camera at about the same position and general view direction as when taking pictures in Fig. 2 and Fig. 3. The only difference is that in Fig. 4 the camera zooms out and points more upward in order to put the tall glass-walled building into view.

Fig. 5.
Fig. 5.

Controlled lab experiment of complex overlapping shadow: (a) Overview of the experiment setup. A metal pillar on a optical table illuminated by a strong incandescent light from the side opposite to the camera, while another much weaker fluorescent light illuminating from the right hand side of the picture. The polarization of the observed reflection from the side illuminating fluorescent light is weaker because they are all diffusely scattered reflection, as opposed to the mostly Fresnel reflection [34] coming from the incandescent light shining directly opposing the view of the camera. (b) Intensity-only image. (c) Degree-of-polarization image.

Fig. 6.
Fig. 6.

Left: Segmentation results from region-growing analysis (starting with the entire image divided into 2x2 regions and with adjacent similar regions merging in each iteration) of Fig. 5 (c) into 21 regions. Right: Hidden shadow area extracted from Fig. 5 (c). Note that this pattern is only a portion of a larger shadow of the metal pillar cast by the source at right, and that this larger shadow is partially obscured by both the small knob and the shadow of the small knob cast by the source opposing the camera.

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

I ( φ ) = I U + I A cos [ 2 ( θ φ ) ] = I U { 1 + p cos [ 2 ( θ φ ) ] } ,
I U = ( I 0 + I 90 ) / 2
I A = ( I 45 I U ) 2 + ( I 90 I U ) 2
θ = arctan [ ( I 45 I U ) / ( I 90 I U ) ] / 2 .

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