A SYSTEM OF THE SHADOW DETECTION AND SHADOW REMOVAL FOR HIGH 
RESOLUTION CITY AERIAL PHOTO 
a.c 
Yan Li*, Tadashi Sasagawa 5 Peng Gong * 
“International Institute for Earth System Science, Nanjing University, Nanjing, Jiangsu, 210093,P.R.C. liyan@nju.edu.cn 
?PASCO Corporation, 1-1-2 Higashiyama, Meguro-ku, Tokyo, 153-0043, Japan, tadashi sasagawa(a)pasco.co.jp 
“Center for Assessment and Monitoring of Forest and Environmental Resources (CAMFER), UC Berkeley, 151 Hilgard Hall, 
Berkeley, CA, 94720-3110,U.S.A. gong@neture.berkeley.edu 
KEY WORDS: Aerial, Ortholmage, High resolution, Surface, Integration, Photogrammetry, Extraction, Building 
ABSTRACT: 
This paper presents a methodology to automatically detect and remove the shadows in high-resolution urban aerial images for urban 
GIS applications. The system includes cast shadow computation, image shadow tracing and detection, and shadow removal. The cast 
shadow is computed from digital surface model (DSM) and the sun altitudes. Its projection in the pseudo orthogonal image is 
determined by ray tracing using ADS40 model, DSM and RGB image. In this step, all the cast shadows will be traced to determine if 
they are visible in the projection image. We used parameter plane transform (PPT) to accelerate the tracing speed. An iterative tracing 
scheme is proposed. Because of the under precision of the DSM, the fine shadow segmentation is taken on the base of the traced 
shadow. The DSM itself is short of the details, but the traced shadow gives the primarily correct location in the image. The statistics of 
the shadow area reflects the intensity distribution approximately. A reference segmentation threshold is obtained by the mean of the 
shadow area. In the fine segmentation, the segmentation threshold is derived from the histogram of the image and the reference 
threshold. The shadow removal includes shadow region and partner region labeling, the histogram processing, and intensity mapping. 
The adjacent shadows are labeled as a region. The corresponding bright region is selected and labeled as its partner. The bright region 
supplies the reference in the intensity mapping in the removal step. 
Key Words: Shadow Detection, Shadow Removal, Aerial, Photogrammetry 
1° INTRODUCTION to remove the shadows (Chen and Rau, 1993), (Zhou, Qin, 
Kauffmann, and Rand, 2003). A mathematical model was 
In image matching, change detection and other remote sensing — proposed in literature (Zhou, Qin, Kauffmann, and Rand, 2003) 
applications, cast shadows caused by buildings will interfere the ^ to detect the occlusion by visibility analysis and 
analysis and cause wrong results. The objective of our task is to photogrammetric engineering. When the building model is given 
detect the shadow area by image processing and itis projected to the image and the coordinates of the corners in 
photogrammetric engineering, and restore their color and the image are calculated. Shadow area is fulfilled by the same 
intensities. position of the slave image acquired in the meanwhile with the 
master one. Ray tracing is widely used in computer graphics as a 
Shadow removal is a critical problem in image processing. In kind of method to determine the intersection of a ray with a 3D 
some literatures, binocular image computations have been used surface. It is used in the visibility analysis to decide if the light 
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