Guehring, Jens 
  
Taking into account these results, we implemented our peak detection algorithm based on the detector of Blais and 
Rioux. After removing the effects of ambient lighting, the images are convolved by a fourth or eighth order linear filter: 
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We estimate the peak center position by linear interpolation at positions where a change in sign is encountered in the 
convolved image. This way, subpixel accuracy estimates for the peak center position are obtained. 
3.3.4 Correction for Reflectance Discontinuities 
Reflectance discontinuities on the object surface are a major source of errors for most 3-D sensors based on the 
evaluation of structured light patterns. In previous work, Curless and Levoy (Curless and Levoy, 1995) have introduced 
space-time analysis to address this problem for a laser stripe range finder. 
Implementing space-time analysis for a stripe projector, however, means to establish correspondences between camera 
coordinates and sub-stripe projector coordinates. In consequence, we would loose the direct link between different 
cameras seeing the same projector pattern. 
In contrast to laser stripe range finders, our system allows to acquire an “all-white” image of the work space. The 
information, gathered by this image and by a second image, containing only the effects of ambient lighting allows us to 
normalize the stripe images. This step considerably reduces the influence of reflectance discontinuities on the surface of 
the object. For example, Figure 8 shows the effects of a strong surface intensity variance on the result of phase and line 
shift processing. In this example, the word "Intensity" is printed in black letters onto a white, planar surface. As a result, 
phase shift processing obtains height variations of up to 800 um. Using line shift processing with intensity 
normalization, this can be reduced to 120 um. 
  
(a) (b) 
  
(c) (d) 
  
(e) (f) 
Figure 8. (a) Fully illuminated image. (b) Image without illumination by sensor. (c) Line shift image on a surface with 
high reflectance discontinuities. (d) Corrected line shift sequence. (e) Rendered view of the 3-D surface. The image 
coordinates have been obtained using phase shift processing. (f) Rendered view of the same extract using line shift 
processing. 
  
334 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000.