True orthophoto generation of built-up areas using multi-view images

Hidden areas and shadow effects are major causes of information loss in large-scale aerial photos of built-up areas. Both types of loss severely degrade the interpretability of orthophotos. An abrupt change of surface height is the primary cause of these defects. Thus, surface discontinuities, the orientation parameters of the sensors, and solar orientation are all key factors in determining the extent of defects. We thus propose an ortho-rectification scheme, which will compensate for hidden areas and shadow effects in built-up areas, by using multi-view images. The proposed scheme utilizes projection geometry to detect hidden and shadowed areas. For hidden areas, lost information is recovered from corresponding images. A seamless mosaic technique, utilizing gray-value balance, is suggested to reduce gray value discontinuity. For shadowed areas, dimmed features are enhanced using the local histogram matching method to improve image interpretability. Experimental results indicate that the proposed scheme can significantly reduce hidden and shadow defects. Both radiometric and geometric aspects of the proposed product and process are investigated.