Tan Chew Lim, Zhang Li, Zhang Zheng, Xia Tao
School of Computing, National University of Singapore 3, Science Drive 2, Singapore.
IEEE Trans Pattern Anal Mach Intell. 2006 Feb;28(2):195-208. doi: 10.1109/TPAMI.2006.40.
Scanning a document page from a thick bound volume often results in two kinds of distortions in the scanned image, i.e., shade along the "spine" of the book and warping in the shade area. In this paper, we propose an efficient restoration method based on the discovery of the 3D shape of a book surface from the shading information in a scanned document image. From a technical point of view, this shape from shading (SFS) problem in real-world environments is characterized by 1) a proximal and moving light source, 2) Lambertian reflection, 3) nonuniform albedo distribution, and 4) document skew. Taking all these factors into account, we first build practical models (consisting of a 3D geometric model and a 3D optical model) for the practical scanning conditions to reconstruct the 3D shape of the book surface. We next restore the scanned document image using this shape based on deshading and dewarping models. Finally, we evaluate the restoration results by comparing our estimated surface shape with the real shape as well as the OCR performance on original and restored document images. The results show that the geometric and photometric distortions are mostly removed and the OCR results are improved markedly.
从一本装订厚实的书籍中扫描文档页面，扫描图像通常会出现两种失真情况，即沿书籍“书脊”的阴影以及阴影区域的扭曲。在本文中，我们提出了一种基于从扫描文档图像中的阴影信息发现书籍表面三维形状的高效恢复方法。从技术角度来看，现实环境中的这种从阴影恢复形状（SFS）问题具有以下特点：1）近距且移动的光源，2）朗伯反射，3）非均匀反照率分布，4）文档倾斜。考虑到所有这些因素，我们首先针对实际扫描条件构建实用模型（由三维几何模型和三维光学模型组成），以重建书籍表面的三维形状。接下来，我们基于去阴影和去扭曲模型，利用此形状恢复扫描的文档图像。最后，我们通过将估计的表面形状与真实形状进行比较，以及对比原始文档图像和恢复后的文档图像上的光学字符识别（OCR）性能，来评估恢复结果。结果表明，几何和光度失真大多被消除，OCR结果显著改善。
