Shading Correction of Camera Captured Document Image with Depth Map Information

摘要

Camera modules have become more popular in consumer electronics and office products. As a consequence, people have many opportunities to use a camera-based device to record a hardcopy document in their daily lives. However, it is easy to let undesired shading into the captured document image through the camera. Sometimes, this non-uniformity may degrade the readability of the contents. In order to mitigate this artifact, some solutions have been developed. But most of them are only suitable for particular types of documents. In this paper, we introduce a content-independent and shape-independent method that will lessen the shading effects in captured document images. We want to reconstruct the image such that the result will look like a document image captured under a uniform lighting source. Our method utilizes the 3D depth map of the document surface and a look-up table strategy. We will first discuss the model and the assumptions that we used for the approach. Then, the process of creating and utilizing the look-up table will be described in the paper. We implement this algorithm with our prototype 3D scanner, which also uses a camera module to capture a 2D image of the object. Some experimental results will be presented to show the effectiveness of our method. Both flat and curved surface document examples will be included.