Accuracy Improvement and Objective Evaluation of Annotation Extraction from Printed Documents

There is an approach of annotation extraction from printed documents in which annotations are extracted by comparing the image of an annotated document and its original document image. In one of the previous methods, the image of an original document is actually printed and scanned in order to reproduce image degradations of the image of the annotated document. However such a method lacks convenience since users have to use the same printer and scanner to obtain images of an annotated document and its original document. In this paper, we propose an improved annotation extraction method in which the image degradations are compensated by image processing. In the proposed method, the difference between original and annotated document images due to image degradations is reduced by not only removal of the degradations in the annotated document images but also reproduction of the degradations in the original document images. The proposed method consists of three steps of processing which are for dithering, for color change, and for local displacement. We also propose an objective evaluation of extracted annotations to compare the experimental results accurately. Experimental results of the proposed method have shown that the recall of extracted annotations was 80.94% and the precision was 85.59%.