Document image thresholding using foreground and background clus

Details Document image thresholding using foreground and background clus Document image thresholding using foreground and background clus

1997-11-26

2000-03-28

Lee, Thomas D.

Image analysis

Image enhancement or restoration

Variable threshold, gain, or slice level

382272, 358464, 358466, G06K 938

Patent

active

060441798

ABSTRACT:
Document image thresholding using foreground and background is disclosed. A document (16) is scanned and a region (30) and a sub-region (32) of the document is selected. The intensity value of a pixel in the region is compared to an average intensity value of pixels in a foreground cluster and to an average intensity value of pixels in a background cluster (50). The pixel is assigned to the foreground cluster (53) if the intensity value of the pixel is closer to the average intensity of the foreground cluster, or to the background cluster (54) if the pixel intensity is closer to the average intensity value of the background cluster. A new average intensity value is calculated for the foreground cluster (55) and the background cluster (56). A new pixel is compared to the new average intensity values for the foreground and background clusters and the process is repeated until all pixels in the region have been compared (57). A threshold value is computed (62) based on a function of the average intensity value of pixels in the foreground and background cluster. Each pixel in the sub-region is then converted to a white pixel if the pixel intensity level is greater than the threshold value, or converted to a black pixel if the pixel intensity level is less than the threshold value (62).

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patent: 5583659 (1996-12-01), Lee et al.
patent: 5703971 (1997-12-01), Asimopoulos et al.
P.K. Sahoo, S. Soltani, A.K.C. Wong and Y. Chen, "A Survey of Thresholding Techniques," Computer Vision Graphics Image Processing, vol. 41, pp. 233-260, 1988.
P. Palumbo P. Swaninathan and S. Shrihari, "Document Image Binarization: Evaluation of Algorithms," SPIE Applications of Digital Image Processing IX, vol. 697, pp. 278-285, 1986.
J.S. Weszka, "A Survey of Threshold Selection Techniques," Computer Graphics Image Processing, vol. 7, pp. 259-265, 1978.

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