| 摘要 |
An automatic method detects missing lines occurred in an image, thereby identifying possible internal problems in the scanner. The method comprises the following steps. First, from the image of a slanting line, the pixel having gray levels closest to the median value of the predetermined highest gray levels and set a fault tolerance value are identified. Then the pixel as (Xi,Yj). Then, the gray levels of the pixels on (Xi,Yj) and (Xi-1,Yj+1) are compared. If the gray-level difference between these two pixels is larger than the fault tolerance value, the occurrence of a missing line is determined. To determine the total number of missing lines on that row, the gray levels to check if (Xi-2,Yj+1)<=(Xi,Yj)<(Xi-1,Yj+1) are compared. If not, the shift index k is incremented by one repeatedly until the gray-level difference is correspondent to the predetermined comparison condition. However, if the gray-level difference between the pixels on (Xi,Yj) and (Xi-1,Yj+1) is smaller than the fault tolerance value, then it is determined that no missing line occurs on that row. During the comparison process, the number of missing lines will be incremented. If the total number of missing lines exceeds an allowable range, the optical scanner is not qualified.
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