| 摘要 |
A robust technique for determining whether a field (43, 45, 47a-d) on a form (40'), which has been converted to a binary input image, contains a mark utilizes an approach of making an initial determination of the approximate location of the field, and then refining such determination. The form is assumed to have registration marks (fiducials) with the field at a known location relative to the fiducials. The fiducials are identified (50), and the approximate location of the field is determined (55) from the fiducial positions and the known relation between the fiducials and the field. At this point, a portion of the image (referred to as the subimage) is extracted (57). The subimage is typically somewhat larger than the field so that it can be assumed that the field is within the subimage. The field has machine-printed lines along at least part of the field perimeter. In order to distinguish these lines from hand-printed marks in the field, a copy of the subimage is subjected to a set of operations (60) on the actual pixels in the subimage that provides nominal information on the location of these lines. The boundaries of the subimage are then changed (62) to nominally exclude the lines.
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