Reading checkboxes on a page may seem like the easiest of all types of recognition, but accurate OMR has many nuances both in recognition and in what to do with the recognition results.
Think about all the different kinds of forms that you have ever filled in and how you were asked to fill them in. In school you probably took standardized tests and filled in "bubbles" - small ovals next to the question. And you've probably gotten many opinion questionnaires with rectangular check boxes. Sometimes, of course, you are just given a circle to fill in. All of these can be read with OMR.
The tricky part of OMR is knowing whether the bubble or box or circle is actually filled in or not. Some form fillers may just draw a line across a series of boxes to indicate that they are selecting all boxes - but the line may wander in and out of individual boxes. Or a zealous form filler using bold check marks may draw the "tail" of the check right into an adjoining box. Good OMR recognition has to try to flag these situations as "uncertain" so that a user can decide what is happening.
When a user selects a response on an OMR form, the value associated with the box must be mapped to meaningful values. For the user responsible to verify the recognition results, the value may be the text corresponding on the form with each mark, or it may simply be the number of the box from one to the total number of possible responses. But the value that you may need to store into the target application may be entirely different. Make sure your OMR engine gives you separate display and export mapping!
Most multiple-choice fields only allow a single response. Some, however, allow you to select more than one valid response. These are known as "multi-punch" fields. With multi-punch the underlying recognition is exactly the same as for "single-punch", but the display and export mapping must be adjusted to provide multiple values for a single field.
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