QAID # 115 Published
Question / Problem:
Are there any tips to get better OMR results for checkboxes?
Answer / Solution:
What follows is an overview.
Complete information is contained in the online help for the Kofax Capture Administration module.
- A pixel count threshold is an OMR configuration option in Admin. If the percentage of black pixels (compared to total pixels) is above the limit you specify, then the zone returns a "1." Otherwise, it returns a "0." The default threshold value is 25.
- Because the "success" of the zone relies on comparing the "black" to "white" area, it is important to keep all of your OMR zones roughly equal in size. A larger zone, especially one that is much larger than your shape, will tend to have less black filled in as compared to the total (and thus require a lower threshold). A small zone that is drawn tightly around the shape will have much of the region filled in with black, even when not "marked." In this case, a higher threshold is required to only allow the truly marked zones to produce 1's.
- The perfect zone size (at least from our testing) seems to be a zone that is slightly larger than the main shape or checkbox. There should be enough white space around the shape so that you don't "lose" part of the shape if the scanned image is stretched and isn't registered exactly right. Conversely, don't draw your zone so big that registration deviations might cause that zone to accidentally include other OMR shapes or text.
- You may not be able to draw all your zones at the same size. In this case, you will probably need to create different recognition profiles (with different OMR thresholds) based on the different sizes of zones.
- Your accuracy may be improved by using horizontal and vertical line removal to completely eliminate square OMR shapes (like the checkbox border) from the zone in question. This makes it much easier to set a threshold that works consistently.