Form Recognition Settings

FormReturn's default recognition settings will usually be correct for detecting checkbox marks on scanned images. The 'Recognition Panel' at the left of the Recognition Preview screen, is used for modifying the recognition settings.

recognition settings panel

Recognition Panel showing Default Recognition Settings

What Recognition Settings are Used for.

Recognition Settings are used by FormReturn's processor to determine which checkboxes on the scanned forms contain response marks.

The default recognition settings will most often be the correct settings for determining which checkboxes contain marks. Sometimes the settings must be changed if the scanned forms don't produce accurate results. A Recognition Test Preview tests the scanned template.

Mark Detection.

Mark Detected

Detected marks are determined by the difference between the black pixel count and the white pixel count, detected in each checkbox of a fragment.


Silhouettes shows the calculated pixel count and threshold.

FormReturn detects the number of white and black pixels contained inside each checkbox, this includes the dark borders, as well as any stray marks that run outside the checkbox borders, as far as the fragment edges.

If checkbox marks aren't accurately detected on the scanned form images, the Mark Threshold and Luminance settings can be changed. Any changes you make to the Recognition Settings will be saved to the published form template and used when processing of the scanned forms.


The Luminance setting only affects images that have been scanned in color, usually because the respondents used pencil to mark in the checkboxes. The luminance setting (default 200) is used as the cut off point at which the pixels in checkboxes are determined as black or white. Some shades of grey, for instance in a pencil mark, could be determined as either black or white, depending on the quality of the scanned image. If too much of the checkbox mark is determined as white, the black pixel count won't be high enough, for the black to be detected using the mark threshold setting of 40.

Note: Increasing the luminance setting too high can cause little black dots to appear on the scanned image which could cause checkboxes that weren't marked to be detected as marked.

Ideally the Luminance setting can be set anywhere between 100 and 220, but this will depend on the quality of the images your scanner produces.


Mark Threshold

The default Mark Threshold is set at 40, FormReturn will detect checkboxes as marked if the black pixel count is over 40% of the total pixels count.

The percentage that the Mark Threshold is set at is used by the form processor to detect the marked checkbox or checkboxes. The default threshold is 40% which means any checkbox with a count of 40% more black pixels than the white pixels, will be detected as a marked checkbox.

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Click on a checkbox in the Test Preview, to open the Mark Detection Details dialog. Here you can see the percentages of the pixel counts in each checkbox. You can see the Threshold percentage of the marked checkbox is way above the default mark threshold setting and the unmarked checkboxes are a long way under the default mark threshold setting.

Fragment Padding

The Fragment padding is the white area between the checkbox borders and the red detected Fragment border. The reason for having a padding around the checkboxes is to stop checkbox mark areas from coming in contact with each other and to detect checkbox shading that might go outside the checkbox edges.

fragment padding

Increasing the Fragment Padding setting, increases the amount of white area around the checkboxes.

The advantage of increasing the Fragment Padding, is if the scanned image quality isn't very good it improves detection because more of the Fragment area is captured in the data capture process.

The disadvantage of increasing the Fragment Padding is that it takes up more room on the form. If any other areas on the form touch or overlap the edges of the Fragment area, the risk is taken that the detection of the boxes could be broken.

Deskew Threshold

It is highly recommended that the automatic Perform Deskew box is left checked, unless you are completely sure your images were scanned in straight. Keeping the Perform Deskew box checked, will automatically perform a Deskew if the scans are more than 5% skewed. The setting determines the angle at which FormReturn will perform the deskew of a scanned image.

deskew threshold

The Deskew Threshold setting indicates the angle at which an automatic deskew will be performed.


*In the Recognition Test Preview, the Skew of the scanned Image is detected and is shown in degrees. * 0.24 deg skew

The form was scanned in on a slight angle which isn't enough for an auto deskew to be performed as it isn't enough to cause detection or recognition problems.

As of version 1.1 which was released in June 2010, FormReturn's recognition settings will detect either:

  • Single checkboxes
  • Multiple checkboxes with complete checkbox selection.

The new detection algorithm is very robust, which means heavy lines and borders added near the mark areas won't affect the detection of response data during the data capture process.