FormFix v6.0 for .NET - Updated
Perform Drop-Out
Developer Guide > How To > Use FormFix > Perform Drop-Out

Drop-out is a process whereby the pre-printed content (template data) on an image is removed, leaving only the data that was added to a form (filled data). When filled and template data overlap, the filled data will be reconstructed as accurately as possible.

FormFix provides the capability to generate a clip of field in a filled form, and to optionally dropout the template from the image, leaving only the filled data in the resulting clip image.

The FormFix API also allows you to control whether the dropout process attempts to reconstruct areas of the filled image where the filled pixels overlapped with the template pixels. FormFix dropout requires that the image identification is known, and precise registration information can be provided; both of which are capabilities of FormFix’s identification processor.
There are alternates to using FormFix's drop-out algorithm, which are better in some cases.

Many forms processing applications achieve very good results using a drop-out bulb on each scanner. You must match the color of the bulb to the color of the form and you must be careful not to allow your user's to enter filled data using the drop-out color. Although the drop-out performance using this method is excellent, identification and registration can be quite difficult unless you can use a barcode or other technique for identification and some form of registration marks for registration. FormFix has functionality to help you register your images using registration marks.

Note: ScanFix has line removal, comb removal, and virtual bulb technology that you can use in place of FormFix's drop-out in some cases. Unlike using color drop-out bulbs on a scanner, you can select between ScanFix and FormFix on a field-by-field basis to get the best performance in every case.
The most common uses of ScanFix are to deskew images before identification and to remove noise on field clips before extracting data from them.

Because drop-out is an important part of forms processing, it's important to follow certain guidelines as described below.

Improving the Quality of Drop-Out

Drop-out problems are usually caused by poor registration, but some may also be due to distortion of the form.

If drop-out leaves pieces of the form across the entire page, the problem is probably poor registration. Please refer to the sections on identifying images for more information. If drop-out leaves pieces of the form in only one or a few areas, the problem is probably distortion of the images. In rare cases, a large difference between the thickness of lines in the filled image and the template image also contributes to dropout issues across the entire page.

When resolving distortion problems, the first thing to consider is the possibility that two separate revisions of the same form are being processed. Sometimes this can be caused by the creator of the form making a change without recording it, or the form's revision number having been changed. This can also be caused by differences in printers. The same form printed by separate printers can contain font changes that cause drop-out to fail. If this is the case, see the section on handling similar forms during identification for additional suggestions.

Possible Methods to Improve Drop-Out Performance

Alternatives

Form drop-out is very similar to the line removal, comb removal, and virtual bulb operations within ScanFix. In some cases, you will get better results by using those technologies.

Comb Removal in ScanFix - before and after images:

 

Before Comb Removal

 

After Comb Removal

 

See Also
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