The patch code was originally created by Kodak to signal document processing applications while reading large documents. The different codes will signal certain events such as a page/section break or a change from single sided to duplex scanning. Six distinct barcode patterns (Patch 1, 2, 3, 4, 6 and T) were defined. A common use now is to use the Patch T code or the Patch 2 code as a Page (document) separator.
Note that no data is encoded in a patch code. Similarly although there may be 4 identical patch codes on a page (one in each orientation) patch code readers (hardware or software) would only ever return one.
It is also possible to add conventional barcodes (typically Code 39) to a sheet to, for example, indicate the document type.
It is possible to incorporate a patch code into a form (typically a Patch 2 code on the first page of the form), to indicate a new file should be started for each form.
The exact action taken on recognising a patch code will depend upon the system and software used, and may be configurable in a given application.
Typically patch Type 2 is used for Document Separation, Type 3 for Batch Separation and Type T can be used for either Document or Batch Separation.
Patch types 1, 4 and 6 are not used for document separation but to enable other features such as colour or multifeed detection.
Download and print patches-for-printing-on-A4-paper.pdf (for A4 size paper)
Download and print patches-for-printing-on-US-Letter-paper.pdf (for US Letter size paper)
Patch code T is often used as a separator page between different documents when scanning.
Patch Codes are wide/narrow 1D barcodes (as are Code 39 barcodes, for example).
Patch Codes are best printed in black on white paper, however you can use light pastel coloured paper to make patch pages more visible to operators.
Thanks to Kodak for this further technical information about patch-codes.