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MACHINE READABLE DOCUMENTS AND READING METHODS

  • US 20090103803A1
  • Filed: 09/22/2008
  • Published: 04/23/2009
  • Est. Priority Date: 10/22/2007
  • Status: Active Grant
First Claim
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1. A method of independently encoding an image with two information channels, comprising:

  • generating an image which encodes a primary information channel, the image comprising image portions, wherein the image portions are generated as an image portion with brightness above a first threshold, or as an image portion with brightness below a second threshold, the brightness levels encoding the primary information channel; and

    modifying the image to encode a secondary information channel, wherein the image modification is applied to at least some of the image portions and comprises applying one of two image output values to the image portion, wherein the brightness of a modified image portion is not changed such as to cross the first or second thresholds, wherein the image output values are used to encode the secondary information channel.

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