Encoding information using disjoint highlight and shadow dot patterns

An apparatus comprising:

• a receiver to receive a set of greyscale source pixels corresponding to an image to be printed;
• a pattern generator to generate a first dot pattern of shadow dots and second dot pattern of highlight dots, the first dot pattern and second dot pattern comprising information to be encoded across the image;
• a pattern mapper to map the first dot pattern and the second dot pattern to a corresponding subset of the greyscale source pixels;
• a pixel modifier to modify a value of a greyscale pixel in the subset of the greyscale source pixels based on a predetermined threshold pixel value, wherein the value of the greyscale pixel is set to a highlight dot value in response to detecting that the predetermined threshold pixel value is exceeded or set to a shadow dot value in response to detecting that the predetermined threshold value is not exceeded;
• and
• a printer to print the image comprising the subset of pixels with modified values.

A non-transitory machine-readable storage medium encoded with instructions executable by a processor, the machine-readable storage medium comprising instructions to direct the processor to:

• receive a set of greyscale source pixels corresponding to an image to be printed;
• generate a first dot pattern of shadow dots and second dot pattern of highlight dots, the first dot pattern and second dot pattern comprising information to be encoded across the image;
• map the first dot pattern and the second dot pattern to a corresponding subset of the greyscale source pixels;
• modify a value of a greyscale pixel in the subset of the greyscale source pixels based on a predetermined threshold pixel value, wherein the value of the greyscale pixel is set to a highlight dot value in response to detecting that the predetermined threshold pixel value is exceeded or set to a shadow dot value in response to detecting that the predetermined threshold value is not exceeded;
• and
• print the image comprising the subset of pixels with modified values.