Patent ID: 8112339

Claim:
An optically imaging pen for interacting with a printed substrate, said printed substrate including human-readable content and a plurality of contiguous tags, each tag having a plurality of target elements, each tag containing coded data indicative of a substrate identity and of a tag location on the substrate, said pen comprising: a nib for interacting with the printed substrate; an image sensor for imaging an area of the printed substrate to provide image data; and a processor configured for: (i) identifying target elements in the image data and inferring a perspective transform using perspective distortion of the target elements due to a tilt of the pen; (ii) acquiring and decoding the coded data contained in the image data, the decoded coded data identifying the substrate identity and the tag location on the substrate; (iii) calculating a nib position using the tag location, the perspective transform and a known geometry of pen optics, said nib position being different than the tag location; and (iv) generating digital ink identifying the nib position and the substrate identity.