Camera-based handwriting tracking

A writing implement touching detector system, comprising:

• a single image acquisition device, capable of being moved to a plurality of different locations relative to a writing implement, and producing an output indicative of a scene imaged by the single image acquisition device;
• and
• a processor, responsive to said output from the single image acquisition device, and operating to detect when a writing implement that is in the scene and unconnected to said image acquisition device is touching an associated writing surface, and when said writing implement is not touching the writing surface based on only the output of the single image acquisition device, by obtaining a probability that the writing implement is touching or not touching based on clues about the environment, and using a best estimate probability to determine the likelihood whether the writing implement is touching;
• wherein said clues include shadows of the implement and ink being present near the implement tip.

A method of determining a position of a writing implement relative to a writing surface, comprising:

• obtaining signal from a single image acquisition device, which can be oriented in any of a plurality of different orientations relative to the writing implement, indicative of a scene of the acquisition device;
• applying a stochastic model to the signal to obtain a probability that the writing implement is touching or not touching based on clues about the environment including shadows of the writing implement,
• determining a best estimate probability based on the stochastic model to determine the likelihood whether the writing implement is touching;
• and
• based on the best estimate, determining which parts of the scene represent portions where a writing implement is touching a writing surface and which parts of the scene represents portions where the writing implement is not touching the writing surface.

A method of determining a position of a writing implement relative to a writing surface comprising:

• obtaining an output from a single image acquisition device, which can be oriented in any of a plurality of different orientations relative to the writing implement, indicative of a scene of the acquisition device;
• and
• processing the signal to determine which parts of the scene represent portions where a writing implement is touching a writing surface based on an analysis of changes in the image made by said writing implement, and which parts of the scene represents portions where the writing implement is not touching the writing surface;
• wherein said determining comprises:
• acquiring information about a current system including looking for ink traces on the paper and looking for shadow information;
• defining a model of probability which depends on said information;
• and
• using said model to determine whether the writing implement is touching the surface based on said model.

A method of signature verification, comprising:

• using an image acquisition device to obtain an image of a scene, said scene including a writing implement and a writing surface;
• from a position unconnected to a writing implement, following positions of the writing implement relative to the writing surface;
• defining a trajectory of a tip of said writing implement, including a path of said tip, and both down portions where the writing implement tip is touching the writing surface and up portions where the writing implement tip is not touching the writing surface;
• selecting a dynamic time warping function;
• and
• applying the dynamic time warping function to said trajectory which dynamic time warping function includes both said down portions where the writing implement tip is touching the surface, and up portions of the writing tip where the tip is not touching the surface and comparing the function to other trajectories to determine if said trajectory matches one of said other trajectories that would indicate a match between an entire trajectory including both said up and down portions, and outputting a result indicative thereof.

A method of signature verification, comprising:

• using an image acquisition device to obtain an image of a scene, said scene including a writing implement and a writing surface;
• following positions of a writing implement relative to the writing surface;
• defining a trajectory of a tip of said writing implement, including at least up portions where the writing implement tip is not touching the writing surface;
• selecting a time warping function that minimizes cost of aligning said trajectory including both said down portions where the writing implement tip is touching the surface, and up portions of the writing tip where the tip is not touching a surface, comparing said function to other functions of other trajectories including both said down portions where the writing implement tip is touching the surface, and up portions of the writing tip where the tip is not touching the surface and
• applying the dynamic time warping function to compare said trajectory to said other trajectories to determine if said trajectory matches one of said other trajectories between an entire trajectory including both said up and down portions, and outputting a result indicative thereof.