Data Compression of Digital-Ink with Pen-Slips Using Multi-level L1 Smoothing Splines

In this paper, we consider a problem on data compression of "Digital-Ink" which is a sequence of position data sampled from the traced curve at a sampling rate. Here we suppose that a set of digital-ink is measured and stored by electronic device (e.g. Smart-phone and pen-tablet PC, etc.) and that ink data include sudden deviations corresponding to pen slips during the handwriting input due to a frictionless sheet on the display, etc. For such a problem, we here develop a robust method of digital-ink compression by employing multi-level L1 smoothing spline method based on B-splines, where the term ´multi-level´ indicates that not only the measured digital ink data (i.e. Position data) but also its derivatives (i.e. Velocity and acceleration data) are considered. Then, it is shown that multi-level L1 smoothing splines can be used effectively for excluding the influence due to the pen slips. The effectiveness and usefulness are examined by some experimental studies.