HTML5 canvas, palm rejection

We are trying to use html5 canvas with tablet stylus, but we have a problem with palm touching with multitouch tablets. When a person try to draw something and touch the display surface with the palm, lines occurs because of the multitouch.

Do you know how to disable multitouch on tablet through js or canvas option, or do you know if there is a html5 canvas palm rejection techonology.

There are some newer web APIs available in current browsers. In particular, the radiusX and radiusY of the touches from a touch event can be used to compute the area of touch. The areas larger than that of a finger, or stylus, could be ignored.