Tips for recording pen and paper

Question

I've got a set-up where I'm using an iPad to record myself writing something on a white sheet of paper (with less-than-perfect lighting, of course). I'm recording a video in 1080p, and would like to improve its quality.

The kind of things I'd like to do are:

• Even out the paper tone or, better yet, make the paper invisible. Other objects in the frame (the writing and my hand) are 'less white', so I'd like to keep them.
• If possible, get rid of my hand altogether, leaving only the stuff that's on the page. Not sure how feasible it is, but I thought that since my hand is moving, maybe it can be filtered out. (Writing is 'moving' too, but stays persistent after I move my hand away.)

I'd appreciate any ideas for how this can be achieved. I know the second-part is science-fiction (or maybe not, but not doable with stock tools). Thanks!

Answer 1

The old school way is stop-motion animation. You basically take snapshots of the paper at regularly timed intervals, where you remove you hand and take the snapshot, then compile a video from the stills. You can use interpolation to smooth out the framerate.

Another idea to remove your hand and pencil is to chroma-key your hand and drawing implement (green-screen). If you keep the hand and pencil away from the center of the frame, you might have some success with this, and touch up any problems with elements from earlier or later frames. Problems with this: reflectance of the mask color on the paper; cast shadows etc.

Lastly, and probably most difficult, is to use a secondary camera (such as a video camera with "night-mode") and an IR pass filter. Cover or disable the IR spotlight on the camera, and attach an IR LED (extracted from a tv remote etc) very close to the business end of the pencil. With the right setup, one might wind up with a dark video field with light area where the LED is shining. With some manipulation, and {magic}, you now have a mask of the pencil area.