Drawing tablets are a great way to make digital art, and iPads and other tablets are similarly popular in this area. However, they all typically involve using some sort of special stylus for input. [Richard Greene] developed another method, with Light Strokes for the iPad letting one “paint” with real paint brushes instead!
The system uses a Fresnel prism in view of the iPad’s camera. This allows the camera to see only the parts of a paint brush, sponge, or other implement, as they make contact with the surface of the prism itself. This is via the principle known as total internal reflection.
Thus, simply wetting a paintbrush, sponge, or even a finger, allows one to paint quite authentically on the surface of the prism. The corresponding Light Strokes app on the iPad turns this into the pretty pixels of your creation. The app also allows one to experiment with all manner of fancy brush effects, too.
The build requires some finesse, with the lamination of the special Fresnel film onto glass using liquid optically clear adhesive, or LOCA. A series of mirrors are then assembled in an enclosure, allowing the iPad to be mounted with the camera having a good view of the glass painting area.
The project takes advantage of a simple physical effect in order to create a great artistic tool. Alternatively, if you prefer to draw directly, consider whipping up your own screen-based drawing tablet. Video after the break.
Brilliant execution of a nice idea. It´s a pity that the framerate of the camera is too low, leading to a scale effect as soon as the tool moves swiftly.
Looking forward for an upgraded version of this peripheral, with something like >100fps, lower lantecy, and no dependency to an Apple tablet.
More accurately, the technique is *Frustrated* Total Internal Reflection – the panel is lit so that in the ordinary case all the light is reflected via TIR back towards the camera. When an object is pressed against the panel, that breaks or “frustrates” the reflection so now the light at those places passes straight through, leaving a dark spot in the image. It’s why you get that strange effect highlighting your fingerprints when holding a glass with condensation on it.
There was a whole craze for FTIR multitouch panels about 15 years ago, with lots of diy efforts, a few of which showed up on HaD. Of course this was before capacitive touch displays became commonplace and comprehensively ate the entire market.
Uhm, not quite, in this case. You describe the brightfield approach. Here, the camera normally sees a dark reflection of a black light absorber through TIR. When something on the glass frustrates the TIR, then the camera sees that object light up, which is brightly lit from underneath.
Great project and a well-written instructable.
Now I want to learn more about how the “Brightness Enhancement Film” works, both in its intended use and this application.
Why don’t you ask the author of the original content in the Instructables comments?
Neat idea. Those optical films afford a lot of flexibility in optical system design.
I have never touched an iPad so I’m speaking a little blind here, but it seems like an awful lot of trouble rigging a mirror path from the tablet’s camera to view the target area, and also rigidly constrains the display position. It also makes the rig subject to the frame rate limitations of the internal camera.
I wonder if it would be simpler to just build a rig with a dedicated USB camera (or firewire or lightning or whatever kind of I/O that tablet has). No mirrors needed, maybe smaller desk footprint, more flexibility in positioning the display, and ability to get a higher frame rate.
Heck, that way you wouldn’t even need to be locked into that particular model and form factor of tablet, even.
I’m curious what the camera image looks like when the brush is in contact with the surface. Very cool idea!
Painting with real and wet brushes making use of Frustrated Total Internal Reflection has been demonstrated in 2009 with the “FluidPaint” System at University Hasselt, Belgium.
Youtube video: https://www.youtube.com/watch?v=fkl782OqqmA
white paper: P. Vandoren, L. Claesen, T. Van Laerhoven, J. Taelman, C. Raymaekers, E. Flerackers, F. Van Reeth, “FluidPaint: an Interactive Digital Painting System using Real Wet Brushes”, ITS ’09: Proceedings of the ACM International Conference on Interactive Tabletops and Surfaces, Nov. 23-25, 2009, ACM, ISBN: 978-1-60558-733-2