IPhone Polarizing Camera Solves Filter Orientation Problem Using Flash

One of last year’s Hackaday Prize finalists was the DOLPi, [Dave Prutchi]’s polarimetric camera which used an LCD sheet from a welder’s mask placed in front of a Raspberry Pi camera. Multiple images were taken by the DOLPi at different polarizations and used to compute images designed to show the polarization of the light in each pixel and convey it to the viewer through color.

The polarizer and phototransistor taped to the iPhone.
The polarizer and phototransistor taped to the iPhone.

[Dave] wrote to tip us off about [Paul Wallace]’s take on the same idea, a DOLPi-inspired polarimetric camera using an iPhone with an ingenious solution to the problem of calibrating the device to the correct polarization angle for each image that does not require any electrical connection between phone and camera hardware. [Paul]’s camera is calibrated using the iPhone’s flash. The light coming from the flash through the LCD is measured by a phototransistor and Arduino Mini which sets the LCD to the correct polarization. The whole setup is taped to the back of the iPhone, though we suspect a 3D-printed holder could be made without too many problems. He provides full details as well as code for the iPhone app that controls the camera and computes the images on his blog post.

We covered the DOLPi in detail last year as part of our 2015 Hackaday Prize finalist coverage. You can also find its page on Hackaday.io, and [Dave]’s own write-up on his blog.


Looptaggr: Endless Graffiti

If your problem is how to put out a maximum amount of repetitive graffiti with a minimum amount of effort, we’ve got your solution. Or rather, [Ariel Schlesinger] and [Aram Bartholl] had your solution way back in 2010. The banner image says it all.

Of course, it doesn’t have to be graffiti that you’re spraying. This idea could be easily adapted to stencil that repeating floral pattern that my grandmother had on her walls too. It’s like a patterned paint roller, but for a spray can.

There’s room for improvements here. For instance, we can’t cut out stencils to save our life but we know where to find a laser cutter. From the look of things, they could use a slightly bigger stencil and something to catch the drips. There’s probably an optimal size for this gizmo, which calls for experimentation.

We’re somewhat obsessed with graffiti machines. Whether it’s a graffiti quadcopter or the elegant and non-permanent sidewalk-chalker style bots, we like machines that make “art”. What’s your favorite graffiti hack?

Thanks [n0p;n0p;n0p;] for the (archival) tip!