The Considerable Value of Accidental Pinhole and Pinspeck Cameras

I was reminded of 'accidental pinhole cameras', when observing a solar eclipse last year,  You can commonly (and safely) observe the phenomenon when seeing the reflected eclipsed sun shining through the leaves of a tree onto a surface below.  My picture at the right, the eclipsed sun images are interspersed between the leaf images.

 The phenomenon was known in China BC.  Hundreds, thousands of pinhole cameras are accidentally created by gaps in the leaves.  And also by objects that block light.   This same phenomenon is created all around us, all the time ...  not just by leaves, but by corners, reflections,  blocking objects ... and you can use such cameras to construct images of things we cannot see directly. 

In other words you can do things that are very interesting to many people, like seeing around corners.   The Quantum Magazine article pointed to below describes efforts underway.   Very enlightening piece that drove home the possibilities to me.  Includes images and pointers to scientific papers.

The New Science of Seeing Around Corners   By Natalie Wolchover   Senior Writer/Editor In Quanta Magazine.

Computer vision researchers have uncovered a world of visual signals hiding in our midst, including subtle motions that betray what’s being said and faint images of what’s around a corner.

While vacationing on the coast of Spain in 2012, the computer vision scientist Antonio Torralba noticed stray shadows on the wall of his hotel room that didn’t seem to have been cast by anything. Torralba eventually realized that the discolored patches of wall weren’t shadows at all, but rather a faint, upside-down image of the patio outside his window. The window was acting as a pinhole camera — the simplest kind of camera, in which light rays pass through a small opening and form an inverted image on the other side. The resulting image was barely perceptible on the light-drenched wall. But it struck Torralba that the world is suffused with visual information that our eyes fail to see.

“These images are hidden to us,” he said, “but they are all around us, all the time.”   .... "

Research on seeing around corners and inferring information that’s not directly visible, called “non-line-of-sight imaging,” took off in 2012 with Torralba and Freeman’s accidental-camera paper and another watershed paper by a separate group at MIT led by Ramesh Raskar. In 2016, partly on the strength of those results, the Defense Advanced Research Projects Agency (DARPA) launched the $27 million REVEAL program (for “Revolutionary Enhancement of Visibility by Exploiting Active Light-fields”), providing funding to a number of nascent labs around the country. Since then, a stream of new insights and mathematical tricks has been making non-line-of-sight imaging ever more powerful and practical.

 Along with obvious military and spying applications, researchers rattle off possible uses in self-driving cars, robotic vision, medical imaging, astronomy, space exploration and search-and-rescue missions.   ...." 

See also 'Pinspeck Cameras'

More on my image above and more images:  Camera Obscura Eclipse.