Mike Stay <metaweta@gmail.com> wrote:

Sounds a lot like http://graphics.stanford.edu/papers/dual_photography/

Interesting, especially that that dates only to 2005. I had basically the same idea maybe 40 years ago. My idea was to project a blank (solid white) raster from a TV onto whatever I wished to photograph. I realized that a photocell would pick up an NTSC video feed suitable for showing on a TV (complete with vertical and horizontal blanking intervals), and that the scene would look as if the camera was where the TV was, the light source was where the photocell was, and that if there was any other light source the image would look foggy. My proposed application was a poor man's black and white video camera, since in those days TVs and photocells were plentiful and video cameras weren't. Note that no computers were involved. In retrospect it wouldn't have worked very well because CRT TVs had a slow phosphor. But I'm sure it would have worked if they had had fast phosphors. And that, in turn, reminds me of a 2002 demonstration that it's possible to reconstruct an image from a CRT if you aim a photocell at any surface illuminated by that CRT and throw lots of computer power at it to compensate for the slow phosphor: http://csdl2.computer.org/persagen/DLAbsToc.jsp?resourcePath=/dl/proceedings/&toc=comp/proceedings/sp/2002/1543/00/1543toc.xml&DOI=10.1109/SECPRI.2002.1004358 However, I don't see the application to constructing an Earth map from earthshine, given that the Moon is illuminated by all sun-illuminated parts of the Earth in its view at once, rather than one pixel at a time.