Photosynth is an impressive software application developed by Microsoft Live Labs. It takes a large collection of photos of a place or an object, analyzes them for similarities, and displays them in a three-dimensional framework. The software is in effect discovering hyperlinks between images based on unique features within them.

Photosynth enables users to:

• Walk or fly through a scene to see photos from any angle.
• Smoothly zoom in or out of a photo irrespective of its size.
• Identify where pictures were taken in relation to one another.

Computer vision algorithms encoded in the software process each photo to extract distinctive features for example, the corner of a window frame or a door. Photos are then linked together using shared distinctive features as a guide. 3D positioning of features can be calculated when the same feature is found in multiple images. In addition, Photosynth can figure out where all of the cameras would have to have been and which way they were aimed.

Objects analyzed by Photosynth appear as a 3D point cloud with the original pictures overlaid on the model. Microsoft suggest that one imagines it as slide projector placed at each original camera position, aimed how the camera was, and projecting the picture that camera took. A screen is placed in the 3D environment at an appropriate distance from the projector. When moving around a Photosynth 3D model “projectors” turn on and off, giving virtual reconstruction of a subject built entirely out of the original photos.

The very nature of Photosynth makes it difficult to describe in words, so have a look at the presentation below made by Blaise Aguera at the March 2007 TED conference. You can also download a demonstration version of Photosynth from Microsoft.