CLOUDS are not normally a boon for image-processing algorithms because their shadows can distort objects in a scene, making them difficult for software to recognise.
However, and colleagues at Washington University in St Louis, Missouri, are making shadows work for them, helping them to create a depth map of a scene from a single camera.
鈥淭he shadows clouds cast create a depth map of a scene from one camera, a notoriously difficult task鈥�
Advertisement
Depth maps record the geography of a 3D landscape and represent it in 2D for surveillance and atmospheric monitoring. They are usually created using lasers, because adjacent pixels in camera images do not equate to adjacent geographic points: one pixel might form the line of a hill in the near distance, while an adjoining one is from a more distant landmark.
Enter the clouds 鈥� the shadows they cast can hint at real-world geography, Jacobs鈥檚 team says. By comparing a series of images and recording the time at which the passing shadows change a pixel鈥檚 colour they can estimate the distance between each pixel. 鈥淚f the wind speed is known you can reconstruct the scene with the right scale,鈥� says Jacobs. 鈥淭hat is notoriously difficult from a single camera viewpoint.鈥�
Compared with laser-created maps, average positional error in the cloud map was just 2 per cent, Jacobs says. The work is to be presented at the conference in San Francisco this week.
