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GRASP Seminar: Ramesh Raskar,Mitsubishi Electric Research Labs, “Less is More: Coded Computational Photography”

September 18, 2007 @ 3:00 pm - 4:00 pm

Abstract: Computational photography combines plentiful computing, digital sensors, modern optics, actuators, and smart lights to escape the limitations of traditional cameras, enables novel imaging applications and simplifies many computer vision tasks. Unbounded dynamic range, variable focus, resolution, and depth of field, hints about shape, reflectance, and lighting, and new interactive forms of photos that are partly snapshots and partly videos are just some of the new applications found in Computational Photography.

I will discuss Coded Photography which involves encoding of the photographic signal and post-capture decoding for improved scene analysis.With film-like photography, the captured image is a 2D projection of the scene. Due to limited capabilities of the camera, the recorded image is a partial representation of the view. Nevertheless, the captured image is ready for human consumption: what you see is what you almost get in the photo. In Coded Photography, the goal is to achieve a potentially richer representation of the scene during the encoding process. In some cases, Computational Photography reduces to ‘Epsilon Photography’, where the scene is recorded via multiple images, each captured by epsilon variation of the camera parameters. For example, successive images (or neighboring pixels) may have a different exposure, focus, aperture, view, illumination, or instant of capture. Each setting allows recording of partial information about the scene and the final image is reconstructed from these multiple observations. In Coded Computational Photography, the recorded image may appear distorted or random to a human observer. But the corresponding decoding recovers valuable information about the scene.

‘Less is more’ in Coded Photography. By blocking light over time or space, we can preserve more details about the scene in the recorded single photograph. (a) Coded Exposure: By blocking light in time, by fluttering the shutter open and closed in a carefully chosen binary sequence, we can preserve high spatial frequencies of fast moving objects to support high quality motion deblurring. (b) Coded Aperture Optical Heterodyning: By blocking light near the sensor with a sinusoidal grating mask, we can record 4D light field on a 2D sensor. And by blocking light with a mask at the aperture, we can extend the depth of field and achieve full resolution digital refocussing. (c) Coded Illumination: By observing blocked light at silhouettes, a multi-flash camera can locate depth discontinuities in challenging scenes without depth recovery. (d) Coded Sensing:: By sensing intensities with lateral inhibition, a gradient sensing camera can record large as well as subtle changes in intensity to recover a high-dynamic range image.

I will show several applications of coding exposure, aperture, illumination and sensing and describe emerging techniques to recover scene parameters from coded photographs.


September 18, 2007
3:00 pm - 4:00 pm
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