Talk WHAT: John McCann (McCann Imaging; IS&T Visiting Lecturer): High-Dynamic Range Imaging: Algorithms that Mimic Human Vision WHEN: Wednesday, April 14, 2004 at 4:30 PM EST WHERE: Bartos Theatre, MIT Media Lab (E15) SUMMARY: Receptors in the human retina respond to a range of light that is 10 billion to 1 in radiance, yet the optic nerve has a dynamic range of less than 100 to 1. In 1953, Kuffler and Barlow showed that the optic neurons transmitted information about spatial comparisons. Observers easily discriminate details in scenes with dynamic ranges of 10,000 to 1. High-dynamic-range Retinex algorithms share a common mechanism with vision; namely, they are based on spatial comparison of pixels in all regions of the captured image. These algorithms, now available in commercial products, mimic human image processing. They use multi-resolution spatial comparison techniques to render high-dynamic range scenes. As shown by Ansel Adams, and Jones & Condit, outdoor scenes typically have dynamic ranges of 1000 to 1 in radiances. Scenes with specular reflections, that are images of the sun, have much greater ranges. Print paper in actual viewing conditions has a dynamic range of about 30 to 1. Tone-scale transforms, such as S-shaped H&D curves, cannot render output images to match human sensations. Tone-scale transforms compress the highlights and shadows too much. Spatial-comparison algorithms automatically "dodge and burn" the image based on the spatial content of the input image. They automatically generate the equivalent of scene-dependent spatial-frequency filters. Many other visual phenomena can be modeled by spatial comparisons. Color constancy, visibility of gradients and edges, appearance of transparency, and color gamut transformations are more closely related than one might think. Experiments have shown that they share a common property, namely they can be explained by human spatial-comparison mechanisms. BIO: John McCann is a consultant on color, color imaging, and image processing. He had been working part-time for Polaroid while an undergraduate at Harvard. In 1964, under the direction of Edwin Land, he became the manager of the Vision Research Laboratory, where his work on human psychophysics has included research on rods as color receptors, low-spatial-frequency vision, mathematical models of color vision, and quantitative tests of Retinex theory. As senior manager in the research division of Polaroid, he directed the Vision Research Laboratory until retiring from Polaroid in 1996. From 1979 to 1996 he managed research on very-large-format Polaroid photography, which includes the 20x24 cameras, the Museum Camera, and Polaroid Replicas. Since 1974, he has been studying vision with computer-processed digital images. This activity combines interests in mathematical models of vision with electronic imaging techniques. This basic research has concentrated on techniques for calculating color sensations and developing film recorders that control film exposures so that the photographic image is a record of color sensations rather than the record of light coming from the scene. His work has led to 102 publications and 14 patents. In 1984 he was elected a fellow of the SPSE (IS&T). He has served as vice president, and president of the Society of Imaging Science and Technology. McCann co-chaired the IS&T/SPIE 2000 Electronic Imaging Meeting. He is secretary of the Inter-Society Color Council. In 2003, he received the IS&T/OSA Edwin Land Medal. McCann has a bachelor's degree in biology from Harvard University. MIT Media Laboratory Home Page | Events Main Index