The Ansel Adams Zone System: HDR Capture and Range Compression by Chemical Processing

Google Tech Talk January 21, 2010 ABSTRACT Presented by John McCann. We tend to think of digital imaging and the tools of Photoshop(TM) as a new phenomenon in imaging. We are also familiar with multiple-exposure HDR techniques intended to capture a wider range of scene information, than conventional film photography. We know about tone-scale adjustments to make better pictures. We tend to think of everyday, consumer, silver-halide photography as a fixed window of scene capture with a limited, standard range of response. This description of photography is certainly true, between 1950 and 2000, for instant films and negatives processed at the drugstore. These systems had fixed dynamic range and fixed tone-scale response to light. All pixels in the film have the same response to light, so the same light exposure from different pixels was rendered as the same film density. Ansel Adams, along with Fred Archer, formulated the Zone System, starting in 1940. It was earlier than the trillions of consumer photos in the second half of the 20th century, yet it was much more sophisticated than today's digital techniques. This talk will describe the chemical mechanisms of the zone system in the parlance of digital image processing. It will describe the Zone System's chemical techniques for image synthesis. It also discusses dodging and burning techniques to fit the HDR scene into the LDR print. These techniques introduced spatial changes in the print causing dynamic range compression of the high-dynamic-range scene into the low-dynamic-range print. Preserving edge information is key to successful scene rendition. Note: The recording missed the first couple minutes (the start of John's story of Ansel's visiting Polaroid and trying out a prototype SX-70 camera). John McCann received a B.A. degree in Biology from Harvard University in 1964. He worked in, and later managed, the Vision Research Laboratory at Polaroid from 1961 to 1996. He has studied human color vision, digital image processing, large format instant photography and the reproduction of fine art. He is a Fellow of IS&T. He is a past President of IS&T and the Artists Foundation, Boston. He is currently consulting and continuing his research on color vision. He is the IS&T/OSA 2002 Edwin H. Land Medalist and IS&T 2005 Honorary Member and a 2008 Fellow of the Optical Society of America.