Kodak obviously wants its inventors and researchers to be doing their primary scientific work and not answering idle questions from blokes like me, but thanks to Bruce Graham at Kodak I was able to put a few questions directly to Dr. John F. Hamilton, Jr., of the Photographic Science and Technology Center at Kodak Research Labs, one of the inventors responsible for the just-announced partial-panchromatic array.
A graduate of Cornell University, John Hamilton received his Ph.D. in mathematics at Indiana University. In 1974, he accepted a position at the Kodak Research Laboratories where he applied mathematics to various problems in graphic arts (printing), medical imaging, clinical diagnostic imaging, and electronic digital imaging. He is a Research Fellow, a recipient of the Eastman Innovation Award (2003), a recipient of the Rochester Intellectual Property Law Association (RIPLA) Distinguished Inventor of the Year Award (2005), and a member of Kodak’s Distinguished Inventors Gallery with 41 patents in the area of digital image processing. Currently, he is developing novel image processing algorithms for Kodak's digital camera business, Kodak's sensor business, and related applications.
The Online Photographer: Dr. Hamilton, to what extent is Kodak's new sensor filtration array really a new idea? Doesn't the Bayer standard already allow for panchromatic pixels or undyed photosites?
John Hamilton: The Bayer patent shows a 3-channel sensor, but the new sensor has four. Other patents show four channels, but not the family of patterns that interest us.
T.O.P.: My readers are mainly interested not in the high-volume applications that probably greatly interest Kodak, but in high-quality applications. Is this something we are likely to see in high-end DSLRs and digital medium-format backs?
I have no idea what to expect regarding product offerings. We are in research and that is a business decision.
T.O.P.: I speculated that one thing that made this new type of array possible is the greatly increased number of pixels in modern sensors. Is this one of the factors that enables this new array design?
John Hamilton: Yes.
T.O.P.: If the panchromatic pixels permit one stop more light sensitivity, doesn't that also mean that they'll saturate one stop earlier too? Wouldn't that affect highlight resolution?
John Hamilton: Yes, the panchromatic pixels would saturate before the others. The exposure controls should be set to suit the panchromatic pixels.
T.O.P.: One of my readers expressed surprise that the new array maintains the old G-G-B-R ratio in the colored photosites. Why is it important to still have double the number of green pixels?
John Hamilton: Many cameras have video ASICs that require Bayer RGB input. The new filters were designed to accommodate that fact.
T.O.P.: Would the new array lend itself better to B&W-only implementations?
John Hamilton: I would expect a B&W sensor to be entirely panchromatic pixels, such as the one used in the Kodak Professional DCS760M from about five years ago.
T.O.P.: The human eye puts an emphasis on luminance information for the sake of image detail. Is the new sensor likely to increase the level of real detail in digital images?
John Hamilton: Not really. The panchromatic pixels function just like the green pixels of the Bayer pattern except that they are photographically faster. However, under low light conditions, the new patterns will outperform Bayer because of improved signal-to-noise.
T.O.P.: I appreciate that part of what will make this new array practical is that new interpolation algorithms will have to be devised for it, and some of that work is still in the future. But knowing what you know, do you anticipate that the likely problems or advantages will make the new array best suited for certain applications as opposed to others?
John Hamilton: The new filter patterns were designed with low-light conditions in mind, but it's too soon to say where they work best. Under well-controlled lighting conditions, such as in a studio, I would expect the new filters and a Bayer filter to be roughly equivalent.
T.O.P.: One last question—so how come the new array isn't named after its inventors, like the Bayer Array was named after its inventor, Kodak's Dr. Bryce Bayer, in 1976?
John Hamilton: We are just the tip of the iceberg. Many sensor and algorithm people are involved in bringing this technology forward.
T.O.P.: Thank you, Dr. Hamilton.
John Hamilton: Thank you.
As a follow-up, I should add that I did press both Bruce and John about likely applications and possible products, but I was brought around to their view that the story for now is the success of the technical research—it's really too early to tell how the idea will be implemented and in what kinds of products it will be most successful. Kodak can make sensors for its own products, or make sensors as OEM products for other cameramakers, or design products to be fabricated by others, or license its intellectual property (IP) for products designed and built by other companies. How any given research will "filter" through to the market is dependent on many people and tiers of decisions in other departments of Kodak and at many other companies, so the inventors can't really speculate about such things.
One little tidbit that doesn't quite come through in the foregoing is that Kodak is working with a G-G-B-R color arrangement so far only because that's what established technology demands, but the inventors are actively experimenting with other color pixel combinations. Obviously, the biggest hurdle to overcome is that the new array only yields half as much color information directly. A Bayer array requires interpolation, but the new array requires more interpolation. It's at least possible that the most successful implementation of the new array (I still think it needs a name...) won't be RGB at all.
My thanks to Bruce Graham and John Hamilton at Kodak for their generous cooperation.