This sounds very clever. Start with a very sensitive black and white
imager, by eliminating the three color filters entirely, then add in the
color using signals from less sensitive red, green, and blue sensors.
Not clear to me how you trade off sensitivity reductions resulting from
smaller pixel sensors, caused by having to crowd in that fourth sensor,
against the increased sensitivity offered by the transparent fourth
pixel sensor.
Bert
-----------------------------------
Kodak lets light shine in with fourth-pixel advance
Junko Yoshida
(06/14/2007 9:29 AM EDT)
URL: http://www.eetimes.com/showArticle.jhtml?articleID=199904259
MANHASSET, N.Y. - Eastman Kodak Co. unveiled Thursday (June 14) what it
says are "next-generation color filter patterns" designed to more than
double the light sensitivity of CMOS or CCD image sensors used in camera
phones or digital still cameras.
The new color filter system, offered in a family of new patterns
depending on applications and system architecture, are a departure from
the widely used standard Bayer pattern-an arrangement of red, green and
blue pixels-also created by Kodak.
While building on the Bayer pattern, the new technology adds a "fourth
pixel, which has no pigment on top," said Michael DeLuca, market segment
manager responsible for image sensor solutions at Eastman Kodak. Such
"transparent" pixels-sensitive to all visible wavelengths-are designed
to absorb light.
DeLuca claimed the invention is "the next milestone" in digital
photography, likening its significance to ISO 400 color film introduced
in the mid-1980's. The earlier innovation enabled consumers to take
pictures in low light conditions.
The new color filter pattern approach, called "panchromatic pixels,"
allows "a [black and white] image to be detected with high sensitivity,"
according to Kodak. The remaining RGB pixels then collect color
information, which is combined with the information from the
panchromatic pixels to generate the final image.
"The technique is admirably simple: open the window to let in more
light," said Tony Henning, editor of The Mobile Imaging Report. "It's
almost inconceivable that nobody else thought of, or acted on this idea,
until now."
In the age of mega-pixel warfare among camera vendors, image sensor
companies have scrambled to pack more pixels into sensors. The move to
higher resolution in the same form factor, however, requires smaller
pixels with a reduced ability to gather light.
"Much of the effort to improve sensor sensitivity has been to boost the
gain in the signal from the pixels. But this introduces noise [and]
grain in the images," said Ed Lee, director of consumer services and
digital photography trends service at InfoTrends. "So the trade-off has
been sensitivity versus signal noise."
Noting that such a trade off is not new, many major manufacturers of
CMOS image sensors "claim at least a degree of success in compensating
for smaller pixel sizes and reduced light sensitivity," said Henning.
Some reduce the number of transistors per pixel, leaving more room for
the photodiode, or they reduce the size of metal layers to make more
room for the photodiode, explained Henning. "Others reduce the distance
between the photodiode and the microlenses above them."
But what may potentially set the fourth-pixel photo approach apart is
that "Kodak is looking at it from a different direction" by using new
color filter pattern technology, said Jon Erensen, senior research
analyst at Gartner. Other image sensor companies are also experimenting
with color filters based on different arrays of pixels, Erensen said,
but he hasn't heard of anyone implementing it.
The advance may be exactly what Kodak needs to compete in the CMOS image
sensor market against rivals such as Micron or Omnivision. Kodak
introduced its first CMOS image sensors for digital cameras and camera
phones two years ago, but has made little headway in the market, said
Gartner's Erensen.
Kodak said its color filter pattern technology can be used in both CMOS
or CCD image sensors, or even on future image sensors with advanced
pixel architectures. Kodak's primary target, however, is its homegrown
CMOS sensors designed for consumer cameras. The first Kodak sensor using
the technology is expected to sample in the first quarter of 2008,
according to DeLuca.
Technical challenges
To reconstruct full-color images, Kodak has also developed new software
algorithms specifically designed to process raw data generated from
image sensors using new color filter patterns. In theory, the algorithms
use more sensitive panchromatic pixels as a luminance channel to create
the final image. They also derive chrominance information from color
pixels on the sensor.
DeLuca said Kodak will offer several different color filter pattern
options, optimized for specific applications and system designs and with
different levels of processing power.
There is one concern, however. Several analysts cited the additional
processing overhead that may be needed as image information based on the
new color filter patterns is compiled. Henning noted, "It does introduce
an extra layer of complexity or artificiality in the algorithms
necessary to reconstruct the RGB color at every pixel."
Unlike the well-understood Bayer pattern, "with these new patterns where
you have pixels with no color information...it has to be harder to make
an educated guess," Henning said.
InfoTrends' Lee agreed. "Kodak has not said whether this [will require]
more or less processing than today's Bayer pattern," Lee said.
Kodak's DeLuca acknowledged that its new code still needs more
optimizing.
While industry observers are enthusiastic about Kodak's approach,
Henning said its technology remains unproven until it delivers a product
with a noticeable improvement in picture quality. "The only thing that
matters is the quality of the pictures," Henning said.
All material on this site Copyright 2007 CMP Media LLC. All rights
reserved.
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