Foveon: New CMOS sensor captures triple the data! By
Michael R. Tomkins, The Imaging Resource
(Monday, February 11, 2002 - 18:35 EST)Will Foveon's X3 CMOS imagers change the face of digital imaging as we know it?Foveon Inc., a privately held company based in Santa Clara, California, founded by electronics pioneer Dr. Carver Mead (who amongst other things devised a gallium-arsenide transistor and laid down the original design rules for etching microchips) has today made what we consider to be an extremely significant announcement that has the potential to turn the world of digital imaging on its head. The company has taken the wraps off its new X3 image sensor, a CMOS device which is capable of recording all three colors (red, green and blue) at every cell.
Current digital camera designs use one of two main techniques: in the first, a single CCD or CMOS sensor records only one color at each cell, and then interpolates (read: makes an educated guess) the remaining color values to produce the final color for each pixel in the digital image. The other technique, much less commonly used since it adds significantly to the cost of the camera, is to use a beam-splitting prism to direct light of each color to three separate image sensors, each of which records only one color. Other techniques do exist, such as moving an optical refraction plate in front of the sensor to cause light to fall on different cells, hence recording multiple color values and increasing the data collected - but movement of the subject between separate exposures renders the final results useless, so such techniques are of no use for anything other than static scenes.
Foveon's X3 image sensor, demonstrating how light penetrates to the different layers of 'stacked' cells. Click for a bigger picture!
Foveon's new sensor works in a completely different way, as demonstrated in the image above - using the natural properties of the silicon where light of different wavelengths is absorbed at differing depths. The X3 sensor essentially 'stacks' photo-detectors in three layers, so that for each location on the sensor, all three colors are recorded. Foveon draws a parallel to traditional color film, where each color is recorded in stacked layers of emulsion to result in a final full-color image. In the X3 sensor, this approach triples the data collected as compared to a standard CCD or CMOS sensor of similar resolution, which by itself should bring a significant boost in overall image quality. There are numerous other advantages as well, though...
Traditional CCD sensors use a manufacturing process that is unique, meaning that there is a significant expense in creating a CCD fab to manufacture only CCD chips - causing high costs to manufacturers (and eventually the consumer) for CCD-based cameras. Since the X3 sensors use a CMOS process, they should be able to be made using the same equipment and techniques as many other types of computer chips, meaning that resources can be shared with production of other items to help defray costs - and this should result in savings to manufacturers of X3 cameras and to the consumer. (As an example of how CMOS can save money, look no further than Canon's EOS D30 digital camera, which has for some time been about the lowest-priced option for a true digital SLR - thanks in part to its use of a CMOS imager).
Foveon compares how film and the X3 sensor capture color. Click for a bigger picture!
A further benefit to the X3 chips over CCD sensors should be a reduction in power consumption, with quoted power levels of 50mW during readout, 10mW in standby mode and 100μW in power-down mode. This could allow for the final product - an X3 digital camera - to be smaller, lighter, cheaper, or run longer than a similar product using a CCD sensor, thanks to extended battery life, or smaller / cheaper batteries. Foveon also claims that its design will offer "extremely low-noise readout and very high dynamic range" - something which once again seems believable considering the very clean images we've already seen from Canon's proprietary CMOS sensors. If Foveon have done as good a job, chalk up another potential benefit over the CCD cameras!
Another advantage of the design is that since real color values are recorded for every pixel, there is no need to interpolate data - which brings two bonuses. Images should be able to be captured more quickly - just pass the data to buffer memory and write it to flash, rather than having to first spend time on complex mathematical operations to interpolate the missing color values whilst trying to avoid artifacts and moire effects. Secondly, there is a potential to further save on cost, since manufacturers may be able to avoid using extra chips that are dedicated to this interpolation process.
How traditional CCD or CMOS-based cameras record color information. Click for a bigger picture!
How Foveon X3 CMOS-based cameras record color information. Click for a bigger picture!
Not only should images have better color, but there is the potential for them to have better detail as well, again thanks to the lack of any interpolation. Just how much of an improvement there is we'll wait with interest to see once we get an X3-based camera in our labs to test, but with triple the data the improvement should be very real. There should also be a very significant lessening of problems like moire effects on images - caused by fine detail that is too high-frequency for the sensor to capture. With traditional CCD and CMOS cameras, this is exacerbated by the way colors are spaced - and whilst techniques for reducing the impact of the problem during interpolation do exist, they're not foolproof.
The company also says that its sensor design allows for some other features - such as what it calls 'VPS' (Variable Pixel Size). Essentially, this allows multiple pixels to be combined together for higher ISO images and faster frame rates, albeit at a lower final resolution. This seems very similar to what Fuji is doing with its pixel data coupling and pixel mixing technologies in its proprietary third-generation SuperCCD imager, although it isn't clear whether VPS is performed in-chip in the same manner as Fuji does. Essentially though, VPS allows for cells of the same color to be linked together in groups to either reduce the data that must be read-out and/or manipulated (for higher frame rates) or to increase the total light gathered for the final pixel value - effectively increasing ISO sensitivity.
Foveon has initially announced two products based on its X3 design; the F7 and F10 image sensors - part numbers F7-35X3-A25B and F10-14X3-D08A respectively. The F7 is a 2304 x 1536 pixel (2268 x 1512 effective) chip that would be a 3.43 megapixel sensor in terms of dimensions of the image alone, but actually records 10.29 megapixels of color data. The F7 chip has an ISO rating of 100, a 3:2 aspect ratio, a photo detector pitch of 9.12μm and an effective area of 20.7 x 13.8mm (which would give a focal length multiplier of 1.74x as compared to 35mm film). Foveon claims a resolution of 756lp/picture height, a full-resolution frame rate of 2 frames per second, and a maximum rate of 25 fps using VPS at a resolution of 576 x 384 pixels. For the F7 chip, VPS offers resolutions of 1152 x 768, 768 x 512 and 576 x 384 pixels for still images, and video in the lowest resolution only. We do note one oddity, in that the VPS resolutions are all neatly divisible into the total resolution of the chip, not the effective resolution. We'd have expected these resolutions to divide evenly into the effective resolution if there were no interpolation going on, since the extra pixels above the effective resolution are masked off for dark current calibration, etc. We also note that Foveon doesn't state what packaging the F7 chip uses.
The F10 meanwhile is a lower-resolution 1344 x 1024 pixel (1280 x 960 effective) chip that has an image resolution of 1.23 megapixels and gathers 3.69 megapixels of color data. It also has an ISO rating of 100, but has a 4:3 aspect ratio and a photo detector pitch of 5μm. It has an effective area of 6.4 x 4.8mm, which results in a diagonal of exactly 8mm / 0.315" - unfortunately that doesn't translate directly to a nice fraction (154129/489359ths anybody?) :) but it is somewhat smaller than the 0.370"/9.4mm and 0.555"/14.1mm sensors used in most consumer digital cameras. Foveon's speed rating for the chip is a swift 10 frames per second at the maximum resolution, and over 30fps at 640 x 480 pixels using VPS. On the F10 chip, VPS combines pixels in integer multiples (2, 3, etc.) It isn't clear what the lowest resolution is for the chip when using VPS. The F1 chip comes in a CLCC 100 pin package...
Foveon's F7 Reference Design Kit.
Also announced alongside the F7 and F10 image sensors is the F7-RDK Reference Design Kit, which consists of the higher-resolution F7 image sensor coupled with an IEEE-1394 FireWire port, mechanical shutter, PC Synch connector, 2mm stereo-jack remote shutter release port, Canon EOS lens mount, 3/8-inch tripod socket, and composite video out connectivity. An optional 1.8 inch LCD display is available, the unit is compatible with Type-I and Type-II CompactFlash cards, features a 206MHz Intel StrongARM processor and 128MB of SDRAM, and can output either NTSC or PAL composite video. The RDK serves as a platform for development of digital camera designs based on the X3 image sensors, and allows control of aperture and shutter speed, real-time full-frame video preview, full resolution image capture, VPS image resizing, and the ability to capture 4-second digital video streams. The F7-RDK can output 48-bit S-RGB TIFF files, raw images, dark-frame subtracted images, gray-balanced images and digital video.
A final announcement is the FX3-SDK software development kit. Designed for manufacturers to produce the software their cameras will run, as well as software for the user's host PC to download and process images, the SDK is based on C++ Object libraries. Supported camera hardware includes an Intel StrongARM processor, CompactFlash media, a color LCD display, USB or IEEE-1394 FireWire interfaces, and an I2C bus. Supported host operating systems are Windows 98, 2000, XP and Me, or MacOS 9 or OSX. Image formats supported include Foveon RAW, 24-bit or 48-bit TIFF, JPEG and Embedded Color Profiles. The specific libraries can be found listed on Foveon's site.
Foveon notes in its press release that the first X3-based camera will be an SLR called the SD-9 manufactured by Tokyo, Japan-based Sigma corporation. The camera will be on display at the upcoming Photo Marketing Association 2002 show which starts in a couple of weeks from now, and should be shipping by May of this year. We'll have further details on the SD-9 digital camera in a further news item to follow shortly.
For those interested in image quality, three large sample images can be found on the Foveon website. Note however that we don't know what hardware captured the images, what conditions they were captured under nor how they have been post-processed or retouched. None of the images match up to the sizes available from either the F7 or F10 sensors or the prototype X3 sensor, which was a square 2048 x 2048 pixel chip - so at the very least all of the images have been resized and/or cropped. Also, the 'Pool Table' image is taller than the maximum size available from the higher-res F7 chip, so this image in particular definitely didn't originate from one of the chips announced today. You can also find several small thumbnails and 100% crops of shots from a prototype X3 camera using the larger prototype chip from our friends at the Digital Photography Review - there are no full-sized images here, but Phil's 240 x 240 pixel crops are certainly interesting since they were taken by a third-party and not Foveon themselves.
Foveon says that it intends to offer a range of X3 products aimed at everything from professional SLR digital cameras to low-cost consumer point'n'shoots. It will certainly be interesting to see how well Foveon does with the X3 image sensor line-up - one potential question-mark is how well the consumer will deal with comparing (and understanding) megapixel ratings before they purchase a digital camera. We'll now have three different numbers, none of which are directly comparable - standard megapixel ratings from color-interpolating cameras, Fuji's ratings for its proprietary SuperCCD-based cameras, and now the ratings from the new X3-based cameras. Thus far, the company seems to have taken the approach of stating a rating such as "2MP x 3" to attempt to get the point across that it captures more information than the other cameras - but will the consumer understand what that means? If the company were to instead publish megapixel numbers for the number of cells of color-data it captures though, it may find itself dealing with an uproar from those consumers who are better informed who might feel that they're overstating their case, so perhaps adding "X 3" to the rating is the safest approach.
There is also the question of whether the other manufacturers of CCD and CMOS imagers will take this sitting down - or will they have something up their sleeves? If another manufacturer finds a way to market imagers which capture color values for every pixel, then Foveon will have a much harder time marketing itself to manufacturers of consumer digicams who've already built up a history of purchasing imagers from the likes of Sony - or building their own, like FujiFilm and Canon have done with certain models. You can be sure the company is patenting its developments from every conceivable angle, but we can't imagine the likes of Sony taking second-place to the X3 sensors without a fight...
As usual with any new technology, we'll reserve final judgement until we've had a chance to put an X3 camera through our usual battery of tests... There are many questions that won't be answered until that time, and it is possible that the new design may bring new challenges of its own. Hopefully with plans for the Sigma SD-9 digital camera to ship around May 2002, the answers will be forthcoming soon. In the meantime, this is definitely one to watch - on paper at least, X3 seems to have the potential to revolutionise imaging in much the same way that the CCD sensor has done since its conception around 30 years ago...
FOVEON INTRODUCES WORLD'S FIRST FULL-COLOR IMAGE SENSOR
New Chip Is First To Work Like Film And Dramatically Improves Color Resolution
SANTA CLARA, CA - (February 11, 2002) - Foveon Inc., a technology leader in high quality digital photography has announced the introduction and immediate availability of its new Foveon® X3? image sensor. The Foveon X3 represents a true breakthrough in digital photography, bringing significant advantages over all other CCD and CMOS image sensors. Foveon X3 image sensors dramatically improve photographs from digital cameras by capturing three times the color resolution of comparable image sensors found in today's digital cameras. The use of Foveon X3 image sensors will lead to digital cameras that are simpler to design for manufacturers and that provide more image quality and performance value to customers.
"The Foveon X3 represents the most significant breakthrough in digital camera technology since the invention of CCDs over 30 years ago. This new technology combines the immediacy and excitement of the digital photography experience with the quality that exceeds what consumers have previously come to expect only from film," says Jim Lau, Foveon's CEO.
In addition to increased color resolution, the new technology integrates high-resolution still photography with professional-quality full-motion video within a single image sensor enabling a new class of dual mode still/video digital cameras. "Current image sensor technology has not enabled digital cameras to realize their full potential. We believe the breakthroughs of the Foveon X3 technology will form the foundation of a new generation of digital cameras in all classes.", continued Lau.
The Foveon X3 is the world's first color image sensor that captures red, green and blue light at each pixel, resulting in brilliantly sharper images, enhanced color, and freedom from unwanted "color rainbow" artifacts common in photographs from today's digital cameras. Foveon X3 image sensors detect color in a manner similar to that of color film. With film, different colors of light penetrate to different layers of photosensitive material, with each layer detecting a specific color. Using a similar concept, Foveon X3 image sensors consist of three layers of photo detectors embedded in silicon and are the first to detect three colors at every pixel location. The name X3 comes from a unique capability that the Foveon X3 technology brings - the ability to capture three colors at each single pixel location.
The Foveon X3 technology is highly scalable and will be used in designs for small, mid-range and large size image sensors. Foveon's first image sensors are targeted for professional, advanced amateur and high-end point-and-shoot camera users. Additional Foveon X3 image sensors are being designed that are suitable for a wide range of cameras including digital still/video cameras, PDA's, cell phones, security cameras, and fingerprint-recognition systems.
Higher Quality Photographs, Smaller File Sizes Today's CCD and CMOS image sensors detect only one color of the three required colors at each pixel and must mathematically estimate the remaining two colors not detected. This limits the range and accuracy of the color captured thereby increasing the possibility of unwanted color artifacts in the photograph. By capturing three colors at every pixel instead of just one, Foveon X3 based cameras have measured information for all three colors. This results in high quality photographs with fewer numbers of pixels because the pixels are based on real measurements. Fewer pixels results in smaller file sizes allowing digital camera users to send a higher quality photograph more quickly through e-mail. It also means that more digital photos can be stored on a digital camera storage card.
The first camera that will use the Foveon X3 chip is the SD9 SLR digital camera made by Sigma Corporation. Photographs from the SD9 can be enlarged up to 30 inches, exceeding the quality of 35 mm film. Sigma Corporation will demonstrate the SD9 camera at the Photo Marketing Association convention, Booth # 1635 in Orlando, Florida on Feb 24-27, 2002.
High-Quality, Low-Cost Solutions for Dual Mode Digital Cameras In addition to the breakthrough in color resolution, Foveon X3 image sensors are the first to incorporate a capability known as Variable Pixel Size (VPS). Foveon X3 full-color pixels can be grouped together to create larger, full-color "super pixels" ushering in a new class of dual capability still/video cameras. The size of the pixel groups is variable and can be configured instantaneously on the camera. VPS technology allows a Foveon X3 enabled digital camera to capture high-resolution still photographs and full-motion video that offers photo quality superior to 35 mm film, and video quality that rivals high-end digital camcorders.
Parents for example, could use this new type of camera to capture video of their child playing soccer. Mid-way through video recording they could press a shutter button, capture a high-resolution photograph and then seamlessly continue recording video. Security applications could also benefit from this high-quality dual-mode capture capability. Foveon X3 enabled airport security cameras could record video for general surveillance and capture high-resolution still photographs targeting suspected individuals or at timed intervals.
"The photographic detail and color that can be achieved with this technology is unsurpassed," said Lau. "Pixel for pixel, Foveon X3 based digital cameras will deliver higher quality images than any other image sensor."
About Foveon Foveon, Inc. was founded in 1997 by Dr. Carver Mead, a pioneer in solid-state electronics and VLSI design. Foveon's mission is to develop innovative products and technology that allow photographers to fully realize the potential of digital photography. The company's recent accomplishments include: the world's highest quality professional studio portrait camera, the worlds first 16.8 million pixel CMOS image sensor and Foveon X3, the worlds first full color image sensor. Foveon is a privately held company. Investors include: National Semiconductor Inc., Synaptics Inc. and New Enterprise Associates.
PERFORMANCE ADVANCES OF FOVEON X3 TECHNOLOGY
Image sensors with Foveon X3 technology are much less susceptible to digital artifacts and create sharper images. Current color image sensors (CCD and CMOS) contain just one layer of monochromatic photo detectors, with one photo detector per pixel. To capture color, the pixels in the image sensor are organized in a mosaic pattern resembling a three-color checkerboard. As a result, each pixel captures just one color-red, green or blue. The use of mosaic color filters in image sensors has inherent drawbacks, no matter how many pixels a mosaic-based image sensor might contain. Image sensors with Foveon X3 technology produce accurate color every time because it captures three colors at every pixel instead of one.
VPS: Video Performance and High Resolution in a single chip. Foveon X3 sensors come with a new feature known as Variable Pixel Size (VPS), bringing the benefits of small and large pixels together into a single image sensor. Smaller pixels offer higher resolution and sharper images demanded by still photography. Larger pixels promote higher light sensitivity that is needed for low light situations, faster auto focus systems and video applications. The changing of pixel sizes can be accomplished instantaneously and is only achieved with the full-color capture of the Foveon X3 technology.
The only image sensors that capture color images by taking advantage of the natural color-separating properties of silicon. Foveon X3 image sensors are the world's first to use silicon as a color filter. It is a well-known property of silicon that light of different colors is absorbed at different depths in the silicon. Each Foveon X3 pixel consists of three photo detectors located at different depths within the sensor to detect the absorption of the red, green and blue light that has penetrated the silicon. Foveon is the first and only company to use silicon color separation for designing color image sensors for digital cameras.
Less Complex, Lower Cost. Foveon X3 image sensors will streamline the electronic designs of digital cameras. Today's digital cameras use mosaic color filters and require complex mathematical algorithms to estimate the red, green and blue value of pixel, since only one color per pixel is being truly measured. To accomplish this interpolation, dedicated processing hardware and software are required inside the camera. Color interpolation adds cost and complexity to a camera while increasing delays between clicking the shutter button and capturing a picture, which can result in the difference between capturing a great picture or missing an important moment. By capturing all three colors at every pixel, Foveon X3-based image sensors eliminate the need for costly, complex and error-prone color interpolation. Foveon X3 enables improved image quality, simplified camera designs and increased click-to-capture performance.