Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
2001-10-18
2004-05-11
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
Reexamination Certificate
active
06734905
ABSTRACT:
TECHNICAL FIELD
This invention relates to dynamic range extension for CMOS image sensors.
BACKGROUND
A CMOS (Complementary Metal-Oxide Semiconductor) image sensor is an imaging device built with CMOS technology for capturing and processing light signals. Results produced by the CMOS image sensor can be displayed. Chips that are built based on CMOS technology may include transistors having two alternate polarities. CMOS chips are attractive because they require less power than chips using transistors with only a single polarity for battery-powered and handheld devices.
A type of CMOS image sensors, called a CMOS Active Pixel Sensors (APS), has been shown to be particularly suited for handheld imaging applications.
The CMOS APS comprises an array of pixel processing elements, each of which processes a corresponding pixel of a received image. Each of the pixel processing elements includes a photo-detector element (e.g., a photodiode or a photogate) for detecting brightness information in the received image, and active transistors (e.g., an amplifier) for reading out and amplifying the light signals in the received image. The amplification of the light signals allows circuitry in the CMOS APS to function correctly with even a small amount of the received light signals.
The CMOS APS also has color processing capabilities. The array of pixel processing elements employs a color filter array (CFA) to separate red, green, and blue information from a received color image. Specifically, each of the pixel processing elements is covered with a red, a green, or a blue filter, according to a specific pattern, e.g., the “Bayer” CFA pattern used by Kodak®. As a result of the filtering, each pixel of the color image captured by a CMOS APS with CFA only contains one of the three colors.
An imaging system that employs the CMOS APS for sensing images typically has 8-bit or 12-bit resolution, whether monochrome or color. The resolution translates into a dynamic range of around 48-72 dB. The dynamic range determines the ratio of illumination between the brightest area and the darkest area an image can have for an image sensor to detect and process it without saturation.
It is desirable to maximize dynamic range. When the dynamic range is less than the contrast in an actual scene the image sensor may become saturated. When that happens, the image sensor cannot capture details from bright and dark areas of such an image at the same time. Adjusting or increasing the sensitivity of the dark areas may result in over-saturation of the bright areas, and conversely, adjusting or increasing the sensitivity of the bright areas may result in over-saturation of the dark areas.
SUMMARY
An image sensor for capturing and producing an image is disclosed. The image sensor amplifies pixel signal levels of the image, using two distinct gains to produce two output signal levels. A fusion module combines the two output signal levels in a way that may increase dynamic range.
Embodiments of this aspect of the invention may include one or more of the following features. The amplification circuitry may include two parallel gain amplifiers that provide the two distinct gains at the same time, or may include a single gain amplifier that provides the two distinct gains at different times. The fusion module is analog or digital. The image sensor further includes a time-multiplexed analog-to-digital converter that precedes the fusion module for performing digitization, or two parallel analog-to-digital converters that precede the fusion module for performing digitization. The two gains are chosen based on a pre-determined degree of improvement in a dynamic range of the image sensor with respect to the output signal levels. The amplification circuitry and the fusion module may be located on a single chip.
In certain embodiments of this aspect of the invention, the amplification circuitry further includes switches that are controlled by a reset signal and a switch timing signal for the gain amplifier to provide the two distinct gains at different times, the switch timing signal leading the reset signal by a part of an overall cycle.
Another aspect describes a method of capturing and producing an image with an image sensor. The method includes: amplifying pixel signal levels of the image, using two distinct gains to produce two output signal levels; and combining the two output signal levels.
Embodiments of this aspect of the invention may include one or more of the following features. The amplifying may provide the two distinct gains at the same time or at different times. The combining is performed in analog or digitally. The combining of the two output signal levels may include adding the two output signal levels, or merging the two output signal levels. The amplifying further includes controlling the gain amplifier with a reset signal and a switch timing signal to provide the two distinct gains at different times, the switch timing signal leading the reset signal by a part of an overall cycle.
In certain embodiments of this aspect of the invention, the method further includes digitizing the two output signal levels by a time-multiplexed analog-to-digital converter before the combining, or digitizing the two output signal levels by two analog-to-digital converters before the combining. The two gains may be chosen based on a pre-determined degree of improvement in a dynamic range of the image sensor with respect to the output signal levels.
Still another aspect describes an image sensing system for capturing and producing an image. The image sensing system includes: a photoreceptor array receiving light and producing a signal indicative thereof; readout circuitry amplifying said signal with two separate gains to produce two output signal levels; an analog-to-digital converter for digitizing the two output signal levels; and a fusion module for combining the two output signal levels.
Embodiments of this aspect of the invention may include one or more of the following features. The image sensing system further includes: a color filter array preceding the photoreceptor array to separate color information in the image; and a color processing unit following the fusion module to restore the color information. The photoreceptor array, the readout circuitry, the analog-to-digital converter, and the fusion module may be located on the same chip.
In certain embodiments of this aspect of the invention, the readout circuitry may include two parallel gain amplifiers to provide the two distinct gains at the same time, or may include a single gain amplifiers to provide the two distinct gains at different times.
Embodiments may have one of more of the following advantages. With these aspects of the invention, the CMOS active pixel sensors (APS) can have an extended dynamic range with a small amount of hardware. This allows the CMOS APS to be used for handheld digital cameras or video cameras.
REFERENCES:
patent: 3737794 (1973-06-01), Kurz
patent: 5387930 (1995-02-01), Toh
patent: 5389971 (1995-02-01), Ishida et al.
patent: 5392069 (1995-02-01), Koyama et al.
patent: 5572256 (1996-11-01), Egawa et al.
patent: 5708263 (1998-01-01), Wong
patent: 6073848 (2000-06-01), Giebel
patent: 6130710 (2000-10-01), Yasuda
patent: 6137533 (2000-10-01), Azim
patent: 6501504 (2002-12-01), Tatko et al.
patent: 09-184823 (1997-07-01), None
patent: 09184823 (1997-07-01), None
Fossum Eric R.
Sandor Barna L.
Wang Yibing
Dickstein , Shapiro, Morin & Oshinsky, LLP
Garber Wendy R.
Micro)n Technology, Inc.
Whipkey Jason T.
LandOfFree
Dynamic range extension for CMOS image sensors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dynamic range extension for CMOS image sensors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dynamic range extension for CMOS image sensors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3256090