IMAGE SENSOR AND IMAGE CAPTURE SYSTEM WITH EXTENDED DYNAMIC RANGE
An image sensor includes a plurality of pixels; a color filter pattern spanning at least a portion of the pixels, wherein the color filter pattern forms a color filter kernel having colors in a predetermined arrangement; and a mechanism for controlling integration time of the pixels, wherein the integration time of the plurality of pixels is spatially variant in a pattern that is correlated with the color filter array kernel.
This is a continuation application of U.S. application Ser. No. 10/654,313 filed Sep. 3, 2003.
FIELD OF THE INVENTIONThe present invention pertains to semiconductor-based image sensors with increased dynamic range.
BACKGROUND OF THE INVENTIONSolid state image sensors are now used extensively in many types of image capture applications. The two primary image sensor technologies utilized are Charge Coupled Devices CCD and CMOS x-y addressable devices. Currently, there exists many different specific embodiments of both technologies, including Active Pixel Sensors (APS) and Passive Pixel Sensors (PPS) for CMOS x-y addressable devices. All are basically comprised of a set or array of photodetectors that convert incident light into an electrical signal that can be readout and used to construct an image correlated to the incident light pattern. The exposure or integration time for the array of photodetectors can be controlled by well known mechanisms. The signal represents the amount of light incident upon a pixel photosite. The dynamic range (DR) of an imaging sensing device is defined as the ratio of the effective maximum detectable signal level, typically referred to as the saturation signal, (Vsat), with respect to the rms. noise level of the sensor, (σnoise). This is shown in Equation 1.
Dynamic Range=Vsat /θnoise Equation 1
Image sensor devices such as charge coupled devices (CCD) that integrate charge created by incident photons have dynamic range limited by the amount of charge that can be collected and held in a given photosite, (Vsat). For example, for any given CCD, the amount of charge that can be collected and detected in a pixel is proportional to the pixel area. Thus for a commercial device used in a megapixel digital still camera (DSC), the number of electrons representing Vsat is on the order of 13,000 to 20,000 electrons. If the incident light is very bright and creates more electrons that can be held in the pixel or photodetector, these excess electrons are extracted by the anti-blooming mechanism in the pixel and do not contribute to an increased saturation signal. Hence, the maximum detectable signal level is limited to the amount of charge that can be held in the photodetector or pixel. The DR is also limited by the sensor noise level, θnoise. Due to the limitations on Vsat, much work has been done in CCD's to decrease θnoise to very low levels. Typically, commercial megapixel DSC devices have a DR of 1000:1 or less.
The same limitations on DR also exist for APS and PPS devices. The Vsat is limited by the amount of charge that can be held and isolated in the photodetector. Excess charge is lost. This can become even more problematic with APS and PPS compared to CCD due to the active and passive components within the pixel, limiting the area available for the photodetector, and due to the low voltage supply and clocks used in CMOS devices. In addition, since APS devices have been used to provide image sensor systems on a chip, the digital and analog circuits used on APS devices such as timing and control and analog to digital conversion, that are not present on CCD's, provide a much higher noise floor on APS devices compared to CCD. This is due to higher temporal noise as well as possibly quantization noise from the on-chip analog to digital converter.
In commonly assigned U.S. Pat. No. 6,069,377,issued May 30, 2000, entitled IMAGE SENSOR INCORPORATING SATURATION TIME MEASUREMENT TO INCREASE DYNAMIC RANGE, by Prentice et al., Prentice discloses the prior art approaches to extending dynamic range of APS devices, and discloses a new invention to extend dynamic range. This method has the disadvantage of requiring more than four transistors per pixel and limits the size of the pixel that can be made. In U.S. Pat. No. 6,307,195, issued Oct. 23, 2001, entitled VARIABLE COLLECTION OF BLOOMING CHARGE TO EXTEND DYNAMIC RANGE, and U.S. Pat. No. 6,486,504, issued Nov. 26, 2002, entitled CMOS IMAGE SENSOR WITH EXTENDED DYNAMIC RANGE, both by Guidash, Guidash discloses extending dynamic range by collection of the charge that blooms from the photodetector, and by co-integration of the photodetector and floating diffusion within a single pixel. These approaches have the potential disadvantage of spatial variation of the photodetector saturation level contributing to fixed pattern noise in the sensor, and does not increase the sensitivity of the sensor.
Prior art APS devices also suffer from poor sensitivity to light due to the limited fill factor induced by integration of active components in the pixel, and by loss of transmission of incident light through the color filter layer placed above the pixel.
From the foregoing discussion it should be apparent that there remains a need within the prior art for a device that retains extended dynamic range while retaining low fixed pattern noise, small pixel, and high sensitivity.
SUMMARY OF THE INVENTIONThe present invention provides a means to control the integration separately for any given spatial pattern on the image sensor, and more specifically for a pattern that is compatible with one or two dimensions of the kernel in the CFA pattern. This is done by providing separate TG or RG busses for pixels in a given row or set of rows, or by providing any means to control integration time separately for a given pattern of pixels in the image sensor array. By doing so, valid data is always available for the dark and bright regions of an image simultaneously.
Advantageous Effect Of The InventionThese and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
Typical prior art image sensor pixel arrays are shown in
Referring to
The sensor architecture of
A second embodiment of the present invention is shown in the array in
Referring to
As previously discussed, this provides an image sensor and image capture system with wide intra-scene dynamic range and wide exposure latitude. A single image capture can render a full range of image information with optimization of the integration time for low light levels without clipping signal information in the high light regions of an image. This can greatly simplify the exposure control system and algorithms in an imaging system since choice of exposure or integration time does not need to be as precise.
It should also be noted that an image capture system using such a sensor can be used to measure or determine the dynamic range of a scene to set the two integration times appropriately. During the metering phase of a camera system, two widely separated integration times can be used to determine the maximum and minimum light levels in the scene. The two integration times can then be adjusted to cover the range of illumination in the scene. For example, if the dynamic range of the scene to be captured is within the inherent dynamic range of the image sensor, then the two integration times can be set to the same value. If the scene contains a dynamic range that is wider than the true dynamic range of the sensor, then the two integration times can be set to match or optimally cover the dynamic range of the scene.
Referring to
The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.
PARTS LIST
- 10 pixel array
- 20 pixel array
- 30 pixel array
- 40a mated pair of rows
- 40b mated pair of rows
- 50 sensor array
- 60a 2 by 2 pixel pattern
- 60b 2 by 2 pixel pattern
- 70 multiple signal line
- 80 single integration time control line
- 90 camera
Claims
1. An image sensor comprising:
- (a) a plurality of pixels arranged in an array of rows and columns;
- (b) a color filter pattern spanning at least a portion of the pixels, wherein the color filter pattern forms a plurality of color filter kernels having at least one color of every color in the color filter pattern in a predetermined arrangement with an identical pattern of colors in each color filter kernel, and wherein the color filter kernels are arranged in at least two different uniformly distributed sets that are correlated with the color filter pattern; and
- (c) a mechanism for independent control of an integration time of each uniformly distributed set, wherein a first uniformly distributed set has a first integration time and a second uniformly distributed set has a second integration time that is different from the first integration time.
2. The image sensor as in claim 1, wherein the color filter pattern is a Bayer color filter pattern.
3. The image sensor as in claim 1, wherein the color filter pattern is a 2×2 kernel.
4. The image sensor as in claim 3, wherein the at least two different uniformly distributed sets comprise an alternating pattern of two lines of 2×2 kernels.
5. The image sensor as in claim 3, wherein the at least two different uniformly distributed sets comprise 2×2 kernels.
6. The image sensor as in claim 5, wherein the integration time pattern of adjacent two lines groups is offset by two pixels.
7. The image sensor of claim 1 wherein the integration time pattern is a multiple of the color filter kernel.
8. An image sensor comprising:
- (a) a plurality of pixels arranged in an array of rows and columns; and
- (b) an integration time control line for each row of pixels, wherein each integration time control line is routed to a portion of the pixels in one row and to a portion of the pixels in an adjacent row to provide output signal values having signals that are generated from pixels within at least two physically separate rows within the array.
9. A camera comprising:
- (a) an image sensor comprising: (a1) a plurality of pixels arranged in an array of rows and columns; (b) a color filter pattern spanning at least a portion of the pixels, wherein the color filter pattern forms a plurality of color filter kernels having at least one color of every color in the color filter pattern in a predetermined arrangement with an identical pattern of colors in each color filter kernel, and wherein the color filter kernels are arranged in at least two different uniformly distributed sets that are correlated with the color filter pattern; and (c) a mechanism for independent control of an integration time of each uniformly distributed set, wherein a first uniformly distributed set has a first integration time and a second uniformly distributed set has a second integration time that is different from the first integration time.
10. The camera as in claim 9, wherein the color filter pattern is a Bayer color filter pattern.
11. The camera as in claim 9, wherein the color filter pattern is a 2×2 kernel.
12. The camera as in claim 11, wherein the at least two different uniformly distributed sets comprise an alternating pattern of two lines of 2×2 kernels.
13. The camera as in claim 11, wherein the at least two different uniformly distributed sets comprise 2×2 kernels.
14. The camera as in claim 13, wherein the integration time pattern of adjacent two lines groups is offset by two pixels.
15. The camera as in claim 1, wherein the integration time pattern is a multiple of the color filter kernel.
16. The camera as in claim 9 further comprising a mechanism that reads out at least a subset of the plurality of pixels and uses the signal values obtained from the readout to determine the integration times of the plurality of pixels.
17. A camera comprising:
- (a) an image sensor comprising:
- (a1) a plurality of pixels arranged in an array of rows and columns; and
- (a2) an integration time control line for each row of pixels, wherein each integration time control line is routed to a portion of the pixels in one row and to a portion of the pixels in an adjacent row to produce output signal values having signals that are generated from pixels within at least two physically separate rows within the array.
18. The camera as in claim 17, further comprising:
- (b) memory; and
- (c) means for writing the output signal values into two row locations in the memory for each row of pixels, wherein the output signal values are reconstructed in the memory.
19. The image sensor of claim 1, further comprising an integration time control line for each row of pixels, wherein each integration time control line is routed to a portion of the pixels in two adjacent rows to provide output signal values having signals that are generated from pixels within the adjacent rows within the array.
20. The camera of claim 9, wherein the image sensor further comprises an integration time control line for each row of pixels, wherein each integration time control line is routed to a portion of the pixels in two adjacent rows to provide output signal values having signals that are generated from pixels within the adjacent rows within the array.
21. The image sensor of claim 8, further comprising a color filter pattern spanning at least a portion of the pixels, wherein the color filter pattern forms a plurality of color filter kernels having at least one color of every color in the color filter pattern in a predetermined arrangement with an identical pattern of colors in each color filter kernel, and wherein the color filter kernels are arranged in at least two different uniformly distributed sets that are correlated with the color filter pattern.
22. The image sensor of claim 21, wherein the color filter pattern is a 2×2 kernel.
23. The image sensor of claim 8, further comprising:
- a memory; and
- means for writing the output signal values into two row locations in the memory for each row of pixels to reconstruct an image.
24. An image sensor comprising:
- (a) a plurality of pixels arranged in an array of rows and columns;
- (b) a color filter pattern spanning at least a portion of the pixels, wherein the color filter pattern forms a plurality of color filter kernels having at least one color of every color in the color filter pattern in a predetermined arrangement with an identical pattern of colors in each color filter kernel, and wherein the color filter kernels are arranged in at least two different uniformly distributed sets that are correlated with the color filter pattern; and
- (c) a mechanism for independent control of an integration time of each uniformly distributed set, wherein a first uniformly distributed set has a first integration time and a second uniformly distributed set has a second integration time that is different from the first integration time, and wherein at least a portion of the pixels in at least one of the uniformly distributed sets does not contain valid signal level information.
Type: Application
Filed: Oct 6, 2010
Publication Date: Jan 27, 2011
Inventor: Robert M. Guidash (Rochester, NY)
Application Number: 12/898,809
International Classification: H04N 5/335 (20060101);