# Patent

## Title
Multi-imager video camera with automatic exposure control

## Abstract

One embodiment relates to a multi-imager video camera that includes a plurality of imagers, a plurality of image flow processors, a multi-imager video processor, a plurality of exposure control circuits, and a statistics circuit. Each imager includes a sensor array that is configured to capture image frames, and each image flow processor is configured to receive and process the image frames captured from at least one of said imagers. The multi-imager video processor is configured to receive the processed image frames from the plurality of image flow processors. The statistics circuit is configured to determine an auto exposure level based on the captured image frames from a single imager. The multi-image video processor is further configured to receive said auto exposure level and transmit said auto exposure level to all other imagers of the plurality of imagers. Other embodiments and features are also disclosed.

## Background
CROSS-REFERENCE TO RELATED APPLICATION(S)
The present application claims the benefit of U.S. Provisional Application No. 61/244,869, filed Sep. 22, 2009, the disclosure of which is hereby incorporated by reference.


BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to generally to video camera systems.
Description of the Background Art
Video camera systems are commonly used for video surveillance of prescribed areas. For example, such systems are used for surveillance of parking lots, department stores, casinos, banks, and other areas of interest.
Conventional video cameras commonly used in such systems include fixed-type and movable-type cameras. The fixed-type cameras may be configured to observe a fixed area, and the movable-type cameras may be configured with pan-and-tilt motor units to observe a wide area range.
SUMMARY
One embodiment relates to a multi-imager video camera that includes a plurality of imagers, a plurality of image flow processors, a multi-imager video processor, a plurality of exposure control circuits, and a statistics circuit. Each imager includes a sensor array that is configured to capture image frames, and each image flow processor is configured to receive and process the image frames captured from at least one of said imagers. The multi-imager video processor is configured to receive the processed image frames from the plurality of image flow processors. The statistics circuit is configured to determine an auto exposure level based on the captured image frames from a single imager. The multi-image video processor is further configured to receive said auto exposure level and transmit said auto exposure level to all other imagers of the plurality of imagers.
Another embodiment relates to a method of automatic exposure control for a multi-imager video camera. Each imager of an array of imagers in the camera captures image frames and transmits the captured image frames to an associated image flow processor. Each image flow processor processes the captured image frames and transmits the processed image frames to a multi-imager video processor. A statistics circuit receives the captured image frames from a single imager and thereby determines an auto exposure level for the single imager. The multi-imager video processor receives the auto exposure level for the single imager and transmits the auto exposure level for the single imager to all other imagers in the array. Exposure control circuits for all the imagers of the array apply the auto exposure level.
Another embodiment relates to a multi-imager camera which includes an array of imagers, each imager being configured to capture image frames. The camera includes means for determining an auto exposure level based on the captured image frames from a single imager, means for transmitting the auto exposure level for the single imager to all other imagers in the array, and means for applying the auto exposure level in all imagers in the array.
Other embodiments and features are also disclosed.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows a top schematic view showing select components of a video camera in accordance with an embodiment of the invention.
FIG. 1B shows a front perspective view of a video camera in accordance with an embodiment of the invention.
FIG. 2A is a schematic diagram of an imager board of the video camera in accordance with one embodiment of the invention.
FIG. 2B is a schematic diagram of an imager board of the video camera in accordance with another embodiment of the invention.
FIG. 3 is a schematic diagram depicting selection of primary image frames from source image frames for multiple sensors of a video camera in accordance with another embodiment of the invention.
FIG. 4 is an example final image frame resulting from the primary image frames for the multiple sensors of the video camera in accordance with another embodiment of the invention.
FIG. 5 is a schematic diagram showing pixel processing components of an image flow processor in accordance with another embodiment of the invention.
FIG. 6 is a diagram showing two sets of color temperature ranges for the application of anti-rolloff configuration parameters in accordance with another embodiment of the invention.
FIG. 7 is a schematic diagram illustrating a technique for auto-exposure-control and auto-white-balance for multiple sensors of a video camera in accordance with another embodiment of the invention.
FIG. 8 is a schematic diagram illustrating a technique for enabling frame-by-frame view switching in accordance with another embodiment of the invention.
FIG. 9 illustrates re-sizing of an image frame in accordance with an embodiment of the invention.
FIG. 10A illustrates horizontal cropping of an image frame in accordance with an embodiment of the invention.
FIG. 10B illustrates vertical cropping which may be applied after horizontal cropping in accordance with an embodiment of the invention.
FIG. 11 is a schematic diagram illustrating the video camera disclosed herein as interconnected to a plurality of user computers via a network in accordance with an embodiment of the invention.



DETAILED DESCRIPTION
FIG. 1A shows a top schematic view showing select components of a video camera in accordance with an embodiment of the invention. The video camera includes a camera body 102, a main board 104, a multi-imager video processor 106, and five imager boards 108. The camera has a diameter D, and each imager board is of a width W. Shown in FIG. 1A are a field of view 110 for a single imager and a field of view 116 from two adjacent imagers.
Within each single-imager field of view 110, a select-angle field of view 112 may be selected. In a preferred implementation, the single-imager field of view 110 is 38 degrees wide, and the select-angle field of view 112 is 36 degrees wide.
As further shown, there is a small vertical slice 114 (approximately an inch wide, for example) which is between select-angle fields of view 112 of adjacent imagers. As seen in FIG. 1A, his small vertical slice 114 is defined by approximately parallel lines such that the width of the vertical slice 114 is approximately constant and independent of the distance away from the camera. These vertical slices between adjacent imagers are not captured within the final image generated by combining the select-angle fields of view 112 from the five imagers.
FIG. 1B shows a front perspective view of a video camera in accordance with an embodiment of the invention. As shown, the front of the camera may include five faces 120 (-0 through -4) corresponding to the five imager boards 108. In this embodiment, each imager board 108 includes two sensors 122 and 124. In a preferred embodiment, one sensor 122 may be configured to capture daylight images, while the other sensor 124 may be configured to capture nightlight (low light) images. In another embodiment, one sensor 122 may be configured to capture lower resolution images, while the other sensor 124 may be configured to capture higher resolution images.
FIG. 2A is a schematic diagram of an imager board 210 of the video camera in accordance with one embodiment of the invention. As shown, the image light 201 that is received by a first imager (image sensor) 212 is focused by a first barrel lens 202 and filtered by a first infra-red cut filter 204, and the image light 205 that is received by a second imager (image sensor) 214 is focused by a first barrel lens 206 and filtered by a first infra-red cut filter 208. For example, the first barrel lens 202 may be 12 mm or less in length and have an F# greater than 2.2, and the second barrel lens 206 may be 12 mm or less in length and have an F# less than 2.2. The first infra-red cut filter 204 may cutoff (block) infrared light in the wavelength range of 600 nm to 700 nm. The second infra-red cut filter 206 may cutoff (block) infrared light with wavelengths greater than 700 nm, or, alternatively, the second infra-red cut filter 206 may be absent.
In one embodiment, the first imager 212 may be configured as a “day” imager that is optimized for good color fidelity and sharpness, and the second imager 214 may be configured as a “night” imager that is optimized for good low-light performance. In this embodiment, the first imager may be implemented, for example, as a CMOS image sensor array with more than 1.2 million pixels and a pixel size less than 4 microns in width. The image output by the first imager 212 may have a signal-to-noise ratio of greater than 10 dB when scene lighting is greater than 200 Lux. The second imager may be implemented, for example, as a CMOS image sensor array with less than 1.2 million pixels and a pixel size greater than 3 microns in width. The image output by the second imager 214 may have a signal-to-noise ratio of greater than 10 dB when scene lighting is less than 2 Lux.
The first and second imagers 212 and 214 may be controlled by way of control signals received via a control bus 215. The control bus 215 may be implemented as an I2C bus, for example.
A first serial bus 216 may be used to communicate the output image data from the first imager 212 to a day/night multiplexer 220 on the image flow processor (IFP) 211, and a second serial bus 218 may be used to communicate the output image data from the second imager 214 to the day/night multiplexer 220 on the IFP 211. For example, the first and second serial buses may be implemented as MIPI buses.
Based on a multiplexer select (mux select) signal, the multiplexer 220 selects the image data from either the first serial bus 216 (i.e. from the first imager) or the second serial bus 218 (i.e. from the second imager). The selected image data is then received by the IFP core 222. The IFP core 222 may output image data via a serial bus (for example, an MIPI bus) 224 to a multi-imager video processor (MIVP). A connector 215 may be used to connect the control bus 215 and the serial bus 224 to the MIVP.
FIG. 2B is a schematic diagram of an imager board 250 of the video camera in accordance with another embodiment of the invention. The imager board 250 of FIG. 2B differs from the imager board 210 of FIG. 2A in a few ways. First, instead of one IFP core 222, there are two IFP cores 252 and 254 which each receives data from one of the two imagers 212 and 214. These IFP cores 252 and 254 may be integrated with the integrated circuits (ICs) of their respective imagers 212 and 214, or they may be implemented as separate ICs. Second, instead of a multiplexer 220 to select the image data and a serial bus 224 to output the select image data, a shared parallel bus 256 is used to select and output the image data the the MIVP. In this case, control signals from the control bus 258 ensures that only one IFP core is driving the parallel bus 256 at any one time (to avoid contention). The connector 260 may be used to connect the control bus 258 and the parallel bus 256 to the MIVP.
FIG. 3 is a schematic diagram depicting selection of primary image frames from source image frames for multiple sensors of a video camera in accordance with another embodiment of the invention. The five source rectangles (CTG0 SOURCE-RECT, CTG1 SOURCE-RECT, CTG2 SOURCE-RECT, CTG3 SOURCE-RECT, CTG4 SOURCE-RECT and CTG5 SOURCE-RECT) are the source image data within the field of view of the five imagers of the video camera. The source rectangles (for example, each 1536×2048 pixels) are depicted as non-aligned because the imagers are expected to have mechanical imperfections. The five primary rectangles (CTG0 PRIMARY-RECT, CTG1 PRIMARY-RECT, CTG2 PRIMARY-RECT, CTG3 PRIMARY-RECT, and CTG4 PRIMARY-RECT) are selected by each IFP core “cherry picking” a smaller rectangle (for example, 1300×1800 pixels) within its field of view. For example, as discussed above in relation to FIG. 1A, while the source rectangles may obtain image data from a 38 degree wide field of view, the primary rectangles may represent the image data from a slightly narrower 36 degree field of view.
FIG. 4 is an example final image frame resulting from the multiple sensors of the video camera in accordance with another embodiment of the invention. In this example, after cropping and resizing such that each of the five component image frames is 384×1080 pixels, the final image frame may be 1920×1080 pixels, as shown in FIG. 4. Note that no digital stitching is required to obtain this final image.
FIG. 5 is a schematic diagram showing pixel processing components of an image flow processor (IFP) in accordance with another embodiment of the invention. As shown, the image sensor array (imager) output raw pixel data to the IFP core. The IFP core includes, among other components, an anti-roll-off block, a color recovery block, a color correction block, and a gamma correction block. These blocks process the pixel data. The processed pixel data is then transmitted to the multi-imager video processor.
FIG. 6 is a diagram showing two sets of color (black-body) temperature ranges for the application of anti-rolloff configuration parameters in accordance with another embodiment of the invention. Each set includes four color temperature ranges for the application of different anti-rolloff configuration parameters. The four color temperature ranges in each set are labeled 2900K, 4000K, 5000K, and 6500K. The first set of color temperature ranges 502 are shifted in temperature compared with the second set of color temperature ranges 504. A transition to a higher range (for example, from the 2900K range to the 4000K range) occurs according to the first set of ranges 502, while a transition to a lower range (for example, from the 4000K range to the 2900 K range) occurs according to the second set of ranges. This provides an advantageous hysteresis effect in the application of the anti-rolloff configuration parameters.
FIG. 7 is a schematic diagram illustrating a technique for auto-exposure-control (AEC) and auto-white-balance (AWB) for multiple sensors of a video camera in accordance with another embodiment of the invention. The AEC and AWB for each sensor is controlled by a control blocks for the sensor and associated IFP and uses a statistics block to analyze data from the associated IFP.
As shown, the video camera is configured such that the AEC and AWB is turned on at the microcontroller (μcontroller) for only one of the five imagers, and turned off at the microcontroller for the other four imagers. In a preferred embodiment, the AEC and AWB is turned on only at the microcontroller for the middle imager of the array of imagers (for example, the imager being used, either day 122 or night 124, of face 120-2 in FIG. 1B). By disabling the AEC and AWB controls on all but one of the imagers, the AEC and AWB updates from the single AEC/AWB-enabled imager may be transmitted 702 to the MIVP. The MIVP may then clone (copy) the AEC and AWB updates and send 704 them to the other imagers. This configuration is very low cost and efficient to implement and advantageously provides AEC and AWB across all the five imagers in a synchronized manner.
FIG. 8 is a schematic diagram illustrating a technique for enabling frame-by-frame view switching in accordance with another embodiment of the invention. Shown in this figure is one imager of the multiple imagers in the camera.
As shown, the sensor array of each imager performs cropping from the source rectangular frame (CTG SOURCE-RECT) to the primary rectangular frame (CTG PRIMARY-RECT). In addition, circuitry may be included in the sensor IC for integration time control and analog gain control. The integration time control is used to provide exposure control, while the analog gain control is used to provide white balance control.
As further shown, the IFP for each imager may include resizing and cropping circuitry. The IFP may be incorporated onto the same integrated circuit as the sensor array, or the IFP may be implemented on a separate integrated circuit. In one embodiment, the IFP first resizes the image in the primary rectangular frame, and then performs a “horizontal” cropping of the resized image. In an alternative embodiment, the horizontal cropping may be performed in the sensor by appropriate adjustment of the primary rectangular frame so as to implement the desired horizontal crop. An example of a resizing of an image is shown in FIG. 9. The horizontal cropping reduces a number of pixels in a vertical dimension of the image. An example of a horizontal cropping of an image is shown in FIG. 10A.
The MIVP receives the horizontally-cropped resized images from the multiple imagers to obtain a combined image. The MIVP may then perform a “vertical” cropping of the combined image to create a final image frame. The vertical cropping reduces a number of pixels in a horizontal dimension of the image. An example of a vertical cropping of an image is shown in FIG. 10B. The technique of performing the horizontal cropping in the IFP (or sensor circuitry) and vertical cropping in the MIVP is advantageously efficient and reduces the amount of image data that is needed to be received and processed by the MIVP.
As further shown in FIG. 8, there may be a plurality of update queues, one for each imager. Each update queue may be configured to hold parameters to be sent on a frame-by-frame basis to the corresponding imager. The parameters may include, for example, the resizing and horizontal cropping parameters for a frame. The parameters may also include integration time control and analog gain control parameters to be applied by certain sensors as described above in relation to FIG. 7. In one implementation, a falling edge of a Frame_Valid signal from an imager may cause an interrupt signal to be sent to a microcontroller within the MIVP. The microcontroller may then cause the parameters at the top of the corresponding queue to be released to be applied to the next frame by that imager.
The above-described capability to switch views (i.e. to re-size and crop) on a frame-by-frame basis may be advantageously applied to enable the camera to simultaneously provide different views to multiple users.
FIG. 11 is a schematic diagram illustrating the video camera disclosed herein as interconnected to a plurality of user computers 1106 via a network 1104 in accordance with an embodiment of the invention. As shown, the video camera includes a network processor (packetizer) 1102. While the embodiment shown in FIG. 11 has a network processor 1102 as a separate processor that is interconnected with the MIVP, another embodiment may have the network processor 1102 as part of the MIVP.
The MIVP may be configured to encrypt and compress the final image frames to generate encoded image frames. The network processor 1102 may be configured to receive the encoded image frames generated by the MIVP and to generate data packets therefrom which are addressed to a plurality of user computers. The data packets addressed to a particular user computer contain the encoded image frames which are customized for that user computer.
For example, consider that the above-discussed camera is networked to a network which includes three user computers: User A; User B; and User C. Further consider that each user computer may select a different view for display by way of a user interface on the user computer. For example, the user interface may allow the user to crop and re-size the image to be viewed. In this particular example, consider that the camera obtains image data at 60 frames per second, and that the priorities between the users is such that User A is to receive video at 30 frames per second, User B is to receive video at 10 frames per second, and User C is to receive video at 20 frames per second. The Update Queues in FIG. 8 may each contain the following sequence of parameters, where A indicates parameters for the view requested by User A, B indicates parameters for the view requested by User B and C indicates parameters for the view requested by User C).

CACBCACACBCACACBCACACBCA . . .

For frames taken with parameters A, the network processor may packetize those frames with the network address of User A and transmit those packets to User A via the network. For frames taken with parameters B, the network processor may packetize those frames with the network address of User B and transmit those packets to User B via the network. For frames taken with parameters C, the network processor may packetize those frames with the network address of User C and transmit those packets to User C via the network.

In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

## Claims

1. A multi-imager video camera apparatus comprising:
a plurality of imagers, each imager comprising a sensor array that is configured to capture image frames;
a plurality of image flow processors, each image flow processor being configured to receive and process the image frames captured from a corresponding one of said imagers;
a multi-imager video processor configured to receive the processed image frames from the plurality of image flow processors;
a plurality of auto exposure control circuits, each auto exposure control circuit being coupled to a corresponding imager of the plurality of imagers; wherein the auto exposure control circuit associated with only one imager is kept active while the auto exposure control circuit associated with each remaining imager other than said one imager is deactivated; and
a statistics circuit configured to determine a n auto exposure level based on the captured image frames from the said one imager wherein the multi-image video processor is further configured to clone said auto exposure level and to transmit said auto exposure level to a plurality of control blocks, each associated with the remaining imagers whose auto exposure control circuits have been deactivated to enable each control block to synchronize the auto exposure level of its associated imager with the auto exposure level determined for said one imager.

2. The apparatus of claim 1,
wherein the statistics circuit is further configured to determine updates to an auto white-balance level based on the captured image frames from said one imager, wherein the multi-image video processor is further configured to receive the updates to said auto white-balance level and transmit the updates to said auto white-balance level to the control blocks of circuits in all other imagers of the plurality of imagers, and
wherein each control block receives the updates to said auto white-balance level and applies said auto white-balance level to control exposure level of its associated imager.

3. The apparatus of claim 1, wherein the plurality of imagers form an array, and wherein said one imager is in a central position in the array.

4. A method of automatic exposure control for a multi-imager video camera, the method comprising:
each imager of an array of imagers in the camera capturing image frames;
each imager transmitting the captured image frames to an associated image flow processor;
each image flow processor processing the captured image frames;
each image flow processor transmitting the processed image frames to a multi-imager video processor;
the multi-imager video processor configured to keep an auto exposure control circuit associated with only one imager active while deactivating an auto exposure control circuit associated with each remaining imager other than said one imager;
a statistics circuit receiving the captured image frames from said one imager and thereby determining an auto exposure level for the said one imager;
the multi-imager video processor receiving the auto exposure level for said one imager from the statistics circuit;
the multi-imager video processor transmitting the auto exposure level for the said one imager to each imager in the array besides-said one imager to synchronize auto exposure levels across the imagers based on the auto exposure level for said one imager.

5. The method of claim 4, wherein said one imager is in a central position in the array.

6. The method of claim 4, further comprising:
the statistics circuit determining updates to an auto white-balance level for said one imager based on the captured image frames from said one imager.

7. The method of claim 6, further comprising:
the multi-image video processor receiving the updates to said auto white-balance level; and
the multi-image video processor transmitting the updates to said auto white-balance level to a control block associated with each remaining imager of the array.

8. The method of claim 7, further comprising:
the control block associated with each remaining imager of the array applying said auto white-balance level.

9. A multi-imager camera comprising:
an array of imagers in the camera, wherein each imager is configured to capture image frames;
means for activating auto exposure control in respect of only one imager in the array of imagers;
means for deactivating auto exposure control in respect of each imager in the array of imagers other than said one imager;
means for determining an auto exposure level based on the captured image frames from said one imager;
means for transmitting the auto exposure level for said one imager to all other imagers in the array; and
means for applying the auto exposure level in all imagers in the array.

10. The multi-imager camera of claim 9, wherein said one imager is in a central position in the array.

11. The multi-imager camera of claim 9, further comprising:
means for determining an auto white-balance level based on the captured image frames from said one imager; and
means for applying the auto white-balance level in all imagers in the array.