System and apparatus for adjusting luminance levels of multiple channels of panoramic video signals

Panoramic imaging system and process for adjusting luminance levels of a set of video signals captured by a set of cameras in the panoramic imaging system is disclosed. In some embodiments, the disclosed panoramic imaging system includes a housing, the set of cameras and an integrated circuit (IC) chip coupled to the set of cameras and configured to adjust luminance levels of a set of video signals captured by the set of cameras, thereby enabling the set of cameras to capture the set of video signals having substantially the same luminance level. The panoramic imaging system further includes an image processor coupled to the IC chip and configured to receive the set of video signals having substantially the same luminance level and to post-process the set of video signals.

TECHNICAL FIELD

The present disclosure generally relates to the field of panoramic imaging, and more specifically to the systems and techniques for adjusting the luminance levels of a set of video signals captured by a set of cameras in a panoramic imaging system.

BACKGROUND

Panoramic photography, the taking of a photograph or photographs covering an elongated field of view, has a long history in photography. Perhaps the most primitive method of panoramic photography is the taking of several adjoining photos with a conventional camera and then mounting the prints together in alignment to achieve a complete panorama. Modern techniques adapt this method by using digital cameras to capture the images, and then using computer image processing techniques to align the images and stitch the images together as a single panoramic image.

The continuous development of digital camera technologies along with constantly increasing speed and processing power of computers have laid the foundation for digital imaging systems that are capable of acquiring image data for the automatic creation of wide to entire 360° panoramas, including both still panoramic images and dynamic panoramic movies.

Currently, main-stream panoramic imaging solutions can be generally categorized into the multi-lens approach and the single-lens approach. Multi-lens panoramic camera systems utilize a set of cameras for simultaneous image or video capturing. The cameras are typically arranged in either a parallel fashion or a converged fashion, such that each camera's field of view overlaps with that of at least one other camera. This way, the total field of view covered by the multi-camera systems is significantly enlarged as compared to a conventional single-lens camera. Hence, during panoramic video capturing, a multi-camera panoramic system generates multiple channels of simultaneous video signals, which are immediately output from the multiple cameras and transmitted to a processor, such as an accelerated processing unit (APU) of the multi-camera panoramic system for post-processing.

When using a multi-camera panoramic imaging system to capture multiple video signals, what can happen is that lighting conditions for the different cameras are not uniform, which can result in differences in luminance for the different channels of the video signals. This situation can subsequently lead to non-uniformities in luminance within a panoramic image generated by stitching together the multiple channels of camera images having different luminance levels. Conventional techniques address the problem of non-uniformities in luminance associated with the stitched panoramic images by post-processing the stitched images after the multi-channel of cameras images have been stitched together.

SUMMARY

Described herein are systems and techniques for adjusting luminance levels of a set of video signals captured by a set of cameras in a panoramic imaging system. The proposed systems and techniques provide a solution for resolving non-uniformities in luminance within a composite panoramic image generated by stitching multiple camera images having different luminance levels. In various embodiments, a proposed system includes two or more cameras for capturing a set of video signals and a field-programmable gate array (FPGA) coupled to the two or more cameras for processing the set of video signals captured by the two or more cameras and adjusting the operating settings of the two or more cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level. The proposed systems and techniques provide a solution to resolve non-uniformities in luminance within composite panoramic images prior to constructing the composite panoramic images and thereby avoiding post-processing the panoramic images on a separate computer after the multi-channel camera images have been stitched together.

In one aspect, a panoramic imaging system capable of adjusting luminance levels of a set of video signals captured by a set of cameras in the panoramic imaging system is disclosed. This panoramic imaging system includes a housing, the set of cameras and an integrated circuit (IC) chip coupled to the set of cameras and configured to adjust luminance levels of a set of video signals captured by the set of cameras, thereby enabling the set of cameras to capture the set of video signals having substantially the same luminance level. The panoramic imaging system further includes an image processor coupled to the IC chip and configured to receive the set of video signals having substantially the same luminance level and to post-process the set of video signals. In some embodiments, post-processing the set of video signals using the image processor includes stitching a set of video images captured by the set of cameras and having substantially the same luminance level to construct a composite panoramic video image.

In some implementations, the IC chip includes: an input interface configured to receive a set of video images captured by the set of cameras; a set of luminance statistics modules coupled to the input interface and configured to generate a set of luminance histograms corresponding to the set of video images; an analysis module coupled to the set of luminance statistics modules and configured to generate a set of adjustment parameters indicative of operating settings of the set of cameras; a luminance uniformity adjustment module coupled to the analysis module and configured to process the adjustment parameters to generate a set of control parameters for adjusting the operating settings of the set of cameras; and a set of luminance control modules coupled to the luminance uniformity adjustment module and configured to use the set of control parameters to adjust the operating settings of the set of cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level.

In some implementations, the input interface is coupled to the set of cameras through a parallel YUV data path.

In some implementations, the set of luminance control modules is coupled to the set of cameras through an I2C bus.

In some implementations, the set of luminance control modules is implemented as an I2C master controller.

In some implementations, the IC chip includes a field-programmable gate array (FPGA).

In some implementations, the image processor includes an accelerated processing unit (APU).

In another aspect, an integrated circuit (IC) chip implemented on a panoramic imaging system for adjusting luminance levels of a set of video signals captured by a set of cameras in the panoramic imaging system is disclosed. This IC chip includes: an input interface configured to receive a set of video images captured by the set of cameras; a set of luminance statistics modules coupled to the input interface and configured to generate a set of luminance histograms corresponding to the set of video images; an analysis module coupled to the set of luminance statistics modules and configured to generate a set of adjustment parameters indicative of operating settings of the set of cameras; a luminance uniformity adjustment module coupled to the analysis module and configured to process the adjustment parameters to generate a set of control parameters for adjusting the operating settings of the set of cameras; and a set of luminance control modules coupled to the luminance uniformity adjustment module and configured to use the set of control parameters to adjust the operating settings of the set of cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level.

In some implementations, the set of luminance control modules is configured to adjust the operating settings of the set of cameras by increasing the sensor gain for a camera in the set of cameras determined to have a lower lighting condition than other cameras in the set of cameras or decreasing the sensor gain for a camera in the set of cameras determined to have a higher lighting condition than other cameras in the set of cameras. In some embodiments, the operating settings include at least an exposure value.

In some implementations, the IC chip further includes an output interface configured to output the set of video signals having substantially the same luminance level to an image processor in the panoramic imaging system for post-processing. In some embodiments, the IC chip includes a field-programmable gate array (FPGA).

In yet another aspect, a process for adjusting luminance levels of a set of video signals captured by a set of cameras in a panoramic imaging system is disclosed. This process includes some or all of the following steps: receiving a set of video images captured by the set of cameras; generating a set of luminance histograms corresponding to the set of video images; analyzing the set of luminance histograms to generate a set of adjustment parameters indicative of operating settings of the set of cameras; generating a set of control parameters for adjusting the operating settings of the set of cameras based at least on the set of adjustment parameters; and using the set of control parameters to adjust the operating settings of the set of cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level.

In some implementations, the process analyzes the set of luminance histograms to generate an overall luminance level for each of the received set of video images.

In some implementations, the set of control parameters includes at least a sensor gain.

In some implementations, the set of control parameters includes a sensor gain and a white balance value.

In some implementations, the process adjusting the operating settings of the set of cameras by increasing the sensor gain for a camera in the set of cameras determined to have a lower lighting condition than other cameras in the set of cameras or decreasing the sensor gain for a camera in the set of cameras determined to have a higher lighting condition than other cameras in the set of cameras.

In some implementations, the process further includes transmitting the set of video signals having substantially the same luminance level to a panoramic image processor for post-processing.

DETAILED DESCRIPTION

Described herein are systems and techniques for adjusting luminance levels of a set of video signals captured by a set of cameras in a panoramic imaging system. The proposed systems and techniques provide a solution for resolving non-uniformities in luminance within a composite panoramic image generated by stitching multiple camera images having different luminance levels. In various embodiments, a proposed system includes two or more cameras for capturing a set of video signals and a field-programmable gate array (FPGA) coupled to the two or more cameras for processing the set of video signals captured by the two or more cameras and adjusting the operating settings of the two or more cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level. The proposed systems and techniques provide a solution to resolve non-uniformities in luminance within composite panoramic images prior to constructing the composite panoramic images and thereby avoiding post-processing the panoramic images on a separate computer after the multi-channel camera images have been stitched together.

In one aspect, a panoramic imaging system capable of adjusting luminance levels of a set of video signals captured by a set of cameras in the panoramic imaging system is disclosed. This panoramic imaging system includes a housing, the set of cameras and an integrated circuit (IC) chip coupled to the set of cameras and configured to adjust luminance levels of a set of video signals captured by the set of cameras, thereby enabling the set of cameras to capture the set of video signals having substantially the same luminance level. The panoramic imaging system further includes an image processor coupled to the IC chip and configured to receive the set of video signals having substantially the same luminance level and to post-process the set of video signals. In some embodiments, post-processing the set of video signals using the image processor includes stitching a set of video images captured by the set of cameras and having substantially the same luminance level to construct a composite panoramic video image.

In another aspect, an integrated circuit (IC) chip implemented on a panoramic imaging system for adjusting luminance levels of a set of video signals captured by a set of cameras in the panoramic imaging system is disclosed. This IC chip includes: an input interface configured to receive a set of video images captured by the set of cameras; a set of luminance statistics modules coupled to the input interface and configured to generate a set of luminance histograms corresponding to the set of video images; an analysis module coupled to the set of luminance statistics modules and configured to generate a set of adjustment parameters indicative of operating settings of the set of cameras; a luminance uniformity adjustment module coupled to the analysis module and configured to process the adjustment parameters to generate a set of control parameters for adjusting the operating settings of the set of cameras; and a set of luminance control modules coupled to the luminance uniformity adjustment module and configured to use the set of control parameters to adjust the operating settings of the set of cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level.

In yet another aspect, a process for adjusting luminance levels of a set of video signals captured by a set of cameras in a panoramic imaging system is disclosed. This process includes some or all of the following steps: receiving a set of video images captured by the set of cameras; generating a set of luminance histograms corresponding to the set of video images; analyzing the set of luminance histograms to generate a set of adjustment parameters indicative of operating settings of the set of cameras; generating a set of control parameters for adjusting the operating settings of the set of cameras based at least on the set of adjustment parameters; and using the set of control parameters to adjust the operating settings of the set of cameras, thereby enabling the set of cameras to capture a set of video signals having substantially the same luminance level.

FIG. 1is a schematic top view of an example panoramic imaging system in accordance with some embodiments described herein. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided.

As shown inFIG. 1, panoramic imaging system100ofFIG. 1includes four cameras101-104, a control system110, and housing120. Each of four cameras101-104may be a digital camera. In some aspects, each of cameras101-104may include a wide-angle lens (e.g., fisheye lens) to capture image data. The horizontal angle of view of a wide-angle lens may be greater than 180 degrees and the vertical angle of view of a wide-angle lens may be greater than 180 degrees.FIG. 1shows cameras101-104are distributed evenly across on a frame of housing120, for example, on four sides of the frame having a rectangular shape. Each of cameras101-104may face a ⅛ of a 360° field. It can be appreciated that cameras101-104may be distributed in any other arrangement and each of cameras101-104may face any portion of a 360° field. Furthermore, panoramic imaging system100may include a greater or a fewer number of cameras than the four cameras shown inFIG. 1. For example, panoramic imaging system100may include 2, 3, 6, 8, 10, or 12 cameras.

The control system110may include one or more electronic circuitries, such as a system on chip (SOC) with a field-programmable gate array (FPGA), Accelerated Processing Unit (APU) and peripheral electronic circuitries, for processing the image data captured by cameras101-104to produce wide to entire 360° panoramas, including both still images and movies. It can now be appreciated that outputs of panoramic imaging system100may be panoramas stitched from a set of original images captured by cameras101-104.

When panoramic imaging system100is used to capture multiple channels of video images using cameras101-104, lighting conditions for the different cameras may be non-uniform. For example,FIG. 1illustrates lighting120incident on panoramic imaging system100from the upper left so that cameras101and102receive more lighting120than camera103and104do. As a result, the two channels of video signals captured by cameras101and102may have a higher luminance level than the other two channels of video signals captured by cameras103and104. Without compensating for such non-uniform lighting conditions can lead to non-uniformities in luminance within a panoramic image generated by stitching together the multiple channels of camera images. In various embodiments, control system110is configured to process the multiple channels of video images captured by cameras101-104and output multiple channels of adjusted video images of substantially the same luminance. Notably, the above luminance adjustment operations are performed on the raw video signals prior to using the processed raw video signals to construct panoramic images. In some embodiments, the luminance adjustment functions of the control system110are implemented on and performed by a field-programmable gate array (FPGA) or one or more application specific integrated circuits (ASICs).

Cameras101-104and the control system110may be enclosed in housing120, such as a protective housing to reduce environmental effects on the components. In some embodiments, the protective housing is waterproof, dustproof, shockproof, freeze-proof, or any combination thereof. In some aspects, housing120may include one or more mechanical parts for mounting, housing and/or moving the cameras101-104and/or other optical components. Furthermore, in some embodiments, cameras101-104can be reversibly coupled to or detached from the remaining system, such that an end user may select different models of cameras101-104to be used with panoramic imaging system100according to particular needs or preferences.

It can be appreciated that a variety of embodiments of cameras101-104may be employed. These embodiments may have different numbers and/or arrangements of cameras than cameras101-104, but a common feature may be that each camera's field of view overlaps with that of at least one other camera, thereby enabling panoramic imaging system100to capture a total field of view according to the design.

Those of ordinary skills in the art upon reading the present disclosure should become aware of how a panoramic imaging system according to the present disclosure can be designed to satisfy particular needs. Particularly, skilled persons in the art would follow the guidance provided by the present disclosure to select a suitable number of cameras with reasonable fields of view and arrange the set of cameras such that neighboring cameras' fields of view have reasonable overlap that enables the system to cover a desirable total field and reliably process image information in the overlapping field to produce panoramas.

FIG. 2illustrates a block diagram of an exemplary implementation of the panoramic imaging system100described inFIG. 1in accordance with some embodiments described herein. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided.

Receiving module201may receive image or video data captured by the multiple cameras101-104in a YUV format. Detection module202may detect a signal format of the received image or video data by receiving module201. The signal format of the image or video data may include resolution, pixel clock, line frequency information, and/or field frequency information. First processing module203may process the detected image or video data, e.g., including, but not limited to adjusting the luminance levels of multiple channels of image or video signals captured by cameras101-104, and the processed image or video signals can be sent to second processing module206for further processing. First processing module203may also output the detected image or video data to a memory unit (not shown inFIG. 2), such as a double date rate (DDR) memory unit.

The processing at second processing module206may include projection and panoramic image stitching, or distortion correction to produce 360-degree panoramic image and/or video. Second processing module206may also include an encoding mechanism configured to encode the 360-degree panoramic image or video data using H.264 standard. Second processing module206may be implemented as an accelerated processing unit (APU), a CPU, a micro-controller or other types of microprocessors. In some embodiments, receiving module201, detection module202and first processing module203may be collective implemented by an FPGA or one or more application specific integrated circuits (ASICs). Transmitting module207may transmit the processed image or video data from second processing module206to a client device.

Acquisition module204may capture panoramic image or video data, such as 360-degree panoramic image or video data, using a plurality of cameras, such as the set of cameras101-104shown in system100ofFIG. 1. In some aspects, a horizontal angle of view of each of the plurality of cameras capturing the 360-degree panoramic image data is 360 degrees divided by the number of the plurality of cameras (e.g., N) and a vertical angle of view of each of the plurality of cameras capturing the 360-degree panoramic image or video data is 360 degree divided by the number of the plurality of cameras.

In some aspects, when N>6, each of the plurality of cameras may include a wide-angle lens; when N>8, each of the plurality of cameras may include a regular (e.g., narrow-angle) lens; and when N<=6, each of the plurality of cameras may include a fisheye lens. In some aspects, when N=>8, each of the plurality of cameras may include a regular (e.g., narrow-angle) lens to capture an image without distortion, therefore distortion correction may not be required. In some aspects, when N<=8, each of the plurality of cameras may include a fisheye lens, and distortion may exist in the captured image, therefore distortion correction may be required.

Input module205may receive the captured panoramic image or video data in a first data format, convert the first data format to a second data format, and output the panoramic image or video data in the second data format to a downstream FPGA. Input module205may also receive the captured panoramic image or video data in the second data format and output the panoramic image or video data in the second data format to a downstream FPGA.

FIG. 3illustrates a block diagram of an exemplary implementation of input module205inFIG. 2in accordance with some embodiments described herein. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided.

As shown inFIG. 3, input module205may include first input unit301, and second input unit302. In some aspects, first input unit301may receive the panoramic image or video data from acquisition module204described inFIG. 2in YUV data format and transmit the panoramic image or video data through a parallel YUV data interface to the FPGA. In some aspects, second input unit302may receive the panoramic image or video data from acquisition module204in MIPI data format and transmit the 360-degree panoramic image or video data through a MIPI data interface and output to the FPGA through an interface chip which converts the MIPI data format to a parallel YUV data format.

FIG. 4illustrates a block diagram of an exemplary implementation of the panoramic imaging system100which includes a FPGA configured to adjust the luminance levels of multiple channels of video signals captured by multiple cameras in accordance with some embodiments described herein. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided.

As shown inFIG. 4, panoramic imaging system100includes cameras101,102,103and104, FPGA410, APU450, memory units456and458, SD card440, WIFI module446, USB module444, and HDMI module442. In particular embodiments, FPGA410is configured to process the multiple channels of video images captured by cameras101-104and to generate adjustment parameters which are used to control the set of cameras by adjusting the exposure (for example, by adjustment the “sensor gain”) and white balance parameters so that the video signals generated by the set of cameras can have substantially the same luminance level. FPGA410may also be configured to output multiple channels of adjusted video images of substantially the same luminance to APU450. An exemplary implementation of FPGA410is provided below in conjunction withFIG. 5. As mentioned above, panoramic imaging system100may include a greater or a fewer (≥2) number of cameras than the four cameras shown inFIG. 4. For example, panoramic imaging system100may include 2, 3, 6, 8, 10, or 12 cameras.

In one or more implementations, one or more of cameras101,102,103and104may simultaneously establish connections with FPGA410. As shown inFIG. 4, the output from each of the cameras101-104may be coupled to FPGA410using two different connection options. More specifically, the output of camera101may be coupled to FPGA410through a direct connection402. Alternatively, the output of camera101may be coupled to FPGA410by a path comprising a first connection412between the output of camera101and a data conversion module432and a second connection422between data conversion module432and FPGA410. Similarly, the output of camera102may be coupled to FPGA410through a direct connection404. Alternatively, the output of camera102may be coupled to FPGA410by a path comprising a first connection414between the output of camera102and a data conversion module434and a second connection424between data conversion module434and FPGA410. Similarly, the output of camera103may be coupled to FPGA410through a direct connection406. Alternatively, the output of camera103may be coupled to FPGA410by a path comprising a first connection416between the output of camera103and a data conversion module436and a second connection426between data conversion module436and FPGA410. Finally, the output of camera104may be coupled to FPGA410through a direct connection408. Alternatively, the output of camera104may be coupled to FPGA410by a path comprising a first connection418between the output of camera104and a data conversion module438and a second connection428between data conversion module438and FPGA410.

In some embodiments, each of the connections402,404,406, and408includes a parallel YUV data connection. This connection option may be used when the output data from a given camera101,102,103, or104is already in YUV data format. In some embodiments, each of the connections422,424,426, and428includes a parallel YUV data connection, and each of the connections412,414,416, and418includes a MIPI data connection. Moreover, each of the data conversion modules432,434,436and438is configured to convert an input data from MIPI data format to parallel YUV data format. This alternative connection option may be used when the output data from a given camera101,102,103, or104is in MIPI data format.

In some embodiments, FPGA410is configured to receive the four channels of panoramic video signals captured by the set of cameras101-104as inputs, process the four channels of video signals to generate control parameters, and use the control parameters to adjust operating conditions of the set of cameras so that they capture a set of video signals having substantially the same luminance level. In the embodiment shown, FPGA410and the set of cameras101-104are also coupled via a control bus470, which may be implemented as an I2C control bus. In some embodiments, FPGA410can adjust luminance levels of cameras101-104via control bus470using the generated control parameters. More specifically, each of the cameras101-104receives specific control parameters, which can be used to adjust settings for the camera sensors to obtain desired luminance in the capture images. In particular embodiments, FPGA410includes a set of sequentially coupled modules configured to perform the above luminance adjustment functions. This set of sequentially coupled modules can include: an input interface module configured to receive a set of (4) video images captured by the set of (4) cameras and a luminance statistics module coupled to the outputs of the input interface module and configured to perform histogram statistics on the luminance component of each image of the set of video images and generate a set of (4) luminance histograms corresponding to the set of video images.

The set of sequentially coupled modules can also include a luminance histogram analysis module coupled to the outputs of the luminance statistics module and configured to perform histogram analysis on the set of luminance histograms and to subsequently generate adjustment parameters for each of the set of (4) cameras. The set of sequentially coupled modules can additionally include a luminance uniformity adjustment module coupled to the output of the luminance histogram analysis module and configured to process the adjustment parameters and output the processed adjustment parameters to a downstream control module, such as an I2C master control module. The set of sequentially coupled modules can further include a luminance control module coupled to the outputs of the luminance uniformity adjustment module and configured to control the set of cameras by controlling the exposure (for example, by controlling the sensor gain) and white balance parameters of each of the set of cameras based on the processed adjustment parameters, thereby enabling the set of cameras to capture the multiple channels of video signals having substantially the same luminance level. In some embodiments, the luminance control module controls the set of cameras through an I2C bus which interconnects the luminance control module and the set of cameras.

As illustrated inFIG. 4, FPGA410may be connected to a memory unit456, such as a DDR chip456. In some implementations, FPGA410may execute instructions that are stored on FPGA410itself, such as on one or more integrated circuits within FPGA410. In other implementations, FPGA410may execute instructions that are stored on memory unit456. While the above discussion primarily refers to FPGA410that executes instructions, some implementations are performed by one or more integrated circuits, for example, application specific integrated circuits (ASICs). In some aspects, some implementations may be performed by one or more processors that execute instructions.

APU450may establish a connection460with FPGA410. Connection460may include an I2C connection, to allow easy communication between components which reside on the same circuit board. FPGA410may establish one or more connections462and464with APU450. Connections462and464may include one or more video data connections. In some embodiments, APU450includes only a single video input port and hence connections462and464become a signal connection. In other embodiments, APU450includes two video input ports and hence connections462and464can include two connections.

In some embodiments, panoramic imaging system100may transmit the processed panoramic image and video data from APU450to a downstream computing device (not shown) for storage and playback via a Universal Serial Bus (USB) interface444, e.g., which can be a USB 3.0 interface. In some other embodiments, panoramic imaging system100may transmit the processed panoramic image and video data from APU450to the downstream computing device for playback via a High-Definition Multimedia Interface (HDMI). In some embodiments, panoramic imaging system100may output the processed panoramic image and video data from APU450to be stored in a SD card440on panoramic imaging system100or to a memory unit458, such as a DDR chip but different from the DDR chip456. Furthermore, panoramic imaging system100may transmit the processed panoramic image and video data from APU450to a wireless access point and a smart device through WIFI446.

FIG. 5illustrates a block diagram of an exemplary implementation of FPGA410described inFIG. 4configured to adjust the luminance levels of multiple channels of video signals in accordance with some embodiments described herein. Not all of the depicted components shown inFIG. 5may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided.

As shown inFIG. 5, FPGA410includes a set of four luminance statistics modules501-504for receiving the four channels of video signals captured by four cameras101-104, respectively. In the embodiment shown, the input video signal in each of the four channels is in parallel YUV data format as it is transmitted from the corresponding camera to the corresponding input on each of the set of luminance statistics modules501-504. However, the input video signals can be in a data format other than the YUV data format. In some embodiments, each of the luminance statistics modules501-504includes an input cache/buffer operating as an input interface for FPGA410to receive the respective video signal. In some embodiments, FPGA410can include a set of separate input caches/buffers coupled between the cameras101-104and the luminance statistics modules501-504to serve as an input interface for FPGA410to receive the set of video signals. In some embodiments, each of the luminance statistics modules501-504is configured to perform histogram statistics on the luminance component of the respective received video image and generate a luminance histogram corresponding to the respective video images. As results, luminance statistics modules501-504generate and output four luminance histograms corresponding to the set of video images captured by the set of cameras. Note that while the exemplary embodiment illustrates four parallel luminance statistics modules501-504, luminance statistics modules501-504can also be implemented as a single luminance statistics module without departing from the scope of the disclosed techniques.

Further referring toFIG. 5, FPGA410also includes a luminance histogram analysis module510coupled to the outputs of luminance statistics modules501-504to receive the four luminance histograms. In some embodiments, luminance histogram analysis module510is configured to perform histogram analysis on the set of luminance histograms and subsequently generate a set of adjustment parameters which are indicative of the operating settings of the set of cameras. For example, the set of adjustment parameters can include a separate luminance level for each of the set of cameras. In one embodiment, after obtaining the individual luminance levels for the set of cameras, an average luminance level for the set of cameras can then be computed based on the individual luminance levels, for example, by computing an average of the individual luminance levels.

As shown inFIG. 5, FPGA410also includes a luminance uniformity adjustment module520coupled to the output of luminance histogram analysis module510. In some embodiments, luminance uniformity adjustment module is configured to process the adjustment parameters generated by luminance histogram analysis module510and generate processed adjustment parameters which can be used to adjust the operating settings of the set of cameras to allow the set of cameras to capture multiple channels of video signals having substantially the same luminance level. For example, under the example lighting condition shown ofFIG. 1, processing the adjustment parameters may determine the luminance levels in the video signals captured by cameras101and102are higher than the luminance levels in the video signals captured by cameras103and104, and the processed adjustment parameters may include higher exposure values (for example, by increasing the sensor gains) for cameras103and104, or lower exposure values (for example, by decreasing the sensor gains) for cameras101and102, or a combination thereof. In one embodiment, the processed adjustment parameters may include a separate global exposure/gain for each of the set of cameras. The separate global exposures/gains may be determined based on an average luminance level of the individual luminance levels for the set of cameras generated by the luminance histogram analysis. Hence, the set of global exposures/gains can be used to reset the exposure settings (e.g., the sensor gains) for the set of cameras so that the luminance levels of the captured images by the set of cameras can be substantially the same. In addition to a global exposure/gain, the processed adjustment parameters can also include one or more of the following parameters for adjusting the camera sensors: an analog gain, a digital gain, a red gain, a green gain, and a blue gain.

Also shown inFIG. 5, FPGA410additionally includes a set of luminance control modules531-534coupled to the output of the luminance uniformity adjustment module520to receive the respective processed adjustment parameters, wherein the output of each of the luminance control modules531-534is further coupled to a respective camera in the set of cameras101-104through a control bus, such as an I2C bus. In some embodiments, each of the set of luminance control modules531-534is configured to control a respective camera101-104by adjusting the associated exposure/sensor gain and white balance parameters of the camera based on the associated processed adjustment parameters, thereby enabling the set of cameras101-104to capture the multiple channels of video images having substantially the same luminance level.

FIG. 6presents a flowchart illustrating a process600of adjusting the luminance levels of multiple channels of video signals captured by multiple cameras using the proposed technique in accordance with some embodiments described herein.

The process begins by receiving in parallel a set of video images captured by a set of cameras in the panoramic imaging system (step602). In some embodiments, the set of received video images can have non-uniform luminance levels as a result of non-uniform light conditions for the set of cameras. The process next performs histogram statistics on the luminance component of each received video image and generates a set of luminance histograms corresponding to the set of video images (step604). Next, the process performs histogram analysis on the set of luminance histograms and subsequently generates a set of adjustment parameters which are indicative of the operating settings of the set of cameras (step606). In some embodiments, the set of adjustment parameters can include an overall luminance level associated with each of the set of cameras. The process next processes the adjustment parameters and generates processed adjustment parameters for adjusting the operating settings of the set of cameras to allow the set of cameras to capture multiple channels of video signals having substantially the same luminance level (step608). Next, the process uses the respective processed adjustment parameters to adjust the respective exposure and white balance parameters of the respective cameras, thereby enabling the set of cameras to capture the multiple channels of video images having substantially the same luminance level (step610).

FIG. 7conceptually illustrates an exemplary electronic system700including a panoramic imaging system710and various peripheral modules configured in an internet-enabled application environment with which some implementations of the subject technology can be implemented. Not all of the depicted components may be used, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made without departing from the scope of the subject technology. Additional components, different components, or fewer components may be provided.

Exemplary panoramic imaging system710within exemplary panoramic imaging electronic system700may be implemented by panoramic imaging system100as described above with reference toFIG. 1. According to the present disclosure, the example panoramic imaging system710further includes an optical system720which includes a plurality of cameras722, and a control system740that controls the functions of the optical system720and includes at least an image processing program to process image data output from optical system720. The plurality of cameras722may be implemented by cameras101-104in system100. However, the plurality of cameras722may include more or less cameras than cameras101-104in system100.

Control system740described inFIG. 7may be used to implement control system110described inFIG. 1. Particularly, the control system740includes at least a processor741, a memory742, a storage device743, a camera interface744, an external communication interface745, and a user control interface746. The control system740can be a general-purpose computer system such as a Personal Computer (PC), or preferably a custom-designed computing system. Particularly in some embodiments, the control system740is a system on chip (SOC); that is, an integrated circuit (IC) integrates all components and functions of the control system740into a single chip, which makes the present panoramic imaging system710portable and electronically durable as a mobile device. In some embodiments, the control system740may be located internally within a same housing where the optical system720is located. Alternatively, in other embodiments, the control system740is separated from the optical system720to allow end users' selection of different models of an optical system720to be used with the control system740.

The storage device743is preloaded with at least the image processing programs of the present disclosure, including stereoscopic video image capturing and 3D video image playback programs. The stereoscopic video image capturing programs may include real-time parallax vector field generation programs described in more detail below. Other customer-designed software programs may be preloaded during manufacture or downloaded by end users after they purchase the system. Exemplary customer-designed software programs to be used with the present panoramic imaging system include but are not limited to software that further processes panoramic images or videos according to an end user's needs, such as 3D modeling, object tracking, and virtual reality programs. Further exemplary customer-designed software includes but is not limited to image editing programs that allow users to adjust color, illumination, contrast or other effects in a panoramic image, or film editing programs that allow users to select favorite views from a panoramic video to make normal videos.

The electronic circuitry in the processor741carries out instructions of the various algorithms. Thus, the various software programs, stored on the storage device743and executed in the memory742by the processor741, direct the control system740to act in concert with the optical system720to perform various functions, which include but are not limited to receiving commands from an end user or an external device or service780,782,784and786, defining the precise geometry of the cameras722, commanding the cameras722to capture raw image data, tagging and storing raw data in a local storage device743and/or commuting raw data to an external device or service780,782,784and786, detecting and adjusting the luminance levels of multiple channels of video signals from cameras722to enable the cameras722to capture the multiple channels of video images having substantially the same luminance level, presenting generated panoramas on a local display750and/or communicating generated panoramas to be stored or presented on an external device or service780,782,784and786.

The processor741of the present disclosure can be any integrated circuit (IC) that is designed to execute instructions by performing arithmetic, logical, control and input/output (I/O) operations specified by algorithms. Particularly, the processor can be a central processing unit (CPU) and preferably a microprocessor that is contained on a single IC chip. In some embodiments, the control system740may employ a multi-core processor that has two or more CPUs or array processors that have multiple processors operating in parallel. In some embodiments, the processor741is an application specific integrated circuit (ASIC) that is designed for a particular use rather than for general purpose use. Particularly, in some embodiments, the processor741is a digital signal processor (DSP) designed for digital signal processing. More particularly, in some embodiments, the processor741is an on-chip image processor, specialized for image processing in a portable camera system. In some embodiments, the control system740includes a graphic processing unit (GPU), which has a massively parallel architecture consisting of thousands of smaller, more efficient cores designed for handling multiple tasks simultaneously. Particularly, in some embodiments, the control system740may implement GPU-accelerated computing, which offloads compute-intensive portions of an algorithm to the GPU while keeping the remainder of the algorithm to run on the CPU.

In particular embodiments, processor741of the present disclosure includes the proposed FPGA410described in conjunction withFIGS. 4-5. Hence, the FPGA410within processor741may be configured to adjust the luminance levels of multiple channels of video signals from cameras722to allow the set of cameras to capture the multiple channels of video images having substantially the same luminance level.

The memory742and the storage743of the present disclosure can be any type of primary or secondary memory device compatible with the industry standard, such as read-only memory (ROM), random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), and flash memory. In the embodiments where the control system240is a single chip system, the memory742and storage743blocks are also integrated on-chip with the processor741as well as other peripherals and interfaces. In some embodiments, the on-chip memory components may be extended by having one or more external solid-state storage media, such a secure digital (SD) memory card or a USB flash drive, reversibly connected to the imaging system. For example, the various memory units include instructions for removing an obstructing object in a panoramic image. From these various memory units, the processor741retrieves instructions to execute and data to process in order to execute the processes of some implementations.

The camera interface744of the present disclosure can be any form of command and data interface usable with a camera742, such as a digital. Exemplary embodiments include USB, FireWire and any other interface for command and data transfer that may be commercially available. Additionally, it is preferred, although not required, that the optical system720be equipped with a single digital control line that would allow a single digital signal to command all the cameras722simultaneously to capture an image of a scene and to acquire positional signals of the camera body.

The external communication interface745of the present disclosure can be any data communication interface, and may employ a wired, fiber-optic, wireless, or another method for connection with an external device or service780,782,784and786. Ethernet, wireless-Ethernet, Bluetooth, USB, FireWire, USART, SPI are exemplary industry standards. In some embodiments, where the control system740is a single chip system, the external communication interface745is integrated on-chip with the processor741as well as other peripherals and interfaces.

The user control interface746of the present disclosure can be any design or mode that allows effective control and operation of the panoramic imaging system from the user end, while the system feeds back information that aids the user's decision making process. Exemplary embodiments include but are not limited to graphical user interfaces that allow users to operate the system through direct manipulation of graphical icons and visual indicators on a control panel or a screen, touchscreens that accept users' input by touch of fingers or a stylus, voice interfaces which accept users' input as verbal commands and outputs via generating voice prompts, gestural control, or a combination of the aforementioned modes of interface.

Control system740of the present disclosure may further include other components747that facilitate its function. For example, control system740may optionally include a location and orientation sensor that could determine the location and orientation of the panoramic imaging system. Exemplary embodiments include a global positioning system (GPS) that can be used to record geographic positions where image data are taken, and a digital magnetic compass system that can determine the orientation of camera system in relation to the magnetic north. Control system740may optionally be equipped with a timing source, such as an oscillator or a phase-locked loop, which can be used to schedule automatic image capture, to time stamp image data, and to synchronize actions of multiple cameras to capture near simultaneous images in order to reduce error in image processing. Control system740may optionally be equipped with a light sensor for environmental light conditions, so that control system740can automatically adjust hardware and/or software parameters of the system.

In some embodiments, the present electronic system700is further equipped with an internal power system760such as a battery or solar panel that supplies the electrical power. In other embodiments, electronic system700is supported by an external power source. In some embodiments, electronic system700is further equipped with a display750, such that panoramic photos may be presented to a user instantly after image capture, and panoramic videos may be displayed to a user in real time as the scenes are being filmed.

In some embodiments, the present electronic system700may be used in conjunction with an external device for displaying and/or editing panoramas generated. Particularly, the external device can be any electronic device with a display and loaded with software or applications for displaying and editing panoramic images and videos created by the present system. In some embodiments, the external device can be smart phones, tablets, laptops or other devices programmed to receive, display, edit and/or transfer the panoramic images and videos. In some embodiments, the present panoramic imaging system may be used in conjunction with an external service, such as Cloud computing and storage780, online video streaming and file sharing782, remote surveillance784, and alert786for home and public security.