Systems and Methods for Measuring Scene Information While Capturing Images Using Array Cameras

[0001] The present invention generally relates to digital cameras and more specifically to systems and methods for evaluating imaging conditions.

[0002] Current camera technology typically limits image capture possibilities to very specific conditions in which an image of acceptable quality can be produced. As a result of this limitation, several camera settings need to be appropriately chosen before an image of optimal quality can be taken. Cameras have long had the ability to assess the scene conditions and automatically adjust settings such as: exposure time, iris/lens aperture, focus, sensor gain, and the use of neutral density filters. While film-based cameras have traditionally relied on external measuring sensors to select these settings, modern compact digital cameras make use of several through-the-lens measurements that provide image-based data to automatically adjust settings through algorithms that compare these measurements and decide on optimal settings.

[0003] The mechanism of exposure provides adjustment of the device sensitivity to the light intensity in the scene. This is in part motivated by the limited dynamic range (ratio of highest to lowest light intensity) of the camera system compared to the dynamic range of intensities in the real world. In an image capture device, a metering and auto-exposure algorithm finds optimal values for the above parameters (some of these parameters may be specified or fixed). An auto-exposure algorithm aims to find the optimal exposure settings for the camera system by modifying a subset of the following parameters: exposure time, iris/lens aperture, sensor gain, and the use of neutral density filters.

[0004] Cameras equipped with auto-focus lens can generally capture an image of acceptable quality at a certain focus setting, while relying on an auto-focus algorithm to select the accurate focus position where the chosen parts of the image are considered to be acceptably sharp. In a traditional compact digital camera, auto-focus can be achieved by capturing successive images at varying focus positions through “focus sweep” and selecting the setting corresponding to the image of best “focus”. An auto-focus algorithm aims to find the optimal focus setting for the camera system. The auto-exposure and auto-focus functions in digital cameras share the characteristic that they both generally rely on taking multiple measurements in order to estimate the best camera settings prior to actual image capture.

[0005] Auto-exposure algorithms may rely on external light meters/sensors or may evaluate optimal exposure time through the lens by successive image capturing as described above. In many legacy cameras auto-exposure algorithms run concurrently with image preview mode. Due to the fact that preview mode provides real time video, the auto-exposure algorithm is typically configured to make small adjustments in the exposure time since changes in exposure are immediately visible in the preview video. These small adjustments result in delays in identifying optimal exposure times.

[0006] Autofocus is another feature that generally runs when the device is in preview mode. Again, since image preview mode provides real time video, the autofocus process typically involves gradually varying the focus point in a slow sweep. Although there are multiple approaches to performing autofocus (including phase detection that uses dedicated focusing sensors), methods appropriate for compact cameras typically involve capturing several images and analyzing the captured images for parameters such as contrast or blur amount. Such autofocus methods, along with slow sweep, can also result in delays.

[0007] The High Dynamic Range (HDR) feature provides a means to produce images that convey higher dynamic range (higher ratio of intensities corresponding to light and dark areas in image). In a conventional image capture mode (i.e. one that does not involve capturing HDR information), images are traditionally captured at one exposure level (may vary for each color channel in architectures allowing this). The camera system's dynamic range is typically limited by several factors, including the finite number of bits in the analog-to-digital converters, reduced full-well sensor capacity as well as optical characteristics. HDR mode utilizes a set of methods that sample a scene's dynamic range more aggressively by capturing multiple images of the scene at different exposure levels. Each exposure creates brackets of smaller or regular dynamic range that can be sampled to produce a composite image of high (increased) dynamic range. Various blending models and/or algorithms can be utilized to create a single HDR image from the multiple images. The High Dynamic Range mode typically includes two steps: High Dynamic Range capture and High Dynamic Range Image Blending and Compression. In the High Dynamic Range capture step, multiple images may be captured at a pre-defined difference in exposure setting from the reference exposure; for example, if the reference exposure is EV0, an image with a smaller exposure by a factor of 2 may be captured and an image with a greater exposure by a factor of 2 may be captured as following: EV0, EV−1 (short exposure), EV+1 (long exposure). (Note: numbers follow the exposure value convention and correspond to base-2 logarithmic scale such that EV−1 corresponds to half of EV0 exposure, EV+1 corresponds to double the EV0 exposure).

[0008] Systems and methods for measuring scene information while capturing images using array cameras in accordance with embodiments of the invention are disclosed. In one embodiment, a method of measuring scene information while capturing an image using an array camera includes defining at least two subsets of active cameras, configuring the active cameras using image capture settings for each subset, capturing image data using the active cameras, synthesizing at least one image using image data captured by a first subset of active cameras, measuring scene information using image data captured by a second subset of active cameras, and determining whether the image capture settings satisfy at least one predetermined criterion for at least one image capture parameter using the measured scene information, where new image capture settings are determined and utilized to configure the active cameras upon a determination that the image capture settings do not satisfy the at least one predetermined criterion for at least one image capture parameter.

[0021] Turning now to the drawings, systems and methods for measuring scene information while capturing images using array cameras in accordance with embodiments of the invention are illustrated. Array cameras including camera modules that can be utilized to capture image data from different viewpoints are disclosed in U.S. patent application Ser. No. 12/935,504, entitled “Capturing and Processing of Images using Monolithic Camera Array with Heteregeneous Images”, filed May 20, 2009, the disclosure of which is incorporated by reference herein in its entirety. In several embodiments of the invention, two or more subsets of active cameras within an array camera module are defined. Each subset of active cameras is configured using image capture settings specific to either the entire subset or to each individual active camera within the subset. Image data of a scene is captured using the active cameras. In many embodiments, the systems and methods synthesize a high resolution image using image data captured by a first subset of active cameras using a variety of processes including (but not limited to) fusion processes and super-resolution processes. Fusion and super-resolution processes in accordance with embodiments of the invention are disclosed in U.S. patent application Ser. No. 12/967,807, entitled “System and Methods for Synthesizing High Resolution Images Using Super-Resolution Processes”, filed Dec. 14, 2010, the disclosure of which is incorporated by reference herein in its entirety. In further embodiments, scene information is measured using the image data captured by at least a second subset of active cameras. The scene information is used to determine whether the image capture settings satisfy a set of predetermined criteria for parameters including (but not limited to) exposure, focus settings, shutter speed, aperture, and light sensitivity. In several embodiments of the invention, the image capture settings for one subset of active cameras are determined based on image data that includes image data captured by a different subset of active cameras. In further embodiments, the image data captured by any of the active cameras can be utilized to create HDR images. In further embodiments, active cameras are used to measure scene information in parallel and, once the scene information is used to determine image capture settings, active cameras (which may include one or more cameras used to measure scene information) capture image data using the image capture settings and the image data is used to synthesize an image. Systems and methods for measuring scene information while capturing images in accordance with embodiments of the invention are discussed further below.

[0022] Array cameras in accordance with embodiments of the invention can include a camera module and a processor. An array camera in accordance with an embodiment of the invention is illustrated in FIG. 1. The array camera 100 includes a camera module 102 with an array of individual cameras 104 where an array of individual cameras refers to a plurality of cameras in a particular arrangement, such as (but not limited to) the square arrangement utilized in the illustrated embodiment. The camera module 102 is connected to the processor 106 and the processor 106 is connected to a memory 108. Although a specific array camera is illustrated in FIG. 1, any of a variety of different array camera configurations can be utilized in accordance with many different embodiments of the invention.

[0023] Camera modules in accordance with embodiments of the invention can be constructed from an imager array and an optic array. A camera module in accordance with an embodiment of the invention is illustrated in FIG. 2. The camera module 200 includes an imager array 230 including an array of focal planes 240 along with a corresponding optic array 210 including an array of lens stacks 220. Within the array of lens stacks, each lens stack 220 creates an optical channel that forms an image of the scene on an array of light sensitive pixels within a corresponding focal plane 240. Each pairing of a lens stack 220 and focal plane 240 forms a single camera 104 within the camera module. Each pixel within a focal plane 240 of a camera 104 generates image data that can be sent from the camera 104 to the processor 108. In many embodiments, the lens stack within each optical channel is configured so that pixels of each focal plane 240 sample the same object space or region within the scene. In several embodiments, the lens stacks are configured so that the pixels that sample the same object space do so with sub-pixel offsets to provide sampling diversity that can be utilized to recover increased resolution through the use of super-resolution processes.

[0024] In several embodiments, color filters in individual cameras can be used to pattern the camera module with π filter groups as further discussed in U.S. Provisional Patent Application No. 61/641,165 entitled “Camera Modules Patterned with pi Filter Groups” filed May 1, 2012, the disclosure of which is incorporated by reference herein in its entirety. These cameras can be used to capture data with respect to different colors, or a specific portion of the spectrum. In contrast to applying color filters to the pixels of the camera, color filters in many embodiments of the invention are included in the lens stack. For example, a green color camera can include a lens stack with a green light filter that allows green light to pass through the optical channel. In many embodiments, the pixels in each focal plane are the same and the light information captured by the pixels is differentiated by the color filters in the corresponding lens stack for each filter plane. Although a specific construction of a camera module with an optic array including color filters in the lens stacks is described above, camera modules including π filter groups can be implemented in a variety of ways including (but not limited to) by applying color filters to the pixels of the focal planes of the camera module similar to the manner in which color filters are applied to the pixels of a conventional color camera. In several embodiments, at least one of the cameras in the camera module can include uniform color filters applied to the pixels in its focal plane. In many embodiments, a Bayer filter pattern is applied to the pixels of one of the cameras in a camera module. In a number of embodiments, camera modules are constructed in which color filters are utilized in both the lens stacks and on the pixels of the imager array.

[0025] In several embodiments, an array camera generates image data from multiple focal planes and uses a processor to synthesize one or more images of a scene. In certain embodiments, the image data captured by a single focal plane in the sensor array can constitute a low resolution image (the term low resolution here is used only to contrast with higher resolution images), which the processor can use in combination with other low resolution image data captured by the camera module to construct a higher resolution image through Super Resolution processing.

[0026] Although specific array cameras are discussed above, many different array cameras are capable of utilizing π filter groups in accordance with embodiments of the invention. Imager arrays in accordance with embodiments of the invention are discussed further below.

[0027] An imager array in which the image capture settings of a plurality of focal planes can be independently configured in accordance with an embodiment of the invention is illustrated in FIG. 3. The imager array 300 includes a focal plane array core 302 that includes an array of focal planes 304 and all analog signal processing, pixel level control logic, signaling, and analog-to-digital conversion (ADC) circuitry. The imager array also includes focal plane timing and control circuitry 306 that is responsible for controlling the capture of image information using the pixels. In a number of embodiments, the focal plane timing and control circuitry utilizes reset and read-out signals to control the integration time of the pixels. In other embodiments, any of a variety of techniques can be utilized to control integration time of pixels and/or to capture image information using pixels. In many embodiments, the focal plane timing and control circuitry 306 provides flexibility of image information capture control, which enables features including (but not limited to) high dynamic range imaging, high speed video, and electronic image stabilization. In various embodiments, the imager array includes power management and bias generation circuitry 308. The power management and bias generation circuitry 308 provides current and voltage references to analog circuitry such as the reference voltages against which an ADC would measure the signal to be converted against. In many embodiments, the power management and bias circuitry also includes logic that turns off the current/voltage references to certain circuits when they are not in use for power saving reasons. In several embodiments, the imager array includes dark current and fixed pattern (FPN) correction circuitry 310 that increases the consistency of the black level of the image data captured by the imager array and can reduce the appearance of row temporal noise and column fixed pattern noise. In several embodiments, each focal plane includes reference pixels for the purpose of calibrating the dark current and FPN of the focal plane and the control circuitry can keep the reference pixels active when the rest of the pixels of the focal plane are powered down in order to increase the speed with which the imager array can be powered up by reducing the need for calibration of dark current and FPN.

[0028] In many embodiments, a single self-contained chip imager includes focal plane framing circuitry 312 that packages the data captured from the focal planes into a container file and can prepare the captured image data for transmission. In several embodiments, the focal plane framing circuitry includes information identifying the focal plane and/or group of pixels from which the captured image data originated. In a number of embodiments, the imager array also includes an interface for transmission of captured image data to external devices. In the illustrated embodiment, the interface is a MIPI CSI 2 output interface (as specified by the non-profit MIPI Alliance, Inc.) supporting four lanes that can support read-out of video at 30 fps from the imager array and incorporating data output interface circuitry 318, interface control circuitry 316 and interface input circuitry 314. Typically, the bandwidth of each lane is optimized for the total number of pixels in the imager array and the desired frame rate. The use of various interfaces including the MIPI CSI 2 interface to transmit image data captured by an array of imagers within an imager array to an external device in accordance with embodiments of the invention is described in U.S. Pat. No. 8,305,456, entitled “Systems and Methods for Transmitting Array Camera Data”, issued Nov. 6, 2012, the disclosure of which is incorporated by reference herein in its entirety.

[0029] Although specific components of an imager array architecture are discussed above with respect to FIG. 3, any of a variety of imager arrays can be constructed in accordance with embodiments of the invention that enable the capture of images of a scene at a plurality of focal planes in accordance with embodiments of the invention. Independent focal plane control that can be included in imager arrays in accordance with embodiments of the invention are discussed further below.

[0030] Imager arrays in accordance with embodiments of the invention can include an array of focal planes that can independently be controlled. In this way, the image capture settings for each focal plane in an imager array can be configured differently. As is discussed further below, the ability to configure active focal planes using different image capture settings can enable different cameras within an array camera to make independent measurements of scene information that can be combined for use in determining image capture settings for use more generally within the camera array.

[0031] An imager array including independent control of image capture settings and independent control of pixel readout in an array of focal planes in accordance with an embodiment of the invention is illustrated in FIG. 4. The imager array 400 includes a plurality of focal planes or pixel sub-arrays 402. Control circuitry 403, 404 provides independent control of the exposure timing and amplification gain applied to the individual pixels within each focal plane. Each focal plane 402 includes independent row timing circuitry 406, 408, and independent column readout circuitry 410, 412. In operation, the control circuitry 403, 404 determines the image capture settings of the pixels in each of the active focal planes 402. The row timing circuitry 406, 408 and the column readout circuitry 410, 412 are responsible for reading out image data from each of the pixels in the active focal planes. The image data read from the focal planes is then formatted for output using an output and control interface 416.

[0032] Although specific imager array configurations are discussed above with reference to FIG. 4, any of a variety of imager array configurations including independent and/or related focal plane control can be utilized in accordance with embodiments of the invention including those outlined in U.S. patent application Ser. No. 13/106,797, entitled “Architectures for Imager Arrays and Array Cameras”, filed May 12, 2011, the disclosure of which is incorporated by reference herein in its entirety. The use of independent focal plane control to capture image data using array cameras is discussed further below.

Capturing Image Data with Subsets of Active Cameras

[0033] Active cameras in an array camera module in accordance with embodiments of the invention can be grouped into subsets for capturing image data and for measuring scene information. A 4×4 array camera module including a first subset of active cameras that capture image data used to synthesize an image from the viewpoint of a reference camera and a second subset of cameras that capture image data used to obtain (additional) measurements of scene information in accordance with embodiments of the invention is illustrated in FIG. 5. The 4×4 camera module 500 includes a first subset 502 of 3×3 active cameras patterned using a π filter group and utilized to capture image data that can be utilized to synthesize color images and/or video sequences. In the illustrated embodiment, π filter group includes a green camera at each corner, a green reference camera in the center indicated by a box 504, blue cameras above and below the reference camera, and red cameras to the left and rights sides of the reference camera. In several embodiments, the locations of the red and blue cameras within the π filter group are swapped and/or an alternative collection of cameras can be utilized to capture image data to synthesize images. In various embodiments, a second subset 506 of active cameras includes a row of blue, green, and red cameras placed below the π filter group and a column of blue, green, and red cameras placed to the right side of the π filter group with a green camera connecting the row and the column. In various embodiments, the second subset of active cameras is configured to capture image data for measuring scene information as discussed further below. Although all of the cameras in the array camera module illustrated in FIG. 5 are shown as capturing image data, in many embodiments one or more of the cameras within the array camera module can be idle during image capture to conserve power as appropriate to the requirements of a specific application.

[0034] Although specific array camera module configurations and partitions of cameras into subsets for synthesizing images and measuring scene information are discussed above with respect to FIG. 5, partitions of active cameras into subsets for the purpose of capturing image data for synthesizing images and for obtaining (additional) measurements of scene information can be utilized with any of a variety of camera module configurations including array camera modules including any number of cameras, array camera modules in which one or more of the cameras capture image data within multiple color channels (i.e. are not monochromatic), and/or array camera modules in which not all cameras of the camera array are active (i.e. not capturing image data or performing measurements) as appropriate to the requirements of a specific application in accordance with embodiments of the invention. Processes for using subsets of active cameras to measure scene information and capture images in accordance with embodiments of the invention are discussed further below.

Measuring Scene Information while Capturing Images

[0035] The image capture settings of different subsets of active cameras can be independently configured in accordance with embodiments of the invention. In many embodiments, the image data from a first subset of active cameras can be optionally used to synthesize an image and the image data from a second subset of active cameras can be used to measure scene information. In various embodiments, the image data from any combination of subsets can be used to synthesize images and/or measure scene information. In a number of embodiments, active cameras are used to measure a scene information and a preview image is not generated until image capture settings are determined using the measurements.

[0036] A process for using subsets of active cameras to measure scene information and synthesize images in accordance with an embodiment of the invention is illustrated in FIG. 6. The process 600 includes defining (602) two or more subsets of active cameras and configuring the cameras using predetermined image capture settings. In several embodiments, the predetermined image capture settings can be determined based upon specific imaging applications and/or desired image qualities. The active cameras of each subset are set to capture (604) image data utilizing methods including (but not limited) to those discussed above. In many embodiments, the image data captured by the first subset of active cameras is used to optionally synthesize (606) an image using a variety of processes including (but not limited to) fusion processes and super-resolution processes as discussed above. In various embodiments, the image data captured by the second subset of active cameras is used to measure (608) scene information. The measurements of scene information alone or in combination with the image data captured by the first subset of images can be used determine image capture settings that are appropriate for the specific scene imaged by the array camera. In various embodiments, the captured image data that is used to measure scene information can be captured by any combination of multiple cameras. In several embodiments, a determination (610) is made as to whether image capture settings used by any of the cameras in the first or second subsets of cameras satisfy a set of predetermined criteria for parameters including (but not limited to) exposure, focus settings, shutter speed, aperture, and/or light sensitivity. If the image capture setting satisfies the set of predetermined criteria, additional image date can be optionally captured (616). If the image capture settings do not satisfy the set of predetermined criteria, new image capture settings are determined (612) based upon scene information measured by the cameras in the first and/or second subsets of cameras and/or scene information image data captured by the first and/or second subsets of cameras. Using the new image capture settings, the cameras are configured (614) and image data is again captured (604) using the active cameras. In many embodiments, any of a variety of techniques can be utilized to select image capture settings for the cameras in the first and second subsets of cameras. Various processes in accordance with embodiments of the invention for determining image capture settings in accordance with embodiments of the invention based upon measurements of scene information are discussed further below. The process repeats until image capture settings satisfy the predetermined criteria.

[0037] Although specific processes for using subsets of active cameras to measure scene information while synthesizing images are discussed above with respect to FIG. 6, any of a variety of processes can be utilized as appropriate to the requirements of a specific application in accordance with embodiments of the invention. Processes for using measured scene information for determining image capture settings are further discussed below.

[0038] Image data captured by any subset of active cameras can be used to measure scene information to determine new image capture settings. In many embodiments, the scene information is analyzed to further determine various image capture settings including, but not limited to, exposure, focus settings, shutter speed, aperture, and/or light sensitivity.

[0039] A process for determining new image capture settings in accordance with an embodiment of the invention is illustrated in FIG. 7. The process 700 includes determining (702) new image capture settings for cameras in a first subset of active cameras. The new image capture settings are used to configure the first subset of active cameras to capture an additional set of image data used to synthesize an image that can be displayed to a user (e.g. preview mode), and/or saved (e.g. as part of a video sequence). The process also includes determining (704) new image capture settings for cameras in a second subset of active cameras. The new image capture settings for the second subset of active cameras configure the second set of active cameras to capture additional image data in order to measure information concerning the scene. Given that the image data captured by the second set of cameras is not used in synthesizing images, the image capture settings need not be consistent across all cameras and/or across cameras within the same color channel. Indeed, utilizing different image capture settings can be useful in simultaneously sampling the scene using different sets of image capture settings in order to identify a set of image capture settings that satisfies a predetermined set of criteria. In several embodiments, the set of criteria are specified in such a way that use of image capture settings that satisfy the set of criteria when capturing image data used to synthesize an image is likely to yield a predetermined level of image quality within the synthesized image.

[0040] Where the cameras in the first subset are utilized to synthesize images used to provide a preview image of the scene and/or to capture images or video of the scene a gradual transition in image capture settings may be preferred. Accordingly, a sweep (full search) across a range of image capture parameters can be performed. In various embodiments, a preview image of the scene can be postponed until the sweep across the range of image capture parameters has reached desired values, where the desired values can be predetermined or be based upon the measurements of scene information. In this way, more cameras can be utilized in parallel to perform the sweep and the sweep can be completed in a shorter amount of time. In several embodiments, the speed of the sweep across a range of image capture settings can be determined based upon the measurements of scene information. In several embodiments, image capture settings of the second subset of cameras is determined to rapidly converge on a set of image capture settings that satisfy a set of predetermined criteria. For example, the range of image capture parameters can be swept at a faster sampling rate by using multiple sets of image capture parameters in parallel. Alternatively, a search can be conducted within the space of image capture that employs a search technique designed to achieve rapid convergence upon a set of image capture settings that satisfy the set of predetermined criteria. With each new set of measurements of scene information obtained with a new set of image capture parameters, the range of image capture settings may be bounded by increasingly narrower bounds and the sweep of image capture settings used to determine the image capture setting for the first subset of cameras is determined to rapidly sweep to the edge of the bounded range of image capture settings. In several embodiments, the number of parallel measurements of scene information is sufficiently large that the process of identifying a set of image capture parameters of the first subset of cameras can be determined using a single set of image capture parameters in a similar manner to that used to determine the image capture settings of cameras in the second subset of cameras. As can readily be appreciated, the specific process used to set the image capture settings of the active cameras in each subset of an array camera module based upon measurements of scene information captured using a first set of image capture settings can be determined using any of a variety of processes as appropriate to the requirements of a specific application in accordance with embodiments of the invention.

[0041] Although specific processes for determining image capture settings for two subsets of active cameras are discussed above with respect to FIG. 7, any of a variety of processes can be utilized for determining image capture settings as appropriate to the requirements of a specific application in accordance with embodiments of the invention. Processes for determining image capture setting for utilizing an auto-exposure feature in accordance with embodiments of the invention are further discussed below.

[0042] In many auto-exposure algorithms, an image is first captured at a known exposure setting and the captured image is analyzed to determine a more appropriate exposure setting. The iterative process continues until an image is captured that satisfies one or more auto-exposure criteria. In many embodiments, the iterative process can continue until statistics based on image histogram are reached. Such image statistics can include (but not limited to) analyzing histogram distribution, amount of saturated pixels and/or mean pixel values. In several embodiments, the iterative process can continue until a desired number of pixels are underexposed and/or overexposed. In other embodiments, the iterative process can continue until one or more auto-exposure criteria appropriate to the requirements of a specific application are met. As illustrated in FIG. 8, the dynamic range of a scene 802 can be much greater than the dynamic range of the imaging system 806. The difference in dynamic ranges creates a so called clipping effect at the limits of the imaging system's dynamic range 804, 808. The regions of the scene's dynamic range that are outside the imaging system's dynamic range 806 are either underexposed or overexposed and thus image data is not accurately captured. Exposure settings can be adjusted in an iterative approach to identify the exposure setting that best satisfy a set of predetermined criteria and/or to capture image data over the entire dynamic range of the scene for the purposes of HDR imaging. Processes for selecting exposure settings for performing image data capture and for performing HDR image capture in accordance with embodiments of the invention are discussed further below.

[0043] A process for determining image capture settings for auto-exposure utilizing two subsets of active cameras within a camera array in accordance with an embodiment of the invention is illustrated in FIG. 9. The process 900 includes capturing (902) image data using the active cameras. In several embodiments, the image data captured by a first subset of active cameras can be used to optionally synthesize an image as discussed above. In many embodiments, the image data captured by the second subset of active cameras are used to measure (904) scene information. In various embodiments, scene information can be measured in parallel to synthesizing images or before synthesizing an image altogether. The measured scene information is used to determine (906) exposure value parameters of the captured image data including (but not limited to) scene luminance intensity and/or scene dynamic range. The process further includes determining (908) whether the image capture settings satisfy a set of predetermined criteria for exposure settings by measuring scene information. In many embodiments, the predetermined criteria can include a particular mean pixel intensity level. In several embodiments, the predetermined criteria can include a particular number of pixels that are underexposed and/or overexposed. In other embodiments, the predetermined criteria can include any number of criteria as appropriate to the requirements of a specific application. If the image capture settings do not satisfy the predetermined criteria for exposure settings then new image capture settings for the active cameras in both the first subset and the second subset can be determined (910) based upon the determined exposure value parameters in accordance with techniques similar to those discussed above. The new image capture settings are used to configure (912) the active cameras and new images data is captured (914). Scene information is measured (904) using the image data captured by at least the second subset of active cameras and the process repeats until image capture settings satisfy predetermined criteria for exposure settings. When the image capture settings satisfy the predetermined criteria for exposure settings, new image capture settings are determined (916) for a set of active cameras and image data is captured (918) using the active cameras. In many embodiments, the active cameras include the first subset of active cameras. In several embodiments, the active cameras can include a different set of active cameras including fewer cameras, more cameras, and/or a subset of cameras including some or all of the first subset of cameras. In many embodiments, the image capture settings are used to capture video with the first subset of cameras. In several embodiments, the image capture settings are used to capture a still image with all of the cameras in the camera array.

[0044] Although specific processes for automatically determining image capture settings for auto-exposure using two subsets of active cameras are discussed above with respect to FIG. 9, any of a variety of processes for automatically determining exposure settings can be utilized as appropriate to the requirements of a specific application in accordance with embodiments of the invention. Process for using subsets of active cameras to synthesize HDR images in accordance with embodiments of the invention are further disclosed below.

[0045] Subset of active cameras can be configured to capture image data in order to determine image capture settings for use in the capture of HDR images. By taking measurements of scene information using different sets of image capture parameters, the image capture settings of various cameras utilized during HDR image capture can be set to capture image data that correspond to various exposure levels within the dynamic range of a scene. In many embodiments, one or more subsets of active cameras capture image data in parallel.

[0046] A process for capturing image data at various exposure levels to determine image capture settings for use in the capture of HDR images in accordance with an embodiment of the invention is illustrated in FIG. 10. The process 1000 includes configuring (1002) the image capture settings of a second subset of active cameras to various exposure settings to enable rapid measurement of the dynamic range of the scene. With the image capture settings for the first and second subset of active cameras set to various exposure settings, image data is captured (1004) using the active cameras. In several embodiments, the first and second subsets of active cameras capture image data in parallel. In many embodiments, the captured image data from the second subset of active cameras is used to measure (1006) the dynamic range of the scene. In various embodiments, the image data captured by both the first and second subsets of active cameras can be utilized to measure the scene information. The process of measuring the dynamic range of the scene using different image capture settings continues until a determination (1008) is made that measurement of the dynamic range is complete. The manner in which the settings of the active cameras are modified during the measurement of the dynamic range of the scene can be determined using criteria similar to those discussed above. When the measurement of dynamic range is complete, the process determines image capture settings for HDR image capture and configures (1014) the active cameras at multiple exposure levels that can be utilized to capture (1016) HDR image data. In many embodiments, the exposure bracketing (i.e. differences in exposure settings between subsets of active cameras) can be selected (1009) using the determined dynamic range of the scene. In several embodiments, the exposure bracketing can be predetermined. In other embodiments, the exposure bracketing can be selected depending on predetermined criteria. Such criteria can include (but is not limited to) number of exposure groups available for HDR mode and the difference in scene dynamic range and imaging system's dynamic range. In many embodiments, new image capture settings are determined (1010) and active cameras are then configured (1012) using the new image capture settings to capture image data at each of the exposure settings. As discussed above, the image data at the different exposure settings can then be combined to synthesize HDR images. In some embodiments, the determination that measurement of dynamic range is complete is achieved by comparing the percentage of both under-exposed and over-exposed pixels against pre-determined threshold values. In various embodiments, the auto-exposure and dynamic range determination is not significantly affected by the inherent disparity among the various images of the array. This is because the measurements are based on image histograms which are stable across various views.

[0047] In some embodiments, one can use the depth information from the camera array to automatically bracket the exposures to capture HDR. For instance, the depth information from the camera array allows one to determine where the focal plane is (based on the object closest to the camera in the focus window) and the associated depth of field around the focal plane. The exposure for one camera subset can be set to be optimal for the objects in the depth of field, while the exposure for the other subset is set to be optimal for the regions outside the depth of field. In the case of the regions outside the depth of field, there are two of them—the region in front of the in-focus region and the region behind the in-focus region. The exposure for the out-of-focus regions can be set to be optimal either for the region behind the in-focus region or the region in front of the in-focus region or both depending on what is optimal for ensuring the optimal contrast for the in-focus region.

[0048] Although specific processes for capturing image data using subsets of active cameras to determine image capture settings at multiple exposure levels that can be utilized to capture HDR image data are discussed above with respect to FIG. 10, any of a variety of processes for determining image capture settings at multiple exposure levels that can be utilized to capture HDR image data based upon measurements of scene information captured by a subset of cameras within a camera array can be utilized as appropriate to the requirements of a specific application in accordance with embodiments of the invention. Processes for using subsets of active cameras to determine autofocus settings are further discussed below.

[0049] Different image capture settings can be used to configure subsets of active cameras to measure scene information relevant for controlling the focus of optical systems of individual cameras within a camera array. In particular, image data regarding contrast levels among pixels of a single focal plane and relative blur amounts of pixels at various focus settings can be relevant to determining whether image capture settings satisfy predetermined criteria related to focus.

[0050] A process for using subsets of active cameras to determine focus settings for optical systems within cameras in a camera array in accordance with an embodiment of the invention is illustrated in FIG. 11. The process 1100 includes capturing (1102) image data using active cameras where the active cameras are defined into a plurality of subsets. In several embodiments, a first subset of cameras is used to capture image data that is used to synthesize an image that can be displayed in a preview mode and/or captured. In many embodiments, automatically determining focus settings can consider spatial correspondences by measuring corresponding image data and/or specific regions of interest within a scene. In various embodiments, this can be achieved by designating at least two individual cameras with the same focus settings such that parallax can be employed for those cameras. This in turn can identify the parallax-induced shift in region of interest in the other cameras compared to the reference camera. In several embodiments, parallax detection and correction can be performed (1103) on each set of cameras sharing focus settings using methods including (but not limited) to techniques disclosed in U.S. Pat. No. 8,619,082, entitled, “Systems and Methods for Parallax Detection and Correction in Images Captured Using Array Cameras that Contain Occlusions Using Subsets of Images to Perform Depth Estimation” filed Aug. 21, 2013, the disclosure of which is incorporated by reference herein in its entirety. In many embodiments, using image data captured by a second subset of active cameras, pixel contrast levels within image data captured using cameras with optical systems configured using specific focal settings can be measured (1104). In a number of embodiments, pixel contrast is also measured using image data captured by the first subset of cameras. In several embodiments, autofocus parameters are determined (1106) using the pixel contrast measurements for the entire image and/or a predefined region of interest. The process further includes determining (1108) whether the image capture settings satisfy predetermined criteria. If the image capture settings do not satisfy the predetermined criteria, then new focus settings are determined (1110) for the active cameras. The focus settings can be determined using techniques similar to those described above and/or in a manner designed to rapidly sample different focus settings in parallel using different cameras within the camera array. The active cameras are configured (1112) using the new focal settings and image data is captured (1114). The process repeats and parallax can be performed (1103) again and pixel contrast with respect to the different focus settings is again measured (1104) and autofocus parameters determined (1106). If focus settings are identified that satisfy the predetermined criteria with respect to autofocus, then identified focus settings are used to configure (1116) a set of active cameras and image data is captured (1118). In many embodiments, the active cameras include the first subset of active cameras. In several embodiments, the active cameras can include a different set of active cameras including fewer cameras, more cameras, and/or a subset of cameras including some or all of the first subset of cameras. In many embodiments, the image capture settings are used to capture video with the first subset of cameras. In several embodiments, the image capture settings are used to capture a still image with all of the cameras in the camera array.

[0051] Although specific processes for using subsets of active cameras to measure scene information while capturing video are discussed above with respect to FIG. 11 including processes that involve use of pixel contrast measurements, any of a variety of processes for measuring focus can be utilized as appropriate to the requirements of a specific application in accordance with embodiments of the invention. Processes for using subsets of active cameras to measure scene information during video capture mode are discussed further below.

[0052] Subsets of active cameras can be configured to capture image data to measure scene information during video capture, where the measurements of scene information can be used to adapt in real time the image capture settings of the subset of cameras used to capture image data from which frames of video are synthesized. A process for using subsets of active cameras to measure scene information while capturing image data for video in accordance with an embodiment of the invention is illustrated in FIG. 12. The process 1200 includes defining (1202) two or more subsets of active cameras and configuring the cameras using image capture settings appropriate to each subset. In several embodiments, a first subset of cameras is configured with uniform image capture settings and the cameras in the first subset capture image data that is used to synthesize frames of video. A second subset of cameras can be configured with image capture settings that differ from the image capture settings used to configure the first subset of cameras. In many instances, the image capture settings of cameras within the second subset can differ. In this way multiple measurements of scene information can be performed in parallel and the measurements used to adjust the image capture parameters of the first subset of imagers during the capture of image data used to synthesize subsequent frames of video. Once the image capture settings of the respective subsets have been configured, the active cameras capture (1204) image data.

[0053] Image data captured by a first subset of active cameras is used to synthesize (1206) an image. In some embodiments, the captured image data is saved and/or compressed and an image is synthesized in a decoupled manner. The image data captured by a second subset of active cameras can be used to measure (1208) scene information. If the video capture is complete (1210), then the process is complete. If video capture is not complete (1210), new image capture settings are determined (1212) based upon the measured scene information. In many embodiments, the image capture settings of the second subset of cameras are determined relative to the image capture settings determined for the first subset of cameras. In this way, subsequent measurements of scene information are made using image capture settings to which the first subset of cameras can smoothly transition until a stable set of image capture settings are identified. In this way, the aesthetic quality of the video can be enhanced by providing smooth transitions between the image capture settings of the cameras in the first subset of cameras that capture image data used to synthesize successive frames of video. Once the new image capture settings are determined, they can be used to configure (1214) the active cameras. The active cameras again capture (1204) image data and the process repeats until video capture is completed.

[0054] In several embodiments, the rate at which the second subset of cameras captures image data differs from the rate at which the first subset of cameras captures image data. In several embodiments, the rate at which the second subset of cameras captures image data can vary depending upon the measured scene information. For example, as parameters such as auto-exposure and/or autofocus stabilize the rate at which image data is captured by the second subset of cameras can be reduced and the rate can be increased in response to detection of such factors including (but not limited to) changes in the measurement of scene information, detection of motion using accelerometers within an array camera, and/or receipt of a user instruction to modify the focal plane of the captured images.

[0055] Although specific processes for using subsets of active cameras to measure scene information while capturing video are discussed above with respect to FIG. 12, any of a variety of processes for measuring scene information while capturing video can be utilized as appropriate to the requirements of a specific application in accordance with embodiments of the invention.

[0056] While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as an example of one embodiment thereof. It is therefore to be understood that the present invention may be practiced otherwise than specifically described, without departing from the scope and spirit of the present invention. Thus, embodiments of the present invention should be considered in all respects as illustrative and not restrictive.