Patent Publication Number: US-2017353649-A1

Title: Time of flight ranging for flash control in image capture devices

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates generally to flash control in image capture devices such as digital cameras, and more specifically to the utilization of time of flight range detection in flash control of image capture devices. 
     Description of the Related Art 
     In image capture devices, such as digital cameras, control of a flash device is primarily performed based on ambient light. When ambient light is low, the flash device is activated to illuminate an object for capture of an image of the object. Conversely, the flash device is deactivated when ambient light is high, making activation of the flash device unnecessary. The distance of the object being imaged from the image capture device, however, can greatly influence the effectiveness of the flash device and quality of the captured image. When the object is close to the image capture device and the flash device activated, the flash illumination of the object can be too strong and result in the captured image being “washed out,” such as where the object is a person&#39;s face, for example. If the object is farther away, the flash illumination of the object may be too weak, resulting in the object being too dark in the captured image. 
     Professional photographers will, for these reasons, measure a distance of an object from an image capture device and then adjust a flash device so that the flash illumination of the object has a proper intensity and is not too weak or too strong. In many everyday image capture devices, such as digital cameras in smart phones and other mobile devices, the control of the flash device is primarily triggered, or not triggered, based upon the detection of ambient light in the environment in which the mobile device and object being imaged are present. This can result in the issues noted above. In addition, where an object is located within a field of view of an image capture device also affects how effective the flash device is in properly illuminating the object being images. Multiple objects within the field of view can result in similar issues during image capture. In this situation, the flash device may possibly illuminate some objects too much so they appear washed out in the captured image while other objects are not illuminated enough and thus appear too dark in the captured image. There is a need for improved control of flash devices in image capture devices. 
     BRIEF SUMMARY 
     In one embodiment of the present disclosure, a flash control circuit for an image capture device includes a time-of-flight ranging sensor configured to sense distances to a plurality of objects within an overall field of view of the time-of-flight ranging sensor. The time-of-flight sensor is configured to generate a range estimation signal including a plurality of sensed distances to the plurality of objects. Flash control circuitry is coupled to the time-of-flight ranging sensor to receive the range estimation signal. The flash control circuitry is configured to generate a flash control signal to control a power of flash illumination light based upon the plurality of sensed distances. The flash control circuitry may be configured to determine an average of the plurality of distances and to control the power of the flash illumination light based upon the average distance or to determine a number of the plurality of objects and to control the power of the flash illumination light based upon the determined number. 
     In one embodiment, the time-of-flight sensor is configured to transmit an optical pulse signal and to receive return optical pulse signals corresponding to portions of the transmitted optical pulse signal that reflect off the plurality of objects. The time-of-flight sensor in this embodiment is further configured to generate a signal amplitude for each of the plurality of sensed objects where the signal amplitude of each object is based on a number of photons of the return optical pulse signal received by the time-of-flight sensor for the object. The flash control circuitry may determine a reflectance of each of the plurality of objects based upon the sensed distance and the signal amplitude for the object and generate the flash control signal based upon the reflectance of each of the plurality of objects. 
     In one embodiment, the time-of-flight sensor includes a light source configured to transmit an optical pulse signal and a return array of light sensors, the return array of light sensors configured to receive return optical pulse signals corresponding to portions of the transmitted optical pulse signal that reflect off the plurality of objects. The light source may be a vertical-cavity surface-emitting laser and the return array of light sensors may be an array of single photon avalanche diodes (SPADs). The return array of SPADs may include a single array zone of light sensors or multiple zones. Each of multiple array zones of the return array is configured to receive return optical pulse signals from a corresponding one of a plurality of spatial zones of a receiving field of view of the time-of-flight sensor. The flash control circuitry is configured to determine positions of the plurality of sensed objects in the receiving field of view based upon which of the plurality of array zones sense an object, and to control the power of the flash illumination based upon the determined positions of the plurality of sensed objects. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing and other features and advantages will become apparent from the following detailed description of embodiments, given by way of illustration and not limitation with reference to the accompanying drawings, in which: 
         FIG. 1  is a functional block diagram of an image capture device including flash control circuitry that controls flash illumination of multiple objects being imaged based upon time-of-flight (TOF) sensing according to one embodiment of the present disclosure. 
         FIG. 2  is a functional diagram illustrating the operation of the TOF ranging sensor of  FIG. 1 . 
         FIG. 3  is a functional block diagram illustrating in more detail one embodiment of the TOF ranging sensor of  FIGS. 1 and 2 . 
         FIG. 4A  is a functional diagram of a single zone embodiment of the return single photon avalanche diode (SPAD) array contained in the TOF ranging sensor of  FIG. 3 . 
         FIG. 4B  is a functional diagram of a multi zone embodiment of the return SPAD array contained in the TOF ranging sensor of  FIG. 3 ; 
         FIGS. 5A and 5B  are graphs illustrating operation of the TOF ranging sensor of  FIG. 3  in detecting multiple objects within a field of view of the sensor; 
         FIG. 6  is a histogram generated by the TOF ranging sensor in the embodiment of  FIGS. 5A and 5B  which provides detected distance information for multiple objects within the field of view of the sensor; and 
         FIG. 7  is a diagram illustrating multiple spatial zones where the TOF ranging sensor of  FIG. 3  is a multiple zone sensor. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a functional block diagram of an image capture device  100  including flash control circuitry  102  that controls flash illumination of objects  103  and  105  being imaged based upon sensed distances D TOF1  and D TOF2  between each of the objects and the image capture device according to one embodiment of the present disclosure. A time of flight (TOF) ranging sensor  104  transmits an optical pulse signal  106  that is incident upon the objects  103  and  105  within an overall field of view FOV of the TOF ranging sensor. The transmitted optical pulse signal  106  reflects off the objects  103  and  105  and portions of the reflected pulse signals propagate back to the TOF ranging sensor  104  as return optical pulse signals  108 . The TOF ranging sensor  104  determines the ranges or distances D TOF1  and D TOF2  between each of the objects  103 ,  105  and the image capture device  100 , and the flash control circuitry  102  thereafter controls flash illumination of these objects based upon these determined distances. In one embodiment, a histogram based time-of-flight detection technique is utilized by the TOF ranging sensor  104  to detect distances to multiple objects present within multiple spatial zones or subfields of view within the overall field of view FOV of the sensor, as will be described in more detail below. 
     In the present description, certain details are set forth in conjunction with the described embodiments to provide a sufficient understanding of the present disclosure. One skilled in the art will appreciate, however, that the other embodiments may be practiced without these particular details. Furthermore, one skilled in the art will appreciate that the example embodiments described below do not limit the scope of the present disclosure, and will also understand that various modifications, equivalents, and combinations of the disclosed embodiments and components of such embodiments are within the scope of the present disclosure. Embodiments including fewer than all the components of any of the respective described embodiments may also be within the scope of the present disclosure although not expressly described in detail below. Finally, the operation of well-known components and/or processes has not been shown or described in detail below to avoid unnecessarily obscuring the present disclosure. 
     The TOF ranging sensor  104  generates first and second range estimation signals RE 1  and RE 2  indicating the sensed distances D TOF1  and D TOF2  that the objects  103  and  105 , respectively, are positioned from the image capture device  100 . The TOF ranging sensor  104  may generate more than two range estimation signals RE 1 , RE 2 , where more than two objects are present within the overall field of view FOV. All the range estimation signals generated by the TOF ranging sensor  104  are collectively designated as the range estimation signal RE in  FIG. 1 . In one embodiment, each of the range estimation signals RE 1  and RE 2  includes a detected or sensed distance D TOF  to the detected object in the field of view FOV and also includes a signal amplitude SA (not shown) of the corresponding return optical pulse signal  108 . Utilizing the sensed distances D TOF1  and D TOF2  and the signal amplitude SA of the return optical pulse signals  108 , which are independent of the reflectance of each of the objects  103 ,  105 , information about the reflectance of each of the objects may be determined and utilized in combination with the detected distances and positions of the detected objects to control flash illumination of the objects  103  and  105 , as will also be discussed in more detail below. 
     The flash control circuitry  102  receives the range estimation signal RE and utilizes the range estimation signal to control the operation of a flash circuit  110 . In the embodiment of  FIG. 1 , the flash control circuitry  102  is shown as being part of processing circuitry  112  contained in the image capture device  100 . The processing circuitry  112  also includes other circuitry for controlling the overall operation of the image capture device  100 . The specific structure and functionality of the processing circuitry  112  will depend on the nature of the image capture device  100 . For example, the image capture device  100  may be a stand-alone digital camera or may be digital camera components contained within another type of electronic device, such as a smart phone or tablet computer. Thus, in  FIG. 1  the processing circuitry  112  represents circuitry contained in the image capture device  100  but also generally represents circuitry of other electronic devices, such as a smart phone or tablet computer, where the image capture device  100  is part of another electronic device. For example, where the image capture device  100  is part of a mobile device like a smart phone, the processing circuitry  112  controls the overall operation of the smart phone and also executes applications or “apps” that provide specific functionality for a user of the mobile device. The flash control circuitry  102  and TOF ranging sensor  104  may together be referred to as a flash control circuit for the image capture device  100 . The flash circuit  110  that generates the flash illumination light  114  may also be considered to part of this flash control circuit of the image capture device  100 . 
     In operation, the flash control circuitry  102  generates a flash control signal FC to control the flash circuit  110  to illuminate the objects  103 ,  105  when the image capture device  100  is capturing an image of the objects. This illumination of the objects  103 ,  105  by the flash circuit  110  is referred to as flash illumination in the present description and corresponds to flash illumination light  114  that is generated by the flash circuit and which illuminates the objects. Some of the flash illumination light  114  reflects off the objects  103 ,  105  and propagates back towards the image capture device  100  as return light  116 . 
     The image capture device  100  includes optical components  118  that route and guide this return light  116  to an image sensor  120  that captures an image of the objects  103 ,  105 . The optical components  118  would typically include a lens and may also include filtering components and autofocusing components for focusing captured images on the image sensor  120 . The image sensor  120  may be any suitable type of image sensor, such as a charge coupled device (CCD) type image sensor or a CMOS image sensor, and captures an image of the objects  103 ,  105  from the light provided by the optical components  118 . The image sensor  120  provides captured images to the processing circuitry  112 , which controls the image sensor to capture images and would typically store the captured images and provide other image capture related processing of the captured images. 
     In operation, the flash control circuitry  102  controls the flash circuit  110  to adjust the power of the flash illumination light  114  based upon the sensed distances to an object or the multiple objects, namely distances D TOF1  and D TOF2  in the example of  FIG. 1 , the number and positions of detected multiple objects  103 ,  105  within the overall field of view FOV, and information about the reflectance of each of the multiple objects based on the signal amplitude SA and sensed distance associated with each of the objects, as will be explained in more detail below. The flash control circuitry  102  generates the flash control signal FC to control the flash circuit  110  to generate the light  114  having a power or other characteristic that is adjusted based upon these sensed parameters. Two objects  103 ,  105  are illustrated merely by way of example in  FIG. 1 , and more than two objects are detected by the TOF ranging sensor  104  in some embodiments of the present disclosure, as will be described in more detail below. In addition, the processing circuitry  112  generates an autofocus signal AF based upon the sensed distance or distances D TOF  to focus the image sensor  120  on the objects being imaged. The precise manner in which the processing circuitry  112  generates the autofocus signal AF using the sensed distance or distances D TOF  may vary. 
       FIG. 2  is a functional diagram illustrating components and operation of the TOF ranging sensor  104  of  FIG. 1 . The TOF ranging sensor  104  may be a single chip that includes a light source  200  and return and reference arrays of photodiodes  214 ,  210 . Alternatively, these components may be incorporated within the circuitry of the image capture device  100  or other circuitry or chip within an electronic device including the image capture device. The light source  200  and the return and reference arrays  214 ,  210  are formed on a substrate  211 . In one embodiment, all the components of the TOF ranging sensor  104  are contained within the same chip or package  213 , with all components except for the light source  200  being formed in the same integrated circuit within this package in one embodiment. 
     The light source  200  transmits optical pulse signals having a transmission field of view FOV TR  to irradiate objects within the field of view. A transmitted optical pulse signal  202  is illustrated in  FIG. 2  as a dashed line and irradiates an object  204  within the transmission field of view FOV TR  of the light source  200 . In addition, a reflected portion  208  of the transmitted optical pulse signal  202  reflects off an integrated panel, which may be within a package  213  or may be on a cover  206  of the image capture device  100 . The reflected portion  208  of the transmitted pulse is illustrated as reflecting off the cover  206 , however, it may be reflected internally within the package  213 . 
     The cover  206  may be glass, such as on a front of a mobile device associated with a touch panel or the cover may be metal or another material that forms a back cover of the electronic device. The cover will include openings to allow the transmitted and return signals to be transmitted and received through the cover if not a transparent material. 
     The reference array  210  of light sensors detects this reflected portion  208  to thereby sense transmission of the optical pulse signal  208 . A portion of the transmitted optical pulse signal  202  reflects off objects  204  within the transmission field of view FOV TR  as return optical pulse signals  212  that propagate back to the TOF ranging sensor  104 . The TOF ranging sensor  104  includes a return array  214  of light sensors having a receiving field of view FOV REC  that detects the return optical pulse signals  212 . The field of view FOV of  FIG. 1  includes the transmitting and receiving fields of view FOV TR  and FOV REC . The TOF ranging sensor  104  then determines respective distances D TOF  between the TOF ranging sensor and the objects  204  based upon the time between the reference array  210  sensing transmission of the optical pulse signal  202  and the return array  214  sensing the return optical pulse signal  212 . The TOF ranging sensor  104  also generates a signal amplitude SA for each of the detected objects  204 , as will be described in more detail with reference to  FIG. 3 . 
       FIG. 3  is a more detailed functional block diagram of the TOF ranging sensor  104  of  FIGS. 1 and 2  according to one embodiment of the present disclosure. In the embodiment of  FIG. 3 , the TOF ranging sensor  104  includes a light source  300 , which is, for example, a laser diode such as a vertical-cavity surface-emitting laser (VCSEL) for generating the transmitted optical pulse signal designated as  302  in  FIG. 3 . The transmitted optical pulse signal  302  is transmitted in the transmission field of view FOV TR  of the light source  300  as discussed above with reference to  FIG. 2 . In the embodiment of  FIG. 3 , the transmitted optical pulse signal  302  is transmitted through a projection lens  304  to focus the transmitted optical pulse signals  302  so as to provide the desired field of view FOV TR . The projection lens  304  can be used to control the transmitted field of view FOV TR  of the sensor  104  and is an optional component, with some embodiments of the sensor not including the projection lens. 
     The reflected or return optical pulse signal is designated as  306  in  FIG. 3  and corresponds to a portion of the transmitted optical pulse signal  302  that is reflected off objects within the field of view FOV TR . One such object  308  is shown in  FIG. 3 . The return optical pulse signal  306  propagates back to the TOF ranging sensor  104  and is received through a return lens  309  that provides the desired return or receiving field of view FOV REC  for the sensor  104 , as described above with reference to  FIG. 2 . The return lens  309  in this way is used to control the field of view FOV REC  of the sensor  104 . The return lens  309  directs the return optical pulse signal  306  to range estimation circuitry  310  for generating the imaging distance D TOF  and signal amplitude SA for each object  308 . The return lens  309  is an optional component and thus some embodiments of the TOF ranging sensor  104  do not include the return lens. 
     In the embodiment of  FIG. 3 , the range estimation circuitry  310  includes a return single-photon avalanche diode (SPAD) array  312 , which receives the returned optical pulse signal  306  via the lens  309 . The SPAD array  312  corresponds to the return array  214  of  FIG. 2  and typically includes a large number of SPAD cells (not shown), each cell including a SPAD for sensing a photon of the return optical pulse signal  306 . In some embodiments of the TOF ranging sensor  104 , the lens  309  directs reflected optical pulse signals  306  from separate spatial zones within the field of view FOV REC  of the sensor to certain groups of SPAD cells or zones of SPAD cells in the return SPAD array  312 , as will be described in more detail below. 
     Each SPAD cell in the return SPAD array  312  provides an output pulse or SPAD event when a photon in the form of the return optical pulse signal  306  is detected by that cell in the return SPAD array. A delay detection circuit  314  in the range estimation circuitry  310  determines a delay time between transmission of the transmitted optical pulse signal  302  as sensed by a reference SPAD array  316  and a SPAD event detected by the return SPAD array  312 . The reference SPAD array  316  is discussed in more detail below. The SPAD event detected by the return SPAD array  312  corresponds to receipt of the return optical pulse signal  306  at the return SPAD array. In this way, by detecting these SPAD events, the delay detection circuit  314  estimates an arrival time of the return optical pulse signal  306 . The delay detection circuit  314  then determines the time of flight TOF based upon the difference between the transmission time of the transmitted optical pulse signal  302  as sensed by the reference SPAD array  316  and the arrival time of the return optical pulse signal  306  as sensed by the SPAD array  312 . From the determined time of flight TOF, the delay detection circuit  314  generates the range estimation signal RE ( FIG. 1 ) indicating the detected distance D TOF  between the hand  308  and the TOF ranging sensor  104 . 
     The reference SPAD array  316  senses the transmission of the transmitted optical pulse signal  302  generated by the light source  300  and generates a transmission signal TR indicating detection of transmission of the transmitted optical pulse signal. The reference SPAD array  316  receives an internal reflection  318  from the lens  304  of a portion of the transmitted optical pulse signal  302  upon transmission of the transmitted optical pulse signal from the light source  300 , as discussed for the reference array  210  of  FIG. 2 . The lenses  304  and  309  in the embodiment of  FIG. 3  may be considered to be part of the glass cover  206  or may be internal to the package  213  of  FIG. 2 . The reference SPAD array  316  effectively receives the internal reflection  318  of the transmitted optical pulse signal  302  at the same time the transmitted optical pulse signal is transmitted. In response to this received internal reflection  318 , the reference SPAD array  316  generates a corresponding SPAD event and in response thereto generates the transmission signal TR indicating transmission of the transmitted optical pulse signal  302 . 
     The delay detection circuit  314  includes suitable circuitry, such as time-to-digital converters or time-to-analog converters, to determine the time-of-flight TOF between the transmission of the transmitted optical pulse signal  302  and receipt of the reflected or return optical pulse signal  308 . The delay detection circuit  314  then utilizes this determined time-of-flight TOF to determine the distance D TOF  between the hand  308  and the TOF ranging sensor  104 . The range estimation circuitry  310  further includes a laser modulation circuit  320  that drives the light source  300 . The delay detection circuit  314  generates a laser control signal LC that is applied to the laser modulation circuit  320  to control activation of the laser  300  and thereby control transmission of the transmitted optical pulse signal  302 . The range estimation circuitry  310  also determines the signal amplitude SA based upon the SPAD events detected by the return SPAD array  312 . The signal amplitude SA is based on the number of photons of the return optical pulse signal  306  received by the return SPAD array  312 . The closer the object  308  is to the TOF ranging sensor  104  the greater the sensed signal amplitude SA, and, conversely, the farther away the object the smaller the sensed signal amplitude. 
       FIG. 4A  is a functional diagram of a single zone embodiment of the return SPAD array  312  of  FIG. 3 . In this embodiment, the return SPAD array  312  includes a SPAD array  400  including a plurality of SPAD cells SC, some of which are illustrated and labeled in the upper left portion of the SPAD array. Each of these SPAD cells SC has an output, with two outputs labeled SPADOUT 1 , SPADOUT 2  shown for two SPAD cells by way of example in the figure. The output of each SPAD cell SC is coupled to a corresponding input of an OR tree circuit  402 . In operation, when any of the SPAD cells SC receives a photon from the reflected optical pulse signal  306 , the SPAD cell provides an active pulse on its output. Thus, for example, if the SPAD cell SC having the output designated SPADOUT 2  in the figure receives a photon from the reflected optical pulse signal  306 , then that SPAD cell will pulse the output SPADOUT 2  active. In response to the active pulse on the SPADOUT 2 , the OR tree circuit  402  will provide an active SPAD event output signal SEO on its output. Thus, whenever any of the SPAD cells SC in the return SPAD array  400  detects a photon, the OR tree circuit  402  provides an active SEO signal on its output. In the single zone embodiment of  FIG. 4A , the TOF ranging sensor  104  may not include the lens  309  and the return SPAD array  312  corresponds to the return SPAD array  400  and detects photons from reflected optical pulse signals  306  within the single field of view FOV REC  ( FIG. 2 ) of the sensor. 
       FIG. 4B  is a functional diagram of a multiple zone embodiment of the return SPAD array  312   FIG. 3 . In this embodiment, the return SPAD array  312  includes a return SPAD array  404  having four array zones ZONE 1 -ZONE 4 , each array zone including a plurality of SPAD cells. Four zones ZONE 1 -ZONE 4  are shown by way of example and the SPAD array  404  may include more or fewer zones. A zone in the SPAD array  404  is a group or portion of the SPAD cells SC contained in the entire SPAD array. The SPAD cells SC in each zone ZONE 1 -ZONE 4  have their output coupled to a corresponding OR tree circuit  406 - 1  to  406 - 4 . The SPAD cells SC and outputs of these cells coupled to the corresponding OR tree circuit  406 - 1  to  406 - 4  are not shown in  FIG. 4B  to simplify the figure. 
     In this embodiment, each of zones ZONE 1 -ZONE 4  of the return SPAD array  404  effectively has a smaller subfield of view corresponding to a portion of the overall field of view FOV REC  ( FIG. 2 ). The return lens  309  of  FIG. 3  directs return optical pulse signals  306  from the corresponding spatial zones or subfields of view within the overall field of view FOV REC  to corresponding zones ZONE 1 -ZONE 4  of the return SPAD array  404 . In operation, when any of the SPAD cells SC in a given zone ZONE 1 -ZONE 4  receives a photon from the reflected optical pulse signal  306 , the SPAD cell provides an active pulse on its output that is supplied to the corresponding OR tree circuit  406 - 1  to  406 - 4 . Thus, for example, when one of the SPAD cells SC in the zone ZONE 1  detects a photon that SPAD cell provides and active pulse on its output and the OR tree circuit  406 - 1 , in turn, provides an active SPAD event output signal SEO 1  on its output. In this way, each of the zones ZONE 1 -ZONE 4  operates independently to detect SPAD events (i.e., receive photons from reflected optical pulse signals  306  in  FIG. 3 ). 
       FIGS. 5A and 5B  are graphs illustrating operation of the TOF ranging sensor  104  of  FIG. 2  in detecting multiple objects within the field of view FOV of the TOF ranging sensor  104  of  FIGS. 2 and 3 . The graphs of  FIGS. 5A and 5B  are signal diagrams showing a number of counts along a vertical axis and time bins along a horizontal axis. The number of counts indicates a number of SPAD events that have been detected in each bin, as will be described in more detail below. These figures illustrate operation of a histogram based ranging technique implemented by the TOF ranging sensor  104  of  FIGS. 1-3  according to an embodiment of the present disclosure. This histogram based ranging technique allows the TOF ranging sensor  104  to sense or detect multiple objects within the field of view FOV of the TOF ranging sensor. 
     This histogram based ranging technique is now described in more detail with reference to  FIGS. 3, 4A, 4B, 5A and 5B . In this technique, more than one SPAD event is detected each cycle of operation, where the transmitted optical pulse signal  302  is transmitted each cycle. SPAD events are detected by the return SPAD array  312  (i.e., return SPAD array  400  or  404  of  FIGS. 4A, 4B ) and reference SPAD array  316 , where a SPAD event is an output pulse provided by the return SPAD array indicating detection of a photon. Thus, an output pulse from the OR tree circuit  402  of  FIG. 4A  or one of the OR tree circuits  406 - 1  to  406 - 4  of  FIG. 4B . Each cell in the SPAD arrays  312  and  3216  will provide an output pulse or SPAD event when a photon is received in the form of the return optical pulse signal  306  for target SPAD array  212  and internal reflection  318  of the transmitted optical pulse signal  302  for the reference SPAD array  316 . By monitoring these SPAD events an arrival time of the optical signal  306 ,  318  that generated the pulse can be determined. Each detected SPAD event during each cycle is allocated to a particular bin, where a bin is a time period in which the SPAD event was detected. Thus, each cycle is divided into a plurality of bins and a SPAD event detected or not for each bin during each cycle. Detected SPAD events are summed for each bin over multiple cycles to thereby form a histogram in time as shown in  FIG. 6  for the received or detected SPAD events. The delay detection circuit  314  of  FIG. 3  or other control circuitry in the TOF ranging sensor  104  implements this histogram-based technique in one embodiment of the sensor. 
       FIGS. 5A and 5B  illustrate this concept over a cycle. Multiple cells in each of the SPAD arrays  312  and  316  may detect SPAD events in each bin, with the count of each bin indicating the number of such SPAD events detected in each bin over a cycle.  FIG. 5B  illustrates this concept for the internal reflection  318  of the transmitted optical pulse signal  302  as detected by the reference SPAD array  316 . The sensed counts (i.e., detected number of SPAD events) for each of the bins shows a peak  500  at about bin  2  with this peak being indicative of the transmitted optical pulse signal  302  being transmitted.  FIG. 5A  illustrates this concept for the reflected or return optical pulse signal  306 , with there being two peaks  502  and  504  at approximately bins  3  and  9 . These two peaks  502  and  504  (i.e., detected number of SPAD events) indicate the occurrence of a relatively large number of SPAD events in the bins  3  and  9 , which indicates reflected optical pulse signals  306  reflecting off a first object causing the peak at bin  3  and reflected optical pulse signals reflecting off a second object at a greater distance than the first object causing the peak at bin  9 . A valley  506  formed by a lower number of counts between the two peaks  502  and  504  indicates no additional detected objects between the first and second objects. Thus, the TOF ranging sensor  104  is detecting two objects, such as the objects  103  and  105  of  FIG. 1 , within the FOV of the sensor in the example of  FIGS. 7A and 7B . The two peaks  502  and  504  in  FIG. 5A  are shifted to the right relative to the peak  500  of  FIG. 5B  due to the time-of-flight of the transmitted optical pulse signal  302  in propagating from the TOF ranging sensor  104  to the two objects  103 ,  105  within the FOV but at different distances from the TOF ranging sensor. 
       FIG. 6  illustrates a histogram generated by TOF ranging sensor  104  over multiple cycles. The height of the rectangles for each of the bins along the horizontal axis represents the count indicating the number of SPAD events that have been detected for that particular bin over multiple cycles of the TOF ranging sensor  104 . As seen in the histogram of  FIG. 6 , two peaks  600  and  602  are again present, corresponding to the two peaks  602  and  604  in the single cycle illustrated in  FIG. 5A . From the histogram of  FIG. 6 , either the TOF ranging sensor  104  determines a distance D TOF  to each of the first and second objects  103 ,  105  in the FOV of the TOF ranging sensor. In addition, the TOF ranging sensor  104  also generates the signal amplitude SA for each of the objects  103 ,  105  based upon these counts, namely the number of photons or SPAD events generated by the return SPAD array  312  in response to the return optical pulse signal  306 . 
       FIG. 7  is a diagram illustrating multiple spatial zones within the receiving field of view FOV REC  where the TOF ranging sensor  104  is a multiple zone sensor including the return SPAD array  404  of  FIG. 4B . In this embodiment, the receiving field of view FOV REC  includes four spatial zones SZ 1 -SZ 4  as shown. Thus, the four spatial zones SZ 1 -SZ 4  collectively form the receiving field of view FOV REC  of the TOF ranging sensor  104 . The transmitted optical pulse signal  302  ( FIG. 3 ) illuminates these four spatial zones SZ 1 -SZ 4  within the receiving field of view FOV REC . The number of spatial zones SZ corresponds to the number of array zones ZONE 1 -ZONE 4  in the return SPAD array  404  of  FIG. 4B . Where the return SPAD array  404  includes a different number of array zones ZONE 1 -ZONE 4  or a different arrangement of the array zones within the return SPAD array, then the number and arrangement of the corresponding spatial zones SZ within the overall field of view FOV REC  will likewise vary. In such a multiple zone TOF ranging sensor  104  as functionally illustrated in  FIG. 7 , the return lens  309  ( FIG. 3 ) is configured to route return optical pulse signals  306  from each of the spatial zones SZ within the overall field of view FOV REC  to a corresponding array zone ZONE 1 -ZONE 4  of the return SPAD array  404  of  FIG. 4B . This is represented in the figure through the pairs of lines  700  shown extending from the return SPAD array  404  to each of the spatial zones SZ 1 -SZ 4 . 
     Each of the array zones ZONE 1 -ZONE 4  outputs respective SPAD event output signals SEO 1 -SEO 4  as previously described with reference to  FIG. 4B , and the TOF ranging sensor  104  accordingly calculates four different imaging distances D TOF1 -D TOF4 , one for each of the spatial zones SZ 1 -SZ 4 . Thus, in this embodiment the range estimation signal RE generated by the TOF ranging sensor  104  includes four different values for the four different detected imaging distances D TOF1 -D TOF4 . Each of these detected imaging distances D TOF1 -D TOF4  is shown as being part of the generated range estimation signal RE to have a value  5 . This would indicate objects in each of the spatial zones SZ 1 -SZ 4  are the same distance away, or there is one object covering all the spatial zones. The value  5  was arbitrarily selected merely to represent the value of each of the detected imaging distances D TOF1 -D TOF4  and to illustrate that in the example of  FIG. 7  each of these detected imaging distances has the same value. As seen in  FIG. 7 , the TOF ranging sensor  104  also outputs the signal amplitude SA signal for each of the spatial zones SZ and corresponding array zones ZONE. Thus, for the spatial zone SZ 1  the TOF ranging sensor  104  generates the range estimation signal RE 1  including the sensed distance D TOF1  and signal amplitude SA 1  generated based on SPAD events detected by array zone ZONE 1 . The signals RE 2 -RE 4  for spatial zones SZ 2 -SZ 4  and array zones ZONE 2 -ZONE 4  are also shown. 
     Referring back to  FIG. 1 , embodiments of the overall operation of the flash control circuitry  102  in controlling the flash circuit  110  based upon the range estimation signal RE generated by the TOF ranging sensor  104  will now be described in more detail. Initially, a user of the image capture device  100  activates the image capture device  100  and directs the image capture device to place an image scene within a field of view of the device. The image scene is a scene that the user wishes to image, meaning capture a picture of with the image capture device  100 . The field of view the image capture device  100  is not separately illustrated in  FIG. 1 , but is analogous to the field of view FOV shown for the TOF ranging sensor  104  for the optical components  118  of the image capture device  118 . The field of view of the image capture device  100  would of course include or overlap with the field of view FOV of the TOF ranging sensor  104  so that the sensor can detect the distances to objects within the field of view of the image capture device (i.e., of the optical components  118 ). 
     When the image capture device  100  is activated, the TOF ranging sensor  104  is activated and begins generating a starting histogram such as the histogram illustrated in  FIG. 6 . The TOF ranging sensor  104  then utilizes this starting histogram to detect the distance D TOF  to an object or multiple objects  103 ,  105  in the image scene to be captured. The TOF ranging sensor  104  may utilize a variety of suitable methods for processing the starting histogram to detect the distance or distances D TOF  to objects  103 ,  105  in the image scene, as will be understood by those skilled in the art. For example, detection of maximum values of peaks in the starting histogram or the centroid of the peaks in the starting histogram may be utilized in detecting objects in the imaging scene. The TOF ranging sensor  104  may perform ambient subtraction as part of generating this starting histogram, where ambient subtraction is a method of adjusting the values of detected SPAD events using detected SPAD events during cycles of operation of the TOF ranging sensor  104  when no transmitted optical pulse signal  106  is being transmitted. The TOF ranging sensor  104  may utilize ambient subtraction in order to compensate for background or ambient light in the environment of the imaging scene containing the objects being imaged, as will be appreciated by those skilled in the art. 
     The TOF ranging sensor  104  processes the generated histogram to generate the range estimation signal RE including a distance D TOF  and signal amplitude SA for each detected object. Thus, in the example of  FIG. 1  the TOF ranging sensor  104  generates a range estimation signal RE including a first range estimation signal RE 1  including the sensed distance D TOF1  and signal amplitude SA 1  for the object  103  and further including a second range estimation signal RE 2  including the sensed distance D TOF2  and signal amplitude SA 2  for the object  105 . 
     The flash control circuitry  102  receives the first and second range estimation signals RE 1 , RE 2  from the TOF ranging sensor  104  and then controls the flash circuit  110  to adjust the power of the flash illumination light  114  based upon these range estimation signals. The flash control circuitry  102  generally controls the flash circuit  110  based upon multiple detected objects sensed by the TOF ranging sensor  104  and thus based upon the range estimate signal RE generated by this sensor. The specific manner in which the flash control circuitry  102  controls the flash circuit  110  based upon the range estimation signal RE varies in different embodiments of the present disclosure. In general, when sensed objects are father away, the flash control circuitry  102  controls the flash circuit  110  to increase the power of light  114  transmitted by the flash circuit to illuminate objects being imaged. Conversely, the flash control circuitry  102  in general controls the flash circuit  11  to decrease the power of the flash illumination light  114  if sense objects are nearer the image capture device. 
     Where the TOF ranging sensor  104  detects multiple objects, the flash control circuitry  102  may adjust or control the power of the flash illumination light  114  generated by the flash circuit  110  in a variety of different ways, as will now be described in more detail. In the following description, the flash control circuitry  102  is described, for the sake of brevity, as controlling or adjusting the power of the flash illumination light  114 , even though the flash control circuitry actually generates the flash control signal FC to control the flash circuit  110  to thereby generate the flash illumination light  114  having a power based upon these sensed parameters. In one embodiment, the flash control circuitry  102  balances the power of the flash illumination light  114  by using the average of the sensed distances D TOF  to multiple sensed objects. The flash control circuitry  102  can adjust the flash illumination light  114  to a maximum power when the sensed distance D TOF  to a nearest one of multiple sensed objects is greater than a threshold value. The TOF ranging sensor  104  has a maximum range or distance D TOF-MAX  beyond which the sensor cannot accurately sense the distances to objects. Thus, in one embodiment the flash control circuitry  102  also adjusts the flash illumination light  114  to a maximum power where all objects within the field of view FOV of the TOF ranging sensor  104  are beyond this maximum range D TOF-MAX . 
     As discussed above, the TOF ranging sensor  104  generates a signal amplitude SA in addition to the sensed distance D TOF  for each of multiple objects detected by the sensor. The signal amplitude SA is related to the number of photons of the return optical pulse signal  306  ( FIG. 3 ) sensed by the return SPAD array  400  ( FIG. 4A ) or by each zone of the multiple zone return SPAD array  404  ( FIG. 4B ) as previously discussed. In one embodiment, the flash control circuitry  102  utilizes the sensed signal amplitude SA and sensed distance D TOF  for each object to estimate a reflectivity of the object, and then controls the power of the flash illumination light  114  based upon this estimated reflectivity. For example, where the sensed distance D TOF  for a detected object is relatively small and the corresponding signal amplitude SA is also small, the flash control circuitry  102  may determine the sensed object is a low reflectivity object. The flash control circuitry  102  would then increase the power of the flash illumination light  114  to adequately illuminate the objects for image capture. Conversely, if the sensed distance D TOF  for a detected object is relatively large and the corresponding signal amplitude SA is also large, the flash control circuitry  102  may determine the sensed object is a high reflectivity object. In this situation, the flash control circuitry  102  decreases the power of the flash illumination light  114  so that the objects do not appear too bright in the captured image. 
     In other embodiments, the flash control circuitry  102  controls the power of the flash illumination light  114  based on other parameters of sensed objects. For example, in one embodiment the flash control circuitry  102  adjusts or controls the power of the flash illumination light  114  based upon the locations or positions of the objects within the overall field of view FOV REC . Where the multiple zone return SPAD array  404  of  FIG. 4B  is used, the position of a sensed object within the overall field of view FOV REC  is known based upon which array zones ZONE sense an object. For example, where the array zone ZONE 1  senses an object the flash control circuitry  102  determines an object is located in spatial zone SZ 1  of  FIG. 7  and thus in the upper left corner of the overall field of view FOV REC . Where sensed objects are not positioned near the center of the overall field of view FOV REC , the flash control circuitry  102  in one embodiment increases the power of the flash illumination light  114  relative to the power of the flash illumination light that would be provided based simply on the detected distances D TOF  to the objects. 
     The flash control circuitry  102  determines where objects are positioned within the overall field of view FOV REC  based upon which zones ZONE of the multiple zone return SPAD array  404  of  FIG. 4B  sense an object. The return SPAD array  404  includes only four zones ZONE, but this embodiment is better illustrated where the array includes more than four zones, such as where the array includes a 4×4 array of sixteen zones. In this case, when the objects are sensed only in a zone or several zones in one corner of the overall field of view FOV REC  the flash control circuitry  102  increases the power of the flash illumination light  114 . In yet another embodiment, the flash control circuitry  102  adjusts the power of the flash illumination light  114  to balance the power based upon the number of sensed objects within the overall field of view FOV REC . 
     In the single zone return SPAD array  400  embodiment of  FIG. 4A , the TOF ranging sensor  104  need not include the return lens  309  of  FIG. 3 . In order to get a more accurate estimate of the reflectance of an object in the infrared spectrum, the object must be assumed to cover the full field of view of the sensor. In the multiple zone embodiments, the different zones of the return SPAD array effectively have separate, smaller fields of view as discussed with reference to  FIG. 7 . In these embodiments, there is more confidence of smaller objects at distance D TOF  covering the entire field of view of a given zone. The multiple zone lensed solution discussed with reference to  FIG. 4B  provides information on where objects are within an image scene. Finally, it should be noted that the TOF ranging sensor  104  need not use the histogram-based ranging technique described with reference to  FIGS. 5 and 6 . The TOF ranging sensor  104  could use other time-of-flight techniques to extract range information. For example, analog delay locked loop based systems, time-to-amplitude/analog converters, and so on could be utilized by the TOF ranging sensor  104  to detect distances to objects instead of the described histogram-based ranging technique. 
     While in the present disclosure embodiments are described including a ranging device including SPAD arrays, the principles of the circuits and methods described herein for calculating a distance to an object could be applied to arrays formed of other types of photon detection devices. 
     The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not to be limited to the embodiments of the present disclosure.