Patent Publication Number: US-11044417-B2

Title: HDR image sensor with LFM and reduced motion blur

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/135,647, filed Sep. 19, 2018 in the U.S. Patent and Trademark Office, the contents of which are incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The following relates generally to image sensor technology, and more specifically to LED flicker mitigation in image sensors. 
     DISCUSSION OF RELATED ART 
     High Dynamic Range (HDR) imaging is a technique used to reproduce a greater dynamic range of luminance with, for example, standard digital imaging. HDR sensors are image sensors that may be used in extreme dynamic range applications. HDR image sensors are being used in increasing frequency in numerous applications including automotive applications, such as side and rear view camera monitoring systems (CMS) that can replace or supplement rear view and side mirrors, thereby eliminating blind spots and reducing problems with glare. 
     A pixel in conventional lighting may include three continuous exposures, that may be, for example, medium and short exposures, and this arrangement may be subject to having issues with flicker. In the case of HDR sensors, a pixel with three continuous exposures may be configured so that the continuous exposures are medium and short exposures. The exposures may be executed in a sequence. Such a structure has posed a challenge to manufacturers and users alike, particularly when HDR sensors are implemented, for example, in certain vision systems. LED usage has become more widespread because of their efficient use of energy and superior brightness when compared with conventional lighting, and thus LED lights are becoming more popular for use in outdoor illumination, such as illuminated traffic signs, flood lights, headlights and tail lights of motor vehicles and bicycles, etc. 
     However, LED lighting can negatively affect the operation of image sensors, particularly HDR sensors. For example, LEDs may be modulated with “on” times that are sometimes smaller than the HDR sensor frame rate. In such instances, it is possible that short exposures may not overlap with the LED “on” time, causing the short exposure image to perceive the LED as being “off”. For example, in the case of HDR sensors, the medium exposures may perceive the LED as being “on”, and the short exposures may perceive the LED as being “off”. Since the coincidence between the LED “on” time and the sensor exposure may result in that some frames perceive the LED as being “on” and others as being “off”. This variation in the LED state in the captured image sequence is regarded as LED flicker. 
     Some attempts to mitigate the LED flicker (e.g., LED Flicker Mitigation) has resulted in blurry images. For example, operating the HDR sensor with an increased exposure time and then compensating for the increased exposure time by reducing the sensor responsivity, or by fragmenting the exposures. However, the aforementioned attempt to mitigate LED flicker may create unacceptable amounts of image blur. 
     SUMMARY 
     An apparatus for light emitting diode (LED) flicker mitigation in image sensors is described. The apparatus may include a timing controller circuit that generates at least one control signal that controls an operation of the image sensor, at least one pixel, in which the at least one pixel comprises a split photodiode pixel including at least two or more photodiodes that are configured to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, the two or more photodiodes include a first photodiode that has a first exposure period that is longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, and the timing controller circuit is configured to control a plurality of exposures performed by the second photodiode of the at least one pixel to include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     A method of manufacturing an apparatus for LED flicker mitigation in image sensors is described. The method may include providing a timing controller circuit that generates at least one control signal that controls an operation of the image sensor, providing at least one pixel, in which the at least one pixel comprises a split photodiode pixel including at least two or more photodiodes that are configured to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, the two or more photodiodes include a first photodiode that has a first exposure period that is longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, and the timing controller circuit is configured to control a plurality of exposures performed by the second photodiode of the at least one pixel to include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     A method of using an apparatus for LED flicker mitigation in image sensors is described. The method may include using a timing controller circuit that generates at least one control signal that controls an operation of the image sensor, using at least one pixel, in which the at least one pixel comprises a split photodiode pixel including at least two or more photodiodes that are configured to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, the two or more photodiodes include a first photodiode that has a first exposure period that is longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, and the timing controller circuit is configured to control a plurality of exposures performed by the second photodiode of the at least one pixel to include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     In some examples of the apparatus and method described above, the timing controller circuit is configured to control the second photodiode to perform a fragmented exposure operation in which a plurality of exposure periods of the second photodiode are shorter in duration than the first exposure period of the first photodiode, and the plurality of exposure periods of the second photodiode include both continuous and fragmented exposure periods to capture the one or more bursts of light. 
     In some examples of the apparatus and method described above, the first exposure period of the first photodiode comprises a continuous exposure, and the timing control circuit is configured to control the fragmented exposure operation performed by the second photodiode that includes dividing the plurality of exposure periods into N parts that are distributed evenly over operation of the second photodiode. 
     In some examples of the apparatus and method described above, the fragmented exposure operation performed by the second photodiode occurs during the first exposure period of the first photodiode. In some examples of the apparatus and method described above, the timing controller circuit receives an input signal to activate the image sensor and capture bursts of light from a light source. In some examples of the apparatus and method described above, the light source comprises an LED light source. In some examples of the apparatus and method described above, the image sensor comprises an High Dynamic Range (HDR) image sensor. 
     A method for LED flicker mitigation in image sensors is described. The method may include generating, by a timing controller circuit, at least one control signal that controls an operation of the image sensor, the image sensor including at least one pixel having a split photodiode pixel including at least two or more photodiodes that are configured by the control signal from the timing controller circuit to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, controlling, by the timing controller circuit, a first exposure period of a first photodiode of the two or more photodiodes to be longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, performing by the second photodiode, a fragmented exposure operation in which a plurality of exposure periods of the second photodiode are shorter in duration than the first exposure period of the first photodiode, and the plurality of exposure periods of the second photodiode include both continuous and fragmented exposure periods to capture the one or more bursts of light, outputting by the split photodiode (split-PD) pixel to at least one of a memory or the timing controller circuit, and the plurality of exposure periods of the second photodiode of the at least one pixel in the image sensor include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer in duration than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     An apparatus for LED flicker mitigation in image sensors is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be operable to cause the processor to generate, by a timing controller circuit, at least one control signal that controls an operation of the image sensor, the image sensor including at least one pixel having a split photodiode pixel including at least two or more photodiodes that are configured by the control signal from the timing controller circuit to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, control, by the timing controller circuit, a first exposure period of a first photodiode of the two or more photodiodes to be longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, perform by the second photodiode, a fragmented exposure operation in which a plurality of exposure periods of the second photodiode are shorter in duration than the first exposure period of the first photodiode, and the plurality of exposure periods of the second photodiode include both continuous and fragmented exposure periods to capture the one or more bursts of light, output by the split-PD pixel to at least one of a memory or the timing controller circuit, and the plurality of exposure periods of the second photodiode of the at least one pixel in the image sensor include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer in duration than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     A non-transitory computer readable medium storing code for LED flicker mitigation in image sensors is described. In some examples, the code comprises instructions executable by a processor to: generate, by a timing controller circuit, at least one control signal that controls an operation of the image sensor, the image sensor including at least one pixel having a split photodiode pixel including at least two or more photodiodes that are configured by the control signal from the timing controller circuit to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, control, by the timing controller circuit, a first exposure period of a first photodiode of the two or more photodiodes to be longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, perform by the second photodiode, a fragmented exposure operation in which a plurality of exposure periods of the second photodiode are shorter in duration than the first exposure period of the first photodiode, and the plurality of exposure periods of the second photodiode include both continuous and fragmented exposure periods to capture the one or more bursts of light, output by the split-PD pixel to at least one of a memory or the timing controller circuit, and the plurality of exposure periods of the second photodiode of the at least one pixel in the image sensor include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer in duration than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the first exposure period of the first photodiode comprises a continuous exposure, and controlling, by the timing control circuit, operation of the fragmented exposure periods performed by the second photodiode that includes dividing the plurality of exposure periods into N parts, and distributing the N parts evenly over operation of the second photodiode. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the fragmented exposure operation by the second photodiode is performed during the first exposure period of the first photodiode. In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the image sensor comprises an HDR image sensor. 
     An apparatus for LED flicker mitigation in image sensors is described. The apparatus may include a timing controller circuit that generates at least one control signal that controls an operation of the HDR image sensor, at least one pixel, in which the at least one pixel comprises a split photodiode pixel including at least two or more photodiodes that are configured to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, the two or more photodiodes include a first photodiode that has a first exposure period that is longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, and the timing controller circuit is configured to control a plurality of exposures performed by the second photodiode of the at least one pixel to include at least five exposures. 
     A method of using an apparatus for LED flicker mitigation in image sensors is described. The method may include using a timing controller circuit that generates at least one control signal that controls an operation of the HDR image sensor, using at least one pixel, in which the at least one pixel comprises a split photodiode pixel including at least two or more photodiodes that are configured to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other, the two or more photodiodes include a first photodiode that has a first exposure period that is longer in duration than a second exposure period of a second photodiode of the two or more photodiodes, and the timing controller circuit is configured to control a plurality of exposures performed by the second photodiode of the at least one pixel to include at least five exposures. 
     In some examples of the apparatus and method described above, the at least five exposures include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer in duration than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     An apparatus for LED flicker mitigation in image sensors is described. The apparatus may include an array of split photodiode pixels configured to be exposed and blanked independently of each other together with fragmented exposures, at least a first photodiode in the array of split photodiode pixels is configured for a continuous long exposure, a second photodiode is configured for fragmented exposures including medium exposures and shorter exposure, and a timing controller for outputting control signals to average an LED modulation and to synchronize the medium exposures and the shorter exposures. 
     A method of using an apparatus for LED flicker mitigation in image sensors is described. The method may include using an array of split photodiode pixels configured to be exposed and blanked independently of each other together with fragmented exposures, using at least a first photodiode in the array of split photodiode pixels is configured for a continuous long exposure, a second photodiode is configured for fragmented exposures including medium exposures and shorter exposure, and using a timing controller for outputting control signals to average an LED modulation and to synchronize the medium exposures and the shorter exposures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of a frame of a predetermined duration in accordance with aspects of the present disclosure. 
         FIG. 2  shows an example of an image of ghosting of an object in accordance with aspects of the present disclosure. 
         FIG. 3  shows an example of a schematic of an image sensor in accordance with aspects of the present disclosure. 
         FIG. 4  shows an example of a temporal illustration of the operation of the split photodiode (split-PD) pixel and the fragmented exposures in accordance with aspects of the present disclosure. 
         FIG. 5  shows an example of a temporal illustration of an embodiment of the inventive concept in accordance with aspects of the present disclosure. 
         FIG. 6  shows an example of a temporal illustration in which an additional fragmented exposure is performed to mitigate light emitting diode (LED) flicker in extremely illuminated conditions in accordance with aspects of the present disclosure. 
         FIG. 7  shows an example of a process for mitigating LED flicker in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an example of a frame  100  of a predetermined duration in accordance with aspects of the present disclosure. The example shown includes frame  100 , longer exposure periods  105  (T L ), medium exposure periods  110  (T M ), shorter exposure periods  115  (T S ), light on periods  120 , and light off periods  125 . 
     In some cases, the duration of frame  100  may be the reciprocal of the frequency. Shown is a non-limiting example of the exposure periods of an image sensor. For example, an image sensor may have, as shown in  FIG. 1 , exposure periods T L , T M  and T S  respectively referring to a longer exposure period  105 , a medium exposure period  110 , and a shorter exposure period  115  (relative to each other), and “Blank” refers to a blanking period. It can also be seen that a relatively short burst of a blinking light source (e.g.  FIG. 1  shows a duty cycle of about 10%) may be missed by image sensor in the medium exposure period  110  T M  and in the shorter exposure period  115  T S  in a frame  100 . For example,  FIG. 1  shows that in the medium T M  period and the shorter T S  period, for this particular frame  100 , the burst of lights are missed completely. In other words, the source (in this case blinking with a relative low duty cycle) may be perceived by the medium exposure and the shorter exposure as being off. 
     However, although  FIG. 1  shows a case where the exposure period of an image sensor misses a burst of light during a T M  exposure period or a T S  exposure period, over the course of several frames, the image sensor may not always miss the burst of light. Accordingly, the light emitting diode (LED) burst of light may be visible in one frame  100  but not visible (e.g., missed) in the next or future frame. Such intermittent missing of the LED bursts of light in a frame  100  may appear as a flickering of an image sequence. In applications such as autonomous vehicles, flickering may impact the quality of the image sensor. For example, in an autonomous vehicle there may be a result where the state of a traffic light is missed (e.g., red or green light) because of asynchronicity between the exposure time and light modulation. In addition, other parts of the vehicle (e.g., LED headlights and LED tail lights) may have a flickering output that could affect the sensing of the present vehicle by other autonomous vehicles within proximity of the present vehicle. 
     Frame  100 , longer exposure periods  105 , medium exposure periods  110 , shorter exposure periods  115 , light on periods  120 , and light off periods  125  may be an example of, or include aspects of, the corresponding elements described with reference to  FIGS. 4, 5, and 6 . 
       FIG. 2  shows an example of an image  200  of ghosting  210  of an object in accordance with aspects of the present disclosure. The example shown includes image  200 . Image  200  may include person  205  and ghosting  210 . 
     In a high dynamic range imaging, the use of multiple exposures to obtain an image  200  may create an inherent synchronicity between the different exposures of the same scene. In a static scene, the inherent synchronicity may be negligible. However, when there is motion, dynamic scenes having different exposures may result in ghosting  210  of moving objects. For example, in  FIG. 2 , the person  205  moved his arm, and the use of multiple exposures resulting in ghosting  210  of the moving arm. 
       FIG. 3  shows an example of a schematic of an image sensor  300  in accordance with aspects of the present disclosure. Image sensor  300  may include an array of pixels  305 , timing controller circuit  315  (which may include or operate in conjunction with one or more processors), and memory  320 . Each pixel  305  may include one or more photodiodes  310 . 
     The image sensor  300  may be a complementary metal-oxide-semiconductor (CMOS) image sensor  300  including an array of pixels  305 . The image sensor  300  may be configured as a High Dynamic Range (HDR) sensor. For example, an HDR sensor may be constructed of one or more split photodiode (split-PD) pixels  305  (e.g., a specialized pixel  305  with two or more photodiodes  310  that can be exposed and blanked independently of each other) together with fragmented exposures (e.g., a method in which medium exposures and shorter exposures (e.g., T M , T S  in  FIG. 1 ). 
     The exposure time of the split-PD pixels  305  may be divided into N parts and distributed evenly throughout the long exposure (e.g., T L  in  FIG. 1 ) may address some of the issues associated with LED flickering and ghosting. However, the use of one or more split-PD pixels  305  with a method of fragmented exposures may be performed by selecting one photodiode  310  in the split-PD pixel  305  for a continuous long exposure, and by fragmenting the medium exposures and the shorter exposures over the second photodiode  310  in the split-PD pixel  305 . By the use of two split pixels  305  selected for different exposure times, as described in more detail herein below, the LED modulation and the medium exposures and the shorter exposures may be synchronized For example the split-PD pixel  305  maybe selected for a continuous long exposure, and the split-pixel  305  PD may be selected for fragmenting the medium exposures T M  and the shorter exposures T S . 
     A timing controller circuit  315 , in response to an input, may generate control signals used to operate the image sensor  300 . For example, the timing controller circuit  315  may generate a control signal that controls operation of pixels  305 , so that they are controlled to provide exposure periods and blank periods of predetermined durations. It is during the exposure periods that the split-PD pixels  305  may sense the bursts of light output by the light source. Although the timing controller circuit  315  shows a single input, there may be an additional input, for example, a clock signal from an external source. 
     The pixel  305  may be a split photodiode pixel including at least two or more photodiodes  310  that are configured to be exposed to one or more bursts of light from a light source, where the at least two or more photodiodes  310  are configured to be exposed and blanked independently of each other. The pixel  305  may output to at least one of a memory or the timing controller circuit  315 . The pixels  305  may be exposed and blanked independently of each other together with fragmented exposures. 
     A photodiode  310  may perform a fragmented exposure operation in which a plurality of exposure periods of the second photodiode  310  are shorter in duration than the first exposure period of the first photodiode  310 , and the plurality of exposure periods of the second photodiode  310  include both continuous and fragmented exposure periods to capture the one or more bursts of light. The photodiode  310  may be one of an array of split photodiode pixels configured for a continuous long exposure, including a second photodiode  310  configured for fragmented exposures including medium exposures and shorter exposure. 
     In some examples, the two or more photodiodes  310  may include a first photodiode  310  that has a first exposure period that is longer in duration than a second exposure period of a second photodiode  310  of the two or more photodiodes  310 . 
     The timing controller circuit  315  may generate at least one control signal that controls an operation of the image sensor  300 , the image sensor  300  including at least one pixel  305  having a split photodiode pixel including at least two or more photodiodes  310  that are configured by the control signal from the timing controller circuit  315  to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes  310  are configured to be exposed and blanked independently of each other. The timing controller circuit  315  may also control a first exposure period of a first photodiode  310  of the two or more photodiodes  310  to be longer in duration than a second exposure period of a second photodiode  310  of the two or more photodiodes  310 . The timing controller circuit  315  may also output control signals to average an LED modulation and to synchronize the medium exposures and the shorter exposures. 
     In some examples, the timing controller circuit  315  is configured to control a plurality of exposures performed by the second photodiode  310  of the at least one pixel  305  to include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode  310  is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode  310 . 
     In some examples, the timing controller circuit  315  is configured to control the second photodiode  310  to perform a fragmented exposure operation in which a plurality of exposure periods of the second photodiode  310  are shorter in duration than the first exposure period of the first photodiode  310 , and the plurality of exposure periods of the second photodiode  310  include both continuous and fragmented exposure periods to capture the one or more bursts of light. 
     In some examples, the first exposure period of the first photodiode  310  comprises a continuous exposure, and the timing control circuit is configured to control the fragmented exposure operation performed by the second photodiode  310  that includes dividing the plurality of exposure periods into N parts that are distributed evenly over operation of the second photodiode  310 . In some examples, the fragmented exposure operation performed by the second photodiode  310  occurs during the first exposure period of the first photodiode  310 . In some examples, the timing controller circuit  315  receives an input signal to activate the image sensor  300  and capture bursts of light from a light source. In some examples, the light source comprises an LED light source. 
     In some examples, the plurality of exposure periods of the second photodiode  310  of the at least one pixel  305  in the image sensor  300  include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer in duration than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode  310  is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode  310 . 
     In some examples, the first exposure period of the first photodiode  310  comprises a continuous exposure, and controlling, by the timing control circuit, operation of the fragmented exposure periods performed by the second photodiode  310  that includes dividing the plurality of exposure periods into N parts, and distributing the N parts evenly over operation of the second photodiode  310 . In some examples, the fragmented exposure operation by the second photodiode  310  is performed during the first exposure period of the first photodiode  310 . 
       FIG. 4  shows an example of a temporal illustration of the operation of the split-PD pixel and the fragmented exposures in accordance with aspects of the present disclosure. The example shown includes frame  400 , longer exposure periods  405 , medium exposure periods  410 , shorter exposure periods  415 , light on periods  420 , and light off periods  425 . 
       FIG. 4  includes all exposures have a same duration but the accumulation time is long. It can be seen from  FIG. 4  that the sliced T M /T S  exposure includes the medium exposure T M  and the shorter exposure T S . Although the use of a split-PD and fragmented exposures may address the LED flicker and ghosting issues as described herein above, a motion blur may be introduced, and such motion blur may result in overall blurry images. 
     Frame  400 , longer exposure periods  405 , medium exposure periods  410 , shorter exposure periods  415 , light on periods  420 , and light off periods  425  may be an example of, or include aspects of, the corresponding elements described with reference to  FIGS. 1, 5, and 6 . 
       FIG. 5  shows an example of a temporal illustration of an embodiment of the inventive concept in accordance with aspects of the present disclosure. The example shown includes frame  500 , longer exposure periods  505 , medium exposure periods  510 , continuous medium exposure period  512 , shorter exposure periods  515 , continuous shorter exposure period  517 , light on periods  520 , and light off periods  525 . 
     In this embodiment, a split-PD with fragmented exposure includes adding two continuous shorter exposures T S  and medium exposures T M  that may reduce the motion blur caused by the fragmented exposure as discussed herein above. Moreover, this embodiment of the inventive concept does not sacrifice the performance with respect to LED flicker mitigation and ghosting prevention. 
     With reference to  FIG. 5 , in the frame  500  T frame  there is both a sliced exposure (T M /n T S /n and blank) and two continuous exposures T M-MB  and T S-SB . The use of the additional information, for example, one shorter exposure being fragmented and another shorter exposure being continuous, may facilitate identifying contradictions between the different exposures. For example, there is a contradiction in the instance where a flickering LED will be clearly visible in a fragmented short exposure, but may not be visible (or alternatively may saturate) the continuous short exposure. This contradiction (noise/saturation vs. acceptable value) may lead to a determination that the pixel is a flickering light source and adjust the merging accordingly by redistributing the merging weights. In addition, according to an embodiment of the inventive concept, the longer exposure T L  may not be sufficiently long to negate LED flickering in, for example a very brightly lit scene. In this embodiment of the inventive concept, additional exposures may also be fragmented to enhance capturing and averaging the LED. 
     Frame  500 , longer exposure periods  505 , medium exposure periods  510 , shorter exposure periods  515 , light on periods  520 , and light off periods  525  may be an example of, or include aspects of, the corresponding elements described with reference to  FIGS. 1, 4, and 6 . 
       FIG. 6  shows an example of a temporal illustration in which an additional fragmented exposure is performed to mitigate LED flicker in extremely illuminated conditions in accordance with aspects of the present disclosure. The example shown includes frame  600 , longer exposure periods  605 , fragmented medium exposure periods  610 , continuous medium exposure periods  615 , fragmented short exposure periods  620 , continuous short exposure periods  625 , light on periods  630 , and light off periods  635 . 
     With reference to  FIG. 5 , it can be seen, for example, that  FIG. 6  shows additional fragmented exposures. That is, according to an embodiment of the inventive concept, the split-pixel PD may includes five exposures: Long, Fragmented Medium, Continuous Medium, Fragmented Short, and Continuous Short. The split-pixel PD provides information regarding the scene to reduce motion blur and to ensure that all flickering LED information is captured in the images. According to embodiments of the inventive concept, the motion blur that may be introduced by LED flicker mitigation (LFM) is addressed by modifying an image sensor comprised of one or more split-pixel PDs that includes a medium and short continuous exposure to the sensor. 
     Frame  600 , longer exposure periods  605 , light on periods  630 , and light off periods  635  may be an example of, or include aspects of, the corresponding elements described with reference to  FIGS. 1, 4, and 5 . 
       FIG. 7  shows an example of a process for mitigating LED flicker in accordance with aspects of the present disclosure. In some examples, these operations may be performed by a processor executing a set of codes to control functional elements of an apparatus. Additionally or alternatively, the processes may be performed using special-purpose hardware. Generally, these operations may be performed according to the methods and processes described in accordance with aspects of the present disclosure. For example, the operations may be composed of various substeps, or may be performed in conjunction with other operations described herein. 
     At step  700 , a system may generating at least one control signal that controls an operation of the image sensor, the image sensor including at least one pixel having a split photodiode pixel including at least two or more photodiodes that are configured by the control signal from the timing controller circuit to be exposed to one or more bursts of light from a light source, the at least two or more photodiodes are configured to be exposed and blanked independently of each other. In some cases, the operations of this step may be performed by a timing controller circuit as described with reference to  FIG. 3 . 
     At step  705 , a system may control a first exposure period of a first photodiode of the two or more photodiodes to be longer in duration than a second exposure period of a second photodiode of the two or more photodiodes. In some cases, the operations of this step may be performed by a timing controller circuit as described with reference to  FIG. 3 . 
     At step  710 , a system may perform a fragmented exposure operation in which a plurality of exposure periods of the second photodiode are shorter in duration than the first exposure period of the first photodiode, and the plurality of exposure periods of the second photodiode include both continuous and fragmented exposure periods to capture the one or more bursts of light. In some cases, the operations of this step may be performed by a photodiode as described with reference to  FIG. 3 . 
     At step  715 , a system may output by the split-PD pixel to at least one of a memory or the timing controller circuit. In some cases, the operations of this step may be performed by a pixel as described with reference to  FIG. 3 . 
     In some cases, the plurality of exposure periods of the second photodiode of the at least one pixel in the image sensor include a fragmented medium exposure, a continuous medium exposure, a fragmented short exposure, and a continuous short exposure, wherein the fragmented medium exposure and the continuous medium exposure are longer in duration than the net exposure time of the fragmented short exposure and the continuous short exposure, respectively, and the first exposure period of the first photodiode is a continuous long exposure that is longer in duration than any of the plurality of exposure periods of the second photodiode. 
     The description and drawings described herein represent example configurations and do not represent all the implementations within the scope of the claims. For example, the operations and steps may be rearranged, combined or otherwise modified. Also, structures and devices may be represented in the form of block diagrams to represent the relationship between components and avoid obscuring the described concepts. Similar components or features may have the same name but may have different reference numbers corresponding to different figures. 
     Some modifications to the disclosure may be readily apparent to those skilled in the art, and the principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein. 
     The described methods may be implemented or performed by devices that include a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. A general-purpose processor may be a microprocessor, a conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a digital signal processor (DSP) and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). Thus, the functions described herein may be implemented in hardware or software and may be executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored in the form of instructions or code on a computer-readable medium. 
     Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of code or data. A non-transitory storage medium may be any available medium that can be accessed by a computer. For example, non-transitory computer-readable media can comprise RAM, ROM, electrically erasable programmable read only memory (EEPROM), compact disk (CD) ROM or other optical disk storage, magnetic disk storage, or any other non-transitory medium for carrying or storing data or code. 
     Also, connecting components may be properly termed computer-readable media. For example, if code or data is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology such as infrared, radio, or microwave signals, then the coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology are included in the definition of medium. Combinations of media are also included within the scope of computer-readable media. 
     In this disclosure and the following claims, the word “or” indicates an inclusive list such that, for example, the list of X, Y, or Z means X or Y or Z or XY or XZ or YZ or XYZ. Also the phrase “based on” is not used to represent a closed set of conditions. For example, a step that is described as “based on condition A” may be based on both condition A and condition B. In other words, the phrase “based on” shall be construed to mean “based at least in part on.”