Anti flicker filter for dToF sensor
Method, having detecting from a first histogram signal delivered by a sensor device, successive sets of targets at respective successive instants, determining for a current set of current detected targets, a current histogram output, the current histogram output having for each current detected target of the current set, a current group of parameters stored in a memory including a confidence indicator, performing a matching operation between the current set of detected targets and previous sets of detected targets stored in the memory, and performing a filtering operation of at least one parameter of the current group of parameters of at least some of the current detected targets of the current set, on the basis of the result of the matching operation, the filtering operation being weighted on the basis of at least the confidence indicators of current and previous sets of detected targets.
1 . A method, comprising:
identifying successive sets of targets at respective successive instants from a first histogram signal delivered by a sensor device, the identifying of the successive set of targets comprising identifying pulses in the first histogram signal that exceed a detection threshold, wherein the sensor device comprises a time-of-flight (ToF) sensor, the first histogram signal representing photon event detection counts for a number of time bins;
determining a histogram output for a current set of the successive sets of targets, the histogram output having a group of parameters stored in memory for each current set, each group of parameters having a confidence indicator, wherein a group of parameters for the current set includes a rate parameter, an ambient rate parameter, and a distance parameter;
performing a matching operation between the current set of the successive sets of targets and previous sets of the successive sets of targets stored in the memory;
performing a filtering operation of at least one parameter of the group of parameters of the current set based on results of the matching operation, the filtering operation weighted based on at least confidence indicators of the current set of targets and the previous sets of the successive sets of targets; and
generating a stabilized target detection output with reduced temporal flicker effects from filtered parameters.
2 . The method of claim 1 , wherein the confidence indicator of a current set is based on a target z-score in the first histogram signal.
3 . The method of claim 1 , wherein the matching operation comprises using an affinity criterion having a condition based on the rate parameter, the distance parameter, or the confidence indicator.
4 . The method of claim 3 , wherein the affinity criterion includes an affinity-based distance matrix.
5 . The method of claim 1 , wherein the current set of the successive targets matches a previous set of the successive targets stored in the memory at the end of the matching operation.
6 . The method of claim 1 , wherein the current set of the successive targets does not match a previous set of the successive targets stored in the memory at the end of the matching operation.
7 . The method of claim 6 , wherein the current set of the successive targets is added to the memory based on the availability of empty slots in memory.
8 . The method of claim 1 , wherein the method further comprises performing a selective memory replacement based on confidence indicators for storing the current set of the successive targets.
9 . The method of claim 1 , wherein a previous set of the successive targets in the memory is not matched in the current set of successive targets and, based thereon, a virtual target is added to the input of the filtering operation with a new confidence indicator.
10 . The method of claim 9 , wherein the new confidence indicator is very low in response to high confidence in its corresponding previous target.
11 . The method of claim 9 , wherein the new confidence indicator is close to a confidence indicator of the previous set of the successive targets in response to the confidence indicator of the previous set of the successive targets is low.
12 . The method of claim 1 , further comprising a double weighted filtering operation based on target parameters and confidence indicator.
13 . The method of claim 1 , wherein the sensor device includes a direct time-of-flight (ToF) device.
14 . A system, comprising:
a sensor device configured to transmit a first histogram signal to identify successive sets of targets at respective successive instants, the identifying of the successive set of targets comprises identifying pulses in the first histogram signal that exceed a detection threshold, wherein the sensor device comprises a time-of-flight (ToF) sensor, the first histogram signal representing photon event detection counts for a number of time bins;
a first processor configured to determine a histogram output for a current set of the successive sets of targets, the histogram output having a group of parameters stored in memory for each current set, each group of parameters having a confidence indicator; and
a second processor configured to:
perform a matching operation between the current set of the successive sets of targets and previous sets of the successive sets of targets stored in the memory, wherein a group of parameters for the current set includes a rate parameter, an ambient rate parameter, and a distance parameter,
perform a filtering operation of at least one parameter of the group of parameters of the current set based on results of the matching operation, the filtering operation weighted based on at least confidence indicators of the current set of targets and the previous sets of the successive sets of targets, and
generate a stabilized target detection output with reduced temporal flicker effects from filtered parameters.
15 . The system of claim 14 , wherein the confidence indicator of a current set is based on a target z-score in the first histogram signal.
16 . The system of claim 14 , wherein the matching operation comprises using an affinity criterion having a condition based on the rate parameter, the distance parameter, or the confidence indicator.
17 . The system of claim 16 , wherein the affinity criterion includes an affinity-based distance matrix.
18 . The system of claim 14 , wherein the current set of the successive targets matches a previous set of the successive targets stored in the memory at the end of the matching operation.
19 . The system of claim 14 , wherein the current set of the successive targets does not match a previous set of the successive targets stored in the memory at the end of the matching operation.
20 . The system of claim 19 , wherein the current set of the successive targets is added to the memory based on the availability of empty slots in memory.
21 . The system of claim 14 , wherein the second processor is further configured to perform a selective memory replacement based on confidence indicators for storing the current set of the successive targets.
22 . The system of claim 14 , wherein a previous set of the successive targets in the memory is not matched in the current set of successive targets and, based thereon, a virtual target is added to the input of the filtering operation with a new confidence indicator.
23 . The system of claim 22 , wherein the new confidence indicator is very low in response to high confidence on its corresponding previous target.
24 . The system of claim 22 , wherein the new confidence indicator is close to a confidence indicator of the previous set of the successive targets in response to the confidence indicator of the previous set of the successive targets is low.
25 . The system of claim 14 , wherein the second processor is further configured to perform a double weighted filtering operation based on target parameters and confidence indicator.
26 . The system of claim 14 , wherein the sensor device includes a direct time-of-flight (ToF) device.
27 . The system of claim 14 , wherein the first processor and the second processor are implemented as firmware.
28 . The system of claim 14 , wherein the first processor includes a first circuit configured to determine the confidence indicators and a second circuit configured to determine the other parameters, the first circuit and the second processor being implemented as software and the second circuit being implemented as firmware.
29 . A device, comprising:
a sensor device configured to transmit a first histogram signal to identify successive sets of targets at respective successive instants, the identifying of the successive set of targets comprising identifying pulses in the first histogram signal that exceed a detection threshold, wherein the sensor device comprises a time-of-flight (ToF) sensor, the first histogram signal representing photon event detection counts for a number of time bins;
a non-transitory memory storage comprising instructions; and
a first processor in communication with the non-transitory memory storage and the sensor device, wherein the instructions, when executed by the first processor, cause the first processor to determine a histogram output for a current set of the successive sets of targets, the histogram output having a group of parameters stored in memory for each current set, each group of parameters having a confidence indicator, wherein a group of parameters for the current set includes a rate parameter, an ambient rate parameter, and a distance parameter; and
a second processor in communication with the first processor, the non-transitory memory storage, and the sensor device, wherein the instructions, when executed by the second processor, cause the second processor to:
perform a matching operation between the current set of the successive sets of targets and previous sets of the successive sets of targets stored in the memory,
perform a filtering operation of at least one parameter of the group of parameters of the current set based on results of the matching operation, the filtering operation weighted based on at least confidence indicators of the current set of targets and the previous sets of the successive sets of targets, and
generate a stabilized target detection output with reduced temporal flicker effects from filtered parameters.
30 . The device of claim 29 , wherein the matching operation comprises using an affinity criterion having a condition based on the rate parameter, the distance parameter, or the confidence indicator.
31 . The device of claim 30 , wherein the affinity criterion includes an affinity-based distance matrix.