SDK CV Algorithms

class Metavision::ActiveMarkerTrackerAlgorithm

A class that tracks an active marker in 2D.

An active marker is a rigid object composed of several blinking LEDs. It is tracked by tracking its LEDs based on the events they generate (i.e. EventSourceId), the latter of which form blobs in the sensor array. The blobs are not directly detected and tracked. Instead, events are associated to tracks using a radius criterion. A monitoring process is then regularly executed to:

  • re-assess this radius criterion (i.e. proportionally to the lowest distance between the tracks)

  • remove the tracks that are no longer tracked (i.e. based on an inactivity period, meaning with no update) The first time an event with a valid ID that doesn’t match any existing track is received, a new one is created.

Public Functions

ActiveMarkerTrackerAlgorithm(const Params &params, const std::set<std::uint32_t> &sources_to_track)

Constructor.

Parameters

  • params – The configuration parameters

  • sources_to_track – List of unique IDs of the LEDs that constitute the active marker to be tracked

template<typename InputIt, typename OutputIt>
void process_events(InputIt begin, InputIt end, OutputIt inserter)

Tracks the 2D position of the active marker’s LEDs from EventSourceId events.

Template Parameters

  • InputIt – Input event iterator type, works for iterators over containers of EventSourceId

  • OutputIt – Output iterator type, works for iterators over containers of EventActiveTrack

Parameters

  • begin – [in] Iterator pointing to the first event in the stream

  • end – [in] Iterator pointing to the past-the-end element in the stream

  • inserter – [out] Back inserter

void notify_elapsed_time(timestamp ts)

Notifies the tracker that time has elapsed without new events, which may trigger several calls to the internal monitoring process.

Parameters

ts – Current timestamp

struct Params

Parameters for configuring the ActiveMarkerTrackerAlgorithm.

Public Members

bool update_radius = true

Flag indicating whether to update the radius during the monitoring process.

Duration inactivity_period_us = 10000

Inactivity period above which a track is considered as lost.

float monitoring_frequency_hz = 30.f

Frequency (in camera time) at which the monitoring process is executed

float radius = 30.f

Influence radius used to associate events to tracks.

float distance_pct = 0.3f

Percentage on the lowest distance between two tracks used to update the radius criterion

float alpha_pos = 0.01f

Influence of a new associated event on the position update of a track.

template<typename Use64Bits = std::true_type>
class Metavision::ActivityNoiseFilterAlgorithm

Filter that accepts events if a similar event has happened during a certain time window in the past, in the neighborhood of its coordinates.

Public Functions

inline ActivityNoiseFilterAlgorithm(std::uint32_t width, std::uint32_t height, timestamp threshold)

Builds a new ActivityNoiseFilterAlgorithm object.

Parameters

  • width – Maximum X coordinate of the events in the stream

  • height – Maximum Y coordinate of the events in the stream

  • threshold – Length of the time window for activity filtering (in us)

~ActivityNoiseFilterAlgorithm() = default

Default destructor.

template<class InputIt, class OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the Activity Noise filter to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline timestamp get_threshold()

Returns the current threshold.

Returns

Threshold applied while filtering

inline void set_threshold(timestamp threshold)

Sets the threshold.

Parameters

threshold – threshold

inline bool operator()(const Event2d &event)

Checks if the event is filtered.

Returns

true if the event is filtered

class Metavision::AntiFlickerAlgorithm

Algorithm used to remove flickering events given a frequency interval.

Public Functions

AntiFlickerAlgorithm(int width, int height, const FrequencyEstimationConfig &config)

Builds a new AntiFlickerAlgorithm object.

Parameters

  • width – Sensor’s width

  • height – Sensor’s height

  • config – Frequency estimation’s configuration

~AntiFlickerAlgorithm() = default

Destructor.

bool set_min_freq(double min_freq)

Sets minimum frequency of the flickering interval.

Note

The value given has to be strictly inferior to maximum frequency

Parameters

min_freq – Minimum frequency of the flickering interval

Returns

false if value could not be set (invalid value)

bool set_max_freq(double max_freq)

Sets maximum frequency of the flickering interval.

Note

The value given has to be strictly superior to minimum frequency

Parameters

max_freq – Maximum frequency of the flickering interval

Returns

false if value could not be set (invalid value)

bool set_filter_length(unsigned int filter_length)

Sets filter’s length.

Parameters

filter_length – Number of values in the output median filter

Returns

false if value could not be set (invalid value)

void set_difference_threshold(double diff_thresh)

Sets the difference allowed between two periods to be considered the same.

Parameters

diff_thresh – Maximum difference allowed between two successive periods to be considered the same

template<class InputIt, class OutputIt>
OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Processes a buffer of events and outputs the non-flickering ones.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

class Metavision::DenseFlowFrameGeneratorAlgorithm

Algorithm used to generate visualization images of dense optical flow streams.

Public Types

enum class AccumulationPolicy

Policy for accumulating multiple flow events at a given pixel.

Values:

enumerator Average

Computes the average flow from the observations at the pixel.

enumerator PeakMagnitude

Keeps the highest magnitude flow amongst the observations at the pixel.

enumerator Last

Keeps the most recent flow amongst the observations at the pixel.

Public Functions

DenseFlowFrameGeneratorAlgorithm(int width, int height, float maximum_flow_magnitude, VisualizationMethod visualization_method = VisualizationMethod::Arrows, AccumulationPolicy accumulation_policy = AccumulationPolicy::Last, int resolution_subsampling = -1)

Constructor.

Parameters

  • width – Input stream width

  • height – Input stream height

  • maximum_flow_magnitude – Scale for highest flow magnitude in the visualization.

  • visualization_method – Method used to visualize flow field

  • accumulation_policy – Method used to accumulate multiple flow values at the same pixel.

  • resolution_subsampling – For Arrows representation, subsampling factor used to accumulate flow events. If negative, accumulation is done at resolution 1/8th. For DenseColorMap representation, this parameter is ignored and flow events are always accumulated in full resolution.

template<typename EventIt>
void process_events(EventIt it_begin, EventIt it_end)

Processes a buffer of flow events.

Note

Successive calls to process_events will accumulate data at each pixel until generate or reset is called.

Template Parameters

EventIt – Read-Only input event iterator type. Works for iterators over buffers of EventOpticalFlow or equivalent

Parameters

  • it_begin – Iterator to the first input event

  • it_end – Iterator to the past-the-end event

void generate(cv::Mat &frame, bool allocate = true)

Generates a flow visualization frame.

Note

In DenseColorMap mode, the frame will be reset to zero prior to being filled with the flow visualization. In Arrows mode, the flow visualization will be overlaid on top of the input frame.

Parameters

  • frame – Frame that will contain the flow visualization

  • allocate – Allocates the frame if true. Otherwise, the user must ensure the validity of the input frame. This is to be used when the data ptr must not change (external allocation, ROI over another cv::Mat, …).

Throws

invalid_argument – if the frame doesn’t have the expected type and geometry

void generate_legend_image(cv::Mat &legend_frame, int square_size = 0, bool allocate = true)

Generates a legend image for the flow visualization.

Parameters

  • legend_frame – Frame that will contain the flow visualization legend

  • square_size – Size of the generated image

  • allocate – Allocates the frame if true. Otherwise, the user must ensure the validity of the input frame. This is to be used when the data ptr must not change (external allocation, ROI over another cv::Mat, …)

Throws

invalid_argument – if the frame doesn’t have the expected type

void reset()

Resets the internal states.

template<typename Converter>
class Metavision::EventConverterAlgorithm

This algorithm applies the () operator of the Converter class to the input.

Public Functions

inline constexpr EventConverterAlgorithm(const Converter &converter = Converter())

Constructor

Parameters

converter – Instance of the Converter class

class Metavision::EventCounterAlgorithm

This class counts the number of events happening during a simulation step.

Public Functions

inline EventCounterAlgorithm(double threshold = 19)

Builds a new EventCounterAlgorithm object.

Parameters

threshold – Threshold in average rate for the analog_output overlay in Mev/S

inline EventCounterAlgorithm(const std::string &output_filename, timestamp step_time, timestamp scaling_time, bool enable_log = true, double threshold = 19., bool compute_variance = false)

Builds a new EventCounterAlgorithm object.

Parameters

  • output_filename – Name of the output file to be generated

  • step_time – Time interval (in us) used to compute the peak event rate

  • scaling_time – Time interval (in us) used to compute the average event rate

  • enable_log – true to save a log file

  • threshold – Threshold in average rate for the analog_output overlay in Mev/S

  • compute_variance – true to compute the variance

inline ~EventCounterAlgorithm()

Destructor.

inline void enable_log(bool state)

Enables or disables data logging.

Parameters

state – If true, the logging will start, otherwise it will stop

inline void set_log_destination(const std::string &csv_file_name)

Sets the output file.

inline void set_step_time_us(timestamp step_time_us)

Sets step time.

Parameters

step_time_us – Time interval (in us) used to compute the peak event rate during the step time (must be smaller than scaling time). Default is 1 ms.

inline void set_scaling_time_us(timestamp scaling_time_us)

Sets scaling time.

Parameters

scaling_time_us – Time interval (in us) used to compute the average event rate during the scaling time. Default is 1000 ms

inline void polarity_to_count(int polarity)

Counts only the events that have the input polarity.

All events are counted by default. Use -1 to disable the filter after setting a value If the event doesn’t have a polarity, the compilation will fail

Parameters

polarity – The polarity to count

inline void print_stats()

Prints statistics.

inline std::pair<double, double> get_average_rate()

Gets the average rate last computed.

Returns

End time (in seconds) of the last average rate that has been computed (first element of the pair) and the average rate (kEv per second) during this interval

inline std::pair<double, double> get_peak_rate()

Gets the peak rate last computed.

Returns

Time (in seconds) of the last peak rate that has been computed (first element of the pair) and the average peak rate (kEv per second)

inline uint64_t get_events_number()

Gets number of events.

Returns

Total number of events counted from the input producer since the beginning

inline uint64_t get_events_number_by_polarity()

Gets number of events of the polarity set by polarity_to_count.

Returns

Total number of events of the polarity set by polarity_to_count counted from the input producer since the beginning

inline size_t add_callback_on_scale(const std::function<void(double, double)> &cb)

Adds a function to be called every time an event rate has been computed.

Parameters

cb – Function that takes as input the timestamp (in seconds) of the last event the average event rate has been computed on and the average event rate (kEv per second)

Returns

Callback id

inline void remove_callback_on_scale(size_t cb_id)

Removes the function to call every time an event rate has been computed.

Parameters

cb_id – Callback id

template<typename InputIt>
inline std::enable_if_t<!std::is_base_of<Metavision::Event2d, typename Metavision::iterator_traits<InputIt>::value_type>::value> process(InputIt it, InputIt it_end, timestamp ts)

Processes a set of events using iterators.

Note

Two implementations are provided, the first one for events derived from Event2d, the other one for non Event2d-derived events

Parameters

  • it – Iterator to the first event

  • it_end – Iterator to the past-the-end event

  • ts – Timestamp of current timeslice

class Metavision::FrequencyAlgorithm

Algorithm used to estimate the flickering frequency (Hz) of the pixels of the sensor.

Public Functions

FrequencyAlgorithm(int width, int height, const FrequencyEstimationConfig &frequency_config)

Builds a new FrequencyAlgorithm object.

Parameters

  • width – Sensor’s width

  • height – Sensor’s height

  • frequency_config – Frequency estimation’s configuration

~FrequencyAlgorithm()

Destructor.

bool set_min_freq(double min_freq)

Sets minimum frequency to output.

Note

The value given has to be < maximum frequency

Parameters

min_freq – Minimum frequency to output

Returns

false if value could not be set (invalid value)

bool set_max_freq(double max_freq)

Sets maximum frequency to output.

Note

The value given has to be > minimum frequency

Parameters

max_freq – Maximum frequency to output

Returns

false if value could not be set (invalid value)

bool set_filter_length(unsigned int filter_length)

Sets filter filter length.

Parameters

filter_length – Number of values in the output median filter

Returns

false if value could not be set (invalid value)

void set_difference_threshold(period_precision diff_thresh)

Sets the difference allowed between two periods to be considered the same.

Parameters

diff_thresh – Maximum difference allowed between two successive periods to be considered the same

template<class InputIt, class OutputIt>
void process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Processes a buffer of events and output inserter for Event2dFrequency<float>

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of Event2dFrequency

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter for Event2dFrequency<float>

class Metavision::ModulatedLightDetectorAlgorithm

A class that detects modulated lights per pixel.

Modulated light sources encode and transmit their ID by using frequency modulation: symbols can be encoded using the time elapsed between two blinks. Every symbol duration is a multiple of a base period p:

  • p : logical ‘0’

  • 2p: logical ‘1’

  • 3p: start bit The size of a word (i.e. the number of bits used to encode the ID) is configurable and limited to 32 bits.

Public Functions

explicit ModulatedLightDetectorAlgorithm(const Params &params)

Constructs a ModulatedLightDetectorAlgorithm object with the specified parameters.

Parameters

params – The parameters for configuring the ModulatedLightDetectorAlgorithm

Throws

std::invalid_argument – if the resolution is not valid or if the size of a word is greater than 32

template<typename InputIt, typename OutputIt>
OutputIt process_events(InputIt begin_it, InputIt end_it, OutputIt output_it)

Tries to detect modulated light sources per pixel from events.

One EventSourceId is produced per input EventCD. The id field of an output event will be valid only if the corresponding input event allowed decoding a light ID.

Template Parameters

  • InputIt – Input event iterator type

  • OutputIt – Output iterator type, works for iterators over containers of EventSourceId

Parameters

  • begin_it – [in] Iterator pointing to the first event in the stream

  • end_it – [in] Iterator pointing to the past-the-end element in the stream

  • output_it – [out] Iterator to the first source id event

Returns

The iterator to the past-the-last source id event

struct Params

Parameters for configuring the ModulatedLightDetectorAlgorithm.

Public Members

std::uint16_t width = 0

EB field of view’s width in pixels.

std::uint16_t height = 0

EB field of view’s height in pixels.

std::uint8_t num_bits = 8

Size of a word.

std::uint32_t base_period_us = 200

Base period for encoding bits.

float tolerance = 0.1f

Tolerance used for blink measurement.

class Metavision::PeriodAlgorithm

Algorithm used to estimate the flickering period of the pixels of the sensor.

Public Types

using period_precision = float

Timestamp precision.

Public Functions

PeriodAlgorithm(int width, int height, const PeriodEstimationConfig &config)

Builds a new PeriodAlgorithm object.

Parameters

  • width – Sensor’s width

  • height – Sensor’s height

  • config – period estimation’s configuration

~PeriodAlgorithm()

Destructor.

bool set_min_period(double min_period)

Sets minimum period to output.

Note

The value min_period has to be smaller than the maximum period

Parameters

min_period – Minimum period (us) to output

Returns

false if value could not be set (invalid value)

bool set_max_period(double max_period)

Sets maximum period to output.

Note

The value max_period has to be larger than the minimum period

Parameters

max_period – Maximum period to output

Returns

false if value could not be set (invalid value)

bool set_filter_length(unsigned int filter_length)

Sets filter filter length.

Parameters

filter_length – Number of values in the output median filter

Returns

false if value could not be set (invalid value)

void set_difference_threshold(period_precision diff_thresh)

Sets the difference allowed between two periods to be considered the same.

Parameters

diff_thresh – Maximum difference allowed between two successive periods to be considered the same

template<class InputIt, class OutputIt>
void process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Processes a buffer of events and output inserter for Event2dPeriod<T>

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of Event2dPeriod

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter for Event2dPeriod<T>

class Metavision::PlaneFittingFlowAlgorithm

This class is an optimized implementation of the dense optical flow approach proposed in Benosman R., Clercq C., Lagorce X., Ieng S. H., & Bartolozzi C. (2013). Event-based visual flow. IEEE transactions on neural networks and learning systems, 25(2), 407-417.

See also

TripletMatchingFlowAlgorithm algorithm for a more efficient but more noise sensitive dense optical flow approach.

See also

SparseOpticalFlowAlgorithm algorithm for a flow algorithm based on sparse feature tracking, estimating the full scene motion, staged hence more efficient on high event-rate scenes, but also more complex to tune and dependent on the presence of trackable features in the scene.

Note

This dense optical flow approach estimates the flow along the edge’s normal, by fitting a plane locally in the time-surface. The plane fitting helps regularize the estimation, but estimated flow results are still relatively sensitive to noise. The algorithm is run for each input event, generating a dense stream of flow events, but making it relatively costly on high event-rate scenes.

Public Functions

inline PlaneFittingFlowAlgorithm(int width, int height, int radius = 3, float normalized_flow_magnitude = 100, float min_spatial_consistency_ratio = -1, float max_spatial_consistency_ratio = -1, timestamp fitting_error_tolerance = -1, float neighbor_sample_fitting_fraction = 0.3f)

Constructor.

Parameters

  • width – Sensor’s width

  • height – Sensor’s height

  • radius – Radius used to select timestamps in a time surface around a given location

  • normalized_flow_magnitude – Normalized magnitude of the optical flow. Pass a negative value or 0 to disable normalization.

  • min_spatial_consistency_ratio – Lower bound of the acceptable range for the spatial consistency ratio quality indicator. Pass a negative value to disable this test.

  • max_spatial_consistency_ratio – Upper bound of the acceptable range for the spatial consistency ratio quality indicator. Pass a negative value to disable this test.

  • fitting_error_tolerance – Tolerance used to accept visual flow estimates with low enough fitting error. Pass a negative value to disable this test.

  • neighbor_sample_fitting_fraction – Fraction used to determine how many timestamps from the timesurface neighborhood are used to fit the plane.

template<typename InputIt, typename OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the get flow function to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – [in] Iterator to first input event

  • it_end – [in] Iterator to the past-the-end event

  • inserter – [out] Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

class Metavision::ProximityFilterAlgorithm

Class filter that only propagates events close enough to a particular point in the sensor.

Public Functions

inline explicit ProximityFilterAlgorithm(const Eigen::Vector2f &center, float max_distance)

Constructor.

Parameters

  • center – Point with which the distance is computed

  • max_distance – Maximal distance to center allowed to keep an event

~ProximityFilterAlgorithm() = default

Default destructor.

template<class InputIt, class OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the Proximity filter to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline bool operator()(const Event2d &ev) const

Basic operator to check if an event is accepted.

Parameters

ev – Event2D to be tested

inline void set_center(const Eigen::Vector2f &center)

Sets the center point of the filter.

Parameters

center – Point to be used in the filtering process

inline void set_distance(float max_distance)

Sets the maximal allowed distance of the filter.

Parameters

max_distance – Maximal distance to be used in the filtering process

inline Eigen::Vector2f center() const

Returns the center point used to filter the events.

Returns

Current reference point used in the filtering process

inline float max_distance() const

Returns the maximal distance used to filter the events.

Returns

Current maximal distance used in the filtering process

class Metavision::RoiMaskAlgorithm

Class that only propagates events which are contained in a certain region of interest.

The Region Of Interest (ROI) is defined by a mask (cv::Mat). An event is validated if the mask at the event position stores a positive number.

Alternatively, the user can enable different rectangular regions defined by the upper left corner and the bottom right corner that propagates any event inside them.

Public Functions

inline explicit RoiMaskAlgorithm(const cv::Mat &pixel_mask)

Builds a new RoiMaskAlgorithm object which propagates events in the given window.

Parameters

pixel_mask – Mask of pixels that should be retained (pixel <= 0 is filtered)

template<class InputIt, class OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the ROI Mask filter to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline void enable_rectangle(int x0, int y0, int x1, int y1)

Enables a rectangular region defined by the upper left corner and the bottom right corner that propagates any event inside them.

Parameters

  • x0 – X coordinate of the upper left corner

  • y0 – Y coordinate of the upper left corner

  • x1 – X coordinate of the lower right corner

  • y1 – Y coordinate of the lower right corner

inline int max_height() const

Returns the maximum number of pixels (height) of the mask.

Returns

Maximum height of the mask

inline int max_width() const

Returns the maximum number of pixels (width) of the mask.

Returns

Maximum width of the mask

inline const cv::Mat &pixel_mask() const

Returns the pixel mask of the filter.

Returns

cv::Mat containing the pixel mask of the filter

inline void set_pixel_mask(const cv::Mat &mask)

Sets the pixel mask of the filter.

Parameters

mask – Pixel mask to be used while filtering

template<typename T>
inline bool operator()(const T &ev) const

Basic operator to check if an element is filtered.

Parameters

ev – Event to check

inline bool operator()(int x, int y) const

Basic operator to check if a position is filtered.

Parameters

  • x – X coordinate or the position to check

  • y – Y coordinate or the position to check

class Metavision::RotateEventsAlgorithm

class that allows to rotate an event stream.

Note

We assume the rotation to happen with respect to the center of the image

Public Functions

inline explicit RotateEventsAlgorithm(std::int16_t width_minus_one, std::int16_t height_minus_one, float rotation)

Builds a new RotateEventsAlgorithm object with the given width and height.

Parameters

  • width_minus_one – Maximum X coordinate of the events (width-1)

  • height_minus_one – Maximum Y coordinate of the events (height-1)

  • rotation – Value in radians used for the rotation

~RotateEventsAlgorithm() = default

Default destructor.

template<class InputIt, class OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the rotate event filter to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline std::int16_t width_minus_one() const

Returns the maximum X coordinate of the events.

Returns

Maximum X coordinate of the events

inline void set_width_minus_one(std::int16_t width_minus_one)

Sets the maximum X coordinate of the events.

Parameters

width_minus_one – Maximum X coordinate of the events

inline std::int16_t height_minus_one() const

Returns the maximum Y coordinate of the events.

Returns

Maximum Y coordinate of the events

inline void set_height_minus_one(std::int16_t height_minus_one)

Sets the maximum Y coordinate of the events.

Parameters

height_minus_one – Maximum Y coordinate of the events

inline void set_rotation(const float new_angle)

Sets the new rotation angle.

Parameters

new_angle – New angle in rad

class Metavision::SparseFlowFrameGeneratorAlgorithm

Public Functions

template<typename InputIt>
inline void add_flow_for_frame_update(InputIt first, InputIt last)

Stores one motion arrow per centroid (several optical flow events may have the same centroid) in the motion arrow map to be displayed later using the update_frame_with_flow method.

inline void update_frame_with_flow(cv::Mat &display_mat)

Updates the input frame with the centroids’ motion stored in the history.

Clears the history afterwards

class Metavision::SparseOpticalFlowAlgorithm

Algorithm used to compute the optical flow of objects.

See also

PlaneFittingFlowAlgorithm and TripletMatchingFlowAlgorithm algorithms for simpler methods, with the drawbacks of estimating only the component of the flow along the edge normal and with higher cost on high event-rate scenes.

Note

This sparse optical flow approach tracks small edge-like features and estimates the full motion for these features. This algorithm runs flow estimation only on tracked features, which helps remaining efficient even on high event-rate scenes. However, it requires the presence of trackable features in the scene, and the tuning of the feature detection and tracking stage can be relatively complex.

Public Functions

SparseOpticalFlowAlgorithm(int width, int height, const SparseOpticalFlowConfig &config)

Constructor.

Parameters

  • width – Sensor’s width

  • height – Sensor’s height

  • config – Sparse optical flow’s configuration

~SparseOpticalFlowAlgorithm()

Destructor.

template<typename InputIt, typename OutputIt>
OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the optical flow algorithm to the given input buffer storing the result in the output buffer.

Note

the available implementations provided are:

  • InputIt = std::vector<Event2d>::iterator, OutputIt = std::back_insert_iterator<std::vector<EventOpticalFlow>>

  • InputIt = std::vector<Event2d>::const_iterator, OutputIt = std::back_insert_iterator<std::vector<EventOpticalFlow>>

  • InputIt = std::vector<Event2d>::iterator, OutputIt = std::vector<EventOpticalFlow>::iterator

  • InputIt = std::vector<Event2d>::const_iterator, OutputIt = std::vector<EventOpticalFlow>::iterator

  • InputIt = const Event2d *, OutputIt = EventOpticalFlow *

Template Parameters

  • InputIt – Read-Only input event iterator type

  • OutputIt – Read-Write output event iterator type

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

template<class itype>
class Metavision::SpatioTemporalContrastAlgorithmT

The SpatioTemporalContrast Filter is a noise filter using the exponential response of a pixel to a change of light to filter out wrong detections and trails.

For an event to be forwarded, it needs to be preceded by another one in a given time window, this ensures that the spatio temporal contrast detection is strong enough. It is also possible to then cut all the following events up to a change of polarity in the stream for that particular pixel (strong trail removal). Note that this will remove signal if 2 following edges of the same polarity are detected (which should not happen that frequently).

Note

The timestamp may be stored in different types 64 bits, 32 bits or 16 bits. The behavior may vary from one size to the other since the number of significant bits may change. Before using the version with less than 32 bits check that the behavior is still valid for the usage.

Public Functions

inline SpatioTemporalContrastAlgorithmT(int width, int height, timestamp threshold, bool cut_trail = true)

Builds a new SpatioTemporalContrast object.

Parameters

  • width – Maximum X coordinate of the events in the stream

  • height – Maximum Y coordinate of the events in the stream

  • threshold – Length of the time window for filtering (in us)

  • cut_trail – If true, after an event goes through, it removes all events until change of polarity

template<typename InputIt, typename OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Processes a buffer of events and outputs filtered events.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline timestamp get_threshold()

Returns the threshold for STC filtering.

Returns

Threshold applied while STC filtering (in us)

inline void set_threshold(timestamp threshold)

Sets the threshold for STC filtering.

Parameters

threshold – Length of the time window for STC filtering (in us)

inline bool get_cut_trail()

Returns the cut_trail parameter for STC filtering.

Returns

The cut_trail parameter for STC filtering used for STC filtering

inline void set_cut_trail(bool v)

Sets the cut_trail parameter for STC filtering.

Parameters

v – If true, after an event goes through, it removes all events until change of polarity

template<typename timestamp_type>
class Metavision::TimeGradientFlowAlgorithmT

This class is a local and dense implementation of Optical Flow from events.

Note

This approach is dense in the sense that it processes events at the sensor resolution and produces OpticalFlowEvents potentially on the whole sensor matrix. It computes the optical flow along the edge’s normal by analyzing the recent timestamps at only the left, right, top and down K-pixel far neighbors (i.e. not the whole neighborhood). Thus, the estimated flow results are still quite sensitive to noise. The algorithm is run for each input event, generating a dense stream of flow events, but making it relatively costly on high event-rate scenes. The bit size of the timestamp representation can be reduced to accelerate the processing.

Template Parameters

timestamp_type – Type of the timestamp used in to compute the optical flow. Typically Metavision::timestamp. Can be used with lighter type (like std::uint32_t) to lower processing time when critical.

Public Functions

TimeGradientFlowAlgorithmT(int input_width, int input_height, const TimeGradientFlowAlgorithmConfig &config)

Constructor.

Parameters

  • input_width – Maximum width of input events

  • input_height – Maximum height of input events

  • config – Configuration for the algorithm

template<typename InputIt, typename OutputIt>
OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Processes each input event to estimate the optical flow from them into the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventOpticalFlow or equivalent

Parameters

  • it_begin – [in] Iterator to first input event

  • it_end – [in] Iterator to the past-the-end event

  • inserter – [out] Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

template<typename TTimestampType>
class Metavision::TrailFilterAlgorithmT

Filter that accepts an event either if the last event at the same coordinates was of different polarity, or if it happened at least a given amount of time after the last event.

Public Functions

inline TrailFilterAlgorithmT(uint16_t width, uint16_t height, TTimestampType threshold)

Builds a new TrailFilterAlgorithmT object.

Parameters

  • width – Maximum X coordinate of the events in the stream

  • height – Maximum Y coordinate of the events in the stream

  • threshold – Length of the time window for activity filtering (in us)

~TrailFilterAlgorithmT() = default

Default destructor.

template<class InputIt, class OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the Trail filter to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of Event2d or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of Event2d or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline TTimestampType get_threshold() const

Returns the current threshold.

Returns

Threshold applied while filtering

inline void set_threshold(TTimestampType threshold)

Set the current threshold.

Parameters

threshold – Current threshold

inline bool operator()(const Event2d &event)

Check if the event is filtered.

Returns

true if the event is filtered

class Metavision::TransposeEventsAlgorithm

Class that switches X and Y coordinates of an event stream. This filter changes the dimensions of the corresponding frame (width and height are switched)

Public Functions

template<class InputIt, class OutputIt>
inline OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the Transpose filter to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type. Works for iterators over buffers of EventCD or equivalent

  • OutputIt – Read-Write output event iterator type. Works for iterators over containers of EventCD or equivalent

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output

inline void operator()(Event2d &ev) const

Applies the Transpose filter to the given input buffer storing the result in the output buffer.

Parameters

ev – Event2d to be updated

class Metavision::TripletMatchingFlowAlgorithm

This class implements the dense optical flow approach proposed in Shiba S., Aoki Y., & Gallego G. (2022). “Fast Event-Based Optical Flow Estimation by Triplet Matching”. IEEE Signal Processing Letters, 29, 2712-2716.

See also

PlaneFittingFlowAlgorithm algorithm for slightly more accurate but more expensive dense optical flow approach.

See also

SparseOpticalFlowAlgorithm algorithm for a flow algorithm based on sparse feature tracking, estimating the full scene motion, staged hence more efficient on high event-rate scenes, but also more complex to tune and dependent on the presence of trackable features in the scene.

Note

This dense optical flow approach estimates the flow along the edge’s normal, by locally searching for aligned events triplets. The flow is estimated by averaging all aligned event triplets found, which helps regularize the estimates, but results are still relatively sensitive to noise. The algorithm is run for each input event, generating a dense stream of flow events, but making it relatively costly on high event-rate scenes.

Public Functions

TripletMatchingFlowAlgorithm(int width, int height, const Config &config)

Constructor.

Parameters
~TripletMatchingFlowAlgorithm()

Destructor.

template<typename InputIt, typename OutputIt>
OutputIt process_events(InputIt it_begin, InputIt it_end, OutputIt inserter)

Applies the optical flow algorithm to the given input buffer storing the result in the output buffer.

Template Parameters

  • InputIt – Read-Only input event iterator type on EventCD objects

  • OutputIt – Read-Write output event iterator type on EventOpticalFlow objects

Parameters

  • it_begin – Iterator to first input event

  • it_end – Iterator to the past-the-end event

  • inserter – Output iterator or back inserter

Returns

Iterator pointing to the past-the-end event added in the output