Note

If you acquired a sensor or an EVK from Prophesee, you can find datasheets and user manuals in our Knowledge Center once you will have requested an account. In this page, we give complementary information about sensor’s ESP.

Event Signal Processing

Some of the Prophesee’s sensors provide an Event Signal Processing (ESP) block that provide some event filtering features:

Anti-Flicker (AFK) that removes flicker (often considered as noise)

Event trail filter (STC and Trail) that removes redundant events

Event Rate Control (ERC) that adjusts the events spatially and temporally to maintain the event rate below the maximum processing capacity

Anti-Flicker (AFK)

The anti-flicker function detects and cancels flicker events in 4x4 divided pixel regions on Gen4.1 and IMX636 sensors. It is a countermeasure for events generated due to light source with flicker such as fluorescent light. The flicker to be canceled can be set in the range of 2 ms to 20 ms period (50 Hz to 500 Hz).

In Metavision Studio, AFK can be configured (if available on your camera):

The AFK can also be enabled using HAL and SDK Driver API:

HAL C++ API: Metavision::I_AntiFlickerModule facility

HAL Python API: metavision_hal.I_AntiFlickerModule

SDK Driver C++ API: Metavision::AntiFlickerModule class

Note that Metavision SDK CV module also provides a pure software algorithm that is mostly equivalent to this hardware filter:

C++ API: Metavision::AntiFlickerAlgorithm demonstrated in Data Rate C++ application

Python API: metavision_sdk_cv.AntiFlickerAlgorithm demonstrated in Data Rate Python sample

Event Trail Filter (STC/Trail)

Gen4.1 and IMX636 sensors have 2 filters to cancel redundant information. Those filters consider successive events of the same polarity generated in a short time as burst, and will remove some of the events depending on the filter:

Trail retains the first event of a burst after a polarity transition and cancels events of the same polarity that are generated within the Trail threshold period.

Spatio-Temporal-Contrast (STC) retains the second event of a burst. Hence, STC filters out isolated events.

Burst event filtering drastically reduces the event rate but it also removes texture information. The time range supported by both filters for treatment as a burst event is 1 ms to 100 ms.

In Metavision Studio, STC and Trails can be configured (if available on your camera):

The Event Trail filter can also be enabled using HAL and SDK Driver API:

HAL C++ API: Metavision::I_EventTrailFilterModule facility

HAL Python API: metavision_hal.I_EventTrailFilterModule

SDK Driver C++ API: Metavision::EventTrailFilterModule class

Note that Metavision SDK API provides algorithms that are mostly equivalent to this hardware filter:

C++ API: Metavision::TrailFilterAlgorithm and Metavision::SpatioTemporalContrastAlgorithm demonstrated in Noise Filtering C++ sample

Python API: metavision_sdk_cv.TrailFilterAlgorithm and metavision_sdk_cv.SpatioTemporalContrastAlgorithm demonstrated in Noise Filtering Python sample

Event Rate Controller (ERC)

The ERC performs adjustment by spatially and temporally dropping events to output at the target event rate on Gen4.0, Gen4.1 and IMX636 sensors. This filter is located in the final stage of the ESP data processing circuit in order to reduce the event rate after AFK and STC/Trail filtering. It is useful to avoid flooding the computing unit with peaks of events, but keep in mind that signal quality will be degraded when filtering is triggered.

In Metavision Studio, ERC can be configured (if available on your camera):

The ERC can also be enabled using HAL and SDK Driver API:

HAL C++ API: Metavision::I_ErcModule facility

HAL Python API: metavision_hal.I_ErcModule

SDK Driver C++ API: Metavision::ErcModule class