Biases (Sensor Settings)

Prophesee’s sensors provide a set of adjustable settings allowing to tune the sensor performance for different applications requirements and conditions (higher speed, lower background activity, higher contrast sensitivity, etc.). These sensor settings are called biases.

Each sensor generation has its own default biases values and supports its own range of biases values:

  • In Gen3, all the biases are expressed in mV.

  • In Gen4, most of biases are expressed in IDAC, and the conversion from IDAC to mV is not linear.

There is also some difference in biases tuning between sensor generations.

Available Biases and Their Tuning

Prophesee’s sensors have the following biases:

  • Photoreceptor bandwidth (bias_pr) controls the front-end part of the pixel, the photoreceptor bandwidth. High “bias_pr” value leads to small bias currents in the amplifier, hence limiting the bandwidth of the photoreceptor. We recommend not changing this bias, unless very specific conditions. Note that since Gen41 sensor generation, this bias is not visible anymore.

  • Buffer bandwidth (bias_fo) controls the pixel low-pass cut-off frequency (sets the bandwidth of the post-photoreceptor source follower). It is useful to control noise events, i.e. background activity:

    • In Gen3, “bias_fo” is a voltage, in mV. Decreasing “bias_fo” value will increase the bandwidth (make the sensor faster) and also increase the background noise. Increasing “bias_fo” value will decrease both speed and noise

    • In Gen4, “bias_fo” is Idac value. Increasing “bias_fo” value will increase the bandwidth (make the sensor faster) and also increase the background noise. Decreasing “bias_fo” value will decrease both speed and noise

  • Deadtime (bias_refr) sets the “refractory period” during which the Change Detector is switched off after generating an event. This parameter controls the sampling rate of the pixels and hence the output data rate of the sensor.

  • Contrast sensitivity biases (bias_diff, bias_diff_on, bias_diff_off) control the light sensitivity of the sensor, so that the sensor’s pixels are triggered when there is a required difference of illumination (i.e. contrast). The contrast sensitivity is expressed as the difference between “bias_diff_on” and “bias_diff” values (for positive light changes) and “bias_diff” and “bias_diff_off” values (for negative light changes). “bias_diff” stands for the threshold reference value and should not be modified. To adjust the contrast sensitivity:

    • approach “bias_diff_on” value to “bias_diff” (decrease the difference between them) to increase the sensitivity to positive light changes

    • approach “bias_diff_off” values to “bias_diff” (decrease the difference between them) to increase the sensitivity to negative light changes

  • High-Pass Filter (bias_hpf) controls the strength of a High-Pass Filter that removes low frequency noise (spontaneous background activity):

    • In Gen3, With low “bias_hpf” values, high frequencies are filtered out, but if the value is too low, the quality of the signal can be impacted.

    • In Gen4, with high “bias_hpf” values, low frequencies are filtered out, but if the value is too high, the quality of the signal can be impacted.

Note

When setting biases outside of the supported range, the biases values are rounded to the supported range.

To get more information on tuning Gen3 biases, consult the Application Note in the Knowledge Center (accessible for Professional users and Prophesee Camera customers).

To get more information on tuning Gen4 biases, contact us to receive the sensor datasheet.

BIAS file

We store the biases values in files with a .bias extension. These BIAS files can be used in most of applications and samples in Metavision SDK.

The format of the BIAS files is the following:

  • the file is a text file where each line configures a specific bias

  • each line is made of bias_value and bias_name separated by percentage sign (%).

For example:

80   % bias_diff
52   % bias_diff_off
115  % bias_diff_on
74   % bias_fo_p
0    % bias_hpf
105  % bias_pr
68   % bias_refr

Several BIAS files are deployed within Prophesee’s software. For example, after installing Metavision SDK, several BIAS files can be found in <install-prefix>/share/metavision/hal/resources/biases/. Those BIAS files store default biases settings for every sensor generation.

Please, note that in addition to the main biases described in this section, the pre-installed BIAS files could contain other biases which should not be modified.

To adjust biases values, you can have a look to the default biases files, create your own file in a similar manner, and use it in Metavision SDK.