Contrast threshold of Genx320 camera

OpenMV Boards
1

Hi, thanks for your nice products. I am using Genx320 event camera with RT1062 board. I want to know if it is possible to change the contrast threshold of the camera in somewhere?

2

Yes, you just do sensor.set_contrast() the default is 16 but increase it to increase the contrast.

3

Hi, to change the contrast sensitivity of the sensor’s pixels you need to set the biases bias_diff_on and bias_diff_off via IOCTL settings.

Something like this
sensor.ioctl(sensor.IOCTL_GENX320_SET_BIASES, sensor.GENX320_BIAS_DIFF_ON, value)

4

Thanks for your reply, I want to know does this really changes the sensitivity of the camera pixels instead of visualization. I saw some featrures about the Genx320 camera like the following, should the ‘value’ of sensor.ioctl be a percentage like 25%?

KEY FEATURES

Resolution (px) 320×320
Ultra-low power mode (down to 36μW)
Optical format: 1/5”
Pixel latency @1k lux (μs) <150
Dynamic Range (dB) >140
Nominal contrast threshold (%) 25
Pixel size (μm) 6.3 x 6.3
Embedded features: Anti-flicker filtering (AFK) + Event-rate Controller (ERC) + Spatio-temporal Contrast filter (STC)

5

Hi, you just pass a numeric value for these. Prophesee created some default ones for different situations: sensor — camera sensor — MicroPython 1.24 documentation

If you want more information about these please contact Prophesee and request a full datasheet for the sensor.

Default values:

6

Hi,
Indeed usually we talk about contrast sensitivity using a Weber contrast definition in %.
The default values of bias_diff_on and _off should correspond to about 25% Weber contrast between a moving object and its background. However the precise value depends on few other factors.

However, here when setting biases we use a different scale. The default values of Bias_diff_on is 25 and bias_diff_off is 28.
If you need to make pixels more sensitive to contrast, then decrease the value (set it smaller than 25).
If you need to make pixels less sensitive, then increase the value (set is larger than 25).

Please note that ON events are generated when the contrast increases and OFF events are generated when the contrast decreases. They are not symmetric and can be set independently based on your needs.

More information is here Biases — Metavision SDK Docs 5.1.1 documentation