Minimum skip_frames() time to ensure settings take effect?

OpenMV Products
1

Hi,

most examples include the following line:

sensor.skip_frames(time = 2000) # Let new settings take affect.

Depending on the application, especially when waking up from deep sleep, 2000 ms is a long time.

What would be the minimum setting that still works in most cases?

And how is “works” defined, image quality?

Kind regards,
Thomas

2

You can find out the exact time for register updates to take effect in frames/ms or the numbers of frames to skip after wakeup from low-power/standby etc… from the sensors datasheets. This time is just a number large enough for most sensors.

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3

Thanks! I think the OpenMV Cam H7 Plus uses OV5640, i.e.

Searching for “ms” I find

  • “power up sequence” timing, below 30 ms, p.29
  • “settling time for register setting <300 ms” p.168

Not sure which one, but both better than 2000 ms :slight_smile:

4

You can use 0. We have a 300ms wait in the sensor driver to prevent corrupted image outputs. After that it’s just the auto exposure algorithm adjusting the image brightness.

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5

300ms wait in the sensor driver

This one, right? https://github.com/openmv/openmv/blob/master/src/omv/sensors/ov5640.c#L692

After that it’s just the auto exposure algorithm

I assume skipping this would change the image quality?

Or is auto exposure just a “filter” that could be applied later on?

6

Auto exposure changes the image brightness/contrast. You don’t need to wait for it. However, the 300ms is required in the driver as the camera will output very corrupted frames on resolution change.

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