Data back and # of frame to skip

Discussion related to "under the hood" OpenMV topics.
pierrekeunen
Posts: 4
Joined: Mon Feb 03, 2020 6:00 am

Data back and # of frame to skip

Postby pierrekeunen » Tue Mar 03, 2020 6:15 am

Hello everyone,

What I am actually doing is taking pictures from the camera at different exposure times.
I have 2 questions.
1. Is it possible to get those pictures back from the Micro SD card through the USB port on my computer? (To avoid removing the card every time and put it in my computer)
2. I see that every time I change the exposure time with set_auto_exposure it takes some time to change the settings. My objective is to be as fast as possible so skipping many frames isn't very effective for me.
How can I be as fast as possible while being sure my exposure time is correctly set before taking a new snapshot?

Thanks a lot in advance!
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kwagyeman
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Joined: Sun May 24, 2015 2:10 pm

Re: Data back and # of frame to skip

Postby kwagyeman » Tue Mar 03, 2020 11:00 am

Hi, here's the code that sets the exposure: https://github.com/openmv/openmv/blob/m ... 725.c#L389

It doesn't skip frames... so, what you are seeing is called the pipe delay of the camera. Typically, register settings take a few frames to actually work their way to being used versus applied immediately.

If you want to send files to the PC you can open the file up and send it over the UART using the VCP connection.
Nyamekye,
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kwagyeman
Posts: 3985
Joined: Sun May 24, 2015 2:10 pm

Re: Data back and # of frame to skip

Postby kwagyeman » Tue Mar 03, 2020 11:02 am

If you change exposures blindly they may get pipelined. I.e. if you change the exposure every frame you'll see the effect start changing every frame in the future delayed by N number of frames. OmniVision doesn't publish this info on how this works. If you want precise control us the global shutter camera which has the pipe delay in the data sheet.
Nyamekye,

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