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What triggers long exposure 15fps mode for color? RRS feed

  • Question

  • Hi,

    As most of us are aware the color stream automatically switches to 15fps long exposure mode when it detects low light situations.
    No this is not a thread to complain about the sensitivity of it (although some control would be very welcome), but I have a question:


    What exactly triggers this mode?

    Does it measure an average brightness in the color channel?
    Or just the darkest pixel?
    Am I correct in assuming it's purely based on the color and the IR is not referenced at all for this?


    I am working with HDFace and figuring out how I can best ensure 30fps mode by proper lighting.
    Since it references color only for detecting blinks (according to the docs) HDFace tracking is really sensitive, and very negatively impacted, when the color switches to 15fps mode. Especially since it internally always uses synchronized frames so IR then also switches to 15fps.


    Greets,

    Brekel

    Wednesday, December 17, 2014 12:15 PM
    Moderator

All replies

  • From my experience my guess would be that autoexposure is based off of the darkest pixel. When trying to light an interior scene there have been times where I've had half of the frame completely blown out with the darker half of the screen properly exposed.

    Even still I've had issues with over exposure when the entire frame is well lit. I suspect there is another factor in play that attempts to detect "low light".

    I've noticed when working during the day, with a little bit of diffuse natural daylight in the room the Kinect rarely drops below 30fps. However at night, when the room is only lit by tungsten bulbs, no matter how much light is in the room it struggles to maintain 30, is blown out and has a very long shutter speed.

    I haven't had a chance to properly test it with a light meter, but it seems that the Kinect treats tungsten lighting (color temperature 3200k) as darker than daylight lighting (color temperature 5500k) even if it is the same or more amount of light.

    Again, this is just going by eye so I could be completely wrong. I will try and do proper tests this weekend.

    Friday, December 19, 2014 7:11 PM
  • Interesting, I've had very similar experiences.
    Dark areas can have a negative impact and daylight ambient light can have a positive impact.

    Hence I thought I'd ask here in hopes for an answer by Carmine explaining some of the internals :)


    Recently I've been using a cheap photography softbox which seems to work quite well at night.
    I don't know the exact color temperature but I'm pretty sure it's daylight balanced.


    Understanding what triggers low light mode could at least give us some control where the SDK lacks such.

    Brekel

    Saturday, December 20, 2014 7:12 PM
    Moderator
  • Bumping this thread as the Holidays are now over.
    Monday, January 5, 2015 6:20 PM