Page 1 of 3 123 LastLast
Results 1 to 10 of 24

Thread: Discovery!

  1. #1
    Join Date
    May 2003
    Location
    Vancouver's Island
    Posts
    41,979

    Default Discovery!

    I have been fiddling with another web cam, a Microsoft Life Cam. I bought it for a project to monitor the night sky for aurora because it has very good low light sensitivity. I have been slightly disappointed that it isn't as good as I would have liked even with maximum fiddling of the camera settings.

    EUREKA! While playing with it this early am in our nearly dark living room I discovered a way to increase the sensitivity by an order of magnitude! It's entirely counterintuitive but makes perfect sense. I was pointing the camera at the floor and it showed almost nothing. Then I moved it toward the computer screen and was astounded to see the floor image come into perfect clarity along with a bright diffuse glow from the edge of the field of view caused by light from the screen. The ability to image in the dark is increased many times by simply shining some light on the sensor.

    What this does is sort of "prime the pump" of the sensor. It takes the imager out of the non-linear range where there isn't enough light to produce a signal at all into the middle of the sensitivity range. Once the pixels are producing a signal then even slight differences in brightness are visible because it is operating in the middle of the dynamic range. VERY COOL!

    I tried it with one of the outside cameras. It doesn't have the resolution or quality of the MS cam but the same effect applies as it should to all digital image sensors.

    This is the outside camera that looks out to the driveway from the north side of the house. The driveway is illuminated by a single 50 watt incandescent floodlight only so the low light performance of this camera isn't too bad.



    Then I shined a powerful flashlight into the camera from the side to flood the sensor. Note that the camera is mounted upside down so it looks as though the light is coming from above rather than below. Also note that I did NOT shine any light on the scene. The only change is the amount of total light reaching the sensor which brings it up to the useful part of the dynamic range. See also how well it images the distant tree shadows in the snow, completely invisible in the first picture. The structure in the foreground is a "tent" garage for the car.



    This is going to be very useful. This effect should apply to many types of sensors and in the case of silicon based sensors it should be sufficient to use an infrared LED to flood the sensor. With proper placement it also should be possible to avoid the spot of glare in the image. I shall be experimenting with this.

    I should also point out that this effect has been used by astronomers with film in the past. By using a controlled pre fogging of the film the effective film speed can be increased dramatically. I don't know why this didn't occur to me but as I said, the effect is counterintuitive.
    Free software for calculating bolt circles and similar: Click Here

  2. #2
    Join Date
    May 2006
    Posts
    13,723

    Default

    Very cool, My sony handycam has a nightvision button that throws off a little infrared and makes a huge Diff...

    Somthing kinda related, Sony produced an earlier version of my nightvision camera --- but it was pulled off the market, tests showed that it could actually see through clothing with kind of an X-ray vision, Damn, what a thing to bring to the beach ehh?

  3. #3
    Join Date
    May 2003
    Location
    Vancouver's Island
    Posts
    41,979

    Default

    This has nothing to do with illuminating the scene as with the infrared illuminators. It's all about increasing the useful dynamic range of the sensor by flooding it with light. It's an effect that should work with almost any sort of solid state sensor and is very easy to implement.
    Free software for calculating bolt circles and similar: Click Here

  4. #4
    Join Date
    May 2006
    Posts
    13,723

    Default

    So in effect could you do this internally inside the sensor? and not even have the red lights that I have to use? this would in turn make your unit completely stealth (if im catching what your saying)

    Ev, have you heard of that particular X-ray sony im talking about? is it for real, If so how did that happen...

  5. #5
    Join Date
    May 2003
    Location
    Vancouver's Island
    Posts
    41,979

    Default

    So in effect could you do this internally inside the sensor?
    Exactly. This is about increasing the sensor sensitivity for pennies. I've tried it on two totally different web cams and it works the same on both. I will be trying it on a few more cameras including possibly my Canon Rebel.

    Yes, the Sony night shot camera can see "through" some articles of clothing that are transparent in infrared light. Infrared transparency is common for articles that seem opaque in visible light. A piece of exposed and developed color negative film looks completely black to the eye but it is as clear as window glass to infrared light.
    Free software for calculating bolt circles and similar: Click Here

  6. #6
    Join Date
    Dec 2004
    Location
    Western New York U.$.A
    Posts
    7,272

    Default

    Quote Originally Posted by A.K. Boomer
    Very cool, My sony handycam has a nightvision button that throws off a little infrared and makes a huge Diff...

    Somthing kinda related, Sony produced an earlier version of my nightvision camera --- but it was pulled off the market, tests showed that it could actually see through clothing with kind of an X-ray vision, Damn, what a thing to bring to the beach ehh?
    Boomer, I have the camera you are talking about. What it actually sees are the whitners in laundry detergent so a foxy persons vuluptious and pendoulous.........I digress. It shows underwear and not much else. Not worth the $10,000 I paid on ebay for it when the story hit Just kidding of course !

    Evan, just curious. How often does your wife have to wind you up?
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

    It is true, there is nothing free about freedom, don't be so quick to give it away.

  7. #7
    Join Date
    May 2004
    Location
    Toronto, ON
    Posts
    514

    Default

    Evan,

    I don't think I understand your explanation. Are you saying the photo diodes (the pixel sensors) have a lower quatum efficiency at lower luminosity, and by offsetting into the linear region you can get better sensitivity?

  8. #8
    Join Date
    May 2003
    Location
    Vancouver's Island
    Posts
    41,979

    Default

    Yes. It is more likely the amplifiers though, not the actual quantum efficiency of the detectors. CMOS detectors, which is nearly all cameras now (all webcams), have an amplifier per pixel. The amplifiers almost certainly have a built in low level cutoff to reduce noise in an ordinary low light situation. Pumping in some photons will take the sensor+amplifier into the linear range.
    Free software for calculating bolt circles and similar: Click Here

  9. #9
    Join Date
    Feb 2006
    Location
    Phoenix
    Posts
    3,277

    Default the Williams Effect

    Quote Originally Posted by Evan
    This is going to be very useful. This effect should apply to many types of sensors and in the case of silicon based sensors it should be sufficient to use an infrared LED to flood the sensor.
    I'll be very interested in the results of your experiments with this. Can the proposed infrared fogging can be effective if held to a level just below the threshold of visibility by the sensor? Your experiments may quantify how little (or how much) is needed to just get into the linear-response range. I think visible fogging must degrade image contrast, but perhaps that could be tweaked. After all, there are contrast adjustments on higher-end cameras.
    Allan Ostling

  10. #10
    Join Date
    Mar 2003
    Location
    South Central Tennessee
    Posts
    275

    Default

    Quote Originally Posted by A.K. Boomer
    .....Somthing kinda related, Sony produced an earlier version of my nightvision camera --- but it was pulled off the market, tests showed that it could actually see through clothing with kind of an X-ray vision, Damn, what a thing to bring to the beach ehh?
    I just recently bought a Sony DCR-TVR80 off of eBay. It has the night vision feature. Would this be the model you are talking about?
    No matter where you go, there you are!

    Hal C.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •