things can go wrong during a motion detection process, resulting in
misses and false positives. Because conditions change
day, you need to optimize the setup in order to get reliable results.
Here are the things to watch out for.
Get the right
camera for the job
is no substitute for good video source, there is no such thing as a
software "enhance" feature that takes a crappy image and
cleans it up.
of the camera refers to the amount of pixels in an image. This can be
represented as a width/height measure (640x480), a mega-pixel value
(640x480 = 0.3 mega pixel), or number of lines in the case of analog
cameras. A good image resolution is useful when you want to record
images or video, but it has little impact on the quality of motion
price of the camera is usually the better clue for the camera's
quality; remember that a cheap camera can have a high resolution, but
this does not mean that it will provide great colors and decent frame rate, nor that
it will perform well under low
images put a larger load on the video capture, which may slow down the
computer. You may need to experiment and tune the settings to find a
do not have adjustable lens,
have a simple lens that you need adjust manually to set the focus. A
few high end webcams have auto-focus mechanical lens, which provide
better images, but at a cost: if something moves out of focus, the
camera will try to re-focus, which may trig the motion detection.
is no substitute for a good source image. Webcam behavior changes with
When the scene goes darker, the camera compensates by increasing the
voltage in the video sensor, making it more sensitive. The downside is
that this voltage increase produces noise in the sensor, resulting in
grainy images (see picture below for example).
a camera measures 1% noise from a well light room, the same camera may
well measure 3% noise from the same dim light room. Another camera may
behave differently. This lack of stability in light reading is a
problem because it makes it harder to adjust the motion sensitivity.
scenes produce noisy images.
darker scene also means that camera may spend more exposition time for
each frame, resulting in a lower frame rate acquisition.
other side, it is possible to provide too much light, this can sometime
happen for cameras looking outdoors. In this case, the image, or part
of the image, will saturate to white, making it impossible to see
quality cameras can deal with a wider range of lighting scheme. Cheap
cameras will usually mis-behave in dark or too-bright environments.
Here are a
few important points that you should consider when setting
up motion detection:
- Good motion detection results require contrast between
moving subjects and the background.
light means less contrast, resulting in misses.
and lens flares
can also produce important changes in contrast, generating
a dark scene, if a moving subject passes between a light source and the
camera, this produces major contrast, which results in reliable trigs.
detection Hot Spots strategically
is where the Webcam
software gives you a huge advantage over standard motion
software. You get to choose the size and position of the area to
monitor by placing a motion detection Hot Spot object on the image.
How to Use
motion detection Hot Spots
- Place the Hot Spot over a stable area, where
you expect there will not be irrelevant motion, or where there is less
- The percentage next to the Hot Spot is the
measured motion and noise.
- More motion means a higher percentage.
- Set the Spot's sensitivity to a slightly higher
- Make sure the spot turns blue when the motion
you expect occurs.
- If the Hot Spot is too sensitive, it will turn
blue for no reason, slide the sensitivity to the left to make it less
- If the spot does not turn blue upon motion,
slide it more to the right until it does.
tips to get better results with Hot Spots:
smaller hot spots. They will require less motion to trig,
and you can tune them more precisely.
Hot Spots as trip-wire. In a dark scene, place
Hot Spots over a light source (see image above), this way if something
moves between the light and the camera, this will produce optimal
can use many hot spots. You can overlap them. You can set
a different sensitivity settings for each one.