Image artefacts are a fact of web-camera life. They are intrusive degradations on
the image that may lead to the loss of contrast, colour, sharpness, white balance
and even, the entire image. If an artefact is a persistent intrusion, the web-camera
should be repositioned to avoid the cause.
Some common artefacts seen on a weather web-camera include:
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A cyan colour cast. Often seen in twilight, this is caused by a confused white balance.
Try restarting the camera as the white balance may have been set for a different
colour temperature. However, this may impact the colour balance at other times of
the day.
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A pink colour cast on the edges of clouds during the afternoon. This is a result
of the way the sensor chip inside the camera reacts to ultraviolet light, and just
has to be lived with.
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Burn out. The whole scene turns white due to over-exposure. Try lowering
the brightness and, or, the contrast settings. With a weather web-camera, to resolve
the detail in clouds, a low contrast should be selected.
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Block out. Much of the scene turns dark due to under-exposure. Try increasing
the brightness setting.
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De-saturation. At low light levels or under cloudy skies, an image will lose the
intensity of it's colours. Try increasing the saturation setting, remembering the
image may look overblown in bright sunlight.
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Noise. Typical of low light, this is where the scene turns grainy. Even the
most expensive web-cameras suffer low light noise.
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White lines. When too much light enters the web-camera, the excess photons bounce
around the sensor chip creating bright horizontal lines. Usual offenders are the
Sun or sunlight reflecting off bright objects like car windscreens. Potentially,
street lights and the Moon will also cause white lines. Decreasing the exposure
will not reduce the effect.
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Bad-ass pixels. At low light levels, some pixels misbehave as they glow red,
green, blue or a mixture thereof. In normal daylight, these pixels should function
correctly or, go unnoticed.
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Broken images. Where an image has failed to render completely, this may indicate
a fault with either the camera or, some intervening equipment. Check all interconnecting
cables and ensure the the camera is receiving a correct and clean power supply.
The fault may also be down to a timeout on a remote FTP server; the image
did not upload fast enough or, the FTP server did not respond fast enough. Ensure
FTP connections are set to passive.
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De-focusing. Some web-cameras seem to de-focus all by themselves. This is often
due to the mechanical stresses on the lens assembly from temperature cycling. Set
the lens in place with a small piece of tape. Avoid using glue.
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Maltemps. Condensation, rain, snow and ice will all deposit around the lens. In
a maritime environment, salt crystals may also form. Cameras should be positioned
where they are least likely to be affected by the weather. External cameras must
be placed in enclosures that are weather proof and, are accessible for easy and
safe cleaning.
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Fogging. Where condensation is an issue, the lens may become wet. In worse cases,
water condenses on the lens which does not evaporate at ambient temperatures. Ensure
housings are water proof, otherwise condensation will occur inside the enclosure.
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Hazing. In dusty or smoky locations, pollutants will deposit over a lens, reducing
contrast. Clean the lens when symptoms occur.
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Combing. With interlaced web-cameras or video cameras connected to video servers,
when an object moves at speed across the scene, the outline of the object can resemble
a comb. This is an effect and not a fault.
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Bending. With non-interlaced or progressively scanned web-cameras, an object moving
at speed across the field of view will appear to bend away at the bottom of the
object. This is an effect and not a fault.
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Fauna. It is normal to see spider webs spun across a web camera, along with any
flies caught in them. A web camera may also be unfortunate to suffer a bird strike.
Always ensure a camera is accessible for easy and safe cleaning. |