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Configuring weather web-camera images and common image artefacts

This section describes the basics of configuring a weather web-camera for video. In particular it covers the main camera settings, issues with image compression and bandwdidth, common web-camera image sizes and, image artefacts. Network configuration is covered in the next section.


First read the manual

Setting up an IP Camera differs from a USB webcam. In principle, a USB webcam is plugged in to a USB port and then a window pops up prompting the user for driver software; which is usually on a supplied CD. An IP Camera is a stand-alone device which does not need a computer. So how does one configure an IP camera?

IP cameras can be configured using either a web browser or, a camera setup wizard, which is supplied on a CD with the web-camera. After the IP camera is plugged into the network, the wizard is run on a computer attached to the same network, and the wizard locates and logs into the IP camera. A default administrator account is available on the IP Camera which, will allow the camera to be configured either by using the setup wizard or, remotely with a browser. For network savvy person, the wizard is not strictly needed. Read the manual to discover how to configure without installing software. Other software to expect with an IP Camera is a browser plug-in to view the camera streaming in real time and possibly, some security-style monitoring software.

Configuring a web camera is always device specific, but in principle configuration deals with image and network settings. The image settings are those that deal with how the web camera processes its image. Network settings are those that deal with how the camera interacts with the network.

Pictured, before removing a brand-new camera from its carton, always read the manual first!
Picture of a boxed web-camera


Common image sizes

Picture of the common web camera image sizes

The common sizes for web cameras are 640 x 480 and 320 x 240 pixels. These are sometimes called VGA and CGA sizes respectively, as they relate to computer screen dimensions.

For video servers running from a PAL video source, some common sizes are 768 x 576 and
352 x 288 pixels. For NTSC video sources, common sizes are 486 x 648 and 243 x 324 pixels.

Diminutive 160 x 120 pixel sized images (and smaller) are often used for video streaming.

Some web-camera services based on digital cameras produce images with dimensions of 1024 x 768 and even, 2400 x 1800 pixels. These also produce file sizes in the region of 300 kilobytes per image and, are not recommended for ordinary weather web-camera use.



Image settings

Configuring an IP camera's video or image settings is straightforward. Settings often include:

  • Saturation. This tells the camera how colourful to make the image. A very low value will produce a near black and white image. A very high value will make the colours very garish. Saturation should be set slightly high as this will help keep the sky blue and accent the colours in sunsets.
  • Contrast. To maintain the detail in bright clouds the contrast should be kept on the low side, otherwise clouds in bright sun will turn into white blobs.
  • Exposure. Exposure should be set so that the scene looks bright, but not to the point where the clouds become white blobs.
  • Frame Rate. This dictates how often the camera refreshes the image inside the camera. With a weather web-camera, this need only be once a second.
  • Video Resolution. Typically, web-camera's offer resolution in pixels of 320 x 240 and 640 x 480. Typically, 320 x 240 is a standard size used in most websites, although 640 x 480 gives much more detail and is friendlier to persons with large monitors.
  • Compression or quality. This governs the size of the final image in bytes. At the lowest compression value (highest quality), the image will be sharp, but the file size will be large.
    As the compression value increases (quality lowers), the file size decreases, but the image becomes indistinct. A normal setting will do for most uses. See below for issues with image compression.
  • Sharpness. Some web-cameras allow an image to be sharpened. This has the effect of returning definition to objects with strong lines and edges, like buildings and tree branches. Useful for small sized images.
  • Date and time. Sets the date and time for the web-camera. Often a web-camera can be configured to find the correct time from a network time server; this is a computer on the internet whose clock is synchronised against an atomic clock.
  • Tarry light. On some cameras the monitoring light on the front of the camera can be turned off for discretion. Turn off the tarry if the camera can see it's own light as a back reflection in a window or when mounted inside an enclosure.
  • On image Text. Most, but not all, cameras support on-image titles and time stamping. Enable this feature as to emboss the camera's identity on the image. If there is space, mark the image as copyrighted thus: (c)
  • Anti flicker and light frequency settings are only required for live streaming under artificial light; these are ignored for a weather web-camera.


Image configuration example

Often a web-camera's default factory settings are only suitable for use indoors and under strong artificial lighting. When used as a weather web-camera, the settings will need to be experimented with over a range of sky conditions. Generally, most web-camera's will not reproduce sky scenes as well as that viewed by the human eye; some parts of the sky will block out (turn to black) and others will burn out (turn to white), and sometimes the colours will just not seem quite right! Aim to achieve optimum settings for the most interesting weather phenomina such as sunsets, cumulonimbus clouds and cirrus. The midday Sun often produces harsh contrasts which are difficult to reproduce successfully, on any camera.

Picture of image configuration screen

There is often very little control when it comes to configuring a video camera attached to a video server. This is because settings such as colour, contrast and brightness are controlled automatically by the video camera itself. Some video cameras may have small screw terminals for trimming their video settings, but unlike an IP web-camera that can be calibrated using a web-browser from anywhere in the world, a video camera has to be set up on site and in situ. Most video servers do have browser controlled colour, contrast and brightness settings, but these affect the output image and not the input video.



Image compression issues

Images produced by web cameras are compressed using Jpeg compression. Without Jpeg compression, a web-camera would produce an image with a potential file size in the megabytes, instead of one compressed into kilobytes. Which is a good thing; an image a thousand times smaller loads a thousand times faster.

Jpeg compression works by analysing the complexity of an image and then, reduces the numbers of bytes required to represent the least complex parts of that image. When an image contains more complexity, such as a tree, a larger file size is always produced. When an image contains less complexity, such as a blue sky, the file size is always smaller. With a weather web-camera, subtle changes in the sky will always affect the final file size; even a bird walking along on a wire will produce a minor change in file size. For most applications, the web-camera's normal compression setting will be adequate.

Pictures of an image at high and low Jpeg compression levels
The degree of Jpeg compression is dictated by the quality setting. A high quality setting (left) produces an image that is sharp in detail but, with a file size of 45,430 bytes. The low quality setting (right) produces a file size of only 8,991 bytes, but it suffers significant loss of
image information. Even so, the highly compressed image is still useable!

A rule-of-thumb is that VGA resolution images (640 x 480 pixel) create in daylight a file size of around 50K to 75K bytes. This may jump to 100K overnight as noise levels increase.
CGA resolution images (320 x 320 pixel) produce file sizes in daylight of around 8K to 12K bytes. Sadly, some web camera services send needlessly large file sizes which, consume bandwidth for
a zero increase in perceived picture detail.



Data Bandwidth

It is important to understand how the file size of the image impacts data bandwidth. For example, where an image is uploaded every fifteen minutes, this will tally up to 2,800 images a month.
At 40 kilobytes per image, that's a total in excess of 100 megabytes, which may consume a critical segment of the monthly bandwidth allowance allotted by an ISP.

If bandwidth is an issue, try reducing the dimensions of the uploaded image rather than the quality setting; this can save proportionally more bytes than reducing quality alone and, is less perceptible than a drastic reduction in image quality. Furthermore, big image files take longer for a web site visitor to download. Respect internet users and aim for the most readable image with the lowest file size. Especially those with expensive mobile-device data tarrifs.

Curiously, many web-cameras produce larger file sizes at night than during the daytime, even though the image looks black? This discrepancy arises because the noise implicit at low light levels adds extra complexity to an image. This deceives the Jpeg algorithm into creating an unnecessarily large file size. Use the scheduling feature to avoid sending images overnight.

Picture of image noise at night



Common image artefacts

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:

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.
Pink tinge to clouds. Some budget sensor chips will register the infrared content of light and reproduce this as a pink or magenta colour cast on clouds which, should be neutral greys. Restarting the camera can help by resetting the white balance but, often this effect just has to be lived with.
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.
Block out. Much of the scene turns dark due to under-exposure. Try increasing the brightness setting.
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.
Horrid hues. An image digitised from video may show a disturbing green or magenta hue. Be sure all leads are pushed home and the hardware is not overheating. If present, try adjusting the colour phase setting.
Noise. Typical of low light, this is where the scene turns grainy. Even the most expensive web-cameras suffer low light noise.
Embossing. Objects may have an embossed effect as a result of the image being over-sharpened. Try reducing the sharpness setting.
Pixelation. An image can look overtly blocky if the compression level is set too low. Increase the image's quality setting.
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. 
Solar eclipse. When the sun or a car headlight enters the frame, some cameras will prevent the detector from overloading by shutting down those pixels. The result is a curious grey or black spot.
Black frame. When too much light enters the lens, some IP cameras will shut down the detector and send a black frame instead. The camera is actually functioning correctly.
Defective pixels. At very low light levels, some pixels will be seen to glow red, green, blue or a mixture thereof. In normal daylight, these pixels should function correctly or, just go unnoticed as they are swamped by their neighbours.
Part grey out. Usually sporadic, this indicates a timeout occured when attempting to upload the image to the remote FTP server. Ensure FTP connections are configured as passive. If it is possible, also configure both camera and server's timeout periods to ten seconds or more.
Fragmented images. An image assembled in the wrong order indicates a camera's image chip or internal memory is mapped incorrectly. The cause could be overheating or external electrical interference.
Excessive download times. The image quality setting may be set too high, producing an excessive file size. Reduce the image quality setting.
A typical 640 x 480 pixel jpeg image will be around 70K bytes.
Image placeholder. The camera's image failed to load into the browser because a filename reference may be wrong, there is a password or firewall issue or, there is some physical connection problem.
De-focusing. Mechanical stresses on the lens assembly from shock or temperature cycling will often defocus a camera. Set the lens in place with a small piece of tape, especially when the camera is inaccessible.
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.
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.
Hazing. In dusty or smoky locations, pollutants will deposit over a lens, reducing contrast. Clean the casing window and lens when symptoms occur.
Herring bones. Prime suspects for interfering with analogue video servers are PMR, police and CB radios, plus crosstalk from other video and data equipment. Use shielded cables and, keep cable runs as short as is practical.
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 will resemble a comb.
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.
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!


Summary
  • Respect the bandwidth; aim for the most readable image, with the lowest file size.
  • Experiment with video settings under varying lighting conditions.
  • Respect bandwidth and aim for the most readable image with the lowest file size.
  • Live streaming is unnecessary for a weather web-camera.
  • Update the image every five to thirty minutes.
  • Image artefacts may have to be lived with.
  • Always read the manual first!
Connecting up a weather web-camera Configuring a weather-web-camera video