In China, after an earthquake measuring 7.9 on the Richter scale caused more than 55,000 deaths and billions of dollars worth of damage in May 2008, rivers blocked by landslides threatened to worsen the tragedy with torrential flooding. To prevent further loss of life, local government offices sent emergency text alerts to residents downstream, warning them of the rising waters and urging them to leave [source: Yahoo News/AP].
© Wang Jian/China Fotopress/Getty ImagesWeather alerts are used for tragedies like the May 12, 2008 earthquake in China.In Boone County, Ill., an unseasonal tornado surprised Poplar Grove residents in January 2008, flattening four houses and spurring neighboring Winnebago County to adopt a Reverse 911 system that now sends residents alerts of bad weather and other emergencies via landline phones, cell phones, e-mail and voice-over Internet protocol (VoIP) numbers [source: Rockford Register Star].
Loud sirens are increasingly being replaced by the use of digital and Web technology for emergency alerts. Weather alerts provide the warnings we need to head to shore, batten down the house or simply seek shelter. And while a siren may be the first thing that comes to mind as a bad weather alert, emergency alerts can be sent using many different forms of communication. In fact, Internet and wireless technology make it possible to receive emergency weather alerts as notifications on your PC, cell phone or other mobile device.
Friday, November 14, 2008
Cell Phone Weather Alerts
Whether you're on your way to a soccer game or waiting to board a plane headed across the country, you'll want to know about problems with the weather at your destination. The easiest way to receive a bad weather alert may be on your cell phone or other mobile device. And you don't necessarily have to pay a premium for weather updates.
© George Doyle/Stockbyte/Getty ImagesCell phone weather alerts can notify users of impending storms, such as tornadoes or hurricanes.
Application developers offer cell phone weather alerts ranging from simple weather alerts to notifications that offer broader types of emergency alerts. But media sources, such as The Weather Channel, also can provide an emergency weather alert on your cell phone, often based on reports they've received from the National Weather Service via the EAS. And even some cities are starting to offer these services.
Prices and options vary widely for cell phone weather alerts. Service availability depends on your wireless provider. While some services are free, you'll still need to pay your provider's rate for text messages. Here are some, but certainly not all, of the options:
The Emergency Email Network will send free e-mails to your cell phone, wireless device or PC notifying you about homeland security emergencies, local natural disasters, severe weather and other emergencies in your area. All you have to do is provide your ZIP code, e-mail address and device on which you want to receive the messages. You can choose the topic content you want to receive.
The Weather Channel provides a variety of weather information, including free 4CAST text-message alerts ranging from severe weather alerts to those specifically for next-day rain, extreme heat, extreme cold, icy precipitation and snow by subscription, as well as on-demand pollen alerts.
My-Cast from Digital Cyclone offers forecasts, maps and other weather information, including automatic phone alerts that make your phone beep when storms approach or lightning strikes nearby. My-Cast also brings you weather watches and warnings from the National Weather Service. This is a $3.99 per month subscription service for BlackBerry devices, iPhones and many other phones. The alerts aren't available on AT&T's network.
Norfolk Alert is a city-offered emergency alert service. If you live in Norfolk, Va., you can register a valid e-mail address and choose the alerts you'd like to receive, such as inclement weather, road closings and emergency notifications. Alerts can be sent to your home phone, cell phone or e-mail. Other towns also offer this type of service, so check what's available locally for you.
WeatherBug Protect from WireFly delivers severe weather alerts and daily forecasts to BlackBerry devices and other cell phones for $2.99 per month. The notification service pinpoints the subscriber's cellular location and gives any alerts for that location. Alerts can be formatted as recorded voice, text message or e-mail. Two-way messaging gives the subscriber a way to respond and report back personally on weather conditions.
Finally, if you're looking for weather alerts about somewhere more distant -- check out NOAA's Space Weather Prediction Center. You can sign up for free e-mails that'll alert you about comets, asteroids, geomagnetic storms, radio blackouts and more.
© George Doyle/Stockbyte/Getty ImagesCell phone weather alerts can notify users of impending storms, such as tornadoes or hurricanes.
Application developers offer cell phone weather alerts ranging from simple weather alerts to notifications that offer broader types of emergency alerts. But media sources, such as The Weather Channel, also can provide an emergency weather alert on your cell phone, often based on reports they've received from the National Weather Service via the EAS. And even some cities are starting to offer these services.
Prices and options vary widely for cell phone weather alerts. Service availability depends on your wireless provider. While some services are free, you'll still need to pay your provider's rate for text messages. Here are some, but certainly not all, of the options:
The Emergency Email Network will send free e-mails to your cell phone, wireless device or PC notifying you about homeland security emergencies, local natural disasters, severe weather and other emergencies in your area. All you have to do is provide your ZIP code, e-mail address and device on which you want to receive the messages. You can choose the topic content you want to receive.
The Weather Channel provides a variety of weather information, including free 4CAST text-message alerts ranging from severe weather alerts to those specifically for next-day rain, extreme heat, extreme cold, icy precipitation and snow by subscription, as well as on-demand pollen alerts.
My-Cast from Digital Cyclone offers forecasts, maps and other weather information, including automatic phone alerts that make your phone beep when storms approach or lightning strikes nearby. My-Cast also brings you weather watches and warnings from the National Weather Service. This is a $3.99 per month subscription service for BlackBerry devices, iPhones and many other phones. The alerts aren't available on AT&T's network.
Norfolk Alert is a city-offered emergency alert service. If you live in Norfolk, Va., you can register a valid e-mail address and choose the alerts you'd like to receive, such as inclement weather, road closings and emergency notifications. Alerts can be sent to your home phone, cell phone or e-mail. Other towns also offer this type of service, so check what's available locally for you.
WeatherBug Protect from WireFly delivers severe weather alerts and daily forecasts to BlackBerry devices and other cell phones for $2.99 per month. The notification service pinpoints the subscriber's cellular location and gives any alerts for that location. Alerts can be formatted as recorded voice, text message or e-mail. Two-way messaging gives the subscriber a way to respond and report back personally on weather conditions.
Finally, if you're looking for weather alerts about somewhere more distant -- check out NOAA's Space Weather Prediction Center. You can sign up for free e-mails that'll alert you about comets, asteroids, geomagnetic storms, radio blackouts and more.
Tuesday, November 11, 2008
How the scanner builds the image
When scanners only scanned in black and white, the actual scanning process was fairly straightforward. The scanner motor would move one step, capture a single horizontal line of the image from the CCD array, save the results, and move on. When color scanners hit the market, there were several possible ways to scan in color, each one with different advantages and disadvantages.
The first color scanners used a black-and-white CCD array and featured three colored lamps--red, green and blue--or used a single white lamp and had three colored filters for the CCD. The traditional way to scan in color was to scan the entire document three times, one pass for each color, and then build up a composite image that was sent back to the computer. This method had some marked disadvantages. If the image moved even the slightest bit during the scanning process, the resulting misregistration of colors would make the scan useless. (It was also slow, since it required the scan to be done three times in a row.)
One-pass color scanning was eventually introduced, although there were several different ways to pull off the same trick, each again with its own benefits and drawbacks. The first method was to simply scan the whole document once in white light with a color-sensitive CCD array--which required a CCD array that may be much more expensive to produce than a single black-and-white CCD. Another method was a variant on the old three-pass system: at each step of the scan, the scanner turned on the red, green, and blue lamps in sequence and recorded the results from each, creating a composite image at each step. Many current LED-based scanners use this method, since LEDs can be switched on and off very quickly.
There are two basic methods for scanning an image at a resolution lower than the hardware resolution of the scanner. Method 1 simply involves taking the output from certain pixels in the CCD. For instance, if you scanned at 300 DPI on a 600 DPI CCD, the scanner would only sample the results from every other CCD pixel. Method 2 involves scanning at the full resolution of the CCD and then downsampling the results in the scanner's own memory. Most better scanners do this instead, since it yields far more accurate results.
When color scanners scan in grayscale, there are also a number of methods used. Scanners with multiple lamps (such as LED-based scanners) often scan in grayscale by switching on the green lamp and scanning that as black-and-white. This does not always yield the most accurate results with colored documents, but works fine for most black-and-white originals and it is slightly faster than taking a three-channel color image and removing the chrominance values from it (which is how some other scanners work).
As we will find, every single one of the elements in this setup is critical to a good scanner. Let's examine each one in turn, starting with the lamp.
Lamps
Without a bright and consistent light source, no scanner can deliver good results. The vast majority of scanners these days use one of several basic types of lamp:
Cold-cathode fluorescent lamp. So named because they emit very little heat, which prevents image distortion and also prolongs the life of the lamp and other scanner elements.
Xenon-gas cold cathode lamp. Superior to fluorescent lamps, in that they come up to brightness faster and last longer, but they are also considerably more expensive. They also have the advantage of more closely resembling natural light.
LEDs. LEDs are now being used in many inexpensive scanners as light sources. For one, they use very little power, which makes it possible for a scanner to be powered by the USB or FireWire connection, and have a far greater lifespan than cold-cathode fluorescent light sources. LEDs are also much cheaper and more compact, making smaller, lighter scanners possible. The downside is that scanners that use LEDs don't quite provide the same level of richness of color or detail that non-LED scanners do.
Focus and lenses
There's also some variety in the type of lens in a scanner. Most cheaper scanners use a fixed-focus lens--the focus of the lens is set to what is just beyond the surface of the glass and nothing more than that. This is fine if you're putting a flat original on the bed, as is generally the case--although if you are scanning from a book where the spine does not lie completely flat, fixed-focus scanners will not be able to reliably reproduce what's near the spine as well as a scanner with focus control.
The more expensive and advanced scanners have focus control, where the focus of the lens is changed depending on the distance of the document from the glass and mirror. This not only helps you scan a three-dimensional object on the scanner but also provides better control over scans of slides or chromes in slide holders, since the slide holders places them slightly farther away from the lens than other objects. Also, cheaper scanners generally use plastic lenses; the more expensive and professional-quality scanners use genuine glass lenses.
Sensors
Scanners typically use two kinds of sensor arrays. The CCD, or Charge Coupled Device, is the most common type of sensor, and is usually very precise and accurate. It's also a time-tested technology: CCDs are used in many applications, including video and digital still cameras.
Another variety of sensor is the CIS, or Contact Image Sensor. CIS arrays are much smaller and more compact than CCDs, since the signal-amplification circuitry is placed directly onto the sensor itself. CISs are cheaper, but they also yield less impressive and often noisier-looking results, and the scans from CIS-based scanners often need more tweaking to look good. Most people will want to opt for having a CCD rather than a CIS array in their scanner at this point.
Once the scanner has the data, the information needs to be transferred to the host PC. There are, as you might imagine, a variety of ways to accomplish this--some of them extremely archaic but still being used today.
The first color scanners used a black-and-white CCD array and featured three colored lamps--red, green and blue--or used a single white lamp and had three colored filters for the CCD. The traditional way to scan in color was to scan the entire document three times, one pass for each color, and then build up a composite image that was sent back to the computer. This method had some marked disadvantages. If the image moved even the slightest bit during the scanning process, the resulting misregistration of colors would make the scan useless. (It was also slow, since it required the scan to be done three times in a row.)
One-pass color scanning was eventually introduced, although there were several different ways to pull off the same trick, each again with its own benefits and drawbacks. The first method was to simply scan the whole document once in white light with a color-sensitive CCD array--which required a CCD array that may be much more expensive to produce than a single black-and-white CCD. Another method was a variant on the old three-pass system: at each step of the scan, the scanner turned on the red, green, and blue lamps in sequence and recorded the results from each, creating a composite image at each step. Many current LED-based scanners use this method, since LEDs can be switched on and off very quickly.
There are two basic methods for scanning an image at a resolution lower than the hardware resolution of the scanner. Method 1 simply involves taking the output from certain pixels in the CCD. For instance, if you scanned at 300 DPI on a 600 DPI CCD, the scanner would only sample the results from every other CCD pixel. Method 2 involves scanning at the full resolution of the CCD and then downsampling the results in the scanner's own memory. Most better scanners do this instead, since it yields far more accurate results.
When color scanners scan in grayscale, there are also a number of methods used. Scanners with multiple lamps (such as LED-based scanners) often scan in grayscale by switching on the green lamp and scanning that as black-and-white. This does not always yield the most accurate results with colored documents, but works fine for most black-and-white originals and it is slightly faster than taking a three-channel color image and removing the chrominance values from it (which is how some other scanners work).
As we will find, every single one of the elements in this setup is critical to a good scanner. Let's examine each one in turn, starting with the lamp.
Lamps
Without a bright and consistent light source, no scanner can deliver good results. The vast majority of scanners these days use one of several basic types of lamp:
Cold-cathode fluorescent lamp. So named because they emit very little heat, which prevents image distortion and also prolongs the life of the lamp and other scanner elements.
Xenon-gas cold cathode lamp. Superior to fluorescent lamps, in that they come up to brightness faster and last longer, but they are also considerably more expensive. They also have the advantage of more closely resembling natural light.
LEDs. LEDs are now being used in many inexpensive scanners as light sources. For one, they use very little power, which makes it possible for a scanner to be powered by the USB or FireWire connection, and have a far greater lifespan than cold-cathode fluorescent light sources. LEDs are also much cheaper and more compact, making smaller, lighter scanners possible. The downside is that scanners that use LEDs don't quite provide the same level of richness of color or detail that non-LED scanners do.
Focus and lenses
There's also some variety in the type of lens in a scanner. Most cheaper scanners use a fixed-focus lens--the focus of the lens is set to what is just beyond the surface of the glass and nothing more than that. This is fine if you're putting a flat original on the bed, as is generally the case--although if you are scanning from a book where the spine does not lie completely flat, fixed-focus scanners will not be able to reliably reproduce what's near the spine as well as a scanner with focus control.
The more expensive and advanced scanners have focus control, where the focus of the lens is changed depending on the distance of the document from the glass and mirror. This not only helps you scan a three-dimensional object on the scanner but also provides better control over scans of slides or chromes in slide holders, since the slide holders places them slightly farther away from the lens than other objects. Also, cheaper scanners generally use plastic lenses; the more expensive and professional-quality scanners use genuine glass lenses.
Sensors
Scanners typically use two kinds of sensor arrays. The CCD, or Charge Coupled Device, is the most common type of sensor, and is usually very precise and accurate. It's also a time-tested technology: CCDs are used in many applications, including video and digital still cameras.
Another variety of sensor is the CIS, or Contact Image Sensor. CIS arrays are much smaller and more compact than CCDs, since the signal-amplification circuitry is placed directly onto the sensor itself. CISs are cheaper, but they also yield less impressive and often noisier-looking results, and the scans from CIS-based scanners often need more tweaking to look good. Most people will want to opt for having a CCD rather than a CIS array in their scanner at this point.
Once the scanner has the data, the information needs to be transferred to the host PC. There are, as you might imagine, a variety of ways to accomplish this--some of them extremely archaic but still being used today.
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