A webcam, a computer camera, is a video camera, and input device that feeds or streams its image in real time to or through a computer to a computer network. When “captured” by the computer, the video stream may be saved, viewed or sent on to other networks via systems such as the internet, and emailed as an attachment. When sent to a remote location, the video stream may be saved, viewed or on sent there.
Unlike an IP camera (which connects using Ethernet or Wi-Fi), today, most webcams are either embedded into the display with laptop computers or connected to the USB or FireWire port on the computer.
How does a webcam or computer camera work?
Photo: Unlike the computer camera, which you can focus by twisting its lens, this Microsoft LifeCam VX-800 has a preset focus. If you look closely, you can just see the power indicator light (top left, not currently lit up) and the microphone (top right). The stand can simply rest on a table or open up to clip on top of your laptop.
A computer camera is a compact digital camera you can hook up to your computer to broadcast video images in real time (as they happen). Just like a digital camera, it captures light through a small lens at the front using a tiny grid of microscopic light-detectors built into an image-sensing microchip (either a charge-coupled device (CCD) or, more likely these days, a CMOS image sensor).
The image sensor and its circuitry converts the picture in front of the camera into digital format—a string of zeros and ones that a computer knows how to handle. Unlike a digital camera, a webcam has no built-in memory chip or flash memory card: it doesn’t need to “remember” pictures because it’s designed to capture and transmit them immediately to a computer. That’s why webcams have USB cables coming out of the back.
The USB cable supplies power to the webcam from the computer and takes the digital information captured by the webcam’s image sensor back to the computer—from where it travels on to the Internet.
How does an image sensor convert a picture into digital form?
When you take a digital photo or stare into your webcam, light zooms into the lens. This incoming “picture” hits the image sensor, which breaks it up into individual pixels that are converted into numeric form. CCDs and CMOS chips, the two kinds of image sensor, do this job in slightly different ways. Both initially convert incoming light rays into electricity, much like photoelectric cells (used in things like “magic eye” intruder alarms or restroom washbasins that switch on automatically when you put your hands under the faucet). But a CCD is essentially an analog optical chip that converts light into varying electrical signals, which are then passed on to one or more other chips where they’re digitized (turned into numbers).
By contrast, a CMOS chip does everything in one place: it captures light rays and turns them into digital signals all on the one chip. So it’s essentially a digital device where a CCD is an analog one. CMOS chips work faster and are cheaper to make in high volume than CCDs, so they’re now used in most low-cost cellphone cameras and webcams. But CCDs are still widely used in some applications, such as low-light astronomy.
Whether images are being generated by a CMOS sensor or a CCD and other circuitry, the basic process is the same: an incoming image is converted into an outgoing pattern of digital pixels. Let’s just refer to “the image sensor” from now on (and forget about whether it’s a CCD and other chips or a CMOS sensor). First, the image sensor measures how much light is arriving at each pixel. This information is turned into a number that can be stored on a memory chip inside the camera. Thus, taking a digital photograph converts the picture you see into a very long string of numbers. Each number describes one pixel in the image—how bright or dark and what color it is.
The most popular use of webcams is the establishment of video links, permitting computers to act as videophones or videoconference stations. Other popular uses include security surveillance, computer vision, video broadcasting, and for recording social videos.
The video streams provided by webcams can be used for a number of purposes, each using appropriate software:
Most modern webcams are capable of capturing arterial pulse rate by the use of a simple algorithmic trick. Researchers claim that this method is accurate to ±5 bpm.
Webcams may be installed at places such as childcare centres, offices, shops and private areas to monitor security and general activity.
Computer cameras have been used for augmented reality experiences online. One such function has the webcam act as a “magic mirror” to allow an online shopper to view a virtual item on themselves. The Webcam Social Shopper is one example of software that utilizes the webcam in this manner.
Videocalling and videoconferencing
Further information: Videophone, Videoconferencing, and Videotelephony
Webcam can be added to instant messaging, text chat services such as AOL Instant Messenger, and VoIP services such as Skype, one-to-one live video communication over the Internet has now reached millions of mainstream PC users worldwide. Improved video quality has helped webcams encroach on traditional video conferencing systems. New features such as automatic lighting controls, real-time enhancements (retouching, wrinkle smoothing and vertical stretch), automatic face tracking and autofocus, assist users by providing substantial ease-of-use, further increasing the popularity of webcams.
Webcam features and performance can vary by program, computer operating system, and also by the computer’s processor capabilities. Video calling support has also been added to several popular instant messaging programs.
Webcams can be used as security cameras. Software is available to allow PC-connected cameras to watch for movement and sound, recording both when they are detected. These recordings can then be saved to the computer, e-mailed, or uploaded to the Internet. In one well-publicised case, a computer e-mailed images of the burglar during the theft of the computer, enabling the owner to give police a clear picture of the burglar’s face even after the computer had been stolen.
Video clips and stills
Webcams can be used to take video clips and still pictures. Various software tools in wide use can be employed for this, such as PicMaster (for use with Windows operating systems), Photo Booth (Mac), or Cheese (with Unix systems).
Input control devices
Special software can use the video stream from a webcam to assist or enhance a user’s control of applications and games. Video features, including faces, shapes, models and colors can be observed and tracked to produce a corresponding form of control. For example, the position of a single light source can be tracked and used to emulate a mouse pointer, a head-mounted light would enable hands-free computing and would greatly improve computer accessibility. This can be applied to games, providing additional control, improved interactivity and immersiveness.
FreeTrack is a free webcam motion-tracking application for Microsoft Windows that can track a special head-mounted model in up to six degrees of freedom and output data to mouse, keyboard, joystick and FreeTrack-supported games. By removing the IR filter of the webcam, IR LEDs can be used, which has the advantage of being invisible to the naked eye, removing a distraction from the user. TrackIR is a commercial version of this technology.
The EyeToy for the PlayStation 2, PlayStation Eye for the PlayStation 3, and the Xbox Live Vision camera and Kinect motion sensor for the Xbox 360 and are color digital cameras that have been used as control input devices by some games.
Small webcam-based PC games are available as either standalone executables or inside web browser windows using Adobe Flash.
With very-low-light capability, a few specific models of webcams are very popular to photograph the night sky by astronomers and astro photographers. Mostly, these are manual-focus cameras and contain an old CCD array instead of comparatively newer CMOS array. The lenses of the cameras are removed and then these are attached to telescopes to record images, video, still, or both. In newer techniques, videos of very faint objects are taken for a couple of seconds and then all the frames of the video are “stacked” together to obtain a still image of respectable contrast.
Laser beam profiling
A webcam’s CCD response is linear proportional to the incoming light. Therefore, webcams are suitable to record laser beam profiles, after the lens is removed. The resolution of a laser beam profiler depends on the pixel size. Commercial webcams are usually designed to record color images. The size of a webcam’s color pixel depends on the model and may lie in the range of 5 to 10µm. However, a color pixel consists of four black and white pixels each equipped with a color filter (for details see Bayer filter). Although these color filters work well in the visible, they may be rather transparent in the near infra-red. By switching a webcam into the Bayer-mode it is possible to access the information of the single pixels and a resolution below 3µm was possible.
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