Document cameras, also known as visual presenters, visualizers (in the United Kingdom), digital overheads, or docucams, are real-time image capture devices for displaying an object to a large audience. Like an opaque projector, a document camera is able to magnify and project the images of actual, three-dimensional objects, as well as transparencies. They are, in essence, high resolution web cams, mounted on arms so as to facilitate their placement over a page. This allows a teacher, lecturer or presenter to write on a sheet of paper or to display a two or three-dimensional object while the audience watches. Theoretically, all objects can be displayed by a document camera. Most objects are simply placed under the camera. The camera takes the picture which in turn produces a live picture using a projector. Different types of document camera/visualizer allow great flexibility in terms of placement of objects. Larger objects, for example, can simply be placed in front of the camera and the camera rotated as necessary,or a ceiling mounted document camera can also be used to allow a larger working area to be used.
Typical applications for a document camera include:
- Lecture hall or classroom use
- Presentation of material in conferences, meetings and training sessions
- Videoconferencing and telepresence
- Presentation of evidence in courtrooms
- Various medical applications (telemedicine, telepathology, display of x-rays)
Document cameras replaced overhead projectors, which were formerly used for this purpose. By means of the zoom feature a document camera can enlarge the small print in books and project a printed page as if it were a traditional transparency. Also the room lighting does not have to be darkened to operate a document camera; in a classroom setting this is an asset. Most document cameras can also send a video signal to a computer via USB cable. Sometimes document cameras are connected to an interactive whiteboard instead of a standard screen.
Some document cameras can be supplied with an accessory so that they can be used with a microscope. According to recent research by Futuresource Consulting over 11k visualisers were sold in UK in 2008 and Futuresource forecasts that over 17,000 will be sold in 2009. The market is valued at £12 million in 2009 increasing 53% in 2010 to £18 million. One in 30 UK school classrooms now have a visualiser. That is expected to increase to 1 in 10 by 2010.
As of 2008, the most economical document cameras capture XGA resolution images of 1024×768 pixels. Document cameras that capture SXGA images capture a resolution of 1280×1024 which equates to 66% more pixels than XGA images. Higher-resolution images contain more (smaller) pixels and provide sharper detail. UXGA is considered high-definition and equates to 1920×1080 pixels.
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