Video magnifier

This article is about tools for visually-impaired people. For image-processing techniques not related to the visually impaired, please create other articles such as Eulerian video magnification.

Video magnifiers are electronic devices that use a camera and a display screen to perform digital magnification of printed materials. The display screen is usually LCD or a similar flat-screen technology (although older video magnifiers have used CRT displays), and the device usually includes a lamp to illuminate the source material. Video magnifiers are designed to be mostly used by people with low vision that cannot be helped using a conventional magnifying glass.

The main benefit of a video magnifier over purely optical magnification is that the video magnifier allows greater magnification across a larger field of view. With optical lenses, the field of meaningful, in-focus view is reduced with increased magnification. Thus, while a "full page magnifier" based on a fresnel lens can span some 625 cm² (A4), it typically achieves no more than 1.4x magnification (advertised as "2x" if measured by area instead of the scale factor); an aspheric segment hand magnifier can achieve a scale factor in excess of 2 (area factor in excess of 4) but typically measures no more than 10 cm x 3 cm, and higher magnification factors require conventional lenses that focus on a very small area. A video magnifier however is limited only by its display size and its electronics; video magnifiers that can be switched between 2 and 50 times magnification are common, and displays can range from smartphone-sized to TV-sized.

Most video magnifiers can automatically focus the image, and the more advanced models are capable of further electronic image processing to change the colours, enhance the contrast, and/or assist in the tracking of images. Some can be set to save "snapshots" of previously-seen images.

Video magnifiers require power, either via mains electricity or from a battery. This may make battery life an issue if the magnifier is required for an extended period of time away from power, whereas a purely optical magnification device could be used indefinitely without needing to be connected to power.

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