IP Cameras & Projectors: Image Quality

Firstly cheap IP security cameras are generally wide-angle, but a camera on the back wall of a seminar room needs to be fairly narrow. A security camera with an optical zoom is the simplest solution which will still give a good quality image.

a washed-out projector screen

The next problem is the large range of brightnesses present between the room, especially if there is a blackboard, and a projector screen, where the "blacks" are actually quite bright white (think what happens when the projector is turned off), and the whites are very bright. The above image used a standard camera, and is useless. To improve, one needs some form of high dynamic range compensation. The cheap way of achieving this in a video camera is to shoot each frame twice, with the second frame being shot with a shutter speed of one quarter (or less) of the first. Things which are over-exposed in the first frame will be less over-exposed, or perhaps correctly-exposed, in the second. Then some clever tricks are used to combine the two frames based on the levels of brightness seen in each.

projector screen with rainbows

Many projectors use a technology called DLP. These typically show red, green, blue and white images for about 1/240th of a second each, so building up the whole image in 1/60th of a second. A camera with a fast shutter is unlikely to see the combined image, but is likely to see rainbow-coloured bands, or worse. The above image has wide dynamic range compensation turned on, and the second picture taken for each frame is being taken with a shutter speed of less than 1/60th of a second.

projector screen successfully captured

Fortunately there are projection technologies which are more camera-friendly. Here an LCD projector is used. Epson has an article on this effect, although Epson does not have a monopoly on LCD technology in projectors. The projector used here is actually an NEC one.