Nipkow disk

A Nipkow disk is a mechanical, geometrically operating image scanning device (by itself, it performs neither image acquisition or reproduction), invented by Paul Gottlieb Nipkow, which was primarily used as a fundamental component in mechanical television.

How it works

A lens projects an image of the scene in front of it directly onto the disk http://users.swing.be/philippe.jadin/nipkowdisk.htm. Each hole in the spiral takes a horizontal "slice" through the image which is picked up as a pattern of light and dark by a sensor. If a light powered by a signal from the sensor is placed behind a second Nipkow disk rotating in synch at the same speed and direction, the image can be reproduced line-by-line, however it remains no larger than the one projected onto the original receiving disk.

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When spinning the disk while observing an object "through" the disk, preferably through a relatively small circular sector of the disk (the viewport), for example, an angular quarter or eighth of the disk, the object seems "scanned" line by line, first by length or height or even diagonally, depending on the exact sector chosen for observation.

Related Topics:
Circular sector - Viewport

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By spinning the disk rapidly enough, the object seems complete, in a way

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similar to cinematography, and capturing of motion becomes possible.

Related Topics:
Cinematography - Motion

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This can be intuitively understood by covering all of the disk but a small

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rectangular area with black cardboard (which stays fixed), spinning the disk and observing an object through the small area.

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Here arises one of the drawbacks of the Nipkow disk as an image scanning

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device: the scanlines are not straight lines, but rather curves.

Related Topics:
Scanlines - Curves

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So the ideal Nipkow disk should have either a very large diameter, which means smaller curvature, or a very narrow angular opening of its viewport. Another way would be that of drilling smaller holes (millimeter or even micrometer scale) closer to the outer sectors of the disk, but technological evolution favoured electronic means of image acquisition.

Related Topics:
Curvature - Angular - Millimeter - Micrometer - Electronic

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