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Encoding Schemes for Video Disk

IP.com Disclosure Number: IPCOM000053028D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Tseng, SC: AUTHOR

Abstract

In the video disk described below information is written by burning holes with a laser in a layer of thin film which is deposited on a disk substrate.

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Encoding Schemes for Video Disk

In the video disk described below information is written by burning holes with a laser in a layer of thin film which is deposited on a disk substrate.

Multi-level (analog) signals can be represented by different sizes of holes on such a disk. For instance, the smallest optically readable hole size is D=0.8 micron in diameter. This minimum size hole can be used as one level of signal, say, representing a value zero. Let us call this minimum size hole a BASIC hole. Then the next level signal can be represented by a larger hole which is slightly elongated in the direction of the recording track. The width of this elongated hole is still D, but the length of this hole in the direction of the recording track is 1=D+d. Thus the nth level signal can be represented by a length of 1=D+nd. The minimum detectable increment d is typically 0.04 micron.

When a multi-level information signal has sign as well as magnitude, one must represent negative as well as positive numbers with holes in the video disk.

The first method described is for bipolar multi-level signals. In this method it is assumed that the space between holes can not be used for encoding. The negative sign is represented by a basic hole. Positive levels +n are represented by elongated holes of length 1=D+(n+1)d, where n=0,1,2,3,.... Negative levels -n are represented by a basic hole followed by an elongated hole of length 1=D+nd, where n=1,2,3,.... Fig. 1 illustrates the method for typical codings.

A second method will now be described for encoding bipolar signals. In this method, it is assumed that the space between holes as well as the size of the hole can be used for encoding. The magnitude of the level ||n|| is encoded by an elongated hole of 1=D+nd, n=0,1,2,3,.... The space following this hole is S, if the number is positive. The space following this hole is S+s, if the number is negative, where s is the minimum detectable increment in addition to S. Fig. 2 illustrates this second encoding method.

A third more compact method will now be described for encoding unipolar signals. Without loss of generality, let us discuss the case for encoding 16 levels of unipolar signals on a video disk. The most straightforward implementation of encoding unipolar signals would be to represent the nth level signal by an elongated...