Browse Prior Art Database

Vector Generation on a TV Monitor

IP.com Disclosure Number: IPCOM000076353D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Duke, KA: AUTHOR

Abstract

A standard TV monitor, because of its low cost, is an attractive candidate for a computer terminal display device. Much work has been done to enable coded alphanumeric characters to be displayed on a TV monitor using local decoding and refresh techniques. Fig. 1 shows a logical method of displaying coded vectors on a TV monitor using local decoding and refresh techniques.

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Vector Generation on a TV Monitor

A standard TV monitor, because of its low cost, is an attractive candidate for a computer terminal display device. Much work has been done to enable coded alphanumeric characters to be displayed on a TV monitor using local decoding and refresh techniques. Fig. 1 shows a logical method of displaying coded vectors on a TV monitor using local decoding and refresh techniques.

A U.S. standard TV picture is scanned in 525 lines, 30 times per second. The vertical scan frequency is 60 frames per second, alternate lines being scanned on alternate frames. This "interlacing" is introduced to reduce the flicker apparent to the viewer. The horizontal to vertical "aspect ratio" of the picture is 4:3 and thus, the active picture area may conveniently be divided into 680 x 512 coordinate positions. (Then only 9 binary bits are needed to specify the vertical position of any point).

To define a vector it is necessary to specify one of the following sets of parameters: 1) The complete coordinates of both ends of the vector. 2) The complete coordinates of one end, the slope of the vector and its length. 3) The complete coordinates of one end, the slope of the vector and one coordinate of the other end.

The last set is the most convenient to use in the present context, though care must be taken in the cases of exactly vertical and horizontal lines to choose the appropriate coordinate of the other end. A slight modification of the specification of the slope and the horizontal coordinate of the initial end of the vector is therefore introduced.

In general, a vector will be displayed as a series of horizontal bars. The bar on each scan line will begin where the bar on the adjacent line finishes. An example is shown in Fig. 2.

The slope of a vector may clearly be defined by specifying the length of the bar on each scan line. A complete vector may thus be defined by specifying: 1) The scan line on which it first appears (y) 2) The horizontal position of that same end (x) 3) The length of each bar (l) 4) The line on which the vector last appears (y').

If the vector has a negative slope, the first part of the vector to be scanned is not the end point but the left-hand end of the first bar, (see Fig. 2). It is, therefore, convenient to specify the vector in terms of that point rather than its true end coordinate, and to specify the slope of the line as the bar length wi...