International Business Machines Corporation

Robert W Farr

Ian David Judd

Ronald John Bowater

David Andrew Clarke

Michael I Davis

Colin V Powell

A curve generator for a display system with an arc generator has for generating an arc (10) of a circle (14) from data defining the locations of two end points P.sub.1 and P.sub.3 and an intermediate point P.sub.2 on the arc. The arc generator has an initializer (40) for calculating the angle subtended between a first vector (21), from a first of the end points, P.sub.1 to the intermediate point P.sub.2, and a second vector (32), from the second of the end points P.sub.3 to the intermediate point P.sub.2, and an arc plotter (44) for defining a succession of further vectors n1 from the first end point P.sub.1 and for calculating, for each further vector, its point of intersection P.sub.n with a counterpart vector 3n, from the second end point P.sub.3, with which it subtends the same angle, whereby a succession of further points P.sub.n are plotted on the circular arc.

Curve generation in a display system

The specification describes a method of storing alphanumeric characters in a graphics display terminal comprising a raster-scan display device and a refresh buffer including a plurality of bit planes each having a respective bit storage location corresponding to each addressable pel position on the screen of the display device. In the method, a first bit plane stores high resolution luminance data defining alphanumeric characters each as a selection of 'on' bits within a respective n.times.m array where n is the width of the character box in the scan line direction, and at least one further bit plane stores low resolution color data for the characters. The attribute plane comprises a respective n-bit set of storage locations which corresponds to each n-bit wide by one pel deep portion of a character box in the luminance plane and defines at least the color and/or intensity of the foreground and background of the character for the width of the character box in respect of a single scan line. The specification also describes a graphics display terminal in which data in the luminance and attribute planes may be selectively decoded either as alphanumeric data stored as above, or as bit-mapped graphics data.

Graphics display terminal and method of storing alphanumeric data therein

In order to compensate for image distortion introduced into a digitally-controlled raster-scan CRT by the finite video amplifier rise and fall times, the digital video drive waveform is subject to selective pulse stretching to extend where possible the duration of pels which represent critical features of the image. This is achieved by decoding means for examining each pel at least in relation to its two immediate neighbors on either side in order to detect predetermined relationships between the values of the pels, and retiming means for selectively advancing or delaying the transitions between consecutive pels of different value in accordance with the relationships so detected. In one embodiment, suitable for multibit or single bit video, the decoding means comprises means (40, 25) for comparing each pel with its immediate successor, a shift register (26 to 28) for storing the result of each comparison together with the results of a plurality of immediately preceding comparisons, and a logic circuit (30 to 33) connected to the shift register stages, and the retiming means comprises a delay path (41 to 44) for the waveform having an output register (44) and means (34 to 39) responsive to the logic circuit for clocking the output register at a predetermined time in relation to non-selected transitions, earlier than the said predetermined time in relation to transitions selected for advancement, and later than the said predetermined time in relation to transitions selected for delay.

Growing community of inventors

Eastleigh, United Kingdom

Robert W Farr