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Interleaved Smoothing Raster for Vector CRT Displays

IP.com Disclosure Number: IPCOM000088146D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Axford, JG: AUTHOR

Abstract

When a normal discrete picture element (pel) raster scan CRT (Cathode-ray tube) is used to display vectors (that is, lines) at orientations other than 0 Degrees and 90 Degrees to the raster lines, the resulting visual image is marred by the visibility of individual pels giving a staircasing or graininess effect. This is particularly true of lines at a shallow angle to the horizontal. This places the raster CRT at a disadvantage compared with the alternative directed beam method of creating the image, the latter being intrinsically more suitable for vector graphics displays.

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Interleaved Smoothing Raster for Vector CRT Displays

When a normal discrete picture element (pel) raster scan CRT (Cathode-ray tube) is used to display vectors (that is, lines) at orientations other than 0 Degrees and 90 Degrees to the raster lines, the resulting visual image is marred by the visibility of individual pels giving a staircasing or graininess effect. This is particularly true of lines at a shallow angle to the horizontal. This places the raster CRT at a disadvantage compared with the alternative directed beam method of creating the image, the latter being intrinsically more suitable for vector graphics displays.

The appearance of the raster CRT can be improved by inserting a displaced or smoothing raster (or rasters) in between the lines of the normal raster. The pels of the displaced raster are calculated `on-the-fly', and the system thus involves no increase in buffer cost or data rate from the buffer. The method does, however, demand line scanning at a multiple of the normal rate. The method described is specifically intended for graphics applications where the material displayed contains a high proportion of one-pel wide long straight lines that have been transformed from a vector display list to raster form.

The simplest system (Fig. 1) consists of one intermediate raster and involves interpolation from just four adjacent pels. The normal bit stream from the refresh bit buffer is loaded into two line-lone shift registers 7 and B which thus contain consecutive lines. A group of four latches on tie end creates the conventional moving window as the data is shifted through. A smoothing or interpolation function F operates on the state of these four latches to create the input to a third shift register C which provides the bit stream for the intermediate raster line. The interpolation function F can be chosen to suit the type of data. The logic to implement...