In a typical raster scan type cathode ray tube, an image is generated by allowing a scanning electron beam to strike the phosphor on the face of a cathode ray tube only at selected locations and by blanking or keeping off the electron beam as it scans over all other locations. To maintain an image generated in this manner on the cathode ray tube, it is necessary for the electron beam continuously to repeat scanning the same data. To allow this repeated scanning, the data is normally stored in a memory. In the past, the memory in order to be able to address any point on the face of the cathode ray tube had to contain M storage positions where M is equal to the number of scan lines per frame times the number of elements of resolution in one scan line. A display, for example, of 240 visible scan lines and 256 resolvable elements per scan line would require 240.times.256 or 61,440 addressable storage elements. If the beam is to be just on or off at each location, the storage elements are only required to be single bit memories.
The present invention has found that in the special case of a display of a wave form which is single valued in one direction, e.g. perpendicular to the scan line, the number of storage positions need only be equal to the number of resolvable elements in one scan line. Each storage position must be large enough to indicate which scan line the display at the resolvable element it represents is to appear. In the example given above of 240 visible scan lines and 256 resolvable elements, 256 storage positions would be required. Each of the storage positions would have to be able to address any one of the 240 lines. This is to say, each storage position must have the ability to take any one of 240 different values. In the case of a solid state memory made up of memory bits, each bit having two states, each memory position must have N memory bits where 2.sup.N .gtoreq.number of scan lines. To be able to address 240 different scan lines eight memory bits are needed. Thus, 256 memory positions, each with eight bits, uses 2,048 bits of memory as opposed to the 61,440 bits used in a 256.times.240 bit matrix memory. Of course, the present invention applies to displays of any size.
If there is only one storage position for each position on the raster scan lines, then the data at that position can be displayed on only one scan line. Such a display on a cathode ray tube would appear as a series of disjointed points of horizontal line segments, vertical lines could not be displayed. The present invention, without increasing the amount of memory required, generates vertical lines to connect each of the points or horizontal line segments. Thus, the present invention allows any single valued function such as sine wave, series of step functions, exponential, to be stored as discrete points or horizontal line segments, yet be displayed as a continuous function.
The present invention can supply vertical connecting lines, i.e. interpolate, between discrete data points or horizontal line segments.