Abstract: In a video conference between N parties, each video conferencing terminal produces a respective video signal comprising, in the case of the National Television Standard Committee (NTSC) standard, sixty fields per second. The input video signals are input to an analog multi-point control unit which selects every Nth field from each input video signal and derives therefrom a single output video signal also of sixty fields per second, in which consecutive fields are derived cyclically from each of the N input video signals in turn. The single output video signal is transmitted to each video conferencing terminal, which separates out the fields of the input video signals present in the single output video signal to provide N individual reduced field rate video signals each comprising 60/N fields per second and each having fields derived from a respective one of the input video signals.

Abstract: The present invention relates a communication terminal for the synchronization of audio and visual information within a communication system. Audio communication between the parties to a video conference is achieved by digitizing the speech and transmitting the same over a packet based data network. Each party to the conference can draw the attention of the other party to an object on the screen using a pointer controlled by, say, a mouse or ball. The co-ordinates of each parties' pointer are incorporated, via a multiplexer, into the data packets containing the digitized speech and transmitted to the other party's terminal thereby ensuring the synchronization the pointer information with the digitized speech.

Abstract: In a memory addressable by row and by column and operable in page mode whereby multiple column cycles are performed within a single row cycle, an arrangement is provided for stepping the row address for selected column cycles whereby sustained page mode operation can be provided throughout memory address space. Preferably, stepping occurs in response to a row change signal supplied when a column address strobe becomes active and the direction of stepping is determined by a mode signal supplied when a row address strobe becomes active. Memory segmentation is employed to facilitate simultaneous activation and restoring of multiple rows.

Abstract: A computer graphics system includes display logic (92) comprising a destination bit map (11) containing a plurality of image bits which map to a plurality of pixels for presenting an image, an auxiliary bit map (1) containing a plurality of area boundary bits representing pixels defining an area boundary line which encloses an area of the image, area filling logic (7) for operating upon those image bits enclosed by the area boundary line in order to fill the area with a particular pattern and color, characterized in that the display logic further comprises area boundary drawing logic (5) having line segmentation means to resolve the specified boundary line into a plurality of intersecting two pixel line segments which can, from that time forward, be operated upon separately to define the area boundary bits in accordance with conventional area boundary drawing rules.

Abstract: A digital arithmetic logic unit in which the carry chain is subdivided into a series of bit fields allowing independent and simultaneous data manipulation to be undertaken in each of the bit fields. Division of the carry chain is achieved via a carry chain selector consisting of a series of multiplexers, one being placed between each pair of adjacent stages of the carry chain. Each multiplexer has two data inputs, one of which forms the carry to the next stage of the carry chain. The carry selected either continues the computation or defines the end of one bit field and provides the least significant carry-in bit to the next bit field. This selection of the carry by the multiplexer is under control of a programmable register, thus allowing variable division of the carry chain.

Abstract: In a line generator and a method for determining the individual pixels to be plotted for a line to be drawn in a display system, coded representations of a plurality of lines are stored in a line definition table. The coded representation of each individual line is a string of data items representing the transitions between adjacent pixels to be plotted for drawing the individual line. Preferably, only coded representations of lines up to a predetermined size (i.e. the length of the line in the case of a straight line) are stored in the line definition table. Strings of data items for representing the pixels to be plotted for longer lines to be drawn are still calculated as in the prior art. In this case, control logic determines whether there are coded representations of a line to be drawn in the line definition table, or not, and passes control to appropriate processing logic for determining the pixels to be plotted.

Abstract: A graphics processing system has the capability of generating a map of an image in terms of the individual picture elements or pixels from data defining the boundaries of component areas of the image. The disclosed generating system comprises a plurality of paired storage locations, called a convex area table, with each pair of locations being associated with a line of individual picture elements on the image. Processing logic computes display line and displacement values for a component area of the pair of storage locations for the corresponding display line. The stored displacement values can then be used for generating the full pixel map of the image.

Abstract: In a method of storing characters in a display system having a display device with an orthogonal matrix of addressable points, each character is represented as a succession of strokes each constrained to lie in one of the eight fundamental directions of the matrix and, except for the first stroke, each starting at the end of the previous stroke. Each such stroke is stored in a binary coded form which includes a first binary number (direction code) defining the angular direction of the stroke, a second binary number (length code) defining a number of matrix steps from one addressable point to the next along the stroke in that direction, and a third binary number (move/draw code) defining the visibility of the stroke. In order to facilitate character rotation by any multiple of 45.degree. the direction code defining each fundamental direction corresponds to the addition modulo 2.sup.n of a binary constant to the direction code which defines the fundamental direction of 45.degree.

Abstract: The invention concerns a graphics display system of the kind having a refresh raster display device, a line clipping mechanism for clipping line primitives for viewing in a selected rectangular viewport having horizontal and vertical edges parallel to the X and Y axes respectively of the display area of the display device, and a vector-to-raster converter for converting the clipped lines to patterns of discrete pels in a refresh buffer, the vector-to-raster converter including an incremental line drawing mechanism responsive to line information supplied by the clipping mechanism to draw the line starting at one endpoint and proceeding towards the other.