The present invention relates generally to apparatus for presentation of raster format imagery signals in relocatable inset windows on video displays, and more particularly to such apparatus useful in processing of real-time continuously updated imagery signals within a display generation device.
Although apparatus of this general type are available, they are currently limited in their performance. Many methods of providing continuous image updates to inset windows do not permit arbitrary window size, variable input frequency or relocation of the window to any region of the display. By fixing the size, update rate and location of the inset window, as is popular in picture within picture (pix-in-pix) television receivers, most of the complications of synchronization of input and output signals are avoided. Although this method can be used to obtain an artifact free output signal, it is undesirable for applications requiring multiple input signal formats or relocation of the inset window on the display.
Another method of synchronizing the input signal with the display refresh of the frame buffer uses a parallel double buffer architecture. In this scheme, the display is refreshed out of one buffer, while the input image is loaded into the other. At the end of the display refresh following a conclusion of one input frame, the roles of these two buffers alternate. If the end of the display refresh does not occur prior to the start of the next input frame (as is often the case), it is necessary to hold off input for one frame time or provide some other mechanism to ensure the input data does not overlap the display refresh. This method is undesirable due to the need to periodically interrupt the input signal, causing a lack of continuity in the display output. Also, parallel double buffer architectures provide complications when other processes utilizing other windows are involved since it is necessary to accommodate these activities with the two alternating frame buffers.
Accordingly, it is an object of this invention to provide an image data input interface and memory system which can process real time continuous updates of new image frames, placing the data in relocatable windows on a display.
Another object of the invention is to provide a display free of artifacts while maximizing the display update rate.
A further object of the invention is to provide a display system which operates with any raster image data input over a wide range of input frequencies and display dimensions.