A display apparatus for use with a cathode-ray tube capable of displaying patterns in interlaced scanning and non-interlaced scanning operation modes, comprising a composite video signal synthesizer, a memory for storing pattern data, a mode setting circuit for the memory, a data selection signal generator and a raster line number signal generator. The memory stores data for relatively simple patterns such as alphabetical letters and those for relatively complicated patterns such as Chinese characters in individually particular areas in the memory addresses of these different areas are identified by a combination of the data selection signal and the raster line number signal supplied to the memory from the data selection signal generator and the raster line number signal generator. Accordingly, the apparatus is capable of displaying both relatively simple and relatively complicated patterns with satisfactory resolution and with a relatively small-scale structure.

A video display apparatus for composing video signals for a raster scanned display on a line-by-line basis. Objects are stored in a video RAM and are packed in the RAM without regard to their location on the display. A separate dispatch table contains information on each object and commands. A dispatcher operates on this information, allowing lines of data and commands to be extracted from the RAM as each video line is composed in a buffer.

A method of selectively displaying data, whereby the data is arranged in a consecutive series of data-blocks, each data-block being a matrix of information such as a Lofargram. The method comprises selecting an initial set of data-blocks from the series of data-blocks, wherein the initial set of data-blocks comprises an initial data-block and every following nth data-block in the series and then displaying this initial set. The method includes displaying different sets of data-blocks subsequent to the initial set. Each different set of data-blocks comprises an initial data-block, differing from the initial data-block of the preceeding set by an integer m, and every subsequent nth data-block in the series. The method further comprises, displaying a reference data-block adjacent to any one of the sets of data-blocks for comparing with any one of the data-blocks in the series.

A video display memory expansion system for expanding the graphics memory within the video display. The memory expansion system is suited for increasing the resolution of a graphics display from a low-resolution to a high-resolution display. A video display device is adapted to receive a relatively simple graphics memory expansion accessory to thereby easily and inexpensively provide the increased graphics memory capability.

An image synthesizer of an image editing apparatus not only stores image data of two or more source images and includes a display device for displaying an image according to received image data, but also is provided with an address generator which, controlled by a data processor, transmits address signals sequentially to have a synthesized image of these source images displayed such that the individual source images appear superposed and transparent to each other. Each pixel of the display device displays only one of the source images and area densities of pixels displaying each of the source images very over the two-dimensional screen of the display device. When one of the source images is superposed on top of another, a pattern is stored in a pattern memory such that pixels displaying one of the images are scattered into the area of the other image according to the pattern such that the boundary between source images can be made controllably less conspicuous.