This invention provides a simple system for simultaneous raster scan display of video and alpha-numeric data on a single screen with provision for periodic image refreshment. It includes means for encoding the electrical signals representing the spatial intensity distribution of the video signal and the alpha-numeric signal. The coded signals are stored in a single bit map memory at the desired addresses. For display, the information is simply read from the memory through a single digital-to-analog convertor.

A video signal processing circuit receiving an input sample data relating to sample positions in a video field and in association with the sample data for each sample position associated z data indicating the apparent position of the sample data in a direction perpendicular to a video display of the video field, a first memory for storing the sample data relating to each sample position in the video field, a second memory for storing the z data relating to each sample position in the video field, and a comparator circuit for comparing for each sample position in the video field the value of the input said data with the z data for that sample position stored in the second memory and for supplying a write enable signal only if the value of the input z data represents a sample position in front of that represented by the stored data, the input sample data being written into the first memory and the new z data being written into the second memory under control of a write enable signal.

A video system for assisting automobile traffic is provided. Radio frequency signals concerning traffic flow and build-up are transmitted to a receiver unit contained within a motor vehicle. The receiver unit contains road map information stored in a memory and only information relating to traffic flow is transmitted. The receiver superimposes the traffic flow information with the map information to produce a composite image of traffic conditions. The traffic flow informationis updated and stored in a memory while obsolete information is blanked out so that current traffic information may be presented to the viewed.

An image register for a graphics display includes a pair of static random access memory (SRAM) devices for respectively storing image data associated with even numbered and odd numbered pixels, which correspond to even numbered and odd numbered addresses. The register includes a counter presettable to an initial value corresponding to a starting address of the stored image data. When the counter outputs an even address (an even state), the even SRAM is enabled for a write operation if an input layer code has a higher priority than the priority of the layer code for the image data stored in the even SRAM, although the odd SRAM is always enabled for a read operation in the even state. The read and write operations occur simultaneously. During the read operation on the odd SRAM, the layer code portion of the image data retrieved therefrom is latched in an associated buffer, whose output is fed to an associated comparator. When the counter is incremented during the next clock cycle, the counter outputs an odd address (an odd state), wherein the odd SRAM is enabled for a write operation if an input layer code has a higher priority than the priority of the retrieved layer code buffered from the prior cycle, although the even SRAM is always enabled for a read operation in the odd state. Both operations occur simultaneously. In both the even and odd states, if the priority of the input layer code is not higher than the priority of the layer code associated with the current image data, the original image data is retained in the even and odd SEAMs, respectively.

The invention relates to a system for giving an audio-visual presentation consisting of a basic part and at least a complementary part, such as a video film. The system comprises different storage media for storing the basic part and the complementary pan and merging means for merging the basic part with the complementary part into the audio-visual presentation. The complementary part is intended for enhancing the audio-visual presentation quality that can be achieved with the basic part. A provider may provide a basic part free of charge on a CD-i disc, after which the user is to pay for the complementary pan which may be transmitted to him via a telephone line from a databank.