Browse Prior Art Database

Compressed Refresh System for Use With CRT Image Display

IP.com Disclosure Number: IPCOM000089370D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 78K

Publishing Venue

IBM

Related People

Chesarek, DJ: AUTHOR

Abstract

In the compressed refresh system shown in Fig. 1, a high decompression bit rate is achieved by multiple decompressors 22, 24 operating independently and in parallel. The use of multiple decompressors requires independent compressed data for each scan line. A decompressor-compressor translator pair 12, 14 connected to control unit 10 translates the image information from a representation which minimizes storage efficiency to one which optimizes display refresh cost. The compression algorithm chosen for display refresh use is designed to balance average compression efficiency against worst-case compression inefficiency.

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Compressed Refresh System for Use With CRT Image Display

In the compressed refresh system shown in Fig. 1, a high decompression bit rate is achieved by multiple decompressors 22, 24 operating independently and in parallel. The use of multiple decompressors requires independent compressed data for each scan line. A decompressor-compressor translator pair 12, 14 connected to control unit 10 translates the image information from a representation which minimizes storage efficiency to one which optimizes display refresh cost. The compression algorithm chosen for display refresh use is designed to balance average compression efficiency against worst-case compression inefficiency.

Because of the dynamics associated with the bit rate from the decompressors 22, 24, the decompressors are isolated from the display by use of refresh unit buffers 26, 28. These buffers not only isolate the decompressors from the display but also serve to reduce the average data rate by extending the averaging over several scan lines.

First, the process of loading the compressed image data store 18 and the compressed data length increment store 20 are described, and then the scan line mapping which establishes the processing of information between the compressed image data storage 18 and the display head.

Data is supplied to the compressed refresh system from the control unit 10 in either of two forms - compressed or uncompressed. In compressed form, the data bit stream is directed to display decompressor 12 where the compressed data is decompressed to raw bit stream format. The algorithm used in decompressor 12 is designed to minimize storage requirements. Raw bit format data is sent directly to the display compressor 14. The algorithm used in the display compressor 14 is designed to balance worst-case compression against average compression. The address generation logic 16 associated with compressor 14 develops a stream of addresses required to store the compressed image data for each scan line in the compressed image data storage unit 18. In addition to developing the address stream for the compressed image data storage, the address generation logic develops the incremental length count for the compressed representation of each scan line, and its storage address (e.g., scan line number) in the compressed data length increment store
20. The compressed representation of a scan line is a variable length string. In order to provide efficient and fast string addressing for refresh address generation, the length of the compressed representation of each scan line is held in the compressed data length increment store 20. When the entire input image has been translated and stored in the compressed image data storage, a compressed refresh cycle begins.

In order to understand how the decompressors parallel process compressed data into the refresh unit buffers and how the refresh unit buffers deliver uncompressed image data to the display head, consider the scan line map...