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Browse Prior Art Database

Halftones Combining Spatial and Temporal Modulation

IP.com Disclosure Number: IPCOM000050852D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Thompson, DR: AUTHOR

Abstract

Pictorial halftone images that are generated for use on small telephone sized bi-level displays, such as AC plasma storage display devices, are useful but not typically high quality displays in a 256-line with 256 pels (picture elements) per line. A method to configuration provide 3 intensity levels for each pel such that a spatial halftone pattern provides 8 "gray levels" expandable to 24 operates as follows.

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Halftones Combining Spatial and Temporal Modulation

Pictorial halftone images that are generated for use on small telephone sized bi-level displays, such as AC plasma storage display devices, are useful but not typically high quality displays in a 256-line with 256 pels (picture elements) per line. A method to configuration provide 3 intensity levels for each pel such that a spatial halftone pattern provides 8 "gray levels" expandable to 24 operates as follows.

Referring to Fig. 1, a flow diagram of the sequence is illustrated. Original gray level coded data bytes of typically 6-8 bits per pel may be derived from a conventional scanner shown as Gray Level Data/Byte/Pel 1. This data is reduced to 2 high-order bits by a table lookup apparatus 3 which contains 3 threshold values which are repetitive in both X and Y dimensions for each pel in a fixed coded 4 x 4 number matrix, as shown in Fig. 2. The threshold level from table lookup 3 on line 5 is applied through pre-processor 7 to an image buffer 9, which may comprise a read-only memory for generating the appropriate intensity values from the Fig. 2 table and table lookup 3. In the table shown in Fig. 2, the full gray level range will vary between 1 and 24 for the example described herein and varies as the number of cells lit within a given area. With respect to the table of Fig. 2, the gray level range varies from 1 to 24. If the intensity level is 18 or greater, the pel is coded 11; if between 10 and 17, it is coded 10; and between 2 and 9, it is coded 01.

Each pel can achieve three brightness levels by an operational sequence of the plasma display device comprised of an erase cycle followed by 3 write cycles from write/erase apparatus 11, and a time-out for all pel lines in the image. This sequence is then repeated by the 4-step refresh logic 13 at a rate sufficient to provide a fli...