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OVERLAY PLANES IN DIGITAL IMAGE DISPLAYS

IP.com Disclosure Number: IPCOM000025871D
Original Publication Date: 1988-Aug-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 80K

Publishing Venue

Xerox Disclosure Journal

Abstract

The display refresh memories in modern digital image displays, in addition to the planes used to store the image pixels, frequently also provide "overlay" planes. The image is shown by sending the stored image pixels through lookup tables, which can be used to modify the colors (or gray shades) displayed. That is, each pixel value is used as an address to the lookup table and the table value is used as the color to display. The overlay planes are typically connected as the most significant bits in the address to the lookup table. For example, the lookup table may be 1024 elements long, thus requiring a 10-bit address. The stored image would provide the lower 8 bits and 2 overlay planes would provide the upper 2 bits of the address. As a result, the appearance of an image stored in display memory can be modified in real-time, simply by changing the values within the lookup tables.

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XEROX DISCLOSURE JOURNAL

OVERLAY PLANES IN DIGITAL IMAGE DISPLAYS U.S. C1.358/29 Paul G. Roetling

Proposed Classification

Int. C1. H04n 9/64

The display refresh memories in modern digital image displays, in addition to the planes used to store the image pixels, frequently also provide "overlay" planes. The image is shown by sending the stored image pixels through lookup tables, which can be used to modify the colors (or gray shades) displayed. That is, each pixel value is used as an address to the lookup table and the table value is used as the color to display. The overlay planes are typically connected as the most significant bits in the address to the lookup table. For example, the lookup table may be 1024 elements long, thus requiring a 10-bit address. The stored image would provide the lower 8 bits and 2 overlay planes would provide the upper 2 bits of the address. As a result, the appearance of an image stored in display memory can be modified in real-time, simply by changing the values within the lookup tables.

One use of this design is to allow separate modification of multiple images, or of separate parts of any image. For the standard display, the overlay planes would be cleared, that is, set to zero, and in the example given above, the 8-bit images would be displayed through the part of the lookup table between addresses 0 and 255. If some part is now to be controlled separately, the area of an overlay plane corresponding to the area to be treated sepa...