Browse Prior Art Database

Background Transparency using a Transparent Color

IP.com Disclosure Number: IPCOM000041017D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Fortino, RS: AUTHOR

Abstract

Disclosed is an implementation of a background transparency attribute for alphanumeric, graphic, and image data in an all points addressable (APA) display device in which multiple presentation spaces are combined immediately prior to processing for display on the CRT. The implementation eliminates the need for a separate background transparency attribute plane in each such presentation space, thereby reducing the cost of implementation.

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Background Transparency using a Transparent Color

Disclosed is an implementation of a background transparency attribute for alphanumeric, graphic, and image data in an all points addressable (APA) display device in which multiple presentation spaces are combined immediately prior to processing for display on the CRT. The implementation eliminates the need for a separate background transparency attribute plane in each such presentation space, thereby reducing the cost of implementation.

In conventional implementations of multiple presentation space architecture, a character generator continuously generates the proper stream of pixel data to present the alphanumeric information stored in a character attribute buffer for overlay over a second stream of pel data from a graphics APA presentation space. Conventionally, the overlaying operation is controlled by a background transparency attribute. When the background transparency attribute bit is set, the color overlay is suppressed, allowing the underlying graphic information to be viewed.

The elimination of the background transparency attribute plane is achieved by dedicating a stored pixel color value to the indication of background transparency. This "color" can be detected in order to trigger the aforementioned suppression function. This results in the loss of one color that would otherwise be available for display. For example, if N planes are used to store the pixel color value, in prior art implementations, 2N c...