Video compositing using a software linear keyer

• US 4,827,253 A
• Filed: 09/26/1988
• Issued: 05/02/1989
• Est. Priority Date: 05/18/1987
• Status: Expired due to Term

• Current Assignee: The Grass Valley Group, Inc. (Belden Inc.), Discovision Associates (Pioneer Corporation)
• Original Assignee: Dubner Computer Systems, Inc.
• Inventors: Maltz, Ivan J.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Brier, Jeffery A.
• Application Number:
  US07/249,215
• Time in Patent Office: 218 Days
• Field of Search: 340/730, 340/734, 340/735, 340/748, 340/790, 340/701, 340/703, 358/183, 358/22
• US Class Current: 345/640
• CPC Class Codes: H04N 5/275 Generation of keying signals

Abstract

A method for compositing a graphic image with a background image to produce translucent effects identifies a key signal for each portion of the graphic image. The key signal is varied according to the amount of translucency desired for the graphics image from completely transparent to completely opaque. When the graphic image is mixed with the background image, the key signal is used to define the ratio of the graphic image to the background image at each part of the graphic image to produce a mixed image output.

Claims

1. An apparatus comprising:

means for defining a graphics image in an encoded form;

means for providing a key signal in the form of a look-up table value for each portion of the graphics image according to a desired graphics effect;

means for programming the look-up table value independently for each portion of the graphics image to produce the desired graphics effect; and

means for combining the graphics image with a background image according to the key signal to produce a mixed image output incorporating the desired graphics effect.

2. A method for providing translucency of a graphic image comprising the steps of:

defining a key signal in the form of a look-up table value for each portion of the graphic image according to a desired translucency;

programming the look-up table value independently for each portion of the graphics image according to the desired translucency; and

mixing the graphic image with a background image in a proportion determined by the key signal at each portion of the graphics image to produce a mixed image output wherein the graphic image has the desired translucency.

3. A graphics generator comprising:

means for storing a data representation of a graphics image to be composited with a background video signal to produce a desired video effect;

means for decoding the data representation to produce a color address;

means for outputting an encoded video signal representing the graphics image and an associated variable key signal in response to the color address;

means for programming the variable key signal on a pixel by pixel basis in the outputting means as a function of the desired video effect; and

means for combining the encoded video signal and the background video signal according to the variable key signal to produce a composited video signal representing the desired video effect.

4. An improved graphics generator of the type having a memory for storing encoded data representing a graphic image, a decoder for decoding the encoded data to produce a color address, a palette look-up table for outputting color components corresponding to the color address, and means for combining the color components to form an encoded video signal corresponding to the graphic image, wherein the improvement comprises:

means for storing programmable key values in the palette look-up table so that when the palette look-up table is addressed by the color address a variable key signal is output according to a desired video effect; and

a linear keyer having the encoded video signal, a background video signal and the variable key signal as inputs and a composited video signal as an output, the composited video signal being a function of the variable key signal whereby the desired video effect is produced.