US 5,398,075 A · Analog chroma keying on color data

Abstract

A circuit for analog chroma keying on color data permits display of graphics, generated from a computer system, and video on an output display. The analog chroma keying circuit receives the graphics signals and the video signals, wherein the graphics signals include color data to designate a color key. The analog chroma keying circuit includes a plurality of digital to analog converters that generate a plurality of color key limits for defining a range to detect the color data denoting the color key. The analog chroma keying circuit also includes a plurality of comparators coupled to receive the graphics signals and the color key limits for each primary color. The plurality of comparators generate a key on indicator when the graphics signals fall within the color key limits. The key on indicator is input to a plurality of analog switches that couples the graphics signals to the output display when the key on indicator indicates the graphics signals are not within the color key limits, and couples the video signals to the output display when the graphics signals are within the color key limits.

Claims21

Dependent claims

A method for analog chroma keying on color data computer system comprising a high resolution output display, said method comprising the steps of:

generating, in a frame buffer of said computer system, a plurality of pixel indexes, said pixel indexes including said color data to designate a color key;
converting said pixel indexes to a color definitions;
converting said color definition to analog graphics signals;
receiving said analog graphics signals and video signals;
generating analog color key limits for said color key, said color key limits defining a range for each primary color in said graphics signals defining said color key;
comparing said analog graphics signals for each primary color with said analog color key limits to determine whether said analog graphics signals fall within said analog color key limits;
selecting said analog graphics signals for display on an output display when said analog graphics signals are not within said analog color key limits;
and
selecting said video signals for display on said output display when said graphics signals are within said color key limits.

6 more elements

An apparatus for analog chroma keying on color data in a computer system to display graphics and video on a high resolution output display, said apparatus comprising:

a graphics subsystem including:
a frame buffer for storing a plurality of pixel indexes, said pixel indexes including said color data to designate a color key;
a random access memory/digital to analog converter (RAM DAC) coupled to said frame buffer to receive said pixel indexes for converting said pixel indexes to a color definition, and for converting said color definition to analog graphics signals;
color limit generation means for generating color key limits for said color key, said color key limits defining a range for each primary color defining said color key;
comparison means, coupled to receive said graphics signals and to said color limits generation means, for comparing said graphics signals for each primary color with said color key limits to determine whether said graphics signals fall within said color key limits;
and
output display selection means, coupled to said comparison means, and coupled to receive said video signals and said graphics signals, said output display comparison means for selecting said graphics signals for display on said output display when said graphics signals are not within said color key limits, and for selecting said video signals for display on said output display when said graphics signals are within said color key limits.

4 more elements

An apparatus for analog chroma keying on color data in a computer system to display graphics and video on a high resolution output display, said apparatus comprising:

a graphics subsystem including:
a frame buffer for storing a plurality of pixel indexes, said pixel indexes including said color data to designate a color key;
a random access memory/digital to analog converter (RAM DAC) coupled to said frame buffer to receive said pixel indexes for converting said pixel indexes to a color definition, and for converting said color definition to analog graphics signals;
a plurality of digital to analog converters (DACs) for generating a plurality of color key limits for said color key, said plurality of color key limits defining a range for each primary color to define said color key;
a plurality of comparators, coupled to said plurality of DACs to receive said graphics signals and said color key limits for each primary color for generating a key on indicator when said graphics signals fall within said color key limits;
and
a plurality of analog switches coupled to said output display and said plurality of comparators, wherein a first analog switch is coupled to receive said graphics signals and a second analog switch is coupled to receive said video signals, said first analog switch being configured to couple said graphics signals to said output display when said key on indicator indicates said graphics signals are not within said color key limits, and said second analog switch being configured to couple said video signals to said output display when said key on indicator indicates said graphics signals are within said color key limits.

4 more elements

A computer system comprising:

a central processing unit (CPU);
a memory coupled to said CPU;
a graphics subsystem, coupled to said CPU, including:
a frame buffer for storing a plurality of pixel indexes, said pixel indexes including said color data to designate a color key;
a random access memory/digital to analog converter (RAM DAC) coupled to said frame buffer to receive said pixel indexes for converting said pixel indexes to a color definition, and for converting said color definition to analog graphics signals:
a video subsystem for generating video signals;
a high resolution output display for displaying graphics and video;
and
an analog chroma keying circuit coupled to said graphics subsystem, said video subsystem, and to said output display, said analog chroma keying circuit being coupled to receive said graphics signals and video signals, and being configured to couple said video signals to said output display when said analog chroma keying circuit detects said color key in said graphics signal, and being configured to couple said graphics signals to said output display when said analog chroma keying circuit does not detect said color key in said graphics signal.

6 more elements

Dependencies are inferred from the claim text.

Analog chroma keying on color data

Life of this patent

Analog chroma keying on color data

Life of this patent

Abstract

Claims21