Color control circuit for teletext-type decoder

• US 4,388,639 A
• Filed: 05/18/1981
• Issued: 06/14/1983
• Est. Priority Date: 05/18/1981
• Status: Expired due to Fees

• Current Assignee: Zenith Radio Corporation
• Original Assignee: Zenith Radio Corporation
• Inventors: Turner, Rudolf, Cox, Charles M.
• Primary Examiner(s): Martin, John C.
• Application Number:
  US06/264,773
• Time in Patent Office: 757 Days
• Field of Search: 358/21 R, 358/22, 358/27, 358/40, 358/147, 340/701, 340/703, 340/704, 340/723, 340/744, 340/748, 340/750, 340/793
• US Class Current: 348/468
• CPC Class Codes: H04N 9/641 Multi-purpose receivers, e.g. for auxiliary information H04N9/642 takes precedence

Abstract

A color control circuit for selectively modifying the red, green and blue color signals developed at the output of a teletext-type decoder comprises a common input stage responsive to the teletext decoder for developing a bi-level control voltage identifying the portions of the color signals representing background and foreground display information. Each color signal is coupled to a respective output stage which causes the associated color signal to assume a first intensity level in response to the control voltage being at its first level and a second intensity level greater than the first intensity level in response to the control voltage being at its second level. As a result, background colors are displayed at a reduced contrast level relative to foreground colors. In addition, selected single color foreground information may be displayed at a further increased intensity level to improve the readability of the display.

Claims

1. A color control circuit for selectively modifying the red, green and blue color signals developed at the output of a teletext-type decoder, said teletext-type decoder further developing a bi-level output control signal identifying the portions of said color signals representing background and foreground display information, said color control circuit comprising:

means responsive to said bi-level output control signal for developing at a common circuit node a control voltage having a first level identifying portions of said color signals representing background display information and a second level identifying portions of said color signals representing foreground display information; and

output means comprising a red output stage, a green output stage and a blue output stage, each of said output stages summing the control voltage developed at said common circuit node with the corresponding one of said red, green and blue color signals for causing the respective color signal to assume a first intensity level when the control voltage developed at said common circuit node is at said first level and a second intensity level greater than said first intensity level when the control voltage developed at said common circuit node is at said second level.

2. A color control circuit for selectively modifying the red, green and blue color signals developed at the output of a teletext-type decoder, said teletext-type decoder further developing a bi-level output control signal identifying the portions of said color signals representing background and foreground display information, said color control circuit comprising:

means responsive to said bi-level output control signal for developing at a common circuit node a control voltage having a first level identifying portions of said color signals representing background display information and a second level identifying portions of said color signals representing foreground display information;

output means comprising a red output stage, a green output stage and a blue output stage, each of said output stages summing the control voltage developed at said common circuit node with the corresponding one of said red, green and blue color signals for causing the respective color signal to assume a first intensity level when the control voltage developed at said common circuit node is at said first level and a second intensity level greater than said first intensity level when the control voltage developed at said common circuit node is at said second level;

means responsive to said teletext-type decoder for developing an identification signal identifying the portions of at least one of said color signals representing single color foreground display information; and

means for coupling said identification signal to the corresponding one of said output stages for causing the corresponding color signal to assume a third intensity level greater than said second intensity level.

3. A color control circuit for selectively modifying the red, green and blue color signals developed at the output of a teletext-type decoder, said teletext-type decoder further developing a bi-level output control signal identifying the portions of said color signals representing background and foreground display information, said color control circuit comprising:

means responsive to said bi-level output control signal for developing at a common circuit node a control voltage having a first level identifying portions of said color signals representing background display information and a second level identifying portions of said color signals representing foreground display information; and

output means comprising first, second and third transistor means each including an emitter terminal coupled for receiving the control voltage developed at said common circuit node and a respective one of said color signals, each of said transistor means being operated for processing its respective color signal by causing it to assume a first intensity level when the control voltage developed at said common circuit node is at said first level and a second intensity level greater than said first intensity level when the control voltage developed at said common circuit node is at said second level.

4. A color control circuit for selectively modifying the red, green and blue color signals developed at the output of a teletext-type decoder, said teletext-type decoder further developing a bi-level output control signal identifying the portions of said color signals representing background and foreground display information, said color control circuit comprising:

means responsive to said bi-level output control signal for developing at a common circuit node a control voltage having a first level identifying portions of said color signals representing background display information and a second level identifying portions of said color signals representing foreground display information;

means responsive to said teletext-type decoder for developing an identification signal identifying the portions of at least one of said color signals representing single color foregound display information; and

output means comprising first, second and third transistor means each including an emitter terminal coupled for receiving the control voltage developed at said common circuit node and a respective one of said color signals with said identification signal being coupled to the base terminal of the corresponding transistor means, each of said transistor means being operated for processing its respective color signal by causing it to assume a first intensity level when the control voltage developed at said common circuit node is at said first level and a second intensity level greater than said first intensity level when the control voltage developed at said common circuit node is at said second level, the conduction of the transistor means receiving said identification signal being reduced in response thereto for causing the corresponding color signal to assume a third intensity level greater than said second intensity level.

5. A color control circuit according to claim 4 including user-operable means for developing a picture control signal, said control voltage developing means being responsive to said picture control signal for adjusting said first and second levels of said control voltage for varying the conduction of said transistors and thereby said first, second and third intensity levels.