Television – Image signal processing circuitry specific to television – Gray scale transformation
Reexamination Certificate
1998-04-01
2001-11-06
Eisenzopf, Reinhard J. (Department: 2614)
Television
Image signal processing circuitry specific to television
Gray scale transformation
C348S677000, C348S254000, C358S519000
Reexamination Certificate
active
06313884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a gamma correction circuit, and to a display apparatus, e.g., a TV set or a PC (plus) monitor, comprising such a gamma correction circuit.
2. Description of the Related Art
The use of gamma correction is well known, as the gamma at the camera side does not exactly match the gamma of a CRT display. When LCD display devices are used, a gamma correction is also required as the LCD gamma is far stronger than the gamma at the camera side, so that the camera gamma should be augmented by a correction gamma in order to compensate the LCD display gamma.
U.S. Pat. No. 4,847,524 discloses a gamma correction circuit for use at the camera side. It has not less than 8 transistors.
U.S. Pat. No. 5,258,658 shows a gamma correction circuit for use with an LCD display. The gamma correction circuit is rather complex and has no less than 13 transistors.
SUMMARY OF THE INVENTION
It is, inter alia, an object of the invention to provide a simple and effective gamma correction circuit. To this end, a first aspect of the invention provides a gamma correction circuit which comprises an amplifier coupled to receive an input signal, and a non-linear impedance coupled to the amplifier for determining a gain of the gamma correction circuit in such a manner that the gain increases when the input signal increases. A second aspect of the invention provides a display apparatus comprising such a circuit.
The gamma correction circuit of the present invention is particularly suitable for use with a linear display, such as a plasma display, in which the light output is linearly dependent on the input signal amplitude. With such a display, the camera gamma should be completely compensated before the signal is applied to the display.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 3708615 (1973-01-01), Wharton
patent: 3836706 (1974-09-01), Keegan et al.
patent: 4689678 (1987-08-01), Klemmer
patent: 5335068 (1994-08-01), Hanajima
patent: 5455635 (1995-10-01), Keller
patent: 5539459 (1996-07-01), Bullitt et al.
patent: 5900918 (1999-05-01), White
patent: 5990979 (1999-11-01), Koyama et al.
patent: 06261228A (1993-03-01), None
Eisenzopf Reinhard J.
Goodman Edward W.
Tran Trang U.
U.S. Philips Corporation
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