JP2674175B2 - Color temperature correction device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a color temperature correction that can be used when changing the color temperature for bright white (telop characters, etc.) in a CRT output section of a television receiver and the like. It relates to the device.

2. Description of the Related Art With the recent increase in size of color television receivers,
In order to make an image look clearer, a color temperature correction device that raises the color temperature by changing the balance of the three primary colors of red, blue and green has been emphasized. Hereinafter, the conventional color temperature correction device as described above will be described with reference to the drawings.

FIG. 4 shows a block of a conventional color temperature correction device. In FIG. 4, reference numeral 1 denotes a slice circuit which compares the input luminance signal with the voltage from the slice level voltage generating circuit 2 and outputs an input luminance signal equal to or lower than the voltage as a correction signal. Reference numeral 2 is a slice level voltage generating circuit, which generates a DC voltage for determining the level at which the luminance signal is sliced. There is also a technique of adding this voltage to a contrast control voltage or an APL (average video signal level) voltage. A subtraction circuit 3 subtracts the correction signal and the input color difference signal and outputs the correction color difference signal.

The operation of the color temperature correction device configured as described above will be described below.

 FIG. 5 shows signals in the conventional example.

First, the input luminance signal a (the lower the voltage, the brighter it is) is input to the slice circuit 1 and compared with the voltage b from the slice level voltage generation circuit 2, and the luminance signal portion lower than this voltage b is corrected by a correction signal. Output as c. Next, the correction signal c is input to the subtraction circuit 3, is subtracted from the input color difference signal d (referred to as BY signal), and the correction color difference signal e is output. Thus, the color temperature can be corrected by detecting the bright portion of the input luminance signal and adding this portion to the color difference signal.

However, in the above-described configuration, since only the luminance signal is corrected as a determination factor, if the luminance is bright even in a colored portion, the color temperature correction works, and the color balance is improved. However, there is a problem in that the hue changes.

In view of the above problems, the present invention provides a color temperature correction device capable of preventing the color temperature correction from operating in a colored portion.

Means for Solving the Problems To achieve this object, a color temperature correction device of the present invention comprises a color signal detection circuit, an addition circuit, a clamp circuit, a slice circuit, and a subtraction circuit.

With this configuration, the magnitude of the color signal is detected by the color signal detection circuit, and this is added to the input luminance signal by the addition circuit, and when there is a color, the luminance signal is moved in a direction in which it is difficult to slice. The clamp circuit functions to align the pedestal levels of the luminance signal before and after the addition. The corrected luminance signal output from the adder circuit is used for color temperature correction detection in the same manner as the input luminance signal in the conventional example. This allows
The color temperature correction is not performed in the part with color.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a color temperature correction device according to an embodiment of the present invention. In FIG. 1, 1 is
The slice circuit, 2 is a slice level voltage generation circuit, 3 is a subtraction circuit, and the above is the same as the configuration of FIG. 4 is a color difference signal from the color demodulation circuit (RY, BY, G-
Y) is input and the color signal detection circuit detects the color by taking the maximum value of these. Reference numeral 5 denotes an addition circuit that adds the luminance signal and the color detection signal. A clamp circuit 6 restores the pedestal level of the luminance signal shifted by the addition to the original level.

The operation of the color temperature correction device configured as described above will be described below. FIG. 3 shows the waveform of each part.

First, the color difference signals RY, G- output from the color demodulation circuit
Input Y and BY to the color detection circuit 4. This circuit 4 is 3
It operates so as to take the maximum value of the book input signal. FIG. 2 shows an example of the color detection circuit. Transistors with RY, GY, and BY signals input to their bases
It is composed of 11,12,13 and its base resistors 14,15,16, and the emitters are commonly connected to serve as a color detection signal output terminal. 17 is a common emitter resistance. The detected color signal is output as the color detection signal h. Next, the color detection signal h
The input luminance signal a is added by the adder circuit 5 and output as the corrected luminance signal i. In order to fix the pedestal level of the output signal, the clamp circuit 6 performs clamping with the input luminance signal a and the horizontal synchronizing pulse.
Next, the corrected luminance signal i is sliced by the slicing circuit 1, and thereafter, the same operation as in the conventional example is performed to obtain a corrected color difference signal e, which is output to the CRT drive circuit.

As described above, according to the present embodiment, the color detection signal is added to the luminance signal, and in the colored portion, the luminance signal is shifted to the black side according to the size of the color so that it is not sliced, The color luminance correction works only on bright white (telop characters, etc.), and it is possible to prevent hue shift, which is a conventional defect.

In the present embodiment, the input of the color signal detection circuit 4 is changed to R
Although -Y, G-Y, and BY are used, two or only one of them may be used. It is also easy to apply the DC voltage together with the color difference signal so that the correction is performed on the color signal, which is larger than this voltage, by using the circuit of FIG. Also, the clamp circuit can be deleted if there is no difference in the pedestal level before and after the adder circuit.

EFFECTS OF THE INVENTION As described above, according to the present invention, the color detection circuit and the addition circuit can prevent the color temperature correction circuit from operating in a colored portion, and the hue of the colored portion is shifted. It can be solved and its practical effect is great.

[Brief description of the drawings]

FIG. 1 is a block diagram of a color temperature correction device in one embodiment of the present invention, FIG. 2 is a circuit diagram showing an embodiment of a color detection circuit, and FIG. 3 is a signal waveform diagram of each part in this embodiment. ,
FIG. 4 is a block diagram of a conventional color temperature correction device, and FIG. 5 is a signal waveform diagram of each part in the conventional example. 1 ... Slice circuit, 2 ... Slice level voltage generation circuit, 3 ... Subtraction circuit, 4 ... Color signal detection circuit, 5 ... Addition circuit, 6 ... Clamp circuit.

Claims (1)

(57) [Claims] 1. A color signal detection circuit for detecting the maximum value of color difference signals R-Y, G-Y, and B-Y to check the presence / absence of a color component, an output signal of this color signal detection circuit, and a video luminance signal. An adder circuit for adding, a clamp circuit for clamping the output signal of the adder circuit, a slice circuit for slicing the clamped output signal according to the output voltage of the slice level generation circuit,
A color temperature correction device comprising a subtraction circuit for subtracting an output signal of the slice circuit from a color difference signal.