JP2740377B2 - Contour correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction circuit for a television receiver or the like.

[0002]

2. Description of the Related Art Conventionally, a television receiver is disclosed in
JP-A-3-87878 (H04N5 / 59) and JP-A-6-7878
A circuit that controls contrast and brightness according to the brightness of a screen is generally used as seen in Japanese Patent Application Laid-Open No. 3-171704 (H04N5 / 59). Cathode ray tube (CR
T) and not for improving the image quality.

To improve the image quality, a contour correction circuit for correcting the contour of the luminance signal and a noise reduction circuit (hereinafter referred to as YNR) for reducing the noise of the luminance signal are used. The contour correction amount and the noise reduction level were kept constant regardless of the brightness.

[0004] For this reason, when emphasizing the contour emphasis in the high luminance portion, noise in the low luminance portion is conspicuous, and when emphasizing the noise reduction in a dark screen, the contour emphasis in the high luminance portion is blurred. There is a drawback that sufficient image quality cannot be obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the image quality by emphasizing contours and reducing noise according to the brightness of a screen in order to solve the above-mentioned drawbacks.

According to the present invention, a contour extracting means for extracting a contour of a luminance signal and creating a contour emphasizing signal, a noise reducing means for removing a noise component contained in the contour emphasizing signal, and a noise reducing means are provided. Gain control means for amplifying the output contour emphasis signal, brightness signal level detection means for detecting a predetermined level of the brightness signal, and average brightness of the video signal level based on the beam current flowing to the cathode ray tube. A contour correction circuit comprising brightness detection means for detecting, wherein the brightness signal level detection means controls the gain of the gain control means, and the brightness detection means controls noise reduction means.

[0007]

According to the present invention, the gain of the gain control circuit is increased in the high luminance portion of the luminance signal by adopting the above-described configuration.
In a low luminance portion, the gain is reduced, and in a dark screen, the beam current is detected and the noise reduction level is increased.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG.
1 shows a block diagram of an embodiment of the present invention.

1 is an input terminal to which a luminance signal is input, 2 is a clamp circuit, 3 is a circuit for extracting a contour signal of the luminance signal, 4 is a noise reduction circuit (YNR) for reducing noise of the luminance signal, and 5 is contour enhancement. A gain control circuit for controlling the amplitude of the signal, 6 a circuit for adding the edge enhancement signal and the luminance signal, 7 a low-pass filter (LPF), 8 a circuit for detecting a constant level of the luminance signal, 9 a beam current flowing to the CRT A circuit for detecting the amount, a terminal 10 for inputting a control signal for an operator to adjust the contour emphasis level, and a reference numeral 11 for a luminance signal output terminal.

Next, the operation will be described. The luminance signal input to the terminal 1 is DC-clamped by the clamp circuit 2 at the leading end of the synchronization signal. The contour extraction circuit 3 extracts a contour portion of the luminance signal to create a contour emphasis signal and also extracts a noise component.

Then, the noise component is removed by deleting the small amplitude signal which is input to the YNR circuit 4 and which is the contour emphasizing signal. The coring level of the YNR circuit 4 is changed by the detection output detected by the beam current detection circuit 4. That is, when the average beam current flowing through the CRT falls below a certain level (dark screen), the coring level of the YNR circuit 4 is increased, and the amount of noise reduction is increased.

The gain of the contour emphasizing signal having passed through the YNR circuit 4 is adjusted by a gain control circuit 5. In the gain adjustment of the gain control circuit 5, the operator can arbitrarily change the adjustment voltage from the sharpness adjustment terminal 10. Further, the output of the luminance detection circuit 8 detecting a luminance signal level (high luminance portion) equal to or higher than a certain level of the luminance signal increases the gain of the gain control circuit 5 to clarify the outline emphasis in the high luminance portion. Like that.

The luminance signal is output to the adding circuit 6 via the LPF 7 and added to the contour emphasizing signal from the gain control circuit 5 to obtain a noise-enhanced luminance signal without noise.

Next, a specific embodiment of the present invention is shown in FIG. 2, and its operation will be described below. The luminance signal input to the terminal 1 is output to the emitter of the transistor Q3 via the transistor Q1 of the clamp circuit 2, and is clamped at a constant DC voltage. The output of this Q3 emitter is
This is a signal containing noise as shown in FIG.

The luminance signal a is input to the contour extracting circuit 3, and first, the delay signal DL is supplied to the delay line DL via a resistor R4.
1 and output to the base of transistor Q5. The signal to Q5 is a signal delayed by Tα as shown in FIG. 3B. On the other hand, the matching resistor R4 of DL1
Therefore, the output side of DL1 becomes high impedance, so that the reflection of the luminance signal occurs, and the input side of DL1 is
A signal as shown in FIG.

The signal shown in FIG. 3C is supplied to the base of the transistor Q4, and the difference signal between FIGS. 3B and 3C is output to the collector of Q5. This difference signal is as shown in FIG. 3D and is output from the emitter of the transistor Q7. still,
The power supply E2, the transistor Q6, and the resistor R7 are constant current sources.

Then, the emitter output of Q7 is supplied to the YNR circuit 4. FIG. 3d supplied to diodes D2 and D3 via capacitors C2 and C3 is biased by resistors R10, R11, R12 and R13, respectively. At this time, D2 is the resistance R1 in the waveform of FIG.
8, turns on when the voltage exceeds the cathode bias voltage (DC 0.6 V) of D2 given by R19, and conversely, D3
Turns on at the lower side, and the signal input to the transistor Q11 is as shown in FIG. 3E, and is a signal from which noise has been removed.

The bias voltage of the anode of the diode D2 and the bias voltage of the cathode of the diode D3 are
The bias voltage is supplied from a differential amplifier circuit composed of Q8, Q9, and Q10, and by varying the base of Q8, the bias voltage changes. For example, when the base voltage of Q8 is increased, Q8
, The collector voltage of Q9 rises, and the coring level increases.

The signal for controlling the base of the transistor Q8 is a control signal from the beam detection circuit 9, and is controlled so as to increase the base voltage of Q8 when a dark screen is displayed.

FIG. 4 shows a specific diagram of the beam detection circuit 9, and the operation related to the YNR circuit 4 will be described. Power supply V2
Is supplied to the anode of the CRT 14 through the high voltage generation circuit 13. Here, at the time of a dark screen, the beam current decreases and the resistance R10
The voltage at the node between R1 and R102 increases. Then, the voltage is smoothed by the capacitor C101, an average value voltage of the brightness of the screen is generated, the voltage is applied to the transistor Q19 and turned on, and the emitter voltage of the transistor Q20 is increased. Join the base and increase the coring level.

Next, the output from the YNR circuit 4 is input to the transistor Q16 of the gain control circuit 5. The gain of the gain control circuit 5 is controlled by the transistor Q1
2, the base of Q15 and the bases of the transistors Q13, Q14. That is, increasing the base voltage of Q12 and Q13 increases the gain, and increasing the base voltage of Q13 and Q14 decreases the gain.

Therefore, the brightness detection circuit 9 is connected to Q12 and Q15, and the sharpness adjustment terminal 10 is connected to Q13 and Q14, and the gain is adjusted respectively.

Here, the luminance detection circuit 8 and the gain control circuit 5
Will be described. FIG. 5 shows a specific embodiment of the luminance detection circuit 8. In this figure, the luminance signal from the clamp circuit 2 is input to the base of the transistor Q21 via the resistor R37. When the level of the luminance signal is higher than the base voltage of the transistor Q22, the signal is output from the emitter of the transistor Q21, and the gain control circuit 5 operates to increase the base voltage of the transistors Q12 and Q13 to increase the gain.

The contour emphasizing signal obtained as described above is as shown in FIG. 3F. The signal is guided to the adding circuit 6 via the transistor Q18 and added to the signal shown in FIG. As shown in FIG. 3H, a signal whose edge is emphasized is obtained.

[0025]

According to the present invention, when the entire screen is dark, the coring level is increased to reduce noise that is conspicuous on a dark screen, and the gain of the contour emphasizing signal is increased in a partially high luminance portion. Good image quality can be obtained because the outline is further emphasized and a delicate image in a high luminance portion is not spoiled.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of the embodiment of the present invention.

FIG. 3 is a waveform chart for explaining the present invention.

FIG. 4 is a circuit diagram for explaining the operation of the embodiment of the present invention.

FIG. 5 is a circuit diagram for explaining the operation of the embodiment of the present invention.

[Explanation of symbols]

 3 contour signal extraction circuit 4 noise reduction circuit 5 gain control circuit 8 luminance detection circuit 9 beam detection circuit

Claims (1)

(57) [Claims] 1. A contour extraction unit for extracting a contour of a luminance signal and creating a contour emphasis signal, a noise reduction unit for removing a noise component included in the contour emphasis signal, and an output from the noise reduction unit. Gain control means for amplifying the contour emphasis signal, luminance signal level detection means for detecting a predetermined level of a luminance signal, and detecting an average brightness of a video signal level based on a beam current flowing to a cathode ray tube. A contour correction circuit comprising brightness detection means, wherein the gain of the gain control means is controlled by the luminance signal level detection means, and noise reduction means is controlled by the brightness detection means.