JPH05176201A - Contour correction device - Google Patents

Abstract

PURPOSE:To add a preshoot and an overshoot to a video signal so that a contour of a video image has a symmetry at a white level side and a black level side by providing an inverse gamma correction circuit, a contour correction circuit arid a gamma correction circuit in series with the device. CONSTITUTION:The device is provided with a series connection circuit comprising an inverse gamma correction circuit 1 restoring a gamma characteristic of a camera side to the original characteristic, a contour correction circuit 2 using a delay line, a gamma correction circuit 3 to correct a gamma characteristic of a CRT(cathode ray tube). Thus, a video signal with the gamma characteristic of the camera side applied thereto is converted into a linear signal and filter processing as contour correction processing is applied to the signal, then a preshoot and an overshoot to a video to provide excellent symmetry are added to a black level and a white level. Then the gamma correction is applied to the signal and an output signal with asymmetry to the white level and the black level is obtained, the signal is made symmetrical by a current of the CRT and an optical output is proportional to the current and the width of the preshoot and the overshoot is apparently unchanged and the contour is effectively emphasized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a cathode ray tube (hereinafter referred to as CRT).
And a video signal processing circuit used in a display device, etc., particularly an image contour correction circuit.

[0002]

2. Description of the Related Art In recent years, horizontal contour correction circuits for home color television receivers, etc. have been required to have finer and sharper preshoots and overshoots along with the increase in screen size and wide band of video signals. A circuit configuration is devised so that blooming does not occur with respect to overshoot on the white side at a high brightness level.

A conventional contour correction circuit will be described below with reference to the drawings. As shown in FIG. 4, the contour correction circuit delays the input video signal c by the delay lines 5 and 6 for T time, and the resistors R6 and R10 are terminated by the matching resistors of the delay lines 5 and 6 at the characteristic impedance value. .. The resistor R8 is connected to the midpoint signal of the delay line, and the resistors R7 and R9 are connected to the delay line 5,
6 are connected to the signals at both ends of the amplifier 6 via diodes D12 and D13, respectively, and a signal d obtained by adding the signals at the three terminals of the delay line is obtained at the connection point 14 and then added / subtracted amplifier 7 and addition amplifier 8 It outputs after passing through.

The operation of the contour correction device having the above-described structure will be described below. First, regarding the frequency characteristic of the signal d, when the diodes D12 and D13 are conducting,
If they are added at the ratio of / 2, 1, 1/2, the low-pass characteristic of (1 + COSωT) is obtained by the Fourier transform.

When the diodes D12 and D13 are not conducting, the signal at the middle point of the delay line is output as it is to the connection point 14 and the characteristic becomes flat.

The adder / subtractor amplifier 7 adds the signal d at the connection point 14 and subtracts the signals at both ends of the delay line to output a signal e.
If the ratio is set to -1/2, 1, -1/2, the frequency characteristic of the output signal e of the adder / subtractor amplifier 7 becomes a high-pass characteristic of (1-COSωT).

In the summing amplifier 8, the signal d at the connection point 14 and the output signal e of the summing amplifier 7 are adjusted by the variable attenuator 9 and added. As a result, the frequency characteristic can be varied from the low-pass characteristic to the peaking characteristic, so that a symmetrical preshoot and overshoot can be obtained in the contour portion of the input signal.

A contour correction circuit (generally called a delay line aperture compa- nator) using a normal delay line has no diodes D12 and D13 (and resistors 7 and 9 in some cases). As shown by the solid line, the output signal has a symmetrical preshoot and overshoot, but due to the gamma characteristic of the CTR, the beam current becomes larger due to the overshoot on the white side than the preshoot on the black side, resulting in symmetry. Collapse. As a result, the white parts appear thicker and the black parts appear thinner.

The diodes D12 and D13 are provided to improve the above-mentioned problems. When a large contour edge signal is present on the white side, the diodes are made conductive to reduce the frequency characteristic and suppress overshoot.

(Eg JP Bingham et al: "A NEW LOW
LEVEL LUMINANCE PROCESSING SYSTEM ", ICCE TRANS CE-2
2, May, 1976, pp.136-146) In a recent example, a time compression type contour correction circuit has been developed to solve the above problems. In this method, the time on the white side is cut in advance by the delay line and the analog OR circuit to thicken the black side, and then the contour correction is performed, and a certain improvement effect is obtained.
However, this method is not preferable because it distorts the signal in time.

[0011]

However, in the above-mentioned conventional structure, the effect of suppressing the overshoot is insufficient, so that there is a problem that the black side is still thinner.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a natural contour correction device for preshoot and overshoot that does not cause blooming even in white overshoot at high brightness. ..

[0013]

In order to achieve this object, a contour correcting apparatus of the present invention comprises an inverse gamma correcting means for restoring the gamma characteristic of the camera side, a contour correcting means, and C.
The gamma correction means for correcting the RT gamma is connected in series.

[0014]

According to the present invention, in the above structure, a video signal having a gamma characteristic on the camera side is converted into a linear signal,
Since a filtering process called contour correction processing is applied to the signal, preshoot and overshoot with good symmetry are added to the black side and the white side, and then gamma correction is applied to the white side and the black side. It is output asymmetrically, but
The current of the CRT becomes symmetrical again, and the optical output is proportional to the current, and the widths of the preshoot and the overshoot do not change, and the contour can be effectively emphasized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the contour correction device includes an inverse gamma correction circuit 1 that restores the gamma characteristic of the camera.
A contour correction circuit 2 using a delay line and a gamma correction circuit 3 for correcting the gamma characteristic of a CRT are the main components. Furthermore, an example of the internal configuration of each component will be described. Here, the inverse gamma correction circuit 1 includes resistors R1,
R2, R3, R4, R5 and diodes D1, D
2, D3, D4, D5, D6 and the like constitute a tangential approximation circuit for obtaining the inverse gamma characteristic, which is amplified by the video amplifier 4.

Next, the contour correction circuit 2 includes a diode D
FIG. 4 showing the conventional example except that 12 and D13 are not used.
The circuit configuration is the same. Here, the resistors R7 and R9 do not necessarily have to be used.

In the CRT gamma correction circuit 3, the resistor R1
1, R12, R13, R14, diodes D7, D8,
The inverse gamma characteristic is tangentially approximated by D9, D10, D11, and D12, and the output signal h is obtained after being amplified by the video amplifier 10.

The operation of the contour correcting device configured as described above will be described below with reference to FIGS. 1, 2 and 3. First, FIG. 2 shows the characteristics of the inverse gamma correction circuit, in which the voltage level of the input signal a changes from 0 to Vd (V
d is the output voltage b up to the forward voltage of one diode)
Has a value divided by the resistors R1 and R5. When the input voltage is from Vd to 2Vd, it is divided by the parallel resistance of resistors R1 and R2 and R5. When the input voltage is from 2Vd to 3Vd, it is divided by the parallel resistance of resistors R1, R2 and R3 and R5, and the input voltage is 3Vd. To 4Vd, resistors R1, R2, R3
It is divided by the parallel resistance of R4 and R5.

The inverse gamma characteristic can be realized by selecting the resistors R1, R2, R3, R4 and R5 so that the inverse characteristic of the gamma characteristic on the camera side is obtained by tangential approximation.

As shown in FIG. 3, the characteristic of the gamma correction circuit 3 of the CRT is that the resistance value on the numerator side of the voltage division ratio is different from that of FIG. 2 depending on the voltage level of the output voltage g. Parallel resistance of R13, resistors R12, R13, R
14 parallel resistors. ． Then, the gamma characteristic is realized by selecting the resistance value so as to tangentially approximate the gamma characteristic of the CRT.

As described above, according to this embodiment, the inverse gamma correction circuit for restoring the gamma characteristic of the camera side, the contour correction circuit, and the gamma correction circuit for correcting the CRT gamma are provided in series. The preshoot and the overshoot are symmetrical with respect to the beam current of the CRT on the white side and the black side, a natural contour correction effect is obtained, and the white blooming phenomenon can be eliminated even when a large correction is performed.

In the contour correction apparatus of this embodiment, the gamma correction circuit and the inverse gamma correction circuit are realized by tangential approximation by analog circuits. However, by using the A / D and D / A converters, the table look is performed by the digital memory. According to the up method, the approximation can be made even better.

[0024]

As is apparent from the above embodiments, the present invention is provided with an inverse gamma correction circuit that restores the gamma characteristic of the camera, an outline correction circuit, and a gamma correction circuit that corrects CRT gamma. As a result, an excellent contour correction device having symmetry between preshoot and overshoot can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a contour correction device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of an inverse gamma correction circuit according to the same embodiment.

FIG. 3 is a characteristic diagram of a gamma correction circuit in the same embodiment.

FIG. 4 is a circuit diagram of a conventional contour correction device.

FIG. 5 is an operation waveform diagram of the contour correction circuit.

[Explanation of symbols]

 1 inverse gamma correction circuit 2 contour correction circuit 3 gamma correction circuit

Claims (1)

[Claims] 1. An inverse gamma correction means for restoring a gamma characteristic on the camera side, a contour correction means, and a gamma correction means for correcting a gamma characteristic of a cathode ray tube are connected in series to convert a video signal. A contour correction device which is arranged to correct the contour through the respective means in order.