JPH0444492A - Picture quality adjustment circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Field of Industrial Application) This invention is directed to the resolution of luminous saturation images of NTSC SPAL and SECAM television signals degraded in the transmission path.
This invention relates to an image quality adjustment circuit that compensates for

(Prior art) In a television signal transmission system, NTSC, P
In systems such as the AL and SECAM systems in which a composite signal is transmitted through one channel, the luminance signal and color signal are encoded into a format suitable for each system and transmitted. In this case, γ correction is performed to compensate for the characteristics on the receiving side. Further, the color signal band is transmitted with the band limited to about 0.5 MHz in order to limit interference with other signals.

Gamma correction and band-limiting of the color signal will result in non-linear characteristics of the transmitted signal.

However, due to this nonlinear characteristic, the high chroma signal (luminance high frequency component) that aims to improve the image quality is affected, resulting in deterioration of the image quality of the high chroma image, that is, a decrease in the level of the high frequency component of the luminance signal. It becomes.

To solve this problem, when a highly saturated signal is transmitted on the receiving side, the gain of the high frequency component of the luminance signal is increased according to the chroma, thereby improving the above image quality degradation. is possible. In this way, in a highly saturated image, the gain of the brightness high-frequency component is adaptively increased, so that it is possible to compensate for the level reduction due to the nonlinear characteristics.

(Problem to be Solved by the Invention) However, a new problem arises when the high frequency component of the luminance signal in a high chroma image is amplified as described above.

That is, when a signal with poor S/N is input, if the above compensation (intensity ml of the high frequency component of the luminance signal) is performed at high saturation,
On the contrary, even noise components are emphasized, resulting in a signal with an even worse S/N ratio, which may result in deterioration of the image quality of the negative layer.

Therefore, this invention prevents overcompensation at high saturation and obtains stable image quality improvement when the receiving side readjusts the level of the high frequency component of the luminance signal whose level has decreased due to γ correction using a simple circuit configuration. The purpose of the present invention is to provide an image quality adjustment circuit that can.

[Structure of the Invention (Means for Solving the Problem) This invention provides a means for detecting saturation information from a color signal to obtain a linear control signal corresponding to the level of saturation, and a linear control signal obtained from this means. The apparatus includes means for converting a control signal into a nonlinear control signal, and means for controlling the gain of a high-frequency component of a luminance signal using the nonlinear control signal obtained from the means.

(Function) With the above means, the high-frequency component of the luminance signal is not overcompensated at the time of high chroma, and deterioration of the image quality of the high chroma image is prevented.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. A luminance signal Y separated by a luminance color separation circuit is input to the input terminal 11 .

This luminance signal Y is passed through a delay circuit 12 and a high-pass filter (
HPF) 13.

From the HPF 13, the luminance signal high frequency component YH is extracted,
It is input to the variable gain amplifier 14. The brightness signal high-frequency component YH whose gain has been adjusted by the variable gain amplifier 14 is input to an adder 15 and added to the brightness signal output from the delay circuit 12. The output of the adder 15 is then delivered to the output terminal 16 as a luminance signal that has undergone high chroma compensation.

Note that the delay circuit 12 is for obtaining time adjustment with the path of the high frequency component of the luminance signal.

The gain control signal supplied to the variable gain amplifier 14 is created as follows.

The input terminal 21 receives the color signal C separated by the luminance color separation circuit. This color signal C is input to the decoder 23 via the delay circuit 22.

In the decoder 23, the color signal is detected using carriers of four axes whose phases differ by 90 degrees, for example, and each of the four axes including positive and negative signals is detected.
Obtain two detection outputs. This detection output is weighted with fixed value coefficients by coefficient multipliers 25, 26, 27, and 28, respectively.
The signal is input to the logical operation circuit 29. The logic operation circuit 29 is
A linear control signal is output depending on whether the color saturation is high or low based on a preset color (for example, blue or white).

This linear control signal is supplied to the nonlinear circuit 30 and converted into a nonlinear control signal, and this signal is used as a gain control signal for the variable gain amplifier 14 described above.

Decoder 23, coefficient unit 25, 25, 26, 27 described above
, the logical operation circuit 29 constitutes a saturation information detection means that detects saturation information from the color signal and obtains a linear control signal corresponding to the level of saturation.

Characteristic A shown by a solid line in FIG. 2 is an example of the characteristic of the nonlinear circuit 30.

From a low saturation state to a (for example, 40 to 60 saturation), the control signal is gradually increased to increase the gain of the high frequency component of the luminance signal, and the γ correction compensates for the level drop. are doing. However, above a, the control signal remains constant. In other words, the high-frequency component of the luminance signal is not amplified from the vicinity where the S/N ratio increases, and further amplification of the S/N is suppressed.

The nonlinear characteristic of the control signal according to the present invention is not limited to the characteristic A shown in FIG. 2, but is also effective as the characteristic A'. If the control signal has a linear characteristic like characteristic B in the figure, overcompensation may occur for the luminance signal and high frequency components.

Furthermore, the characteristics of the nonlinear circuit 30 may be those of a log function (level compression function) characteristic, as shown in FIG.

Furthermore, in order to control the high frequency component of the luminance signal as described above, a variable gain amplifier may be used as shown in FIG.

Figure 4 shows a configuration similar to that of a balanced modulator, in which the differential pair of transistors Q1 and Q2 have their emitters connected to resistors R.
1 and are commonly connected to a constant current source I via R2. The base of the transistor Q2 is connected to the brightness signal high frequency component Y.
H is input, and the bias power supply voltage E1 is supplied to the base of the transistor Q1. The collector of transistor Ql is connected to transistor Q3. Q4 is connected to the common emitter of transistor Q4, and the collector of transistor Q2 is connected to the common emitter of transistor Q4.
5, connected to the common emitter of Q6.

A bias power supply voltage E2 is supplied to the bases of the transistors Q1 and Q6, and a gain control signal is supplied to the bases of the transistors Q4 and Q5.

And transistor Q4. The collector of Q6 is led out as an output terminal and is connected to the power supply line via a resistor R3. Further, the collectors of transistors Q3 and Q5 are connected to the power supply line.

When such a variable gain amplifier is used, the amplification factor of the high frequency component of the luminance signal can be reduced as the control signal becomes larger, without performing nonlinear processing on the control signal.

[Effects of the Invention] As explained above, according to the present invention, when the receiving side readjusts the level of the high frequency component of the luminance signal whose level has been lowered due to γ correction using a simple circuit configuration, the excessive saturation at high chroma can be corrected. It is possible to prevent compensation and obtain stable image quality improvement.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of this invention, FIGS. 2 and 3 are diagrams showing an example of the characteristics of the nonlinear circuit shown in FIG. 1, and FIG. 4 is a diagram showing a variable gain in another embodiment of this invention. FIG. 2 is a circuit diagram showing an example of an amplifier. 12.22... Delay circuit, 13... High pass filter, 14... Variable gain amplifier, 15... Adder, 2
3...Decoder, 25-28...Coefficient unit, 29...
- Logic operation circuit, 30... nonlinear circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Scope of Claims] Means for detecting saturation information from a color signal to obtain a linear control signal corresponding to the level of saturation; and means for converting the linear control signal obtained from this means into a nonlinear control signal; An image quality adjustment circuit characterized by comprising means for controlling the gain of high-frequency components of a luminance signal using a nonlinear control signal obtained from the means, and suppressing the amplification factor on the high-saturation side rather than on the low-saturation side.