JPH0654989B2 - Image quality improvement circuit of color television receiver - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a circuit for improving the image quality of a color television receiver.

[Background of the Invention]

Current color television signals consist of superposed luminance signals having a frequency band of about 4.5 MHz and carrier color signals obtained by modulating color difference signals having a frequency band of 0.5 to 1.5 MHz. Therefore, an image reproduced by a color television receiver can be reproduced as a contour having a sharp change in brightness as a boundary where the brightness changes, but the boundary where the color changes is less sharp. Image quality. Therefore, as a circuit for improving the image quality of such a reproduced image, an image quality improving circuit as disclosed in, for example, Japanese Patent Laid-Open No. 54-140825 has been proposed. FIG. 3 is a block diagram showing an image quality improving circuit according to the above-mentioned proposal. In the figure, 1 is a high-pass filter, 2 is a trigger generation circuit, 3 is a delay circuit, 4 is a switch switching circuit, and 5 is a comparison circuit.

FIG. 4 is a waveform chart of each part of the circuit shown in FIG. Third
The circuit operation will be described below with reference to FIGS.

Since the luminance signal Y has a frequency component up to 4.5 MHz as shown in FIG. 4 (a), it has a sharp rising signal waveform even in the contour portion of a colored image. This waveform
When (a) passes through the high-pass filter 1 shown in FIG. 3, it becomes only the high-pass component of the luminance signal as shown in the waveform (b), and is delayed a little.

On the other hand, the color difference signal C is divided into a signal supplied to the switch switching circuit 4 through the delay circuit 3 and a signal supplied directly to the switch switching circuit 4. The latter signal is shown in Fig. 4.
The waveform is shown in (c), and the former is the waveform shown in (d).

As can be seen from the figure, the color difference signal waveforms (c) and (d) have a fairly gentle waveform because the frequency band is about 0.5 to 1.5 MHz. It will also be understood that the waveform (c) and the waveform (d) come before and after the waveform (b) of the high frequency component of the luminance signal. The color difference signal is first output from the switch switching circuit 4
The color difference signal waveform (d) delayed by is output.

Next, a switching signal is given from the trigger generation circuit 2 to the switch switching circuit 4 by the high frequency component b1 of the luminance signal, that is, a signal indicating the contour position of the image, so that the color difference signal waveform (c) which is not delayed is output. Switch to. Then waveform (c)
From the comparison circuit 5 that compares the waveform (d) with the waveform (c)
When (d) matches, the switch signal (f) is applied to the switch switching circuit 4 again, and switching is performed so that the color difference signal waveform (d) is output. Further, the switch switching circuit 4 is activated by the high frequency component b2 of the luminance signal, and the color difference signal output (e) changes from the waveform (d).
Switch to (c).

In this way, the color difference signal waveform is switched from (d) to (c) every time the high frequency component of the luminance signal comes, and the color difference signal waveform is changed from (c) to (d) every time the waveforms match in the comparison circuit 5. Switch. As a result, the color difference signal output becomes as shown in Figure 2 waveform (e),
It is possible to obtain an image with a clear contour even at the color boundary.

As described above, the conventional image quality improving circuit according to the proposed method detects the contour position of the image in the luminance signal, switches the color difference signals having different delay times according to the detection signal, and outputs the color difference signals thereafter. When different color difference signals are compared and coincident with each other, the color difference signals are switched and output again to sharpen the color contour.

However, since this method switches the color difference signal output when the color difference signals having different delay times match each other, an image in which the color difference signal changes gradually immediately after the portion where the luminance signal largely changes is displayed. In this case, in this period, the color difference signals having different delay times do not coincide with each other, and a time difference occurs between the luminance signal and the color difference signal output, which causes a color shift phenomenon in the reproduced image. In the case of the NTSC system, the color difference signal is composed of two or more types of signals such as I signal and Q signal or RY signal and BY signal, and has been proposed for color difference signals having different signal characteristics. In general, the switching signals (f) given to the switch switching circuit 4 for the respective color difference signals do not match in time. Therefore, in the vicinity of the contour portion of the reproduced image, a time difference occurs between the color difference signals,
Transiently different hues will occur.

[Object of the Invention]

An object of the present invention is to reproduce an image in which a contour of a color that changes according to a contour of luminance is clear even in an image in which a color difference signal gradually changes immediately after a portion where a luminance signal largely changes. Another object of the present invention is to provide an image quality improving circuit for a color television receiver which can suppress the transitional hue shift in the contour portion.

[Outline of Invention]

In the present invention, normally, the property that the brightness is slightly changed at the boundary portion where the color is changed is used, and in order to solve the above problem, the carrier color signal before demodulation is used as the color difference signal. By suppressing the hue shift, the contour part of the image in the brightness signal is detected, and the delay time is adjusted by adapting to the level change of the brightness signal at the position before and after the contour part. The color signal is switched and output, that is, the color boundary is adaptively reproduced only from the luminance signal to sharpen the contour of the image in which the color is changed.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, the input luminance signal 6 is input to the luminance signal delay circuits 8 and 8 ', and the subtraction circuits 9 and 9'have a certain delay time difference, that is, the waveform (a) and the waveform shown in FIG.
The signals of (b) and the waveforms (b) and (c) are input. The output signals of the subtraction circuits 9 and 9'are difference signals between the input signals as shown in the waveforms (d) and (e). The waveform shaping circuits 10 and 10 'align the polarities of the difference signals and output signals as shown in the waveform (g) and the waveform (h) in FIG.

As a concrete circuit example of the waveform shaping circuits 10 and 10 ', for example, a double wave rectification detection circuit or an absolute value conversion circuit can be considered.

Further, the output signals of the waveform shaping circuits 10 and 10 'are input to the subtraction circuit 11, and the difference signal, that is, the switching control signal as shown in the waveform (i) of FIG. 2 is generated. Here, as is clear from the relationship between the delayed luminance signal shown in the waveform (b) of FIG. 4 and the switching control signal shown in the waveform (b), the switching control signal has a positive polarity immediately before the contour portion of the luminance signal, It can be understood that the negative polarity is shown immediately after the contour portion of the luminance signal.

On the other hand, the input carrier color signal 7 is a carrier color signal delay circuit 12, 12 '.
The phase relationship between the input carrier color signal and the color synchronization signal is made equal by the phase compensation circuits 13 and 13 'that correct the phase shift with the color synchronization signal (color burst signal) caused by the delay. To the switching circuit 14, carrier color signals having different delay times shown in the waveforms (n), (l) and (w) are input.

However, the term delay time in this specification includes zero delay time.

When the switching control signal exceeds a positive predetermined level, the switching circuit 14 switches so that a carrier color signal (wo) having a long delay time is output, and the switching control signal has a negative predetermined level. When it exceeds the value, the carrier color signal (nu) is switched so that the delay time is small, and when the switching control signal is at a level that does not belong to any of the above, the carrier color signal (rule) ) Is output.

In this embodiment, the delay time of the carrier color signal is set to (n + 1/1 /) of the color synchronization signal so that the operation of the phase compensation circuit can be easily understood.
2) The waveform of FIG. 2 is shown as the time corresponding to the cycle (n is an integer).

As described above, the contour portion of the luminance signal is detected, and the carrier color signal is switched by the switching circuit 14 according to the magnitude of the level change of the luminance signal of the contour portion, and the waveform (W) is shown in FIG. Such an output carrier color signal 15 can be obtained, and when it is demodulated into a color difference signal, it becomes a waveform (F), a contour of the color is clear, and a reproduced image without color shift and hue shift can be obtained.

In the above embodiments, the switching circuit 14 has been described as switching carrier color signals having three kinds of delay times, but four or more kinds of color difference signals having different delay times are finely discriminated from the switching control signal. It may be a switching circuit for switching and outputting by doing so.

Also, as is clear from the fact that the relationship between the waveform (d) and the waveform (e), or the waveform (g) and the waveform (h) in FIG. 2 is the same waveform with a predetermined delay time difference, the luminance signal delay Circuit 8,
8 ', the subtraction circuits 9, 9'and the waveform shaping circuits 10, 10' are provided in only one system, and the input of the subtraction circuit 11 is a waveform (g) and this is delayed for a predetermined time to obtain a waveform (h). Subtracting circuit 1 by setting the waveform (h) obtained by providing a delay circuit
It can be easily understood that the waveform (i) described in the embodiment can be obtained at the output of 1.

Further, the switching control signal for controlling the switching of the switching circuit 14 is
Any signal can be used as long as it can discriminate the brightness level at the positions before and after the outline of the brightness, and the present embodiment does not specify the signal format of the switching signal and the signal creating method.

〔The invention's effect〕

According to the present invention, it is possible to provide an image quality improving circuit of a color television receiver capable of preventing a color shift and a hue shift of a reproduced image and sharply reproducing a contour portion of a colored image, As a result, it is possible to obtain a good image quality that has never been obtained.

Further, since the carrier color signal is processed instead of processing two or more kinds of color difference signals, only one processing system is required, and the circuit can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of each signal in the circuit of FIG. 1, FIG. 3 is a block diagram showing a conventional image quality improving circuit, and FIG. FIG. 3 is a waveform diagram of signals at various parts in the circuit of FIG. 1. 1 ... High-pass filter, 2 ... Trigger generating circuit 3 ... Delay circuit, 4 ... Switch switching circuit 5 ... Comparison circuit, 6 ... Input luminance signal 7 ... Input carrier color signal, 8, 8 '... ... Luminance signal delay circuit 9,9 '... Subtraction circuit, 10, 10' ... Waveform shaping circuit 11 ... Subtraction circuit 12, 12 '... Carrier color signal delay circuit 13, 13' ... Phase compensation circuit, 14 ...... Switching circuit 15 …… Output carrier color signal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-84426 (JP, A) JP-A-54-140825 (JP, A) JP-A-61-274490 (JP, A)

Claims (1)

[Claims] 1. A first delay means for outputting a first luminance signal with a delay time added to an incoming luminance signal; and the first luminance signal, wherein the first luminance signal is at the image contour position as a boundary. It is located at the front part (hereinafter, abbreviated as the front part) having the same time length as the delay time in the delay means, or the rear part having the same time length as the delay time in the first delay means ( Hereafter, a position identification means for identifying whether or not it is located in the rear portion) and a luminance signal between the front portion and the rear portion with the image contour position as a boundary in the first luminance signal. A change level detecting means for detecting the magnitude of the change level, a second delay means for giving an incoming carrier color signal a delay time and outputting at least three kinds of carrier color signals having different delay times; and the delay time. Carrier color signal and color synchronization signal One is selected from a phase correction unit that corrects the phase of the carrier color signal having a delay time and at least three types of the carrier color signals that have different delay times that have been phase-corrected so that the phase relationship becomes constant. Output means, based on the position identification result by the position identification means and the change level detection result by the change level detection means, the magnitude of the change level of the luminance signal is larger than a predetermined value, and When it is located at the front part with the image contour position as a boundary, the delay time having the first luminance signal is selected from the delay time having the first luminance signal among the three types of carrier color signals whose phases have been corrected by the selecting means with different delay times. A carrier color signal having a large delay time is selected and output, the magnitude of the change level of the luminance signal is larger than the predetermined value, and the rear portion is defined with an image contour position as a boundary. When it is positioned, the selecting means selects and outputs a carrier color signal having a delay time smaller than the delay time of the first luminance signal among the three types of carrier color signals, and outputs the selected carrier color signal. The selecting unit is controlled so that the selecting unit selects and outputs the carrier color signal having the same delay time as that of the first luminance signal while the level is smaller than the predetermined value. An image quality improving circuit for a color television receiver, comprising: