JPS61274490A - Picture quality improvement circuit of color tv receiver - Google Patents

Abstract

PURPOSE:To make the outline of a picture variable in color sharp by detecting an outlined portion of the picture in luminance signals and permitting the outlined portion of its picture to accommodate to the level variation of luminance signals which are generated at the forth and back of portions bordered by the outlined portion and also outputting color-difference signals respectively different in delay time after changing over them. CONSTITUTION:The inputted color-difference signals 7 are delayed by color-difference signal delay circuits 4 and 4' and these color-difference signals having different delay times which are shown in wave-forms (i), (j) and (k) are inputted to a changing-over circuit 5. When a changing-over control signal (h) exceeds a positive specified level, its color-difference signal wave-form (k) large in delay time is outputted by the changing-over circuit 5. When the changing-over control signal (h) exceeds the negative specified level, the color-difference signals are changed over so that its color-difference signal wave-form (i) is outputted. When the changing-over control signal (h) doesn't belong to either level mentioned as above, the color-difference signals are changed over so that its color-difference signal wave-form (j) is outputted. Thus, this approach makes the color's outline sharp and also a reproduced picture eliminate the slipping off of color by detecting the outlined portions of the luminance signals and changing over the color-difference signals through the changing-over circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application 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 a luminance signal with a frequency band of about 4.5 MHz and a color difference signal with a frequency band of 0.5 to 1.5 MHz superimposed. For this reason, in images reproduced on a color television receiver, contours as boundaries where brightness changes can be reproduced as having sharp brightness changes, but boundaries where color changes are less sharp. The image quality is good.

Therefore, as a circuit for improving the image quality of such reproduced images,
For example, an image quality improvement circuit has been proposed as shown in Japanese Patent Laid-Open No. 54-140825.

FIG. 3 is a block diagram showing an image quality improvement circuit according to the above-mentioned existing proposal. In the figure, 11 is a high-pass filter, 12 is a trigger generation circuit, 13 is a delay circuit, 14 is a switch changeover circuit, and 15 is a comparison circuit.

FIG. 4 is a waveform diagram of each part of the circuit shown in FIG. 3.

The circuit operation will be described below with reference to FIGS. 3 and 4.

゛The brightness signal Y is 4.5MH as shown in Fig. 4 (al).
Since the signal has frequency components up to z, the signal waveform has a sharp rise even in the outline of a colored image.

When this waveform (a) passes through the high-pass filter 11 shown in FIG. 3, it becomes only the high-frequency component of the luminance signal, as shown in waveform ('b), and is slightly delayed.

On the other hand, the color difference signal C is divided into a signal that is supplied to the switch changeover circuit 14 through the delay circuit 13 and a signal that is directly supplied to the switch changeover circuit 14 . The latter signal is
The waveform is shown in FIG. 4 (C1), and the former is the waveform shown in (d).

As can be seen from the figure, the waveform of the color difference signal (C1, (d) has a frequency band of about 0.5 to 1.5 MHz, so it is a fairly smooth waveform. Also, the waveform (C) and waveform (d) are the luminance signal. It can also be seen that the waveform (b) of the high-frequency component comes before and after the waveform (b) of the high-frequency component.As for the output of the color difference signal, first, the color difference signal waveform (d) on the side delayed by the switch switching circuit 14 is output. be done.

Next, a switching signal is given from the trigger generation circuit 12 to the switch switching circuit 14 based on the high frequency component b1 of the luminance signal, that is, a signal indicating the outline position of the image, so that the non-delayed color difference signal waveform (C) is output. Switch to . Thereafter, when the waveform (C1) and the waveform (dl) match, a switching signal (f) is again given to the switch switching circuit 14 from the comparison circuit 15 that compares the waveform (C) and the waveform (d), and the color difference signal waveform ( d) is output.Furthermore, the switch switching circuit 14 is energized by the high frequency component b2 of the luminance signal, and the color difference signal output (fl) is switched from the waveform (dl) to (C).

In this way, the color difference signal waveform is switched from (d) to (C1) every time the high-frequency component of the luminance signal is As a result, the color difference signal output becomes as shown in the waveform (e) in FIG. 4, and an image with clear outlines can be obtained even at color boundaries.

As explained above, the conventional image quality improvement circuit proposed previously detects the contour position of an image in a luminance signal, switches and outputs a color difference signal with a different delay time based on this detection signal, and then outputs a color difference signal with a different delay time. Different color difference signals are compared, and when they match, the color difference signals are switched and outputted again to sharpen the outline of the color.

However, this method switches the color difference signal output when color difference signals with different delay times match, so it cannot be used for images where the color difference signal changes gradually immediately after a portion where the luminance signal changes significantly. In this case, color difference signals with different delay times do not match each other during this period, and a time difference occurs between the luminance signal and the color difference signal output, causing a color shift phenomenon in the reproduced image.

[Purpose of the invention]

An object of the present invention is to reproduce an image in which the outline of the color that changes according to the outline of the luminance is clear even in the case of an image in which the color difference signal changes gradually immediately after a part where the luminance signal changes greatly. The purpose of the present invention is to provide a circuit for improving the image quality of a color television receiver.

[Summary of the invention]

The present invention utilizes the property that the brightness also changes somewhat at the boundary where the color changes, and in order to solve the above problem, the outline of the image in the brightness signal is detected, and The color difference signals with different delay times are switched and outputted in accordance with the level change of the luminance signal at the positions before and after the border of this contour. In other words, the color difference signal is adaptively output from only the luminance signal. This method reproduces the boundaries and sharpens the outline of the image where the color is changing.

[Embodiments of the invention]

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

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram of various signals in FIG. 1.

In FIG. 1, an input luminance signal 6 is input to a luminance signal delay circuit 1.
. is input. The output signals of the subtraction circuits 2 and 2' have waveforms (d) and (
The result is a difference signal between the input signals as shown in e). The waveform shaping circuit 3.3' aligns the polarity of the difference signal and makes the waveform (f
) and waveform (outputs a signal as shown in the figure).

As a specific circuit example of the waveform shaping circuit 3, for example, a double-wave rectification detection circuit or an absolute value conversion circuit can be considered.

Furthermore, the output signal of the waveform shaping circuit 3.3' is input to the subtraction circuit 9, which generates a difference signal, that is, a switching control signal as shown in the waveform (hl) in FIG.
) As is clear from the relationship between the delayed luminance signal and the switching control signal shown in the waveform (hl), the switching control signal has positive polarity immediately before the outline of the luminance signal, and negative polarity immediately after the outline of the luminance signal. You can understand what it shows.

On the other hand, the input color difference signal 7 is delayed by the color difference signal delay circuit 4゜4', and the color difference signals having different delay times shown in waveform (1), waveform (''), and waveform (k) are input to the switching circuit 5. be done.

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

When the switching control signal exceeds a predetermined positive level, the switching circuit 5 controls the color difference signal waveform (k
) is output, and when the switching control signal exceeds a predetermined negative level, the switching control signal is switched so that the delay time color difference signal waveform (1) is output, and the switching control signal is If the level does not belong to any of the above,
The signal is switched so that the color difference signal waveform ('') is output.

As described above, the contour part of the luminance signal is detected, and the color difference signal is switched by the switching circuit 5 in accordance with the level change of the luminance signal in the contour part, and the waveform shown in FIG.
) can be obtained, and a reproduced image with clear color outlines and no color shift can be obtained.

In the above embodiments, the switching circuit 5 has been described as switching between color difference signals having three types of delay times, but the switching control signal is used to finely determine the level of four or more types of color difference signals having different delay times. It may also be a switching circuit that switches and outputs depending on the situation.

Furthermore, as is clear from the fact that the relationship between waveform (d) and waveform (e) or waveform (f) and waveform (g) in FIG. 2 is the same waveform with a predetermined delay time difference, the luminance signal There is only one system of delay circuit 1.1", tA calculation circuit 2.2' and waveform shaping circuit 3.3', and the input of the subtraction circuit 9 is connected to the waveform (
f) and the waveform obtained by providing a delay circuit that delays this for a predetermined time to obtain the waveform (g'l) (by making it phantom, the output of the subtraction circuit 9 has the waveform explained in the embodiment) It is easy to understand that fh) can be obtained.

Further, the switching control signal for controlling the switching of the switching circuit 5 may be a signal that can distinguish the luminance level at the positions before and after the outline of the luminance as a boundary, and this embodiment uses the switching control signal. It does not specify the signal format or signal creation method.

〔Effect of the invention〕

According to the present invention, it is possible to provide an image quality improvement circuit for a color television receiver that can prevent color shift in a reproduced image and sharply reproduce the outline of a colored image. It is possible to obtain good image quality that is not found in other cameras.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of various signals in the circuit shown in Fig. 1, Fig. 3 is a block diagram showing a conventional image quality improvement circuit, and Fig. 4 is a block diagram showing an example of the present invention. 4 is a waveform diagram of various signals in the circuit of FIG. 3. FIG. Explanation of symbols 1.1'... Luminance signal delay circuit, 2.2'... Subtraction circuit, 3.3'... Waveform shaping circuit, 4.4'... Color difference signal delay circuit, 5. ...Switching circuit, 6...Input luminance signal, 7...Input color difference signal, 8...Output color difference signal,
9 subtraction circuit, 11...high-pass filter, 12...trigger generation circuit, 13...delay circuit, 14...switch changeover circuit, 15...comparison circuit Representative Patent Attorney Akio Namiki 1 figure 112i111 13m1 I4all

Claims (1)

[Claims] 1) A first delay means for outputting a first luminance signal by adding a delay time to an incoming luminance signal; a position identification means for outputting a position identification signal by identifying whether the image is at a position or a rear position; and a luminance between a front part and a rear part bordering on the image contour position in the first luminance signal. a change level detection means for detecting the magnitude of the change level of the signal; a second delay means for outputting color difference signals having at least three different delay times by adding a delay time to the incoming color difference signal; and selecting means for selecting and outputting one of the color difference signals having three different delay times, wherein the magnitude of the change level of the luminance signal is greater than a certain predetermined value, and the image When the signal is at a position before the contour position, a color difference signal having a delay time larger than the delay time of the first luminance signal is selected from among the three types of color difference signals having different delay times. and when the magnitude of the change level of the luminance signal is larger than the predetermined value and is located at a position after the image contour position, the first luminance signal among the three types of color difference signals is output. A color difference signal having a delay time smaller than the delay time of the first luminance signal is selected and output, and while the magnitude of the change level of the luminance signal is smaller than the predetermined value, the delay is the same as the delay time of the first luminance signal. An image quality improvement circuit for a color television receiver, characterized in that a color difference signal having time is selected and output.