JPH0468974A - Contour emphasis circuit - Google Patents

Abstract

PURPOSE:To emphasize only a contour part even when a change in a luminance level of an input luminance signal is comparatively slow by using a position information generating circuit so as to obtain position information of a contour part and adding a differentiating signal and a delayed differentiating signal to a delayed luminance signal. CONSTITUTION:An internal effective signal required for contour emphasis is extracted based on output signals g, h of a position information generating circuit comprising a slice circuit 5 and a delay circuit 11 through the use of a differentiating signal (e) and a delayed differentiating signal (f) obtained by differentiating a difference signal (c) between an input luminance signal (a) and a delayed luminance signal (b) and added to the delayed luminance signal (b). Then an output signal (i) emphasizing the contour of the input luminance signal (a) is extracted from an adder circuit 3. Thus, as to a signal whose brightness change is comparatively slow, only its contour part is emphasized without changing the behavior of the brightness change in an original luminance signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an edge enhancement circuit that enhances an edge portion of a reproduced luminance signal reproduced by a video tape recorder (VTR) or the like.

(Prior Art) An edge enhancement circuit is used to add sharpness to images reproduced from a VTR or the like.

Conventionally, this type of edge enhancement circuit calculates the difference between an input reproduced luminance signal and a delayed luminance signal delayed by one horizontal scanning period (IH), and then slices the difference signal into slices. Vertical contour enhancement can be performed by adding the result to the IH delayed luminance signal.

(Problem to be Solved by the Invention) By the way, when attempting to perform vertical edge enhancement of an input reproduced luminance signal using the conventional edge enhancement circuit described above, although the amplitude of the input luminance signal is large, the change in luminance is relatively small. When the target area is too high, areas other than the outline where the brightness changes are emphasized, resulting in an unnatural reproduced image where the brightness changes differ from the original brightness signal. There was a point.

The present invention was proposed to solve these problems, and for signals whose brightness changes are relatively wide,
It is possible to emphasize only the outline of the original luminance signal without changing the appearance of the luminance change, and it is also possible to perform emphasis according to the rate of luminance change, emphasizing both the front and rear sides of the luminance change. The purpose of the present invention is to provide an edge enhancement circuit that can perform the following steps.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, an edge enhancement circuit according to the present invention includes: a first delay circuit that delays an input luminance signal for a predetermined period;
a subtraction circuit that takes the difference between the input luminance signal and the delayed input luminance signal output from the first delay circuit; a differentiation circuit that differentiates the difference signal output from the subtraction circuit after amplitude limitation; a second delay circuit that delays a differential signal output from the differential circuit for a predetermined period; and a first amplifier circuit that amplifies the differential signal output from the differential circuit based on a rate of change in the luminance level of the input luminance signal. , the second above
a second circuit for amplifying the delayed differential signal output from the delay circuit based on the rate of change in the luminance level of the input luminance signal;
contour position information for extracting signal components before and after a luminance change corresponding to the contour position from the differential signal output from the differential circuit and the delayed differential signal output from the second delay circuit; a position information generation circuit that generates
Adding an amplified differential signal output from the first amplifier circuit and an amplified delayed differential signal output from the second amplifier to the delayed input luminance signal output from the first delay circuit,
The present invention is characterized in that it includes an addition circuit that performs addition based on the contour position information output from the position information generation circuit, and extracts from the addition circuit an output signal that emphasizes the contour of the input luminance signal.

(Function) According to the above-described configuration, the differential signal obtained by differentiating the difference signal between the input luminance signal and the delayed luminance signal and the delayed differential signal are used to generate the output signal necessary for contour enhancement based on the output signal of the position information generation circuit. Since only the effective signal can be extracted and added to the delayed luminance signal, it is possible to emphasize only the contour part and also to emphasize both the front and rear sides of the luminance change.

Furthermore, contour enhancement can be performed based on the rate of change in the brightness level of the input brightness signal.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

The circuit diagram of FIG. 1 shows an embodiment of an edge enhancement circuit according to the present invention, and FIG. 2 shows an operational waveform diagram of this edge enhancement circuit. Note that the waveform in FIG. 2 is a spatial waveform that indicates the brightness level in the vertical direction when a screen of a video signal is constructed.

In these figures, a luminance signal a reproduced from a VTR or the like enters from an input terminal in and is supplied to a first delay circuit 1 and a subtraction circuit 2. In the delay diagram 81, the input luminance signal a is 1
The delayed input luminance signal, which is delayed by a horizontal scanning period (IH) and produced by the delay circuit 1, is supplied to a subtraction circuit 2 and an addition circuit 3. In Fig. 2, (a) shows the input luminance signal, and (
b) shows the delayed input luminance signal.

In the subtraction circuit 2, the input luminance signal a is subtracted from the delayed input luminance signal a, and the obtained difference signal C ((
The waveform shown in c) is supplied to the amplifier circuit 4 and the slice circuit 5. The difference signal C amplified by the amplifier circuit 4 is supplied to the limiter 6 to limit the amplitude level, and is converted into a square wave signal d shown in FIG. 2(d).

The square wave signal d output from the limiter 6 is transmitted to the differentiating circuit 7
and this differential times F! By differentiating the square wave signal at @7, a differential signal e shown in (e) in FIG. 2 is produced. This differential signal e is supplied to the second delay circuit B8 and the first amplifier circuit 9.

In the delay circuit 8, the differential signal e is delayed by the IH period, and the obtained delayed differential signal f (waveform shown in (f) in FIG. 2) is supplied to the second amplifier circuit 10.

On the other hand, in slice #15, the difference signal C is sliced at a predetermined slice level S, and a slice difference signal g shown in (g) in FIG. 2 is created. This slice difference signal g
is supplied to the delay circuit 11 and the gain control input terminal of the amplifier circuit 10. In this delay circuit 11, the slice difference signal g is delayed by the IH period to produce a delayed slice difference signal shown in FIG. 2 (h). This delayed slice difference signal is supplied to the gain control input terminal of the amplifier circuit 9.

Here, the slice circuit B5 and the delay circuit 11 constitute a position information generation circuit, and after the luminance change corresponding to the contour position is determined from the differential signal e by the delayed slice difference signal of the device information constituted by the delay circuit 11. The slice difference signal g is output from the slice circuit 5.
A signal component on the front side of the luminance change corresponding to the contour position is extracted from the delayed differential signal f. That is, in the adding circuit 3, a differential signal e (described later), a positive polarity pulse component e1 and a negative polarity pulse component e2, which should be added to the delayed luminance signal for contour enhancement, is extracted by the delayed slice difference signal, and the delayed luminance signal is Negative polarity pulse component element 1 and positive polarity pulse component element 2, which will be described later, of the delayed differential signal f to be added to the slice difference signal g are extracted.

In the first amplifier circuit 9, the differential signal e from the differentiating circuit 7 is amplified based on the amplitude level of the delayed slice difference signal, and the positive polarity pulse component e obtained by the amplification is
1 and a negative pulse component e2 is supplied to the adder circuit 3.

Further, in the second amplifier circuit 10, the slice difference signal g
The delayed differential signal f from the delay circuit H8 is amplified based on the amplitude level of the delay circuit H8, and the delayed differential signal f′ consisting of the amplified negative pulse component 1 and positive pulse component 2 is added. Supplied to circuit 3.

Note that the amplitude levels of the delayed slice difference signal 1 and the slice difference signal g correspond to the rate of change in the brightness level of the input brightness signal a. Weighted differential signal e output from circuit 9
- and the weighted delayed differential signal f'' output from the amplifier circuit 10, the output terminal OUT outputs only the outline portion according to the brightness level as shown in (i>) in FIG. A brightness signal i in which the contour is emphasized is collected.The brightness signal i in which the contour is emphasized is such that both the front side and the rear side of the brightness change corresponding to the contour portion are emphasized.

Note that the weighting ratios in the first and second amplifier circuits 9.10 are not necessarily proportional to the amplitude levels of the delayed slice difference signal g and the slice difference signal g;
For example, if the brightness change of the input brightness signal a is large and there is no need to emphasize the contour part, based on the amplitude levels of the delayed slice difference signal and the slice difference signal g,
When the amplitude level exceeds a certain level, the amplifier circuit 9.10
It is also possible to perform no weighting or to perform weighting by a certain predetermined amount.

〔Effect of the invention〕

As explained above, according to the present invention, the differential signal obtained by differentiating the difference signal between the input luminance signal and the delayed luminance signal and the delayed differential signal are added to the delayed luminance signal to emphasize the contour part. , the position information of the contour is obtained by the position information generation circuit and the differential signal and delayed differential signal are added to the delayed luminance signal, so even if the luminance level of the input luminance signal changes relatively slowly, the contour It is possible to emphasize only a portion, and there is no problem that occurs in the conventional method where the appearance of changes in brightness differs from the original input brightness signal.

In addition, it is possible to change the level of edge enhancement according to the degree of change in the brightness level of the input brightness signal, and it is also possible to emphasize both the front and rear sides of the brightness change in the contour part, so the screen after contour emphasis It becomes possible to obtain reproduced images that are free from unnaturalness and have sharpness.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an edge enhancement circuit according to the present invention, and FIG. 2 is an operation waveform diagram for explaining the operation of the edge enhancement circuit of FIG. 1. 1...First delay circuit 2...Subtraction circuit 3...Addition circuit 4...Amplifier 5...Slice circuit 6...Limiter 7...Differentiation circuit 8...Second Delay circuit 9...first amplifier 10...second amplifier 11...delay circuit

Claims (1)

[Scope of Claims] A first delay circuit that delays an input luminance signal for a predetermined period; a subtraction circuit that takes a difference between the input luminance signal and a delayed input luminance signal output from the first delay circuit; a differentiating circuit that differentiates the differential signal output from the subtracting circuit after limiting the amplitude; a second delay circuit that delays the differential signal output from the differentiating circuit for a predetermined period; a first amplification circuit that amplifies the delayed differential signal output from the second delay circuit based on the rate of change in the brightness level of the input brightness signal; a second amplifying circuit for amplifying; and extracting signal components before and after the luminance change corresponding to the contour position from the differential signal output from the differentiating circuit and the delayed differential signal output from the second delay circuit. a position information generation circuit that generates contour position information; and a delayed input luminance signal output from the first delay circuit, an amplified differential signal output from the first amplifier circuit, and an amplified differential signal output from the second amplifier. The amplified delayed differential signal to be
An outline emphasizing circuit comprising: an adding circuit that performs addition based on outline position information output from the position information generating circuit, and extracting an output signal emphasizing the outline of the input luminance signal from the adding circuit.