JPH0326070A - Contour emphasis 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 [Object of the Invention] (Industrial Application Field) The present invention relates to an edge enhancement circuit used in, for example, a digital television receiver, which processes a baseband video signal.

(Prior Art) Generally, a digital television receiver is provided with an edge enhancement circuit that amplifies the Takagi component of a luminance signal or a color difference signal.

FIG. 2 shows a conventional contour enhancement system.

In the NTSC system, per field (525/2)
Images are transmitted using the scanning lines of a book, but in recent years, by applying scanning line interpolation processing between lines and between full fields, images consisting of 525 scanning lines per field can be projected. A television receiver has been developed.

The input terminal 11 receives a luminance signal that has been subjected to interpolation processing for sequential scanning as described above.

The luminance signal is multiplied by (-1/4) by a coefficient multiplier 21 and an IH.
The signal is supplied to delay line 12. IH delay line 1 connected in series
2, 13, and 14 all have the same configuration, and each has a delay amount in the early stage of one water. The output of the delay line is input to filters 20 and 30.

The filter 20 has coefficient units 21, 22, and 23, the coefficient unit 22 has the output of the delay line 13, and the coefficient unit 23 has the output of the delay line 1.
5 outputs are provided. Further, the filter 30 includes a coefficient unit 3
1, 32, and 33, the output of the delay line 12 is supplied to the coefficient unit 31, the output of the delay line 13 is supplied to the coefficient unit 32, and the output of the delay line 14 is supplied to the coefficient unit 33.

The outputs of the coefficient multipliers 21, 22, and 230 are added in an adder 24, and after being adjusted to an appropriate amplitude in a coefficient multiplier 25, the outputs are added in an adder 16.
is input. Further, the outputs of the coefficient units 31, 32, and 33 are added by an adder 34, and after being adjusted to an appropriate amplitude by a coefficient unit 35, the outputs are input to an adder 16. The output of the adder 16 is delivered to an output terminal via a limiter circuit 17 as an edge emphasis signal.

The characteristic of the filter 20 is the frequency characteristic 40 shown in FIG. 3, and the center frequency is (525/4) (cpl1).

On the other hand, the characteristics of the filter 30 are (525/2) (cp
By setting the center frequency at h), it can be expressed as the frequency characteristic 41 in FIG. Therefore, from the adder 16, (525/4) (cph
), (525/2) (cph) components are outputted, and the amplitude is limited by the limiter circuit 17 and the output is eliminated.

In order to facilitate the explanation of vertical contour enhancement, luminance encapsulation in the vertical direction will be expressed and explained using the method shown in FIGS. 4 and 5.

In this method, a picture in one field is cut vertically, and the brightness at the cut point is schematically expressed for each scanning line. The vertical axis is the brightness, and the horizontal axis is the scanning line number. Input terminal 11
The luminance signal input from the output terminal 18 has a value of 0 to 255, and the signal output from the output terminal 18 also has a value of 0 to 255.
It can take values up to 5. Further, the coefficient values of the coefficient multiplier 25 and the coefficient multiplier 35 are both assumed to be 1 in the explanation.

The pattern 51 in FIG. 4 is a pattern (525/2) (cph), and is emphasized as an output by the vertical contour emphasizing circuit as shown in the pattern 61 in FIG. Also, the fourth
The picture 52 in the figure is a picture (525/4) (cph), and the output is emphasized as shown in the picture 62 in FIG. In both cases, the difference in brightness increases, making the image clearer in appearance. This principle provides contour enhancement.

By the way, if the outline of the pattern 53 and pattern 54 in FIG. 4 is emphasized, the pattern 63 and pattern 64 in FIG.
get. This kind of step-like pattern is (525/4
)(cph) and (525/2)(cph), so if the above circuit is used to enhance the contour, overshoot and brishoot will appear on the two lines above and below the edge. And apparently, (525/4) (
cph) Only a certain amount (lower frequency components) becomes noticeable. However, in such an edge part,
Emphasizing (525/2) (cph) results in a more natural and detailed image.

(Problem M to be Solved by the Invention) As mentioned above, according to the conventional contour enhancement circuit, when multiple frequency components are emphasized, lower frequency components are Only the emphasis on the minutes is noticeable and is visually undesirable.

Accordingly, the present invention provides an edge enhancement circuit that reduces the degree of emphasis of some contours with low frequencies and does not impair the effect of emphasizing contour components with high frequencies in a step-like pattern with a spread in frequency components. The purpose is to

[Effects of the Invention] (A! Means for Solving Problem) The present invention provides an edge enhancement circuit that extracts components in different frequency bands from a baseband video signal using transversal filters and enhances their amplitude. In addition to the target filter that extracts the lowest frequency component of the transversal filter and emphasizes its amplitude, multiple delay lines are connected in series with the baseband video signal as input, and each delay line tap has a A delay means for obtaining a plurality of baseband video signals with different delay times, and a first difference between a signal of this main tap and a signal of a tap with a larger delay amount, centering on the main tap of this delay means. and means for obtaining the absolute value thereof, and means for obtaining a second difference between the signal of the main tap and the signal A of the tap with a smaller delay amount and its absolute value, also centering on the main tap of the delay means. and the above first and second
The control signal is calculated using the absolute value of ε to extract a control signal representing the degree of level change in the edge portion, and is provided with means for reducing the gain of the output of the filter in the edge portion of the control signal.

(Function) With the above means, the filter that emphasizes the contours of low frequency components has its gain controlled at the edges, so the gain does not decrease in sinusoidal patterns.
The gain can be lowered for a step-like pattern in which a high frequency band exists at the edge. Therefore, the contour enhancement effect can be effectively exhibited.

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

FIG. 1 shows an embodiment of the present invention, in which a video signal is supplied to an input terminal 11 and introduced into a delay circuit 52. In FIG. The delay circuit 52 has a plurality of taps, and each tap can obtain a video signal with a different delay time.

A plurality of filter circuits are connected to this delay circuit 52, and each of them constitutes a transversal type filter together with the delay circuit, and each transversal type filter has a tap connection devised so that the center frequency is different. The frequency bands of the extracted components are different. In the figure, two filter circuits 53 and 54 are illustrated.

Here, the filter circuit 54 is set to extract components with a lower frequency than the filter circuit 53.

The filter circuit 54 includes coefficient units 55, 56, 57 and T-7.
However, the coefficient multiplier 56 is supplied with a signal from the main tap. Coefficient multipliers 55 and 57 have coefficients of (-174), and coefficient multiplier 56 has a coefficient of (1/4).

The outputs of the coefficient units 56 and 55 are added together in an adder 58, and the outputs of the coefficient units 56 and 57 are added together in an adder 59.

The outputs of the adders 58 and 59 are added in an adder 60, and the output is adjusted in amplitude by a coefficient multiplier 61 and supplied to an adder 62.

On the other hand, the output of the adder 58 (representing the signal difference between the main tap and the tap on the coefficient unit 55 side) is further input to the absolute value circuit 71. Further, the output of the adder 59 (representing the signal difference between the main tap and the tap on the coefficient unit 57 side) is further input to the absolute value circuit 72. The outputs of the absolute value circuits 71 and 72 are supplied to a maximum value circuit 73 and a minimum value circuit 74. Maximum value circuit 7
The maximum value taken out from No. 3 and the minimum value taken out from the minimum value circuit 74 are input to an arithmetic circuit 75. The arithmetic circuit 75 can use the maximum value and the minimum value ε to obtain a control signal indicating whether the edge portion is sharp or not.

The control signal is supplied to the control terminal of the coefficient multiplier 61 via the limiter circuit 76. The signal thus extracted through the filter 54 is gain-controlled by the coefficient multiplier 61 and then input to the adder 62 .

The outputs of other filter circuits are also supplied to the adder 62, and the outputs thereof are led out to an output terminal 63 as an edge emphasis signal.

According to the above-described contour enhancement circuit, the frequency characteristics of the transversal filter section are the same as those shown in FIG. However, when contour emphasis is applied to low-frequency components, the gain is controlled at the edges, so the gain does not decrease with sinusoidal patterns, and high-frequency components exist at the edges. The gain can be lowered for step-like patterns. Therefore, the contour enhancement effect can be effectively exhibited.

The operation of the above circuit will be further explained.

Now, an explanation will be added assuming that the output of the maximum value circuit 73 is x1 and the output of the minimum value circuit 74 is y.

The arithmetic circuit 75 inputs the maximum value among the outputs of the picture normalization circuit including the absolute value circuits 71 and 72, and when the value is small, it outputs a large absolute value, and when it is large, it outputs the maximum value. a first nonlinear circuit that outputs a value with a small absolute value, and a second nonlinear circuit that receives the above-mentioned minimum value as an input and outputs a value with a small absolute value when the value is small, and outputs a value with a large absolute value when the value is large. and fourth adder means ε for summing the outputs of the first and second nonlinear circuits.

That is, if the output of the arithmetic circuit 75 is f (X.y), then
Due to its internal circuit, the arithmetic circuit has f (X, y) = MAX (Φ, c-ax) 10 by
(a.b.c. are positive numbers)...(1) (However, MAX (α, β) is a function that outputs large values of α and β.) The following calculation is performed. f (X.y) is the limiter circuit 7
6, and the limiter circuit 76 obtains an output α. The characteristics of the limiter circuit 76 are as follows.

a-k. (f(X.y) >k)=f (
X. y) (k≧f (X.y) a O ) Therefore, α takes the range of 0≦α≦k.

α is supplied to the coefficient multiplier 61 as a control signal, and
1 multiplies the output from the adder 60 by (α/k).

At the edge portion of the step-like pattern, the value of α approaches O, so the output of the coefficient multiplier 61 that adjusts the gain of the transversal filter becomes small. In addition, since the value of α approaches k in areas other than the edge portions of the step-like pattern, the transversal filter simply follows the adder 62.
will be introduced in

Furthermore, an explanation will be added regarding equation (1). Equation (1) is composed of the sum of two terms. The edge portion of the step-like pattern is characterized by a large value of X, and furthermore, a value of y-0. Therefore, we prepare the first term whose value decreases as X increases (however, it becomes 0 when C-aX is negative) and the second term whose value decreases as y decreases, and then add I try to take it.

f (X-y) obtained in this way approaches O only at the above-mentioned edge portion, and the value tends to increase elsewhere. When f (X.y) reaches a predetermined level k or higher, the output of the transversal filter is adopted as is, assuming that it is not the above-mentioned edge. Also, when (X.y) becomes below the predetermined level k,
The coefficients of the coefficient unit 61 are changed according to the value of t (X.y), and control is performed so that the emphasis on the low frequency components of the edge is suppressed and the high frequency components are made more noticeable. In addition, as specific numerical values, values were taken from 0 to 255<8 bits), and good results were obtained in the case of a-1, b-2, and e-8 when k-8.

[Effects of the Invention] As explained above, the present invention reduces the degree of emphasis of contour components with low frequency and impairs the effect of emphasizing contour components with high frequency in a step-like pattern with spread in frequency components. Therefore, it is possible to improve the visual contour enhancement effect.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a conventional edge enhancement circuit, and FIG. 3 is a diagram showing "characteristics shown to explain the operation of the circuit in FIG. 4 and 5 are signal waveform diagrams shown to explain the problems of the conventional contour enhancement circuit. 52...delay circuit, 53, 54...filter circuit,
55, 56, 57...Coefficient unit, 58, 59, 60...
- Adder, 61... Coefficient unit, 62... Adder, 71
, 72... Absolute value circuit, 73... Maximum value circuit, 74
... Minimum order circuit, 75 ... Arithmetic circuit, 76 ... Limiter circuit.

Claims (2)

[Claims] (1) In an edge enhancement circuit that uses transversal filters to extract components in different frequency bands from the baseband video signal and emphasize their amplitude, the components in the lowest frequency band of the transversal filters are extracted and the amplitude In addition to the target filter to be emphasized, a delay means receives the baseband video signal as input and obtains a plurality of baseband video signals having different delay times at the taps of each delay line, in which a plurality of delay lines are connected in series; means for obtaining a first difference and its absolute value between a signal of the main tap and a signal of a tap with a larger delay amount, centered on the main tap of the delay means; , means for obtaining a second difference between the main tap signal and a tap signal with a smaller delay amount and its absolute value, and calculating using the first and second absolute values. Extract the control signal that represents the degree of level change at the edge,
An edge enhancement circuit characterized in that the control signal includes means for reducing the gain of the output of the filter at edge portions. (2) a first coefficient multiplier that multiplies the input video signal by (-1/4); a first delay element that delays the input video signal by τ; 4) a second coefficient multiplier, a second delay element that delays the output of the first delay element by τ, and a third coefficient multiplier that multiplies the output of the second delay element by (-1/4). a first adder that adds the output of the first coefficient unit and the output of the second coefficient unit; the output of the second coefficient unit and the output of the third coefficient unit; a second adder that adds the outputs of the first and second adders; a third adder that adds the outputs of the first and second adders; The input is a picture normalization circuit that outputs the maximum and minimum absolute values of these two inputs; a first nonlinear circuit means that outputs a value and outputs a value with a small absolute value when the value is large; is a second nonlinear circuit means that outputs a value with a large absolute value; a fourth adder means that sums the outputs of the first and second nonlinear circuits; and inputs the output of the fourth adder. a limiter circuit that limits the upper limit of the output value; and a fourth limiter circuit that receives the output of the third adder and the output of the limiter circuit and adjusts the gain of the output of the third adder based on the output of the limiter circuit. A contour emphasizing circuit characterized by comprising a coefficient unit.