JPH0738780A - Image contour enhancer - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an image contour enhancer capable of smoothly enhancing the contour of an image. A bandpass filter BP that forms a transfer characteristic for inputting a video signal and generating an enhanced signal component that is a multiplication of a linear function and an attenuation function of an exponential function when the video signal has a step response. An amplifier 4 that amplifies the output signal and changes the slope of the linear function to reduce the maximum and minimum amplitude difference of the emphasized signal, and a signal output from this amplifier 4 and a signal of the high-pass filter 5 are combined. A first adder 6 and a second adder 9 for synthesizing the emphasized signal of the gain control circuit 7 with the video signal delayed by the delay device 8 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image contour enhancer used in an image device of electronic equipment and communication equipment.

[0002]

2. Description of the Related Art In recent years, image contour enhancers have come to be used in various video equipment such as television receivers and VTRs. The conventional image contour enhancer will be described below. That is, FIG. 5 is a block diagram of a conventional image contour enhancer, in which 1 is an input end of a video signal and 21 is a first primary
High pass filter (hereinafter referred to as HPF) of 22 and 1
The next second HPF, 7 is a gain control circuit (hereinafter referred to as GCA), 8 is a video signal delay device, 9 is an adder for adding the output signal of GCA 7 to the delayed video signal, and 10 is an output end. is there.

The operation of the image contour enhancer configured as described above will be described below. That is, first consider the transient waveform of a video signal, for example, the response of a step wave and the transfer characteristic of each filter. When a video signal is input to the input terminal 1, the transfer characteristic H _HPF1 (s) of the first-order first HPF 21 becomes s function H _HPF1 (s) = s / (s + 1 / RC) (1). Here, R is a resistor forming a filter, and C is a capacitor forming a filter. Next, when a transfer characteristic equivalent to that of the first HPF 21 of the first order is given to the second HPF 22 of the first order, the total pass characteristic H by the two-stage filter is obtained.
₁ (s) becomes H ₁ (s) = {s / (s + 1 / RC)} ² (2). The step response of this system is H ₁ (S) · U (s) = s / (s + 1 / RC) ² considering the Laplace transform U (s) = (1 / s) of the step function. The inverse Laplace transform of the s function is the step response enhancement signal h ₁ (t), and h ₁ (t) = (1−t / RC) exp (−t / RC) (3).

The signal amplitude of this emphasized signal is adjusted to an appropriate level by the GCA 7, and this signal is added to the video signal delayed by the delay device 8 in antiphase by the adder 9 to emphasize the front and rear of the step function. To do. The edge-enhanced signal is output 10
To output. Waveforms of the step responses of the respective parts a to d in FIG. 5 are shown in (a) to (d) of FIG.

[0005]

However, in the configuration of this conventional image contour enhancer, the first portion of the enhancement of the enhancement signal by the step response is overemphasized more than the other portions, resulting in an unnatural screen. It had drawbacks. For example, the maximum value and the minimum value of the emphasis signal h ₁ (t) are h ₁
(0) = 1, h ₁ (2RC) = − e ⁻² . That is, the strongest edge enhancement occurs at t = 0, and there is an amplitude difference of 1: 0.135 between the peaks before and after the enhanced portion.

Therefore, an object of the present invention is to solve the above-mentioned conventional drawbacks and to provide an image contour enhancer capable of smoothly enhancing the contour of an image.

[0007]

An image contour enhancer according to claim 1 is an enhancement signal component which is a multiplication of a linear function and an exponential decay function when a video signal is input and the video signal is a step response. A bandpass filter that forms a transfer characteristic that generates a signal, an amplifier that amplifies the output signal of the bandpass filter and changes the slope of the linear function to reduce the maximum and minimum amplitude difference of the emphasis signal, and a video signal Inputting a high-pass filter, a first adder for synthesizing the signal output from the amplifier and the signal component output from the high-pass filter, and adjusting the amplitude of the emphasized signal output from the first adder. A gain control circuit, a delay device for delaying the video signal, and a second adder for combining the emphasis signal of the gain control circuit with the video signal delayed by the delay device to emphasize before and after the step function. It includes those were.

According to a second aspect of the present invention, in the image contour enhancer according to the first aspect, the bandpass filter is composed of a first high-pass filter and a low-pass filter for sequentially inputting a video signal, and a high-pass filter for inputting a video signal. The first high-pass filter also serves as the pass filter.

[0009]

According to the image contour enhancer of claim 1, when the video signal is input to the bandpass filter, when the video signal has a step response, the transfer function of the filter multiplies the linear function and the attenuation function of the exponential function. And the signal component of the video signal input to the high-pass filter, where the slope of the linear function is properly set by the amplifier so that the maximum and minimum amplitudes of the emphasized signal are approximately equal. The emphasized signal is combined by the first adder, its amplitude is adjusted by the gain control circuit, and this emphasized signal is combined with the video signal delayed by the delay device by the second adder. An output is obtained in which the front and back are emphasized and the contour of the image is emphasized.

In this case, since the emphasized signal component is generated by the band pass filter and the maximum value width and the minimum value width of the emphasized signal are made equal by the amplifier to eliminate the amplitude difference,
You can get a well-balanced correction to the contours of the image,
It is possible to realize an excellent image contour enhancer capable of smoothly enhancing the contour of an image. According to a second aspect of the present invention, in the image contour enhancer according to the first aspect, the bandpass filter includes a first high-pass filter and a low-pass filter that sequentially input a video signal, and a high-pass filter that inputs a video signal. Since the first high-pass filter is also used, the configuration is simplified by the common use in addition to the operation of claim 1.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image contour enhancer according to a first embodiment of the present invention will be described with reference to FIGS. Figure 1
FIG. 3 is a block diagram of the image contour enhancer in the first embodiment. In FIG. 1, reference numeral 1 is an input end of a video signal, and 2 is a first primary of a bandpass filter BP.
High pass filter (hereinafter referred to as HPF), 3 is a first-order low pass filter (hereinafter referred to as LPF) that constitutes a band-pass filter BP, 4 is an amplifier, and 5 is a first-order second filter that inputs a video signal. HPF, 6 is a first adder, 7 is a gain control circuit (hereinafter referred to as GCA), 8 is a delay device, and 9 is a second
The adder 10 is an output end of the video signal whose contour is emphasized.

The first HPF 1 and LPF 3 forming the bandpass filter BP input an image signal, and when the image signal has a step response, an emphasis signal component which is a multiplication of a linear function and an attenuation function of an exponential function. Configure the transfer characteristic to be generated. The amplifier 4 includes the first HPF1 and the LPF3.
The amplitude difference of the maximum and minimum amplitudes of the emphasized signal is reduced by amplifying the output signal of 1 and changing the slope of the linear function. Second H
The video signal is input to the PF 5, and the first adder 6 is the amplifier 4
The signal output from the second HPF 5 is combined with the signal output from the second HPF 5. The GCA 7 adjusts the amplitude of the emphasis signal output from the first adder 6, the delayer 8 delays the video signal, and the second adder 9 adds the emphasis signal of the GCA 7 to the video signal delayed by the delayer 8. To output a contour-enhanced video signal that emphasizes the front and back of the step function.

The operation of the image contour enhancer of the first embodiment thus constructed will be described below. First, the enhancement signal h ₂ (t) is defined as follows. _{That, h 2 (t) = (} 1-at / RC) exp (-t / RC) ...... (4) where, by differentiating h ₂ (t), at time _{t, dh 2 (t) /} dt = [{(At / RC) -1-a} exp (-t / RC)] / RC becomes (5), and h ₂ (t) is t _min = RC (1 + a) / a (6) At this time, the minimum value is taken, and h ₂ (t _min ) = − a × exp {− (1 + a) / a} (7) Here, if the constant a is set to 3.59, the relationship between the maximum value h _2MAX and the minimum value h _2MIN of the emphasis signal h ₂ (t) is h _2MAX ≈−h _2MIN , and the amplitude difference before and after the emphasis part is Can be resolved.

Next, a transfer function for realizing this step response is obtained. When the emphasized signal h ₂ (t) is Laplace transformed, H ₂ (s) · U (s) = 1 / (s + 1 / RC) − (a / RC) / (s + 1 / RC) ² (8) Of the transfer function H ₂ (s) is H ₂ (s) = s / (s + 1 / RC) − (as / RC) / (s + 1 / RC) ² (9).

This system includes a first-order HPF and a first-order LP.
It can be composed of F. That is, the transfer function H of the first-order HPF
_HPF1 (s) is shown by the equation (1). And the primary LPF
The transfer function H _LPF1 (s) of is H _LPF1 (s) = 1 / (RC (s + 1 / RC)) (10). Therefore, if the equation (9) is decomposed into the equations (1) and (10), the system as shown in FIG. 1 can be configured.

Here, the amplifier 4 determines the constant a and optimizes the maximum and minimum amplitudes. Then, the first adder 6 combines the emphasized signals. The GCA 7, the second adder 9, and the delay device 8 operate in the same manner as in the conventional example. Further, the waveforms of the points a to d in the step response of FIG. 1 are shown in FIG. According to this embodiment, the first H constituting the bandpass filter BP is
The PF2 and the LPF3 generate the emphasized signal component, and the amplifier 4
Since the maximum value width and the minimum value width of the emphasis signal are made equal to eliminate the amplitude difference, it is possible to obtain a well-balanced correction for the contour of the image, and to enhance the contour of the image smoothly. An image contour enhancer can be realized.

An image contour enhancer according to the second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a block diagram of the image contour enhancer in the second embodiment. That is, in the image edge enhancer according to the first embodiment, the primary second HPF 5 is replaced with the primary first HPF 2.
It is also used for. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof is omitted.

FIG. 4 shows an example of a concrete circuit for synthesizing the emphasized signals, which is a feature of the system of FIG. In FIG. 4, Vsg
Is the signal source. Capacitor C1, resistor R1, power supply V
1, the transistor Q1, and the current source I1 make the HPF
2 and LPF4 with resistor R2 and capacitor C2
And resistors R3 to R5, transistors Q2 to Q4,
The current sources I2 to I4 form the amplifier 5, and the resistor R6, the transistors Q5 to Q7, the resistor R7, and the current sources I5 to I7 form the first adder 6. 1
Reference numeral 8 is a power source application terminal, and 19 is an emphasis signal output terminal.

As described above, even if the first-order first HPF 2 and the first-order second HPF 5 are common, the transfer function H ₂ (s) of the system described in the first embodiment does not change. Therefore, the system of FIG. 3 is equivalent to the system of FIG. 1, the same step response as that of the first embodiment is obtained, and the image contour enhancement similar to that of the first embodiment can be performed. In addition, the configuration is simplified by sharing as compared with the first embodiment.

Furthermore, the same transfer function H ₂ (s) can be realized because the system is equivalent in a system in which the order of filters is exchanged.

[0021]

According to the image contour enhancer of the first aspect, the enhancement signal component is generated by the band pass filter, and the maximum value width and the minimum value width of the enhancement signal are made equal by the amplifier to eliminate the amplitude difference. It is possible to realize an excellent image contour enhancer capable of obtaining a well-balanced correction for the contour of an image and smoothly enhancing the contour of the image.

According to a second aspect of the present invention, in the image contour enhancing apparatus according to the first aspect, the bandpass filter is composed of a first high-pass filter and a low-pass filter for sequentially inputting a video signal, and a high-pass filter for inputting a video signal. Since the first high-pass filter is also used as the pass filter, the configuration is simplified by the common use in addition to the effect of claim 1.

[Brief description of drawings]

FIG. 1 is a block diagram of an image contour enhancer according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of each part thereof.

FIG. 3 is a block diagram of an image contour enhancer according to a second embodiment.

FIG. 4 is a specific circuit diagram of the main part.

FIG. 5 is a block diagram of a conventional image contour enhancer.

FIG. 6 is a waveform diagram of each part thereof.

[Explanation of symbols]

 BP band pass filter 2 first high pass filter (HPF) 3 low pass filter (LPF) 4 amplifier 5 second high pass filter (HPF) 6 first adder 7 gain adjusting circuit (GCA) 8 Delay device 9 Second adder

Claims (2)

[Claims] 1. A bandpass filter which forms a transfer characteristic for inputting a video signal and generating an enhanced signal component which is a multiplication of a linear function and an attenuation function of an exponential function when the video signal is a step response. An amplifier that reduces the maximum and minimum amplitude difference of the emphasis signal by amplifying the output signal of the bandpass filter and changing the slope of the linear function; a high-pass filter that inputs the video signal; A first adder for combining the signal output from the amplifier and the signal component output from the high-pass filter;
A gain control circuit that adjusts the amplitude of the emphasis signal output from the adder, a delay device that delays the video signal, and a step in which the emphasis signal of the gain control circuit is combined with the video signal delayed by the delay device. An image contour enhancer comprising a second adder for enhancing the front and rear of the function. 2. The bandpass filter comprises a first high-pass filter and a low-pass filter for sequentially inputting a video signal, and the first high-pass filter also serves as a high-pass filter for inputting a video signal. The image contour enhancer according to claim 1.