JP3084695B2 - Contour correction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction device, and more particularly to a contour correction device for adding an aperture signal (contour correction signal) to an image signal.

[0002]

2. Description of the Related Art Conventionally, in a video signal processing apparatus such as a video camera, an aperture signal is generated from an image signal (luminance signal) to clarify the outline of an image, and the aperture signal is superimposed on the luminance signal. Accordingly, a contour correcting device for enhancing the contour is provided.

Conventionally, the aperture signal has been generated by a combination of a band-pass filter (BPF) or a differentiating circuit, and the frequency characteristic of the aperture signal has been fixed. For this reason, in a dark scene in which the S / N is poor such that the gain in the automatic gain control circuit (AGC) is large among the shooting scenes of the video camera, the addition of a constant aperture signal further deteriorates the S / N. Therefore, the gain of the aperture signal is reduced or set to zero (see JP-A-61-15472 and JP-A-62-227279).

[0004]

Therefore, in a dark scene, not only the S / N is bad, but also the outline is not clear,
The sense of resolution had dropped. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a contour correction device capable of obtaining an image with a clear contour even in a dark scene with an image having little noise.

[0005]

According to a first aspect of the present invention, there is provided an outline correction apparatus for inputting an image signal and generating an aperture signal based on the image signal. An aperture signal generating means capable of changing the center frequency of the output aperture signal; an adder for adding the aperture signal generated by the aperture signal generating means to the image signal; and a brightness detecting the brightness of the subject. And a contrast detecting means for detecting the contrast of the subject,
Control means for controlling the aperture signal generation means to change a center frequency of the aperture signal according to a combination of brightness and contrast detected by the brightness detection means and the contrast detection means, comprising: And controlling the aperture signal generating means so that the center frequency of the aperture signal increases as the contrast increases, and the aperture signal generating means controls the center frequency of the aperture signal to decrease as the brightness and contrast of the subject decrease. And control means for controlling

Further, as set forth in claim 2 of the present application, there is provided detecting means for detecting whether or not the camera is in focus, and the control means includes:
When the detecting means is detecting an out-of-focus state, the aperture signal generating means is controlled so that the center frequency of the aperture signal is lowered or generation of the aperture signal is prohibited. Further, the aperture signal generating means includes a band-pass filter that passes a predetermined frequency band component as shown in claim 3 of the present application;
A digital filter disposed before or after the bandpass filter, wherein the first delay element delays an input image signal by a predetermined time; and the second delay element delays an output of the first delay element by a predetermined time. , A first adder for adding the input image signal and the output of the second delay element, a first coefficient α changed by the control means, and a first A first multiplier for multiplying an output of the first adder, a second multiplier for multiplying a second coefficient β changed by the control means and an output of the first adder, And a second adder for adding the output of the second multiplier.

[0007]

According to the present invention, when the center frequency of the aperture signal is increased in a scene having a good S / N ratio, a fine picture can be more easily seen by the fine aperture signal.
When the center frequency of the aperture signal is lowered in a scene having a poor quality, attention is paid to the fact that an aperture signal having a large thickness has a small noise sensation and a clear image can be obtained, and the center frequency of the aperture signal (frequency characteristic ) Can be changed, and its characteristics are changed according to the state of the subject.

The aperture signal generating means capable of varying the center frequency of the aperture signal is provided before or after the band pass filter for passing a predetermined frequency band component.
It is configured by providing a digital filter whose characteristics change from a low-pass filter to a high-pass filter only by changing the coefficient.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the contour correcting apparatus according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a video signal processing device of a video camera including a contour correction device according to the present invention.

In FIG. 1, a solid-state imaging device (CCD) 1
The image signal of the object read out from the preamplifier 1
2 and the luminance signal processing circuit 16 via the A / D converter 14
Is added to The luminance signal processing circuit 16 is a trap circuit,
It includes a low-pass filter, generates a luminance signal from the input signal, and outputs the luminance signal to the adder 20 via the delay circuit 18 and to the aperture signal generation circuit 22.

The aperture signal generation circuit 22 includes two digital filters 24 and 26. The digital filter 24 is a low-pass filter (LP) based on the values of coefficients α and β added from a scene determination circuit 36 described later.
F) to a high-pass filter (HPF), and the digital filter 26 has a band-pass filter (BP) that passes a predetermined frequency band component.
F).

FIG. 2 is a circuit diagram showing details of the aperture signal generation circuit 22. As shown in the figure, the digital filter 24 includes delay elements 24A and 24B, an adder 24,
C, 24D and multipliers 24E, 24F. Each of the delay elements 24A and 24B delays the input luminance signal by, for example, a time equivalent to one pixel.

The adder 24C adds the input luminance signal and the luminance signal output from the delay element 24B, and outputs the added value to a multiplier 24E. The multiplier 24E multiplies the added value by a coefficient β. And outputs the result to the adder 24D. To the other input of the adder 24D, an output from a multiplier 24F for multiplying the luminance signal output from the delay element 24A and the coefficient α is added, and the adder 24D adds these two inputs. It is output to the digital filter 26 at the subsequent stage.

Now, assuming that the luminance signal at the present input time of the digital filter 24 is Y ₀ , the luminance signal output from the delay element 24A is Y ₁ , and the luminance signal output from the delay element 24B is Y ₂ . The digital filter 24
The signal Y ′ shown in the following equation is output. Y ′ = Y ₁ · α + (Y ₀ + Y ₂ ) · β Next, the digital filter 26 will be described.

The digital filter 26 includes a delay element 26
A, 26B, 26C, 26D, adder 26E, multiplier 2
6F and a subtractor 26G. Each of the delay elements 26A to 26D delays the input luminance signal by, for example, a time corresponding to one pixel. The adder 26E adds the input luminance signal and the luminance signal output from the delay element 26D, and adds the added value to a multiplier 26F.
, And the multiplier 26F multiplies this addition value by a coefficient 0.5 and outputs the result to the subtractor 26G.

Another input of the subtracter 26G is a delay element 2
The luminance signal output from 6B is added, the subtracter 26G subtracts the output of the multiplier 26F from this luminance signal, and outputs the subtracted value as an aperture signal. Now, the luminance signal at the current input point of the above-described digital filter 26 is Y ′ ₀ (FIG. 3A), the luminance signal output from the delay element 26B is Y ′ ₂ (FIG. 3B), and the delay element 26
Assuming that the luminance signal output from D is Y ′ ₄ (FIG. 3C), the digital filter 24 outputs a signal Y ″ represented by the following equation (FIG. 3D).

Y ″ = Y ′ ₂ − (Y ′ ₀ + Y ′ ₄ ) / 2 That is, this digital filter 26 is used alone as shown in FIG.
B the frequency f _s / 4 is to pass the frequency band component of ± f _s / 4 which is the center frequency (peak) as shown in (A)
Acts as a PF. (F _s is the sampling frequency.) Here, the coefficient alpha, beta to be applied to the digital filter 24 as described above, for example, alpha = 1, when the beta = 0, the digital filter 24 to directly outputs the input signal Become. In this case, the frequency characteristic of the aperture signal output from the digital filter 26 is as shown in FIG.

On the other hand, coefficients α and β are, for example, α = 1, β =
When −0.3 is set, the digital filter 24 acts as an HPF and cuts low frequency components. As a result, the aperture signal output from the digital filter 26 is
As shown in (B), the center frequency increases. If the coefficients α and β are, for example, α = 0.8 and β = 0.2, the digital filter 24 acts as an LPF to cut high-frequency components, and as a result, the aperture output from the digital filter 26. The signal has a lower center frequency as shown in FIG.

Thus, the aperture signal generating circuit 2
2, the gain signal is multiplied by a coefficient γ in a multiplier 28 as shown in FIG.
It is applied to the adder 20. The adder 20 includes a delay circuit 18
And an aperture signal generated based on this luminance signal. By the addition of the aperture signals, a change portion of the luminance signal (a contour portion of the image) is emphasized.

When the center frequency of the aperture signal is increased in a scene having a good S / N ratio, a fine picture can be more easily seen by the fine aperture signal.
If the center frequency of the aperture signal is lowered in a scene with poor quality, a thicker aperture signal produces a less noisey and sharper image. The scene determination circuit 36 shown in FIG. 1 includes an auto iris circuit (AE circuit) 30, an auto focus circuit (AF circuit)
32. Determine the shooting scene based on various types of information added from the contrast detection circuit 34, and control the coefficients α and β output to the aperture signal generation circuit 22.

That is, the AE circuit 30 includes the A / D converter 14
The image signal of a predetermined area in one screen of the image signal added from the image signal is integrated, and a signal indicating the brightness of the subject is output to an iris control unit (not shown) and to the scene determination circuit 36. The AF circuit 32 also integrates the high-frequency components of the image signal of a predetermined area in one screen of the image signal applied from the A / D converter 14, and outputs the integrated value as focus information to a focus control unit (not shown). The focus control unit controls the focus lens so that the focus information has a peak value. Further, the AF circuit 32 outputs a signal indicating whether or not the focus position is within a predetermined focusing range to the scene determination circuit 36. Further, the contrast detection circuit 34 detects the contrast of the picture based on the image signal applied from the A / D converter 14,
A signal indicating the magnitude of the contrast is output to the scene determination circuit 36.

The scene determination circuit 36 outputs a coefficient α, which is output to the aperture signal generation circuit 22 based on these inputs,
is controlled, and the center frequency of the aperture signal output from the aperture signal generation circuit 22 is controlled. That is, when the subject has a standard brightness (medium), a scene darker than the standard (small), a scene brighter than the standard (large), and when the subject has a standard contrast ( The center frequency (high, medium, low) of the aperture signal is controlled as shown in the following table by the combination of medium contrast, smaller contrast than standard (small), and contrast larger than standard (large). I do.

[0023]

[Table 1] Here, the control for setting the center frequency of the aperture signal as the reference (medium) is performed by using the coefficients α = 1 and β as described with reference to FIG.
= 0, and similarly, control for increasing the center frequency higher than the reference is control for giving the coefficients α = 1, β = -0.3 as described with reference to FIG. The control for lowering the center frequency from the reference is control for giving the coefficients α = 0.8 and β = 0.2 as described with reference to FIG.

As described above, in a scene where the brightness and contrast of the subject are large, control is performed so that the center frequency of the aperture signal is increased. In scenes where the brightness and contrast are small,
Control so that the center frequency of the aperture signal is low,
A thicker aperture signal is used to obtain a clearer image with less noise.

Further, the scene determination circuit 36 includes an AF circuit 3
The control is prohibited during the period of inputting the out-of-focus state from Step 2 so that the center frequency of the aperture signal becomes low regardless of the brightness and contrast of the subject, or the aperture signal is not output. To control. The control of the center frequency of the aperture signal is not limited to the case where the control is performed based on the combination of the brightness and the contrast of the subject. For example, the control may be performed based on either the brightness or the contrast of the subject. Alternatively, the control may be performed based on the color tone of the subject, the magnitude of the gain in AGC, and the like.

In this embodiment, the aperture signal generation circuit 22 generates only one type of aperture signal. The center frequency of each of the two types of aperture signals in the horizontal and vertical directions is controlled as described above. You can also. Further, the digital filter 24 may be provided after the digital filter 26 functioning as a BPF.

Further, the aperture signal generating circuit 22 of the present embodiment can change the center frequency of the output signal with a simple circuit configuration. The configuration of the digital filter 24 according to the present embodiment is not limited to a digital filter whose filter characteristics change from LPF to HPF by controlling two or more coefficients.

[0028]

As described above, according to the contour correction apparatus of the present invention, only a thick and clear aperture is generated at low illuminance, so that it is possible to obtain an image with little noise and a clear contour. It is possible to see fine pictures more easily due to the fine aperture at high illuminance,
The brightness (gloss) of the highlight portion can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a video signal processing device of a video camera including a contour correction device according to the present invention.

FIG. 2 is a circuit diagram showing details of an aperture signal generation circuit in FIG. 1;

3 (A) to 3 (D) respectively show the BPF of FIG. 2;
5 is a timing chart used to explain the above.

FIGS. 4A to 4C are graphs showing frequency characteristics used to explain that the center frequency of the BPF can be changed by giving different coefficients.

[Explanation of symbols]

Reference Signs List 10 CCD 12 Preamplifier 14 A / D converter 16 Brightness signal processing circuit 20, 24C, 24D, 26E Adder 22 Aperture signal generation circuit 24, 26 Digital filter 24A, 24B, 26A, 26B, 26C , 26D delay element 24E, 24F, 26F, 28 multiplier multiplier 26G subtractor 30 AE circuit 32 AF circuit 34 contrast detection circuit 36 scene determination circuit

Claims (3)

(57) [Claims] 1. An aperture signal generating means for inputting an image signal and generating an aperture signal based on the image signal, the aperture signal generating means being capable of changing a center frequency of an output aperture signal, and the aperture An adder for adding the aperture signal generated by the signal generating means to the image signal; a brightness detecting means for detecting the brightness of the subject; a contrast detecting means for detecting the contrast of the subject; Control means for controlling the aperture signal generation means to change the center frequency of the aperture signal in accordance with a combination of brightness and contrast detected by the detection means, wherein the aperture increases as the brightness and contrast of the object increase. So that the center frequency of the signal is higher Control means for controlling the aperture signal generation means, and controlling the aperture signal generation means so that the center frequency of the aperture signal decreases as the brightness and contrast of the subject decrease. Correction device. 2. A control device, comprising: detecting means for detecting whether or not an in-focus state is detected, wherein the control means causes a center frequency of the aperture signal to be low when the detecting means detects an out-of-focus state. 2. The contour correction device according to claim 1, wherein said aperture signal generation means is controlled to inhibit generation of an aperture signal. 3. The apparatus according to claim 1, wherein the aperture signal generating means includes a band-pass filter for passing a predetermined frequency band component, and a digital filter disposed before or after the band-pass filter. A first delay element that delays the time, a second delay element that delays the output of the first delay element for a predetermined time, and a first that adds the input image signal and the output of the second delay element.
, A first multiplier for multiplying a first coefficient α changed by the control means and an output of the first delay element, and a second coefficient β changed by the control means
And a second multiplier for multiplying the output of the first adder and a second multiplier for multiplying the output of the first multiplier and the output of the second multiplier. Contour correction device.