JPH02214381A - Contour compensating device - Google Patents

Abstract

PURPOSE:To improve the sharpness of a picture picked up at a low illuminance by varying a delay time by a delay means in response to an output of a mean value detection means of a luminance signal and generating a horizontal contour compensation signal based on the delay signal from the delay means and the luminance signal. CONSTITUTION:When the illuminance of an image pickup element 2 is low, the mean level of a luminance signal YH is lowered. A switching circuit 11 receives a signal from a discrimination circuit 10 and the connection is switched to input an output of a delay line 6-2 to a horizontal aperture signal generating circuit 5. Thus, the luminance signal YH inputted to the horizontal aperture signal generating circuit 5 is retarded by the delay lines 6-1 and 6-2. Thus, the luminance signal YH is retarded longer than a conventional signal by the delay time depending on the delay line 6-2. As a result, the width of the horizontal aperture signal generated by the horizontal aperture signal generating circuit 5 is increased. Thus, the S/N is improved and the noise effect is reduced and preferable contour compensation is applied even under low illuminance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal processing device for video equipment, and particularly to a contour compensation device.

[Prior Art] In video equipment such as video cameras and television cameras, images are converted into electrical image signals and recorded on magnetic tape (in the case of video cameras) or sent to a transmitting device (in the case of television cameras). (for cameras). The original image can be obtained by playing this magnetic tape and extracting the image signal (in the case of a video camera) or by receiving the transmitted radio waves and extracting the image signal from it (in the case of a television camera). In order to improve the sharpness of an image, it is effective to emphasize the contours of the image in consideration of human visual characteristics. Therefore, conventionally, a device that converts an image into a signal according to an output purpose, that is, an image signal processing device, is provided with a circuit unit called a contour compensation device. This is a circuit that extracts the contour part of the picture of the original image from the brightness signal indicating the brightness of the image among the obtained electric signals, and generates a contour compensation signal that emphasizes the change in brightness of this part.

The contour compensation signal is electrically synthesized with the luminance signal in the image signal processing device, and a final image signal corresponding to the output purpose is obtained.

FIG. 5 is a schematic block diagram of a video camera equipped with a conventional contour compensation device. Referring to the figure, this video camera includes a lens 1 for capturing an external image as an optical image;
The optical image formed by this is converted into an electronic image, that is, the image sensor 2 converts light into an electrical signal, and the AGC (automatic gain control) and gamma A signal processing circuit 3 is provided for performing correction, etc., and for separating a luminance signal YH representing the horizontal luminance of the image and a color signal representing the color of the image. Furthermore, a color separation circuit 4 further separates the color signal obtained from the signal processing circuit 3 into two color difference signals called an R-Y signal and a B-Y signal, and a horizontal contour compensation of the image from the luminance signal Y. A contour compensation circuit 14 for generating a signal (hereinafter referred to as a horizontal contour compensation signal), a horizontal contour compensation signal from the contour compensation circuit 14, and an R signal from the color separation circuit 4.
-Y signal and B-Y signal to output a final image signal to be recorded on a magnetic tape (not shown).

The contour compensation circuit 14 includes a delay line 6-1 for delaying the luminance signal YH obtained from the signal processing circuit 3 by a certain amount of time.
, a horizontal aperture signal generation circuit 5 for generating a horizontal aperture signal that extracts the outline of an image pattern from the luminance signal delayed by this and the original luminance signal Y that is not delayed; The mixing circuit 7 adds the horizontal aperture signal to the original luminance signal YH to produce a final horizontal contour compensation signal.

The operation of the internal functions of this video camera will be explained below. Refer to FIG. 6 for the explanation. FIG. 6 is a waveform diagram showing the process of creating a horizontal aperture signal and a horizontal contour compensation signal from the luminance signal YH.

The reflected light from the subject, that is, the external image, is reflected from lens 1.
is formed on the image sensor 2 as an optical image. As a result, the image sensor 2 is irradiated with light having a wavelength and intensity corresponding to the image. An electrical signal corresponding to this light is output from the image sensor 2 and transmitted to the signal processing circuit 3. The signal processing circuit 3 includes an amplifier circuit, where the electrical signal obtained by the image sensor is amplified according to its magnitude and separated into a luminance signal Y and a color signal.

The separated luminance signal YH is transmitted to the horizontal aperture signal generation circuit 5 and the mixing circuit 7. Further, the luminance signal Y transmitted to the horizontal aperture signal generation circuit 5 is delayed by a minute time ΔX by the delay line 6-1 and returned to the horizontal aperture signal generation circuit 5 again. Here, if the waveform diagram of the horizontal luminance signal YH obtained from the image sensor 2 is as shown in FIG. 6(a), then the horizontal luminance signal YH is as follows. A horizontal aperture signal is created. The signal waveform (FIG. 6(a)) input to the horizontal aperture signal generation circuit 5 from the delay line 6-1 is the luminance signal YH output from the signal processing circuit 3.
(Fig. 6 (a)) shifted to the right by ΔX (Fig. 6 (a))
Figure (b)).

In the horizontal aperture signal generation circuit 5, subtraction processing is performed on these two signals (FIGS. 6(a) and (b)). As a result, a signal as shown in FIG. 6(C) is obtained. This is the horizontal aperture signal.

The luminance signal Y of the image in the horizontal direction is obtained by sequentially detecting accumulated charges from pixels arranged in one horizontal direction in the image sensor 2 as electrical signals. Therefore, in the waveform diagram of FIG. 6, the horizontal axis can be understood not only as time but also as a position in one horizontal direction on the image. Therefore, the subtraction process in the horizontal aperture signal generation circuit 5 is equivalent to first-order differentiation of the image in one horizontal direction. In other words, a portion of the image where the luminance changes greatly in one horizontal direction, that is, a contour portion of the picture is extracted (see FIG. 6(c)).

Next, in the mixing circuit 7, addition processing is performed on the horizontal aperture signal (FIG. 6(C)) and the original luminance signal YH from the signal processing circuit 3 (FIG. 6(a)), and the horizontal contour compensation signal is becomes. For example, for a luminance signal YH with a waveform in one horizontal direction as shown in FIG. 6(a), the mixing circuit 7
In this step, a horizontal contour compensation signal having a waveform as shown in FIG. 6(d) is generated. As can be seen from the figure, this signal corresponds to the parts where the brightness changes (circles in the figure) in the original brightness signal YH (Figure 6(a)), and the brightness of the high or low brightness parts. The absolute value is increased. As a result, changes in the brightness of the image in the horizontal direction are emphasized and the outline of the image becomes clear.

Next, the horizontal contour compensation signal generated by the mixing circuit 7 is combined with the two color difference signals, the R-Y signal and the B-Y signal, from the separation circuit 4 in the encoder circuit 8 to obtain the final video signal output. It will be done. Of course, in a video camera or the like, the final video signal output from the encoder circuit 8 is recorded on a recording medium (not shown) such as a magnetic tape.

[Problems to be Solved by the Invention] In the conventional contour compensation device, the delay time for the luminance signal when generating the horizontal aperture signal is fixed to a value determined by the characteristics of the delay line. As a result, the following good luck occurred.

FIG. 3 is a diagram showing frequency characteristics (modulation characteristics) of a luminance signal. In the figure, the horizontal axis is the frequency, and the vertical axis is the level of the luminance signal. Figure (a) shows that when the amount of light incident on the image sensor is sufficiently large and the level of the electrical signal obtained from this is high, and this is subjected to normal gain amplification in the signal processing circuit, the image to be captured is This is when the light is sufficiently bright.

As can be seen from the figure, the higher the frequency, the lower the level of the luminance signal.

FIG. 2B shows a case where the image to be captured is relatively dark and the illuminance of the image sensor is insufficient.

In this case, the electrical signal obtained from the image sensor is amplified to a maximum gain by the signal processing circuit to a predetermined level.

Generally, the amplification factor of such an amplifier circuit that amplifies a signal is lower than in a high frequency band. Therefore, as shown in the figure, the frequency characteristics of the luminance signal output from the signal processing circuit are worse than in the figure (a). That is, the position where the luminance signal level decreases moves to a lower frequency band than when the illuminance is sufficient.

Figure (e) shows a case where the image to be captured becomes even darker and the electrical signal obtained from the image sensor reaches an impossible low level even after maximum gain amplification in the signal processing circuit. . Therefore, the frequency characteristics of the luminance signal in this case are further degraded than in the case shown in FIG. 6(b), and the signal level itself is also reduced.

On the other hand, in the conventional contour compensation device, the delay time when generating the horizontal aperture signal is constant. Therefore, the frequency of the horizontal aperture signal is also fixed to a value determined by this delay time. Assume now that the frequency of the horizontal aperture signal created from the luminance signal is a value of ■ in the figure. Then, as shown in the figure, the level of the obtained horizontal aperture signal gradually decreases as the illuminance decreases.

Further, by increasing the amplification gain of the signal processing circuit in proportion to the decrease in illuminance, the noise component is increased. Therefore, when a horizontal aperture signal is created from such a luminance signal, the resulting horizontal aperture signal contains a lot of noise.

Therefore, adding such a horizontal aperture signal to the original luminance signal means adding a lot of noise to the original luminance signal. In other words, noise increases in the image, resulting in an image that is difficult to see even though contour compensation has been performed.

Therefore, in the conventional contour compensation circuit, when the illuminance of the image sensor is low, the contour compensation device is not operated or its function is suppressed. However, such means merely prevent contour compensation from being performed under low illuminance. Therefore, the sharpness of images captured under low illumination was not improved.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a contour compensation device that can perform appropriate contour compensation even under low illuminance and generate an image signal that can obtain a sharply reproduced image.

[Means for Solving the Problems] In order to achieve the above objects, the contour compensation device according to the present invention includes means for delaying a luminance signal separated from a video signal, and a means for detecting an average value of the luminance signal. means for changing the delay time by the delay means in response to the output of the average value detection means, and means for creating a horizontal contour compensation signal based on the delay signal and the luminance signal from the delay means.

[Operation] Since the contour compensation device according to the present invention is configured as described above, it is possible to change the delay time of the luminance signal when creating the horizontal contour compensation signal in accordance with the change in the average value of the luminance signal.

[Embodiment] FIG. 1 is a schematic block diagram of a video camera showing an embodiment of the present invention. Referring to the figure, this video camera, like the conventional one, includes a lens 1 for capturing an external image as an optical image, an image sensor 2 for converting the optical image into an electronic image, and an image sensor 2 for converting the optical image into an electronic image. Performs AGC and gamma correction to amplify the electrical signal obtained from the to a predetermined level, and
a signal processing circuit 3 that separates a luminance signal YH and a color signal;
It includes a color separation circuit 4 and an encoder circuit 8 for outputting a final video signal. Furthermore, this video camera includes a contour compensation circuit 12 having a configuration different from the conventional one between the signal processing circuit 3 and the encoder circuit 8.

The contour compensation circuit 12 includes a delay section 13a for delaying the luminance signal Y obtained from the signal processing circuit 3, and a delay section 1
Luminance signal delayed by 3a and signal processing circuit 3
a horizontal aperture signal generation circuit 5 for generating a horizontal aperture signal from the original luminance signal Y obtained from the original luminance signal Y;
A mixing circuit 7 for creating a horizontal contour compensation signal from the horizontal aperture signal obtained from the horizontal aperture signal generation circuit 5 and the original brightness signals Y, l, and an average value of the illuminance of the image sensor 2 from the original brightness signal YH. and a delay section 1 in response to the signal from the average value detection circuit 9.
3a, and a discrimination circuit 10 that generates a signal for switching the delay time of the luminance signal YH at 3a.

The delay section 13a includes the delay lines 6-1 and 6-2 and the switching circuit 1.
1. The switching circuit 11 switches the connection so as to provide either the output of the delay line 6-1 or the output of the delay line 6-2 to the horizontal aperture signal generation circuit 5 in response to a signal inputted from the discrimination circuit 10.

The operation of this video camera will be explained below.

The reflected light from the subject, that is, the image to be captured, is focused by the lens 1 on the image sensor 2 as an optical image. As a result, an electrical signal corresponding to the image is output from the image sensor 2 and transmitted to the signal processing circuit 3. As in the prior art, the electrical signal from the image sensor 2 is amplified in the signal processing circuit 3 according to its level and separated into a luminance signal YH and a color signal.

As before, the color signal is separated into RY and BY signals, which are color difference signals, in the color separation circuit 4 and output. The luminance signal Y is sent to the mixing circuit 7. in the contour compensation circuit 12. Horizontal aperture signal generation circuit5. and is input to the average value detection circuit 9.

First, the average level of the luminance signal YH input to the average value detection circuit 9 is detected and input to the discrimination circuit 10 as a DC voltage signal. In the determination circuit 10, the input signal is compared with a predetermined voltage, and the magnitude relationship therebetween is determined. Furthermore, the discrimination circuit 10 outputs two types of voltage signals corresponding to the discrimination result (whether the input voltage is higher or lower than a predetermined voltage) to the switching circuit 11. The switching circuit 11 inputs either the output of the delay line 6-1 or the output of the delay line 6-2 to the horizontal aperture signal generation circuit 5 in response to the input signal from the discrimination circuit 10! Switch this connection.

Next, the luminance signal YH input to the horizontal aperture signal generation circuit 5 is delayed by only the delay line 6-1 or by both delay lines 6-1 and 6-2 in the delay section 13a, and then a horizontal aperture signal is generated. It is re-inputted into the circuit 5.

In the horizontal aperture signal generation circuit 5, a horizontal aperture signal is generated from the original luminance signal Y and the luminance signal delayed by the delay section 13a through processing similar to conventional processing.

The mixing circuit 7 adds the horizontal aperture signal from the horizontal aperture signal generating circuit 5 and the original luminance signal YH, and outputs the resultant signal to the encoder circuit 8 as a horizontal contour compensation signal. Thereafter, the operation of the encoder circuit 8 is the same as the conventional one.

The processing of the luminance signal Y14 in the contour compensation circuit 12 will be specifically described below.

The predetermined voltage to be compared in the discrimination circuit 10 is set to correspond to the average level of the luminance signal YH obtained at the boundary between illuminance where a desirable horizontal aperture signal is obtained and low illuminance where it is not. Therefore, when the illuminance of the image sensor 2 is high, the average level of the luminance signal YH also becomes high, so that the determination circuit 10 determines that the illuminance is such that a preferable horizontal aperture signal can be obtained.

In this case, the discrimination circuit 10 outputs a signal corresponding to the discrimination result. The switching circuit 11 receives the signal from the discrimination circuit 10 and switches the connection so that the output from the delay line 6-1 is input to the horizontal aperture signal generation circuit 5. As a result, the luminance signal input to the horizontal aperture signal generation circuit 5 is delayed by the same delay time as before by the same delay line 6-1 as before, and then inputted again to the horizontal aperture signal generation circuit 5. . Therefore, the horizontal aperture signal generated by the horizontal aperture signal generation circuit 5 thereafter is the same as the conventional one. Therefore, under high illuminance, the sharp horizontal aperture signal (6th
(see figure (C)) is obtained.

Next, a case where the illuminance of the image sensor 2 is low will be described.

In this case, as described above, the average level of the luminance signal YH decreases (see FIG. 3).

Therefore, the determination circuit 10 determines that the illuminance is such that a preferable horizontal aperture signal cannot be obtained. In this case, the discrimination circuit 10 outputs a signal corresponding to the discrimination result. The switching circuit 11 receives the signal from the discrimination circuit 10 and switches the connection so that the output of the delay line 6-2 is input to the horizontal aperture signal generation circuit 5. As a result, the luminance signal YH input to the horizontal aperture signal generating circuit 5 is delayed by the delay lines 6'-1 and 6-2. Therefore, the luminance signal YH is transmitted to the delay line 6-2 more than before.
The signal is delayed for a long time by the delay time caused by , and is input to the horizontal aperture signal generation circuit 5 . As a result, the width of the horizontal aperture signal (Δ
x (see FIG. 6)) increases. This means that under low illuminance, the frequency of the horizontal aperture signal becomes lower than before. Incidentally, the frequency characteristics of the luminance signal YH were as shown in FIG. Since the luminance signal Y is obtained under low illuminance, its frequency characteristics are as shown in FIG. 3(b) or (C). but,
The frequency of the horizontal aperture signal obtained under low illuminance is lower than the frequency of the conventional horizontal aperture signal obtained under low illuminance (■ in the figure) (for example, the frequency ■ in the figure). As can be seen from the figure, the level of the signal obtained from the frequency (■) in the figure is higher than the level of the signal obtained at the frequency (■) in the figure. That is, by obtaining the horizontal aperture signal in a lower frequency band, the level of the horizontal aperture signal under low illuminance becomes higher than before.

Therefore, the SN ratio is improved compared to the prior art, and the influence of noise is reduced. As a result, it becomes possible to perform preferable contour compensation even under low illuminance, where contour compensation could not be performed conventionally.

FIG. 2 is a waveform diagram showing the process of creating a horizontal contour compensation signal from the luminance signal YH under low illuminance. FIG. 3A is a waveform diagram showing an example of a horizontal luminance signal YH input from the signal processing circuit 3 to the contour compensation circuit 12. FIG. 6B is a waveform diagram of the luminance signal delayed by the delay lines 6-1 and 6-2. As can be seen from these figures, the delay width .DELTA.X is larger than the conventional one by the time taken by the delay line 6-2 (see FIG. 6). (C) of the figure is a waveform diagram of the horizontal aperture signal, which is a signal obtained by subtracting these two luminance signals ((a) and (b) of the figure) in the horizontal aperture signal generation circuit 5. be. 5D shows a horizontal contour compensation signal obtained by adding the horizontal aperture signal shown in FIG. 3C and the original luminance signal YH shown in FIG. In this way, by obtaining the horizontal aperture signal in a lower frequency band than before, the signal level becomes higher, and even under low illumination, a preferable horizontal aperture signal with reduced noise can be added to the original luminance signal Y. becomes possible.

In this embodiment, in order to create a difference between the delay time under low illuminance and the delay time under high illuminance when creating the horizontal aperture signal, the delay line 6 is added to the delay line 6-1, which is the same as the conventional one, in the delay section. -2 were connected in series. However, the configuration of the delay section for switching the delay time depending on the illuminance is not limited to this. FIG. 4 is a diagram showing another example of the configuration of the delay section. The delay section 13b shown in FIG. 4(a) includes two delay lines 6-3 and 6 connected in parallel.
-4 and a switching circuit 11. Of course, the function of the switching circuit 11 is the same as in the previous embodiment. That is, the output of either the delay line 6-3 or 6-4 is selectively input to the horizontal aperture signal generation circuit 5 depending on the average level of the luminance signal YH, that is, depending on the illuminance. Here, the delay lines 6-3 and 6-4 must have different times of delay.

That is, these are used as a delay under low illumination and a delay under high illuminance, respectively.

The delay section 13c shown in FIG. 4(b) is a single delay line 6-5.
and a switching circuit 11 having the same function as the previous embodiment. In this case, under low illumination, the output of the end of the delay line 6-5 is input to the horizontal aperture signal generation circuit by the switching circuit 11, and under high illumination, the output of the intermediate portion of the delay line 6-5 is input to the horizontal aperture signal generation circuit. input to the circuit.

In other words, a single delay line is divided along its length, and the delay time is varied depending on the illuminance.

In both of the above cases, it is necessary to set a delay time when delaying the luminance signal Y11 and use a delay line corresponding to the delay time so that an optimal horizontal aperture signal can be obtained under low illuminance and high illuminance. Needless to say.

In this embodiment, a method was adopted in which the delay time in the delay section was switched to two values in response to low illuminance and high illuminance. However, by increasing the number of delay lines connected in parallel in Figure 4(a) or by continuously moving the dividing position of a single delay line in Figure 4(b), the illuminance can be adjusted. It is also possible to continuously change the delay time accordingly.

Further, in this embodiment, a delay line is used to delay the luminance signal, but this is not limited to a delay line, and any type of line may be used as long as it has a delay function.

In the explanation of this embodiment and the conventional example, for simplicity, a method of first-order differentiation of the luminance signal was used as a method of creating the horizontal aperture signal, but when using a method of second-order differentiation of the luminance signal, A similar effect can be obtained.

[Effects of the Invention] Since the contour compensation device according to the present invention is configured as described above, it brings about the following effects.

Appropriate contour compensation can be performed even under low illumination (ie, dark images) where contour compensation could not be performed conventionally. Therefore, even images captured under low illumination can be reproduced as sharp images with clear patterns. Furthermore, since contour compensation can be performed as before under high illuminance, the illuminance range in which sharply reproduced images can be obtained is expanded.

[Brief explanation of the drawing]

Fig. 1 is a schematic block diagram of a video camera showing an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining an embodiment of the invention, and Fig. 3 is a diagram showing frequency characteristics of a luminance signal. , FIG. 4 is a diagram showing another embodiment of the present invention, FIG. 5 is a schematic block diagram of a video camera showing an example of the prior art, and FIG. 6 is a waveform diagram for explaining the prior art. , 1 is a lens, 2 is an image sensor, 3 is a signal processing circuit, 4 is a color separation circuit, 5 is a horizontal aperture signal generation circuit, 6-1 to 6-5 are delay lines, 7 is a mixing circuit, and 8 is an encoder. circuit, 9 is an average value detection circuit, 10 is a discrimination circuit, 1
1 is a switching circuit, 12 and 14 are contour compensation circuits, 13a
, 13b, and 13c are delay units. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 3 ■ Figure 2 Man 4 Figure 13b, t3c: Follow this rejection b-3, 6-4, 6-3: Delay Tomo Figure 6 - water + dialect

Claims (1)

[Scope of Claims] A contour compensation device for improving the sharpness of images in video equipment, comprising: means for delaying a luminance signal separated from a video signal; means for detecting an average value of the luminance signals; , comprising means for changing the delay time by the delay means in response to the output of the average value detection means, and means for creating a horizontal contour compensation signal based on the delay signal from the delay means and the luminance signal. Contour compensation device.