JPH0591395A - Video signal processor - Google Patents

Abstract

PURPOSE:To obtain the video signal processor capable of providing a good picture quality at all times by reducing the random noise to be generated at the low illuminance without providing more light sources for illuminance. CONSTITUTION:A signal level detection circuit 4 inputting a video signal detects the low illuminance. When outputting a low illuminance detection signal S0, a picture averaging circuit including a line memory 8, changeover circuit 9, picture memory 10, and averaging circuit 11 is activated. The input picture and the input picture which is one frame before are averaged, a video signal AS2 with the random noise to be generated at the low illuminance averaged by time is outputted, resulting in reducing the random noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing device, and more particularly to a video signal processing device for preventing deterioration of image quality under low illuminance.

[0002]

BACKGROUND ART Television door intercoms have become widespread in general households in recent years. The TV intercom has a master unit having a handset integrally provided indoors, and a slave unit having an imaging device such as a camera connected to the master unit in communication outdoors. With such a TV door phone, an outdoor image is taken by the camera of the child device, and the image obtained by this image is displayed on the monitor screen of the indoor parent device, so that the person indoors can stay indoors. It has the advantage of being able to confirm the outdoor situation and visitors.

The installation location of the slave unit of the above-mentioned TV doorphone is a wall surface at the entrance of a house or a gate pillar.
Such an installation place has restrictions on space and position for installation, and these restrictions vary, so that a visitor often does not always stand in front of the camera of the child device. Therefore, when the slave unit is installed, the mounting angle of the camera is adjusted in advance, or the image pickup angle of the camera is driven by a motor or the like so that the motor is remotely controlled from the master unit side in the room. Furthermore, attach a wide-angle lens to the lens of the camera,
Measures have been taken to prevent visitors from falling outside the field of view of the camera.

In addition, when the lighting conditions are extremely bad such as in the evening and at night, infrared lighting is used to maintain the lighting conditions.

As described above, when a wide-angle lens is attached to the camera in order to always keep the visitor within the field of view of the camera, the field of view of the camera becomes wider, but the area in which the visitor is reflected is visible. Becomes smaller. In this state,
Since it is extremely difficult for people in the room to confirm the visitors on a normal screen, it is possible to solve this difficulty by enlarging and extracting only the image of the area where the visitors are reflected from the captured images. Had been dealt with.

FIG. 4 is a schematic configuration diagram of a television door phone as a background of the present invention. In FIG. 4, the TV intercom is configured so as to pick up an image of a visitor and lead the video signal to the monitor unit so that the visitor can be identified remotely.

In the figure, a TV door phone uses a wide-angle lens 1 and an image of a visitor through the wide-angle lens 1 to obtain a video signal AS.
A camera 2 for deriving 1 and an A / D conversion circuit 3 for inputting a video signal AS1 and converting it into a digital signal and outputting a digital signal DS1, a digital video signal DS1 for inputting an enlargement request signal given from the outside Based on S1 and the enlargement area designating signal S2, a signal corresponding to the area desired to be enlarged in the signal DS1 is converted into the digital video signal DS2.
The enlarged area extraction circuit 6, the line memory 8,
Image memory 10, pixel interpolation circuit 13, enlargement request signal S1
Switching circuit 1 for switching the signal input side according to the input of
4 and a D / A conversion circuit 15.

The line memory 8 is provided in association with the image memory 10, and the timing of writing the signal from the camera 2 in the image memory 10 differs from the timing of reading the signal from the pixel interpolation circuit 13 connected to the next stage. Is a kind of buffer memory provided for buffering.

The image memory 10 is a memory in which data is read / written in response to activation of the enlarged area extraction circuit 6, and has a memory capacity of 1/4 field as described later.

The pixel interpolation circuit 13 is provided in the image memory 1 of the preceding stage.
It is a circuit that operates to input a digital video signal read from 0 and interpolate between the two adjacent pixels at the average level of the brightness level (digital amount) of the adjacent pixels. Therefore, the pixel interpolation circuit 13 causes the image data for 1/4 field in the memory 10 to be 1
It is interpolated and output so as to be image data for fields.

The switching circuit 14 receives an enlargement request signal S1 given from the outside, and when enlargement of an image obtained by picking up an image based on the signal S1 is requested, the input side of the signal is the pixel interpolation circuit 13 side. The signal input side is switched to the A / D conversion circuit 3 side while the signal S1 is not applied.

The D / A conversion circuit 15 is the switching circuit 1 in the preceding stage.
The digital video signal supplied from the input terminal 4 is input, converted into an analog amount in accordance with the analog video signal, and converted into a video signal which can be displayed on the screen and transmitted to a monitor unit on the master side (not shown).

The wide-angle lens 1 is a lens that is mounted to forcibly increase the viewing angle of the camera 2 as described above, and is mounted on the front surface of the camera 2 in a detachable manner.

It is now assumed that the user designates a desired image and requests the enlarged display of the image with the wide-angle lens 1 attached to the front surface of the camera 2.

First, in order to increase the viewing angle of the camera 2, the user mounts the wide-angle lens 1 on the front surface of the camera 2 and the camera 2 starts the image pickup operation.

An analog video signal AS1 including a subject image captured by the camera 2 is applied to the A / D conversion circuit 3 and is converted into a digital video signal DS1 which is a digital signal in response thereto.

Next, the digital video signal DS1 is applied to the switching circuit 14 and the enlarged area extraction circuit 6 at the same time. At this time, since the user has requested enlarged display as described above, the switching circuit 14 switches its input side to the pixel interpolation circuit 13 side in response to the input of the signal S1. Further, the enlargement area extraction circuit 6 determines that enlargement display is requested in response to the input of the enlargement request signal S1, and
By inputting the enlargement area designation signal S2,
Recognize which part of the image is the area requested to be enlarged. An area to be expanded and extracted is extracted from the digital video signal DS1 by the expansion area extraction circuit 6, the digital video signal DS2 of the expansion area is given to the line memory 8, passes through the line memory 8, and is written in the image memory 10. Be stored. The operation of the expanded area extraction circuit 6 for extracting the expanded area will be described later.

Here, the extracted digital video signal DS
2 is not directly input to the image memory 10 but is once input to the line memory 8 because the writing speed of data to the image memory 10 is slow (inexpensive) with respect to the input speed of the video signal from the camera 2. This is because the memory is used, and the line memory 8 is used as a temporary timing buffer. Although the line memory 8 and the image memory 10 are separately provided here, they may be integrally provided.

As described above, the enlarged and extracted digital video signal DS2 is stored in the image memory 10 for producing an enlarged image. Image memory 10 is 1/4 of all images
Since it is used for storing (1/4 field), the memory capacity of the TV intercom situation is also reduced.

The digital video signal DS2 for 1/4 field stored in the image memory 10 is read out in order to compensate for the deterioration of the resolution of the image when the digital video signal DS2 for 1/4 field is expanded to a 1-field screen, and then the next pixel interpolation circuit is read. The data is input to 13 and is accordingly interpolated into a digital video signal of one field by a process of enlarging the pixels as described above.
In this way, when the pixel interpolation circuit 13 forms a video signal for one field, this video signal is input to the D / A conversion circuit 15 via the switching circuit 14 and is converted into an analog video signal in accordance with the communication signal. It is output to the monitor unit on the base unit side via the and is enlarged and displayed.

FIGS. 5A and 5B are views for explaining the movement and enlargement of an image by the enlargement area extraction circuit 6 showing the background of the present invention.

FIGS. 6 (a) to 6 (d) are for explaining the video signal and the timing of the scanning signal and the horizontal reading start signal at the time of image enlargement by the enlargement area extraction circuit 6 showing the background of the present invention. It is a figure.

Next, the enlarged area extraction circuit 6 shown in FIG.
The operation of extracting the enlarged area will be described.

The enlargement area extraction circuit 6 inputs the digital video signal DS1 and the enlargement request signal S1 and the enlargement area designation signal S2 from the outside. As a result, a desired portion of the monitor screen (not shown) can be moved to the center portion of the monitor screen based on the signal S1 and the signal S2 provided by the user's button operation (not shown), and the area ratio can be enlarged to 4 times and projected. Is configured as follows.

For example, if a visitor is displayed in the upper left corner of the monitor screen as shown in FIG. 5A, the photographer in the room is set to project the visitor image in the center of the monitor screen. The button is operated to output the enlargement request signal S1, and the button is operated to specify the enlarged portion of the image to output the enlargement area designation signal S2. At this time, the monitor screen moves from the upper left screen set as shown in FIG. 5A to the lower right direction, is enlarged four times, and is displayed in the central portion of the monitor screen. At this time, the extraction of the digital video signal DS1 is performed as follows.

As shown in FIG. 5B, the image displayed on the monitor screen has a two-dimensional pixel array, and this pixel array is (0,0) to (m-1, n). It is assumed that the size is -1).

For example, when the visitor moves while being projected on the screen and is projected to the upper left of the screen as shown in FIG. 5A, the photographer enlarges the visitor image to the center of the monitor screen. First, an enlargement request signal S1 is output by operating a button or the like so that the image is displayed. At this time, in order to move the upper left visitor image to the center, the photographer further operates a button to specify an enlargement area designation signal S.
2 is output. These signals S1 and S2 are supplied to the enlarged area extraction circuit 6.

In the enlargement area extraction circuit 6, the enlargement area designating signal S2 is moved and enlarged as shown in FIG. 5 (a) by the enlargement area designation signal S2, as shown in FIG. With an area ratio of 4 times), it works so as to be displayed in the center of the screen. That is, as shown in FIG. 5B, (0, 0) to (m / 2-1, n / 2-) of the digital video signal DS1 of the monitor screen having a two-dimensional pixel array.
Only the pixel data of 1) will be extracted.

The method of extracting the image data of the area desired by the user from the above-described one-field screen is performed as follows. Enlarged area extraction circuit 6
Inputs the synchronization signal included in the video signal AS1, and accordingly divides the blanking area BL effective area MU and the enlarged memory area MZ of FIG. 6A. The circuit 6 operates so as to perform an operation of extracting image data of a desired area only in the enlarged memory area MZ of the blanking area BL and the effective area MU.

As described above, when the upper left portion of the monitor screen of FIG. 6A is to be enlarged and displayed in the central portion of the screen,
As shown in FIG. 6B, a horizontal synchronizing signal HD as shown in FIG. 6C is extracted and given to the video signal AS1 for one horizontal scanning line. The circuit 6 responds to the input of the synchronizing signals including the signals S1 and S2 and the horizontal synchronizing signal HD, and the image data corresponding to the enlarged memory area MZ in FIG. 6A is enlarged in the entire effective area MU. As shown in FIG. 6D, the horizontal extraction start signal HS for starting extraction is output so as to specify the timing of the enlarged memory area MZ. At this time, although not shown, a vertical direction extraction start signal is similarly output so as to specify the memory area MZ during expansion.

As described above, the enlarged area extraction circuit 6
The area to be enlarged and extracted by the user is extracted from the input image data, and this is output as the digital video signal DS2 to the line memory 8 in the next stage.

The above-mentioned TV door phone uses a wide-angle lens to input an image so that a visitor can always be displayed on a monitor screen regardless of the installation place and the installation position, and the input image is input in an area desired by the user. By enlarging and extracting with, it is possible to prevent the number of visitors from becoming small and making it difficult to confirm.

[0033]

FIGS. 7A and 7B are views for explaining the general relationship between the visual field and the distance due to the difference in the lens of the camera.

In the TV intercom as the background of the present invention described above, illumination using infrared rays is generally adopted when outdoor illumination conditions such as evening or night are extremely poor. When such illumination using infrared rays is adopted, the brightness (illuminance of the illuminance on the surface of the object is different depending on whether the wide-angle lens is used or not even if the same infrared illumination light is used. ) Is different. Figure 7
A description will be given with reference to (a) and (b).

FIG. 7A is a diagram for explaining the relationship between the visual field and the distance when a standard lens is attached to the camera.
FIG. 7B is a diagram for explaining the relationship between the visual field and the distance when a wide-angle lens is attached to the camera.

As shown in FIGS. 7 (a) and 7 (b), assuming a place separated by a distance L from a light source O for illumination mounted on a wall surface, the standard lens of FIG. 7 (a) is used. And the distances OA and OB from the light source O in the case of FIG.
Comparing the distances OC and OD from the light source O when the wide-angle lens of (b) is used, OA <OC and O
Since B <OD, when a wide-angle lens is used as shown in FIG. 7B, the brightness (illuminance) of the surface of the object located at a distance L from the wall surface on which the camera of the TV intercom is mounted is It gets darker (lower). Therefore, a method such as amplifying the signal level of an input image obtained by capturing an image with respect to the rate at which the brightness of the object becomes dark is taken. However, in this amplification processing, there is a problem in that random noise (difference in output signal level in the image pickup element, which is peculiar to the camera) that occurs when the illuminance is low becomes noticeable, and the image quality is extremely deteriorated. Therefore, in order to solve the problem that the image quality is extremely deteriorated by the random noise generated at the time of low illuminance and always obtain the same image quality, the wide-angle lens shown in FIG. 7B is simply used. In this case, it is necessary to take measures such as increasing the number of illumination light sources O as compared with the case where the standard lens of FIG. 7A is used.

However, since a wide-angle lens is used, the method of adding an illumination light source increases the cost of the TV intercom itself and increases the power consumption. did not become.

Therefore, an object of the present invention is to extract a desired portion of an image obtained by picking it up and display it in a magnified manner, regardless of the type of optical lens used, random noise generated at low illuminance. It is an object of the present invention to provide a video signal processing device capable of always obtaining a good image quality by reducing the illumination light without adding an illumination light source.

[0039]

A video signal processing apparatus according to the present invention inputs a video signal obtained by imaging and converts it into a digital signal for each pixel according to the conversion means, and a video obtained by imaging. Detecting means for inputting a signal and correspondingly detecting that the signal level is a low illuminance level, extracting means, reducing means, and storing means capable of sequentially storing a given digital signal for each pixel, It is provided with an interpolating output means for sequentially inputting a given digital signal, and enlarging and outputting pixels while interpolating pixels accordingly, a control means, and an averaging means.

The extraction means inputs the digital signal output from the conversion means in the enlargement mode and extracts the digital signal of a desired portion of one screen accordingly, and the reduction means in the non-enlargement mode,
It is configured to derive one screen while reducing it.

The control means is configured to read out the digital signal output from the extraction means for each pixel while sequentially writing it to the storage means and to control the derivation to the interpolation output means.

The averaging means responds to the detection by the detecting means.
The control means is disabled, the digital signal stored immediately before in the storage means and the digital signal output by the extraction means or the reduction means are input and averaged, and the averaged signal is stored in the storage means, and at the same time, in the interpolation output means. It is arranged to average the images.

[0043]

In the video signal processing apparatus according to the present invention, a part of the circuit for enlarging and extracting the input image is also used as the averaging means activated in the low illuminance, and the image is averaged to generate the image in the low illuminance. Random noise of the video signal is reduced. In other words, when the low illuminance is detected by the detection means, the averaging means first disables the control means and averages the signal derivation path including the storage means to the image, in other words, a signal derivation path for noise reduction. Switch. After that, the digital signal stored immediately before in the storage means and the digital signal output by the extraction means or the reduction means are input and averaged, and the averaged signal is stored in the storage means and is given to the interpolation output means. From the interpolation output means, the averaged image obtained from the input image and the previously averaged image is enlarged and output as one screen. Therefore,
When the illuminance is low, regardless of whether the mode is the expansion mode or the non-expansion mode, good image quality in which random noise is reduced can always be obtained.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 10 is a schematic diagram of a television door phone according to an embodiment of the present invention. The illustrated TV door phone performs an enlargement request signal S1 and an enlargement area designation signal given by a user's external operation to a desired portion of the monitor screen while performing signal processing so that a video signal obtained by imaging is displayed on a monitor. It is configured so that it can be moved to the central portion of the monitor screen based on S2, and can be projected with an area ratio enlarged by 4 times. When the illuminance at the time of image pickup is low, this TV door phone operates to reduce random noise generated at the low illuminance, without increasing the illumination at the low illuminance, and additionally increasing the circuit for the illumination. It is configured to prevent the deterioration of image quality.

Although the present embodiment exemplifies a TV intercom, this is not limited to the TV intercom, and can be applied to all video signal processing devices for processing a video signal obtained by imaging.

The illustrated TV door phone inputs a camera 2 which picks up an image of a visitor and outputs a video signal AS1 in response, a wide-angle lens 1 mounted on the front surface of the camera 2 and a signal AS1, and digitally pixel by pixel. The A / D conversion circuit 3 for converting into a signal and outputting the digital video signal DS1 and the signal AS1 are input, the signal level thereof is detected, and whether or not the current imaging condition is low illuminance is detected according to the detection result. The signal level detection circuit 4 for deriving the low illuminance detection signal S0 indicating the result is included.

Further, this TV door phone has a 1/4 times area extraction circuit 5, an enlarged area extraction circuit 6, switching circuits 7 and 9,
12 and 14, line memory 8, image memory 10, averaging circuit 11, pixel interpolation circuit 13, D / A conversion circuit 15
And an AGC (automatic gain adjustment) circuit 16.

The A / D conversion circuit 3 samples the supplied video signal AS1 for each pixel in synchronization with a predetermined sampling pulse, and outputs a digital video signal DS1.

The 1/4 times area extraction circuit 5 operates so that the supplied digital video signal DS1 is input, and the digital data for each pixel included in the signal DS1 is thinned out in sequence for each pixel and output. As a result, the supplied digital video signal DS1 is derived as the digital video signal DS3 whose data amount is reduced to 1/4. The region extracting operation of the 1/4 region extracting circuit 5 will be further described.

FIGS. 2 (a) and 2 (b) are diagrams for explaining the operation of extracting the image by the 1/4 times area extraction circuit 5 shown in FIG. 1 above.

The 1/4 times area extraction circuit 5 takes in the supplied digital video signal DS1 as an input image. This input image is composed of a two-dimensional pixel array as shown in FIG. The circuit 5 captures every pixel in the sequence in each of the X direction and the Y direction of the input image in FIG. 2A, but as shown in FIG. 2B, one pixel in the sequence in the X direction and the Y direction. The digital video signal DS3 is derived by performing thinning processing for reading each of them. This signal DS3 is an extracted image in the circuit 5. Figure 2
As shown in FIGS. 2A and 2B, if the circuit 5 performs the extraction operation, the 16-pixel region surrounded by the thick frame in FIG. 2A is surrounded by the thick frame shown in FIG. It is reduced to a 4-pixel area and extracted. Therefore, the 1/4 region extraction circuit 5 operates so as to convert the digital video signal DS1 into a signal amount of 1/4 and derive it as the digital video signal DS3. The screen will be reduced to a quarter field screen.

As described with reference to FIGS. 5 and 6, the enlargement area extraction circuit 6 is provided with an enlargement request signal S1 and an enlargement area designating signal S provided in response to an external operation by the user.
Based on 2, the area of the given digital video signal DS1 in which expansion is desired is extracted to extract the digital video signal DS2.
Operates to derive Since the detailed description of the enlarged area extraction circuit 6 has been described with reference to FIGS. 5 and 6 above,
It is omitted here.

The switching circuits 7, 9, 12 and 14 are circuits for inputting the low illuminance detection signal S0 and the enlargement request signal S1 and selectively switching their signal input sides in response.

The signal level detection circuit 4 outputs the low illuminance detection signal S
When 0 is output, the switching circuits 9 and 12 switch their input sides to the averaging circuit output side, and the switching circuit 14 switches their inputs to the pixel interpolation circuit 13 side.

When the enlargement request signal S1 is input by the external operation of the user, the switching circuit 7 switches its input side to the digital video signal DS2 side, and the switching circuit 14 outputs the low illuminance detection signal S0 in the same manner. The input side is switched to the pixel interpolation circuit 13 side.

As described above, according to the input of the low illuminance detection signal S0 output from the signal level detection circuit 4 for detecting the low illuminance at the time of image pickup, each of the switching circuits switches its signal input side in a switching manner. In response to this, the image quality improving circuit at the time of low illuminance becomes operable in the TV door phone.

In the image memory 10, the digital video signal DS1 obtained by picking up the image by the camera 2 is derived through the area extracting circuit 5 or 6 and the digital video signals DS2 and D2.
This is a memory circuit provided for temporarily storing S3, and its size is sufficient if it has a memory capacity enough to store image data of 1/4 field.

The line memory 8 is provided in association with the image memory 10, and is a buffer provided for buffering the deviation between the timing of writing the signal from the camera 2 of the memory 10 and the timing of reading the data from the memory 10. It is a memory and functions as a 1H (1 horizontal scanning period) delay memory.

The pixel interpolation circuit 13 inputs the supplied digital video signal for each pixel, and interpolates between the adjacent pixels according to the average level of the luminance levels of the adjacent pixels according to the pixel resolution. After performing interpolation processing to compensate for this, the switching circuit 14 is enlarged to a screen of one field.
Have been derived.

The D / A conversion circuit 15 converts the supplied digital video signal into an analog signal again and outputs it.

The AGC circuit 16 inputs the video signal converted into the analog signal in the D / A conversion circuit 15, amplifies it when the signal level is below a predetermined level, and outputs the signal when it is above a predetermined level. The video signal AS2 whose gain is adjusted by automatically adjusting the gain of the applied video signal so as to be attenuated is derived to the monitor unit on the master unit side (not shown).

Next, the operation of the averaging circuit 11 will be described. FIG. 3 shows the averaging circuit 11 shown in FIG.
7 is a diagram for explaining the operation of FIG.

By the operation of the averaging circuit 11, it is possible to effectively reduce the random noise generated when the image pickup condition of the TV door phone is low illuminance.

In FIG. 3, the averaging circuit 11 inputs the output signal of the image memory 10 and the output signal of the line memory 8 and, after averaging according to them, outputs this averaging signal to the switching circuits 12 and 9. To do. At this time, the averaged signal is stored again in the image memory 10 via the circuit 9. Then, the immediately preceding averaged signal read from the image memory 10 and the signal read from the line memory 8 are averaged again, and the processed signal is again stored in the image memory 10.

Thus, as shown in the circuit block of FIG. 3, the averaging circuit 11 inputs the input image captured by the camera 2 and the input image one frame before (correctly, The image that has been averaged immediately before and once stored in the image memory 10) is averaged. In other words, the averaging circuit 11 receives the respective data of one pixel read from the line memory 8 and the image memory 10 when viewed instantaneously, takes an arithmetic mean in accordance with the data, and calculates this average value of one pixel. Output as digital data. In the long term, this averaging circuit 11 operates so as to average the current input image and the input image one frame before (the image that has been averaged immediately before and stored in the memory 10). Accordingly, the operation of the averaging circuit 11 temporally averages the random noise that is particularly noticeable when the illuminance is low, so that the random noise included in the image data output can be effectively reduced.

Next, the operation of the TV intercom shown in FIG. 1 will be described for each of the three states of normal use (not in low illuminance and not in expansion mode), expansion mode, and low illuminance. To do.

It is assumed that the wide-angle lens 1 is attached to the front surface of the camera 2, but the same operation is performed even if the wide-angle lens 1 is not attached.

During normal use, the camera 2 uses the wide-angle lens 1
A subject is imaged via the and the video signal AS1 is derived.
The video signal AS1 is supplied to the signal level detection circuit 4 and the A / D conversion circuit 3, and the digital video signal DS1 is derived accordingly.

The signal level detection circuit 4 detects the video signal AS1.
Is input and the signal level is detected accordingly to determine that the low illuminance state is not established, so the low illuminance detection signal S0 is not output.

The digital video signal DS1 is given to the switching circuit 14 and at the same time given to the 1/4 times area extraction circuit 5 and the enlarged area extraction circuit 6. At this time,
Since the low illuminance detection signal S0 and the enlargement request signal S1 are not derived, the digital video signal DS1 is not given to the circuits connected after the switching circuit 7, and passes only the switching circuit 14 to the D / A conversion circuit. Given to 15.

The D / A conversion circuit 15 converts the supplied digital video signal DS1 into an analog video signal, and outputs the video signal AS2 to the outside through the AGC circuit 16 in order to keep the output signal level constant. To do. At this time, A
Since the GC circuit 16 operates only when the video signal level is not appropriate, such as when the lighting condition is bad, the AGC circuit 16 does not particularly operate during normal use, and the analog amount of the video converted by the circuit 15 is not used. The signal is output as it is to the monitor side.

Next, the expansion mode will be described. In the enlargement mode, the user inputs an enlargement request signal S1 and an enlargement area designating signal S2 for designating a desired enlargement area on one screen by performing an external operation. First, a case where the enlargement mode is specified by the user and the imaging condition is not low illuminance will be described.

The digital video signal DS1 obtained in the same manner as described above is simultaneously given to the 1/4 times area extraction circuit 5, the enlarged area extraction circuit 6 and the switching circuit 14. At this time, since the enlargement request signal S1 is input, the switching circuit 14
Switches its signal input side to the pixel interpolation circuit 13 side.
Therefore, the digital video signal DS1 is not led out to the monitor side via the switching circuit 14.

Since the signal S1 is input to the switching circuit 7,
The signal input side is switched to the signal DS2 input side.

Digital video signal DS1 obtained by imaging
In the enlarged area extraction circuit 6, the area designated by the enlarged area designating signal S2 is extracted by the operation shown in FIGS. 5 and 6, and is supplied to the switching circuit 7 as the digital video signal DS2. The switching circuit 7 outputs the supplied digital video signal DS2 to the line memory 8.
The line memory 8 simultaneously supplies the supplied digital video signal DS2 to the switching circuit 9 and the averaging circuit 11.

Since the switching circuit 9 is not supplied with the low illuminance detection signal S0, its signal input side is switched to the line memory 8 side. Similarly, since the switching circuit 12 is not supplied with the low illuminance detection signal S0, its signal input side is switched to the image memory 10 side. Therefore, at this time, the low illuminance detection signal S0
Is not derived, the circuit for averaging the above-mentioned input image and the input image of one frame before is constituted by the line memory 8, the switching circuit 9, the image memory 10 and the averaging circuit 11. Not established, line memory 8
The digital video signal DS2 output via the switching circuit 9 is stored in the image memory 10 via the switching circuit 9, and then sequentially read out and supplied to the pixel interpolation circuit 13 via the switching circuit 12.

In the pixel interpolation circuit 13, the given quarter
The digital video signal DS2 for one field is subjected to pixel interpolation processing to be enlarged to a one-field screen while compensating for the decrease in image resolution, and is supplied to the D / A conversion circuit 15 via the switching circuit 14.

The D / A conversion circuit 15 converts the area designated by the enlargement area designation signal S2 by the user into a digital video signal obtained by enlarging the area on the screen of one field as shown in FIG. It is converted and given to the AGC circuit 16. Since the AGC circuit 16 operates only when the input image signal level is not appropriate such as when the illumination condition is bad, no circuit operation is performed in this case, and the video signal AS2 is directly output to the monitor unit side. ..

Next, description will be made assuming that the illumination condition is low illuminance in the enlargement mode.

The image signal AS1 obtained by the camera 2 through the wide-angle lens 1 is level-detected by the signal level detection circuit 4, and the low illuminance detection signal S0 indicating that the illuminance is low is derived accordingly. On the other hand, the A / D conversion circuit 3 receives the video signal AS1 and, in response, receives the digital video signal DS1.
Derive. At this time, the low illuminance detection signal S0 is applied to the switching circuits 9, 12 and 14 and acts so as to switch the signal input side of those circuits accordingly. The switching circuit 7 receives the signal S1 and changes its signal input side to the digital video signal D
Switch to S2 input side. The switching circuit 9 switches its signal input side to the averaging circuit 11 output side. The switching circuit 12 switches its signal input side to the averaging circuit 11 output side. The switching circuit 14 switches its signal input side to the pixel interpolation circuit 13 side.

The digital video signal DS1 is supplied to the line memory 8 via the switching circuit 7 as the digital video signal DS2 in which the area desired by the user is extracted through the enlarged area extraction circuit 6 in the same manner as described above.

The digital video signal DS2 output from the line memory 8 is applied to the switching circuit 9 and the averaging circuit 11 at the same time. Since the signal input side of the switching circuit 9 is switched to the averaging circuit 11 output side, Thereafter, the digital video signal DS2 is transferred to the image memory 10 via the switching circuit 9.
Never be given to.

The averaging circuit 11 sequentially inputs the pixel signals output from the line memory 8 and the image memory 10 as shown in FIG. 3 and switches the digital data obtained by taking the arithmetic mean of these two pixels accordingly. The image is stored again in the image memory 10 via the circuit 9. By repeating such a closed loop, the averaging circuit 11 operates so as to average the input image and the input image one frame before (the image averaged last time). The digital video signal averaged in this way is given to the pixel interpolation circuit 13 via the switching circuit 12. The image averaging circuit including the averaging circuit 11 thus temporally averages the random noise that is noticeable when the illumination is low, and outputs the image to the monitor unit. It is possible to reduce the random noise of and improve the image quality.

In the pixel interpolation circuit 13, as described above,
A 1-field enlarged image is formed by interpolating the 1 / 4-field pixel data, and the D / A is passed through the switching circuit 14.
It is given to the conversion circuit 15.

The D / A conversion circuit 15 converts the supplied digital signal of the enlarged image of one field into an analog signal again and outputs it as the video signal AS2 via the AGC circuit 16 to the monitor section side. At this time, the image interpolation circuit 13
Acts to reduce quantization noise due to a reduction in resolution when the input image is reduced to 1/4 field in the enlarged area extraction circuit 6. Further, since the random noise generated at low illuminance is temporally averaged and reduced by the image averaging circuit including the averaging circuit 11, the AGC circuit 16 can obtain an image quality with a further improved S / N ratio. It becomes possible to derive a possible video signal AS2.

Next, the case where the enlargement mode is not designated by the user and the imaging condition is low illuminance will be described.

When the illuminance is low, the signal level detection circuit 4 derives the low illuminance detection signal S0 based on the video signal AS1 obtained by imaging. At this time, since the enlargement mode is not designated by the user, the enlargement request signal S1 and the enlargement area designation signal S2 are not derived.

Since the signal S1 is not input, the switching circuit 7 switches its signal input side to the digital video signal DS3 side. Similarly, the switching circuits 9 and 12 switch the signal input side to the output side of the averaging circuit 11 and the switching circuit 14 switches the signal input side to the pixel interpolation circuit 13 side in response to the signal S0 input.

The digital video signal DS1 is applied to the 1/4 times area extraction circuit 5 and the enlarged area extraction circuit 6 at the same time. At this time, since the input of the switching circuit 7 is switched to the circuit 5 side, the digital video signal DS3 derived by the 1/4 times area extraction circuit 5 is derived to the line memory 8 via the switching circuit 7. ..

The 1 / 4-fold area extraction circuit 5 outputs the digital video signal DS3 which is reduced to a 1 / 4-fold area by the pixel thinning processing for the supplied video signal DS1 as shown in FIG. The digital video signal DS3 is given to the line memory 8 via the switching circuit 7 and input to the averaging circuit 11.

The averaging circuit 11 constitutes a circuit for image averaging including the line memory 8, the switching circuit 9 and the image memory 10. The averaging circuit 11 averages the input image and the input image one frame before in the same manner as described above. To work. By this circuit operation, random noise generated at low illuminance is temporally averaged, and the random noise of the digital video signal output from the averaging circuit 11 is reduced.

The random noise reduced digital video signal derived through the averaging circuit 11 is transferred to the switching circuit 12.
The pixel interpolation circuit 13 interpolates the enlarged image for one field. Here, the quantization noise in the resolution reduction when the image is reduced in the circuit 5 is reduced.

The digital video signal which has become an enlarged image of one field in the pixel interpolation circuit 13 is converted into an analog signal in the D / A conversion circuit 15 via the switching circuit 14 and is given to the AGC circuit 16. The AGC circuit 16 is
The gain of the obtained analog video signal is further adjusted, and the video whose noise in the low illuminance has been reduced by the averaging circuit is processed so that the S / N ratio is further improved.

The thus-obtained random noise at the time of low illuminance is reduced, and the quantization noise is reduced, and the video signal AS2 having an extremely good S / N ratio is output to the monitor unit on the master side (not shown). To be done.

As described above, since the enlargement area extraction circuit 6 extracts the image of 1/4 field in order to enlarge the area of the image desired by the user, the capacity of the image memory 10 is 1/4 in accordance with it. Only the fields are prepared. At this time, the 1/4 times area extraction circuit 5 is provided in order to use the existing circuit without increasing the number of illumination light sources in order to reduce random noise at the time of low illuminance and without increasing the number of illumination circuits. .. The circuit 5 operates so as to reduce the obtained one-field screen to one-fourth field, so that the image memory 10 can be used as it is. Further, since the 1/4 times area extraction circuit 5 operates when the image pickup condition is low illuminance, the influence of the resolution reduction due to reducing the image by a factor of 1 is small. That is, since the resolution is low at low illumination,
Even if the field memory is used to reduce the screen to 1/4 times, the effect of the resolution reduction is small (not noticeable).

As described above, in the TV door phone shown in FIG. 1, for the enlargement processing prepared for displaying the image photographed by using the wide-angle lens 1 on the monitor and for enlarging and outputting the desired portion. Since a part of the circuit can also be used as a circuit for reducing random noise in low illuminance, noise can be reduced even in low illuminance in the TV intercom to obtain an image quality with a good S / N ratio. Is possible.

[0098]

As described above, according to the present invention, the averaging means is a signal for averaging the image in the signal derivation path including the storage means by disabling the control means when the detecting means detects low illuminance. After switching to the derivation path, the averaged image of the input image and the previously averaged image is enlarged and output through the interpolation output means, and the images are output while being temporally averaged, so random noise is always reduced. There is an effect that a good image quality can be obtained.

Further, since the averaging means for reducing the noise is configured so as to also serve as a part of the circuit for enlarging and extracting the input image, it is possible to increase the number of conventional circuits without greatly increasing it.
Random noise can be reduced at low illuminance without providing an illumination circuit, so that there is an effect that cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a television door phone according to an embodiment of the present invention.

FIG. 2 (a) and (b) are quarters shown in FIG.
It is a figure for explaining operation which extracts a picture of a double field extraction circuit.

FIG. 3 is a diagram for explaining the operation of the averaging circuit shown in FIG.

FIG. 4 is a schematic configuration diagram of a television door phone showing the background of the present invention.

5A and 5B are diagrams for explaining movement and enlargement of an image showing the background of the present invention.

6A to 6D are diagrams for explaining the timing of a video signal, a scanning signal, and a horizontal read start signal at the time of image enlargement, which shows the background of the present invention.

7A and 7B are diagrams for explaining a general relationship between a field of view and a distance depending on a difference in a lens of a camera.

[Explanation of symbols]

 4 signal level detection circuit 5 1/4 times area extraction circuit 6 enlargement area extraction circuit 10 image memory 11 averaging circuit 13 pixel interpolation circuit 16 AGC circuit AS1 and AS2 video signal DS1, DS2 and DS3 digital video signal S0 low illuminance detection signal S1 Enlargement request signal S2 Enlargement area designation signal In the drawings, the same reference numerals indicate the same or corresponding portions.

Claims (1)

[Claims] 1. A conversion means for inputting a video signal obtained by imaging and converting it into a digital signal for each pixel, and for detecting the signal level being a low illuminance level by inputting the video signal. Detecting means for inputting the digital signal output by the converting means in the enlargement mode and extracting a digital signal of a desired portion of one screen according to the detecting means; and outputting the conversion means in the non-enlargement mode. Reducing means for inputting the digital signal and deriving the one screen while reducing it, storage means for successively storing a given digital signal for each pixel, sequentially inputting a given digital signal, and Interpolation output means for enlarging and outputting to the one screen while interpolating the pixels with each other, and sequentially writing the digital signal output by the extracting means into the storage means for each pixel. Control means for reading the data from the interpolation output means, and controlling it so as to lead it to the interpolation output means; Alternatively, the digital signal output by the reducing unit is input and averaged, the averaged signal is stored in the storage unit, and the averaged signal is provided to the interpolation output unit to average the image. Video signal processing device.