JP2781936B2 - Video signal processing 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 video signal processing device, and more particularly to a video signal processing device for preventing deterioration of image quality at low illuminance.

[0002]

2. Description of the Related Art In recent years, television doorphones have become widespread in ordinary households. The TV door phone is provided indoors with a master unit integrally provided with a handset, and outdoors is provided with a slave unit including an imaging device such as a camera connected to the master unit for communication. In such a TV intercom, an outdoor image is shot by a camera of a slave unit, and an image obtained by shooting is displayed on a monitor screen of an indoor master unit, so that a person indoors can stay indoors. It has the advantage that outdoor conditions and visitors can be checked.

[0003] The installation location of the slave unit of the above-mentioned TV doorphone includes a wall surface or a gate at the entrance of a house or the like.
Such an installation place has a space limitation and a position limitation for installation, and since these restrictions are various, 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 imaging angle of the camera is driven by a motor or the like, and the motor is remotely controlled from the master unit in the room. Furthermore, we attach wide-angle lens to camera lens,
Measures have been taken to make it difficult for visitors to get out of the field of view of the camera.

Further, in a situation where the illumination conditions are extremely poor, such as in the evening or at night, measures have been taken to maintain the illumination conditions by performing infrared illumination or the like.

As described above, when a wide-angle lens is attached to a camera in order to keep the visitor always within the field of view of the camera, the field of view of the camera is widened, but the area where the visitor is reflected is large. Become smaller. In this state, it is extremely difficult for a person in the room to confirm the visitor on a normal screen. Therefore, of the captured images, only the image of the area where the visitor is shown is enlarged and extracted and displayed. This difficulty was being addressed.

FIG. 4 is a schematic structural view of a television doorphone according to the background of the present invention. In FIG. 4, the television doorphone is configured to capture an image of a visitor, derive a video signal thereof to a monitor unit, and identify the visitor remotely.

In the figure, a TV door phone captures a visitor via a wide-angle lens 1 and a wide-angle lens 1 and outputs a video signal AS.
2, 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, and an input for an externally supplied enlargement request signal Based on S1 and the enlargement area designation signal S2, a signal corresponding to an area of the signal DS1 desired to be enlarged is converted into a digital video signal DS2
The expanded area extraction circuit 6, the line memory 8,
Image memory 10, pixel interpolation circuit 13, enlargement request signal S1
Switching circuit 1 for switching its signal input side in accordance with 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 difference between the timing of writing a signal from the camera 2 in the image memory 10 and the timing of reading a signal to the pixel interpolation circuit 13 connected to the next stage. Is a kind of buffer memory provided for buffering data.

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

[0010] The pixel interpolation circuit 13 is provided in the image memory 1 in the preceding stage.
This is a circuit which receives a digital video signal read from 0 and operates so as to interpolate between adjacent pixels with an average level of luminance levels (digital amounts) of adjacent pixels. Therefore, the image data for 1/4 field in the memory 10 is 1 by the pixel interpolation circuit 13.
The image data is interpolated and output as image data for the field.

The switching circuit 14 receives an enlargement request signal S1 given from the outside, and when an enlargement of an image obtained by imaging based on the signal S1 is requested, the input side of the signal is connected to the pixel interpolation circuit 13 side. And the signal input side is switched to the A / D conversion circuit 3 during the period when the signal S1 is not supplied.

The D / A conversion circuit 15 is connected to the switching circuit 1 in the preceding stage.
The digital video signal supplied from the input unit 4 is input, converted into an analog quantity in accordance with the digital video signal, and transmitted to a monitor unit (not shown) of the master unit (not shown).

The wide-angle lens 1 is a lens attached to forcibly increase the viewing angle of the camera 2 as described above, and is detachably attached to the front of the camera 2.

Now, it is assumed that, with the wide-angle lens 1 attached to the front of the camera 2, the user designates a desired image and requests an enlarged display of the image.

First, in order to increase the viewing angle of the camera 2, the user attaches the wide-angle lens 1 to the front of the camera 2, and the camera 2 starts an imaging operation.

An analog video signal AS1 including a subject image obtained by imaging with the camera 2 is supplied to an A / D conversion circuit 3, and is converted into a digital video signal DS1 in response.

Next, the digital video signal DS1 is simultaneously supplied to the switching circuit 14 and the enlarged area extracting circuit 6. At this time, since the user has requested the 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. In addition, the enlarged area extracting circuit 6 determines that the enlarged display is requested in response to the input of the enlarged request signal S1, and inputs the enlarged area designation signal 2 to determine which part of the image of one screen. Is recognized as an area for which enlargement is requested. The digital video signal DS1 is supplied to an enlarged area extraction circuit 6
In, a region to be enlarged and extracted is extracted, and a digital video signal DS2 of the enlarged region is supplied to the line memory 8,
After passing through the line memory 8, it is written and stored in the image memory 10. The operation of the enlarged area extraction circuit 6 for extracting the enlarged area will be described later.

Here, the extracted digital video signal DS
2 is not directly input to the image memory 10 but is input once to the line memory 8 because the speed of writing data to the image memory 10 is lower (lower price) than the input speed of the video signal from the camera 2. This is because a 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 provided integrally.

As described above, the enlarged and extracted digital video signal DS2 is stored in the image memory 10 for creating 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 door phone itself is reduced.

The digital video signal DS2 for 1/4 field stored in the image memory 10 is read out to compensate for a decrease in image resolution when the digital video signal DS2 is expanded to a one-field screen, and then the next pixel interpolation circuit is used. 13, and is interpolated into a one-field digital video signal by a process of enlarging the space between pixels as described above.
When a video signal for one field is obtained by the pixel interpolation circuit 13 in this way, 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 response to the signal. Is output to the monitor unit of the master unit through the display unit and displayed in an enlarged scale.

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

FIGS. 6A to 6D are views for explaining the video signal and the timing of the scanning signal and the horizontal readout start signal when the image is enlarged by the enlarged area extracting circuit 6 showing the background of the present invention. FIG.

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

The enlargement area extracting circuit 6 receives the digital video signal DS1 and also receives an enlargement request signal S1 and an enlargement area designation signal S2 from outside. Thus, a desired portion of the monitor screen (not shown) can be moved to the center of the monitor screen based on the signals S1 and S2 given by the user operating a button (not shown), and can be projected with an area ratio of 4 times. It is configured as follows.

For example, as shown in FIG. 5 (a), if a visitor is offset in the upper left corner of the monitor screen, the photographer in the room is set to project the visitor image in the center of the monitor screen. A button is operated to output an enlargement request signal S1, and a button is operated to specify an enlarged portion of the image to output an enlarged area designation signal S2. At this time, the monitor screen moves from the upper left screen set as shown in FIG. 5A in the lower right direction, is enlarged four times, and is displayed in the center 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). Suppose that it has the size of -1).

While the screen is being projected, for example, when the visitor moves and is shifted 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 as to project the image. At this time, in order to move the upper left visitor image to the center, the photographer further operates a button to specify an enlarged area designation signal S for designating an enlarged area.
2 is output. These signals S1 and S2 are applied to an enlarged area extraction circuit 6.

In the enlarged area extracting circuit 6, the enlarged area designation signal S2 moves and enlarges the upper left screen part of the equally divided sub-screen of the same monitor screen as shown in FIG. (4 times the area ratio) so that the image is projected in the center of the screen. That is, as shown in FIG. 5B, (0,0) to (m / 2-1, n / 2−2) of the digital video signal DS1 on the monitor screen having the two-dimensional pixel array.
Only the pixel data of 1) is extracted.

The method of extracting image data of an 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 divides the blanking area BL effective area MU and the enlarged memory area MZ in FIG. 6A accordingly. The circuit 6 operates to perform an operation of extracting image data of an area desired 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 shown in FIG.
As shown in FIG. 6 (b), a horizontal synchronizing signal HD as shown in FIG. 6 (c) is extracted and provided for the video signal AS1 for one horizontal scanning line. The circuit 6 expands the image data corresponding to the enlarged memory area MZ in FIG. 6A to the entire effective area MU in response to the input of the synchronization signals including the signals S1 and S2 and the horizontal synchronization signal HD. Thus, as shown in FIG. 6D, the horizontal direction extraction start signal HS for starting extraction is output so as to specify the timing of the memory area MZ at the time of enlargement. At this time, although not shown, the vertical direction extraction start signal is also output so as to designate the enlarged memory area MZ.

As described above, the enlarged area extracting circuit 6
A region desired to be enlarged and extracted by the user is extracted from the input image data, and this is converted into a digital video signal DS2 and output to the next line memory 8.

The above-mentioned television doorphone inputs an image using a wide-angle lens so that a visitor can always be displayed on a monitor screen, regardless of the installation location and the installation position, and inputs the image to an area desired by the user. It is possible to prevent the number of visitors from becoming smaller and making it difficult to confirm the result by performing the extraction by enlargement.

[0033]

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

In the above-mentioned television doorphone, which is the background of the present invention, illumination using infrared rays is generally employed when outdoor illumination conditions such as evening or night are extremely poor. When such illumination using infrared rays is adopted, the brightness (illuminance) on the surface of the target object differs depending on whether the wide-angle lens is used or not even if the same infrared illumination light is used. ) Are different. This is shown in FIG.
Description will be made with reference to (a) and (b).

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

As shown in FIGS. 7 (a) and 7 (b), assuming a location L away from the light source O for illumination mounted on the wall, the standard lens of FIG. 7 (a) is used. 7 and distances OA and OB from light source O in case
When comparing the distances OC and OD from the light source O when using the wide-angle lens of (b), OA <OC and O
Since B <OD, when the 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 door phone is mounted is L It becomes dark (low). For this reason, a method of amplifying the signal level of an input image obtained by capturing an image with respect to the rate at which the brightness of the target object becomes dark is adopted. However, in this amplification process, there is a problem that random noise (variation in an output signal level in an image sensor, which is peculiar to a camera) generated at low illuminance is conspicuous, and image quality is extremely deteriorated. Therefore, in order to solve the problem that the image quality is extremely deteriorated due to the random noise generated at the time of low illuminance, and to always obtain the same image quality, first, the wide-angle lens of 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 shown in FIG. 7A is used.

However, since a wide-angle lens is used, the method of increasing the number of illumination light sources increases the cost of the TV door phone 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 imaging and display the image in a magnified manner, regardless of the type of optical lens used, at the time of low illumination. It is an object of the present invention to provide a video signal processing apparatus capable of reducing the image quality without increasing the number of illumination light sources and always obtaining good image quality.

[0039]

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

The extracting means inputs a digital signal output from the converting means in the enlargement mode, and extracts a digital signal of a desired portion of one screen in response to the input.
It is configured to derive while reducing one screen.

The control unit is configured to read out the digital signal output by the extraction unit or the reduction unit while sequentially writing the digital signal for each pixel in the storage unit, and to control the output to the interpolation output unit.

The averaging means responds to the detection by the detection means.
The control means is disabled, the digital signal stored immediately before in the storage means and the digital signal output from the extraction means or reduction means are input and averaged, and the averaged signal is stored in the storage means, and the interpolation output means Giving and averaging the images.

[0043]

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

[0044]

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

FIG. 1 is a schematic configuration diagram of a television doorphone according to one embodiment of the present invention. The illustrated television doorphone processes an enlargement request signal S1 and an enlargement area designation signal given by a user's external operation on a desired portion of a monitor screen while performing signal processing so that a video signal obtained by imaging is displayed on a monitor. It is configured such that it can be moved to the center of the monitor screen based on S2, and can be projected with an area ratio enlarged to four times. And, when the illuminance at the time of imaging is low, this TV doorphone operates so as to reduce random noise generated at the time of low illuminance, without increasing the illumination at low illuminance, and specially increasing the number of illumination circuits. Instead, the image quality is prevented from deteriorating.

In this embodiment, a television intercom is exemplified, but the invention is not limited to the television intercom, but is applicable to all video signal processing apparatuses for processing video signals obtained by imaging.

The illustrated TV door phone captures a visitor and outputs a video signal AS1 in response to a camera 2, a wide-angle lens 1 attached to the front of the camera 2, and a signal AS1. An A / D conversion circuit 3 that converts the signal into a signal and outputs a digital video signal DS1 and a signal AS1 are input, the signal level is detected, and whether the current imaging condition is low illuminance is detected according to the detection result. A signal level detection circuit 4 for deriving a low illuminance detection signal S0 indicating a result is included.

The television doorphone has a 1 / 4-fold area extracting circuit 5, an enlarged area extracting circuit 6, switching circuits 7, 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-fold region extracting circuit 5 operates to receive the supplied digital video signal DS1 and to thin out the digital data for each pixel contained in the signal DS1 for each pixel in sequence and to output it. As a result, the given digital video signal DS1 is derived as a digital video signal DS3 whose data amount is reduced by a factor of four. The area extracting operation of the quarter area extracting circuit 5 will be further described.

FIGS. 2A and 2B are diagrams for explaining the operation of extracting an image by the quarter area extracting circuit 5 shown in FIG.

The 1/4 area extracting 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 one pixel at a time in the sequence in each of the X direction and the Y direction of the input image in FIG. 2A, but one pixel in the X direction and the Y direction in the sequence as shown in FIG. 2B. The digital video signal DS3 is derived by performing a process of thinning out and reading each time. This signal DS3 is an extracted image in the circuit 5. FIG.
As shown in FIGS. 2A and 2B, if the circuit 5 performs the extraction operation, the area of 16 pixels surrounded by the thick frame in FIG. The image is reduced and extracted into an area of four pixels. Therefore, the 1/4 area extracting circuit 5 operates to convert the digital video signal DS1 into a quarter signal amount 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 extracting circuit 6 includes an enlargement request signal S1 and an enlargement area designation signal S1 given in response to a user's external operation.
2 to extract an area where the given digital video signal DS1 is desired to be enlarged, and extract the digital video signal DS2.
To derive. Since the detailed description of the enlarged area extracting circuit 6 has been described with reference to FIGS.
Here, it is omitted.

The switching circuits 7, 9, 12, and 14 are circuits for receiving the low illuminance detection signal S0 and the enlargement request signal S1, and selectively switching the signal input side 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 inputs to the output of the averaging circuit, and the switching circuit 14 switches their inputs to the pixel interpolation circuit 13 side.

When the enlargement request signal S1 is input by a user's external operation, the switching circuit 7 switches its input side to the digital video signal DS2 side, and the switching circuit 14 operates similarly to the case of outputting the low illuminance detection signal S0. The input side is switched to the pixel interpolation circuit 13 side.

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

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

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

The pixel interpolation circuit 13 inputs a given digital video signal for each pixel, and interpolates between adjacent pixels with an average level of luminance levels of adjacent pixels in response to the digital image signal. After the interpolation processing is performed to compensate for the
Is derived.

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

The AGC circuit 16 receives the video signal converted into an analog signal in the D / A conversion circuit 15 and amplifies the signal when the signal level is below a predetermined level, and amplifies the signal when the signal level is above a predetermined level. The video signal AS2 whose gain has been adjusted so as to automatically adjust the gain of the applied video signal so as to be attenuated is derived to a monitor unit (not shown) of the master unit.

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

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 intercom is low illuminance.

In FIG. 3, the averaging circuit 11 receives the output signal of the image memory 10 and the output signal of the line memory 8 and averages them accordingly, and derives this averaged signal to the switching circuits 12 and 9. I do. At this time, the averaged signal is stored again in the image memory 10 via the circuit 9. Then, the average signal immediately before read from the image memory 10 and the signal read from the line memory 8 are averaged again, and the processed signal is stored again in the image memory 10.

As described above, as shown in the circuit block of FIG. 3, the averaging circuit 11 outputs the input image obtained by the camera 2 taken through the line memory 8 and the input image one frame before (correctly, The image that has been averaged immediately before and stored once in the image memory 10 is averaged. In other words, when viewed instantaneously, the averaging circuit 11 takes an arithmetic average in response to the respective data of one pixel read out from the line memory 8 and the image memory 10, and takes the average value of one pixel. Output as digital data. In the long term, the averaging circuit 11 operates 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). Therefore, the operation of the averaging circuit 11 temporally averages the random noise that is particularly conspicuous at low illuminance, thereby effectively reducing the random noise included in the output image data.

Next, the operation of the TV door phone shown in FIG. 1 will be described in three states: normal use (not low illuminance and not in enlarged mode), enlarged mode, and low illuminance. I do.

It is assumed that the wide-angle lens 1 is attached to the front 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 is
Image of the subject via the computer, and derives a video signal AS1.
The video signal AS1 is supplied to the signal level detection circuit 4 and also to the A / D conversion circuit 3, and a digital video signal DS1 is derived accordingly.

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

The digital video signal DS 1 is supplied to the switching circuit 14 and simultaneously to the １ ／ -fold region extracting circuit 5 and the enlarged region extracting circuit 6. At this time,
Since the low illuminance detection signal S0 and the enlargement request signal S1 are not derived, only the digital video signal DS1 is switched to the switching circuit 14.
To the D / A conversion circuit 15. At this time, the digital video signal DS3 is processed by the switching circuit 7 or the pixel interpolation circuit 13. As a result, since the switching circuit 14 is switched to the digital video signal DS1 input side, the D / A conversion circuit 15 is not given.

The D / A conversion circuit 15 converts the supplied digital video signal DS1 into a video signal of an analog amount, and outputs the video signal AS2 via the AGC circuit 16 to the outside in order to keep the output signal level constant. I 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 conditions are bad, the AGC circuit 16 does not particularly operate during normal use, and the analog amount of video converted by the circuit 15 is used. The signal is output to the monitor as it is.

Next, the operation in the enlargement mode will be described. In the enlargement mode, the user inputs an enlargement request signal S1 by external operation and also inputs an enlargement area designation signal S2 for designating a desired enlargement area on one screen. First, a case where the enlargement mode is designated 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 supplied to the 1 / 4-time area extracting circuit 5, the enlarged area extracting circuit 6, and the switching circuit 14. At this time, since the enlargement request signal S1 is input, the switching circuit 14
Switches the signal input side to the pixel interpolation circuit 13 side.
Therefore, the digital video signal DS1 is not guided to the monitor section via the switching circuit 14.

The switching circuit 7 receives the signal S1.
The signal input is switched to the signal DS2 input.

Digital image signal DS1 obtained by imaging
In the enlarged area extraction circuit 6, the area designated by the enlarged area designation signal S2 is extracted by the operation shown in FIGS. 5 and 6 described above, and the extracted area is given to the switching circuit 7 as a digital video signal DS2. The switching circuit 7 derives the applied digital video signal DS2 to the line memory 8.
The line memory 8 supplies the supplied digital video signal DS2 to the switching circuit 9 and the averaging circuit 11 at the same time.

Since the switching circuit 9 does not receive the low illuminance detection signal S0, it switches its signal input side to the line memory 8 side. Similarly, since the switching circuit 12 does not receive the low illuminance detection signal S0, it switches its signal input side 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-described input image and the input image one frame before, which includes 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 is 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 the field is subjected to pixel interpolation processing and enlarged to a one-field screen while compensating for a decrease in the resolution of the image.

The D / A conversion circuit 15 converts the digital video signal obtained by enlarging the area designated by the user with the enlarged area designation signal S2 to a one-field screen as shown in FIG. The signal is converted and supplied to the AGC circuit 16. The AGC circuit 16 operates only when the input image signal level is not appropriate, for example, when the lighting conditions are bad. In this case, the circuit operation is not performed, and the AGC circuit 16 directly outputs the video signal AS2 to the monitor. .

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

The level of the video signal AS1 obtained by the camera 2 through the wide-angle lens 1 is detected by the signal level detection circuit 4, and a low illuminance detection signal S0 indicating low illuminance is derived accordingly. On the other hand, the A / D conversion circuit 3 receives the video signal AS1 and responds to the input of the digital video signal DS1.
Is derived. At this time, the low illuminance detection signal S0 is supplied to the switching circuits 9, 12, and 14, and acts so as to switch the signal input side of those circuits. The switching circuit 7 receives the signal S1 and changes the 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 obtained by extracting the area desired by the user 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 simultaneously supplied to the switching circuit 9 and the averaging circuit 11. Since the signal input side of the switching circuit 9 is switched to the output side of the averaging circuit 11, Thereafter, the digital video signal DS2 is transferred to the image memory 10 via the switching circuit 9.
Will not be given to

The averaging circuit 11 sequentially receives pixel signals output from the line memory 8 and the image memory 10 as shown in FIG. 3 and switches digital data obtained by arithmetically averaging both pixels. The data is stored again in the image memory 10 via the circuit 9. By repeating such a closed loop, the averaging circuit 11 operates to average the input image and the input image one frame before (the image averaged last time). The digital video signal averaged as described above is supplied to the pixel interpolation circuit 13 via the switching circuit 12. By the image averaging circuit including the averaging circuit 11 as described above, the random noise which is remarkably seen when the illumination is low is temporally averaged, and the image output to the monitor unit is obtained. Can be reduced to improve the image quality.

In the pixel interpolation circuit 13, as described above,
One-field enlarged image is interpolated by interpolating the quarter-field pixel data to form a D / A via 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, converts the digital signal into an image signal AS2 via the AGC circuit 16, and outputs the image signal AS2 to the monitor. 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. In addition, since the random noise generated at the time of low illuminance is temporally averaged and reduced by the image averaging circuit including the averaging circuit 11, the AGC circuit 16 can obtain image quality with further improved S / N ratio. A possible video signal AS2 can be derived.

Next, the case where the enlargement mode is not specified 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 a low illuminance detection signal S0 based on the video signal AS1 obtained by imaging. At this time, since the enlargement mode has not been designated by the user, the enlargement request signal S1 and the enlargement region designation signal S2 have not been 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 averaging circuit 11 output side in response to the signal S0 input, and the switching circuit 14 switches the signal input side to the pixel interpolation circuit 13 side.

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

The 1/4 area extracting circuit 5 outputs a digital image signal DS3 obtained by reducing the supplied image signal DS1 to a 1/4 area by pixel thinning processing as shown in FIG. The digital video signal DS3 is provided to the line memory 8 via the switching circuit 7, and is 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, and averages the input image and the input image one frame before in the same manner as described above. To work. With this circuit operation, random noise generated at low illuminance is temporally averaged, and random noise of the digital video signal output from the averaging circuit 11 is reduced.

The digital video signal reduced in random noise derived through the averaging circuit 11 is supplied to the switching circuit 12
, An interpolation process is performed by the pixel interpolation circuit 13 so as to obtain an 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 converted into a one-field enlarged image 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 supplied to the AGC circuit 16. The AGC circuit 16
Further gain adjustment is performed on the obtained analog video signal, and signal processing is performed on the video in which noise in low illuminance has already been reduced by the averaging circuit so that the S / N ratio is further improved.

The thus obtained video signal AS2 having a very good S / N ratio with reduced random noise at low illuminance and reduced quantization noise is output to the monitor unit (not shown) of the master unit. Is done.

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

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

[0098]

As described above, according to the present invention, the averaging means disables the control means when the detecting means detects low illuminance, and averages the signal deriving path including the storage means for averaging the image. After switching to the derivation path, the averaged image of the input image and the previously averaged image is enlarged and output via the interpolation output means, and the image is output while averaging over time, so random noise is always reduced. There is an effect that good image quality can be obtained.

Further, since the averaging means for reducing the noise is also configured as a part of the circuit for enlarging and extracting the input image, the averaging means does not greatly increase the conventional circuit.
Random noise at low illuminance can be reduced without providing a special lighting circuit, which has the effect of reducing costs.

[Brief description of the drawings]

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

FIGS. 2 (a) and (b) show １ ／ of FIG. 1;
FIG. 4 is a diagram for explaining an operation of extracting an image by a double area extraction circuit.

FIG. 3 is a diagram for explaining an operation of the averaging circuit shown in FIG. 1;

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

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

FIGS. 6A to 6D are diagrams for explaining the timing of a video signal, a scanning signal, and a horizontal reading start signal when an image is enlarged, which shows the background of the present invention.

FIGS. 7A and 7B are diagrams for explaining a general relationship between a visual field and a distance due to a difference in a camera lens. FIG.

[Explanation of symbols]

 Reference Signs List 4 signal level detection circuit 5 1/4 times area extraction circuit 6 enlarged 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 illumination detection signal S1 enlargement request signal S2 enlargement area designating signal In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A conversion means for inputting a video signal obtained by imaging and converting the video signal into a digital signal for each pixel, and detecting that the signal level is low illuminance level accordingly. Detecting means for inputting the digital signal output by the converting means in the enlargement mode, and extracting the digital signal of a desired portion of one screen in response to the digital signal; A reducing unit that receives the digital signal and derives the one screen while reducing the size of the screen, a storage unit that can sequentially store a given digital signal for each pixel, and sequentially inputs a given digital signal. Interpolating output means for enlarging and outputting to the one screen while interpolating pixels by means of a pixel, and storing the digital signal output by the extracting means or the reducing means for each pixel in the storage means. Control means for controlling the readout while sequentially writing to the stage and deriving it to the interpolation output means; and disabling the control means in response to the detection of the detection means, and the digital signal stored immediately before in the storage means. And the digital signal output by the extraction means or the reduction means is input and averaged, and the averaged signal is stored in the storage means, and given to the interpolation means,
A video signal processing device comprising an averaging means for averaging images.