JP3298330B2 - Imaging 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 method for correcting a gradation of a blurred image of a main subject in backlit photography or the like to obtain an image rich in gradation expression with less noticeable noise. The present invention relates to a possible imaging device.

[0002]

2. Description of the Related Art In recent years, an image pickup apparatus equipped with many backlight correction means has been developed. A conventional imaging device is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-340875, entitled "Imaging Device".

[0003] A conventional imaging device will be described below. FIG. 16 is a block diagram of a conventional imaging apparatus disclosed in the publication. In FIG. 16, 1 is a lens, 2 is an aperture mechanism, 3 is an image sensor, 4 is a preamplifier that amplifies the output of the image sensor 3 to an appropriate size, 5 is an integration circuit, 6 is an aperture control circuit, 7 is a gamma correction circuit. , A white balance circuit, etc., 8 is an automatic gain control circuit (hereinafter referred to as an AGC circuit), 9 is an integration circuit, and 10 is an AG circuit.
An AGC control circuit for generating a signal for controlling the gain of the C circuit 8, an A / D converter 11 for A / D converting the video signal output of the AGC circuit 8, and a 12 for converting the A / D converted signal into a plurality of areas. An area dividing circuit 13 for calculating an evaluation value corresponding to the brightness of each area from the signal divided for each area; and 14 for counting the signals divided for each area by brightness. 15 is a frequency distribution operation circuit for obtaining a frequency distribution, and 15 is an output of the operation circuit 13 and a frequency distribution operation circuit 1
An interface circuit for inputting the output of 4 to the microcomputer; 16 a microcomputer; 17 a D / A converter for converting the digital signal output of the microcomputer 16 into an analog signal;
Is a control signal generation circuit for generating a control signal in accordance with the output of the D / A converter 17, 19 is a gain control circuit for controlling the gain of the video signal by the control signal output from the control signal generation circuit 18, and 20 is It is a signal processing circuit of a camera.

[0004] The operation of the conventional imaging apparatus configured as described above will be described below. The light passing through the lens 1 is limited in light quantity by the diaphragm mechanism 2, is converted into an electric signal by the image pickup device 3, and is amplified by the preamplifier 4. The output of the preamplifier 4 is integrated by the integrating circuit 5 to become a DC signal corresponding to the output signal level of the preamplifier 4 and input to the aperture control circuit 6. The aperture control circuit 6 compares the input DC signal level with the reference voltage, and outputs a control signal for operating the aperture mechanism 2 so that the output signal level of the preamplifier 4 becomes constant.

On the other hand, the output of the preamplifier 4 passes through a process circuit 7 for performing gamma correction and white balance, and outputs an AGC signal.
Input to the circuit 8. The AGC circuit 8 integrates the output of the AGC circuit 8 by an integration circuit 9 to obtain a DC signal corresponding to the output level of the AGC circuit 8, and then converts the integrated signal to an AGC control circuit 10
The AGC control signal generated by comparing with the reference voltage at
The output signal level of the AGC circuit 8 is made constant.

The output of the AGC circuit 8 is supplied to an A / D converter 11
Is divided into a plurality of regions by the region dividing circuit 12, the arithmetic circuit 13 detects the average luminance distribution of the video signal in each region as the exposure evaluation value of each region, and the frequency distribution Arithmetic circuit 1
4 calculates the luminance distribution in each area, the microcomputer 16 correlates the center of the screen with the other areas, sets the area correlated with the center of the screen as the main subject area, and sets the other areas as the non-main subject areas. And Then, backlight or over-direct light is determined based on the ratio between the main subject area and the non-main subject area, and the gain of the video signal is controlled in accordance with the degree. When controlling the gain of the video signal, the gain is corrected so that the gain of the portion having the lower luminance level is higher than that of the portion having the higher luminance level of the video signal. In this way, the gain control circuit 19 corrects the gradation characteristics of the dark part and outputs a signal with contrast.
After performing various processes by the signal processing circuit 20, a video signal is output from the signal output terminal 21.

[0007]

However, in the above-mentioned conventional example, the degree of backlight or excessive light is determined, and the gain of the video signal is controlled in accordance with the degree. When controlling the gain of the video signal, compared to the part where the brightness level of the video signal is high,
The correction is performed so that the gain of the portion where the luminance level is low increases. Therefore, there is a problem that the gradation correction of the dark part can be performed, but the S / N of the low luminance part of the video signal is largely deteriorated.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, without deteriorating the S / N of a low luminance portion of a video signal.
It is an object of the present invention to provide an imaging apparatus capable of preventing black and white loss and obtaining an output image with rich gradation expression over the entire screen from a normally-lit subject to a strongly backlit subject.

[0009]

In order to achieve this object, an image pickup apparatus according to the present invention comprises an image pickup device for outputting a video signal and an AG for controlling a gain of a video signal output from the image pickup device.
A C circuit; AGC control means for controlling the output signal level of the AGC circuit to be constant;
A gradation correction means for performing gradation correction by varying a gain for each luminance level of a video signal output of the GC circuit, a feature quantity extraction means for extracting a feature quantity of an image from the video signal output of the AGC circuit, An image discriminating means for discriminating the degree of backlight and over-order light from the feature quantity extracted by the quantity extracting means and outputting a correction degree of the gradation correction; and a control signal of the AGC control means for suppressing the degree of correction of the image discriminating means and for controlling the gradation. And a tone correction suppressing means for determining a correction coefficient , wherein the tone correction suppressing means comprises an AGC control.
When the control signal of the means increases the gain of the AGC circuit,
The degree of positive degree suppression is increased, and the level is adjusted according to the suppressed correction degree.
The tone correction coefficient is determined .

Further, the image pickup apparatus of the present invention performs gradation correction by varying the gain for each image signal output luminance level of the image signal output from the image pickup element by using a gradation correction coefficient. Tone correction means, a signal processing circuit for performing signal processing such as contour enhancement of the video signal output of the tone correction means,
A feature amount extraction unit that extracts a feature amount of an image from a video signal output of the imaging device; and an image determination unit that determines a degree of backlight and over-order light from the feature amount extracted by the feature amount extraction unit and outputs a gradation correction coefficient. Contour signal gain control means for controlling the gain of the contour emphasizing signal of the signal processing circuit according to the gradation correction coefficient determined by the image discriminating means , wherein the contour signal gain control means comprises:
The gradation correction coefficient increases the gain of the low luminance part due to the gradation correction.
In such a case, the gain of the contour emphasizing signal in the low luminance portion is reduced .

[0011]

According to the imaging apparatus of the present invention, the AG
The tone correction means suppresses the tone correction means with a tone correction coefficient determined by the tone correction suppression means in conjunction with the AGC control signal of the C control means, and outputs a video signal subjected to tone correction.
It is possible to obtain a gradation corrected image in which noise is not noticeable even for an input image.

Further, according to the image pickup apparatus of the present invention, the tone correction is controlled by the tone correction coefficient of the image discriminating means and the contour signal gain is adjusted by the tone correction coefficient of the image discriminating means. The control means performs control so as to reduce the gain of the contour emphasizing signal in the low-luminance portion, so that it is possible to obtain a tone-corrected image in which noise is not conspicuous even for an input image.

[0013]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an image pickup apparatus according to a first embodiment of the present invention. In FIG. 1, 1
01 is an image sensor, 102 is a process circuit including a gamma correction circuit and a white balance circuit, and 103 is an AG
C circuit, 104 outputs the video signal output of AGC circuit 103 to A
A / D converter for performing D / D conversion, 105 is an integration circuit, 106
A generates a signal for controlling the gain of the AGC circuit 103.
GC control means, 107 is a feature amount extraction circuit for extracting a feature amount of a video signal, 108 is an image discrimination means for discriminating the degree of backlight or excessive light of an input image, and 109 is an AGC control means 106
A tone correction suppression means for determining a tone correction coefficient based on the output of the image discriminating means 108, a tone correction circuit 110 for performing tone correction according to the tone correction coefficient, and a tone correction circuit 110 A signal processing circuit 112 performs signal processing of the video signal whose gradation has been corrected, and a D / A converter 112 performs D / A conversion of the video signal output of the signal processing circuit 111.

FIG. 2 is a diagram showing an image of one field of an input video signal in the embodiment of the present invention. In FIG. 2, reference numeral 201 denotes an effective screen, 320 pixels in the horizontal scanning direction, and 240 pixels in the vertical scanning direction.

FIG. 3 is a diagram showing an example of a luminance histogram extracted by the feature amount extraction circuit 107 in the embodiment of the present invention. In FIG. 3, a is the luminance histogram, b is the number of low luminance pixels, c is the number of medium luminance pixels, and d is the number of high luminance pixels.

FIG. 4 is a block diagram of the feature quantity extraction circuit 107 in the embodiment of the present invention. In FIG.
Is a comparator, 402 is a counter circuit for the number of low-luminance pixels, 40
Reference numeral 3 denotes a counter circuit for the number of medium luminance pixels, and 404 denotes a counter circuit for the number of high luminance pixels.

FIG. 5 is a block diagram of the image discriminating means 108 according to the embodiment of the present invention. In FIG. 5, reference numeral 501 denotes a quantization table, 502 denotes an output table, and 503 denotes a filter circuit.

FIG. 6 is a block diagram of the gradation correction suppressing means 109 according to the embodiment of the present invention. In FIG. 6, 60
Reference numeral 1 denotes a gradation correction suppression characteristic conversion unit, and 602 denotes a subtractor.

FIG. 7 is a graph showing a gradation correction suppression characteristic by an AGC control signal according to the embodiment of the present invention. In FIG.
a is the suppression start gain, and b is the suppression maximum gain.

FIG. 8 is a block diagram of a gradation correction circuit according to an embodiment of the present invention. 8, reference numeral 801 denotes a Y matrix circuit, 802 denotes a Y1 gain generation circuit, 803 denotes a Y2 gain generation circuit, and 804 denotes a luminance averaging circuit (LP
F), 805 is an adder, 806 is a weighted average circuit, 807
Is a delay circuit, and 808 is a multiplier.

FIG. 9 shows gradation correction characteristics in the embodiment of the present invention. FIG. 10 shows gradation correction characteristics and input / output characteristics according to the embodiment of the present invention.

The operation of the imaging apparatus according to the first embodiment of the present invention configured as described above will be described below. In FIG. 1, first, a video signal captured by an image sensor 101 is subjected to processing such as gamma correction and white balance by a process circuit 102, and then input to an AGC circuit 103.
The video signal output of the AGC circuit 103 is supplied to an A / D converter 104
Is converted into a digital signal. The output of the A / D converter 104 is integrated by an integrating circuit 105 to obtain a signal corresponding to the output level of the AGC circuit 103. The signal is generated by comparing with a reference value by an AGC control means 106. The AGC control signal allows the AG
Control is performed so that the output signal level of the C circuit 103 becomes constant.

On the other hand, the video signal digitally converted to 0-255 by the A / D converter 104 is input to the gradation correction circuit 110.

First, the R, G, and B signals converted into digital data of 0 to 255 are input to the gradation correction circuit 110 as input video signals. These color data are R = G = B
= 255 indicates white, and the larger the value is, the brighter it is. A Y matrix circuit 801 calculates a luminance signal Y from the R, G, and B signals. Assuming that the luminance of the input video signal is Y, the luminance can be obtained, for example, by the relational expression of (Equation 1), which also takes a value of 0 to 255. The calculated luminance signal Y is input to the integration circuit 105 and the feature quantity extraction circuit 107.

[0026]

(Equation 1)

FIG. 2 shows an image of one field of the input video signal. This image is an example of a subject in which a person stands in front of a window and has a high degree of backlight. The feature amount extraction circuit 107 performs, for example, one field image 320 × of the effective screen 201 of FIG.
For 240 dots, the number of low-luminance pixels, the number of medium-luminance pixels,
When the distribution of the number of high luminance pixels is obtained, a luminance histogram as shown in b, c, and d of FIG. 3 is obtained. Looking at the luminance histogram (b, c, d in FIG. 3), peaks are formed at two places of low luminance and high luminance, and it can be inferred that the subject is a backlight. In this way, the image discriminating means 108 determines the correction degree of the gradation correction characteristic for correcting the input image from the luminance histogram extracted by the feature amount extraction circuit 107. Next, the gradation correction suppression means 109 suppresses the degree of correction by the AGC control signal of the AGC control means 106 and determines a correction coefficient. Next, the gradation correction circuit 110 obtains a corrected luminance signal Y ′ from the luminance signal Y and the correction coefficient,
The correction gain (Y '/ Y) is calculated, the timing of the R, G, and B signals is adjusted with the correction gain by the delay circuit 807, and the correction gain (Y' / Y) is multiplied by the multiplier 808.
The tone-corrected R ', G', and B 'signals are output. As described above, by using the correction gain commonly for the R, G, and B signals, it is possible to obtain an output image with good color balance and rich in gradation expression over the entire range. Finally, the video signal subjected to the gradation correction is subjected to various signal processings by a signal processing circuit 111, and then the D / A converter 112 outputs an analog-converted video signal.

The operation of the feature extraction circuit 107 will be described in detail with reference to FIG. The input luminance signal Y is output from a comparator 40.
At 1, the threshold 1 and the threshold 2 are compared. Brightness signal Y is threshold 1
When it is smaller, a low luminance count signal is output. When the luminance signal Y is between the threshold 1 and the threshold 2, a medium luminance count signal is output. When the luminance signal Y is larger than the threshold value 2, a high luminance count signal is output. This low brightness count signal,
The counter circuits 402, 403, and 404 count the number of pixels on the effective screen of one field according to the medium luminance count signal and the high luminance count signal, and output the low luminance pixel number, the medium luminance pixel number, and the high luminance pixel number, respectively.

The operation of the image discriminating means 108 will be described in detail with reference to FIG. The quantization table 501 uses the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels supplied from the feature extraction circuit 107 as addresses to quantize data for a normally-lit subject, quantized data for a backlit subject, and a dark subject. Is stored. The output table 502 stores the degree of correction for a normally-lit subject, the degree of correction for a backlit subject, the degree of correction for a dark subject, and the like, using the quantized data output of the quantization table 501 as an address. Therefore, the feature amount extraction circuit 1
When the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels are input to the image determination unit 108 from 07, one correction degree is determined for the input image. Thus, the image discriminating means 1
08 has a two-stage table configuration, so that the size of the table can be reduced. The filter circuit 503 performs filter processing on the correction degree so as to maintain continuity with the previous field or the previous frame, and outputs the correction degree.

Referring to FIG. 6 and FIG.
9 will be described in detail. An AGC control signal is input from the AGC control unit 106 to the gradation correction suppression unit 109. First, the input AGC control signal is converted into a suppression value corresponding to the AGC control signal by a gradation correction suppression characteristic conversion 601. The converted suppression value is subtracted by the subtractor 602 from the degree of correction of the image discriminating means 108, and a correction coefficient is output. As shown in the gradation correction suppression characteristic of FIG.
When the C control signal is small, the suppression value is small, and as the AGC control signal increases, the suppression value increases. Accordingly, by performing the gradation correction in conjunction with the AGC so that the suppression of the gradation correction increases as the gain of the AGC increases, it is possible to perform the gradation correction in which the noise is inconspicuous.

Hereinafter, the operation of the gradation correction circuit 110 will be described in detail with reference to FIG. First, the luminance signal Y is calculated by the Y matrix circuit 801 based on the input RGB signals. The luminance signal Y is supplied to a Y1 gain generation circuit 802 and a Y2 gain generation circuit 803. The Y1 gain generation circuit 802 outputs a first correction gain (Y1 / Y) from the input luminance signal Y and Y1 corrected by the first gradation correction characteristic. Similarly, a second correction gain (Y2 / Y) is output from the Y2 gain generation circuit 803. On the other hand, the average luminance value Ya of the luminance signal Y is obtained by an average value detection circuit (LPF) 804,
The average luminance value Ya and the correction coefficient are added by an adder 805, and X
Output a signal. Finally, the weighted averaging circuit 806 performs weighted averaging of the first correction gain and the second correction gain according to the relational expression (Equation 2) using the X signal, and outputs a correction gain (Y ′ / Y).

[0032]

(Equation 2)

In this embodiment, the first correction gain (Y1
/ Y) by (Equation 3) and the second correction gain (Y2 / Y) by (Equation 4).

[0034]

(Equation 3)

[0035]

(Equation 4)

FIG. 9 shows the gradation correction characteristics in this embodiment. Y1 is the first gradation correction characteristic, and Y2 is the second gradation correction characteristic. For example, when the correction coefficient is 0, the gradation correction characteristic becomes a in FIG. 9 from the relational expression of (Equation 2). Similarly, when the correction coefficient becomes positive, the gradation correction characteristic becomes as shown in FIG. Similarly, when the correction coefficient becomes negative, the gradation correction characteristic becomes as shown in FIG. By changing the correction coefficient in this way, the gradation correction characteristic can be easily and continuously changed. As for the gradation correction characteristics, as the correction coefficient is changed, the correction gains in the low-luminance part and the middle-luminance part gradually increase, and finally, the overall correction gain increases. Therefore, the gradation correction characteristic of Y2 in FIG. 9 is applied to a normally-lit subject, and the gradation correction characteristic of FIG.
By performing gradation correction on a dark subject using the gradation correction characteristic of Y1 in FIG. 9, gradation correction rich in gradation expression can be performed on any subject.

FIG. 10 shows gradation correction characteristics and input / output characteristics. When the average luminance value Ya obtained by the average value detection circuit 804 is equal to the luminance signal Y of the target pixel, the gradation correction characteristic of FIG. 10A is used. When the average luminance value Ya is lower than the luminance signal Y of the target pixel, FIG. When the luminance average value Ya is higher than the luminance signal Y of the pixel of interest in the gradation correction characteristic of 10b, the gradation correction characteristic of FIG. By performing the gradation correction, the gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and an output signal rich in gradation expression can be obtained.

As described above, according to the present embodiment, the image pickup apparatus of the present invention includes an image pickup device 101 and a process circuit 102 including a gamma correction circuit, a white balance circuit, and the like.
An AGC circuit 103, an A / D converter 104 for A / D converting the video signal output of the AGC circuit 103, an integrating circuit 105, and an AGC control means 106 for generating a signal for controlling the gain of the AGC circuit 103. A feature amount extraction circuit 107 for extracting a feature amount of a video signal; an image determination unit 108 for determining the degree of backlight or over-order light of an input image; a correction coefficient based on an output of the AGC control unit 106 and an output of the image determination unit 108 , A gradation correction circuit 110 that performs gradation correction according to a gradation correction coefficient, and a signal process that performs signal processing on a video signal whose gradation has been corrected by the gradation correction circuit 110 A circuit 111 and a D / A converter 112 for D / A-converting the video signal output of the signal processing circuit 111. The AGC control signal interlocks the gradation correction so that the backlight is sequentially turned on. Noise is inconspicuous for every object to the object, the gradation is not crushed, it is possible to color balance to obtain a rich output image gradation over well throughout.

The tone correction means of the present invention comprises a Y matrix circuit 801, a Y1 gain generation circuit 802,
2 gain generating circuit 803 and luminance averaging circuit (LPF) 8
04, an adder 805, a weighted averaging circuit 806, a delay circuit 807, and a multiplier 808, so that a correction gain is generated by a correction coefficient, thereby storing several types of gradation correction characteristics. Extra RO to keep
Since it is not necessary to have M or the like, the circuit scale can be made very small. Also, by changing the correction coefficient, it is possible to generate gradation correction characteristics of the subject of direct light and backlight, so that the gradation is not destroyed for any subject from the backlight subject to the front light subject, and the color balance is good and the whole range is obtained. Thus, an output image rich in gradation expression can be obtained. Further, since the gradation correction characteristics can be continuously changed, natural gradation correction can be performed even for a moving image. In addition, when the input signal is large, the gradation correction characteristic is used so that the input signal becomes almost the same as the output signal. it can.

FIG. 11 is a block diagram showing a configuration of an image pickup apparatus according to the second embodiment of the present invention. In FIG. 11, reference numeral 1101 denotes an image sensor; 1102, a process circuit including a gamma correction circuit and a white balance circuit;
Reference numeral 103 denotes an A / D output of a video signal output from the process circuit 1102.
A / D converter for converting, 1104 is a feature amount extracting means for extracting a feature amount of a video signal, 1105 is backlight of an input image,
Image discriminating means for judging the degree of over-order light, 1106 is a DTL gain control means for determining a DTL gain based on the image discrimination result, 1107 is a tone correction circuit for performing tone correction according to a tone correction coefficient, and 1108 is a tone correction circuit. A signal processing circuit 1109 that performs signal processing such as detail correction of the video signal whose gradation has been corrected by the correction circuit 1107, and a D / A converter 1109 that performs D / A conversion of the video signal output of the signal processing circuit 1108.

FIG. 12 is a block diagram of a signal processing circuit 1107 according to the second embodiment of the present invention. 12, reference numeral 1107 denotes a signal processing circuit; 1201, a vertical detail circuit; 1202, a horizontal detail circuit; 1203, an adder; 1204, a multiplier; 1205, a delay circuit;
206 is an adder.

FIG. 13 is a characteristic diagram of the detail gain corresponding to the luminance signal Y. FIG. 14 is a block diagram of a gradation correction circuit according to the second embodiment of the present invention. In FIG. 14 , reference numeral 802 denotes a Y1 gain generation circuit, 803 denotes a Y2 gain generation circuit, 804 denotes a luminance averaging circuit (LPF), and 805
Is an adder, 806 is a weighted average circuit, 807 is a delay circuit, and 808 is a multiplier.

The operation of the imaging apparatus according to the second embodiment of the present invention configured as described above will be described below. In FIG. 11, first, a video signal captured by an image sensor 1101 is subjected to processing such as gamma correction and white balance by a process circuit 1102, and the video signal output from the process circuit 1102 is converted into a digital signal by an A / D converter 1103. Is converted. The video signal digitally converted to 0 to 255 by the A / D converter 1103 is input to the feature amount extraction unit 1104 and the gradation correction circuit 1107.

The feature extracting means 1104 and the image discriminating means 1
The operation of 105 is exactly the same as in the first embodiment. That is, the image discriminating unit 1105 determines a correction coefficient of a gradation correction characteristic for correcting the input image from the luminance histogram extracted by the feature amount extracting unit 1104. Next, the gradation correction circuit 1
107 calculates a corrected luminance signal Y ′ from the luminance signal Y and the correction coefficient, calculates a correction gain (Y ′ / Y), adjusts the timing of the input video signal with the correction gain by the delay circuit 807, By multiplying by 808 the correction gain (Y '/ Y) and outputting a gradation-corrected output video signal, it is possible to obtain an output image rich in gradation expression over the entire region. On the other hand, based on the correction coefficient determined by the image determination unit 1105, the DTL gain control unit 1106 performs gain control so as to reduce the detail gain of the low luminance portion, and outputs a detail gain corresponding to the luminance signal Y. Next, the video signal subjected to the gradation correction is input to the signal processing circuit 1108, and the detail correction signal processing is performed with the detail gain determined by the DTL gain control unit 1106. By linking the gradation correction and the detail correction in this way, it is possible to perform a gradation correction in which noise in a low-luminance portion is inconspicuous. Finally, the D / A converter 1109 outputs an analog-converted video signal.

The operation of the DTL gain control means 1106 and the signal processing circuit 1108 will be described in detail with reference to FIGS. The DTL gain control means 1106 has a detail gain characteristic corresponding to the luminance signal Y as shown in FIG. That is, it has such a characteristic that the detail gain in the low luminance part is lowered and the detail gain in the high luminance part is increased. This is to prevent the S / N degradation in the low-brightness part and to correct the detail collapsed by the gamma correction in the high-brightness part. Since the tone correction circuit 1107 in the embodiment of the present invention performs tone correction by increasing the gain of the low-brightness section compared to the high-brightness section, the S / N of the low-brightness section deteriorates. Therefore, the image discriminating means 11
By reducing the detail gain of the low-brightness part in conjunction with the correction coefficient determined by 05, the S / S of the low-brightness part is reduced.
N degradation can be made inconspicuous.

FIG. 12 is a block diagram of the signal processing circuit. First, when a video signal is input, it is input to a vertical detail circuit 1201 for performing high-pass filtering in the vertical direction and a vertical detail circuit 1202 for performing high-pass filtering in the horizontal direction. A signal is calculated. Next, an adder 1203
The vertical detail signal and the horizontal detail signal are added to obtain a detail signal. The detail level is adjusted by multiplying the detail signal by a DTL gain in a multiplier 1204. Finally, the timing of the input video signal is adjusted by the delay circuit 1205, and the detail signal is added to the adder 1206 to output a video signal whose detail has been corrected. Therefore, by reducing the detail gain of the low-luminance part in conjunction with the correction coefficient determined by the image determining unit 1105, the S / N deterioration of the low-luminance part can be made inconspicuous.

As described above, according to the present embodiment, the image pickup apparatus of the present invention includes an image pickup device 1101 and a process circuit 110 including a gamma correction circuit, a white balance circuit, and the like.
2, an A / D converter 1103 for A / D converting the video signal output of the process circuit 1102, a feature amount extracting unit 1104 for extracting a feature amount of the video signal, and determining the degree of backlight or over-order light of the input image. Image determination means 1105, a DTL gain control means 1106 for determining a DTL gain based on an image determination result, a gradation correction circuit 1107 for performing gradation correction in accordance with a gradation correction coefficient, and a gradation correction circuit 1107. A signal processing circuit 1108 that performs signal processing such as detail correction of the corrected video signal, and a D / A converter 1109 that performs D / A conversion of the video signal output of the signal processing circuit 1108, and a correction gain is set by a correction coefficient. By making this occur, it is not necessary to have an extra ROM or the like for storing several types of gradation correction properties, so that the circuit scale can be made very small. Can. Also, by changing the correction coefficient, it is possible to generate gradation correction characteristics of the subject of direct light and backlight, so that the gradation is not destroyed for any subject from the backlight subject to the front light subject, and the color balance is good and the whole range is obtained. Thus, an output image rich in gradation expression can be obtained. In addition, since the detail gain of the low-luminance portion is controlled by the correction coefficient, it is possible to perform gradation correction with less noticeable noise. In addition, when the input signal is large, the gradation correction characteristic is used so that the input signal becomes almost the same as the output signal. it can. Further, by performing gradation correction by adaptively changing the gradation correction characteristics in pixel units based on the luminance average value Ya, gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and gradation expression is performed. A rich output signal can be obtained.

FIG. 15 is a block diagram showing a configuration of an image pickup apparatus according to the third embodiment of the present invention. In FIG. 15, reference numeral 1401 denotes an image sensor; 1402, a process circuit including a gamma correction circuit and a white balance circuit;
403, an AGC circuit; 1404, an A / D converter for A / D converting the video signal output of the AGC circuit 1403;
Is an integration circuit, 1406 is an AGC control means for generating a signal for controlling the gain of the AGC circuit 1403, 1407 is a feature amount extraction circuit for extracting a feature amount of a video signal, and 1408 is for judging the degree of backlight or over-order light of the input image. Image discriminating means,
Reference numeral 409 denotes a gradation correction suppression unit that determines a correction coefficient based on the output of the AGC control unit 1406 and the output of the image determination unit 1408. Reference numeral 1410 denotes a DTL gain control unit that controls the DTL gain based on the correction coefficient determined by the gradation correction suppression unit 1409. , 1411 is a gradation correction circuit that performs gradation correction according to the correction coefficient, 1412 is a signal processing circuit that performs signal processing of a video signal whose gradation has been corrected by the gradation correction circuit 1411, 14
Reference numeral 13 denotes a D / A converter for D / A converting the video signal output of the signal processing circuit 1412.

The operation of the imaging apparatus according to the third embodiment of the present invention configured as described above will be described below. In FIG. 15, first, a video signal captured by an image sensor 1401 is subjected to processing such as gamma correction and white balance by a process circuit 1402, and then input to an AGC circuit 1403. The video signal output of the AGC circuit 1403 is converted into a digital signal by the A / D converter 1404, and the output of the A / D converter 1404 is integrated by the integration circuit 1405 to obtain a signal corresponding to the output level of the AGC circuit 1403. , AG
AGC generated by comparing with a reference value by C control means 1406
The control signal controls the output signal level of the AGC circuit 1403 to be constant.

On the other hand, the A / D converter 1404 uses 0 to 255
The digitally converted video signal is input to an integration circuit 1405, a feature amount extraction circuit 1407, and a gradation correction circuit 1411.

The feature amount extracting means 1407 and the image discriminating means 1
The operation 408 is exactly the same as in the first and second embodiments.
That is, the image discriminating means 1408 determines whether the feature amount extraction circuit 14
07 determines the correction degree of the gradation correction characteristic to correct the input image from the extracted luminance histogram. Next, the gradation correction suppressing unit 1409 determines the correction coefficient by suppressing the degree of correction by the AGC control signal of the AGC control unit 1406. Next, the gradation correction circuit 1411 obtains a corrected luminance signal Y ′ from the luminance signal Y and the correction coefficient, and obtains a correction gain (Y ′
/ Y) is calculated, the timing of the input video signal is adjusted to the correction gain by the delay circuit 807, and the input video signal is multiplied by the correction gain (Y '/ Y) by the multiplier 808 to output an output video signal whose gradation is corrected. Accordingly, it is possible to obtain an output image rich in gradation expression over the entire region where noise is inconspicuous. As described above, by performing the gradation correction in conjunction with the AGC and the gradation correction, it is possible to perform the gradation correction in which the noise in the low luminance portion is not conspicuous. On the other hand, tone correction suppressing means 1409
The DTL gain control means 14
The gain control unit 10 performs gain control so as to reduce the detail gain of the low brightness portion, and outputs a detail gain corresponding to the brightness signal Y. Next, the video signal subjected to the gradation correction is input to the signal processing circuit 1412, and the signal processing of the detail correction is performed with the detail gain determined by the DTL gain control unit 1410. By linking the gradation correction and the detail correction in this way, it is possible to perform a gradation correction in which noise in a low-luminance portion is inconspicuous. Finally, the D / A converter 1
An analog-converted video signal is output from 413.

As described above, according to the present embodiment, the image pickup apparatus of the present invention includes an image pickup device 1401 and a process circuit 140 including a gamma correction circuit and a white balance circuit.
2, an AGC circuit 1403, an A / D converter 1404 for A / D converting the video signal output of the AGC circuit 1403,
An integration circuit 1405, an AGC control means 1406 for generating a signal for controlling the gain of the AGC circuit 1403, a feature extraction circuit 1407 for extracting the feature of the video signal, and determining the degree of backlight or over-order light of the input image. Image discriminating means 140
8, the output of the AGC control means 1406 and the image discriminating means 1
A gradation correction suppression unit 1409 for determining a correction coefficient based on the output of the output 408, a DTL gain control unit 1410 for controlling a DTL gain based on the correction coefficient determined by the gradation correction suppression unit 1409, and a gradation corresponding to the gradation correction coefficient. A gradation correction circuit 1411 for performing correction, and a signal processing circuit 14 for performing signal processing on a video signal whose gradation has been corrected by the gradation correction circuit 1411
12 and the video signal output of the signal processing circuit 1412 are D / A
By using a D / A converter 1413 for conversion and generating a correction gain based on a correction coefficient, an extra ROM for storing several types of gradation correction properties is provided.
Since it is not necessary to provide the same, the circuit scale can be made very small. Also, by changing the correction coefficient,
Since it can generate gradation correction characteristics for normal and backlit subjects, it is possible to obtain output images that are rich in gradation expression over the entire area, with no gradation degradation for any subject from backlit subjects to normally-lit subjects. it can. Further, since the gradation correction is linked with the AGC control signal and the detail gain of the low luminance portion is controlled by the correction coefficient, the gradation correction with less noticeable noise can be performed. In addition, when the input signal is large, the gradation correction characteristic is used so that the input signal becomes almost the same as the output signal. it can. Further, the luminance average value Y
By performing the gradation correction by changing the gradation correction characteristics adaptively on a pixel basis by a, the gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and the output signal rich in gradation expression is obtained. Obtainable.

In this embodiment, the luminance signals Y, R, G, and B are used as the input video signals. However, instead of the luminance signals Y, R, G, and B, luminance signals, color difference signals, and composite signals are used. A similar effect can be obtained by using a signal obtained by combining a color signal with a luminance signal as an input video signal.

In this embodiment, the gradation correcting means multiplies each of the input video signals by a correction gain to perform the gradation correction. However, instead of the correction gain (Y '/ Y), the correction value ( Even if Y′−Y) is added to each of the input video signals, the same effect can be obtained.

In this embodiment, the input video signal has been described as being converted from analog to digital into 8 bits. However, the quantization bit number may be another value, and the processing bit number of the correction gain generation circuit or the like may be quantized. It can be configured according to the number of coded bits.

In this embodiment, the feature quantity extraction circuit outputs the number of pixels of three luminance levels. However, the threshold value of each level may be different, or the number of levels may not be three. .

In the present embodiment, the feature amount extraction circuit counts the number of pixels for an effective screen having 320 horizontal pixels and 240 lines. However, the number of pixels to be counted may be different, or a signal representing the number of pixels may be used. The number of bits may be any number as long as the characteristics of the input image are known.

In the present embodiment, the correction coefficient determination circuit determines the input image using the luminance histogram as a characteristic amount. However, instead of the luminance histogram, other characteristic amounts, such as R, G, and B signals, are used. This histogram or any one of the histograms or the effective screen of the image data is divided into blocks, and the maximum value, average value, minimum value, and the like of the luminance signal, RGB signal, and color difference signal of each block are used as feature amounts. The method is not limited to this method as long as it is a feature amount that can classify.

In the present embodiment, the correction coefficient determination circuit may be any method that can determine the gradation correction characteristic by determining an image, such as a method using a neural network, a method using fuzzy control, or a method using template matching. It is not limited to one method.

[0060]

As described above, the image pickup apparatus of the present invention comprises an image pickup device, an AGC circuit, an AGC control means for generating a signal for controlling the gain of the AGC circuit, and a characteristic amount for extracting a characteristic amount of a video signal. An extraction circuit; an image discriminating means for discriminating the degree of backlight or over-order light of the input image; DTL gain control means for controlling the DTL gain based on the gradation correction coefficient determined by the suppression means, a gradation correction circuit for performing gradation correction in accordance with the gradation correction coefficient, and an image gradation-corrected by the gradation correction circuit The configuration of the signal processing circuit that performs signal processing of the signal generates a correction gain based on the correction coefficient, so that there is no need for an extra ROM or the like that stores several types of gradation correction properties. ,circuit Model can also be very small. Also, by changing the correction coefficient, it is possible to generate the gradation correction characteristics of the direct light and the backlight subject, so that the gradation is not destroyed for any subject from the backlight subject to the front light subject, and the gradation is expressed over the entire area. Rich output image can be obtained. Further, since the gradation correction is linked with the AGC control signal and the detail gain of the low luminance portion is controlled by the correction coefficient, the gradation correction with less noticeable noise can be performed. In addition, when the input signal is large, the gradation correction characteristic is used so that the input signal becomes almost the same as the output signal. it can. Further, by performing gradation correction by adaptively changing the gradation correction characteristics in pixel units based on the luminance average value Ya, gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and gradation expression is performed. A rich output signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an imaging apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an image of one field of an input video signal according to the embodiment of the present invention.

FIG. 3 is a feature amount extraction circuit 107 according to the embodiment of the present invention.
Explanatory diagram showing an example of a luminance histogram extracted by

FIG. 4 is a diagram illustrating a feature extraction circuit 107 according to an embodiment of the present invention.
Block diagram

FIG. 5 is a block diagram of an image determining unit according to the embodiment of the present invention.

FIG. 6 shows a gradation correction suppressing means 10 according to the embodiment of the present invention.
Block diagram of 9

FIG. 7 is a graph showing a gradation correction suppression characteristic by an AGC control signal according to the embodiment of the present invention.

FIG. 8 is a block diagram of a gradation correction circuit according to the first embodiment of the present invention.

FIG. 9 is a characteristic diagram showing gradation correction characteristics according to the embodiment of the present invention.

FIG. 10 is a characteristic diagram showing gradation correction characteristics and input / output characteristics according to the embodiment of the present invention.

FIG. 11 is a block diagram of an imaging apparatus according to a second embodiment of the present invention.

FIG. 12 is a block diagram of a signal processing circuit according to a second embodiment of the present invention.

FIG. 13 is a characteristic diagram of detail control according to the second embodiment of the present invention.

FIG. 14 is a block diagram of a tone correction circuit according to the second and third embodiments of the present invention.

FIG. 15 is a block diagram of an imaging device according to a third embodiment of the present invention.

FIG. 16 is a block diagram showing a configuration of an imaging device in a conventional example.

[Explanation of symbols]

 101, 1101, 1401 Image sensor 102, 1102, 1402 Process circuit 103, 1403 AGC circuit 106, 1406 AGC control circuit 107, 1104, 1407 Feature extraction circuit 108, 1105, 1408 Image determination means 109, 1410 Tone correction suppression means 110, 1107, 1411 Tone correction circuit 111, 1108, 1412 Signal processing circuit 1106, 1409 DTL gain control means

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 5/225-5/247 H04N 5/14-5/217

Claims (4)

(57) [Claims] 1. An image sensor for outputting a video signal, and an AG for controlling a gain of a video signal output from the image sensor.
A C circuit; AGC control means for controlling the output signal level of the AGC circuit to be constant; and a gradation by varying a gain for each luminance level of the video signal output of the AGC circuit by a gradation correction coefficient. Gradation correction means for performing correction; feature quantity extraction means for extracting a feature quantity of an image from the video signal output of the AGC circuit; and judging the degree of backlight and excessive forward light from the feature quantity extracted by the feature quantity extraction means. comprising an image determination means for outputting a correction degree of the gradation correction, a tone correction suppression means for determining a suppression to the gradation correction coefficient correction degree of the image determination means by the control signal of the AGC control unit, the The gradation correction suppressing means is a control signal of the AGC control means.
The degree of correction when the signal increases the gain of the AGC circuit.
The suppression is large, and the floor is adjusted according to the suppressed correction degree.
An imaging device, wherein a tone correction coefficient is determined . 2. An image pickup device for outputting a video signal, and a gradation correction means for performing a gradation correction by changing a gain for each luminance level of a video signal output from the image pickup device by using a gradation correction coefficient; A signal processing circuit that performs signal processing such as contour enhancement of a video signal output of the gradation correction unit; a feature amount extraction unit that extracts a feature amount of an image from a video signal output of the imaging device; and the feature amount extraction unit. an image determination means from the extracted feature amount to determine the backlight and excessive follow light degree and outputs the tone correction factor, the gain of the contour enhancement signal of the signal processing circuit by the gradation correction coefficient by the image discriminating means has determined Controlling the contour signal gain, wherein the contour signal gain control means controls the
When increasing the gain of the low-luminance part due to the correction,
An imaging apparatus characterized in that a gain of a contour enhancement signal of a section is reduced . 3. An image sensor for outputting a video signal, and an AG for controlling a gain of a video signal output from the image sensor.
A C circuit; AGC control means for controlling the output signal level of the AGC circuit to be constant; and a gradation by varying a gain for each luminance level of the video signal output of the AGC circuit by a gradation correction coefficient. Tone correction means for performing correction; a signal processing circuit for performing signal processing such as contour enhancement of a video signal output from the tone correction means; and a feature quantity for extracting a feature quantity of an image from the video signal output of the AGC circuit. Extraction means; image determination means for determining the degree of backlight and over-order light from the characteristic amount extracted by the characteristic amount extraction means and outputting a correction degree of gradation correction; and the image determination means based on a control signal of the AGC control means. controls the gradation compensation suppression means for suppressing the correction degree determining the gradation correction coefficient, the gain of the contour enhancement signal of the signal processing circuit by the gradation correction coefficient the gradation compensation suppression means has determined the Contour signal gain control means, wherein the gradation correction suppressing means includes a control signal of the AGC control means.
The degree of correction when the signal increases the gain of the AGC circuit.
The suppression is large, and the floor is adjusted according to the suppressed correction degree.
A tone correction coefficient, and the contour signal gain control means determines that the tone correction coefficient is
When increasing the gain of the low-luminance part due to the correction,
An imaging apparatus characterized in that a gain of a contour enhancement signal of a section is reduced . 4. The imaging apparatus according to claim 1, 2 or 3, characterized in that the feature quantity the feature amount extracting unit extracts was brightness distribution of one field of the video signal.