JPH06253176A - Gradation correction circuit and imaging device - Google Patents

Abstract

(57) [Summary] [Purpose] Even if gradation correction is performed on an image with strong light from normal to strong backlight, gradation is not destroyed and noise is not noticeable. Provided are a gradation correction circuit and an image pickup device capable of obtaining an output image. [Structure] An average brightness value Ya and a correction coefficient are added by an adder 303. With this signal, the first gradation correction characteristic 301 and the second gradation correction characteristic 301
The tone correction characteristic 302 is weighted and averaged to obtain a correction gain of the tone correction characteristic. The gradation correction characteristic can be easily changed by the correction coefficient, and gradation can be corrected for any subject from normal light to backlight. Further, by using the average luminance value Ya, it is possible to obtain the output signal with rich gradation expression by changing the gradation correction characteristic for each pixel and performing the gradation correction so as to maintain the contrast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a gradation correction capable of obtaining an image with rich gradation expression by performing gradation correction on a blurred main image of a main subject due to backlight photography or the like. The present invention relates to a circuit and an imaging device.

[0002]

2. Description of the Related Art In recent years, many gradation correction circuits have been developed. As a conventional gradation correction circuit, for example, Japanese Patent Laid-Open No.
The image quality correction method of the image pickup apparatus is disclosed in Japanese Patent Laid-Open No. 125589.

A conventional gradation correction circuit will be described below. FIG. 15A is a block diagram of a conventional image pickup device with a gradation correction function shown in the same patent. Figure 15
In (a), 1501 is an image sensor, 1502 is a matrix circuit, and 1503 is a luminance signal correction circuit. FIG. 15B is a functional block diagram of the luminance signal correction circuit. In FIG. 15B, 1504 is an attenuation circuit, and 15
Reference numeral 05 is a non-linear amplifier circuit, 1506 is an inverting circuit, and 1507.
Is a first adder for adding the luminance input Y and the output signal of the inverting circuit 1506, and 1508 is a second adder for adding the luminance input Y and the output signal of the first adder. FIG. 15C is a signal diagram of the luminance signal correction circuit.

The operation of the conventional image pickup apparatus having a gradation correction function configured as described above will be described below. The luminance signal Y formed by the matrix circuit 1502 that forms a luminance signal from the color signal obtained by the image pickup by the image pickup device 1501 is supplied to the luminance signal correction circuit 1503. In the luminance signal correction circuit 1503, first, the attenuation circuit 15
At 04, the luminance signal Y is attenuated and the Y1 signal is output. Next, the non-linear amplification circuit 1505 non-linearly amplifies the Y1 signal and outputs Y2.
Output a signal. Next, the inverting circuit 1506 inverts the Y2 signal and outputs the Y3 signal. Next, the first adder 1507 adds the luminance signal Y and the Y3 signal and outputs the Y4 signal. Finally, the Y4 signal is added to the luminance signal Y by the second adder, and the luminance signal Yc whose gradation has been corrected is output. As described above, since the luminance signal correction circuit 1503 emphasizes the intermediate luminance and suppresses the change in the luminance of the black portion and the white portion, the image quality of the main subject and the background can be improved in the backlight subject. .

Another example of the conventional gradation correction circuit is disclosed in Japanese Patent Laid-Open No. 02-206282 gamma correction apparatus. The conventional gradation correction circuit will be described below.

FIG. 16 is a block diagram of a conventional image pickup device with a gradation correction function shown in the patent. In FIG. 16, 1601 is an imaging device, 1602 is a gain control circuit,
Reference numeral 1603 is an attenuation control circuit, 1604 is a level range dividing means, 1605 is an average value detection circuit, and 1606 is a gain control data ROM. Reference numeral 1607 is a gamma correction control circuit.

The operation of the conventional image pickup apparatus with a gradation correction function configured as described above will be described below. The image signal obtained by the image pickup by the image pickup device 1601 is divided into a predetermined signal level range by the level range dividing means 1604, and the average value detection circuit 1605 detects the average value or integrated value of the image signals in each level range. In the gain control data ROM 1606, the gain or the attenuation amount in the gamma correction control circuit 1607 is set according to the average value of the video signal in each level range. Gain control circuit 16
02 and the attenuation control circuit 1603, by controlling the gamma correction characteristic in accordance with the output signal of the gain control data ROM, it is possible to prevent the occurrence of white crushing and black crushing.

[0008]

However, in the above-mentioned first conventional example, since only the intermediate luminance is expanded, if strong backlight correction is performed, there will be no gradation between the medium luminance portion and the high luminance portion. Had the problem. In addition, although the image quality can be slightly improved for a backlit subject, the gradation may be distorted or unnatural for a normal-light subject or a subject having a gradation from low luminance to high luminance. It also had a problem that it became an output image.

Further, in the above-mentioned second conventional example, the gain of the low luminance portion is increased to prevent the black crushing, and the attenuation amount of the middle luminance portion and the high luminance portion is controlled to prevent the white crushing. ,
Although whiteout can be prevented, there is a problem in that the gradation in the high-luminance portion is lost. Further, in the above-mentioned conventional example, there is a problem that the correction characteristics cannot be easily changed even if the gradation correction is performed from the normal-light subject to the backlight subject. Further, in the above-mentioned conventional example, since it is not compatible with moving images, there is a problem that if gradation correction is performed on a moving image, an unnatural output image that is not stable is produced.

The present invention solves the above-mentioned problems of the prior art, and it is possible to obtain an output image with rich gradation expression over the entire screen from a normally lit subject to a strongly backlit subject by preventing black crushing and white crushing. An object of the present invention is to provide a gradation correction circuit that can obtain a natural gradation correction image even when a moving image is corrected.

[0011]

To achieve this object, a gradation correction circuit of the present invention uses a feature amount extraction circuit for obtaining a feature amount of an input video signal and a feature amount obtained by the feature amount extraction circuit. A correction coefficient determining circuit that outputs a correction coefficient that determines a gradation correction characteristic to be corrected based on the correction coefficient, and a correction that generates a correction gain of the gradation correction characteristic from the input video signal and the correction coefficient determined by the correction coefficient determining circuit. A gain generation circuit,
The correction gain generating circuit includes a gradation correction unit that corrects each of the input video signals with the correction gain generated by the correction gain generating circuit.

Further, the image pickup device with gradation correction function of the present invention comprises a solid-state image pickup device, an analog circuit for extracting an input video signal from the solid-state image pickup device, and a characteristic amount extraction circuit for obtaining a characteristic amount of the input video signal. A correction coefficient determining circuit for outputting a correction coefficient for determining a gradation correction characteristic to be corrected based on the characteristic amount obtained by the characteristic amount extracting circuit; a correction coefficient determined by the input video signal and the correction coefficient determining circuit; A correction gain generation circuit that generates a correction gain of the gradation correction characteristic from the above, and a gradation correction unit that corrects each of the input video signals with the correction gain generated by the correction gain generation circuit.

Further, in the gradation correction circuit and the image pickup apparatus with the gradation correction function of the present invention, the correction gain generation circuit obtains the first gradation correction characteristic from the input video signal, and a first gradation correction characteristic circuit, A second gradation correction characteristic circuit for obtaining a second gradation correction characteristic from the input video signal, an average value detection circuit for obtaining an average value of the input video signal, and an adder for adding the average value and the correction coefficient , A weighted average circuit for weighting and averaging the first gradation correction characteristic and the second gradation correction characteristic by the output signal of the adder to output a correction gain.

[0014]

The gradation correction circuit of the present invention has the above-mentioned configuration.
The feature amount extraction circuit extracts the feature amount of the input video signal. The gradation correction coefficient determination circuit determines the gradation correction characteristic to be corrected based on the extracted feature amount, and the gradation correction of the input video signal is performed, so that the gradation correction is stable for any input image. Images can be obtained.

In the image pickup device with a gradation correction function of the present invention, the analog circuit takes in the input video signal from the solid-state image pickup device with the above-mentioned structure. Next, the feature amount extraction circuit extracts the feature amount of the input video signal. The gradation correction coefficient determination circuit determines the gradation correction characteristic to be corrected based on the extracted feature amount, and the gradation correction of the input video signal is performed, so that the gradation correction is stable for any input image. Images can be obtained.

Further, the gradation correction circuit and the image pickup device with the gradation correction function of the present invention are configured as described above, and the first gradation correction characteristic and the second gradation correction characteristic are calculated by using the average value Ya of the input video signal. By calculating the correction gain by weighted averaging
If the brightness in the vicinity is high, the brightness is corrected low, if the brightness in the vicinity is low, the brightness is corrected high, and the gradation is corrected so that the contrast is maintained even if the gradation correction gain is small. A toned image can be obtained.

[0017]

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

FIG. 1 is a block diagram showing the structure of a gradation correction circuit according to the first embodiment of the present invention. In FIG. 1, 101 is a matrix circuit, 102 is a feature amount extraction circuit, 103 is a correction coefficient determination circuit, 104 is a correction gain generation circuit, 105 is a gradation correction means, 106 is a delay circuit, and 107 is a multiplier. FIG. 2 is a block diagram of a video-integrated camera using a gradation correction circuit according to an embodiment of the present invention. In FIG. 2, 201 is a solid-state image sensor, 2
Reference numeral 02 is an analog circuit, 203 is an analog-digital converter (A / D converter), 204 is a gradation correction circuit, 205 is a signal processing circuit, and 206 is a digital-analog converter (D
/ A converter), 207 is an encoder circuit, and 208 is a VT
It is an R circuit. FIG. 3A is a block diagram showing the functional configuration of the correction gain generation circuit in the first embodiment of the present invention. In FIG. 3, 301 is a first gradation correction characteristic circuit, 302 is a second gradation correction characteristic circuit, 303 is an adder, 304 is a weighted average circuit, and 104 is a correction gain generation circuit. FIG. 5 is a diagram showing an image of one frame of an input video signal in the embodiment of the present invention. 501 shows an effective screen. The number of samples of the effective screen 501 is 640 points in the horizontal H direction and 480 points in the vertical V direction. FIG. 6 is a histogram of the luminance signal of the effective screen in the embodiment of the present invention. FIG. 6a is a histogram of the luminance signal. Figure 6b
Is the number of low luminance pixels, FIG. 6c is the number of medium luminance pixels, and FIG. 6d is the number of high luminance pixels. FIG. 7 is a block diagram showing the configuration of the feature quantity extraction circuit in the embodiment of the present invention. In FIG. 7, 701 is a comparator, 702 is a low-luminance pixel number counter circuit, 703 is a medium-luminance pixel number counter circuit, and 704 is a high-luminance pixel number counter circuit. FIG. 8 is a block diagram showing the configuration of the correction coefficient determination circuit in the embodiment of the present invention. In FIG. 8, 801 is a correction coefficient table ROM,
Reference numeral 802 is a filter circuit, and 102 is a correction coefficient determination circuit. FIG. 9 is a characteristic diagram showing gradation correction characteristics in the embodiment of the present invention. In FIG. 9, Y1 is the first gradation correction characteristic, and Y2 is the second gradation correction characteristic.

The operation of the video-integrated camera using the gradation correction circuit according to the first embodiment of the present invention constructed as above will be described below. In FIG. 2, first, the analog circuit 202 captures R, G, and B signals as input video signals from the solid-state image sensor 201. The R, G, B signals are converted into 0 to 25 by the analog-digital converter 203.
5 are converted into digital data. The R, G, B signals converted into the digital data of 0 to 255 are input to the gradation correction circuit 204 of the present invention as an input video signal. The gradation correction circuit 204 determines the optimum gradation correction characteristic for the input video signal and performs gradation correction. The signal processing circuit 205 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. A digital-analog converter 206 converts the signal-processed digital R, G, B signals into analog R, G, B signals. Next, the encoder circuit 207 converts the R, G, B signals into a Y signal (luminance signal) and a C signal (color signal). Finally, the VTR circuit 20
8 records on videotape.

Next, the operation of the gradation correction circuit 204 of the present invention will be described in detail with reference to FIGS. 1, 5, and 6.

First, the R, G, B signals converted into digital data of 0 to 255 are input as an input video signal. These color data show white when R = G = B = 255, and show that the larger the value, the brighter. The matrix circuit 101 calculates the luminance signal Y from the R, G, B signals. Assuming that the luminance of the input video signal is Y, for example, Y = 0.30R + 0.59G + 0.11B (1) (1)
Becomes the value of.

FIG. 5 shows an image of one frame of the input video signal. This image is an example of a subject with a large degree of back light in which a person stands in front of a window. The feature amount extraction circuit 102, for example, one frame image 640 × 480 of the effective screen 501 of FIG.
When the distribution of the number of low-brightness pixels, the number of medium-brightness pixels, and the number of high-brightness pixels is obtained for the dots, a brightness histogram as shown in FIG. 6bcd is obtained. This brightness histogram (Fig. 6
Looking at bcd), the peaks are formed in two places, low brightness and high brightness, and it can be inferred that the subject is a backlit subject. In this way, the correction coefficient determination circuit 103 determines the correction coefficient of the gradation correction characteristic for correcting the input image from the brightness histogram extracted by the feature amount extraction circuit 102. Next, the correction gain generation circuit 104 obtains the corrected luminance signal Y ′ from the luminance signal Y and the correction coefficient, and the correction gain (Y ′ /
Y) is output. Finally, the gradation correction means 105
The delay circuit 106 matches the timing of the G and B signals with the correction gain, and the multiplier 107 corrects the correction gain (Y ′ /
Y) is multiplied, and gradation corrected R ′, G ′ and B ′ signals are output. In this way, by using the correction gain in common for the R, G, and B signals, it is possible to obtain an output image with good color balance and rich gradation expression over the entire area.

The operation of the feature quantity extraction circuit will be described in detail with reference to FIG. The input luminance signal Y is compared with the threshold 1 and the threshold 2 in the comparator 701. When the luminance signal Y is smaller than the threshold value 1, the low luminance count signal is output. When the luminance signal Y is between the threshold 1 and the threshold 2, the 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. The counter circuits 702, 703, and 704 count the number of pixels in the effective screen of one frame according to the low-luminance count signal, the medium-luminance count signal, and the high-luminance count signal.
The number of high-brightness pixels is output.

The operation of the correction coefficient determination circuit will be described in detail with reference to FIG. The correction coefficient table ROM 801 has a low-luminance pixel number, a medium-luminance pixel number, and a high-luminance pixel number supplied from the feature amount extraction circuit 102 as an address, a correction coefficient for a forward-light subject, a correction coefficient for a backlight subject, and a correction for a dark subject. Coefficients and the like are stored. Therefore, when the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels are input from the feature amount extraction circuit 102 to the correction coefficient table ROM 801, one correction coefficient is determined for the input image. The correction coefficient is filtered by the filter circuit 802 so as to maintain continuity with the previous frame or the previous frame, and the correction coefficient is output.

The correction gain generation circuit 1 will be described with reference to FIG.
The operation of 04 will be described in detail. The input luminance signal Y is supplied to the first gradation correction characteristic circuit 301 and the second gradation correction characteristic circuit 302. The first gradation correction characteristic circuit 301 outputs a first correction gain (Y1 / Y) from the input luminance signal Y and Y1 corrected by the first gradation correction characteristic. Similarly, the second gradation correction characteristic circuit 302 outputs the second correction gain (Y2 / Y). On the other hand, the adder 303 adds the luminance signal Y and the correction coefficient and outputs an X signal. Finally,
The weighted average circuit 304 weighted averages the first correction gain and the second correction gain by the relational expression (2) using the X signal,
Outputs the correction gain (Y '/ Y).

(Y ′ / Y) = {(Y1 / Y) · (255−X) + (Y2 / Y) · X} / 255 (2) In the present embodiment, the first correction gain (Y1 / Y ) Is performed by the equation (3), and the second correction gain (Y2 / Y) is performed by the equation (4).

(Y1 / Y) = {1/255 ² · (Y−255) ³ +255} / Y (3) (Y2 / Y) = Y / Y (4) FIG. 9 shows this embodiment. It shows the gradation correction characteristics. 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 is as shown in FIG. 9a from the relational expression (2). Similarly, when the correction coefficient becomes positive, the gradation correction characteristic becomes as shown in FIG. 9c. Similarly, when the correction coefficient becomes negative, the gradation correction characteristic becomes as shown in FIG. 9b. By changing the correction coefficient in this way, the gradation correction characteristics can be easily and continuously changed.
When the correction coefficient of the gradation correction characteristic is changed, the correction gains of the low-luminance portion and the middle-luminance portion gradually increase, and finally the overall correction gain increases. Therefore, the gradation correction characteristic of Y2 of FIG. 9 is applied to the normal-light subject, the gradation correction characteristic of FIG. 9a is applied to the backlight subject, and the gradation correction characteristic of FIG.
By performing gradation correction with the Y1 gradation correction characteristic, it is possible to perform gradation correction with rich gradation expression for all subjects.

As described above, according to the present embodiment, the gradation correction circuit of the present invention is the matrix circuit 101, the feature amount extraction circuit 102, the correction coefficient determination circuit 103, the correction gain generation circuit 104, and the gradation. With the configuration of the correction means 105,
It is possible to obtain an output image in which the gradation is not destroyed for all the objects from the backlight object to the normal object and the color balance is good and the gradation expression is rich over the entire area.

The correction gain generation circuit 104 in the gradation correction circuit of the present invention is called a first gradation correction characteristic circuit, a second gradation correction characteristic circuit 302, an adder 303, and a weighted average circuit 304. Since the correction gain is generated by the correction coefficient in the configuration, it is not necessary to have an extra ROM or the like for storing some kinds of gradation correction characteristics, so that the circuit scale can be made very small. it can.
In addition, by changing the correction coefficient, it is possible to generate the gradation correction characteristics of forward and backlit subjects, so that the gradation is not destroyed for all subjects from the backlit subject to the backlit subject, and the color balance is good. It is possible to obtain an output image with rich gradation expression. In addition, since the gradation correction characteristic can be continuously changed, natural gradation correction can be performed on a moving image. In addition, when the input signal is large, the gradation correction characteristics are set so that the input signal becomes an output signal almost as it is, so that it is possible to clearly reproduce where the gradation of the high-brightness part has been destroyed by the conventional auto knee control. it can.

FIG. 3B is a block diagram showing the configuration of the correction gain generation circuit 104 of the gradation correction circuit according to the second embodiment of the present invention. The difference from the first embodiment shown in FIG. 3A is that an average value detection circuit (LPF) 305 is newly provided in the gradation correction gain generation circuit 104.

The operation of the correction gain generating circuit 104 will be described in detail below with reference to FIG.

The input luminance signal Y is supplied to the first gradation correction characteristic circuit 301 and the second gradation correction characteristic circuit 302. The first gradation correction characteristic circuit 301 outputs a first correction gain (Y1 / Y) from the input luminance signal Y and Y1 corrected by the first gradation correction characteristic. Similarly, the second gradation correction characteristic circuit 302 outputs the second correction gain (Y2 / Y). On the other hand, the luminance signal Y is an average value detection circuit (LP
F) 305 obtains the luminance average value Ya, the adder 303 adds the luminance average value Ya and the correction coefficient, and outputs the X signal.
Finally, the weighted average circuit 304 weighted averages the first correction gain and the second correction gain by the relational expression (2) using the X signal and outputs the correction gain (Y ′ / Y).

FIG. 10 shows gradation correction characteristics and input / output characteristics. When the luminance average value Ya obtained by the average value detection circuit 305 is equal to the luminance signal Y of the pixel of interest, FIG.
10b when the average luminance value Ya is lower than the luminance signal Y of the pixel of interest, the tone correction characteristic of FIG. 10b is obtained when the average luminance value Ya is higher than the luminance signal Y of the pixel of interest.
With the tone correction characteristic of c, the tone correction characteristic is adaptively changed for each pixel to perform the tone correction, so that the tone correction is performed so that the contrast is maintained even if the inclination of the correction gain is small. A richly expressive output signal can be obtained.

FIG. 4 is a block diagram showing a specific structure of the correction gain generation circuit 104 of the gradation correction circuit according to the second embodiment of the present invention. In FIG. 4, 401 is an average value detection circuit (LPF), 402 is a first adder, 403 is a clipping circuit, 404 is a second adder, 405 is a first multiplier, 406 is a third adder, and 407 is a third adder. 1 subtractor, 408
Is a second multiplier, 409 is a second subtractor, 410 is a fourth adder, and 104 is a correction gain generation circuit.

Hereinafter, the correction gain generation circuit 1 will be described with reference to FIG.
The operation of 04 will be described in detail. FIG. 4 shows (2), (3),
The equation (4) is directly converted into a circuit. 255 times,
1/255 and the like correspond to the data bit shift to simplify the circuit. First, when the luminance signal Y is input, the average value detection circuit 401 determines the average value Ya. Next, the average value Ya and the correction coefficient are added by the first adder 402. First
The output signal of the adder is clipped up and down by the clipping circuit 403 with the value “0” and the value “255”. On the other hand, the luminance signal Y is extracted from the average value detection circuit 401 together with the average value Ya with a delay, and the luminance signal 2Y and the luminance signal Y doubled by 1 bit shift are added by the second adder 404 to triple the luminance signal. Three
Make Y Also make luminance signal of the squared luminance signal Y Y ² in the first multiplier 405. The third adder 406 adds the numerical value 3 to the output signal of the first multiplier 405. Next, the output signal of the second adder 404 is subtracted from the output signal of the third adder 406 by the first subtractor 407. Next, the output signal of the clipping circuit 403 is subtracted from the numerical value 255 by the second subtractor 409. The output signal of the second subtractor 409 and the output signal of the first subtractor are multiplied by the second multiplier 408. Finally, the output signal of the clipping circuit 403 and the output signal of the second multiplier are added by the fourth adder 410 and output as a correction gain. This correction gain is controlled in accordance with the gradation correction characteristics shown in FIGS. 9 and 10 by controlling the correction gain with a correction coefficient, so that gradation is not destroyed for all objects from a backlit subject to a frontlit subject, and good color balance is achieved. It is possible to obtain an output image with rich gradation expression over the entire area. further,
The gradation correction characteristics are adaptively changed on a pixel-by-pixel basis by the luminance average value Ya to perform gradation correction, so that gradation correction is performed so as to maintain the contrast even if the inclination of the correction gain is small, resulting in rich gradation expression. An output signal can be obtained.

As described above, according to this embodiment, the correction gain generating circuit 104 in the gradation correction circuit of the present invention is the first
Gradation correction characteristic circuit and second gradation correction characteristic circuit 302
With the configuration of the adder 303, the weighted average circuit 304, and the average value detection circuit 305, some types of gradation correction characteristics are stored by generating a correction gain by a correction coefficient. Since it is not necessary to have a special ROM or the like, the circuit scale can be made very small. In addition, by changing the correction coefficient, it is possible to generate the gradation correction characteristics of forward and backlit subjects, so that the gradation is not destroyed for all subjects from the backlit subject to the backlit subject, and the color balance is good. It is possible to obtain an output image with rich gradation expression. In addition, when the input signal is large, the gradation correction characteristics are set so that the input signal becomes an output signal almost as it is, so that it is possible to clearly reproduce where the gradation of the high-brightness part has been destroyed by the conventional auto knee control. it can. Further, the gradation correction characteristic is adaptively changed for each pixel according to the luminance average value Ya to perform the gradation correction, so that the gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and the gradation expression is performed. A rich output signal can be obtained.

FIG. 11 is a block diagram showing the arrangement of an image pickup apparatus having a gradation correction function according to the third embodiment of the present invention. In FIG. 11, reference numeral 1101 denotes a solid-state image sensor, 110
2 is an analog circuit, 1103 is an analog-digital converter (A / D converter), 1104 is a matrix circuit, 1
Reference numeral 105 is a feature amount extraction circuit, 1106 is a correction coefficient determination circuit, 1107 is a correction gain generation circuit, 1108 is a gradation correction means, 1109 is a signal processing circuit, and 1110 is digital.
-Analog converter (D / A converter) 1111 is an encoder circuit.

The operation of the image pickup apparatus having the gradation correction function according to the third embodiment of the present invention constructed as described above will be described below.

In FIG. 11, first, the solid-state image pickup device 11
From 01, the analog circuit 1102 takes in R, G, and B signals as input video signals. The R, G, B signals are converted into digital data of 0 to 255 by the analog-digital converter 1103. The R, G, B signals converted into the digital data of 0 to 255 are input to the matrix circuit 1104 and the gradation correction unit 1108 as an input video signal. The operations of the matrix circuit 1104, the feature amount extraction circuit, the correction coefficient determination circuit 1106, the correction gain generation circuit 1107, and the gradation correction unit 1108 described below are the same as those of the first and second embodiments. That is, the matrix circuit 1104 calculates the luminance signal Y from the R, G, B signals. The calculated luminance signal Y is used as the feature amount extraction circuit 110.
5 and the correction gain generation circuit 1107. The feature amount extraction circuit 1105 obtains the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels of the luminance signal Y, and the correction coefficient determination circuit 110
Supply to 6. The correction coefficient determination circuit 1106 determines the optimum gradation correction characteristic for the input video signal based on the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels, and outputs a correction coefficient for determining the gradation correction characteristic. To do. Correction gain generation circuit 110
Reference numeral 7 outputs a correction gain from the luminance signal Y and the correction coefficient.
Then, the gradation correction unit 1108 corrects the gradation of the input video signal with the correction gain. The signal processing circuit 1109 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. A digital-analog converter 1110 converts the processed digital R, G, B signals into analog R, G, B signals.
Convert to B signal. Next, the encoder circuit 1111 converts the R, G, B signals into a Y signal (luminance signal) and a C signal (color signal). Finally, the VTR circuit records on video tape.

As described above, according to this embodiment, the solid-state image pickup device 1101 is provided in the image pickup apparatus with the gradation correction function of the present invention.
An analog circuit 1102, an analog-digital converter (A / D converter) 1103, and a matrix circuit 11
04, a feature amount extraction circuit 1105, a correction coefficient determination circuit 1106, a correction gain generation circuit 1107, a gradation correction unit 1108, a signal processing circuit 1109, and a digital-
With the configuration of the analog converter (D / A converter) 1110 and the encoder circuit 1111, the gradation correction characteristic can be easily changed by the correction coefficient. It is possible to obtain an output image in which the color balance is good and the gradation expression is rich over the entire area.

FIG. 12 is a block diagram showing the specific construction of an image pickup apparatus having a gradation correction function according to the third embodiment of the present invention. In FIG. 12, 1201 is a solid-state image sensor, 1
Reference numeral 202 designates an analog circuit, 1203 designates an analog-digital converter (A / D converter), 1204 designates gradation correction means, 1
205 is a signal processing circuit, 1206 is a digital-analog converter, 1207 is an encoder circuit, 1208 is a VTR.
A circuit, 1209 is a histogram creating unit, 1210 is an input unit, 1211 is a correction gain generating unit, 1212 is a microcomputer, 1213 is a ROM for storing a program of the microcomputer 1212 and a template showing the characteristics of gradation correction characteristics to be selected, and 1214 is a histogram. A RAM 1215 for storing the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels calculated by the creating unit 1209 is a bus.

FIG. 13 is a flow chart showing the procedure for determining the gradation correction characteristic in the third embodiment of the present invention.

The operation of the image pickup apparatus having the gradation correction function of the third embodiment of the present invention constructed as above will be described below.

In FIG. 12, first, the solid-state image pickup device 12
From 01, the analog circuit 1202 takes in R, G, and B signals as input video signals. The R, G, B signals are converted into digital data of 0 to 255 by the analog-digital converter 1203. The R, G, and B signals converted into the digital data of 0 to 255 are used as the input video signals, and the histogram creating means 1209 and the gradation correcting means 120.
4 is input. The histogram creating means 1209 calculates the luminance signal Y from the R, G, B signals, and obtains the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels for the effective screen of one frame.

The operation of the microcomputer 1212 for determining the gradation correction characteristic using the template matching method will be described with reference to FIG. First, the microcomputer 1212 reads the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels calculated by the histogram creating unit 1209 into the RAM 1214. Next, the distance between the template showing the characteristics of the input image of the selected gradation correction characteristic in the ROM 1213 and the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels read in the RAM 1214 is obtained. Next, the gradation correction characteristic that minimizes the distance is selected. The gradation correction characteristic selected last is processed so as to be continuous with the gradation correction characteristic of the previous field, and the correction coefficient is set in the correction gain generation circuit 1211.

The correction gain generation circuit 1211 performs a weighted average of the first gradation correction characteristic and the second gradation correction characteristic with a value obtained by adding the average value of the input luminance signal and the correction coefficient, and the correction gain is gradation corrected. The means 1204 is set. Gradation correction means 12
Reference numeral 04 is a delay circuit that matches the timing of the R, G, and B signals with the correction gain, multiplies each of the R, G, and B signals by the correction gain, and outputs the R, G, and B signals whose gradation has been corrected.
The tone-corrected R, G, B signals are applied to the signal processing circuit 12
Reference numeral 05 performs signal processing such as aperture processing. A digital-analog converter 1206 converts the signal-processed digital R, G, B signals into analog R, G, B signals. Next, the encoder circuit 1207 outputs the R, G, B signals to Y.
It is converted into a signal (luminance signal) and a C signal (color signal). Finally, the VTR circuit 1208 records on the video tape.

As described above, according to the present embodiment, the solid-state image pickup device 1201 is used in the image pickup apparatus with the gradation correction function of the present invention.
An analog circuit 1202, an analog-digital converter (A / D converter) 1203, and a gradation correction unit 1204.
A signal processing circuit 1205, a digital-analog converter (D / A converter) 1206, and an encoder circuit 120.
7, VTR circuit 1208, and histogram creating means 1
209, input means 1210, and correction gain generation circuit 1
211, microcomputer 1212, ROM 1213, R
With the configuration of AM1214, it is possible to obtain an output image in which gradations are not destroyed for all objects from a backlit object to a forward-lighted object, color balance is good, and gradation expression is rich over the entire area. In addition, when the input signal is large, the gradation correction characteristics are set so that the input signal becomes an output signal almost as it is, so that it is possible to clearly reproduce where the gradation of the high-brightness part has been destroyed by the conventional auto knee control. it can. Further, the gradation correction characteristic is adaptively changed for each pixel according to the luminance average value Ya to perform the gradation correction, so that the gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and the gradation expression is performed. A rich output signal can be obtained. Further, even if the moving image is corrected, a natural gradation correction image can be obtained.

FIG. 14 is a block diagram showing the structure of a gradation correction circuit according to the fourth embodiment of the present invention. In FIG. 14, 1401 is a feature amount extraction circuit, 1402 is a correction coefficient determination circuit, 1403 is a correction gain generation circuit, 1404 is a gradation correction means, 1405 is a delay circuit, and 1406 is a multiplier. The difference from FIG. 1 is that the input video signal is a luminance signal and a color difference signal, and the matrix circuit is deleted.

The operation of the gradation correction circuit according to the fourth embodiment of the present invention constructed as above will be described below.

In FIG. 14, the luminance signal Y and the color difference signals RY and BY are input to the gradation correction circuit of the present invention. Since the luminance signal Y is input, the matrix circuit for calculating the luminance signal Y becomes unnecessary. The operation of the feature amount extraction circuit 1401, the correction coefficient determination circuit 1402, the correction gain generation circuit 1403, and the gradation correction means 1404 of the gradation correction circuit of the present invention is completely the same as the operation excluding the matrix circuit of the first and second embodiments. It is the same. That is, the input luminance signal Y is converted into the feature amount extraction circuit 1401 and the correction gain generation circuit 1
Supply to 403. The characteristic amount extraction circuit 1401 obtains the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels of the luminance signal Y in the effective screen of one frame, and the correction coefficient determination circuit 1
Supply to 402. The correction coefficient determination circuit 1402 determines the optimum gradation correction characteristic for the input video signal based on the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels, and outputs a correction coefficient for determining the gradation correction characteristic. To do. Correction gain generation circuit 1
Reference numeral 402 outputs a correction gain from the average value of the luminance signal Y and the correction coefficient. Then, in the gradation correction means 1404, the timing of the input video signal is matched in the delay circuit 1405 and multiplied by the correction gain in the multiplier 1406, and the gradation corrected luminance signal Y ′, color difference signal (RY) ′ and (B− Y) 'is output.

As described above, according to the present embodiment, the gradation correction circuit of the present invention includes a feature amount extraction circuit 1401, a correction coefficient determination circuit 1402, a correction gain generation circuit 1403,
The gradation correction means 1404 is used to change the correction coefficient to obtain an output image in which the gradation is not destroyed for all the objects from the backlit subject to the forward-lit subject and the color balance is good and the gradation expression is rich over the entire area. be able to.

Further, since the correction gain is generated by the correction coefficient, it is not necessary to have an extra ROM or the like for storing several kinds of gradation correction characteristics.
The circuit scale can also be made very small. In addition, since the gradation correction characteristic can be continuously changed, natural gradation correction can be performed on a moving image. Also,
When the input signal is large, the gradation correction characteristic is set such that the input signal becomes an output signal almost as it is, so that it is possible to clearly reproduce where the gradation of the high-luminance portion is crushed by the conventional auto knee control or the like.

In this embodiment, R, G, B signals, luminance signals, and color difference signals are used as the input video signals.
Similar effects can be obtained by using a composite signal or a signal obtained by synthesizing a color signal with a luminance signal instead of the G, B signals, the luminance signal, or the color difference signal as the input video signal.

In the present embodiment, the gradation correction means multiplies each input video signal by the correction gain to perform 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 the present embodiment, the input video signal is explained by analog-digital conversion into 8 bits. However, the quantization bit number may be a different value, and the number of processing bits of the correction gain generating circuit etc. is also quantum. It can be configured according to the number of digitized bits.

In this embodiment, since the gradation correction circuit applied to the video-integrated camera has been described, the input image signal is input from the solid-state image pickup device 201 to the analog circuit 202. Instead of the analog circuit 202, another medium such as a laser disk, a video tape or a magnetic disk for analog image recording, or a magnetic disk such as a hard disk or an optical disk for digital recording after analog-digital conversion may be used. In any case, as long as the image data of one frame or one field can be taken out by the gradation correction circuit 303, it is not limited to this embodiment.

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

In the present embodiment, the feature quantity extraction circuit counts the number of pixels for an effective screen having one horizontal pixel number of 640 pixels and 480 lines, but the number of pixels to be counted may be different, or a signal indicating the number of pixels. 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 discriminates the input image using the luminance histogram as the characteristic amount, but instead of the luminance histogram, other characteristic amounts, for example, R, G, and B signals are detected. This histogram or one of the histograms or the effective screen of the image data is divided into blocks and the maximum, average and minimum values of the luminance signal, RGB signal and color difference signal of each block are used as the feature amount. The method is not limited to this method as long as it is a feature value that can be classified into classes.

In this embodiment, the correction coefficient determination circuit may be any method capable of determining the gradation correction characteristics by discriminating 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.

[0061]

As described above, the gradation correction circuit of the present invention is
The optimum gradation correction characteristics can be automatically determined by distinguishing the input image based on the feature amount obtained from the input video signal. With a simple configuration, it is possible to prevent blackout and whiteout, and to obtain strong backlight against a backlit subject. It is possible to obtain an output image with rich gradation expression over the entire screen up to the subject. Further, since the gradation correction characteristic can be continuously changed, natural gradation correction can be performed even on a moving image.

Further, the image pickup apparatus with the gradation correction function of the present invention can automatically determine the optimum gradation correction characteristic by discriminating the input image by the characteristic amount obtained from the input video signal, and has a simple structure. Prevents blackout and whiteout,
It is possible to obtain an output image with rich gradation expression over the entire screen from a normal light subject to a strong backlight subject. Further, since the gradation correction characteristic can be continuously changed, natural gradation correction can be performed even on a moving image.

Further, the gradation correction circuit and the image pickup apparatus with the gradation correction function of the present invention weight-average the first gradation correction characteristic and the second gradation correction characteristic by using the average value Ya of the input video signal. By calculating the correction gain by correcting the brightness, if the brightness in the vicinity is high, the brightness is corrected low, if the brightness in the vicinity is low, the brightness is corrected high, and the gradation correction is performed so that the contrast is maintained even if the gradation correction gain is small. By doing so, it is possible to obtain a gradation correction image with rich gradation expression.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a gradation correction circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a video-integrated camera using a gradation correction circuit according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a functional configuration of a gradation correction gain generation circuit according to an embodiment of the present invention.

FIG. 4 is a block diagram showing a detailed configuration of a gradation correction gain generation circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram showing one frame image of an input video signal in the embodiment of the present invention.

FIG. 6 is a diagram showing a luminance histogram in the example of the present invention.

FIG. 7 is a block diagram showing a configuration of a feature quantity extraction circuit according to an embodiment of the present invention.

FIG. 8 is a block diagram showing the configuration of a gradation correction coefficient determination circuit according to an embodiment of the present invention.

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

FIG. 10 is a characteristic diagram showing a gradation correction characteristic and an input / output characteristic in the embodiment of the present invention.

FIG. 11 is a block diagram showing a functional configuration of an image pickup apparatus with a gradation correction function according to a third embodiment of the present invention.

FIG. 12 is a block diagram showing a specific configuration of an image pickup apparatus with a gradation correction function according to a third embodiment of the present invention.

FIG. 13 is a flowchart showing a procedure for determining a gradation correction coefficient according to the third embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration of a gradation correction circuit according to a fourth embodiment of the present invention.

FIG. 15 is a block diagram and a signal diagram showing a configuration of an image pickup apparatus with a gradation correction function in a first conventional example of the present invention.

FIG. 16 is a block diagram showing a configuration of an image pickup apparatus with a gradation correction function in a second conventional example of the present invention.

[Explanation of symbols]

 101 matrix circuit 102 feature amount extraction circuit 103 correction coefficient determination circuit 104 correction gain generation circuit 105 gradation correction means 201 solid-state image sensor 202 analog circuit 204 gradation correction circuit 301 first gradation correction characteristic circuit 302 second gradation Correction characteristic circuit 303, 402 Adder 304 Weighted average circuit 305, 401 Average value detection circuit 403 Clip circuit 404, 406, 410 Adder 405, 408 Multiplier 407, 409 Subtractor 501 Effective screen

Claims (14)

[Claims] 1. A feature amount extraction circuit for obtaining a feature amount of an input video signal, and a correction coefficient determination for outputting a correction factor for determining a gradation correction characteristic to be corrected based on the feature amount obtained by the feature amount extraction circuit. A circuit, a correction gain generation circuit that generates a correction gain of a gradation correction characteristic from the input video signal and the correction coefficient determined by the correction coefficient determination circuit, and the input video signal with the correction gain generated by the correction gain generation circuit. A gradation correction circuit for correcting each of the above, and the gradation correction circuit obtains the gradation-corrected output image signal from the gradation correction circuit. 2. A luminance signal generation circuit for separating or synthesizing a luminance signal Y from an input video signal, a characteristic amount extraction circuit for obtaining a histogram of the luminance signal Y, and a correction based on the histogram obtained by the characteristic amount extraction circuit. A correction coefficient determining circuit that outputs a correction coefficient that determines a gradation correction characteristic to be generated, and a correction gain of the gradation correction characteristic from the luminance signal Y calculated by the matrix circuit and the correction coefficient determined by the correction coefficient determining circuit. And a gradation correction unit that multiplies the input video signal by the correction gain generated by the correction gain generation circuit, and obtains the gradation-corrected output video signal from the gradation correction unit. A gradation correction circuit characterized by. 3. A matrix circuit for calculating a luminance signal Y of an RGB signal which is an input video signal, a feature amount extraction circuit for obtaining a histogram of the luminance signal Y, and a correction based on the histogram obtained by the feature amount extraction circuit. A correction coefficient determining circuit that outputs a correction coefficient that determines a gradation correction characteristic to be generated, and a correction gain of the gradation correction characteristic from the luminance signal Y calculated by the matrix circuit and the correction coefficient determined by the correction coefficient determining circuit. And a gradation correction unit that multiplies each of the input video signals by the correction gain generated by the correction gain generation circuit, and outputs the gradation-corrected output video signal by the gradation correction unit. A gradation correction circuit characterized by obtaining. 4. A first gradation correction characteristic circuit in which a correction gain generation circuit generates a first gradation correction characteristic from an input video signal, and a second gradation correction characteristic circuit in which a second gradation correction characteristic is generated from an input video signal. Gradation correction characteristic circuit, an adder for adding an input video signal and a correction coefficient, and a correction gain by weighted averaging the first gradation correction characteristic and the second gradation correction characteristic by the output signal of the adder. The gradation correction circuit according to claim 1, 2 or 3, wherein the gradation correction circuit is configured to output a weighted average circuit. 5. A first gradation correction characteristic circuit in which a correction gain generation circuit generates a first gradation correction characteristic from an input video signal, and a second gradation correction characteristic circuit in which a second gradation correction characteristic is generated from an input video signal. Gradation correction characteristic circuit, an average value detection circuit for obtaining an average value of an input video signal, an adder for adding the average value and the correction coefficient, and a first gradation correction characteristic according to an output signal of the adder. The gradation correction circuit according to claim 1, 2 or 3, wherein a weighted average circuit that outputs a correction gain by performing a weighted average of the second gradation correction characteristic and the second gradation correction characteristic. 6. A first gradation correction characteristic Y of the input video signal Y.
1 follows a cubic curve of the form Y1 = {1 / a ² · (Y−a) ³ + a} and the second tone correction characteristic Y2 follows a linear line of the form Y2 = bY. The gradation correction circuit according to claim 4. 7. A correction gain generating circuit is provided for input video signal Y.
And an average value detection circuit for obtaining the average value Ya of
a, a first adder for adding the correction coefficient, a clipping circuit for clipping the output signal of the first adder with a value '0' and the maximum value of the input video signal Y, and the input video signal Y A second adder for adding 3 to output Y and a first adder for squaring the input video signal Y and outputting Y ² .
A multiplier, a third adder for adding a constant to the output signal of the first multiplier, and the second signal from the output signal of the third adder.
A first subtractor for subtracting the output signal of the adder, a second subtractor for subtracting the output signal of the clipping circuit from the maximum value that the input video signal Y can take, an output signal of the first subtractor and the The second multiplier for multiplying the output signal of the second subtractor, and the fourth adder for adding the output signal of the clipping circuit and the output signal of the second multiplier are configured. , 2, 3 or 5, the gradation correction circuit. 8. A solid-state image sensor, an analog circuit for extracting an input video signal from the solid-state image sensor, a feature quantity extraction circuit for finding a feature quantity of the input video signal, and a feature quantity found by the feature quantity extraction circuit. A correction coefficient determination circuit that outputs a correction coefficient that determines a gradation correction characteristic to be corrected based on the correction coefficient, and a correction coefficient that generates a correction gain of the gradation correction characteristic from the input video signal and the correction coefficient determined by the correction coefficient determination circuit. A gain generation circuit; and a gradation correction unit that corrects each of the input video signals with the correction gain generated by the correction gain generation circuit, and obtains the gradation-corrected output video signal from the gradation correction unit. An image pickup device with a gradation correction function. 9. A solid-state image sensor, an analog circuit for extracting an input video signal from the solid-state image sensor, a luminance signal synthesizing circuit for separating or synthesizing a luminance signal Y from the input video signal, and a histogram of the luminance signal Y. A characteristic amount extraction circuit to be obtained, a correction coefficient determination circuit to output a correction coefficient to determine a gradation correction characteristic to be corrected based on the histogram obtained by the characteristic amount extraction circuit, and a luminance signal Y calculated by the matrix circuit. A correction gain generation circuit that generates a correction gain of a gradation correction characteristic from the correction coefficient determined by the correction coefficient determination circuit, and a gradation correction unit that multiplies the input video signal by the correction gain generated by the correction gain generation circuit. An image pickup apparatus with a gradation correction function, comprising: an output image signal whose gradation is corrected by the gradation correction unit. 10. A solid-state imaging device, an analog circuit for extracting an RGB signal which is an input video signal from the solid-state imaging device, a matrix circuit which calculates a luminance signal Y of the RGB signal which is the input video signal, and the luminance signal. A feature amount extraction circuit that obtains a Y histogram, a correction coefficient determination circuit that outputs a correction factor that determines a gradation correction characteristic to be corrected based on the histogram obtained by the feature amount extraction circuit, and the matrix circuit calculates A correction gain generation circuit that generates a correction gain of a gradation correction characteristic from a luminance signal Y and a correction coefficient determined by the correction coefficient determination circuit, and a correction gain generated by the correction gain generation circuit are multiplied by each of the input video signals. And a gradation correction unit for obtaining a gradation-corrected output video signal from the gradation correction unit. Image pickup device with adjustment function. 11. A first gradation correction characteristic circuit in which a correction gain generation circuit generates a first gradation correction characteristic from an input video signal, and a second gradation correction characteristic circuit in which a second gradation correction characteristic is generated from an input video signal. Gradation correction characteristic circuit, an adder for adding an input video signal and a correction coefficient, and a correction gain by weighted averaging the first gradation correction characteristic and the second gradation correction characteristic by the output signal of the adder. 11. The image pickup device with a gradation correction function according to claim 8, 9 or 10, wherein the image pickup device has a configuration of a weighted average circuit for outputting. 12. A first gradation correction characteristic circuit in which a correction gain generation circuit generates a first gradation correction characteristic from an input video signal, and a second gradation correction characteristic circuit in which a second gradation correction characteristic is generated from an input video signal. Gradation correction characteristic circuit, an average value detection circuit for obtaining an average value of an input video signal, an adder for adding the average value and the correction coefficient, and a first gradation correction characteristic according to an output signal of the adder. The image pickup apparatus with a gradation correction function according to claim 8, 9 or 10, wherein a weighted average circuit that outputs a correction gain by performing a weighted average of the second gradation correction characteristic and the second gradation correction characteristic. 13. The first gradation correction characteristic Y1 of the input video signal Y follows a cubic curve in the form of Y1 = {1 / a ^2. (Y−a) ³ + a} 13. The image pickup device with a gradation correction function according to claim 11, wherein Y2 follows a linear line of the form Y2 = bY. 14. A correction gain generation circuit, an average value detection circuit for obtaining an average value Ya of an input video signal Y, a first adder for adding the average value Ya and the correction coefficient, and the first
A clipping circuit for clipping the output signal of the adder with a value of "0" and the maximum value that the input video signal Y can take, and a second adder for adding the input video signal Y and outputting 3 times Y. , A first which squares the input video signal Y and outputs Y ² .
A multiplier, a third adder for adding a constant to the output signal of the first multiplier, and the second signal from the output signal of the third adder.
A first subtractor for subtracting the output signal of the adder, a second subtractor for subtracting the output signal of the clipping circuit from the maximum value that the input video signal Y can take, an output signal of the first subtractor and the The second multiplier for multiplying the output signal of the second subtractor, and the fourth adder for adding the output signal of the clipping circuit and the output signal of the second multiplier. , 9, 10 or 12, the image pickup device with a gradation correction function.