JPH07143359A - Video camera - Google Patents

Abstract

PURPOSE:To obtain an output signal by varying it to a desired gamma characteristic only within a specific range of a video input signal by setting a gamma correction coefficient as a function of a value of a video signal. CONSTITUTION:A gamma correction circuit 5 has an input part 6 and an output part 7 of a video signal, performs a gamma correction to a video image pickup signal (x) inputted to the input part 6, and outputs a corrected signal (y) to the output part 7. A characteristic of a gamma correction is related to a video signal level, and with respect to a level of the input signal (x), a level of the output signal (y) has a characteristic of the 1/gamma-th power of a gamma correction coefficient. The characteristic of the correction is determined by the contents of correction data of digital data constituted of several bytes accumulated in a memory means 1, and the correction data is transferred to a coefficient processing means 3 in a format of parallel data through a transfer line 9. The coefficient processing means 3 transfers it in a format of serial data to the correcting circuit 5 through the transfer line 9, and the gamma correction circuit 5 converts this serial data into parallel data and uses it for the gamma correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera provided with, for example, a gamma correction circuit, and more particularly to a video camera provided with a gamma correction circuit for digitally processing a video signal.

[0002]

2. Description of the Related Art The relationship between the grid signal voltage of a color picture tube and the light emission output is not linear, and the light emission output is proportional to the γth power of the input signal applied to the grid, for example, the second power. This gamma coefficient γ is called image receiving gamma. For this reason,
If the signal from the video camera is applied to the color picture tube as it is, not only the screen volatility but also the hue and saturation are very different. Therefore, before the input signal is applied to the color picture tube, the output signal is raised to the power of 1 / γ, for example, 1 / 2.2.
The overall characteristic is made linear through a gamma correction circuit having an input / output characteristic such that the power is raised to the power of 0.45.

This gamma correction circuit may be inserted just before the signal is applied to the grid of the color picture tube, but from the viewpoint of economy and stability, it is not incorporated in the color receiver installed in the home, but the transmitter side. That is, it is provided in the video camera.

Conventionally, in a video camera, the gamma correction circuit is composed of an analog circuit, and the circuit multiplier is set so that the output signal approximates the 1 / γth power of the input signal.

[0005]

However, in the case of such an analog circuit, in order to switch the gamma correction coefficient of the gamma correction, it is necessary to change the circuit constants forming the polygonal line of the analog line approximation. In the case of a video camera, it is impossible to change this gamma characteristic while the video camera is operating.

In recent years, digital signal processing techniques for digitally processing video signals have been used in video cameras, and the applicant of the present application has studied the digitization of gamma correction circuits. As one proposal of digitization, correction data for replacing the value x of the input signal with the value y of the output signal having a relationship of x to the power of 1 / γ is stored in advance in the memory means and is passed through the coefficient processing means. It was studied to transfer to the gamma correction circuit and obtain the output signal y according to the input signal x.

Also in this case, the gamma correction coefficient 1 / γ is originally used.
Is a constant, the output signal y changes over the entire input signal x, and the entire gamma characteristic changes, which is not applicable when it is desired to change the gamma characteristic only in a specific range of the input signal x.

There is also a demand for a technique capable of easily changing the gamma characteristic while the video camera is operating.

[0009]

The present invention has been made in consideration of the above problems, and in the present invention, as an example, as shown in FIG. 1, a video camera is corrected by performing gamma correction by digital processing. Gamma correction circuit 5 for outputting the signal Y and memory means 1 for storing correction data for replacing the video signal x with the corresponding corrected signal y.
And reading the correction data from the memory means 1,
The correction data has a relationship of the corrected signal y to the power of 1 / γ of the video signal x, and the gamma correction coefficient 1 / γ.
Is a function of x.

Further, in the present invention, the video camera also includes a switch means 2 connected to the coefficient processing means 3, and the memory means 1 contains a plurality of the correction data (correction data, correction data, correction data ... It is also possible that the coefficient processing means 3 that has been accumulated reads out one of the plurality of correction data according to the instruction signal from the switch means 2 and supplies it to the gamma correction circuit 5.

Further, according to the present invention, the video camera relatively increases the gamma correction coefficient 1 / γ in the relatively small range of the video signal x and the gamma correction coefficient 1 / γ in the relatively large range of the video signal x. The relationship is set to be relatively small, so that the magnitude of the corrected signal y in the relatively small range of the video signal x can be relatively increased.

[0012]

According to the present invention, since the gamma correction coefficient 1 / γ is a function of the value of the video signal x, only a specific range of the video input signal x is changed to a desired gamma characteristic to obtain the output signal y. It becomes possible.

Further according to the invention, the memory means 1 is provided.
Since a plurality of gamma correction data are stored in, the gamma correction data can be switched to another gamma characteristic as desired during the operation of the video camera. This switching can be performed by a simple operation of the switch means 2, and the coefficient processing means 3
Selects other correction data corresponding to the instruction signal from the switch means 2 from the memory means 1 to select the gamma correction circuit 5
And the gamma characteristic is switched at the timing of the switch means 2.

[0014]

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

(General Video Camera) In order to easily understand the present invention, a brief description will first be given on general video camera.

FIG. 3 is a diagram showing the overall configuration of a video camera which digitally processes a video signal. The imaging light incident through a lens (not shown) is used as the imaging processing unit 1.
3 primary color imaging signals R, 1 CCD image sensor,
It is converted into G and B and A / D converted into digital image pickup signals R, G and B, which are output to the preprocessor 12. Due to the spatial pixel shift of the CCD image sensor, the green digital signal G and the red digital signal R and the blue digital signal B are out of phase with each other by, for example, 1/2 pitch.

The preprocessor 12 performs signal processing on the digital image pickup signals R, G and B, and corrects defects in the CCD image sensor and shading distortion due to variations in sensitivity.

The green image pickup signal G and the red image pickup signal R
Is supplied to the image enhancer 13, and the green image pickup signal G is supplied to the color detection unit 17 and the digital processing unit 18 via the low pass filter (LPF) 14. Further, the red image pickup signal R and the blue image pickup signal B are passed through interpolation filters (IPF) 15 and 16 respectively, and the color detection unit 1
7 and the digital processing unit 18.

The image enhancer 13 generates a detail signal for contour enhancement processing based on the green image pickup signal G and the red image pickup signal R. This detail signal is supplied to the digital processing unit 18 and the adder 26.

As described above, the phases of the red image pickup signal R and the blue image pickup signal B are shifted from the green image pickup signal G by 1/2 pitch, and the interpolation filters 15 and 16 perform the phase matching. The green image pickup signal G is band-limited by the low-pass filter 14 to have the same frequency characteristics as the red image pickup signal R and the blue image pickup signal B.

The color detecting section 17 functions as a color detecting means and supplies a color detection signal to the coefficient processing means 3.

The coefficient processing means 3 functions as a processing means for various kinds of coefficients, processes various kinds of coefficients given by the memory means 1, and supplies them to the digital processing section 18.

The digital processing section 18 includes a color correction circuit 21.
And the process processing circuits 22G, 22R, 22B, and digital image pickup signals G, B, R based on various coefficients given from the memory means 1 through the coefficient processing means 3.
Is subjected to digital processing such as color correction processing and process processing, and is supplied to the matrix circuit 23.

The matrix 23 circuit includes a digital image pickup signal G, B, R and a luminance signal Y and color difference signals RY, BY.
To produce.

The rate converter 24 converts the luminance signal Y and the color difference signals RY and BY into a predetermined clock rate, and the luminance signal Y and the color difference signals RY and BY for each VTR. Output to the output terminal.

Further, the adder 26 is the up converter 2
The luminance signal Y converted to a higher predetermined clock rate via 5 is added to the detail signal of the same clock rate from the image enhancer 13. This allows
The encoder 27 performs contour enhancement processing on the luminance signal Y.
Supply to.

The encoder 27 has a luminance signal Y subjected to contour enhancement processing and a color difference signal R- from the matrix circuit 23.
Y and BY are encoded into a predetermined video signal.

This video signal is converted to an analog signal by the D / A converter 28 and supplied to the viewfinder or the like as the video signal S _VF , or converted to an analog signal by the D / A converter 29 and output from the signal output terminal. Is output as a decoded video signal S _C.

(Gamma Correction Circuit and Peripheral Circuit) In such a video camera, the process processing circuit 22R is
For example, as shown in FIG. 4, adders 31R, 32R, 35
R, a gamma correction circuit 5R, a knee correction circuit 34R,
And a multiplier 36R. Since the other process processing circuits 12G and 12B are similar to the process processing circuit 12R, only the process processing circuit 12R will be described below.

In the process processing circuit 22R shown in FIG. 4, the adder 31R functions as a pedestal processing means. The coefficient processing means 3 selects an appropriate value from the pedestal value Ped stored in the memory means 1 according to the color detection signal from the color detection section 7 and supplies it to the adder 31R. In this way, the color is reproduced more beautifully for a specific color (for example, skin color) area.

The adders 32R and 35R function as contour correction processing means. The coefficient processing means 3 selects an appropriate value from the contour correction coefficient Gain stored in the memory means 1 according to the color detection signal from the color detection section 17, and supplies it to the multiplier 36R. The multiplier 36R multiplies the detail signal from the image enhancer 13 by the selected contour correction signal and weights it. Then, the adders 32R and 35R perform contour correction processing by adding the weighted detail signal to the red image pickup signal R, for example, for a region of a specific color (for example, skin color), that color is made more beautiful. Reproduce.

The knee correction correction circuit 34R performs knee correction processing of knee characteristics. The coefficient processing means 3 selects an appropriate value according to the color detection signal from the color detection section 7 from the knee slope coefficient Slop and the knee point coefficient Point stored in the memory means 1, and the knee correction circuit Supply to 34R. In this way, the knee processing with the optimum knee characteristic is applied to the region of a specific color (for example, skin color) to reproduce more beautifully.

Next, the gamma correction circuit 5R will be described. The characteristics of gamma correction relate to the video signal level, and generally, the output signal y is compared with the level of the input signal x.
Has a characteristic of the power of 1 / γ, for example, a characteristic of the power of 0.45. In the conventional gamma correction processing that the applicant has studied in the digital signal processing technology of the video signal in the above video camera, correction data for replacing y by 0.45 of x is stored in the memory means 1 in advance, and coefficient processing is performed. The means 3 transfers this correction data to the gamma correction circuit 5R. The gamma correction circuit 5R outputs a value y selected based on the transferred correction data corresponding to the value x of the red image pickup signal R from the color correction circuit 21 (FIG. 3) to perform gamma correction processing. I am giving it.

However, in the case of the above-mentioned gamma correction processing that the applicant has studied, the output signal y is in a relationship of 1 / γ to the value x of the input red signal R, and is uniquely determined. . That is, since the gamma correction coefficient 1 / γ is originally a constant, as shown in FIG. 2A, the output signal y changes over the entire input signal x, and the entire gamma characteristic changes. This is not applicable when you want to change the gamma characteristic only in the specified range.

(Gamma Correction Processing of the Video Camera of the Present Invention) As a concrete configuration example of the gamma correction circuit used in the video camera of the present invention, as shown in FIG. 1, the gamma correction circuit 5 and this gamma correction circuit are shown. 5, coefficient processing means 3 connected to the coefficient processing means 3 via the transfer path 9, memory means 1 connected to the coefficient processing means 3 via the transfer path 4, and switch means 2 connected to the coefficient processing means 3 via the transfer path 8. Equipped with.

The gamma correction circuit 5 has a video signal input section 6
The video pickup signal x input to the input unit 6 is subjected to gamma correction, and the corrected signal y is output to the output unit 7.

The characteristics of the correction are determined by the content of the correction data of the digital data composed of several bytes stored in the memory means 1, and the correction data are transmitted through the transfer path 9 in the form of parallel data. It is transferred to the coefficient processing means 3. The coefficient processing means 3 transfers the data in the form of serial data to the correction circuit 5 via the transfer path 9, and the gamma correction circuit 5 converts this serial data into parallel data and uses it for gamma correction. In this way, the correction data is transferred.

Further, in the present invention, the memory means 1
It is possible to store a plurality of such correction data, ... For example, the above gamma correction coefficient 1
/ Γ = ^{0.45 and} y = k x ^0.45 relationship (k is a coefficient)
In addition to the correction data for x and y obtained from, the gamma correction coefficient 1 / γ is set to another different value, for example, 1 / γ = 0.3
The correction data regarding x and y obtained from the relation of y = x ^0.30 with 0 is accumulated.

Further, using the gamma correction coefficient 1 / γ as a function of x, correction data in which y is the power of x to the power of 1 / γ is stored. The variable 1 / γ is set small when x is relatively small, for example, a value close to 0.30, and set large when x is relatively large, for example, a value close to 0.45.

The switch means 2 is for instructing replacement of the correction data or between them, and the coefficient processing means 3 decodes the logic state output from the switch means 2 and the memory means is operated based on a predetermined rule. The correction data or any of the correction data accumulated in 1 is read out.

The coefficient processing means 3 reads the correction data designated by the switch means 2 from the correction data or the storage data stored in the memory means 1 through the transfer path 9 and causes the gamma correction circuit 5 to read the correction data. It is converted into a suitable format and supplied via the transfer path 4. In this way, every time the correction data is transferred, the gamma characteristic according to the content of the correction data is replaced.

If desired, the switch means 2 may also serve as an instruction for another function in addition to the replacement of the correction data.
In this case, another signal for instructing the correction data exchange mode from the switch means 2 is supplied to the coefficient processing means 3 in advance.

(Operation of the video camera according to the present invention) Next, the operation during operation of the video camera will be described. At the time of power input, the coefficient processing means 3 stores the correction data set at the time of the last power-off, in the memory means. It is called from 1 and transferred to the gamma correction circuit 5. The gamma correction circuit 5 exchanges the video signal x input to the input unit 6 with the output signal y by the output unit 7 with the gamma characteristic based on the transferred correction data.
Output to.

Here, if necessary, the switch means 7 instructs the coefficient processing means 3 that the mode is the correction data exchange mode, and then the setting of the switch means 2 is changed. The coefficient processing means 3 reads the data via 8, and the corresponding correction data or any one of them is called from the memory means 1 and transferred to the gamma correction circuit 5. If the correction data newly transferred by the operation of the switch means 7 is different from the correction data already in the gamma circuit 5, the gamma characteristic will be changed by the operation of the switch means 7.

A plurality of correction data are stored in the memory means 1, and the gamma correction circuit 5 switches the correction data at the switching timing according to the instruction from the switch means 2.
To switch the gamma characteristic.

(Effects of Embodiments) Next, characteristic effects achieved by the above-described embodiments will be described. FIG. 2A is a diagram showing an example of a gamma characteristic that the applicant has studied, and the gamma correction coefficient 1 / γ is a constant here. On the other hand, FIG. 2B is a diagram showing an example of the gamma correction characteristic of the video camera according to the present invention, in which the gamma correction coefficient 1 / γ is a variable of the video signal x.

The input signal x and the output signal y are expressed as percentages because the full scale of each signal is 100.
This is because the percentage is set.

The correction data of FIG. 1 realizes the characteristic 1 shown in FIGS. 2A and 2B, and the correction data realizes the characteristic 2 shown in FIGS. 2A and 2B. -Data is data for realizing the characteristic 3 shown in FIG. 2A, and correction data.
The data is previously stored in the memory means 1 as data for realizing the characteristic 4 shown in FIG. 2B. Switch means 2
With the above operation, it is possible to select the correction data among the correction data and transfer the data to the correction circuit 5 to switch to any gamma characteristic of the characteristics 1 to 4.

The difference between the characteristic 3 (FIG. 2A) which has been studied conventionally and the characteristic 4 (FIG. 2B) according to the present invention is that the input level is close to 0, as is clear from the comparison between the characteristics 3 and 4 and the characteristic 2. Although the slopes of the characteristics 3 and 4 are larger than those of the characteristic 2, the characteristic 4 is less different from the characteristic 2 as the input becomes larger, and is the same when the input is 50% or more. .

Conventionally, in the analog polygonal line type gamma correction circuit, in order to change only the portion where the input is close to 0 and make it the same at a portion where the input level is relatively large of 50% or more, the inclination of the polygonal line is made into the circuit. Since it is realized with a constant,
The switching of the characteristics had to change the circuit constant to another one, and it was not possible to switch it while the camera was operating.

In addition, a digital circuit is also shown in FIG.
Like the characteristics 2 and 3 shown in A, the gamma correction coefficient 1 /
By changing γ, the slope near the input 0 can be changed from the characteristic 2 to the characteristic 3, but since the characteristic curve is raised over the entire range of the input signal x, the characteristic 4 shown in FIG. 2B is obtained. The gamma characteristic cannot be realized.

The above-described embodiment is an example of the present invention, and it goes without saying that various other configurations can be adopted without departing from the scope of the present invention.

[0053]

According to the present invention, the gamma characteristic can be easily changed while the video camera is operating. Furthermore, it is possible to obtain a video signal with a changed gamma characteristic only for a specific range of the input signal.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a gamma correction circuit portion of a video camera according to the present invention.

FIG. 2A is a diagram showing an example of a gamma characteristic of a video camera that the applicant has studied, and FIG. 2B is a diagram showing an example of a gamma correction characteristic of a video camera according to the present invention.

FIG. 3 is a block diagram showing an overall configuration of a video camera according to the present invention.

FIG. 4 is a diagram showing a gamma correction circuit and its peripheral circuit of the video camera according to the present invention.

[Explanation of symbols]

 1 memory means 2 switch means 3 coefficient processing means 4,8 transfer path 5,5R gamma correction circuit 11 image processing unit 12 preprocessor 13 image enhancer 14 low-pass filter 15,16 interpolation filter 17 color detection unit 21 color correction circuit 22G, 22R, 22B Process processing circuit 23 Matrix circuit 24 Rate converter 25 Up converter 26 Adder 27 Encoder 28, 29 D / A converter 31R, 32R, 35R Adder 34R Knee correction circuit

Claims (3)

[Claims] 1. A gamma correction circuit for performing a gamma correction by digital processing to output a corrected signal y, a memory means for storing correction data for replacing a video signal x with a corrected signal y corresponding thereto, The correction data is read from the memory means and supplied to the gamma correction circuit. The correction data is such that the corrected signal y has a relationship of the video signal x to the power of 1 / γ. A video camera whose coefficient 1 / γ is a function of the video signal x. 2. A switch means connected to the coefficient processing means is further provided, wherein a plurality of the correction data are stored in the memory means, and a plurality of the coefficient processing means are provided in accordance with an instruction signal from the switch means. 2. The video camera according to claim 1, wherein one of the correction data of 1 is read out and supplied to the gamma correction circuit. 3. The gamma correction coefficient 1 / γ is set to be relatively large in a relatively small range of the video signal x and small in a relatively large range of the video signal x. The video camera according to claim 1 or 2, wherein the magnitude of the signal y corrected in a relatively small range is relatively large.