JPH0628477B2 - Camera signal processing circuit - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a camera signal processing circuit suitable for a single tube frequency separation type color video camera.

[Outline of Invention]

Various types of single-tube color video cameras have been proposed in the past, but in particular, the single-tube frequency separation type color video camera has a high S / N, a simple structure of the image pickup tube, and is suitable for mass production. Therefore, one of the mainstream color video cameras
I'm playing.

By the way, in such a single tube frequency separation type color video camera, since the output signal of the image pickup tube is not in the format of the standard system color television signal, this output signal is processed to form the standard system color television. A camera signal processing circuit is provided for this purpose.

FIG. 1 is a block diagram showing a conventional example of such a camera signal processing circuit, in which 1 is an input terminal, 2 and 3 are low-pass filters, 4 is a color signal separation circuit, and 5 and 6 are variable gain amplifiers. 7, 8 are control signal input terminals, 9 and 10 are detection circuits,
Reference numerals 11, 12, 13, and 14 are gamma correction circuits, 15 is an arithmetic circuit, and 16, 17, and 18 are output terminals.

In the figure, an output signal of an image pickup tube (not shown) is amplified by a preamplifier (not shown) and supplied to the input terminal 1.
This output signal has a luminance signal on the low frequency side and two modulated color signals (hereinafter referred to as modulated color signals) on the high frequency side, which are frequency-multiplexed and supplied to the low-pass filter 2. Then, the luminance signal Y is supplied to the low-pass filter 3 and the low-frequency component of the luminance signal (hereinafter, referred to as low-frequency luminance signal).
Y _L is also supplied to the color signal separation circuit 4 to separate the modulated red signal R _M and the modulated blue signal B _M from each other.

The luminance signal Y and the low-frequency luminance signal Y _L are gamma-corrected by the gamma correction circuits 11 and 12, respectively. The gamma-corrected luminance signal Y ′ is supplied to the output terminal 16, and the gamma-corrected low-frequency luminance signal Y _L ′ is supplied to the arithmetic circuit 15.

On the other hand, the modulated red signal R _M separated by the color signal separation circuit 4
The modulated blue signal B _M and the modulated blue signal B _M are supplied to variable gain amplifiers 5 and 6, respectively. The gains of the variable gain amplifiers 5 and 6 are set by the output control signals of the white balance circuit (not shown) supplied from the input terminals 7 and 8, respectively. Therefore, the modulated red signal R _M and the modulated blue signal B are set. _The level of each _M is adjusted by a variable gain amplifier to adjust the white balance. Level-adjusted modulated red signal R _M modulated blue signal B
_M is detected by the detection circuits 9 and 10, and the detected red signal R and blue signal B are gamma-corrected by the gamma correction circuits 13 and 14. The gamma-corrected red signal R ′ and blue signal B ′ are supplied to the arithmetic circuit 15.

Arithmetic circuit 15 forms the gamma corrected low frequency luminance signal _Y L ', the red signal R' and the blue signal B 'from the two color difference signals _(R'-Y L') and the _(B'-Y L ') Then, they are supplied to the output terminals 17 and 18, respectively.

The output luminance signal obtained terminal 16, 17, 18 Y 'color difference signals _(R'-Y L') and _(B'-Y L ') is processed by an encoder (not shown), a predetermined color video signal is formed It

By the way, in such a conventional camera signal processing circuit, an error occurs in the green signal, and in particular, the error increases as the red signal R and the blue signal B increase. Hereinafter, this point will be described.

The luminance signal Y, the red signal R, and the blue signal B before gamma correction in FIG. 1 are the gamma correction circuits 11, 13, and 14.
The gamma coefficient of the picture tube is γ
Then, the gamma-corrected luminance signal Y ′, red signal R ′, and blue signal B ′ are represented as follows.

Y ′ = Y ^{1 / γ} , R ′ = R ^{1 / γ} , B = B ^{1 / γ In the} receiver, this luminance signal Y ′ and these color signals R ′,
'Two color difference signals by the _{(R'-Y L' B)} , (B '
-Y _L ′) is transmitted and from these signals the three primary color signals are formed. In these primary color signals, if the red signal is E _R ′, the blue signal is E _B ′, and the green signal is E _G ′, then E _R ′ = R ^{1 / γ} E _B ′ = B ^{1 / γ} E _G ′ = (Y ^{1 / γ-} 0.30R ^{1 / γ-} 0.11B
It becomes ^{1 / γ} ) /0.59. These primary color signals receive the gamma characteristic of the picture tube,
After all, the red signal E _R and the blue signal E _{B for} displaying a color image on the picture tube are: E _R = (E _R ′) ^γ = (R ^{1 / γ} ) ^γ = R ... (1) E _B = (E _B ′) ^γ = (B ^{1 / γ} ) ^γ = B ... (2), but the green signal E _G is And an error occurs.

A case where the color temperature of the light source changes will be described.

Now, a basic design is performed with a color temperature of T ₁ ⁰ K, and the red signal, the green signal, and the blue signal of the multiple modulation obtained from the image pickup tube at this time are set as R ₀ , G ₀ , and B ₀ , respectively. Further, the levels of the red signal and the blue signal obtained by imaging the same copy under the light source of the color temperature T ₂ ⁰ K change, and if K ₁ R ₀ and K ₂ B ₀ are respectively set, then The red signal R, the blue signal B, and the luminance signal Y of are as follows, respectively.

R = K ₁ R ₀ B = K ₂ B ₀ Y = K ₁ R ₀ + G ₀ + K ₂ B ₀ Then, the white balance circuit adjusts the gains of the red signal and the blue signal to be balanced with the green signal, The correction is 1 / K ₁ times and 1 / K ₂ times, respectively. However, since the luminance signal is not corrected, an error ΔY shown in the following equation occurs in the luminance signal as a result.

ΔY = 0.30 (K ₁ −1) R ₀ +0.11 (K ₂ −
1) B ₀ For this reason, the following error ΔG occurs in the green signal.

As described above, in the camera signal processing circuit, the red signal and the blue signal change (that is, K ₁ and K ₂ change) due to the gamma correction and the change of the color temperature of the light source. However, there is a drawback in that this error increases and the color reproducibility deteriorates.

[Object of the Invention]

An object of the present invention is to provide a camera signal processing circuit which is stable against changes in the temperature of a light source and has excellent color reproducibility, excluding the above-mentioned drawbacks of the prior art.

[Outline of Invention]

In order to achieve this object, the present invention provides a green signal by arithmetically processing a low-frequency luminance signal, a red signal, and a blue signal obtained by separating from an output signal of an image pickup device. It is characterized in that two color difference signals are formed after gamma-correcting each of the green signal and the green signal.

The green signal G is obtained by calculating the low band luminance signal Y _L , the red signal R, and the blue signal B obtained from the image sensor as follows.

The green signal G, the red signal R, the blue signal B, and the (broadband) luminance signal Y thus obtained are gamma-corrected. Gamma-corrected red signal R '(=
R ^{1 / γ} ), the blue signal B ′ (= B ^{1 / γ} ) and the green signal G ′ (= G ^{1 / γ} ) (where γ is the gamma coefficient of the cathode ray tube, and in general, γ = 2.2). By the following calculation, two color difference signals (R′−Y _L ″) and (B′−
Y _L ″).

_{(R'-Y L ") =} 0.70R'-0.59G'-0.
_{11B '... (5) (B'} -Y L ") = - 0.30R'-0.59G' +
0.89B '... (6) _{[However, Y L "= 0.30R' +} 0.59G '+ 0.1
1B '... (7)] These color difference signals _{(R'-Y L "),} (B-Y L") and gamma-corrected luminance signal Y' by the (= ^{Y 1 /} γ),
Combined by an encoder to form a color video signal.

Such color video signal is a red signal E _R is the supplied receiver to receiver is the color image three primary color signals from a color video signal is formed issued movies reproduced by _CRT, a green signal E _G and blue signal E _B is represented as follows by the gamma characteristic of the cathode ray tube.

[However, Y = 0.30R + 0.59G + 0.11B] As is clear from the above equation, the equations (1), (2), and (3) shown above are shown.
In contrast to the prior art in which an error occurs only in the green color signal E _G , an equal amount of error (Y ^{1 / γ} −Y _L ″) occurs in the three primary color signals E _R and the tables E _G and E _B. Also, this error (Y ^{1 / γ} −Y _L ″) is also about 1/2 of the error (Y ^{1 / γ} −Y _L ″) /0.59 in the prior art shown in the equation (3). Therefore, the color reproducibility is significantly improved as compared with the above-mentioned conventional technique.

Further, as described above, the red signal R and the blue signal B for forming the green signal G are those before white balance adjustment. Therefore, an accurate green signal is obtained, and when the gain control for white balance adjustment is performed on the red signal R and the blue signal B, the red signal R and the blue signal B are balanced with respect to the green signal G. There is no error in the green signal. As a result, stable color reproducibility with respect to the color temperature change of the light source can be obtained.

In the above-described conventional technique, even if the white balance adjustment is performed with respect to the change in the color temperature of the light source, the correction is performed only on the red signal and the blue signal, so that an error occurs in the green signal.

The present invention has been made in view of the above points.

Example of Invention

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

FIG. 2 is a block diagram showing an embodiment of a camera signal processing circuit according to the present invention, in which 19 is an operational amplifier circuit, 37 is a Y _L RB generating circuit, 39 is an RGB generating circuit,
The parts corresponding to those in the figure are designated by the same reference numerals and the description thereof is partially omitted.

In FIG. 2, the low-pass luminance signal Y _L obtained by the low-pass filter 3 is supplied to the operational amplifier circuit 19.

On the other hand, the modulated red signal and the modulated blue signal separated by the color signal separation circuit 4 are detected by the detection circuits 9 and 10 to obtain a red signal R and a blue signal B, respectively. The red signal R and the blue signal B are level-adjusted by the variable gain amplifiers 5 and 6 whose gains are controlled by the control signals supplied from the input terminals 7 and 8, respectively, and the white balance is adjusted. Gamma correction is performed by the circuits 13 and 14, and the arithmetic circuit 15
Is supplied to.

Further, the red signal R and the blue signal B output by the detection circuits 9 and 10 are also supplied to the operational amplifier circuit 19. The operational amplifier circuit 19 receives the supplied low-frequency luminance signal Y _L and red signal R
The blue signal B and the blue signal B are subjected to the arithmetic processing represented by the above-described equation (4) to form the green signal G. The green signal G is gamma-corrected by the gamma-correction circuit 12 and the arithmetic circuit 1
5 is supplied. The arithmetic circuit 15 arithmetically processes the gamma-corrected red color signal R ', blue color signal B'and green color signal G', and outputs to the output terminals 17 and 18 the color difference expressed by the above equations (5) and (6), respectively. signal _{(R'-Y L "),} (B'-Y L")
Is output. However, Y _L ″ is represented by the above equation (7).

These color difference signals _{(R'-Y L "),} (B'-Y L") and obtained at the output terminal 16, a gamma corrected luminance signal Y '
And are processed by an encoder (not shown) as in the prior art, and a desired color video signal is obtained.

According to this embodiment, as described above, the color reproducibility is improved and the color reproducibility is stable with respect to the change in color temperature.

In this embodiment, the optical conversion filter can be used to reduce the level fluctuations of the red signal R and the blue signal B due to the color temperature change of the light source. As a result, (1) the level change of the modulated red signal and the modulated blue signal supplied to the detection circuits 9 and 10 is reduced, and the detection distortion is reduced.

(2) The variable gain range of the variable gain amplifiers 5 and 6 can be narrowed.

And so on.

By the way, when a color image is displayed on a cathode ray tube with the primary color signals represented by the above formulas (8), (9), and (10), there arises a problem that the degree of saturation is lowered. Displaying a color image with such primary color signals is performed by a frequency separation type color video camera, a phase separation method, a method of directly obtaining a luminance signal, a red signal, a blue signal and a green signal from an image sensor, a luminance separation GRB gamma. The present invention is also applicable to a color video camera of a system such as a system, and the above-mentioned problems in the luminance separation GBR gamma correction system color video camera will be described here.

First, the brightness separation GBR gamma correction system color video camera will be described. The brightness signal, the red signal, the green signal, and the blue signal obtained from the image pickup tube are gamma-corrected, and the red signal, the green signal, and the gamma-corrected red signal, The blue signal is combined to form a low-frequency luminance signal, and the low-frequency luminance signal is subtracted from each of the red signal and the blue signal after gamma correction to form two color difference signals. And the gamma-corrected luminance signal are combined to form a color video signal.

The separated luminance GRB gamma correction type color video camera does not require a wide frequency band other than the luminance signal for the signal obtained from (1) the image pickup tube.

(2) The noise of the color signal does not appear in the luminance signal, and the S / N is good.

(3) Hue error is small.

There are advantages such as.

However, the camera signal processing circuit in such a color video camera has a drawback that the saturation is reduced and the vividness is lacking for a color having a high saturation.

Hereinafter, this point will be described.

FIG. 3 is a block diagram showing an example of a conventional camera signal processing circuit in a brightness separation GRB gamma correction system color video camera, in which 20 is an image sensor, 21 is a preamplifier, 22 is a matrix circuit, and 23 to 26 are. A gamma correction circuit, 27 is a matrix circuit, 28 and 29 are subtraction circuits, and 30 is an encoder.

In the figure, the output signal of the image pickup device 20 is the preamplifier 2
Amplified by 1 and supplied to the matrix circuit 22 to form a red signal R, a blue signal B, a green signal G and a broadband luminance signal Y.

Here, in the case where the output signal of the image pickup device 20 is a signal in which a plurality of signals are multiplexed, as in a single-tube color video camera of a frequency separation method or a phase separation method, after separating each signal, It is supplied to the matrix circuit. Also,
Although there is a color video camera in which a luminance signal, a red signal, a blue signal, and a green signal can be obtained as they are, a matrix circuit 22 is used for such a color video camera.
Need not be provided.

Next, the red signal R, the blue signal B, the green signal G and the luminance signal Y
Is subjected to gamma correction by gamma correction circuits 23, 24, 25 and 26, respectively. Gamma-corrected red signal R and blue signal B
Are supplied to subtraction circuits 28 and 29, respectively, and are further supplied to the matrix circuit 27 together with the gamma-corrected green signal G to form the low-frequency luminance signal Y _L.

Here, the gamma-corrected red signal R ′, blue signal B ′, and green signal G ′ are R ′ = R ^{1 / γ} , B ′ = B ^{1 / γ} , and G ′ = G ^{1 / γ} . The low band luminance signal Y _L ″ is expressed as follows.

Y _L ″ = 0.30R ′ + 0.59G ′ + 0.11B ′ = 0.30R ^{1 / γ} + 0.59G ^{1 / γ} + 0.1
The 1B ^{1 / γ} low-frequency luminance signal Y _L ″ is supplied to the subtraction circuits 28 and 29,
Color difference signal represented by the following formula _{(R'-Y L "),} (B '
-Y _L ″) is formed.

_{(R'-Y L ") =} 0.70R'-0.59G'-0.
11B ′ (B′−Y _L ″) = − 0.30R′−0.59G ′ +
0.89B 'encoder 30, these color difference signals _(R'-Y L ")
(B′−Y _L ″) and the gamma-corrected luminance signal Y ′ are combined to form a color video signal and output to the output terminal 30.

The above is the signal processing in the separated luminance GRB gamma exhaustion type color video camera.

The color video signal thus synthesized is supplied to a television receiver, a primary color signal is formed, and a color image is displayed on a picture tube, but as described above,
In response to the gamma characteristic of the picture tube, a color image is finally displayed by the red signal E _R , the blue signal E _B , and the green signal E _G represented by the following equations similar to the equations (8), (9), and (10). this E _R = will be issued a ^{{R 1 / γ + (Y'} -Y L ")} γ ... (8) E G = {G 1 / γ + (Y'-Y L")} γ ... (9) E _B = {B ^{1 / γ} + (Y′−Y _L ″)} ^γ (10 ′) [However, Y ″ = (0.30R + 0.59G + 0.11
B) ^{1 / γ} ] However, since generally Y ′> Y ″ _L , Y ′ and Y
_L ″ is equal only when R = G = B (that is, the subject is achromatic). Therefore, except for the achromatic subject, the error of (Y′−Y _L ″) has three primary colors. It produces an equal amount in the signal, which results in color errors. (Y'-
Y _L ″) becomes larger as the saturation becomes higher, and thus the color error also becomes larger as the color becomes more saturated. Further, this error occurs in all three primary color signals, and as a result, the saturation is mainly decreased. Will cause

As described above, the camera signal processing circuit in the conventional separated luminance GRB gamma correction type color video camera has a drawback in that the saturation of colors with high saturation is lowered and the color reproducibility is deteriorated. Such a drawback also occurs in the above-mentioned embodiments.

Such a decrease in color saturation can be eliminated based on the following principle.

That is, the color difference signal (R'-
Y _L ″) and (B′−Y _L ″) are respectively multiplied by Y ′ / Y _L ″ to form a new color difference signal, and a color video signal is formed. the color difference signals _{(R'-Y L "),} (B'-
A new color difference signal Y ′ / Y _L ″ times Y _L ″) can be obtained, but a red signal E affected by gamma characteristics in a cathode ray tube.
_R is Becomes Similarly, the green signal E _G and the blue signal E _B are Becomes As a result, E _R : E _G : E _B = R: G: B, the relative ratio of the red signal, the blue signal, and the green signal becomes constant, and color errors such as hue and color do not occur.
Highly saturated colors do not lose saturation.

FIG. 4 is a block diagram of a main part of another embodiment of the camera signal processing circuit according to the present invention based on the above principle.
1, 32, 33 and 34 are input terminals, 35 and 36 are variable gain amplifiers, 37 is a gain control circuit 38 and 39 are output terminals.

In the figure, a variable gain amplifier 35 is provided between the subtraction circuit 28 and the encoder 30 of FIG. 3 and a color difference signal (R'- which is an output signal of the subtraction circuit 28 from an input terminal 31).
Y _L ″) is also supplied. The variable gain amplifier 36 is provided between the subtraction circuit 29 and the encoder 30 of FIG. 3, and the color difference signal (B ′) which is the output signal of the subtraction circuit 29 from the input terminal 32. -Y _L ″) is supplied. Gain control circuit 3
7 includes the input terminal 33 to the matrix circuit 2 of FIG.
Low frequency luminance signal Y _L, which is a 7 output signal _"is supplied, also gamma-corrected luminance signal Y which is the output signal of the gamma correction circuit 26 of FIG. 3 from the input terminal 34 'is supplied.

The gain control circuit 37 operates the supplied low-frequency luminance signal Y _L ″ and the gamma-corrected luminance signal Y ′ to generate a control signal, and the control signal causes the variable gain amplifiers 35 and 36 to operate.
Gain is controlled. The gains of the variable gain amplifiers 35 and 36 are controlled by the control signal of the gain control circuit 37 to be Y '/ Y.
_It is controlled to _L ″ times, and as a result, from the variable gain amplifier 35, Of the color difference signal is obtained, and from the variable gain amplifier 36, Is obtained.

These color difference signals are supplied to the encoder 30 (FIG. 3) from the output terminals 38 and 39, respectively, and processed together with the gamma-corrected luminance signal Y'to form a color video signal. In the receiver, as described above, such a color video signal can provide extremely faithful color reproducibility without deterioration in color saturation.

FIG. 5 is a block diagram showing a specific example of the gain control circuit 37 of FIG. 4, in which 40 is a variable gain amplifier, 41 is a comparator, and 42 is a low-pass filter, and corresponds to FIG. The same symbols are attached to the parts to be marked.

In this specific example, the gain control circuit 37 is configured by a control loop including a variable gain amplifier 40 and a comparator 41 low pass filter 42.

Now, let the gain of the variable gain amplifier 40 be K. The low-frequency luminance signal Y _L from the input terminal 33 is supplied to the variable gain amplifier 40, and the level-adjusted low-frequency luminance signal K (X).
Y ″ _L is obtained. The low-pass luminance signal K (X) Y ″ _L and the gamma-corrected luminance signal Y ′ from the input terminal 34 are compared by the comparator 41, and this difference signal is obtained by the low-pass filter 4
2 to the variable gain amplifier 40, and the variable gain amplifier 40 is negatively fed back. In this case, the comparator 41
To make the loop gain sufficiently high.

As a result, the variable gain amplifier 40, the comparator 41 and the low pass filter 42 form a control loop in which the following relational expression holds.

K (X) Y ″ _L = Y ′ Therefore, the gain K of the variable gain amplifier 40 is Becomes

The variable gain amplifiers 35 and 36 are gain-controlled by the same control signal as the variable gain amplifier 40, and have the same characteristics as the variable gain amplifier 40. Therefore, the gains of the variable gain amplifiers 35 and 36 are equal to the gain of the variable gain amplifier 40, and K = (Y ′ / Y _L ″).

The low pass filter 42 includes a variable gain amplifier 35,
The purpose of this is to prevent the S / N of the color difference signal from being deteriorated by changing the gain of 36 due to this high frequency noise, and to match f with the color difference signal.

FIG. 6 is a drawing showing a gain control circuit 37 in which a low-pass filter 43 is provided between the input terminal 34 and the comparator 41 in order to match the f characteristics of the two signals supplied to the comparator 41. Therefore, it is possible to prevent the transient characteristic of the color difference signal due to the difference in f characteristic between Y _L and Y ′.

As described above, in this embodiment, it is possible to prevent a decrease in the saturation of a high-saturation color found in a separated luminance GRB gamma correction system video camera or the like, and obtain extremely faithful color reproducibility.

The gain control circuit 37 of FIG. 4 is not limited to the configuration shown in FIG. 5 or 6.

〔The invention's effect〕

As described above, according to the present invention, the color reproducibility is improved, and the color reproducibility is stable without being deteriorated by the change of the color temperature of the light source, which is excellent except for the above-mentioned drawbacks of the prior art. A functional camera signal processing circuit can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a conventional camera signal processing circuit, FIG. 2 is a block diagram showing an example of a camera signal processing circuit according to the present invention, and FIG. 3 is a separated luminance GRB gamma correction type color video camera. A block diagram showing an example of
FIG. 4 is a block diagram of a main part showing another embodiment of the camera signal processing circuit according to the present invention, and FIGS. 5 and 6 are block diagrams showing a specific example of the gain control circuit of FIG. 1 ... Input terminal 2, 3 ... Low-pass filter 4 ... Color signal separation circuit 5, 6 ... Variable gain amplifier 7, 8 ... Gain control signal input terminal 9, 10 ... Detection circuit 11, 12 , 13, 14 ... Gamma correction circuit 15 ... Operation circuit 16, 17, 18 ... Output terminal 19 ... Operation amplification circuit.

Claims (1)

[Claims] 1. An image pickup device, signal separation means for respectively generating a wide band luminance signal, a low band luminance signal, a red signal and a blue signal from an output signal of the image pickup device, and a gain adjustment of the red signal and the blue signal. White balance adjusting means for performing, a green signal generating means for generating a green signal by matrix calculation from the red signal and the blue signal before the gain adjustment by the white balance adjusting means and the low-frequency luminance signal, and the wide band Gamma processing means for performing gamma correction on the luminance signal, the red signal and the blue signal after gain adjustment by the white balance adjusting means, and the green signal, and the gamma-corrected red signal, blue signal, and Camera signal processing, comprising: a color difference signal generating means for generating two color difference signals from a green signal. Road.