JPS6038996A - Color temperature correcting circuit - Google Patents

Abstract

PURPOSE:To obtain stable color reproduction even to a wide variety of change of color temperature of a light source by providing an operational amplifier forming a luminance signal comprising red, green and blue signals of a prescribed ratio to eliminate the error component attended with the color temperature change of the luminance signal. CONSTITUTION:The red signal is fed to an input terminal 1, the blue signal is fed to an input terminal 3 and the luminance signal Y is fed to an input terminal 2 respectively. Variable gain control amplifiers 7, 8 are formed by a white balance circuit and the gain is controlled by a control voltage fed respectively from control terminals 9, 10 to attain white balance adjustment of the supplied red and blue signals R and B and correct the level change attended with the change in color temperature. An input/output red signal of a variable gain amplifier 7 and an input/output blue signal of a variable gain amplifier 8 are fed to an operational amplifier 11 and attain the color temperature correction of the luminance signal through the operation processing. The corrected red and blue signals are obtained at output terminals 4, 6 respectively and the corrected luminance signal is obtained at an output terminal 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color temperature correction circuit suitable for use in frequency separation type single tube color video cameras and the like.

[Background of the invention]

In a frequency-separated single-tube color video camera, an output signal obtained by frequency division multiplexing a luminance signal and two modulated color signals obtained from an imaging unit (hereinafter referred to as a multiplexed modulation signal) is passed through a low-pass filter and a bandpass filter. The luminance signal and each modulated color signal are divided into a luminance signal and each modulated color signal, and each modulated color signal is further detected to obtain a luminance signal and each color signal. It is supplied to a variable gain amplifier controlled by a control voltage from the circuit for gain adjustment.

By the way, the color picture tube of a color television receiver has a gamma characteristic, and therefore it is necessary to perform gamma correction, but it is common to perform gamma correction on the color video camera side. In a frequency-separated single-tube color video camera with a pre-stage gamma correction method that performs gamma correction on multiple modulation signals, gamma correction is performed in the basic design to obtain the following luminance and color signals. .

That is, the luminance signal ′? now separated from the gamma-corrected multiplex modulation signal? Y, the luminance component in the multiplex modulation signal before gamma correction is Yo, the red signal and blue signal separated from the gamma-corrected multiplex modulation signal and whose gain is adjusted by the white balance circuit are R and B, respectively, and further gamma correction is performed. Letting the red component, blue component, and green component in the previous multiplexed modulation signal be Ro and BOI Oo, respectively, then Y=Yo−A(Yo)...(1) R=Rib・A(Yo)...( 2) B = Bo・
A (Yo) ... (3) Yo = 0.51 (I
Gamma correction is performed so that O+0.59Go+0.11BO...(4).

When gamma correction is designed in this way, if the color temperature of the light source differs from that of the basic design, the levels of the red component and H component will change. In such a situation, if the levels of the red component and the blue component are doubled by kl (kl) and kB, the luminance component Yo' at this time is Yo' = 0.3ekH@Ro +0.59Go +0
．． 1l-kB-Bo .-(5). On the other hand, the red and green signals are processed by the white balance circuit at approximately 1/k H
, 1/kB gain correction is performed to correct the color temperature.

As a result, a luminance signal Yl and a red signal R' are obtained.

The green signal B' is as follows.

Y'mi Yo'・A (Yo') ...(6) R'mi R
O・A (Yo') ... (7) B'= BoII
A (Yo') ... (8) Equation (5) 1 From Equation (6), Y' = (0,5・kn@rib 10.59Go + 0.
11kB@Bo)・A(Yo')-(0,3Ro +0
．． 59GO+0.11BO)-A(YO')+(0,
3 (1-kR) rib + o, 11 (1-kn) Bo)・A(
Yo') Therefore, this equation and equations (4), (7),
(From 81.

Y'= Yo-A(Yo') +(0,3(1-kR
)R'+0.1t(1-kB)B') (9).

Therefore, looking at equations (71, (81, (91), if the luminance signal Y' is only the first term on the right side of equation (9), then the luminance signal YL, the red signal 几', and the green signal 阠' are the same. Since gamma correction is performed, the hue does not change and the single-color reproducibility is good, but in reality, as is clear from equation (9), the luminance signal Y' has a value of (0,3(1-kR)几'+0.11(1-
kB)B') 7: c error will be mixed in,
For this reason, in color television receivers, errors occur in the green signal. This is true not only for frequency-separated single-tube color video cameras, but also for other types of color video cameras.In this way, in conventional color video cameras, when the color temperature of the light source changes, The drawback was that the hue and color changed and color reproducibility deteriorated.

[Purpose of the invention]

The object of the present invention is to eliminate the drawbacks of the above-mentioned prior art.

To provide a color temperature correction circuit that can obtain stable color reproducibility even when the color temperature of a light source changes over a wide range.

[Summary of the invention]

In order to achieve this object, the present invention detects an error component due to a change in color temperature from a color signal whose level changes as the color temperature changes, and corrects a luminance signal using the error component. It is characterized by the fact that it is

Regarding the correction of the luminance signal, there are two cases as follows. That is, as explained earlier, the luminance signal separated from the multiplex modulation signal is used as the same signal (separated and detected, and the red signal and blue signal are further balanced for IC1 white), and the color difference signal is generated in the matrix circuit. However, in the case where the entire luminance signal Y' is corrected in the previous stage of the IJ Lux path, and in the matrix circuit (i.

Luminance signal Yd that transmits the luminance signal Y' together with the color difference signal
and a luminance signal YL for forming a color difference signal, but there are cases where only the luminance signal YL for forming this color difference signal is corrected.

Regarding the former, the luminance signal Y' (= Yo・A (Yo')) from which the second term on the right side of equation (9) is removed is
is supplied to the IJ Lux path, and the above formula (711B
Red light represented by + 1-17. Since the color difference signals ()M-Y') and (E'-Y') are formed with the blue signal B', in a color television receiver, the primary color signal holes obtained from these luminance signals and color difference signals! , B'
.

G' is as follows. The ratio of these primary color signals R', B', and G' is
It is constant regardless of the color temperature, and therefore extremely stable color reproducibility can be obtained.

On the other hand, in the latter case, that is, when only the luminance signal Yt for forming the color difference signal in the matrix circuit is corrected, the red mark R' expressed by the above equations (71, (8)), # Signal B' and the brightness of only the right side edge and 1 term of equation (9) (color difference signal (R'-YL) by m number YL)
, (B'-YL), these color difference signals do not contain an error component corresponding to the second term on the right side of equation (9). However, the luminance signal Yd transmitted together with these color difference signals contains such error components.

Therefore, in a color television receiver, such luminance signal Yd and color difference signals (R'-Yr, ), (B'-
When primary color signals fll: J31/, G'' are formed from YL), error components will be mixed into these primary color signals.However, the error components mixed into these primary color signals are equal to each other, and this can be expressed as ・ΔY. Then, each primary color signal 1%
I: 13I1. G'' becomes.In this way, since the same error component is mixed in each primary color signal,
The hue hardly changes, which is almost the same as when the entire luminance signal is corrected, and relatively stable color reproducibility can be obtained.

In this way, by correcting only the luminance signal for forming the color difference signal, the luminance signal transmitted to the color television receiver can avoid the S/N deterioration that accompanies color temperature correction. In particular, when the S/N of the red signal and the blue signal is lower than that of the luminance signal, deterioration of the image quality of the reproduced color image can be prevented by using the luminance signal with a high S/N.

[Embodiments of the invention]

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

Figure 1 is a block diagram showing an embodiment of the color temperature correction circuit according to the present invention, in which 1.2.3 are input terminals, J, 5.
6 is an output terminal, 7 and 8 are variable gain amplifiers, 9 and 10 are control terminals, and 11 is an operational amplifier.

In the figure, input terminal 1 is supplied with a red signal, input terminal 6 is supplied with a blue signal, and input terminal 2 is supplied with a luminance signal Y. The variable gain control amplifier 48 is formed of a white balance circuit (not shown), and its gain is controlled by control voltages supplied from the respective control terminals 9610, and performs white balance adjustment 7 of the supplied red signal R9 and blue signal B. , as mentioned earlier, corrects the level change due to the change in color temperature. The operational amplifier 11 is supplied with 70 variable gain amplifiers, an output red signal, 80 variable gain amplifiers, and an output 114' signal, and performs arithmetic processing to correct the color temperature of the luminance signal. Corrected red and blue signals are obtained at the output terminals 4 and 6, respectively, and a corrected luminance signal is obtained at the output terminal 5.

Next, the operation of this embodiment will be explained.

Now, there are red signals ER from input terminals i, 2+3, respectively.

A brightness signal Ey, a blue signal EB are supplied, and a green signal y
Assuming Ec, the luminance signal Ey is expressed as follows.

By=r. , ER+ pOΦEG ten.・EB・
-(12) However, rQ·fjO,bo are coefficients that change depending on the color temperature.

In addition, the red signal Y ER output from the variable gain amplifier 7
', the blue signal output from the variable gain amplifier 8 is EB'
Then, the operational amplifier 11 outputs the luminance signal Ey.

The red signals ER, Eu' and the green signals EB, EB' are processed to obtain the following corrected luminance signal EY'.

0.59 0.59 Ey'=-Ey--roER+o, sEn'-BoEn+o, 11En'go go g.

= 0.5ER' + 0.59EG + 0.11E
B' (Iro) Here, red light ER' 1 back signal En'
is always kept at a constant value with respect to the green signal EB by the gain control of the variable gain amplifier 7.8. The brightness signal obtained at the output terminal 5 consists of the brightness signal Ey'kt obtained at the output terminal 5, the red signal E1, the green signal Ec, and the blue signal EB', which are mixed at a constant ratio regardless of the color temperature, and the brightness signal Ey'kt obtained at the output terminal 5 is mixed at a constant ratio regardless of the color temperature. Error components are removed and stable color reproducibility is obtained.

Figure 2 is a block diagram showing another embodiment of the color temperature correction circuit according to the present invention. , a variable gain amplifier, and 14.15 a gain control circuit, parts corresponding to those in FIG.

In FIG. 112, if the gains of the variable gain amplifier 7.8σ are respectively AB, the red signal ER' and the blue signal EB' from the variable gain amplifier 7.8 are expressed as follows.

The control voltages of each of the control terminals 9, 10 control the gain ALAB of the variable gain amplifier 7.8 and are supplied to a gain control circuit 14.15, which controls the gain ALAB of the variable gain amplifier 12.8.
A control voltage for controlling the gains AR' and AB' of 13 is formed. These control voltages have respective gains AR',
Set AB' as follows, variable gain amplifier 12.1
5 to red light ER''(≠AR'・ER).

A green signal En'' (=AB'・EB) is generated.

Red signal ER' from variable gain amplifier 12.13 - Blue signal EB Il and input terminal 2 are also supplied to Equation (12)
A luminance signal Ey indicated by is supplied to the operational amplifier 11,
The operational amplifier 11 performs the following calculation to generate a corrected luminance signal EY'.

59 Ey' = □・Ey + 0.3・ER”+ o, x
En”・(16)g.

Transforming this equation using equations (12), (14), and (15), we get Ey'-Ey 10,! l・AR'7R+06
・AB'・EB 0.3・(M-scan)-EB="Ukeヱ・By-zuto"'1lER+0.3・ER'-
□・EB+0.3EB・fIc) go t.

=0. ER'+0.59EG + 0.11EB'
・(17) This equation is the same as the equation (10) in the embodiment shown in Figure 1, and the car that did this is the red light E.
R'.

By controlling the gains AR and AB of the variable gain amplifier 7.8σ so that they are constant values for the green signal EB' or the a signal EG, the same effect as the implementation shown in Figure 1 can be obtained. It is prayed for.

FIG. 3 is a block diagram showing still another embodiment of the color temperature correction circuit σ according to the present invention, in which reference numerals 16 and 17 are variable gain amplifiers, 18 and 19 are detection circuits, and 20 and 21 are variable gain amplifiers. , 211 are given the same reference numerals.

This embodiment also includes a means for detecting a modulated red signal and a modulated blue signal before detection, and performs gain control for whitening (lance, etc.) on the modulated red signal and modulated blue signal.

In Fig. 6, a variable gain amplifier 16 is connected from input terminal 1.
A modulated red signal is supplied to the input terminal 6, and a modulated blue signal is supplied to the variable gain amplifier 17 from the input terminal 6. Gain AR of variable gain amplifier 16.17.

AB are controlled by control voltages from control terminals 9 and 10, respectively, to achieve white balance.

The modulated red signal and modulated blue signal from the rjJ gain amplifiers 16.17 are supplied to detection circuits 18.19, respectively.

The red signal detected by the detection circuit 18 is supplied to the output terminal 4° operational amplifier 11 and the variable gain amplifier 20, and the blue signal detected by the detection circuit 19 is supplied to the output terminal 6. An operational amplifier 11 and a variable gain amplifier 21Vc are supplied.

Here, the gains A, R' of the variable gain amplifier 20.21,
AB' is controlled by control voltages from control terminals 9 and 10, respectively, and is set to satisfy the following relationship with the gains of variable gain amplifiers 16 and 17.

AR'=1/AR, AB'=1/AB Now, the modulated red signal and modulated negative signal supplied from input terminal 1.6 are detected before being supplied to variable gain amplifiers L6 and 17. Assuming that the red signal ER and the green signal EB are obtained as follows, the red signal ER' and the blue signal EB' output by the detection circuit 18.19 are ER'=AR-ER EB'=AB@EB, Therefore, the red signal ER' and the 'green signal FB' output by the variable gain amplifier 20 and 21 are as follows from the above equation:
ER"=AR'fist ER'=ER En/1-AB'・ER'=EB.

Here, the gain A of the variable gain amplifier 16+17 is
]・Gain AR of variable gain amplifiers 7 and 8 in Figure 1.

Set in the same way as AB. As a result, the operational amplifier 11 receives red signals ER and ER similar to the operational amplifier 11 shown in Figure 1.
' and green signals EB and EB' are supplied, and the operational amplifier 1
1 performs the calculation of equation (13) above, and a corrected luminance signal is obtained at the output terminal 5.

Therefore, in this embodiment, the same effects as in the embodiment shown in FIG. 1 can be obtained.

FIG. 4 is a block diagram showing still another embodiment of the color temperature correction circuit according to the present invention. The parts are given the same symbol.

This embodiment includes a variable gain amplifier 24 whose gain AR' is controlled by a gain control circuit 22 so as to satisfy the relationship shown in equation (15) above with respect to the gain AR of the variable gain amplifier 16. The red signal ER' detected by the detection circuit 18 (
= AR-ER) is supplied to the operational amplifier 11 via the variable gain amplifier 24, and the gain is controlled so as to satisfy the relationship shown in equation (15) with respect to the gain AB of the variable gain amplifier 17. A variable gain amplifier 25 whose gain AB' is controlled by a circuit 23 is provided, and the blue signal En' (-AB-EB) detected by the detection circuit 19 is sent to the variable gain amplifier 2.
5 to the operational amplifier 11. The operational amplifier 11 converts the supplied red signal into ER'' and the green signal into E.
n'', the formula (1
6) is performed, and as a result, a luminance signal expressed by equation (17) is obtained.

Therefore, in this embodiment as well, the same effects as in the embodiment shown in FIG. 1 can be obtained.

The present invention has been described in detail above, but in these embodiments, the luminance signal Ey supplied to the input terminal 2 may be the luminance signal EYL before being divided into two to form a color difference signal. However, the luminance signal Eyt may be separated to form the color difference signal. As mentioned in the "Summary of the Invention" section, in the former case, the formula (
As shown in equation (10), extremely stable color reproducibility can be obtained, and in the latter case, as shown in equation (11),
Relatively stable color reproducibility and low S/N
A color 111]i image of good image quality can be obtained even for color signals of . Furthermore, in the above embodiment, a case has been described in which the corrected luminance signal EY' consists of a red signal, an H signal, and a green signal mixed in the ratios shown in equations (13) and (17). It goes without saying that the ratio is not limited to this, and that any other desired ratio can be set.

Note that the present invention is applicable to Y-B which employs the first-stage gamma correction method.
The present invention can also be applied to color temperature correction of other color video cameras, such as color video cameras using a gamma correction method and color video cameras that are equipped with an image sensor having inverse gamma characteristics and do not require gamma correction.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to remove error components associated with color temperature changes of the light source not only for red signals and green signals but also for luminance signals. Since the color temperature correction of the luminance signal is performed using the blue signal, the mixing ratio of each color signal forming the luminance signal can be set as desired and accurately, and the error component can be reliably removed. As a result, extremely stable color reproducibility can be realized, and a color temperature correction circuit with excellent functions can be provided without the drawbacks of the above-mentioned conventional technology.

FIG. 7 is a block diagram showing another embodiment of the color temperature correction circuit.

Figure 3 is a block diagram showing still another embodiment of the color temperature correction circuit according to the invention, and Figures 4 and 4 are block diagrams showing still another embodiment of the color temperature correction circuit according to the invention.

1.2.3...Input terminal, 4,5.6...Output terminal, 7
．． 8. Variable gain amplifier, 9, 10... control terminal, 11
...Operation amplifier, 12.15...Variable gain amplifier, 14
．． 15...gain control circuit, 16.17...iiJ variable gain amplifier, 18.19...detection circuit, 20.21.
...Variable gain amplifier, 22.23...Gain control circuit, 24.25...Variable gain amplifier.

Figure 7 Figure 2 3rd close Kayazu

Claims (1)

[Claims] In a color temperature correction circuit that includes a variable gain amplifier whose gain is controlled by a control voltage from a white balance circuit and corrects a red signal and a blue signal to achieve white balance, the red signal, the blue signal, and the luminance signal are An operational amplifier is provided which processes the supplied luminance signal to form a luminance signal consisting of a red signal, a green signal, and a blue signal at a desired fixed ratio, so as to be able to remove error components associated with changes in color temperature of the luminance signal. The color temperature correction circuit is configured to have an f% characteristic.