JPH01305790A - White balance adjusting device - Google Patents

Abstract

PURPOSE:To adequately adjust white balance at the time of low intensity of illumination by providing an image picking up means, an amplifying means, a voltage controlling means and a circumferential light quantity detecting means, and varying the limiting range of controlled voltage by the specified output of the circumferential light quantity detecting means. CONSTITUTION:The component values SR, SG, SB of a light source are induced by a colorimetry sensor 1. They are logarithmic-compressed by a logarithmic compression circuit 2. The differences of them are taken by a differential circuit 3, and log(SR/SG), log(SG/SB) are obtained, and are inputted to a microcomputer 4 together with log SG. The microcomputer 4 refers to a memory 9, and outputs control signals CR, CB so as to correct adequately the white balance through an R signal amplifier 6 and a B signal amplifier 7 respectively. At that time, the circumferential light quantity is detected together with hysteresis. Through the use of this constitution, the large shift of the white balance does not occur even at the time of the low intensity of illumination, and in addition, the variance of color due to the variation of the white balance can be prevented. Especially, influence due to flicker under a fluorescent lamp can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a white balance adjustment device for a color imaging device.

[Conventional technology]

Conventionally, as a white balance adjustment device for a color imaging device, an automatic tracking type device that measures color using an external sensor is known.

Figure 3 is a block diagram showing a conventional white balance adjustment device, in which 1 is a colorimetric sensor that detects the red, green, and blue components of the light source and performs photoelectric conversion, and 2 is the colorimetric sensor that detects the red, green, and blue components of the light source and performs photoelectric conversion. A logarithmic compression circuit that logarithmically compresses the red, green, and blue components of the light source light; 3 is an operating circuit that subtracts the output of the logarithmic compression circuit 2; 5 is a photoelectric conversion circuit for subject light and is detected as R, G, and B outputs; 6.7 is an R signal amplifier and a B signal amplifier that amplify the R and B outputs of the imaging system 5, respectively. 8 is a signal processing system for obtaining a predetermined signal. In addition, 12 is a constant voltage output circuit that outputs a constant voltage for controlling the R signal amplifier 6 and the B signal amplifier 7 instead of the output of the colorimetric sensor when there is little light incident on the color sensor; This is a switch that switches between the output of the color sensor and the output of the constant voltage output circuit 12.

In Figure 3, the colorimetric sensor measures the red of the light source.

Outputs SR+Q, SB signals corresponding to green and blue components. The output SR+G+SR signal is logarithmically compressed in the logarithmic compression circuit 2, and outputs uogs, .

Obtain IL o g S, , It o g sa.

The output compressed by the logarithmic compression circuit 2 is sent to the differential circuit 3, which takes the logarithmic difference between R and G, and between B and G.
It is converted into a control voltage for the signal amplifier 6 and the B signal amplifier 7. The R signal amplifier 6 and the B signal amplifier 7 amplify the imaging signal from the imaging system 5 using the control voltage to produce a white signal.
Perform balance adjustment.

At this time, if the ambient light is low, the colorimetric sensor 1. The error in the output of the logarithmic compression circuit 2 is amplified, and the white balance adjustment becomes inappropriate. Therefore, in the conventional device as shown in FIG. 3, βogS is detected as the illuminance of ambient light, and the detection output is IIogS.

When the colorimetric sensor 1. Logarithmic compression circuit 2. Control was performed by switching the control voltage derived by the differential circuit 3 to a constant voltage output. In this case, the constant voltage output is set to a light source with a low color temperature (equivalent to candle or tungsten light) that is generally assumed in a low illuminance state.

Based on the above, we were trying to reduce the risk of the white balance shifting significantly during low illumination.

(Problems to be Solved by the Invention) As mentioned above, in the conventional white balance adjustment device,
When the ambient light illuminance detection output falls below a certain value, the control voltage is fixed at a constant voltage output, and when it exceeds the -fixed value, it returns to the original value, so the white balance changes after the above-mentioned certain value. This can easily become unsightly, especially if the ambient light is completely different from the color temperature expected with constant voltage, resulting in an extremely large change in white balance that is noticeable. Also, it is more likely to change under a light source with flicker, such as a fluorescent light.

The present invention has been made to solve these conventional problems and reduce the burden of white balance changes.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an imaging means for converting subject light into an electrical signal, an amplification means for amplifying the electrical signal obtained from the imaging means, control voltage limiting means for limiting the output voltage range of the control voltage of the amplifying means;
and means for detecting the amount of ambient light with hysteresis, and has a configuration in which the limiting range of the control voltage is varied based on the output of the ambient light amount detecting means.

[Effect]

By having the above configuration, it is possible to perform appropriate white balance adjustment at low illuminance, and to greatly reduce unpleasant color changes accompanying the white balance adjustment.

〔Example〕

FIG. 1 is a block diagram of a white balance adjustment device which is an embodiment of the present invention, FIG. 4 is a control voltage limit diagram for explaining FIG. 1, and FIG. 5 is a diagram for explaining FIG. 1. It is a flowchart.

In FIG. 1, 4 is a microcomputer (hereinafter referred to as microcomputer) for deriving the gain control voltage from the output of the differential circuit 3, and 9 is a memory that stores constants necessary for calculations in this microcomputer 4. Yes, there is also a third
The same reference numerals as in the figures indicate the same or corresponding parts.

A first embodiment of the present invention will be described below with reference to FIGS. 1, 4, and 5.

First, similarly to the apparatus shown in FIG. 3, the R of the light source light is
, G, B component values, SR, SG, S+1 are derived, the logarithmic compression circuit 2 performs logarithmic compression, the differential circuit 3 takes the difference between fLogR and uogG, J2ogB and ILogG, and
Obtain tOg (SR/SO), log(sa/sa). This output j2og(SR/Sa), Jlog
(So/sa) and ItogS are input to the microcomputer 4, and a control voltage for appropriately performing white balance correction in the R signal amplifier 6 and the B signal amplifier 7 is derived. Hereinafter, a method for deriving the control voltage will be explained using FIG. 5. First, in step (1), N=O is given as an initial value.

Humanized log (SR/So), log (Sa
/sa), uogsa are converted into digital signals by the A/D converter in the microcomputer 4, and are converted to X, Y, and
Read as L. (Step (2)) Next, Lthl stored in the memory is compared with L as the first limit reference value of brightness (Step (3)
). At this time, since L is directly proportional to the logarithm of the surrounding light amount value, if the surroundings are brighter than the brightness indicated by the first limit reference value Lthl, L>Lthl. If L>Lthl, it is compared with the second limit reference value L th2 (step (4)). However, L th2 is a value corresponding to light brighter than Lthl (Lth2>Lthl).

Here, Lty corresponds to the brightness at which low-luminance correction in white balance control begins, Lthl corresponds to the brightness at which low-luminance correction in white balance control is most extreme, and No further corrections will be made.

Now, if L>Lthl and L>Lth2, check whether N=O in step (5) and find that N≠0, that is,
When the brightness does not require low-luminance correction, first compare the lower limit value d for X with X in step (6), and if X≦d, set X=d (step (18)).
, if X>d, leave as is. Next, step (7
), compare the upper limit e for X with X, and find that X≧
If e, set X=e (step (19)),
If so, leave it as is (for the values of d and e,
(as shown in the figure).

Similarly, for Y, from steps (8) and (9), Y≦
If f, Y≧g (f<g), set Y=f (step (20)) and Y=g (step (21)), respectively; if Y>f, Y<g, leave it as is. As described above, according to the flow (a) in FIG. 5, it is possible to limit X and Y to be within the one-dot chain line in FIG.

Next, in step (10), calculate a−x+b,
This value is set as Y' and compared with Y. In other words, it is determined whether the Y coordinate is above or below the straight line Y=a-x+b in FIG. For example, point A is Y=
It is above the straight line a-x+b, and Y'< Y (step (11)).

In this case, the A coordinate/A (X, Y) is left as is.

On the other hand, point B is below the straight line Y=a-x+b and Y'>
Since it becomes Y (step (13)), B (X, Y)
X, Y of X = X' = X - a' / (1
+a''), y=y'' =Y+a/ (1+a2) and step (22)), B''(X'' in Figure 4).

Y''). At this time, point B is changed to point B', that is, B'
If it moves in the direction (X, Y'), it will not move in the direction perpendicular to the straight line n indicating the color change of the black body radiation, which will cause a large error in white balance adjustment. On the other hand, if the movement is to point B'', the direction is perpendicular to the straight line n, so only the influence of the object color is removed, and no error occurs in white balance adjustment.

Next, in step (12), ax+c(cab)
is calculated, and this value is set as Y' and compared with Y. In other words, it is determined whether the Y coordinate in FIG. 4 is above or below Y=aX+c. And if it is below, that is, Y'
>Y (step (13)), leave as is,
If Y'≦Y, then B (X, Y) (7)
=X+a'/(1+a2), Y=Y''=Y-a/ (
1+a2) (step (23)). As described above, (X, Y) can be limited to the shaded area in FIG. 4 using the flows (b) and (a) in FIG. The effect of this limitation is that the image is not affected much by the object color. In addition, by widening the limited range (upper left of straight line n in Figure 4) for the area where the green color is stronger than the blackbody radiation of the straight line n, appropriate white balance adjustment can be made even for light sources that are strong in green, such as fluorescent lamps. I can do it.

Next, L>Lthl, L<Lth2 (L=J!0g5G
is brighter than the first limit value and darker than the second limit value), first in step (4'), N=
1, then proceed to step (27), and calculate m・(L−Lthl) using the constant m stored in the memory to obtain L (here, m is 11 when L = L th+, and L = Lthz, set m-1/(Lth2-Lthl) so that jZ=1), and the convergence point becomes extremely dark, and the values that X and Y should take when L=Lthl. Z (Xz, Yz) is stored in the memory, and d=Xz −(Xz −d) ・1e=Xz by x, yz and °C
+ (e-X2) -Itf =Yz
(Yz −f) ・Lg=Yz + (
g-Yz) ・Calculate 1 (step (28
), (29), (30).

(31)).

Also, since the straight line n has a slope a, its intercept y is Y, −
a-xz +y -", y=Y, -a -X2 Therefore, if the straight line n is expressed as a-Xz, Yz, then Yza-x+
(Y2-a-Xz).

Then, the intercepts and c of the straight line Y-aX+b, Y=aX+c are expressed as b=b+ (Y
z -a Hx2-b)41awc -(C-Y2 +
a-Xz ) -JZ (step (32), (3
3)).

Based on the constants calculated above, the above L〉Lth+
+ L>Lthz (If the range of X and Y is limited in the same way as in case D, the limited range will become narrower as it gets darker and the sentence approaches 0 (direction in Figure 4). And, When u=o, XzXZ and YzY2 are obtained. Then, the process moves to step 6.

Also, in step (3), L < L th+ (L = 1
1 o g S (the brightness indicated by 1 is darker than the first limit value), then d = e = X z, f =
g = Y z, and the values of X and Y are each X
2. Ltr++ + Lt of 0° or more with only Yz
hz is determined according to the specifications of the imaging device, and
．． The value of Y is determined depending on which light source is set at the darkest time.

Now, step (
14), set the control voltage CRr C11 to (a =
Derived from the formula h-X + s, Ca = J-Y + k, CR and CB are sent to the R signal amplifier 6 and B signal amplifier 7 by the D/A converter in the microcomputer 4, and white balance adjustment is performed. (Step (15)).

-〇Figure 2 is a block diagram showing another embodiment of this invention.
0 is the output iogSR of the logarithmic compression circuit 2.

A o g S, to Ilog (sll /sa)
, Arithmetic circuit for deriving jlog(SR,Sa), 1
1 is the output 11oz (Ss /Ss
).

This is an analog limiter circuit that limits by the output of Jog (SR-Sa), and the same reference numerals as in FIGS. 1 and 3 indicate the same or corresponding parts.

In FIG. 2, the red component SR and blue component S6 of the light source are outputted from the colorimetric sensor 1, and are logarithmically compressed by the logarithmic compression circuit 2 to obtain ItOg SR and JZ Og S a. arithmetic circuit 10 j! Og (SR/SR) and frog (
SR-3a) is obtained by differential and addition.

(2) Then, in step (17), set N=1 and proceed to step (6).

After proceeding to step (15), return to step (2) again, input X, Y, and L, and perform the same operation as described above.

However, if N≠O in step (5), step (24
). If L is less than or equal to the third limit value L th3, the process proceeds to step (6). If L>Lths, the process is set to N-0 in step (25), then set to L''L th2 (step (26)), and the process proceeds to step (27).

In other words, unless L<Lthz once and low luminance correction becomes L>Lths, the control voltage will be limited as is, and Lth3 will be set to Lths>Lths.
By setting th2, hysteresis characteristics can be obtained.

Furthermore, by writing N into the E2PROM, the above-mentioned microcomputer operation will be performed even when the camera power is turned off at the next photographing time.

Next 1. Ilog (SR-Sa) is taken as brightness information, and when this value becomes constant and becomes smaller than the bell L, the limiter circuit 11 is activated to limit the value of 10g (SR/SR). Then, the circuit is configured such that the degree of limiter is strengthened according to the value of ILog (SR-3a), and the voltage CR for amplifier control of the R signal amplifier 6 and the B signal amplifier 7 is
, CB. A limiter circuit is constructed by making the threshold level L variable, and hysteresis can be achieved by setting Ll high when the brightness is low and lowering it normally.

〔Effect of the invention〕

As explained above, the present invention makes it possible to prevent large white balance deviations even at low luminance, and to prevent color variations due to changes in white balance. In particular, it was possible to prevent the effects of flicker under fluorescent lighting.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a white balance adjustment device that is an embodiment of the present invention, FIG. 2 is a block diagram of another embodiment of the invention, and FIG. 3 is a conventional white balance adjustment device. FIG. 4 is a control voltage limit diagram for explaining FIG. 1, and FIG. 5 is a flowchart for explaining FIG. 1. In the figure, 1: Colorimetric sensor 2: Logarithmic compression circuit 3: Differential circuit 4: Microcomputer 5: Imaging system 6: R signal amplifier 7: B signal amplifier 8: Signal processing system 9: Memory 10:
Arithmetic circuit

Claims (1)

[Claims] an imaging means for converting subject light into an electrical signal; an amplification means for amplifying the electrical signal obtained from the imaging means; a control voltage limiting means for limiting the output voltage range of a control voltage of the amplification means; 1. A white balance adjustment device comprising: means for detecting with hysteresis, and a limiting range of said control voltage is made variable based on the output of said ambient light amount detecting means.