JPS6225597A - Auto white balancing circuit - Google Patents

Abstract

PURPOSE:To prevent a shift of a white balance without responding to a minute variation of a color temperature, by making a gain of a color signal amplifying circuit constant, if a color temperature which is detected by a color temperature detecting sensor is within a prescribed range. CONSTITUTION:As for an operation of an auto white balance circuit, a color temperature (signal) which is detected by a white balance sensor 5 through a diffusion plate 6 is pre-amplified by a pre-amplifying circuit 7, and also converted by an A/D converter 21. In such a case, when an output of the pre- amplifying circuit 7 is V1<=V<=V2 (namely, at the time of a color temperature T2), a comparator 21a sends out an H level signal, and other comparators 21b-21n send out an L level signal. Accordingly, only an analog switch 26b and 31b turn on, and at the time of the color temperature T2, VR12 is applied to an R system amplifier, and to a B system amplifier, VB12 is applied. On the other hand, an object to be photographed 1 forms an image on an image pickup element 3 through a photographic lens 2, and it is brought to a signal conversion and supplied to a video process circuit 4, and converted to a color video signal therein.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an auto white balance circuit, and more specifically, to an automatic white balance circuit, and more specifically, when photographing the same subject with the same light source, it is possible to obtain a white image by simply changing the pointing range of the color temperature detection sensor. Regarding the auto white balance circuit that prevents the balance from shifting.

[Prior Art 1] In so-called electronic still cameras, which have been actively developed in recent years, it is necessary to perform white balance adjustment in order to obtain high-quality color images, as in color video cameras. That is, if the color temperature of the light source of the subject changes, the white balance will also change, so it is necessary to correct the color temperature of the electronic still camera in accordance with the change in color temperature. To this end, an auto white balance circuit has been proposed that includes a sensor that determines the color temperature of the light source Al1 in addition to the image sensor, and automatically adjusts the white balance according to the output of this sensor.

FIG. 5 is a block diagram showing an example of an auto white balance circuit in a conventional electronic still camera. The subject light emitted by the subject 1 is imaged on the image sensor 3 through the photographing optical lens 2 of the electronic still camera, and the electrical signal from the image sensor 3, which is converted into an electrical signal, constitutes a video processing circuit 4. The signal is sent to the color signal amplification circuit 4a.

On the other hand, a white balance sensor 5 is located near the optical lens 2 for photographing and receives the subject light.
A milky white diffuser plate 6 is arranged in front of the sensor 5. This milky-white diffuser plate 6 is designed to diffuse the reflected light from the subject and add color, based on the idea that adding color to the various colored lights of everyday scenery will bring it closer to white. This is to calculate the total amount of transmitted light over the entire surface of the area.

The output signal from the white balance sensor 5 is guided to a preamplifier circuit 7, and the output of the preamplifier circuit 7 is
It is guided to an R-type amplifier 8 for red-type (hereinafter referred to as R-type) and a B-type amplifier 9 for front thread (hereinafter referred to as B-type). These R
The system amplifier 8 and the B system amplifier 9 are, for example, logarithmic, polygonal, etc. approximation function amplifiers, and their characteristics are as shown in FIG. 6(A). That is, the horizontal axis represents T (color temperature), and the vertical axis represents target values V R and V B of the R system gain and B system gain, respectively. For example, when the color temperature is T2, the R system gain is set to vI? The optimal white balance can be obtained by setting the value of L and setting the gain of the B system to the values of V and l.

The respective outputs of the R-system amplifier 8 and the B-system amplifier 9 are guided to the R-system amplifier and the B-system amplifier of the color signal amplification circuit W84a. The output of the video processing circuit 4 including the color signal amplification circuit 4a is guided to a magnetic head 12 via a recording amplifier 11, and the magnetic head 12 is connected to a small magnetic head mounted on a spindle motor 13 by appropriate means. Magnetic recording with a well-balanced white can be performed on the disk 14. The graph shown in FIG. 6(B) is a rewritten version of FIG. 6(A) using the color temperature value as a parameter, and the gain target value VR at each color temperature is , VB can be understood at a glance.

By the way, although the auto white balance circuit shown in FIG. 5 can sensitively and continuously follow changes in the color temperature of the light source in real time, it has the following problems due to its sensitivity. That is, this method is based on the assumption that, as mentioned above, when an image is mixed with additive colors using the diffuser plate 6 provided in front of the white balance sensor 5, the sum total becomes approximately white. In reality, various objects (subjects) included within the directional range of the diffuser plate 6 each have a hole or color bias. Therefore, even under the same light source, if the object that comes within the field of view (direction range) of the white balance sensor changes, the white balance will be adjusted to correct the color bias, and as a result, the same object Even when photographed with the same light source, the colors may differ slightly depending on the photographing conditions, such as when photographing the same person in front of a blue wall and in front of a red wall.

To explain it another way, as shown in Figures 7(A) and (B), for example, even though the color temperature of the light source does not change at T2, the color of the sum of the light rays entering the field of view of the white balance sensor changes. The temperature may change by ±ΔT,
At that time, in the above method, vR2”B2 which should be originally set.
The setting will deviate by a value corresponding to ±ΔT.

[Problems to be Solved by the Invention] As a means for solving this inconvenience, there is a means called auto white balance lock. This means first operates the auto white balance circuit in the conventional manner, and then when the lock switch is operated, the white balance control voltages VR and VB are fixed at the values at that time, which eliminates the above-mentioned disadvantages. (Japanese Unexamined Patent Publication No. 58-225792).

However, this case has the following problems. For example, if you set the lock switch indoors, you may end up taking pictures under a different light source such as outdoor light without releasing the switch, and in this case, the image quality will deteriorate significantly. .

■For example, - After locking and taking a picture under a variant light source, you can release the lock to take a picture with a different light source, and if you want to take a picture with the original light source again, it will be locked again. However, the situation when locked is slightly different and the control voltage fluctuates, so the same problem as before occurs.

■Since memory elements and switches are added as circuit components for auto white balance locking, the device becomes complicated.

[Means and effects for solving the problems] In order to solve the above problems, the present invention provides an image sensor for photoelectrically converting an image of a subject, and a chromaticity for detecting the color temperature of the light source light related to the subject. a color temperature detection sensor; a preset signal generation means for obtaining a plurality of stepwise preset signals according to the output signal level of the color temperature detection sensor; a color signal amplification circuit that performs automatic color balance adjustment; It is characterized in that it does not respond to minute fluctuations in color temperature.

[Examples] The present invention will be described below based on illustrated examples. In the embodiments described below, the same constituent members as those already explained in FIG. 5 are simply given the same reference numerals, and redundant explanation will be avoided.

FIG. 1 is an electrical circuit diagram of an auto white balance circuit showing one embodiment of the present invention. The output end of the preamplifier circuit 7 has n comparators 21a.

21b, 21c, . . . , 21n.
Each second input of the converter 21 has a comparator level V1. V2. V3. .......

■ has been entered. Here, the converter level is Vl, v2, v3, . . ., vn, and is set to correspond to the threshold level Thn shown in FIG. has been done.

The comparators 21a, 21b, 21c, ---
, 21n, the inverter 22z constituting the logic circuit 22, the exclusive OR gate (
(hereinafter referred to as Ex OR) 22a.

22 b, 22 c, . . . , 22 n. That is, the output terminal of the comparator 21a is connected to the inverter 22z and the first input terminal of the ExOR 22a, and the output terminal of the comparator 21b is connected to the ExOR 22a.
It is connected to the second input terminal of OR22H and the first input terminal of ExOR22b. And the following is connected in the same way,
The output terminal of the comparator 21n is connected to the second input terminal of the ExOR 22n and the analog switches 26n and 3 described below.
1n and the respective control terminals thereof.

The output end of the inverter 22z is connected to the respective control terminals of analog switches 26a and 31a forming alternative analog switches 26 and 31 that operate selectively. Similarly, ExOR22a, 22b, ・
Each output terminal of . . . is connected to an analog switch 26b.
and 31b, analog switch 26c and 31C1...
... are connected to their respective control terminals.

Each of the above analog switches 25a, 26b, ...
・.

The output terminal of 26n is connected to the control terminal of the R system amplifier constituting the color signal amplification circuit 4a, and the input terminals of these analog switches 25a, 26b, . . . 26n are as shown in FIG. 2(A). The voltage VR is a preset voltage as shown.
11' R1□, . . . "Connected to the terminal that supplies Rln.

Similarly, each analog switch 31a, 31b,...
・The output terminals of 31n are connected to the control terminal of the B-system amplifier, and these analog switches 31a + 31b
The input terminals of +..., 31n are supplied with voltages V, V, which are preset voltages as shown in FIG. 2(A).
.

Bll B12 ......” Connected to the terminal that supplies Bin.

That is, if the characteristic curve that provides the proper white balance characteristic shown in FIG. 6(A) is shown by the dotted line in FIG.
4, the target value V of the control voltage of the R system amplifier of the color signal amplification circuit 4a becomes VR1□, and in the range ° before and after the color temperature T1, the target value V of the control voltage of the R system amplifier of the color signal amplification circuit 4a becomes VR1□, and similarly the B system amplifier Target value of control voltage VB
is set to be VBll. Similarly, before and after the color temperature T2, is the target value V1? and Vn, Vl
, 1° and vB12 are set to be output, respectively, and the target values VR and Vn are set to be VR1n and VB□, respectively, before and after the color temperature Tn. It is set to output .

In other words, even if there is a slight change in color temperature before and after color temperature T1, for example, the output voltage as the control voltage of the color signal amplification circuit will be constant at VRll, and the above output voltage will change with a small change in color temperature. It is designed not to. Therefore, since "two feet" R11 is supplied to the R system amplifier of the color signal amplification circuit 4a, the gain of the same color signal amplification circuit 4a does not change even if there is the above-mentioned minute color temperature change.

However, when the color temperature changes from T to T2, the target value of the control voltage V
The output voltages of R and VB are set to change to VR12 and VB12, respectively. In other words, when a certain range is exceeded, the output voltage changes stepwise. In addition, FIG. 2(B) shows the above-mentioned second image using color temperature as a parameter.
This is a redrawn version of Figure (A), showing the classification of threshold levels, ie, T<Thl, Thl≦T<Th2.
Th2≦T<Th3. Th3≦T<Th4. Th4≦
Codes 51, 52, 53, 54 depending on the respective states of T.
．． 55.

The operation of the auto white balance circuit configured as described above is such that the color temperature (signal) detected by the white balance sensor 5 via the diffuser plate 6 is preamplified by the preamplifier circuit 7, and then the color temperature (signal) is preamplified by the A/D converter. Analog-to-digital conversion is performed at 21.

That is, comparators 21a, 21b, . . .
....

The above threshold level T is connected to one input terminal of 21n.
Comparator levels V, , V2 .corresponding to hl , . . . , Thn. . . ., Vn is set, so for example, when the output V of the preamplifier circuit 7 is v1≦v× (i.e., when the color temperature is T2), the comparator 21a sends out an H level signal, The other comparators 21b, 21c, . . . , 21n send out L level signals. Therefore, the inverter 22z outputs an L level signal, and only the EXOR 22a outputs an H level signal, so only the analog switches 26b and 31b are turned on. Therefore, the voltage VR12 is supplied as the control voltage V to the R-system amplifier of the color signal amplification circuit 4a, and the voltage VB□2 is similarly supplied as the control voltage Vn to the B-system amplifier.

That is, as shown in FIG. 2(A), when the color temperature is T2, the R amplifier has vl? 12 is applied, and VB12 is applied to the B-system amplifier. Hereinafter, in the same way, the color temperature T t
, Ta, ..., Tn, respectively (
VV) (VV) ・・・・・・・・・RLL'Bll
The color R13'813 (V, V) is the control voltage.
1n Bin is applied to the signal amplification circuit 4a.

On the other hand, the image of the subject 1 is formed on an image sensor 3 via a photographing lens 2, and the image sensor 3 converts the signal into a signal and supplies it to a video processing circuit 4, where it is converted into a color video signal. . Further, as mentioned above, since the gain of the color signal amplification circuit 4a is determined according to the color temperature with a predetermined width, both the R system and the B system are appropriately amplified and sent to the recording amplifier 11. . The signal appropriately amplified by the recording amplifier 11 is recorded on the magnetic disk 14 by the magnetic head 12.

Next, a modification of the above embodiment will be explained based on FIG. 3.

By the way, in the explanations so far, we have described light sources that are assumed to have a black body radiation spectrum, such as sunlight or incandescent lamps. However, when the light source is a fluorescent lamp or the like, the fluorescent lamp light source has a unique spectrum that is different from the spectrum of black body radiation. A color video camera has a circuit that detects only the R and B components of the incident light under such a light source and controls the gain for the R and B signals based on the detected values. When used, a deviation occurs in the amount of white balance adjustment, and a good white balance effect cannot be expected.

It should be noted that such problems are not limited to color video cameras, but also occur in electronic still cameras.

Therefore, in Japanese Patent Application No. 58-15687, the present applicant used a ripple detection means to detect that a fluorescent light source was used, and corrected the white balance adjustment circuit based on the detection result. A proposal was made to control this.

This modification incorporates such a ripple detection means and a group of manual switches for setting it when performing special photography, for example, in the above embodiment.

As shown in FIG. 3, the output terminal of the preamplifier circuit 7 is
Comparators 21a to 2 forming the /D converter 21
1n, and is also connected to the input terminal of the ripple detection circuit 32. The output terminal of this ripple detection circuit 32 is connected to a first input terminal of an AND gate 25b, and is also connected to a first input terminal of an AND gate 25a via an inverter 24a. ” The output end of the two-legged AND gate 25b is the AND gate 23o.
and 23p, respectively. Output terminals of these AND gates 230 and 23p are connected to respective control terminals of analog switches 26o and 310 and analog switches 26p and 31p, respectively.

These analog switches 26o, 31o, 26p, 31
Each input terminal of p has a voltage v , v , v , v
Provide R1o Blo Rlp Bl
connected to the terminal that supplies p, and the switches 26o and 26p
The respective output ends of the switches 310 and 31p are connected to the R system amplifier of the color signal amplification circuit 4a, and the respective output ends of the switches 310 and 31p are connected to the B system amplifier.

The output terminal of the AND gate 25a is the AND gate 23a.
~23n are connected to each second input terminal. The first input terminals of the AND gates 23a to 23n are connected to the inverter 22Z, ExOR22a, 22b, . . .
..., connected to the output terminal of 22n. The output terminal of the AND gate 23b is connected to the first output terminal of the OR gate 27.
The output terminal of the OR gate 27 is connected to the control terminals of the analog switches 26b and 31b. The above AND gates 23a, 23c,...
..., the output end of 23n is an analog switch (26a
, 31 a).

It is connected to each control terminal (26c, 31c), ----, (26n, 31n).

The output terminal of the manual switch group 33 is the above-mentioned OR gate 2.
7 and the inverter 24
each second of the AND gates 25b and 25a through
is connected to the input end of the

Next, the operation of this modified example configured as described above will be explained in each case. Note that a case will be described in which both the ripple detection circuit 32 and the manual switch group 33 are high-active.

(1) Ripple detection circuit 32 and manual switch group 3
3 both output L level signals.

In this case, the AND gates 23a to 23n and the OR gate 27 all open the gates, and the AND gates 23o and 23p close the gates, so the embodiment described above (
The logic is the same as the operation (see Figure 1). That is, in this case, neither the ripple detection circuit 32 nor the manual switch group 33 acts, and the same operation as in the previous embodiment is performed.

(2) The ripple detection circuit 32 outputs an H level signal,
When the manual switch group 33 outputs an L level signal.

In this case, the AND gates 23a to 23n are turned off and the OR gate 27 is through, so the analog switch 2
6a to 26n and 31a to 31n are all turned off. On the other hand, ANDGATE 23o.

Since the gate of 23p is open, the analog switch (26o, 31o) or (26p,
31p) is opened, and the corresponding control voltages are supplied to the R-system amplifier and the B-system amplifier. At this time, for example, it is assumed that when the output of the comparator 21b is at H level, it is a fluorescent lamp, and when it is at L level, it is a sodium lamp, and voltages suitable for each can be preset.

In this way, as shown in FIGS. 4(A) and (13), the value of the control voltage that provides an appropriate white balance for artificial light sources such as fluorescent lamps and sodium lamps can be set to 41 or 41. Even if they are in the position shown by reference numeral 42, they can be detected by the ripple detection circuit 32 and the corresponding control voltages VR and VB can be supplied to the color signal amplification circuit 4a. Therefore, it is possible to realize a white balance circuit with less deviation even under an artificial light source.

(3) When manual switch 8T33 outputs H level.

In this case, since AND gates 25a and 25b are both turned off, they are irrelevant to the output of ripple detection circuit 32. On the other hand, since the output of the OR gate 27 becomes an H level signal, the analog switches 26b and 31b are turned on. That is, in this example, when the manual switch is turned on, voltage VR12 is supplied as the control voltage for the R system amplifier, and voltage VB12 is supplied as the control voltage for the B system amplifier, regardless of other conditions. Ru.

In this case, the above-mentioned voltages ■R1, ~■2□. .

Of course, an analog switch and another voltage may be added separately from the set voltages of VB11 to VB1n, so that another voltage can be supplied to the R-system amplifier and the B-system amplifier.

In addition, according to the above-mentioned embodiments and modified examples, since a conventional function amplifier is not used, the instability of temperature characteristics caused by the use of this amplifier is eliminated, and the comparator of the A/D converter is Non-linear distortion to the white balance sensor can be absorbed by adjusting the level. Furthermore, even if the required control curve has a variety of shapes, it is highly versatile because it is only necessary to change the setting value of the variable resistor in the same circuit.

[Effects of the Invention] According to the present invention, the color temperature adjustment is constant within each of a plurality of color temperature ranges, so when the same subject is photographed with the same light source, the color temperature detection sensor Simply changing the pointing range (direction) will not cause the white balance to shift.

[Brief explanation of the drawing]

Figure 1 is an electric circuit diagram of an auto white balance circuit showing an embodiment of the present invention, and Figures 2 (A) and (B) show the gain control voltage of the auto white balance circuit shown in Figure 1 above. A characteristic diagram showing the target value, FIG. 3 is an electric circuit diagram showing a modification of the auto white balance circuit shown in FIG. 1, and FIGS.
) is a characteristic diagram showing the target value of the gain control voltage of the auto white balance circuit shown in FIG. 3, FIG. 5 is an electrical circuit diagram of a conventional auto white balance circuit, and FIG. B), FIGS. 7A and 7B are characteristic diagrams of the conventional auto white balance circuit shown in FIG. 5 above. 3... Image sensor 4... Image processing circuit 4a...
......Color signal amplification circuit 5...
・・White balance sensor (color temperature detection sensor) 6・・・・・・・・・・Diffusion plate 7・・・・・・・・・Preamplifier circuit 21...
......A/D converter (preset signal generation means) 22......Logic circuit (preset signal generation means) 26.31...Analog switch (preset signal generation means) ) 32...Ripple detection circuit 33...
...Manual switch Gunei 4 section (A) FI (A) (B) R2

Claims (1)

[Claims] An image sensor for photoelectrically converting an image of a subject, a color temperature detection sensor for detecting the color temperature of light source light related to the subject, and a plurality of color temperature detection sensors according to the output signal level of the color temperature detection sensor. Preset signal generation means for obtaining a stepwise preset signal; and a color signal amplification circuit that performs automatic color balance adjustment on the output signal of the image sensor according to the preset signal of the preset signal generation means. An auto white balance circuit featuring