JPH0246089A - White balance adjusting device - Google Patents

Abstract

PURPOSE:To exert scarcely influence from the colors of a subject and its surroundings by providing a correcting means to correct the rate signal of color components by a chrominance signal before the gain of an image pick-up system is adjusted and a signal to show the focal distance of a photographing optical system. CONSTITUTION:The light of the subject and its surroundings is made incident on sensors 32, 34 and 36 through an optical system 30. The sensors 32, 34 and 36 output electronic signals SR, SG and SB in accordance with the levels of corresponding color components. The outputs of the sensors 32, 34 and 36 are logarithm-compressed by logarithmic amplifiers 38, 40 and 42 respectively. A correction signal generating circuit 48 generates correction signals dR and dB from outputs CR1 and CB1 of subtracters 44 and 46, a focal distance signal SZ from a focal distance detecting circuit 47 and chrominance signals R1, G1 and B1 of a color separating circuit 14. Thus, the adjustment error by the color of the subject in white balance adjustment can be prevented effectively.

Description

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

[Conventional technology]

White balance is one of the important signal adjustments for color television cameras. White balance refers to the three primary colors (red, red,
The objective is to adjust the gain of each color component of the photographic signal so that the component ratio of green and blue is 1:1:1 for a white subject. The component ratio of the three primary colors differs depending on the type of lighting, so if the white balance is improperly adjusted, the entire photographed screen will appear bluish or reddish.
It becomes impossible to obtain images that faithfully reproduce colors.

Therefore, external automatic tracking type white balance adjustment devices have been proposed in the past as a way to accurately and automatically adjust this white balance (Japanese Patent Laid-Open No. 54-53924, Japanese Patent Laid-Open No. 54-53924, 55-158792, etc.). In these devices, an optical system separate from the photographic optical system detects the peripheral light of the subject, and based on the detection results, the gain of each color component of the photographic signal is controlled, and the white balance is automatically adjusted. This is what we do. Specifically, two or three colorimetric sensors each having a color filter on the front side detect two or three different color components from the peripheral light, and the output of the image sensor is adjusted according to the ratio of the detected values. Controls the gain of the color signal amplifier.

[Problem to be solved by the invention]

However, in conventional devices, when a subject or its surroundings have a specific color, the light incident on the colorimetric sensor is affected by that color, resulting in a decrease in colorimetric accuracy. For example, in the case of a red subject, a red signal that is larger than the amount of red component contained in the illumination light enters the colorimetric sensor. As a result, white
The balance adjustment is off and the entire image becomes bluish.

SUMMARY OF THE INVENTION An object of the present invention is to provide a white balance adjustment circuit that is not easily affected by the colors of a subject and its surroundings.

[Means to solve the problem]

The white balance adjustment circuit according to the present invention detects the ratio of color components of illumination light near a subject, separately from the imaging system,
A white balance adjustment circuit that controls the gain of the color signal of the imaging system, which corrects the ratio signal of the color components using the color signal before the gain adjustment of the imaging system and a signal indicating the focal length of the photographing optical system. It is characterized by having a means.

[Effect]

By providing the above-mentioned correction means, it is possible to correct the deviation in white balance due to the color of the subject, and therefore, it is difficult to be influenced by the color of the subject and its surroundings.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. 1
0 is a photographing optical system including a photographing lens, an aperture, an optical filter, etc.; 12 is a CCD type image sensor having, for example, minute red, blue, and green color filters arranged on the front surface; and 14 is an image sensor 12.
A color separation circuit 16 samples and holds the image pickup signal output from the circuit, and separates and outputs the luminance signal Y and each color signal R, G, B, Luminance process circuit for processing, 18
．． 20 and 22 are a red process circuit, a green process circuit, and a blue process circuit, each of which performs the same processing as the luminance process circuit 16 and is equipped with a variable gain amplifier for white balance; 24 is a red process circuit 18, and a green process circuit; A matrix circuit 26 that forms color difference signals R-Y and B-Y from the R, G, and B signals output from the process circuit 20 and the blue process circuit 22 modulates the color difference signal output from the matrix circuit 24, A video encoder 28 is a video output terminal that synthesizes the luminance signals output from the luminance processing circuit 16, adds a synchronization signal, and outputs a video signal.

30 is a colorimetric optical system for white balance having a condensing lens, a diffusion filter, and an infrared removal filter; 22 is an R sensor that detects a red component; 24 is a G sensor that detects a green component; and 26 is a colorimetric optical system that detects a blue component. B sensor to detect, 38.40.
42 is a logarithmic amplifier, and 44.46 is a subtracter. The outputs C□ and C□ of the subtracters 44 and 46 correspond to the white balance gain control signal in the conventional example. 47 is a focal length detection circuit that detects the focal length of the photographing optical system 10 and is composed of, for example, a potentiometer coupled to a zoom ring, and outputs a signal S2 indicating the focal length. Reference numeral 48 denotes a correction signal generation circuit that generates correction signals d, d from the output CI1+C3 of the subtracter 44.46 and the focal length signal S2 and the R, G, B outputs of the color separation circuit 14, 50.5
2 is a correction signal dl to the output C□, C□ of the subtracter 44°46.
This is an adder that adds l and d. Output CRZ of adder 50.52.

C1z is applied to the gain control terminals of the variable gain amplifiers of the red process circuit 18 and the blue process circuit 22, respectively.

The operation shown in FIG. 1 will be explained. The object light enters the imaging surface of the image sensor 12 via the photographing optical system IO, and the image sensor 12 outputs a photoelectric conversion signal of the object image. Color separation circuit 14
forms a luminance signal Y from the output of the image sensor 12, and also generates each color signal R, G.

Separate and output into B. Those signals are processed in a luminance processing circuit 16, a red processing circuit 18, a green processing circuit 20, and a blue processing circuit 22, respectively;
The matrix circuit 24 receives a color difference signal R from the outputs of the red process circuit 18, the green process circuit 20, and the blue process circuit 22.
-Y and B-Y are combined and output. The encoder 26 is
A video signal is synthesized and output from the outputs of the luminance processing circuit 16 and the matrix circuit 24, and the video signal is applied from a video output terminal 28 to video equipment such as a video recorder. Note that the red process circuit 18 and the blue process circuit 22 perform gain control for white balance.

The operation of the white balance control section will be explained. The light of the subject and its surroundings is transmitted to the sensor 32 via the optical system 30.
, 34.36. Each sensor 32, 34, 36 receives an electric signal SR, SG according to the level of the corresponding color component.
Output Sl. The outputs of sensors 32, 34, and 36 are logarithmically compressed by logarithmic amplifiers 3B and 40.42, respectively, a subtracter 44 subtracts the output of logarithmic amplifier 40 from the output of logarithmic amplifier 38, and subtractor 46 subtracts the output of logarithmic amplifier 42. The output of the logarithmic amplifier 40 is subtracted from . That is, the output CIl of the subtracter 44 shows log (SR/Sr, ), and the output CIl of the subtracter 46 shows log (Ss/Sc).

The focal length detection circuit 47 outputs a focal length signal Sz indicating the focal length of the photographing optical system 10. Correction signal generation circuit 48
The details will be described later, but the outputs C, , , of the subtracters 44 and 46 are
, C□, focal length signal S2 from focal length detection circuit 47
and each color signal R, , G, , B of the color separation circuit 14,
A correction signal d,,d, is generated. Adders 50.52 are
Correction signals dl and d are output to the outputs C□ and C□ of the subtracters 44 and 46.
, whose outputs CIlb CBz control the gains of the R process circuit 18 and the B process circuit 22, respectively.

FIG. 2 shows a detailed block diagram of the correction signal generation circuit 48. 60, 62.64 is a smoothing circuit, 66.68 is a variable gain amplifier whose gain control characteristic is an exponential function, To, 7
2 is a subtracter, and 74.76 is a variable gain amplifier. Each color signal R1, G, , B, from the color separation circuit 14 is smoothed by smoothing circuits 60, 62.64, and the output R3+ of the smoothing circuit 60 and the output E3g+ of the smoothing circuit 64 are each output by a variable gain amplifier 66.68. amplified. The gains of the variable gain amplifiers 66 and 68 are controlled by the outputs C□ and C0 of the subtracters 44 and 46, respectively. The subtracter 70 is the amplifier 6
6 output Rs! to the output G of the smoothing circuit 62.

The subtracter 72 subtracts the output G of the smoothing circuit 62 from the output BSt of the amplifier 68. The outputs of the subtracters 7 and 0572 are applied to amplifiers 74 and 76, respectively. The gains of amplifiers 74 and 76 are controlled by focal length signal S2. The outputs of the amplifiers 74, 76 are applied to adders 50.52 as correction signals d, I, d.

Next, the operation in an actual shooting state will be explained. In FIG. 3, 78 is an imaging device having the configuration shown in FIG. 1, 79 is a subject,
80 is the background. The area Q is the viewing range of the colorimetric optical system 30 (or the illumination range of the illumination light source), and the area P is the photographing range of the photographing optical system 10. For example, there is a darkly colored part in the area P. In this case, the influence should be at least on the ratio of P/Q of the light incident on the colorimetric optical system 30.

Expressing this numerically, it is as follows. That is, it is assumed that only the subject image is currently captured in the photographic optical system 10. The illuminance of the subject is L, and the reflectance of the red component of the subject is RR.
1 Let Ro be the reflectance of the green component of the subject and the reflectance of the red and green components of other parts, KL be the component ratio to green in the illumination light, GC be the gain of the imaging system, CW be the gain of the embellishment system, then In FIG. 1, signals R+, G1. SR, SG, Cl1t
It is expressed by the following formula.

Rr = L X R @ X KL X GcG
l=LXRG xQc SR=LXAXKL xG.

Sa = L X Re X GwC*t= lo
g (A X KL /Rc) However, A= (1-P/Q)XRG +R1IxP/Q. If the gain of the amplifier 74 is +t, then the amplifier 66.6
Since the gain control characteristic of No. 8 is an exponential characteristic, the correction signal d,
I is represented by the following formula.

da = (R+ xexp(CRI) Gl)XK
II=t, XcCxRc xKRx (1-P/Q) X (R1-RG)/A where,
Due to the aperture LxC; c=1. When Re = 1, C*l= log (A X KL)
(1) becomes.

Table 1 shows the formula (11, +21, P/Q=0.2, Kt
= 1, K* = 1, the values of Cl11 and dll were calculated by subtracting 1 from R7 (darkening the color), but they drew a similar curve, and KR = -0 If it is around .degree.2, C11I#-d, that is, the error can be almost completely corrected.

Now, let's consider how the correction amount changes when the focal length changes. For example, when the focal length doubles, the area of the head region P in Figure 3 becomes 174 times larger, and if P/Q was initially 0.2, after the focal length change, P
/Q=0.05. Cjll+ d+ at this time
The values of t are shown in Table 2. Table 2 shows that K, 1''=-0,05
This shows that the error can be corrected when the Therefore, the amplifier 7
What is necessary is to determine the gain Kl (Kl) of 4 (and the amplifier 76).

FIG. 4 shows the correction signal generation circuit 48 and adders 50 and 52.
82 is a microcomputer unit;
83 is an analog data switch, 84 is a system switch.
bus, 85 is an A/D converter, 86 is a central processing unit)
(CPU), 87 is a memory comprising random access memory and read-only memory, 88.89
is a D/A converter.

FIG. 5 shows an operation flowchart of the microcomputer unit 82. Each color signal R from the color separation circuit 14
l, CI, and B r are smoothed by smoothing circuits 60, 62, and 64 as in the case of FIG. Subtractor 4
The outputs C□, CI+ of 4.46, the focal length signal S2, and the outputs of the smoothing circuits 60, 62.64 are applied to the A/D converter 85 in a predetermined order by the switch 83 (SL, 3),
The output data of the A/D converter 85 is sent to the system bus 84.
and is written to the memory 87 via the CPU 86 (S
2). The CPU 86 uses the data taken into the memory 87 to perform the same calculation as in the circuit of FIG. 2 (S4). still,
The gain of the amplifier 74.76 is ++, Km is, for example, K*=
Nitsu. /Sz, Km =to*. /S2 (However, K,
. +Kl.

is determined according to (constant). Digital calculation result
Data C1+C12 is converted into analog data by D/A converters 88 and 89 and applied to the R process circuit 1B and B process circuit 22 in FIG. 1, respectively (S5). This results in
The gains in the R process circuit 18 and the B process circuit 22 are controlled, and white balance adjustment is performed.

〔Effect of the invention〕

As can be easily understood from the above description, according to the present invention, adjustment errors due to the color of a subject in white balance adjustment can be effectively prevented with a simple configuration. Also,
The influence of the focal length of the photographic optical system used is also taken into account, so
Allows for more advanced white balance adjustment.

Table 1 However, Q/P = 0.2, Kt = 1,
K++ = 1Table 2 However, Q/P = 0.05. Kt = 1,
K = 1

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, FIG. 2 is a detailed block diagram of the correction signal generation circuit 48 shown in FIG. 1, and FIG. 3 is a field of view of the photographing optical system 10 and colorimetric optical system. A comparison diagram, FIG. 4 is a partial configuration block diagram of a modified example employing digital arithmetic processing, and FIG. 5 is a flowchart of FIG. 4. 10...Yukage optical system 12--Image sensor 14...-
Color separation circuit 16--luminance process circuit, 18--Red process circuit 20--Green process circuit 22--Blue process circuit 24--Matrix circuit 26--Video encoder 28--Video output terminal 30--・
Colorimetric optical system 44.46-Subtractor 47-Focal length detection circuit 48-Correction signal generation circuit 50.52-Adder

Claims (1)

[Claims] Separately from the imaging system, there is a white balance adjustment circuit that detects the ratio of color components of illumination light near the subject and controls the gain of the color signal of the imaging system. A white balance adjustment circuit comprising a correction means for correcting the color component ratio signal based on a signal indicating a focal length of an optical system.