JPH03254294A - White balance adjustment device - Google Patents

Abstract

PURPOSE:To prevent white balance from being unbalanced even when a high brightness object is included in a pickup picture by reducing the contribution of a color information signal to white balance from that of other region at a region where a luminance information signal exceeds a prescribed value. CONSTITUTION:When a luminance evaluation value yij as to a region is inputted to a color evaluation adjustment circuit, the luminance evaluation value is compared with a brightness threshold level Ny and when the luminance evaluation value is larger than the threshold level, it is judged that the object in the region has a high brightness and an H level switching signal S is inputted to a changeover circuit 42, both color evaluation values are attenuated by a prescribed quantity at R and B attenuators 45, 46 and the result is outputted to an output terminal. When the luminance evaluation value yij is smaller than the threshold level, both the color evaluation values are outputted to output terminals 47, 48 without any attenuation. Thus, even when a scene including a high brightness is picked up, the white balance is not unbalanced and proper white balance adjustment is realized.

Description

[Detailed description of the invention]

(B) Industrial Application Field The present invention is based on a captured video signal obtained from an image sensor.
The present invention relates to an automatic mill balance adjustment device for a color video camera that controls mill balance. (b) Conventional technology In color video cameras, it is necessary to control the mortar balance in order to correct for differences in the wavelength distribution of light depending on the light source. This control includes red (hereinafter referred to as R), blue (hereinafter referred to as B), green (hereinafter referred to as G).
) by adjusting the gain of each color signal so that the ratio of the three primary color signals becomes 1:1:1. Generally, as shown in Japanese Patent Application Laid-Open No. 62-35792 (HO4N9/73), color difference signals (R-Y), (B-
A method is used in which the gain is adjusted so that the integral value of Y ) becomes zero. FIG. 6 is a block diagram of a mill balance circuit using this method. The light that has passed through the lens (1) is transferred to an imaging device (CCD) (2).
), the color separation circuit (3, R, G, B
are extracted as three primary color signals, and the G color signal is directly extracted as the R color signal.
and B color signals are sent to the R amplification circuit (4) and the B amplification circuit (5).
After that, the signal is input to the color process and matrix circuit (6), and a luminance signal (Y) and red and blue color difference signals (RY) (B-Y) are generated and sent to the video circuit. At the same time, the two color difference signals are respectively sent to the integrating circuit (17).
In (18), the gain control circuits (13) and (14) adjust R, B so that the integration is performed for a sufficiently long time and the result becomes zero.
The gain of each variable gain amplifier circuit (4), (5) is adjusted. (c) Problems to be Solved by the Invention According to the prior art described above, when there is a subject with extremely high brightness in a part of the image capture screen, such as when a light source such as the sun is directly photographed, the image sensor uses RlG, When at least one of the light receiving section outputs for each color B is saturated, the color separation circuit (
3) R, G, and B output ratio included in the light source light,
G, Bj & min, and as a result, an inconvenient situation arises in which the mill balance deviates in a direction unrelated to the actual color temperature. (d) Means for Solving the Problems The present invention divides the screen into a plurality of regions and detects the amount of luminance signal as a luminance evaluation value and the amount of color signal as a color evaluation value for each region. , if there are areas where the brightness evaluation value is greater than a certain value, the contribution of the color evaluation value in these areas to the entire screen is reduced. (E) Effect The present invention prevents the white balance from shifting even when a high-brightness subject is included in the photographic screen. (F) Example Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a circuit block diagram of an automatic white balance adjustment circuit according to this embodiment. The light that has passed through the lens (1) is imaged on the CCD (2) and photoelectrically converted, and then sent to the color separation circuit (3) by R,
It is extracted as three primary color signals of G and H. The R and B signals among these three primary color signals are processed by R and B amplification circuits (4
)(, 5), it is input to the camera process and matrix (6) along with G(word), and based on these, the luminance signal (
Y) and red, blue celestial color difference signals (RY), (B-Y)
is created, supplied to the video circuit (7), and subjected to well-known processing. Further, the signals (Y), (RY), and (B-Y) are simultaneously supplied to the selection circuit (21). The selection circuit (21) selects one of the three signals, the luminance signal (Y) or the color difference signal (R-Y) (B-Y), according to the selection signal (Sl) from the timing circuit (25). 1. Select each field in sequence. (Y)→('R-Y
) → (B-Y) → (Y) → . . . are output to the subsequent A/D converter (22) field by field. In addition, the selection signal

[
S]) is created based on a vertical synchronization signal obtained from a synchronization separation circuit (24), which will be described later. The A/'D converter (22) receives the signal (Y(R-Y) selected by the selection circuit (21) at a predetermined sampling period.
)(B-Y), converts it into a digital value, and outputs this value to the integrator (23).By the way, the timing circuit (25) receives vertical and horizontal signals from the camera process and matrix circuit (6). Synchronization signal and CCD (
2) Based on the fixed oscillator output that drives , and outputs a switching signal (S2) to the integrator (23) for time-divisionally extracting the outputs of the selection circuit (21) in these regions for each region. Integral! (23) receives the switching signal (S2) and adds the A/'D converted value of the output of the selection circuit (21) for each region over one field period, that is, performs digital integration for each of 64 regions. FIG. 5 shows the internal structure of this integrator (23) in more detail. Each A/D converted data is supplied to a switching circuit (61). This switching circuit (61) receives the switching signal (S2) and converts each A/D converted value into an adder (Fl) prepared for each area.
1) (Fl 2) It has the role of supplying to the adder for the area where the sampling point of the corresponding data exists in (F88). That is, if a certain arbitrary data sampling point is included in the area (All), this data is supplied to the adder (Fll) for the area (All). still,
Hereinafter, adders (Fij) (ij=t to 8) are similarly set for the area (Aij), and a total of 64 adders are prepared. A holding circuit (Qij) is provided after each adder.
are respectively arranged, and each added value is temporarily held in each holding circuit. The data held in each holding circuit is input to the adder again, and
It is added to the next input data. In addition, each holding circuit is reset for each field based on the vertical synchronization signal, and only the held data immediately before this reset is stored in the memory (26
). Therefore, one set of adder and holding circuit constitutes one digital integration circuit, and a total of 64 integration circuits perform integration! (23), and digital integral values are input to the memory (26) for each 64 area from each holding circuit for each field. When the integration for one field is completed, this integrated value is held in the memory (26) as a brightness evaluation value or color evaluation value. As a result, digital integral values for each region of the luminance signal (Y) corresponding to 64 regions in a certain arbitrary field are obtained as 64 luminance evaluation values (yij). Furthermore, in the next field, the color difference signal (R-Y) is selected by the selection circuit (21), so as a result of the integration by the adder (23), the digital integral value for each region of the color difference signal (R-Y) is Obtained as 64 color evaluation values (r i j),
Similarly, in the next field, the color evaluation value (biJ) of the color difference signal (B-Y) is obtained. In this way, the luminance signal ()′) and the color difference signal (RY(B
-Y), the luminance evaluation value (yi'') and color evaluation value (rij (bij) will be stored in the memory (26). From this point on, the same process as described above will be carried out. The operation is repeated and the brightness evaluation fui(yij),
The color evaluation value (rijl (blj)) is updated sequentially. The latest luminance evaluation value (yij) and color evaluation value (rJ) (bij) obtained in this way are sent to the subsequent color evaluation value adjustment circuit (27). ). Note that the reference level, that is, the zero level, of both the color difference signals input to the A and D conversion 5 (22) is set in advance to the level obtained when a completely achromatic surface is photographed. Therefore, it goes without saying that each A/D conversion value can take not only a positive value but also a negative value. If the color evaluation value level of the corresponding area is exceeded by a predetermined amount (P), it is configured as shown in Figure 2.The brightness evaluation value of each area ( yiJ) is the brightness comparator (41)
The brightness evaluation value is input to the brightness value memory (40) and compared with the brightness threshold value (Ny) stored in advance. When the brightness evaluation value is above this threshold value (Ny), it is at the I level, and when it is below this, it is at the L level. The switching signal (S) is connected to the switching circuit (4
2) is done manually. Here, the brightness threshold fffi(Ny) is RlG of the image sensor
, B is experimentally determined and set in advance as a threshold value at which it can be recognized that any one of the light receiving section outputs of each color is saturated. The switching circuit (42) includes two switches (43) (4
4), and the switch (43) selects the color evaluation value (r
Selectively connect the fixed contact (43a) to which the input signal i j) is input, and the fixed contact (43b) coupled to the R attenuator (45) or the fixed contact (43c) coupled to the output terminal (47). The switch (44) is connected to a fixed contact (44a) to which the color evaluation value (bij) is input manually, and a fixed contact (44b) connected to the B attenuator (46) or an output terminal (48). It has a function of selectively connecting fixed contacts (44C) that have been connected. Both switches (43) (4, i) receive a switching signal (S
), and when the switching signal (S is at the L level), the color evaluation values (r i j) (b i j) are on the fixed contact (43c) and (44C) sides, respectively, and the color evaluation values (r i j) (b i j) are the adjusted color evaluation ii (HRi j) (HB 1J) (
That is, HRi j=r i j, HBi j=biJ,
However, the output terminal (47) (i, j = integer from 1 to 8) (
4g), and each fixed contact (, 4g) is output at H level.
3b) (44b) side and the color evaluation value (rij) (
bij) is input to the R and B attenuators (45) (46). R and B attenuator (4s) (46) f! , a preset constant amount (
P) is subtracted to calculate (ri j-P) and (bij-P), and the output terminal (47) (48 is the color evaluation value (HRij) after 11 adjustment (HBij) (that is, HRi j= r
i j −P, HBij=b 1−P). Here, the certain amount (P) is determined in advance through experiments so that it can be sufficiently recognized that the image quality is not unnatural when photographing a subject with high brightness. Next, the operation of the color evaluation value tone U circuit (27) described above will be explained. When the brightness evaluation value (yij) for a certain area is input to the color evaluation value adjustment circuit (27), this brightness evaluation value is compared with the brightness threshold (NyJ), and when it is larger than the threshold, the object in this area is It is determined that the brightness is H
The level switching signal (S) is connected to the switching circuit (42
), and the flesh color evaluation value is input to the R and B attenuator (45 (
46), the signal is attenuated by a certain amount (P) and output to the output terminal. Furthermore, when the brightness evaluation value (yij) is smaller than the threshold value, it is determined that the subject is not of high brightness, and the flesh color evaluation value is output to the output terminals (47) (48) without any attenuation.
) is output. As a result, only the color evaluation value of the area where the high-brightness object exists is attenuated. The non-attenuated or attenuated adjusted color evaluation values (HRij) (HBij) derived from the output terminal (47) (4g) are as follows:
The color evaluation value (Vr) (Vb) of the entire screen of each color difference signal is sent to the screen evaluation circuit (28) based on the following equations (1) and (2).
8 Vr = Σ ΣHRij/64...11)
iFu1 >-1 8 vb = Σ・ΣHBij/64 ... (2
) i ← 1 j to 1 These equations (1) and (2) are expressed by the color evaluation value adjustment circuit (6
The total sum of all adjusted color evaluation values for each of the four regions is divided by the number of regions, and the average value for one region is calculated as the screen color evaluation value for each color. The gain control circuits (29) and (30) control the R and B amplifier circuits (4) and (5) so that the screen color evaluation values (Vr) and (Vb), which are the color evaluation values of the entire screen, are both zero. The gain is controlled. In this way, when the screen color evaluation values (Vr) (Vb) become zero, the mill balance adjustment is completed. Note that the degree of contribution of each area's color evaluation value to the total inner surface is reduced. In addition to directly calculating the color evaluation value of each region, there is also a method of weighting each region and reducing the weight in high-brightness regions. According to the present invention, even when a scene including a high-brightness portion that is not suitable for self-balance adjustment is photographed, appropriate mill balance adjustment can be achieved without shifting the mill balance.

[Brief explanation of drawings]

1, 2, and 5 are circuit block diagrams of one embodiment of the present invention, FIG. 3 is an explanatory diagram of screen division, and FIG. 4 is a circuit block diagram of a conventional example. (23)... Integrator, (27)... Color evaluation value adjustment circuit,
(28)... Screen evaluation circuit, (29) (30)... Gain control circuit.

Claims (2)

[Claims] (1) In a white balance adjustment device that adjusts white balance based on color information signals in captured video signals, the degree of contribution of color information signals to white balance adjustment in areas on the video screen where the luminance information signal exceeds a predetermined value A white balance adjustment device characterized by reducing the white balance compared to other areas. (2) A brightness evaluation value detection means for obtaining a brightness information signal level as a brightness evaluation value for each of a plurality of areas set by dividing an imaging screen, and obtaining a color information signal level for each of the areas as a color evaluation value for each color. a color evaluation value detecting means; and a color evaluation value adjusting means for outputting a color evaluation value for areas where the luminance evaluation value does not exceed a predetermined value while leaving the color evaluation value unchanged for the area and reducing the color evaluation value for the area where the brightness evaluation value is equal to or greater than the predetermined value by a predetermined amount. a screen color evaluation value calculation means for calculating a color evaluation value for the entire screen as a screen color evaluation value from the output of the color evaluation value adjustment means; and a gain for controlling the amplification gain of each color signal based on the screen color evaluation value. A white balance adjustment device comprising a control means.