JPH03259692A - White balance adjustment device - Google Patents

Abstract

PURPOSE:To realize proper white balance adjustment without unbalanced white balance by correcting a color information signal into a signal within a temperature distribution range when the color information signal is not within a distribution range of a constant color temperature change in a picked-up pattern. CONSTITUTION:An integrator 23 receives a switching signal S2 to add an A/D conversion value being an output of a selection circuit 21 over one field period for each area, that is, applies digital integration the signal for each of 64 areas and when the integration by one field is finished, the integration value is stored in a memory 26 as a color evaluation value. Newest color evaluation values (rij), (bij) obtained in this way are fed to a post-stage color evaluation value correction circuit 27. The color evaluation value correction circuit 27 discriminates whether or not a color evaluation value of each area is within a proper color temperature distribution range shown in hatched lines in figure and applies correction in a direction orthogonal to the direction of the color temperature distribution to the color evaluation value when the color evaluation value is not within the range and gives a resulting output.

Description

[Detailed description of the invention] (a) 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 white balance adjustment device for a color video camera that controls white balance.

(b) Conventional technology In color video cameras, it is necessary to control white 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, a method is used in which the gain is adjusted so that the integral value of the screen color difference signals R-Y and B-Y becomes zero, as shown in, for example, Japanese Patent Application Laid-Open No. 62-35792 (HO4N9/73). It is being

FIG. 10 is a block diagram of a white 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, H
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).
The luminance signal Y and the red and blue color difference signals R- are then input to the color process and matrix circuit (6).
Y, B-Y are created 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 In the above method, when photographing a general subject, the value obtained by averaging the color difference signals of the entire screen is equivalent to that when photographing a completely white surface, and the color temperature of the light source is It is based on the empirical rule that when the color temperature changes, the color information of the entire screen changes only within the distribution range of the color temperature change.

By the way, in general shooting conditions, it is relatively common to experience a situation where a chromatic object with a color information signal outside the color temperature distribution range of the light source, such as a green, yellow, or magenta object, occupies a large portion of the screen. If the above-described method is adopted in such a case, the gain will change in a direction that cancels out these colors, resulting in a problem of unnatural image quality.

(d) Means for Solving the Problems The present invention is a white balance adjustment device that adjusts white balance based on a color information signal in a captured video signal. The feature is that when the color information signal is not within the color temperature distribution range, the color information signal is corrected to be within the color temperature distribution range, and more specifically, the screen is divided into a plurality of regions and the color information signal is The amount of signal is detected as a color evaluation value, and if there are areas with evaluation values outside the color temperature distribution range, the color evaluation values in these areas are corrected to the color temperature distribution range, and the color information of the entire screen is If the gain control amount calculated based on this is not in the color temperature distribution direction, it is corrected in the color temperature distribution direction, and the gain control amount is further weighted according to that direction,
The gain of each color signal is controlled by the gain control amount obtained in this way. Embodiments In the following, embodiments 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 a CCD (2), photoelectrically converted, and then separated into R, G by a color separation circuit (3).
, B are extracted as three primary color signals. The R and B signals among these three primary color signals are sent to the R and B amplifier circuits (4), respectively.
(5), it is input to the camera process and matrix (6) together with the G signal, and based on these, the luminance signal (Y) and the red, blue and celestial color difference signals (R-Y) and (B-Y) are created. The video signal is then supplied to a video circuit (7) and subjected to well-known processing. Further, each signal (RY) (B-Y) is also supplied to the selection circuit (21) at the same time.

The selection circuit (21) selects two of the color difference signals (R-Y) (B-Y) by the selection signal (Sl) from the timing circuit (25).
These signals are switched sequentially for each field.
Each field is output to the subsequent A/D converter (22) in the following order: RY)→(B-Y)→(RY)→... In addition, the selection signal (Sl) is connected to the synchronous separation circuit (24) as described later.
It is created based on the vertical synchronization signal obtained from

The A/D converter (22) receives the signal (R-Y) (B-Y) selected by the selection circuit (21) at a predetermined sampling period.
) and convert it to a digital value,
This value is output to the integrator (23). By the way, the timing circuit (25) uses the vertical and horizontal synchronizing signals from the camera process and matrix circuit (6) and the fixed oscillator output that drives the CCD (2) to adjust the imaging screen to an 8×8 screen as shown in FIG. 64 rectangular areas with the same area (Al
l), (A12), (A13)..., that is, (Aij
) (where i, j = integers from 1 to 8), and a switching signal (S2) for time-divisionally extracting the output of the selection circuit (21) in these regions for each region is sent to the integrator ( 23).

The integrator (23) receives the switching signal (S2) and adds the A/D converted values of the output of the selection circuit (21) for each region over one field period, that is, digitally integrates each of the 64 regions. When the integration for one field is completed, this integrated value is held in the memory (26) as a color evaluation value. As a result, the digital integral value for each region of the color difference signal (R-Y) corresponding to 64 regions in a certain arbitrary field is obtained as 64 color evaluation values (rij), and similarly in the next field, Color evaluation value (bij
) is obtained. In this way, the color difference signal (R-Y) (B-Y
), the color evaluation value (
r i j) (b i j) will be held in the memory (26). After this, the same operation as described above is repeated, and the color evaluation values (rij) (bij) are sequentially updated.

FIG. 11 shows the internal structure of this integrator (23) in more detail. Each A/D converted value is supplied to a switching circuit (61). This switching circuit (61) receives the switching signal (S2) and adds each A/D conversion value to an addition@(Pi) prepared for each area.
j) has the role of supplying data to the adder for the area where the corresponding sampling point exists. That is, if a sampling point of an arbitrary A/D conversion value is included in the area (All), this data is added to the adder (
pH). Furthermore, in the following, the adder (Pij)
is set for the area (Aij), and a total of 64 adders are prepared. A holding circuit (Qi
j) are arranged, and each added value is temporarily held in each holding circuit.The held data of each holding circuit is again input to the adder and added to the next A/D converted value. Further, each holding circuit is reset for each field, and only the data held immediately before this reset is supplied to the memory (26). Therefore, one set of adder and holding circuit constitutes one digital integrating circuit, and a total of 64 integrating circuits constitute the integrator (23), and 64 pieces from each holding circuit are added for each field. The digital integral value of each color difference signal is input to the memory (26) for each region.

Note that the color difference signal (R-
The reference level or zero level of Y)(B-Y) is preset to a value at which a completely white achromatic screen is obtained, and therefore, each A/D converter (22) /
The D conversion data includes not only positive values but also negative values, and when a completely white surface is photographed, each color evaluation value becomes zero.

The latest color evaluation value (rij(bij
) is supplied to the subsequent color evaluation value correction circuit (27).

The color evaluation value correction circuit (27) adjusts the color evaluation value of each area to the third
It is determined whether the color temperature is within the appropriate color temperature distribution range shown by the diagonal lines in the figure, and if it is not within the range, the corresponding color evaluation value is set perpendicular to the color temperature distribution direction as shown in Figure 4. A specific correction method will be explained below.

First, if we consider the relationship between the color temperature change of the light source and each color difference signal in general, when the color temperature of the light source illuminating a white subject changes, the color difference signal will change as shown in the light source color temperature axis in Figure 12. do.

Therefore, the color evaluation value (rij
), and the color evaluation value (bij) of (R-Y) is plotted on the vertical axis (Y-axis).
If we take and approximate the light source color temperature axis, we get Figures 3 and 4.
As shown in (Ll) in the figure, a straight line with slope (a) (Y
-aX... ■). Furthermore, this straight line (Ll
) is the color temperature distribution direction.

Centering around this straight line (Ll), there is no problem with the mill balance, that is, an acceptable and appropriate color temperature distribution range.
The diagonal line range can be set. Specifically, this range is:
Shift the straight line (Ll) to the Y axis and the negative direction (d) (c
) (d<c) two straight lines (B2) (B
This is the area surrounded by 3). Here, the straight line (B2) (B
3) are respectively expressed by the following equations.

B2: Y-aX10d ・=■ B3: Y=aX-c ・=■ In the color evaluation value correction circuit (27), these two straight lines (B
2) A correction operation is performed using the coordinate axes on which (B3) is drawn. The color evaluation values (bij) (rij) input for each area from the memo IJ (26) are (bijl r I N
is plotted on the coordinate axes as follows. Then, it is determined whether this plot point is within the appropriate color temperature distribution range, and if it is within the range, it is output as a new color evaluation value (HBij) (HRij) without any processing. For example, plot point Mll for area (All)
If (bll, rll) is at the position shown in Figure 4, it will be within the color temperature distribution range, so HB11 = b11, HRI
1-r Output as 11.

In addition, when a plot point is located in an area above the straight line (B2) outside the color temperature distribution range, a perpendicular line is drawn from this plot point to the straight line (Ll), and the coordinates of the intersection of this perpendicular line and the straight line (B2) are New color evaluation value (HBi j) (HRi
j) is output.

For example, plot point M12 for area (A12)
If (B12.R12) is in the position shown in Figure 4, Y= (-1/a)-(X-Bl 2)+R12-・■
Draw a perpendicular line (LH) shown by , find the intersection (T1) of this perpendicular line (LH) and straight line (B2) using formulas ■ and ■, and determine the coordinates (Xl, Yl) of this intersection point as the new color evaluation value (HRI2).
(HRI2). That is, HB12=X1, HR12
= Y1.

In addition, specifically, HB12=(b12+ar12-ad)/(aX+1)
HR12=a・(b12+ar12-ad)/(a”+
1)+d.

In addition, when a plot point is located outside the color temperature distribution range and below the straight line (B3), a perpendicular line is drawn from this plot point to the straight line (Ll), and the coordinates of the intersection of this perpendicular line and the straight line (B3) are is the new color evaluation value (HBij) (HRi
j) is output.

For example, plot point M13 for area (A13)
If (B13.R13) is in the position shown in Figure 4, Y= (-1/a) ・ (X-B13)+R13・■
Draw a perpendicular line (LL) shown by , find the intersection (T2) between this perpendicular line (LL) and straight line (B3) using the formula ■■, and determine the coordinates (X2.Y2) of this intersection as the new color evaluation value (HRI3).
(HRI3). That is, HB13=X2, HR1
3=Y2 is output.

In addition, specifically, HB13=(b13+ar13+ac)/(aX+1)
HR13=a・(b13+ar13+ac)/(a”+
1) -c.

The uncorrected or corrected new color evaluation values (HRlj and (HBij
) are sent to the screen evaluation circuit (28) and are calculated as the color evaluation values (Vr) (Vb) of the entire screen of each color difference signal based on the following equation (■■).

This formula is calculated by dividing the total sum of the color evaluation values (HRij) (HBij) of each of the 64 areas through the color evaluation value correction circuit (27) by the number of areas. This means that the average value is calculated as the screen color evaluation value (Vr) (vb).

The gain control circuits (29) and (30) output gain control signals (Gr) and (Gb) so that screen color evaluation values (Vr) and (Vb), which are color evaluation values for the entire screen, are both zero.

In addition to the above-mentioned modification method, it is also possible to use a method of modifying plot points located outside the proper color temperature distribution range in the direction of the origin, as shown in FIG. That is, instead of the perpendicular line, each plot point and the origin are connected by a straight line (L4) or (
L5) and connect these lines with the straight line (Ll) or (L
There is a method in which the X and Y components of the coordinates of the intersection point (T3) or (T4) with 2) are output as new color evaluation values (HBij) (HBij).

For example, plot point M for the aforementioned area (A12)
12 (b12.r12), the straight line (L4) becomes Y=(r12/b12)・X, and from this equation and equation ■, the coordinates of the intersection point (T3) are (d/(r12/b12-a)
, d-r12/(r12-a・b12)), and HB 12 =d/(r12/b12-a)HR12=
d-r12/(r12-a-b12).

In addition, in the above-mentioned embodiment, the color evaluation values themselves were modified so that the color evaluation values of the individual regions all fell within the appropriate color temperature distribution range, but instead of this, the color evaluation values themselves were modified as shown in FIG. It is also possible to modify the gain control signals themselves so that the gain control signals (Gr) and (Gb) output from the gain control circuits (29) and (30) fall within the color temperature distribution range. In FIG. 13, the color evaluation value (27) is removed and no correction is made to the color evaluation value, that is, HRi
It is characterized in that j=rij and HBij=bij, and instead, a gain control signal modification circuit (31) is inserted after the gain control circuits (29) and (30).

The correction method in the gain control signal correction circuit (31) at this time is the same as the correction of the color evaluation value described above, that is, the correction method between the gain control signals (Gr) and (Gb) and the appropriate color temperature distribution range. The relationship is as shown in Figure 6, and since the area is surrounded by two straight lines obtained by shifting the approximate straight line (Ll') to the Y axis, the gain control signals (Gr) and (Gb) If the points plotted on this coordinate axis are outside the color temperature distribution range like M3 and M4 in Figure 7, draw a perpendicular line to the straight line (Ll') and find the intersection with the adjacent straight line. and the coordinates of the obtained intersection are corrected gain control signals (G'r and (G'b
), which causes the R and B amplifier circuit (4) (
5) Gain control is performed.

Another correction method is to draw straight lines from the plotted points to the origin as shown in Figure 8, find the points of intersection between these straight lines and the adjacent straight line, and correct the coordinates of the obtained points of intersection. It is also possible to use the later gain control signals (G'r and (G'b)).

Furthermore, as shown in FIG. 9, there is also a method of using the coordinate axes in FIG. 6 as a table for determining the weighting amount (D).

That is, within the appropriate color temperature distribution range, D=2 (weighting amount (D
) is circled), D = 1 in the second and fourth quadrants excluding the appropriate color temperature distribution range, D = 0.5 in the first and third quadrants excluding the appropriate color temperature distribution range, and each plot The weighting amount (D) is determined according to the position of the point, and it is corrected as Gr = D - Gr Gb' = D - Gb, and the above-mentioned perpendicular line is used with emphasis on color information within the appropriate color temperature distribution range. It is also possible to obtain the same effect as the method described above.

It goes without saying that it is also possible to perform the above-described color evaluation value modification and gain control signal modification at the same time.

(g) Effects of the Invention As described above, according to the present invention, even when a scene containing colors outside the color temperature distribution range, which is not suitable for mill balance adjustment, is photographed, the mill balance does not shift and the mill balance can be properly balanced. Adjustments can be made.

[Brief explanation of drawings]

Figures 1 and 11 are circuit block diagrams of an embodiment of the present invention, Figure 2 is an explanatory diagram of screen division, Figure 3 is an explanatory diagram of color temperature distribution range, and Figures 4 and 5 are color diagrams. Figure 6 is an explanatory diagram of the modification of the evaluation value. Figure 6 is a relationship diagram of the gain control signal. Figures 7, 8, and 9 are diagrams of the modification of the gain control signal. Figure 10 is a circuit block diagram of a conventional example. FIG. 12 is a relationship diagram of color difference signals, and FIG. 13 is a circuit block diagram of another embodiment. (23)... Integrator, (27)... Color evaluation value correction circuit, (28)... Screen evaluation circuit, (29) (30)...
...Gain control circuit, (31)...Gain control signal correction circuit

Claims (6)

[Claims] (1) In a white balance adjustment device that adjusts white balance based on the color information signal in the captured video signal, when the color information signal is not within a certain distribution range of color temperature change within the captured screen,
A white balance adjustment device characterized in that the color information signal is corrected to be within the color temperature distribution range. (2) The white balance adjustment device according to claim 1, wherein the color information signal is corrected in a direction perpendicular to a color temperature distribution direction. (3) The white balance adjustment device according to claim 1, wherein the color information signal is corrected in the direction of an origin where the color information signal becomes zero. (4) Color evaluation value detection means for obtaining color information signal levels as color evaluation values for each color for each of a plurality of areas set by dividing an imaging screen; A color evaluation value correction means for correcting the color evaluation value for an area outside the color temperature distribution range and outputting the color evaluation value as it is, and outputting the color evaluation value for the area outside the color temperature distribution range; A white balance adjustment device comprising: a screen color evaluation value calculation means for calculating a color evaluation value; and a gain control means for controlling an amplification gain of each color signal based on the screen color evaluation value. (5) Color evaluation value detection means for obtaining the color information signal level of the imaging screen as a color evaluation value for each color; Screen color evaluation value calculation means for calculating a color evaluation value for the entire screen from the color evaluation value; and the screen. In a white balance adjustment device comprising gain control means for emitting a gain control signal for controlling the amplification gain of each color signal based on a color evaluation value, when the gain control signal is outside a certain color temperature change distribution range, the gain control is performed. A white balance adjustment device characterized by correcting a signal to be within the color temperature distribution range. (6) Color evaluation value detection means for obtaining the color information signal level of the imaging screen as a color evaluation value for each color; Screen color evaluation value calculation means for calculating a color evaluation value for the entire screen from the color evaluation value; and the screen. In a white balance adjustment device equipped with a gain control means for emitting a gain control signal for controlling the amplification gain of each color signal based on a color evaluation value, when the gain control signal is outside a certain distribution range of color temperature change, it is within the range. A white balance adjustment device that performs weighting and correction using a relatively small weighting amount.