JPH03198494A - White balance controller - Google Patents

Abstract

PURPOSE:To prevent white balance from being deviated in a direction to cancel green even when a picture including much green is photographed by reducing the degree of a contribution to white balance control for a color information signal in an area, where a greed component exceeds a prescribed value, in a picked-up picture rather than the other area. CONSTITUTION:The picture is divided into plural areas and for each area, the amount of a chrominance signal is detected as color evaluation values rij and bij. Concerning a certain area, when the color evaluation values rij and bij are inputted to a color evaluation value control circuit 27, the respective color evaluation values are compared with an R threshold value or a B threshold value. When the both evaluation values are smaller than the respective threshold values, it is decided that an object is green, and a switching signal S is inputted to a switching circuit 45. Then, the both color evaluation values are attenuated only for a fixed amount by R and B attenuators 48 and 49 and outputted to an output terminal. Thus, even when photographing the picture including much green not suitable for white balance control, the white balance is not deviated in the direction to cancel green and the white balance control can suitably be executed.

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 a color video camera, it is necessary to control the mill balance in order to correct for differences in the wavelength distribution of light due to the light source.

This control includes red (hereinafter referred to as R), blue (hereinafter referred to as B), green (hereinafter referred to as G).
) is performed by adjusting the gain of each color signal so that the ratio of the three primary color signals becomes l:l:l. 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). ing.

FIG. 6 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) converts R, G,
The B color signal is extracted as the three primary color signals, and the G color signal is directly
The R and B color signals are transmitted through the R amplification circuit (4) and the B amplification circuit (5).
) is input to the camera process and matrix circuit (6), and the luminance signal Y and the red and blue color difference signals R are input to the camera 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).
(18), the gain control circuits (13) and (14) are integrated for a sufficiently long time so that the result becomes zero.
The gain of each variable gain amplifier circuit (4), (5) is adjusted.

(c) Problems to be solved by the invention The above-mentioned method is based on the empirical rule that 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. Therefore, the photographic screen must contain each color on average.

By the way, in general shooting conditions, it is relatively common to experience situations where many parts of the screen, such as grass or plants, are green, and if you use the above method in such cases, the green color will be canceled out. The gain changes, causing problems such as fading of grass and the like, resulting in unnatural image quality.

Furthermore, this phenomenon will be explained theoretically. Generally speaking, when considering the relationship between color temperature changes of a light source and each color difference signal, when the color temperature of a light source illuminating a white subject changes, the color difference signal changes as shown in the light source color temperature axis in Figure 4. . Therefore,
The color difference signals appearing in the first and third quadrants that do not include the light source color temperature axis do not reflect the color temperature of the light source;
For information when adjusting the mill balance: 'ItII! It is preferable not to do so. However, in the color difference signal of the area including the green subject, both R-Y and BY are negative, so it is considered to be located in the third quadrant, and it can be said that it is not suitable for white balance adjustment.

(d) Means for Solving the Problems The present invention divides the screen into a plurality of regions, detects the amount of color signals in each region as a color evaluation value, and detects the amount of color signals for each region when the green color evaluation value is equal to or higher than a certain value. If there are areas, the contribution of color evaluation values in these areas to the entire screen is reduced.

(E) Function The present invention prevents the white lance from shifting in the direction of canceling out the green color even when a screen containing a large amount of green color is photographed.

(f) Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of an automatic mortar lance 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, both the signals (RY) and (B-Y) are simultaneously supplied to the selection circuit (21).

The selection circuit (21) selects the color difference signals (R-Y) and (B-Y) according to the selection signal (Sl) from the timing circuit (25).
) is used to sequentially select one of the two signals for each field, (RY) → (B-Y) → (RY) →...
・A/D converter (22) in the subsequent stage for each field
is output to. Note that the selection signal (Sl) is created based on the vertical synchronization signal obtained from the synchronization separation circuit (24) as described later.

The A/D converter (22) converts the signal (R-Y) (
B-Y) is sampled and slightly converted into digital data, and this value is output to an 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 control the image pickup screen into 64 8x8 pixels as shown in Figure 3. rectangular area (All), (A1
2), (A13)... and outputs a switching signal (S2) to the integrator (23) for time-divisionally extracting the output of the selection circuit (21) in these regions for each region.

The integrator (23) receives the switching signal (S2) and adds the A,/D conversion values of the output of the selection circuit (21) over one field for each area, that is, adds the digital values for each of the 64 areas. Integration is performed, and 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, digital integral values for each region of the color difference signal (R-'N') corresponding to 6.1 regions in a certain arbitrary field are obtained as 64 color evaluation values (rlj). Furthermore, in the next field, the color difference signal (B-Y) is selected by the selection circuit (21), so as a result of the integration of the adder (23), the digital value for each area of the color difference signal (B-'1') is The integral value is obtained as 64 color evaluation values (bij). In this way, when the integration of the two fields of color difference signals (R-Y) (B-Y) is completed, the color evaluation value bij)
(bij) will be held in the memory (26).

After this, the same operation as described above is repeated, and the color evaluation value (rij) is updated in the next field, and the color evaluation value (bij) is updated in the next field.

The latest color evaluation value (rij) (bi
'') is supplied to the subsequent color evaluation value adjustment circuit (27). The color evaluation value adjustment circuit (27) determines whether the subject is green based on the color evaluation value of each area, and if it is green, reduces the corresponding color evaluation value level by a predetermined amount (P). , is configured as shown in FIG.

The color evaluation values (rij) (bij) of each area are input to the R comparator (42) and the B comparator (43), respectively, and the R and B threshold Vi (Nr) (Nb), and when each color evaluation value is smaller than each darkness value, a comparison signal (S++
) (S++), and these comparison signals are sent to an AND circuit (
44), the H level switching signal (S) is input from the AND circuit (44) to the switching circuit (45) only when both comparison signals are issued.

Here, the R and B thresholds (Nr) (Nb) are preset as darkness values when the subject can be recognized as green, but as mentioned above, the flesh color difference signals in the area containing the green subject are both negative. If we consider that it is located in the 3rd @ limit of Figure 4, both the R and B thresholds (Nr) (Nb) are zero (Nr=Nb).
=O), it becomes possible to recognize a green subject.

The switching circuit (45) includes two switches (46) (4
7), and the swifter (46) has a color evaluation value (ri
The fixed contact (46a) to which the signal j) is input, and the R attenuator (46a)
The switch (47) has the function of selectively connecting the fixed contact (=16b) coupled to the output terminal (8) or the fixed contact (46c) coupled to the output terminal (50), and the switch (47)
A function to selectively connect the fixed contact (47a) to which the signal bij) is input, and the fixed contact (47b) coupled to the B attenuator (49) or the fixed contact (47c) coupled to the output terminal (51). have.

Both switches (46) and (47) are switching signals (S)
When the switching signal (S) is at I level, the color evaluation values (rij) (biJ) are output to the fixed contacts (46c) and (47c) side, respectively, and the output terminals (50
) (51), and when the level is H, the respective fixed contacts (
46b) (47b) side, and the color evaluation value (ri
j) (bij) is input to the R and B reducer (48) (49).

The R and B attenuators (48) and (49) calculate a preset constant amount (from the input color evaluation values (rij) and (bij).
P), (rij −P), (bij P
) is calculated and output to the output terminals f(50)(51). Here, the certain amount (P) is determined in advance through experiments so that when a green subject is photographed, it can be sufficiently recognized that the image quality is not unnatural.

Next, the operation of the above-mentioned color evaluation value adjustment circuit (27) will be explained. Color evaluation value (rij) (+) for a certain area!
J) is input to the color evaluation value adjustment circuit (27), each color evaluation value is compared with the R threshold or the B threshold, and when both are smaller than each threshold, it is determined that the subject is green,
A switching signal (S) is input to a switching circuit (45), and the two color evaluation values are attenuated by a certain amount (P) by R and B attenuators (48) and (49), and then outputted to an output terminal.

Furthermore, if at least one of the color evaluation values (rij) (bij) is sufficiently larger than the threshold value, it is determined that the subject is not green, and the two color evaluation values are sent to the output terminal (50 ) (51).

The non-attenuated or attenuated color evaluation values derived from the output terminals (50) and (51) are sent to the screen evaluation circuit (28) and are calculated for the entire screen of each color difference signal based on the following equations (1) and (2). The color evaluation value is calculated as screen color evaluation fa (Vr) (Vb).

\・'r=Σ Σ rij/64...
・(1)+=1 3=1 vb=Σ Σ b ij/64 --(2) lヰ1 J=1 This equation (+) (2) is 6 after passing through the color evaluation value adjustment circuit (27), The total sum of all the color evaluation values (rij) (bij) of each region is divided by the number of regions, and the average value for one region is calculated as the screen color evaluation value.

The gain control circuits (29) and (30) operate the R and B amplifier circuits (4) and (5) so that the screen color evaluation value (~'r) (Vb), which is the color evaluation value of the entire screen, is both zero. The gain of each is controlled. When the screen color evaluation values (Vr) (Vb) become zero in this way, it means that the mill balance adjustment is completed.

The significance of the automatic mill balance operation as described above will be explained using a photographic screen as shown in FIG. 5 as an example. In this shooting screen, the proportion of the leaves in the entire screen is large, and the color distribution over the entire screen is biased.As shown in the conventional example, unless the color evaluation value in the green area is attenuated, the green of the leaves will be distorted. The balance of the mortar shifts in the direction of counteracting. Therefore, in the present invention, since the screen is divided as described above and the color evaluation value of the green area is attenuated, the degree of contribution of the color evaluation value of the shaded area in FIG. 5 to the screen color evaluation value can be reduced. In general, the screen color evaluation value does not shift toward the green side, and appropriate white balance adjustment is performed.

In addition, as a method to reduce the contribution of each area's color evaluation value to the entire screen, in addition to directly reducing the color evaluation value of each area, weighting is performed for each area to reduce the weight in the green area. There are other possible methods.

Furthermore, it is also possible to realize this judgment using fuzzy inference, focusing on the fact that the judgment itself of whether a green object exists contains extremely large ambiguity.

(g) Effects of the Invention As described above, according to the present invention, even when a screen containing a large amount of green, which is not suitable for milling balance adjustment, is photographed, the white balance does not shift in the direction of canceling out the green, and the proper milling balance is maintained. Adjustments can be made.

[Brief explanation of drawings]

1 and 2 are circuit block diagrams of an embodiment of the present invention, FIG. 3 is an explanatory diagram of screen division, FIG. 4 is an explanatory diagram of color temperature change of a light source, and FIG. 5 is an example of a photographing screen. FIG. 6 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 where the green component exceeds a predetermined value within the captured image screen A white balance adjustment device characterized by reducing the white balance compared to other areas. (2) 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 the imaging screen, and color evaluation for areas where the green level does not exceed a predetermined value. A color evaluation value adjusting means for outputting a color evaluation value of an area equal to or higher than a predetermined value by a predetermined amount while leaving the value unchanged; and a screen for calculating a color evaluation value for the entire screen from the output of the color evaluation value adjustment means. A white balance adjustment device comprising a color evaluation value calculation means and a gain control means for controlling the amplification gain of each color signal based on the screen color evaluation value.