JPH0230230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an auto white balance circuit for white balance adjustment for obtaining a composite color video signal with faithful color reproducibility to a subject image from a color imaging device.

Generally, in a color imaging device, three primary color signals obtained by imaging a subject, that is, a red primary color signal E _R ,
Luminance signal E _Y formed from green primary color signal E _G and blue primary color signal E _B and each color difference signal E _R −E _Y , E _B −E _Y
, by using an encoder to perform coding that conforms to the desired standard television format,
It is designed to output a composite color video signal. In order to reproduce an image with faithful color reproducibility to the subject image using the composite color video signal, each signal level of the three primary color signals must be adjusted to E _R = E _G = E when standard white is captured. It is necessary to accurately adjust the white balance so that _B is obtained.

Conventionally, the above-mentioned white balance adjustment involves an optical means that uses a color temperature correction filter that corrects the color temperature of the imaging light to adjust it in the optical system of the imaging device, and a signal level of the three primary color signals obtained as the imaging output. An electrical means for adjusting the signal processing system of the imaging device using an electrically controlled variable gain control amplifier is also used.

In a color imaging device, such as a studio camera, which is permanently installed at an imaging location with predetermined imaging conditions, white balance adjustment is performed in advance under the lighting conditions at the time of imaging. However, with portable color imaging devices used for on-site broadcasting of news programs, the color temperature of the imaging light changes depending on the imaging scene, so the color temperature correction filter must be replaced each time, or the color temperature correction filter must be replaced electrically. Without re-adjusting the balance, it would not be possible to broadcast the scene with faithful images. Therefore, especially when broadcasting news programs that require quick and faithful on-site broadcasting, it becomes a big burden for the cameraman to have to adjust the white balance for each screen one by one as described above. There is.

Therefore, the present invention stores information for each white balance adjustment when capturing images of multiple scenes with different color temperatures in advance in a memory circuit, and selectively reads the information from the memory circuit for each scene. The present invention provides an auto white balance circuit that enables continuous imaging in an appropriate state by instantly changing the white balance adjustment for the first time.

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

FIG. 1 is a block diagram showing the configuration of one embodiment of a signal processing circuit in a color imaging device to which an auto white balance circuit according to the present invention is applied.

In FIG. 1, an imaging unit 1 includes an optical system 4 consisting of a color temperature correction filter 2, a taking lens 3, etc.
By photoelectrically converting the imaging light incident through the three primary color signals E _R ,
Output E _G and E _B. Then, the above three primary color signals E _R ,
The red primary color signal E _R is supplied to the matrix circuit 7 and the first level comparator 8 through amplifiers 6R, 6G, and _6B, respectively, and the green primary color signal E _G is supplied to the matrix circuit 7 _and the first level comparator 8 through amplifiers 6R, 6G, and 6B, respectively. 1st and 2nd
Further, the blue primary color signal E _B is supplied to the matrix circuit 7 and the second level comparator 9.

Here, in each of the amplifiers 6R, 6G, and 6B, the gain of the amplifier 6G for the green primary color signal E _G used as a reference level during white balance adjustment is fixed, and the gain of the other amplifiers 6R, 6B is adjusted by a control signal. It is formed by a variable voltage controlled variable gain amplifier.

During white balance adjustment, the level comparators 8 and 9 compare the signal levels of the red primary color signal E _R and the blue primary color signal E _B with respect to the green primary color signal E _G for the standard white image, and calculate the level difference between them. Outputs each comparison output with the corresponding polarity. The comparison output of the first level comparator 8 is supplied to the first reversible counter 10 as an arithmetic control signal. Further, the comparison output of the second level comparator 9 is sent to the second reversible counter 11 as an arithmetic control signal.
is supplied to. When the level of the red primary color signal E _R is higher than the level of the green primary color signal E _G , a negative comparison output from the first level comparator 8 is given to the first reversible counter 10 as an arithmetic control signal. First reversible counter 10
performs a subtraction operation using the clock signal from the signal input terminal 12. Conversely, when the level of the red primary color signal E _R is lower than the level of the green primary color signal E _G ,
A positive comparison output from the first level comparator 8 is given to the first reversible counter 10 as an arithmetic control signal.
0 performs the addition operation using the clock signal from the signal input terminal 12. Similarly, when the level of the blue primary color signal E _B is higher than the level of the green primary color signal E _G , a comparison output of negative polarity is applied from the second level comparator 9 to the second reversible counter 11 as an arithmetic control signal. The second reversible counter 11 performs a subtraction operation using the clock signal from the signal input terminal 12. Conversely, the blue primary color signal
When the level of E _B is lower than the level of the green primary color signal E _G , a positive comparison output from the second level comparator 9 is given to the second reversible counter 11 as an arithmetic control signal, and The reversible counter 11 performs an addition operation using the clock signal from the signal input terminal 12.

The count value of the first reversible counter 10 is:
The data is supplied to the first storage circuit 13 as white balance adjustment data. Further, the count value of the second reversible counter 11 is supplied to the second storage circuit 14 as white balance adjustment data. Each of the memory circuits 13 and 14 has a plurality of memory addresses, and is formed of, for example, a random access memory (RAM). 1st above
The count values of the second reversible counters 10 and 11 are respectively the output of the first address generator 19 that generates the first address signal according to the type of the color temperature correction filter 2 of the optical system 4, and the output of the first address generator 19 and the imaging The image is stored at an address designated by the output of a second address generator 21 which is controlled by a scene changeover switch 20 and generates a second address signal according to the imaging scene. At this time, each counting output of the first and second reversible counters 10 and 11 is as follows:
the first memory circuit 13 and the second memory circuit, respectively.
from the storage circuit 14 to the digital-to-analog converter 1
5 and 16, and are supplied as gain control signals to the control terminal of the amplifier 6R for the red primary color signal E _R and the control terminal of the amplifier 6B for the blue primary color signal E _B , respectively. The gain of the amplifier 6R for the red primary color signal E _R is controlled based on the comparison output from the first level comparator 8 during white balance adjustment so that E _R = _EG . In addition, the amplifier 6B for the blue primary color signal E _B is
Similarly, the gain is controlled based on the comparison output from the second level comparator 9 so that E _G =E _B.
That is, each of the counting outputs of the reversible counters 10 and 11 is supplied from each of the storage circuits 13 and 14 as each gain control signal via each digital-to-analog converter 15 and 16 to each of the amplifiers 6R and 6.
By controlling the gain of B using the count values of the reversible counters 10 and 11, E _R =E _G =
Adjust the white balance so that E _B.

The comparison outputs of the level comparators 8 and 9 converge to zero in each of the storage circuits 13 and 14.
The count values of the reversible counters 10 and 11 corresponding to the gain control signals of the amplifiers 6R and 6B in the white balance state of E _R =E _G =E _B are stored as white balance adjustment data.

Here, in this embodiment, each of the memory circuits 1
3 and 14 each have 8 storage locations.
It is formed in RAM, and the above white balance adjustment operation is performed in advance under eight types of imaging conditions.
Count values of the first and second reversible counters 10 and 11, which serve as gain control signals for the amplifiers 6R and 6B, can be stored in the first and second storage circuits 13 and 14 as white balance adjustment data. It's summery. Further, the memory locations of each of the memory circuits 13 and 14 are configured to obtain a first address signal corresponding to the type of color temperature correction filter 2 of the optical system 4 from the first address generator 19, and to switch the imaging scene. The second address signal specified by the switch 20 is transmitted to the second address generator 21.
and is specified by each address signal.

In this embodiment, for example, when photographing two locations within the color temperature correction range that can be corrected by the desired color temperature correction filter 2, white balance adjustment is performed at each imaging location using a feedback loop during rehearsal. Each white balance adjustment data, that is, each count value of the first and second reversible counters 10 and 11 is stored in the first and second storage circuits 13 and 14 corresponding to the imaging conditions, that is, the type of color temperature correction filter and the imaging location. The first address generator 19 and the second address generator 21 are controlled according to the imaging location during actual imaging, and the first address generator 19 and the second address generator 21 are
The white balance adjustment data (count values of the first and second reversible counters 10 and 11 at the time of rehearsal) stored in the second storage circuits 13 and 14 is read out, and the amplifier 6R,
By supplying the signal to the gain control terminal of 6B, white balance can be achieved regardless of the feedback loop, and even if the imaging location changes, white balance can be achieved instantly without waiting for the feedback loop to converge. During actual imaging, by simply operating the scene changeover switch 20, the white balance can be instantly adjusted and imaging can be continued in an appropriate state.

Furthermore, the specific operation of the auto white balance circuit of this embodiment will be described using as an example a case where an object to be imaged is imaged outdoors and indoors.

For example, first, a standard white image for white balance adjustment is captured outdoors. When the standard white color is imaged, the signal level of the red primary color signal E _R output from the amplifier 6R is greater than the signal level of the green primary color signal E _G output from the amplifier 6G, and Assume that the signal level of the blue primary color signal E _B outputted is smaller than the signal level of the green primary color signal E _G outputted from the amplifier 6G.

At this time, if the first reversible counter 10 performs a counting operation from, for example, the initial value [100], the signal level of the red primary color signal E _R output from the amplifier 6R and the green signal output from the amplifier 6G are [99], [98], [97]... are supplied as a calculation control signal from the first level comparator 8 which compares the signal level of the primary color signal E _G with a comparison output having a negative level. Perform the subtraction operation as follows. The output of the reversible counter 10 is supplied to the first storage circuit 13, and is also sent to the gain control terminal of the amplifier 6R for the red primary color signal E _R as a gain control signal via the digital-to-analog converter 15. Supplied. The gain of the amplifier 6R is controlled by the gain control signal. The reversible counter 10 receives the red primary color signal.
The subtraction operation is continued until the signal level of E _R becomes equal to the signal level of the green primary color signal E _G , and the output of the first level comparator 8 converges to 0, and the amplifier 6R is in a white balanced state.
It converges to a count value corresponding to the gain of, for example, [80]. When the output of the level comparator 8 converges to 0, the count value [80] of the reversible counter 10 is stored as white balance adjustment data at the first address of the storage circuit 13 (for example, when the color temperature correction filter 2 The imaged scene is
The SCN is stored and held at the address corresponding to the first imaging scene.

Further, if the second reversible counter 11 performs a counting operation from the initial value [100] in the same manner as the first reversible counter 10, the signal level of the blue primary color signal E _B output from the amplifier 6B By supplying a comparison output having a positive level as an arithmetic control signal from the second level comparator 9, which compares the signal level of the green primary color signal E _G outputted from the amplifier 6G,
Addition operations are performed in the manner of [101], [102], [103], and so on. The output of this reversible counter 11 is supplied to the second storage circuit 14, and is also sent to the gain control terminal of the amplifier 6B for the blue primary color signal E _B as a gain control signal via the digital-to-analog converter 16. Supplied. The amplifier 6B is
The gain is controlled by the gain control signal. The reversible counter 11 continues the addition operation until the signal level of the blue primary color signal E _B becomes equal to the signal level of the green primary color signal E _G , and the output of the level comparator 9 converges to 0 and white balance is achieved. The count value converges to, for example, [120], which corresponds to the gain of the amplifier 6B in this state. When the output of the level comparator 9 converges to 0, the count value [120] of the reversible counter 11 is used as white balance adjustment data in the memory circuit 1.
4 (for example, color temperature correction filter 2 is the first filter, and imaging scene SCN is the first address)
(address corresponding to the imaging scene) and is retained.

Next, a standard white image for white balance adjustment is captured indoors. When standard white is imaged indoors, the signal level of the red primary color signal E _R output from the amplifier 6R is smaller than the signal level of the green primary color signal E _G output from the amplifier 6G;
It is assumed that the signal level of the blue primary color signal E _B output from the amplifier 6B is higher than the signal level of the green primary color signal E _G output from the amplifier 6G.

At this time, if the first reversible counter 10 performs a counting operation from, for example, the initial value [100], the signal level of the red primary color signal E _R output from the amplifier 6R and the green signal output from the amplifier 6G are [101], [102], [103], etc. are supplied as a calculation control signal from the first level comparator 8 which compares the signal level of the primary color signal E _G with a comparison output having a positive level. Perform the addition operation as follows. The output of the reversible counter 10 is supplied to the first storage circuit 13, and is also sent to the gain control terminal of the amplifier 6R for the red primary color signal E _R as a gain control signal via the digital-to-analog converter 15. Supplied. The gain of the amplifier 6R is controlled by the gain control signal. The reversible counter 10 receives the red primary color signal.
The addition operation continues until the signal level of E _R becomes equal to the signal level of the green primary color signal E _G , and the output of the first level comparator 8 converges to 0, and the amplifier 6R is in a white balanced state.
converges to a count value corresponding to the gain of, for example, [110]. When the output of the level comparator 8 converges to 0, the count value [110] of the reversible counter 10 is stored as white balance adjustment data at the second address of the storage circuit 13 (for example, when the color temperature correction filter 2 address whose imaging scene SCN corresponds to the second imaging scene in the filter)
stored and retained.

Further, if the second reversible counter 11 performs a counting operation from the initial value [100],
A comparison output having a negative level is output from the second level comparator 9, which compares the signal level of the blue primary color signal E _B output from the amplifier 6B and the signal level of the green primary color signal E _G output from the amplifier 6G. is supplied as an arithmetic control signal, subtracting operations like [99], [98], [97], etc. are performed. The output of the reversible counter 11 is supplied to the second storage circuit 14, and is also sent to the gain control terminal of the amplifier 6B for the blue primary color signal E _B as a gain control signal via the digital-to-analog converter 16. Supplied. The amplifier 6B is
The gain is controlled by the gain control signal. The reversible counter 11 continues the subtraction operation until the signal level of the blue primary color signal E _B becomes equal to the signal level of the green primary color signal E _G , and the output of the level comparator 9 converges to 0 and white balance is achieved. The count value converges to, for example, [70], which corresponds to the gain of the amplifier 6B in this state. When the output of the level comparator 9 converges to 0, the count value [70] of the reversible counter 11 is stored as white balance adjustment data at the second address of the storage circuit 14 (for example, the color temperature correction filter 2
is the second filter, and the imaging scene SCN is stored and held at the address corresponding to the second imaging scene.

In this way, each of the counters 10 and 14 stores the white balance adjustment data corresponding to each imaging scene and each color temperature filter type in the addresses corresponding to each imaging scene and each color temperature filter type in each of the storage circuits 13 and 14, respectively. A count value of 11 is stored in advance.

When the object to be imaged is actually imaged outdoors, the first address generator 19 generates a readout address for each of the storage circuits 13 and 14 corresponding to the outdoor color temperature filter. At the same time, the second address generator 21 generates a read address for each of the storage circuits 13 and 14 corresponding to the imaging scene and supplies it to each of the storage circuits 13 and 14. Based on these read addresses, the count values [80] and [120] of the counters 10 and 11, which were previously stored in the storage circuits 13 and 14 as white balance adjustment data, are read out and read out as the digital data. The signal is supplied as a gain control signal to each gain control terminal of the amplifiers 6R and 6B via analog converters 15 and 16. Therefore, in the white balance adjustment data [80] and [120] read out from the respective storage circuits 13 and 14 in accordance with the color temperature of the light to be imaged outdoors and the type of color temperature filter,
The gains of the amplifiers 6R and 6B are instantly determined,
White balance can be set to an appropriate state instantly.

In addition, when the object to be imaged is actually imaged indoors, the readout address of each of the storage circuits 13 and 14 corresponding to the indoor color temperature filter is set to the first address.
The second address generator 21 generates a read address for each of the storage circuits 13 and 14 corresponding to the imaging scene and supplies the address to each of the storage circuits 13 and 14. It is supplied to each memory circuit 13, 14. Based on these read addresses, the count values [110] and [70] of the respective counters 10 and 11, which have been previously stored in the respective storage circuits 13 and 14 as white balance adjustment data, are read out and the digital The signal is supplied as a gain control signal to each gain control terminal of the amplifiers 6R and 6B via analog converters 15 and 16. Therefore, the white balance adjustment data [110] and [70] read out from the storage circuits 13 and 14 according to the color temperature of the light to be imaged indoors and the type of color temperature filter are used to instantly adjust the amplifier 6R. , 6B are determined, and the white balance can be instantly set to an appropriate state.

In this way, the count values of the counters 13 and 14 are stored in the storage circuits 13 and 14 in advance as white balance adjustment data corresponding to multiple scenes in which the color temperature of the imaged light differs and the type of color temperature correction filter to be used. Then, during actual imaging,
The gain control of the amplifiers 6R and 6B is performed by reading count values corresponding to a plurality of scenes with different color temperatures of imaged light and the type of color temperature correction filter used from the storage circuits 13 and 14. Even if the imaging scene changes from indoors to outdoors, for example, the white balance can be instantly adjusted by simply switching the first and second address generators 19 and 21, without having to image the standard white color for white balance adjustment and readjust the white balance. can be brought into an appropriate state.

Incidentally, the imaging conditions can also be displayed in the viewfinder 22 using address signals from each of the address generators 19 and 21.

In this way, each amplifier 6R, 6G,
Three primary color signals E _R , E _G , and E _B outputted from 6B are supplied to the matrix circuit 7 .

The matrix circuit 7 synthesizes the three primary color signals E _R , E _G , E _B at a ratio defined in a predetermined standard television system to form a luminance signal E _Y , and also generates each color difference signal E _R − Form E _Y , E _B −E _Y. The above color difference signals E _R -E _Y , E _B -E _Y are supplied to a balanced modulator 28. The balanced modulator 28 converts the color subcarrier _SC into each of the above color difference signals E _R -E _Y , E _B
A chroma signal E _C is formed by modulating -E _Y. This chroma signal E _C is sent to the signal mixer 29
It is mixed with the luminance signal _EY . Then, from the output terminal 30 of the signal mixer 29, a predetermined standard television system, for example, NTSC (National
Outputs a composite color video signal based on the Television System Committee) system.

As described above, the auto white balance circuit according to the present invention includes an imaging section that forms three primary color signals from light incident through the color temperature correction filter, and a first and second primary color signal of the three primary color signals output from the imaging section. first and second variable gain circuits that control the signal level of the second primary color signal; and a first variable gain circuit that compares the signal level of the output signal of the first variable gain circuit with the signal level of the third primary color signal. a second level comparator that compares the signal level of the output signal of the second variable gain circuit with the signal level of the third primary color signal, and an output of the first level comparator. a first counter whose addition operation and subtraction operation are switched according to the polarity of the signal; and a second counter whose addition operation and subtraction operation are switched according to the polarity of the output signal of the second level comparator; The first and second counters have a plurality of memory addresses and are output from the first and second counters.
and store the first and second count values respectively in the first and second counts.
and an address signal generator that specifies write and read addresses for the first and second memory circuits, and the color temperature is set in advance. Images are captured under a plurality of different imaging conditions, and the first and second count values output from the first and second counters are sent to the address signal generators of the first and second storage circuits, respectively. Therefore, it is stored at the specified write address, and when taking an image,
The address signal generator specifies a readout address according to the imaging conditions, and the first and second
The first and second data stored in the memory circuit of
By reading out the count value of , and supplying the count value to each control terminal of the first and second variable gain circuits, white can be set by simply selecting and reading out the stored data. Appropriate and well-balanced imaging can be continued. Further, since the gain control signal of the variable gain circuit, that is, the white balance adjustment data is stored in each storage circuit in advance, it is possible to instantly adjust the white balance and continue proper imaging. Moreover, in the auto white balance circuit according to the present invention, a feedback loop is formed when each count value of the first and second counters is stored in the first and second storage circuits. Therefore, the accuracy of each count value, that is, the white balance adjustment data stored in each of the above-mentioned storage circuits can be made extremely high.

Therefore, according to the present invention, it is possible to provide an auto white balance circuit that is highly effective when applied to a portable imaging device such as an imaging device for news reports.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an auto white balance circuit according to the present invention. 1... Imaging unit, 2... Color temperature correction filter, 6
R, 6G, 6B...Amplifier, 7...Matrix circuit, 8, 9...Level comparator, 10, 11
... Reversible counter, 13, 14 ... Memory circuit, 1
5,16...Digital-to-analog converter, 19,
21...Address generator, 20...Scene change switch, 28...Balanced modulator, 29...Signal mixer.

Claims (1)

[Scope of Claims] 1. An imaging section that forms three primary color signals from light incident through a color temperature correction filter, and signals of first and second primary color signals among the three primary color signals output from the imaging section. first and second variable gain circuits that control the level; a first level comparator that compares the signal level of the output signal of the first variable gain circuit with the signal level of the third primary color signal; a second level comparator that compares the signal level of the output signal of the second variable gain circuit and the signal level of the third primary color signal; a first counter whose operation and subtraction operation are switched; and a second counter whose addition operation and subtraction operation are switched according to the polarity of the output signal of the second level comparator, each having a plurality of memory addresses; , the first and second counters output from the first and second counters.
and store the first and second count values respectively in the first and second counts.
a first and second memory circuit that supplies signals to each control terminal of the variable gain circuit; and an address signal generator that specifies write and read addresses of the first and second memory circuits; Images are captured under a plurality of different imaging conditions, and the first and second count values output from the first and second counters are sent to the address signal generators of the first and second storage circuits, respectively. Accordingly, the information is stored at the designated write address, and when imaging, the address signal generator designates a read address according to the imaging conditions, and the data is stored in the first and second storage circuits. An auto white balance circuit, characterized in that it reads out the first and second count values and supplies the count values to respective control terminals of the first and second variable gain circuits.