JP4145704B2 - White balance circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a white balance circuit used in a television camera device or the like.
[0002]
[Prior art]
Conventionally, in a television camera apparatus, light incident from a lens is divided into three systems of Rch, Gch, and Bch (R represents red, G represents green, B represents blue, ch represents channel, and so on). After the separation, it is converted into an electric signal by an image pickup device such as a CCD (Charge Coupled Device), and various processes are performed. Normally, television cameras for business use and broadcasting are adjusted so that a white subject is photographed in a white color when used under a light source having a color temperature of 3200K. For this reason, when shooting under a light source with a color temperature other than 3200K, such as when shooting outdoors under a clear sky or under a fluorescent lamp, a white subject is colored. Therefore, when photographing under a light source with a color temperature other than 3200K, it is necessary to perform white balance adjustment so that a white subject is photographed white.
[0003]
In order to perform white balance adjustment, there is a method using an optical color correction filter. However, since the adjustment range of the color temperature is very wide, it cannot be completely corrected only by the optical color correction filter. Therefore, generally, after performing rough adjustment using an optical color correction filter, a white object is photographed in white by finely adjusting the electrical amplifier gain of each signal of Rch, Gch, and Bch. Adjust the white balance as follows. When television cameras first appeared, engineers such as video engineers performed these white balance adjustments while viewing the display waveform of the measuring instrument, but in recent years there are many devices that automatically perform this white balance adjustment.
[0004]
There is no problem in the range where a general subject is photographed using the TV camera device with the white balance adjusted in this way, but a high brightness white region exceeding the processing range of the TV camera device is set. When a subject included in a part is photographed, there is a problem that the white area is colored even though white balance adjustment is performed. In relation to such a problem, Patent Document 1 proposes a white balance adjustment circuit used in a color imaging device that assumes still image processing. Hereinafter, the cause of the above problem will be described using a conventional white balance adjustment circuit (FIGS. 3, 4, and 5), and then the difference from Patent Document 1 and the significance of the present invention will be described.
[0005]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2000-13808 (full specification, full view)
[0006]
[Problems to be solved by the invention]
FIG. 3 shows a white balance adjustment circuit in the prior art. The configuration includes: (1) gain adjustment circuits 31R, 31B, and 31B corresponding to Rch, Gch, and Bch, (3) MPU 34 as control means for each gain adjustment means, and (3) compressing the signal level within a predetermined value. A gamma correction circuit 32 and a KNEE circuit 33 are included. The television camera apparatus for commercial broadcasting is a circuit capable of processing signals with an amplitude of 400 to 600 [%] when the maximum value of the amplitude of an electric signal normally used is 100 [%]. . Then, as shown in FIG. 4, the gamma correction circuit 32 and the KNEE 33 circuit perform a process of compressing the signal having a maximum amplitude of 400 to 600 [%] to 105 [%] with a nonlinear characteristic.
[0007]
Here, it is assumed that the white balance adjustment is performed on the assumption that shooting is performed under a light source with a color temperature other than 3200K in a television camera apparatus capable of performing signal processing with a maximum amplitude of 600 [%]. Normally, in white balance adjustment, the gain of Gch is set to 1.0 and the gains of Rch and Bch are adjusted. For example, it is assumed that the electrical amplifier gains of the Rch, Gch, and Bch signals are set as shown in FIG. 5 due to the white balance adjustment. That is, the gain value of the Rch gain adjustment circuit 51R is 1.5 times, the gain value of the Gch gain adjustment circuit 51G is 1.0 times, and the gain value of the Bch gain adjustment circuit 51B is 0.5 times. Assume that control is performed by the MPU 52. It is assumed that a white area with a very high luminance that has an amplitude of 600 [%] in this state exists in a part of the subject. First, Gch has no change because the gain is 1.0 times. Rch has a gain of 1.5 times, so the amplitude is 900 [%] in the calculation. However, since it is a television camera that performs signal processing with a maximum amplitude of 600 [%], it is 600 [%]. The amplitude is limited. Thus, the amplitude of Rch and Gch is 600 [%], whereas the amplitude of Bch is about 300 [%]. For this reason, the balance of the Rch, Gch, and Bch in the portion compressed by the gamma correction circuit and the KNEE circuit is lost, and the white area is not white but is colored.
[0008]
Conventionally, in order to solve such problems, for example, Japanese Patent Laid-Open No. 2000-13808 discloses a method for setting a clip level from a white balance adjustment coefficient after white balance adjustment, a signal level of a specific color, and the like. Yes. However, since a TV camera is shooting a moving image, it is necessary to end various video processes during one frame or one field period. Although it differs depending on the standard of the television signal, one frame or one field is usually about 1/25 second to 1/60 second. In order to adapt a publicly available method with a television camera, a very large circuit is required at the current state of the art.
[0009]
Therefore, the present invention has been made in view of the above problems, and the significance thereof is that, in a state in which white balance adjustment is performed, a part of a very high brightness white region that exceeds the processing range of the TV camera device is used. A white balance circuit that has the function of maintaining the white color of the area and can be used with a TV camera device with the current technical level even if the subject is photographed. It is to provide.
[0010]
[Means for Solving the Problems]
The white balance circuit according to the present invention includes:
A plurality of gain adjusting means for adjusting the gains of R (red), G (green) and B (blue) signals output from the image sensor, and provided in a subsequent stage of the plurality of gain adjusting means according to the luminance of the subject A white balance circuit for an imaging apparatus comprising a plurality of color signal limiting means for limiting each color signal level within a predetermined limit reference value and a control means for setting a limit reference value from the gain,
All the restriction reference values are uniformly set to a value obtained by multiplying the smallest value among the gains of the respective color signals used at the time of white balance adjustment by a signal processing upper limit value specific to the imaging apparatus.
[0011]
In addition, the white balance circuit according to the present invention is preferably used for the television camera device that outputs a video signal for each frame or field, among the imaging devices.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of the present invention. The configuration is the same as that shown in FIG. 3. The Rch gain adjustment circuit 11R corresponding to Rch, the Gch gain adjustment circuit 11G corresponding to Gch, and the Bch gain adjustment circuit 11B corresponding to Bch (claims) Corresponding to “Gain adjustment means” described in the scope of (1), the same shall apply hereinafter), (1) MPU 15 for controlling each of the gain adjustment means (corresponding to “Control means” described in the claims, and so on) (2) A gamma correction circuit 13 and a KNEE circuit 14 for compressing the signal level within a predetermined value are included. Further, as configurations corresponding to the above-mentioned problems, (1) an Rch limiter circuit 12R, a Gch limiter circuit 12G, and a Bch limiter circuit 12B for limiting the signal of each channel to a predetermined level (described in the claims) Corresponding to “color signal limiting means”. The control line from the MPU 15 is also connected to each limiter circuit, that is, the Rch limiter circuit 12R, the Gch limiter circuit 12G, and the Bch limiter circuit 12B in addition to the gain adjustment circuits shown in FIG. It has a configuration.
[0013]
FIG. 2 shows the main part of the configuration of FIG. 1 extracted for detailed explanation. The correspondence is as follows: ■ Each channel gain adjustment circuit 21R, 21G, 21B in FIG. 2 corresponds to the adjustment circuits 11R, 11G, and 11B, and each of the ch limiter circuits 22R, 22G, and 22B in FIG. 2 corresponds to each of the limiter circuits 12R, 12G, and 12B in FIG. 1, and the MPU 23 in FIG. This corresponds to the MPU 15 in FIG.
[0014]
Next, the operation of this embodiment will be described with reference to FIGS. When using a TV camera device, an engineer such as a video engineer performs white balance adjustment while watching a waveform on a measuring instrument or automatically, as in the conventional technique. Here, it is assumed that the white balance adjustment is performed for photographing under a light source with a color temperature other than 3200K in a television camera apparatus that performs signal processing with a maximum amplitude of 600 [%] according to the example already described.
[0015]
In FIG. 1, for example, when white balance adjustment is automatically performed, when a white balance adjustment button (not shown) is pressed, the MPU 15 causes each channel gain adjustment circuit, that is, Rch gain adjustment circuit 11R, Gch gain adjustment circuit 11G. , And a control signal related to gain adjustment so that the ratio of the signal level of each channel becomes equal to the gain adjustment circuit 11B for Bch. The MPU 15 also sends a control signal related to the limit reference value calculated from the gain adjustment result to the limiter circuit of each channel. When the signal level input to the limiter circuit of each channel is within the range of the limit reference value from the MPU, the amplitude is not limited by the limiter circuit of each channel, and input from the limiter circuit of each channel. The signal is output as it is. That is, the same operation as a normal white balance circuit is performed. Thereafter, the signal level of each channel signal is compressed to a predetermined value by a known gamma correction circuit 13 and KNEE circuit 14.
[0016]
On the other hand, when the signal level input to the limiter circuit of each channel is equal to or higher than the limit reference value from the MPU 15, the limiter circuit of each channel operates. As a result, the limiter circuit of each channel outputs a signal in which the signal level is limited within a predetermined limit reference value and the ratio of each channel is uniform. As a result, even when a subject that includes a white area with a very high luminance that exceeds the processing range of the TV camera device is photographed with white balance adjusted, false colors are generated in that area. Can be kept white. Hereinafter, the calculation method of the limit reference value will be described with reference to the explanatory diagram of FIG.
[0017]
For example, as a result of white balance adjustment, the gain values of the Rch gain adjustment circuit 21R, the Gch gain adjustment circuit 21G, and the Bch gain adjustment circuit 21B are 1.5 times as shown in FIG. Assume that the state becomes 1.0 times and 0.5 times. In this state, it is assumed that a part of the subject has a white area with extremely high luminance that has an amplitude of 600 [%]. As shown in FIG. 2, until the preceding stage of the limiter circuit, the amplitude of the white region is 600 [%] for Rch and Gch, whereas the amplitude of Bch is 300 [%]. Is the same.
[0018]
However, in the white balance circuit according to the present invention, the Rch limiter circuit 22R, the Gch limiter circuit 22G, and the Bch limiter circuit 22B are all controlled by the control signal from the MPU 23 so that the amplitude is 300 [%] or less. Is done. Bch is already gain value as it is because the amplitude is already 300% by white balance adjustment, but Rch and Gch are limited to 300 [%], so that Rch, Gch, Bch The white balance of the white area is maintained.
[0019]
FIG. 2 is an explanation using an example in which white balance is adjusted, and the limit reference value in the limiter circuit needs to be controlled according to the amplifier gain of each signal of Rch, Gch, and Bch. This limit reference value will be described using a general formula. Of the Rch, Gch, and Bch amplifier gains, let A be the smallest value. The maximum amplitude (signal processing upper limit value) handled by the television camera apparatus is B. At that time, the limit reference value in each limiter circuit is set to B × A. In the example of FIG. 2, from A = 0.5 and B = 600,
[Formula 1]
600 × 0.5 = 300
Thus, the limit reference value in the limiter circuit is set to 300 [%]. Such a series of processing is performed in the MPU 15, and a control signal for limiting the signal level to 300 [%] is output to each limiter circuit. As described above, the case where the high luminance region is white has been described, but according to the present invention, there is no inconvenience that the dynamic range of the color signal is impaired even if the region is other than white. Hereinafter, considerations made by the inventor regarding differences between the present invention and the prior art documents will be described.
[0020]
In Patent Document 1, in the method of Japanese Patent No. 2557620, when a cyan signal, that is, a signal having a small Rch signal level and a large Gch and Bch signal level is input, the cyan color becomes light. The shortcoming is pointed out. In the method of Patent Document 1, this drawback is solved, but how the method according to the present invention will be described.
[0021]
In both of the above two patents (Patent Document 1, Japanese Patent No. 2557620), the amplitude of Rch is the smallest of the three channels of Rch, Gch, and Bch, and therefore cyan is a problem. In FIG. 2 of the present invention, since the amplitude of Bch is the smallest, yellow is lightened when a yellow signal, that is, a signal having a small Bch signal level and a large Rch and Gch signal level is input. I am concerned about the shortcoming.
[0022]
However, as already described, the television camera apparatus for commercial broadcasting has a circuit configuration capable of signal processing with an amplitude several times that of a normally used electric signal. Here, a TV camera apparatus that performs signal processing with a maximum amplitude of 600 [%] is described as an example, but even if the signal levels of Rch and Gch are limited to about 300 [%] by a limiter circuit. In the circuit of the TV camera device, since the amplitude is compressed by the subsequent gamma correction circuit and the KNEE circuit, the problem that the yellow color becomes light does not occur.
[0023]
In addition, although embodiment of this invention was described for the purpose of illustration, this invention is not limited to these. For example, the following modifications and adaptations of the embodiments can be made by ordinary experts in this technical field, and are included in the technical ideas and aspects existing in the claims described in this specification. Is. (1) The television camera apparatus that performs signal processing with a maximum amplitude of 600 [%] has been described as an example. However, the present invention is not limited to these, and the same applies to cases other than the maximum 600 [%]. (1) For example, the present invention can be applied to various television systems including the NTSC system and the PAL system. (3) The present invention is not limited to normal exposure photography, but can be applied to long exposure photography.
[0024]
【The invention's effect】
According to the present invention, the limit reference value of each channel limiter circuit is uniquely determined from the gain value selected from the gain adjustment circuit of each channel and the inherent signal processing upper limit value possessed by each television camera device. Therefore, it is possible to provide a high-accuracy white balance circuit that supports high luminance input with a simple method.
[0025]
In addition, since white balance processing can be performed in a short time, it is possible to provide a white balance circuit that can also be used for a television camera apparatus that requires completion of video processing during one frame or one field period.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a detailed explanatory diagram relating to the operation of the present invention.
FIG. 3 is a block diagram of a conventional white balance circuit.
FIG. 4 is an explanatory diagram of gamma processing and KNEE processing.
FIG. 5 is a detailed explanatory diagram relating to the operation of a conventional white balance circuit;
[Explanation of symbols]
11R, 21R, 31R, 51R Rch gain adjustment circuit 11G, 21G, 31G, 51G Gch gain adjustment circuit 11B, 21B, 31B, 51B Bch gain adjustment circuit 12R, 22R Rch limiter circuit 12G, 22G Gch limiter circuit 12R, 22B Bch limiter circuit 13, 32 Gamma correction circuit 14, 33 KNEE circuit 15, 23, 34, 52 MPU

Claims (2)

A plurality of gain adjusting means for adjusting the gains of R (red), G (green) and B (blue) signals output from the image sensor, and provided in a subsequent stage of the plurality of gain adjusting means according to the luminance of the subject A white balance circuit for an imaging apparatus comprising a plurality of color signal limiting means for limiting each color signal level within a predetermined limit reference value and a control means for setting a limit reference value from the gain,
A white balance circuit that uniformly sets all the limit reference values to a value obtained by multiplying the smallest value among the gains of the respective color signals used at the time of white balance adjustment by a signal processing upper limit value specific to the imaging apparatus. . The white balance circuit according to claim 1, wherein the imaging device is a television camera device that outputs a video signal for each frame or for each field.

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