JPS61234187A - Color television camera - Google Patents

Abstract

PURPOSE:To lower a cost of a constituting material and simplify an operation by performing a white balance adjustment changing an electric field strength in such a manner that an output ratio of a blue and a red channels in a image pick up output signal deletes an influence of a color temperature change in accordance with the color temperature change of an illuminating light. CONSTITUTION:A photoelectric sensitivity has a different rate of change to an electric field strength every wave length of an incident light and a long wave length light has a large rate of change. In such a way, the photoelectric sensitivity has a dependency on the electric field and is substantially linearly changed in a larger area in the electric field strength than the area A shown in the figure. Accordingly, in order to detect the change of the color temperature, the output ratio of the respective color channels can be changed by operating a color temperature detecting circuit, a variable circuit section by picking up a white color field to be pictured to provide a comparison circuit for comparing a blue channel output and a red channel output and changing a voltage applying a quantity of change of a signal obtained from the circuits to a photoconductive film, or a circuit section for an amplifying ratio of both the channels of blue and red together with this variable circuit section.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color television camera, and in particular to improvements in the means.

[Background of the invention]

Generally, in a color television camera, white balance adjustment is performed in order to obtain faithful color tone reproducibility when capturing a color television image. Specifically, when capturing an image of a white subject, the camera's red (R), green (G),
This is done, for example, by adjusting the amplification degree of each color channel amplifier so that the output of each blue (B) color is equal. In this case, adjusting the amplification level alone will result in S/N imbalance in the output of each color channel, resulting in a noisy image, and in particular, single-tube color television cameras often generate spurious signals, so significant amplification is required. In many cases, an optical filter for raising or lowering the color temperature, which converts the color temperature of the light incident on the image pickup tube, is interposed in the imaging optical path without adjusting the temperature.

Note that such a white balance adjustment method is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 19326-1982 and 13th-Sho.
It is described in detail in Japanese Patent No. 1536 and the like.

However, in such a configuration, adding a color temperature correction optical filter for adjusting white balance and a filter switching mechanism to the camera body complicates the camera mechanism and increases the manufacturing cost of the camera. There were problems such as the operation became complicated as the height was raised.

[Purpose of the invention]

Therefore, the present invention has been made in view of the above-mentioned problems, and its object is to provide a color television camera that simplifies camera operation and reduces the manufacturing cost of the camera. It is in.

[Summary of the invention]

In order to achieve such an object, the present invention provides a photoelectric conversion film having a property that the spectral sensitivity depends on the applied voltage.
In a color television camera that uses an imaging method that obtains multiple color signals from a single image pickup tube, the output ratio of the blue and red channels in the imaging output signal cancels out the effects of color temperature changes in response to changes in the color temperature of illumination light. Embodiments of the Invention Next, the present invention will be described in detail with reference to the drawings.

Color television cameras typically use red (
Three types of signals based on the three primary color lights of R), green (G), and blue (B) are involved in some way, and in order to obtain these signals, multiple image pickup tubes are separated on the color signal side. or used in combination. The color television camera to which the present invention is applied uses at least one image pickup tube to obtain a plurality of color light signals from one image pickup tube, and the spectral wavelength sensitivity distribution is adjusted to changes in the illumination light source. Changeable photoelectric conversion unit,
In other words, as the voltage applied to the photoconductive film changes, the spectral wavelength sensitivity in the visible light range changes, and as shown in Figure 1, the sensitivity in the green (G) color light band changes the sensitivity in the red (R) and blue (B) color light bands. An image pickup tube having such characteristics that when normalized, when one becomes large, the other becomes small, or vice versa, for example, it has a photoconductive film mainly composed of Se, All, T. A nine-color television camera with a pn junction type camera tube is most suitable.

Figure 1 shows the spectral output of a photoconductive imaging tube (SATICON tube, Noborikama trademark) whose main components are s@As and Ts. In the figure, B, G, and R are Each color television camera blue.

The photoelectric conversion output when approximately 3,000 white objects were imaged through color separation filters such as those used for the green and red channels was measured by varying the electric field within the photoconductive film. As is clear from this, in the blue light band on the short wavelength side, the right side of the characteristic curve after the shoulder shows a saturation characteristic with almost no change in photoelectric output, but green light with a large wavelength shows saturation characteristics with almost no change in photoelectric output.

In the characteristic curve of red light, saturation is low even on the right side of the shoulder, and the photoelectric output tends to increase as the electric field increases.

Figure 2 shows the f of the aforementioned Se, As, T photoconductive type image pickup tube.
(B) shows the situation in which the sensitivity of green (G) and red (R) color light bands changes depending on the voltage applied to the photoconductive film.
In the figure, the horizontal axis indicates the average electric field strength within the photoconductive film obtained by dividing the applied voltage by the thickness of the photoconductive film. Normally, when the thickness of the photoconductive film is 4 μm, 50 V is applied, so the electric field strength 5
0/4 = 12.5 V/red (R) at 77m,
Green (G).

Blue CB) The vertical axis shows the sensitivity ratio as the electric field intensity changes, assuming that the channel output is 1.

As is clear from the figure, the rate of change of photoelectric sensitivity with respect to electric field strength differs depending on the wavelength of incident light), and blue light band sensitivity! , the green light band sensitivity (■), and the red light band sensitivity (■), the rate of change is the largest for long wavelength light. As described above, the photoelectric sensitivity is dependent on the electric field, and changes almost linearly in areas where the electric field intensity is large, such as in area A in the figure.

Therefore, the present invention focuses on such characteristics and changes the output ratio of each color channel by changing the voltage (electric field strength) applied to the photoconductive film in response to the change in color temperature of illumination light.

A color TV camera driven with an electric field strength of 12.5V//'FM as explained in Fig. 2 and white balance adjusted at the required color temperature of the illumination light is illuminated with high color temperature without readjustment. If used below, the blue light channel output will increase relatively and the red light channel output will decrease relatively, resulting in a loss of white balance. When the voltage applied to the photoconductive film is increased, as shown in FIG. 2, the red light band sensitivity (2) increases the most, followed by the green light band sensitivity (2) and the blue light band sensitivity (4).

Therefore, the relative decrease in the output of the red channel and the relative increase in the output of the blue channel due to the increase in the color temperature of the illumination light are compensated for or at least mitigated. In this case, excessively changing the voltage applied to the photoconductive surface is
Since this will harm other imaging characteristics, it should be done within an acceptable range. In other words, when the applied voltage is increased, the photoconductive film is destroyed or the dark current increases, and when the applied voltage is decreased excessively, it enters the non-linear region indicated by region A in FIG. This results in side effects such as an excessive sensitivity imbalance or a general decrease in sensitivity. Therefore, considering from such a practical point of view, Ss, Am
, 12.5V/μm in To type p-n junction image pickup tube
Approximately 6V/μm to approximately 40V/μm including standard driving conditions of
Variations in the degree range are acceptable. As a result, white balance adjustment for the color temperature of illumination light is naturally achieved by combining the method of changing the voltage applied to the photoconductive film as described above and the conventional method of changing the amplification ratio of the red channel and blue channel. By using this function, you can obtain excellent white balance adjustment characteristics. In addition, in the specific circuit configuration, in order to detect color temperature changes, a color temperature detection circuit is provided, or a comparison circuit is provided that images a white subject and compares the blue channel output and the red channel output. In order to operate a variable circuit section that changes the voltage applied to the photoconductive film based on the amount of change in the signal obtained from the circuit, or a circuit section that changes the amplification ratio of both the red and blue channel amplifier circuits together with this variable circuit section. ), it can be implemented.

Note that the range of voltage applied to the photoconductive film mentioned above is 6V/μ.
m to 40v/μm, but there is no change in the photoelectric conversion gamma characteristics in this range, and the dark current is no more than about 2nA for Ss, As, and Te-based image pickup tubes, impairing practicality. Not at all. If the dark current change is excessive, known methods of detecting and compensating for dark current are useful. Similarly, it is possible to follow and adjust the level change of the bias signal amount based on the bias light illumination mechanism that is often added to color television cameras to improve afterimage characteristics.

In addition, to deal with the general tendency of sensitivity increase/decrease, there is a method known as an auto-iris mechanism that controls the amount of light incident by opening and closing the aperture of the imaging lens to control the image pickup tube output signal level to a predetermined value. Alternatively, since it is compatible with other automatic sensitivity adjustment mechanisms, this embodiment enables excellent white balance adjustment that can follow and respond to changes in the color temperature of the imaging illumination light while maintaining satisfactory image quality. .

〔Effect of the invention〕

As described above, according to the present invention, the white balance adjustment means changes the electric field strength so that the blue and red channel output ratios in the imaging output signal cancel out the influence of the color temperature change according to the color temperature change of the illumination light. By providing this, it is possible to correct the output ratio of each color channel and obtain good white balance characteristics, thereby reducing the cost of constituent materials of a color television camera and simplifying its operation method. Extremely dominant n-order effects such as this can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the photoelectric conversion output current and the electric field strength of the photoconductive film, and FIG. 2 is a diagram showing the relationship between the photoelectric conversion output current and the electric field strength of the photoconductive film, and FIG. FIG. 3 is a diagram showing a situation in which band sensitivity changes depending on the voltage applied to the photoconductive film.

Claims (1)

[Scope of Claims] 1. In a color television camera of an imaging type that is equipped with one photoconductive type image pickup tube and obtains a plurality of color signals from the image pickup tube, the photoconductive film of the photoconductive type image pickup tube has the spectral spectrum. 1. A color television camera, characterized in that the wavelength sensitivity is dependent on applied voltage, and means is provided for adjusting white balance by changing the electric field intensity applied to the photoconductive film. 2. The color television camera according to claim 1, wherein the image pickup tube has a photoconductive film containing Se, As, and Te as main components.