JPS61186090A - Color television camera - Google Patents

Abstract

PURPOSE:To perform sufficiently while balance and shading correction by inserting a reference pulse to a blanking period of a video signal before a preamplifier, detecting the pulse after the preamplifier to obtain a gain of the preamplifier and changing the shading correction quantity based on the result. CONSTITUTION:The gain of analog/digital gain converters 2b, 70 is set to a preset value under the standard lighting condition, shading information stored in a memory 10 is read and the shading quantity included in a video signal (c) is eliminated by a subtractor 30. When the lighting condition changes, a white object is picked up for the image to take white balance and an AWB control circuit 80 controls the gain of the analog gain converter 2b to bring a video signal (v) to a prescribed value. In this case, an SG control circuit 60 measures a level of a reference pulse inserted into the video signal (c) to control the gain of the digital gain converter 70.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] Does the present invention provide a shading correction function? The present invention relates to a color television camera equipped with a color television camera, and particularly relates to a color television camera in which automatic white balance control is performed by analog processing and then digital processing such as shading correction is performed.

[Prior art and its problems]

Camera devices such as image pickup tubes have a phenomenon known as black shading, in which some false signals are output as shown in FIG. 2 even when a beam is scanned in a state where incident light is completely blocked. This false signal occurs regardless of the amount of incident light, so from the state of no amount of incident light shown in FIG. 2 to the amount of incident light shown in FIG. 3! - Even if the (object signal) changes to a certain state, this component remains in the form of being added to the object signal. Further, in a normal image pickup tube or a charge-coupled device (COD), in order to reduce the afterimage χ, half of the light from the bias light is directed onto the imaging surface by σ, and this amount is also added to the video signal.

By the way, this shading amount is distributed with a two-dimensional spread within the screen, as conceptually shown in FIG. Furthermore, since it is difficult to apply the light of the bias light to the imaging surface completely uniformly, two-dimensional light unevenness is likely to occur, similar to shading. Furthermore, the distribution of the shading amount differs depending on the individual image sensor.

Therefore, conventional analog processing type television cameras use sawtooth wave signals T and parabolic wave signals P7 with horizontal and vertical scanning periods as shown in FIG. The method used was to correct shading by mixing the signal with the video signal while adjusting the level appropriately.

However, this method does not provide sufficient shading correction, is difficult to adjust, and requires a large circuit scale. Along with this, digitalization of various video equipment is progressing, and television cameras are no longer an exception.

However, in such digital television cameras, this shading can be easily done using the following method.
and can be completely corrected.

To explain this method, as shown in Figure 6, the screen χ
The shading amount at the center of this square is set as %taIJ, and as shown in Figure 7, it is 00.
...alte 812m "1m" from address O...
・・・・・・a2□, a, 2・・・・・・・・・aa
Store it in digital memory at the head of ll. next,
The memory in which the shading amount is stored in this way is used as the memory 10 in FIG. 8, and the addressing of this memory 10 is synchronized with the scanning of the camera by the address counter 20 which uses the horizontal drive signal HD and the vertical drive signal VD7 manually. The accessed shading data D
g is input to the subtracter 30 and subtracted from the video signal V to obtain a video signal v' from which shading has been removed. Therefore, according to this method, shading correction can be easily performed.
And it can be done accurately.

The overall configuration of a digital television camera is shown in FIG. 9, for example.

Then, a signal current a photoelectrically converted by the image sensor 1
is converted into a voltage signal of a predetermined level by a preamplifier 2, and further converted into a digital signal CIC by an A/D (analog-to-digital converter) 3.

After that, the linear signal processing circuit 4 performs shading correction, hue correction, etc., and the process circuit 5 performs gamma correction to compensate for the nonlinearity of the photoelectric conversion characteristics of the cathode ray tube of the image receiver, nonlinear processing such as white compression, edge enhancement, etc. Do the following.

In the case of a color camera, the signal Vj subjected to such processing is sent to the encoder circuit 6 together with other channel signals vg and vb which have been subjected to similar processing Y, and becomes a composite television signal V, which is converted into a digital signal as necessary. The signal is converted back to an analog signal by an analog conversion circuit (D/A) 7 and becomes an output AV.

By the way, even if the camera's signal processing circuit is digitized in step 5, will the preamplifier be an analog type? It is a common practice to use this method, and it is convenient if the gain of this preamplifier can be changed by control from an automatic white balance circuit, as described below.

Now, to explain the white balance of a color camera, even if a person looks at a white piece of paper outdoors, is it the same paper when viewed indoors under incandescent heat? Do you see this? It can be judged as white. However, since the color white is a color that reflects light of all wavelengths uniformly, if the lighting conditions differ, the wavelength distribution of the light that enters the eye from this white paper will naturally vary. For example, red (R), blue (B), and green (G) light at a ratio of 1:0.
．． The wavelength distribution of light reflected from a white piece of paper illuminated with an intensity of 5:0.5 is the same as the wavelength distribution of light reflected from a white piece of paper when R, B, and G are applied at a ratio of 1:1:1 to a reddish colored paper. Sometimes it is equal to the wavelength distribution of the light reflected from this paper. However, even in such cases, the human brain is able to judge the lighting conditions from the surrounding situation and judge the former as white and the latter as reddish. Because I don't have the ability to make such judgments, I end up copying both the former and the latter in a reddish color in cases like (17).

Therefore, modern cameras are equipped with an automatic white balance circuit, and as in the previous example, a white paper sheet with R, G, and B light in a ratio of 1:0.5:0.5 is used. When this circuit is operated while an image is being captured, the circuit will display R, G
, change the gain of the video signal in each channel of B,
The output level ratio of the video signals is controlled to be 1:1:1. In other words, ordinary gain? Either lower it or increase the G and B gains so that the subject appears white.

By the way, in the digital camera shown in FIG.
The D conversion accuracy becomes a problem, and in order to achieve the best result, the level of the analog signal input to the A/D3 should be adjusted. It is necessary to set it to a predetermined value.

Therefore, in the above-mentioned work 5, white balance? When changing the gain χ in order to obtain the desired output power, it is desirable to change the gain of the preamplifier 2 so that the output level σ) is kept constant under any lighting conditions.

However, this method? If used, the following problems will occur. In other words, with a digital camera, shading correction is performed digitally, but as mentioned above (
If the preamplifier gain changes, there will be excess or deficiency in the amount of shading correction, making it impossible to completely cancel shading. In other words, is it fading correction for analog cameras? This problem did not occur because I had changed the gain for the white balance after doing this, but with a digital camera, the order of the terms is reversed, so
Problems will arise.

Therefore, conventional digital color television cameras have the disadvantage that when automatic white balance control is performed, sufficient shading correction cannot be obtained.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital color television camera that eliminates the drawbacks of the prior art described above and that can always provide sufficient shading correction even when the preamplifier gain changes for white balance control. It is on offer.

[Summary of the invention]

To achieve this objective, the present invention calculates the gain of the preamplifier by detecting the amplitude of a reference pulse inserted into the blanking period of the video signal before the preamplifier, and then calculates the gain of the preamplifier based on this result. is characterized in that the amount of shading correction to be subtracted is changed.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A color television camera according to the present invention will be explained in detail below using illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which 40 is a reference pulse generator, 50 is an adder, 60 is a shading gain control circuit (referred to as SG control circuit), and 70 is a digital gain converter (DG converter). ), 80 is an automatic white balance control circuit (referred to as AWB control circuit), and the others are as shown in FIG.

This is the same as in FIG. In addition, 2a is Darienbu 2
Similarly, 2b represents the gain control section of the preamplifier 2.

The impedance conversion unit 2a is composed of, for example, an amplifier with high input impedance and low output impedance, and converts the video signal aV impedance in a current signal format (high impedance) taken out from an image pickup tube or the like,
It functions to obtain a video signal a' in a voltage signal format (low impedance).

The reference pulse generator 40 has the function of generating a reference pulse pre of a predetermined constant amplitude during the blanking period of the video signal a'.
do.

The adder 50 mixes the reference pulse v with the video signal a', and generates the video signal a with the reference pulse p inserted in the blanking period.
'V get work χ.

The analog gain converter 2b is configured of, for example, a variable gain amplifier, and converts the gain to the video signal l according to the control signal W supplied from the AWB control circuit 80. Control and white balance? A video signal bv is generated which is adjusted to the level required to maintain the level.

The 8G control circuit 60 gates and captures the digitized video signal Ct, which is the output of the A/D 3, only during its blanking period, and calculates the level of the reference pulse inserted therein. It functions to detect and output a control signal 3 in accordance with the detection.

The DG converter 70 is composed of, for example, a digital multiplication circuit, and converts the level of the correction signal read out from the memory 10 according to the control signal S, and converts the level of the correction signal D/D to a level corresponding to the control signal S. y, - serves to supply the subtractor 30.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, under standard lighting conditions, the gains of both analog and digital gain converters 2b and 70 are set to preset values. Therefore, as the address counter reads out the shading information stored in the memory 10 in synchronization with the scanning of the camera, the subtracter 30:
An amount of shading information equal to the amount of shading contained in the video signal C cancels each other, and a signal V without shading is obtained from the output.

Next, when a white subject is imaged under different illumination conditions and automatic white balance is performed, the AWB control circuit 80 changes the level of the video signal V? The gain of the analog gain converter 2b is loop-controlled so that the detected value becomes a predetermined value. As a result, R
, G, and B channels have the same video signal level for a white object, and white balance can be achieved.

At this time, in the conventional method, there was excess or deficiency in shading cancellation due to the change in gain in the analog circuit system, but in this example, as explained next, this? It can be prevented. That is, the SG control circuit 60 measures the level Y of the reference pulse inserted into the video signal C and controls the gain Y of the DG converter 70.

Since this reference pulse is mixed before the analog gain converter 2b in a blanking period in which there is no influence from the 7-edding in the video signal, the SG control circuit 60 does not use this pulse. By measuring and comparing with a predetermined reference value, it is possible to accurately detect a gain change accompanying the white balance control of the analog gain converter 2b, and change the gain of the DG converter 70 to the same extent.

Therefore, in the subtracter 30, shading information that accurately follows the gain change in the analog gain converter 2b is subtracted from the video signal C, and under what conditions the white balance? According to this embodiment, complete correction is always performed and a video signal V without shading can be obtained.

Next, another embodiment of the present invention is shown in FIG.

In this FIG. 10, 90 is an arithmetic processing unit, so that in this embodiment, the DG in the embodiment of FIG.
Instead of gain conversion by the converter 70, a memory rewriting method by the arithmetic processing unit 90 is used, and the rest is the same as the embodiment shown in FIG. The operation will be explained.

When the 8G control circuit 60 measures the reference pulse in the video signal C and detects a gain change caused by the analog gain control section 2b, this is inputted to the arithmetic processing unit 90 in accordance with the control signal SVc. Then, this arithmetic processing unit 90 reads data tHX from the memory 10, multiplies it by the gain change described above, and creates new data. The same address in the memory 10 is sequentially accessed again.

This data +t4, which is read out in synchronization with the scanning of the camera by the address kakunta 20, is always data D/ whose level is adjusted in accordance with the gain change by the analog gain control section 2b. Therefore, according to this embodiment as well, shading can always be accurately canceled and a video signal V% without shading can be obtained.

Generally, digital multipliers are quite expensive; however, arithmetic processing units have become more general-purpose and have become considerably lower in cost.

Therefore, according to the embodiment shown in FIG. 1O, considerable colossalization can be expected. Also, according to this example,
Needless to say, this arithmetic processing unit 1190 is provided with an AWB control circuit 8. This makes it possible to further reduce costs.

In addition, in the above description, in all the embodiments, the reference pulse p is mixed with the video signal a' in the voltage signal format, and the input of the SG control circuit 60 is the video signal which is the output of the A/D 3. It is signal C.

However, it goes without saying that the present invention is not limited to this and can be implemented. For example, the reference pulse p may be inserted into the video signal at any stage before the analog gain converter 2b, Human power may also be introduced from any stage subsequent to the analog gain converter 2b.

〔Effect of the invention〕

As explained above, according to the present invention, even if the gain of the video signal is changed for white balance, it can be made so that it does not affect the digital shading correction at all. However, it is possible to easily provide a color television camera that can obtain sufficient white balance and shading correction while maintaining high quantization accuracy by A/D.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a color television camera according to the present invention, FIG. 2 is an explanatory diagram of a shading waveform, and FIG. 3 is an explanatory diagram of a video signal with shading. Figure 4 is an explanatory diagram showing the two-dimensional distribution of the amount of shading, @Figure 5 (5), (opening) is a waveform diagram showing an example of a shading correction signal χ using the analog method, and Figure 6 is an address on the plane image plane. FIG. 7 is an explanatory diagram of addresses and data of the memory for storing shading information, and FIG.
FIG. 1 is a block diagram illustrating an embodiment. 2a... Preamplifier impedance conversion section,
2b... Analog gain conversion section of preamplifier,
3...Analog-digital converter (A/D
), 10...Digital memory, 20...
...address kakunta, 30...subtractor, 4
0...Reference pulse generator, 50...Adder, 60...Shading gain (SG)
Control circuit, 70...Digital gain (DG)
Control circuit, 80... Automatic white balance (AWB)
Control circuit, 90... Arithmetic processing unit. 1st f! 1 1υ Figure 2 IIA Darkness Figure 3 Figure 4 Figure 5 (A) (B) Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

Claims (3)

[Claims] (1) In a color television camera that is equipped with a digital memory that stores shading correction data in advance and performs automatic white balance control using analog processing, shading correction is performed using digital processing. a reference pulse mixing means for inserting a reference pulse into the blanking period of the video signal at a stage upstream of the variable amplifier for balance control; and detecting the level of the reference pulse in the video signal output from the variable amplifier; 1. A color television camera comprising: level detection means for generating a control signal representing a level; and level control means for controlling the level of shading correction data in accordance with the control signal. (2) In claim 1, the level control means is constituted by a digital gain conversion circuit that receives data read from the digital memory and whose gain is controlled by the control signal. A color television camera characterized by: (3) Claim 1 is characterized in that the level control means is comprised of an arithmetic processing device that rewrites data stored in the digital memory in response to the control signal. Color television camera.