JPH0832050B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image pickup apparatus such as a video camera, and more particularly to improvement of a level control mechanism of a video signal.

[Prior Art] An imaging device such as a video camera captures an object as an optical image through a lens, converts it into an electric signal by an imaging device, and creates a video signal which is a final output signal from the electric signal. By the way, in such an image pickup apparatus, the level of the image electrical signal input to the video signal creating unit is maintained at a suitable constant value so that a video signal that always produces a reproduced image with good brightness is created. Need to Therefore, an image pickup device such as a video camera generally controls the lens diaphragm according to the illuminance of the subject to keep the amount of light incident on the image pickup device constant, thereby keeping the electric signal level output from the image pickup device constant. A diaphragm control mechanism, an automatic gain control (AGC) mechanism for amplifying the electric signal output from the image sensor to a constant level, and the like.

FIG. 2 is a schematic block diagram of a video camera provided with the aperture control mechanism as described above. Referring to the figure, this video camera includes a lens system 1 including an aperture 100, an image sensor 2, a drive circuit 3, a preamplifier 4, and an aperture drive circuit 18.
A video signal generating unit 23 and an aperture control signal generating unit 25.

The lens 1 forms an image of a subject on the image sensor 2. The image pickup element 2 is driven by the drive circuit 3 and converts the formed optical image into an electric signal (image electric signal) corresponding thereto and outputs the electric signal. The preamplifier 4 amplifies the electric signal from the image pickup device 2 to a predetermined level and inputs it to a low-pass filter (hereinafter abbreviated as LPF) 5 and a color separation circuit 7 in the video signal creation unit 23.

The LPF 5 removes a high frequency band component of the electric signal input from the preamplifier 4 to output a brightness signal Y representing the brightness of the subject. The luminance signal Y is input to the mixing circuit 15 after being subjected to necessary processing in the Y signal processing circuit 6.

On the other hand, the electric signal input to the color separation circuit 7 is separated into three primary color signals R (red), B (blue), and G (green) signals representing the color of the subject. These are respectively input to the R signal processing circuit 8, the B and subsequent processing circuits 9, and the G signal processing circuit 10. The R signal processing circuit 8, the B signal processing circuit 9, and the G signal processing circuit 10 perform necessary processing on the primary color signals input to each and output them to the matrix circuit 11. The matrix circuit 11 synthesizes the input primary color signals and creates two color difference signals R-Y and B-Y representing the saturation of colors. These color difference signals RY and BY are respectively
After being subjected to necessary processing in the RY signal processing circuit 12 and the BY signal processing circuit 13, it is input to the chroma modulation circuit 14. The chroma modulation circuit 14 balance-modulates a carrier within the band of the luminance signal, called a color subcarrier, by the input color difference signals RY and BY in order to put the color difference signal on the luminance signal, and the carrier color signal is obtained. create.

The mixing circuit 15 synthesizes the luminance signal Y input through the Y signal processing circuit 16 and the carrier color signal from the chroma modulation circuit 14, and the final video to be recorded on a magnetic tape (not shown). Output a signal.

Next, the aperture control mechanism of this video camera will be described.

The luminance signal Y output from the LPF5 is the Y signal processing circuit 6
And the level detection circuit 16 in the diaphragm control signal generator 25. The level detection circuit 16 detects the level of the luminance signal Y and inputs a DC potential having a level corresponding to the detected level to the operational amplifier 17. The operational amplifier 17 inversely amplifies the DC potential from the level detection circuit 16, that is, functions as a comparator, with the potential V _{ref1 applied} to the non-inverting input terminal as a reference potential. Therefore, the output level of the operational amplifier 17 decreases if the DC potential from the level detection circuit 16 is higher than the reference potential V _ref1 , and conversely, the reference potential V _ref1 is higher than the DC potential from the level detection circuit 16. The bigger it is, the higher it becomes. When the DC potential output from the level detection circuit 16 becomes equal to the reference potential V _ref1 , the output of the operational amplifier 17 is 0. The diaphragm drive circuit 18 is an operational amplifier.
In response to the output of 17, the aperture diameter of the lens diaphragm 100 of the lens system 1 is changed in proportion to the level. On the other hand, the luminance signal Y
Level changes in proportion to the amount of light incident on the image sensor 2, that is, the brightness of the subject. Therefore, the image sensor 2
When the amount of light incident on the aperture is larger than the value corresponding to the reference potential V _ref1 , the signal level input to the aperture drive circuit 18 decreases and the aperture diameter of the aperture 100 decreases. On the contrary, the image sensor 2
When the amount of light incident on is smaller than the value corresponding to the reference potential V _ref1 , the aperture diameter of the diaphragm 100 becomes large. Reference potential V
_ref1 is set to a value corresponding to the level of the luminance signal Y output from the LPF 5 when the amount of light incident on the image sensor 2 is sufficient to obtain a suitable video signal. Therefore, the aperture diameter of the lens diaphragm 100 is appropriately opened / closed according to the amount of light incident on the image sensor 2. As a result, the amount of light incident on the image pickup element 2 is always maintained at a suitable constant amount, and a video signal is always created from a suitable constant level electric signal.

Further, when the AGC mechanism is used, the output of the aperture control signal generator 25 is input to the preamplifier 4, and the gain of the preamplifier 4 is controlled thereby. That is, if the level of the electric signal obtained from the image sensor 2 is lower than a predetermined level, the gain of the preamplifier 4 also increases in response to the increase in the output level of the operational amplifier 17, and the image sensor 2
If the level of the signal obtained from the above is higher than a predetermined level, the gain of the preamplifier 4 also decreases in response to the decrease in the output level of the operational amplifier 17. Such operations are repeated, and the output from the preamplifier 4, that is, the level of the signal input to the video signal creating unit 23 is held constant. However, when both aperture control and AGC are performed, the luminance signal Y for aperture control needs to be taken out before the level control is performed by the AGC.

The electric signal input to the color separation circuit 7 via the preamplifier 4 is divided into two primary color signals R and B and a luminance signal Y _L whose bandwidth is reduced to the same level as the frequency bandwidth of the primary color signal. It may be separated.

[Problems to be Solved by the Invention] As described above, in the conventional image pickup apparatus such as a video camera, the image electric signal level input to the video signal creating unit is always constant only by the luminance signal representing the luminance of the subject. Was controlled to be. On the other hand, the luminance signal is a combination of the primary color signals R, B, and G at the rates of 30%, 11%, and 59%, respectively. Therefore, even under the same illuminance, the level of the obtained luminance signal varies depending on the hue and saturation (color saturation) of the subject. For example, the level of a luminance signal obtained by capturing an image of a red subject with extremely high saturation (high primary color signal level) is the same as that of a low saturation (low primary color signal level) color under the same illuminance. It is lower than that of the luminance signal obtained by imaging the subject. This is because the ratio of the R signal contributing to the luminance signal is as low as 30%, so that the level of the luminance signal does not increase so much even if the level of the R signal increases. Therefore, this tendency becomes even stronger when the color of the subject is highly saturated blue. Therefore, if the lens diaphragm control and the AGC are performed only by the luminance signal level, the aperture diameter of the lens diaphragm becomes larger than necessary or the gain in the AGC becomes higher than necessary. For example, the luminance signal level obtained by imaging a highly saturated red flower under sufficiently high illuminance is lower than that obtained by imaging a less saturated object under sufficiently high illuminance. For this reason, despite being under sufficiently high illuminance,
When the level of the luminance signal obtained by imaging a highly saturated red flower becomes lower than a predetermined reference level, the aperture diameter of the lens aperture increases due to the aperture control mechanism, or the AGC
And the electric signal level input to the video signal creating section rises. Along with that, the level of the primary color signal R rises unnecessarily. Therefore, in the reproduced image obtained from the video signal created from such primary color signal and luminance signal, the saturation and luminance of the color of the flower become unnecessarily higher than it actually is, which is unnatural. Further, when the level of the primary color signal R rises and saturates at a certain maximum value, red is saturated in the reproduced image, and the flowers are just red objects, that is, the petals are not distinguished one by one. Becomes

An object of the present invention is to provide an image pickup apparatus which can solve the above problems and can control the level of an image electric signal according to the hue and saturation of a subject.

[Means for Solving the Problems] In order to achieve the above-mentioned object, an imaging apparatus according to the present invention provides an optical system for extracting a subject as an optical image and an optical image extracted by the optical system for a luminance signal and A means for converting into an image electric signal containing a primary color signal, and a color separation means for separating the red and blue primary color signals from the image electric signal,
A means for detecting the level of the luminance signal included in the image electric signal; and a level detecting means for detecting a level higher than the reference level for the primary color signal having a higher level of the red signal and the blue signal separated by the color separation means. When the level detection means detects a level higher than the reference level, the diaphragm of the optical system is controlled in response to the detection output of the brightness signal level detection means and the level detection output of the level detection means, and the level detection means Therefore, when the level higher than the reference level is not detected, the means for controlling the diaphragm of the optical system is provided only in response to the detection output of the brightness signal level detecting means.

[Operation] Since the image pickup apparatus according to the present invention is configured as described above, it is possible to control incident light from a subject or a physical quantity related thereto by using not only a luminance signal but also a color signal. Therefore, even if the luminance signal level is the same, different control can be performed on the incident light from the subject or the physical quantity related to the high saturation color and the low saturation color.

[Embodiment] FIG. 1 is a schematic block diagram of a video camera showing an embodiment of the present invention. Referring to the figure, this video camera includes a lens system 1 including a diaphragm 100, an image sensor 2, a drive circuit 3 for driving the image sensor 2, and a preamplifier 4 for amplifying the output of the image sensor 2. A video signal creating section 23 for creating a final video signal to be recorded on a magnetic tape (not shown), an aperture control signal generating section 24 having a configuration different from the conventional one, and an aperture drive circuit 18. Including. The internal configuration of the video signal creation unit 23 is the same as that in the conventional example.

Unlike the prior art, the aperture control signal generator 24 includes a level detection circuit 16, an operational amplifier 17, a non-addition matrix circuit (hereinafter abbreviated as NAM circuit) 19, and a high level detection circuit 20.
And an amplifier 21 and an adder circuit 22.

A series of functional units (operational amplifier 17, operational amplifier 17, from the capturing of the subject as an optical image by the lens 1 to the creation of a video signal corresponding to the subject by the video signal creating unit 23)
(Excluding diaphragm drive circuit 18 and diaphragm control signal generator 24)
The operation of is as described in the conventional example.

Next, the aperture control mechanism of this video camera will be described.

The diaphragm control signal generator 24 is different from the conventional one in that the LPF5
In addition to the luminance signal Y from, the primary color signals R and B from the color separation circuit 7 are input. The primary color signals R and B are input to the NAM circuit 19. The NAM circuit 19 outputs the higher level signal of these primary color signals. The high level detection circuit 20 outputs the output signal of the NAM circuit 19 (primary color signal R or B).
Is detected and compared with a predetermined reference potential V _ref2 . Further, as a result of this comparison, the high-level detection circuit 20 determines that the level of the primary color signal R or B is higher than a predetermined reference level. Signal level signal) is output. The amplifier 21 amplifies the output of the high level detection circuit 20 at a predetermined amplification factor and inputs it to the addition circuit 22. On the other hand, the luminance signal Y from the LPF 5 is detected by the level detection circuit 16
Is converted into a DC potential corresponding to the level (hereinafter, referred to as a brightness signal level signal) and input to the adder circuit 22. The adder circuit 22 outputs the output of the level detection circuit 16,
That is, the level signal of the luminance signal Y and the output of the amplifier 21,
That is, the primary color signal R or B is added to a signal whose level is higher than a certain level, and is added to the operational amplifier 17. Subsequent operations of the operational amplifier 17 and the diaphragm drive circuit 18 are as described in the conventional example. That is, if the level of the output signal of the diaphragm control signal generator 24 is lower than the predetermined reference potential V _ref1 corresponding to a suitable signal level, the diaphragm 100
Has a large aperture diameter, and conversely, the aperture diameter of the diaphragm 100 is small. That is, similarly to the conventional example, the aperture diameter of the diaphragm 100 is controlled and the amount of light incident on the image sensor 2 is controlled, so that the level of the electric signal output from the image sensor 2 is always kept constant. However, unlike the past, the diaphragm 100
The signal for controlling the open / closed state, that is, the signal input to the inverting input terminal of the operational amplifier 17 is created from the luminance signal Y and the primary color signal R or B. That is, the level of the signal input to the video signal creation unit 23 is controlled by the brightness of the subject and the hue and saturation of the subject. More specifically, when the levels of the primary color signals R and B are lower than a predetermined reference level, that is, when a subject of a color with low saturation is captured, the output from the high level detection circuit 20 is 0. Become. Therefore, the luminance signal Y is output from the adder circuit 22.
Since the level signal is output as it is, the diaphragm 100 is controlled only by the luminance signal Y as in the conventional case. On the contrary, when a highly saturated object is imaged, the high level detection circuit 20 outputs the level signal of the primary color signal R or B. Therefore, the adder circuit 22 outputs the sum of the level signal of the luminance signal Y and the level signal of the primary color signal R or B. As a result, the level of the signal input from the operational amplifier 17 to the diaphragm drive circuit 18 becomes lower than in the conventional case when a highly saturated color object is imaged, and the aperture diameter of the diaphragm 100 does not become larger than in the conventional case. Therefore, the saturation of the color signal and the unnaturalness of the reproduced image, which have been conventionally caused by the level of the signal input to the video signal creating unit 23 becoming larger than necessary, are eliminated.

The reference potential V _ref2 in the high level detection circuit 20 is set to a value corresponding to the level of the primary color signal at which the above-mentioned conventional problems start to appear particularly prominently. Further, the level of the luminance signal differs depending on the color of the subject. Therefore, the primary color signal added to the luminance signal in the adder circuit 22 is selected by the NAM circuit 19 to have a higher proportion of contribution to the color of the object, that is, the primary color signal of the higher level of the primary color signals R and B. . However, since the primary color signal G contributes to the luminance signal Y at a very high rate of 59%, it is considered that the degree of determining the luminance of the subject is almost the same as that of the luminance signal, and thus is excluded.

The amplification factor of the amplifier 21 is determined in consideration of how much the aperture control when only the luminance signal Y is used is corrected by incorporating the primary color signal.

In the present embodiment, the output of the diaphragm control signal generator 24 is used to control the diaphragm 100, but because of the gain control of the preamplifier 4 that amplifies the output of the image sensor 2,
That is, even when used in the AGC mechanism, the same effect as in the present embodiment can be obtained. In this case, the output of the operational amplifier 17 may be given to the preamplifier 4 as shown by the broken line in FIG. Of course, in this case, the preamplifier 4 must be constructed so that the gain changes in response to the output level of the operational amplifier 17.

[Advantages of the Invention] As described above, the imaging apparatus according to the present invention controls the diaphragm unit in response to the luminance signal and the color signal. Therefore, the signal level input to the video signal creation unit is controlled according to the hue and saturation of the subject. As a result, a preferable video signal can be obtained even from an object having a high color saturation, and the quality of a reproduced image is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a schematic block diagram of a conventional video camera. In the figure, 1 is a lens system, 2 is an image sensor, 3 is a drive circuit, 4 is a preamplifier, 17 is an operational amplifier, 18 is an aperture drive circuit, 19 is a NAM circuit, 20 is a high level detection circuit, 21 is an amplifier, 22 Is an adder circuit, 23 is a video signal generation unit, 24 and 25
Is a diaphragm control signal generator. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An optical system for picking up a subject as an optical image, a unit for converting the optical image picked up by the optical system into an image electric signal containing a luminance signal and a primary color signal, and red and blue from the image electric signal. Color separation means for separating the primary color signal, means for detecting the level of the luminance signal included in the image electrical signal, and the primary color signal of the higher level of the red signal and the blue signal separated by the color separation means A level detection means for detecting a level higher than the reference level, and a detection output of the brightness signal level detection means and a level of the level detection means when the level detection means detects a level higher than the reference level. When the diaphragm of the optical system is controlled in response to the detection output, and the level detecting means does not detect a level higher than the reference level, And means for controlling the aperture of the optical system only in response to a detection output of said luminance signal level detection means, the imaging apparatus.