JPH0588074U - Backlight compensation device for TV camera - Google Patents

Abstract

(57) [Abstract] [Purpose] With a simple configuration in which a video signal of an image sensor is divided into two and processed, proper backlight compensation is always performed without blooming that occurs in conventional optical aperture adjustment. [Structure] An area dividing section 7 for dividing a video signal Si before AGC processing of the image pickup device 3 into a signal of a central portion A and a signal of a peripheral portion B of a light receiving surface 3a, and a signal of the central portion A and a peripheral portion B. The backlight determination unit 15 that determines the backlight state by comparing with the signal and generates the selection signal for AGC control, the average value detection of the entire image-receiving surface for forward light of the video signal Si, and the central portion A for quasi-backlight only And an AGC control section 8 for detecting the average value of each of the detection values and the detection based on the black level of only the central portion A for backlighting and supplying the detection output selected by the selection signal to the AGC circuit 5 as an AGC control signal. Backlight correction is performed by AGC control of the video signal Si.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a backlight compensation device for a television camera.

[0002]

[Prior Art]

 Conventionally, a television camera (video camera) such as a camera-integrated VTR is provided with a backlight correction device described below in order to automatically perform backlight correction by a simple method. This conventional correction device detects the backlit state by eliminating the influence of high brightness light such as sunlight and illumination light. Therefore, the video signal of the image sensor before AGC processing is divided into areas and a specific portion of the light receiving surface (mainly The central part) is extracted.

Then, the extracted signal is subjected to average detection to determine the back light state from the detection level, the diaphragm (iris) of the optical system is adjusted according to the result of this judgment, and the back light is corrected by opening the diaphragm as the light becomes back light. Apply.

[0004]

[Problems to be solved by the device]

 In the case of the conventional correction device, the backlight condition is detected and corrected using only the signal of the specific part of the light receiving surface, so it is extremely difficult to set the area of the specific part so that proper detection and correction can be performed. However, there is a problem in that the correction is likely to be excessive or insufficient, and it is not possible to always perform appropriate correction.

That is, if the specific portion is widened, it is easily affected by the high-intensity light, and conversely, if the specific portion is narrowed, the specific portion is easily displaced from the main subject due to movement of the main subject (person or the like). However, the photometric error becomes large and the backlight state cannot be detected correctly, and a correction error is likely to occur.

Further, since the portion of the main subject becomes darker than the peripheral portion in the case of so-called backlight, the correction may be made with reference to the brightness of the portion of the main subject, but in the case of normal light, the main subject is always Since the part of the subject is not always darker than the peripheral part, the correction based on the brightness of the part of the main subject causes overs and shorts of the correction.

Further, in the case of the conventional correction device, since the backlight is optically corrected by adjusting the diaphragm, especially in the case of the CCD image pickup device, when the diaphragm is opened carelessly by the backlight correction, so-called blooming occurs. Then, light enters the main subject and the image is unsightly, and there is a problem.

It is an object of the present invention to provide a backlight compensation device for a television camera, which has a simple configuration in which an image signal of an image pickup device is divided into two and is processed, thereby preventing blooming and always performing appropriate compensation. And

[0009]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, in the backlight compensation device for a television camera of the present invention, the video signal before AGC processing of the image pickup device which is supplied to the AGC circuit is divided into a signal in the central portion of the light receiving surface and a signal in the peripheral portion. The area division unit to be divided, the backlight determination unit that compares the central signal and the peripheral signal to determine the backlight condition, and generates the selection signal for AGC control based on the determination result, and the video signal in order. The average output of the entire light-receiving surface for light, the average detection of only the central portion for quasi-backlight, and the black level-based detection of only the central portion for backlight are detected, and the detection output selected by the selected signal is output. An AGC control unit that supplies an AGC circuit as an AGC control signal is provided, and backlight compensation is performed by AGC control of a video signal.

[0010]

[Action]

 In the case of the backlight compensation device for a television camera of the present invention configured as described above, the image signal before the AGC processing of the image pickup element is divided into two by the area dividing section into a signal in the central portion of the light receiving surface and a signal in the peripheral portion. To be done.

Then, the backlight determining unit compares the signal in the central portion with the signal in the peripheral portion, and the backlight condition is accurately determined by comparing the relative brightness of the central portion and the peripheral portion to select the AGC control. A signal is formed.

Further, the AGC control unit detects the video signal before AGC processing by a detection method suitable for photometry of forward light, quasi-backlight, and backlight, respectively.

In particular, since the detection based on the black level of the central portion is used at the time of backlighting, even if the central portion is enlarged so as to reliably capture the main object, the influence of unnecessary high-luminance light is eliminated. Appropriate photometric detection can be performed according to the backlight condition.

Further, each detection output of the AGC control section is selectively selected according to the backlight state by the selection signal of the backlight determination section, and the selected detection output is supplied to the AGC circuit as an AGC control signal.

Therefore, the backlight correction is performed by an electrical signal adjustment that switches the AGC of the video signal according to the backlight state, instead of the conventional optical aperture adjustment.

[0016]

【Example】

 One embodiment will be described with reference to FIGS. 1 to 4. As shown in FIG. 1, the imaging light that has passed through the lens 1 and the diaphragm 2 forms an image on the light-receiving surface 3a of the imaging device 3 having a CCD imaging device structure, and the video signal processing circuit 4 from the latter stage of this device 3 to the AGC circuit. The video signal Si before AGC processing is output to 5.

The video signal Si is supplied to the gate pulse generator 6, the area divider 7, the AGC controller 8, and the iris controller 9. Then, the generator 6 separates and extracts the sync signal from the video signal Si by the sync separation circuit 10, and forms various gate pulses used for timing control of each part by the gate pulse creation circuit 11 based on this sync signal.

The area division unit 7 has two signal extraction gates 12 and 13 for area division, and the gate 12 is based on the gate pulse from the video signal Si to the center portion A of the light receiving surface 3a shown in FIG. The signal is extracted, and the gate 13 extracts the signal of the peripheral portion B in the figure from the video signal Si based on the pulse obtained by inverting the gate pulse by the inverter 14. The central portion A is set to a size corresponding to a main subject such as a person photographed at a standard magnification.

Then, the signals of both parts A and B are supplied to the back light determination part 15 at the subsequent stage, detected by average value detection circuits 18 and 19 via clamp circuits 16 and 17, respectively, and the central part A and peripheral parts are detected. B brightness detection signals a and b are formed.

Further, since the backlight state of the photographing light with respect to the main subject in the central portion A is discriminated in three steps of forward light, quasi-backlight, and backlight, the signals a and b are inverted input terminals (−) of the comparators 20 and 21. , Is supplied to the non-inverting input terminal (+).

At this time, the signal b supplied to the non-inverting input terminal (+) of the comparator 21 is appropriately divided by the resistors 22 and 23 so as to become the quasi-backlight detection reference value. Further, the discrimination conditions for normal light (normal) are a = b or a> b, and the discrimination conditions for quasi-backlight and backlight are a <b, a << b.

The outputs of the comparators 20 and 21 both become high level when a << b, only the comparator 20 becomes high level when a <b, and when a = b, a> b. Both are low level. Therefore, if the outputs of the comparators 20 and 21 are I and II, the backlight state can be determined as shown in FIG. 3 by the combination of the high level (H) and the roll bell (L).

In this case, since the backlight state is determined by the relative comparison between the brightness of the central portion A and the brightness of the peripheral portion B, it is possible to make the determination more accurately than the case of determining only the brightness of the central portion A. In FIG. 3, the lowest combination (output I = L, output II = H) does not occur.

The outputs I and II of the comparators 20 and 21 are subjected to logic gate processing by the NOR gate 24, the AND gates 25 and 26 and the inverter 27, and during forward light, the nogate 24 outputs a selection signal of H, The AND gate 25 outputs a selection signal of H during quasi-backlighting, and the AND gate 26 outputs a selection signal of H during backlighting.

On the other hand, the AGC control unit 8 includes an average value detection circuit 28 for forward light, a central average value detection circuit 28 for quasi-backlight, and a central dark detection circuit 30 for backlight. The detection circuits 28 and 29 are well-known average value detectors using an integrating circuit or the like, and the detection circuit 28 detects the average value of the video signal Si for the entire light-receiving surface 3a, and the AGC control signal C for forward light is used.₁ Then, the detection circuit 29 detects the average value of only the video signal Si in the central portion A according to the control of the gate pulse, and the quasi-backlit AGC control signal C ₂ To form.

Further, the detection circuit 30 is formed as shown in FIG. 4, and the video signal Si is supplied to the clamp circuit of the diode 32, the resistors 33 and 34, and the capacitor 35 via the buffer of the transistor 31, and this clamp circuit Causes DC level reproduction of the black level component.

This DC reproduced signal is supplied to the inverting amplifier of the transistor 37 and resistors 38 and 39 via the buffer of the transistor 36, level-inverted by this amplifier, and then to the gate of the transistor 40 via the buffer. It is supplied to the transistor 41 of.

Then, the transistor 41 is switched by the gate pulse of the pulse generating circuit 11 to extract only the signal of the central portion A, and the extracted signal has a low brightness level by the resistors 42, 43, the diode 44 and the capacitor 45. The detection is performed mainly by the person. Further, the signal formed by this detection is supplied to the operational amplifier 47 via the buffer of the transistor 46 and is inverted and amplified by the operational amplifier 47.

By this inverting amplification, a signal obtained by detecting the video signal Si of the central portion A on the basis of the black level is obtained, and this signal forms the AGC control signal G ₃ for backlight. In FIG. 4, 48 to 56 and 68 are resistors, 57 and 58 are capacitors, and 59 is a bias power supply terminal.

The control signals C _{1 to} C ₃ are supplied to the analog switches 60 to 62, respectively, and the analog switches 60 to 62 are turned on by the selection signals of the NOR gate 24 and the AND gates 25 and 26.

By selectively turning on the analog switches 60 to 62, the AGC control signal Cx for gain adjustment given to the AGC circuit 5 is controlled by the control signal C of the detection circuit 28 during forward light. ₁ And the control signal C of the detection circuit 29 during quasi-backlighting₂ And the control signal C of the detection circuit 30 at the time of backlighting₃ become. Then, the AGC circuit 5 AGC-amplifies the video signal Si according to the control signal Cx, and supplies the AGC-processed video signal So to each circuit unit in the subsequent stage.

Therefore, the AGC reference of the video signal Si is switched according to the backlit state, and at the time of the forward light, the so-called average photometry of the entire surface is used to perform the AGC on the basis of the average luminance level of the entire screen and the forward light. During quasi-backlight, where the brightness of the central area A should be emphasized over time, the AGC is applied based on the average brightness level of the central area A by the average photometry of the central area A, and the central area A becomes dark. The AGC is performed by measuring the black level of the central portion A with reference to the low luminance level of the central portion A and eliminating the influence of unnecessary high luminance light.

Therefore, the appropriate AGC according to the backlight condition is applied to the video signal Si, and the backlight correction is performed not by the optical correction for adjusting the diaphragm 2 but by the electrical signal correction for adjusting the control amount of the AGC. .. Since the brightness level of the dark part of the central part A is measured when backlighting is performed, the central part A is set to be large so that the main subject is always positioned, and more accurate than before. The backlight condition is corrected.

Moreover, since it is an electrical signal correction, it is possible to prevent blooming from occurring due to careless opening of the aperture 2 as in the case of performing an optical correction. By the way, in this embodiment, in order to further improve the effect of the correction, the opening of the diaphragm 2 is adjusted as described below.

That is, the iris control unit 9 clamps the video signal Si by the clamp circuit 63 and supplies it to the gate circuit 64. Based on the selection signal of the NOR gate 24, the selection circuit 65 controls the gate circuit 64 to clamp it. The output signal of the circuit 63 is selectively taken out to form an iris control signal.

In this case, when the selection signal of the NOR gate 24 becomes H, the selection circuit 65 is in the through state, the output signal of the clamp circuit 63 is taken out as it is as the iris control signal, and the selection signal of the NOR gate 24 is output. During the quasi-backlight and the backlight at L, the signal of the central portion A of the output signals of the clamp circuit 63 is taken out as the iris control signal by the gate pulse of the preparation circuit 11. Then, the iris control signal of the gate circuit 64 is used to adjust the opening of the diaphragm 2 via the drive circuit 66 and the iris motor 67.

Therefore, during normal light, the aperture of the diaphragm 2 is adjusted in accordance with the change in brightness of the entire screen, and during quasi-backlight and backlight, the focus is on the change in brightness of the central portion A. The aperture of No. 2 is adjusted, and the reference for adjusting the aperture stop 2 is also switched according to the backlight condition. The configuration of each unit is not limited to the embodiment, and it goes without saying that it can be applied to backlight compensation of various TV cameras (video cameras).

[0038]

[Effect of the device]

 Since the present invention is configured as described above, it has the following effects. The image signal Si before the AGC processing of the image pickup device 3 supplied to the AGC circuit 5 is divided into a signal of the central portion A and a signal of the peripheral portion B of the light receiving surface 3a by the area dividing unit 7, and the backlight determining unit 15 divides the signal. Since the signal of the central portion A and the signal of the peripheral portion B are compared, it is possible to accurately determine the backlight state by comparing the relative brightness of the central portion A and the peripheral portion B to generate the selection signal for AGC control. You can

Furthermore, the AGC control unit 8 detects the image signal Si by a detection method suitable for forward light, quasi-backlight, and backlight measurement, and in particular, when the backlight is used, the central black level-based detection is used. Even if the central portion A is enlarged so as to reliably capture an object, unnecessary high-intensity light effects can be eliminated and appropriate photometric detection can be performed according to the backlit state.

Then, each detection output of the AGC control unit 8 is selectively selected according to the backlight condition by the selection signal of the backlight determination unit 15, and the selected detection output is supplied to the AGC circuit 5 as the AGC control signal. Backlight correction can be performed by electrical signal adjustment that switches the AGC of the video signal Si according to the backlit state, instead of the conventional optical aperture adjustment.

Therefore, the video signal Si is divided into two areas and processed, and it is possible to prevent blooming from occurring and perform backlight compensation more accurately than ever before. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a backlight correction device for a television camera according to the present invention.

FIG. 2 is an explanatory diagram of area division in FIG.

FIG. 3 is an explanatory diagram of determination of a backlight state of FIG.

FIG. 4 is a detailed connection diagram of a part of FIG.

[Explanation of symbols]

 3 image sensor 3a light receiving surface 5 AGC circuit 7 area division unit 8 AGC control unit 15 backlight determination unit A central portion B peripheral portion Si video signal before AGC processing

Claims (1)

[Scope of utility model registration request] 1. An AGC of an image pickup device supplied to an AGC circuit.
A backlit state is determined by comparing an area dividing unit that divides the unprocessed video signal into a central signal and a peripheral signal of the light receiving surface of the device, and the central signal and the peripheral signal. Then, a backlight determination unit that generates a selection signal for AGC control based on the determination result, an average value detection of the entire light-receiving surface for forward light of the video signal, an average value detection of only the central portion for quasi-backlight, and a backlight And an AGC control unit that supplies a detection output selected by the selection signal to the AGC circuit as an AGC control signal by detecting each of the black level-based detections of only the central portion of the video signal. Backlight compensation device for TV cameras that compensates for backlight.