JPS60214168A - Back light correction circuit in video camera - Google Patents

Abstract

PURPOSE:To obtain uniformly gradation with fidelity by comparing a mean brightness detecting signal of an image pickup picture obtained by a vidicon with a mean brightness signal at the middle part. CONSTITUTION:A photoelectric converting element 9 arranged at a focus of a lens 7 of a short focal point detects the entire mean brightness of an image pickup picture obtained by the vidicon 2. The mean brightness of the middle part of the image pickup picture obtained by the vidicon 2 is detected by using the photoelectric converting element arranged at the focus of a long focal point lens 8. The detection signal of both the photoelectric converting elements 9, 10 is inputted to a comparison circuit 11, where they are compared and a semiconductor switch 6 is controlled based on the result, correction circuits 4A, 4B are selected and gamma correction is applied properly to a luminance signal at image pickup at the condition of back light.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a backlight supplementary IY4 circuit for a video camera.

Prior Art and Problems When capturing backlight images using a video camera, the so-called backlight compensation is performed by opening the lens diaphragm in the same way as with a normal still camera, or by lowering the sensitivity of the image sensor such as a videocon. stop. By kneading, it is possible to obtain a bright captured image of the subject as a whole, which corresponds to the intermediate 1f (,).

2, from the beginning, the business core in the video camera, C
An image sensor such as a CD has a narrower latitude than a color NECA film or the like. For example, the human output characteristics of the business computer -・
An example is shown by the solid line in 1st U; 4, and usually the subject is imaged in 1. -c Only the straight line portion of this characteristic is used so as to obtain a captured image with faithful 1i4 gradation over the entire predetermined radius from low brightness to high brightness.

On the other hand, when the sensitivity of the vidicon is increased by 1 to compensate for backlight as in 1-it\, the characteristics of the high-brightness portion become non-linear, as shown by the dotted line in FIG. Therefore, in the captured image obtained, although the 1 degree portion of the live bait is bright and faithful, the gradation power (thinner - (l) of the high brightness portion is not enough).

In the end, the overall brightness balance is poor - CL. This same thing also happens to the so-called solid carrier element R-C with narrow latitude cCn.

OBJECTIVE OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems in video cameras, and to provide backlight compensation that enables to obtain a captured image with faithful gradation throughout from low brightness to high brightness during reverse)'L imaging. The objective is to provide a stop circuit.

Structure of the Invention The present invention provides a frontlighting characteristic changing circuit having human output characteristics for frontlighting, and at least one backlighting characteristic having an input/output characteristic in which only an output in an intermediate input region is relatively large compared to the input/output characteristic. A characteristic changing means having a changing circuit, and a selecting means for selecting one of the plurality of characteristic changing circuits of the characteristic changing means and supplying a luminance signal thereto.

Embodiment of the Invention FIG. 2 is a block diagram showing an embodiment of a video camera according to the invention. In the figure, l is a lens, 2 is a vidicon as an image sensor placed at the focal point of the lens l, and 3 is a video signal input from the vidicon 2, and a luminance signal (Y), a red signal (R), and a blue signal (B). ) (however, these red signals (R) and blue signals (B) are not shown); 4 is a gamma correction circuit that inputs the luminance signal (Y) from the signal separation circuit 3 and performs gamma correction; Reference numeral 5 denotes an encoder which receives the gamma-corrected luminance signal (Y) from the gamma correction circuit 4, the red signal (R), and the blue signal (B) to obtain a color composite video signal.

The gun correction circuit 4 as a characteristic changing means is a first correction circuit 4 having a gamma value (input/output characteristic) such that a properly gamma-corrected luminance signal can be obtained during imaging under front light.
A, and a second correction having a gamma value smaller than the gamma value of the first correction circuit 4A (that is, an input/output characteristic in which only the output of the intermediate input region is relatively large compared to the input/output characteristic of the first correction circuit 4A). It has a circuit 4B. Two correction circuits 4A
and 4B are selectively selected by the semiconductor switch 6, and the selected correction circuit gamma-corrects the luminance signal (Y) from the signal separation circuit 3 and supplies it to the encoder 5. This semiconductor switch 6 is controlled by a comparison circuit described later.

Lenses 7 and 8 are arranged so that their optical axes are parallel to the optical axis of lens l, with lens 7 having a short focus and lens 8 having a longer focal length than lens 7. ing.

At the focal points of both lenses 7 and 8, photoelectric conversion elements 9 and 1O having the same light-receiving area are arranged, respectively.

Therefore, the overall average brightness of the captured image obtained by the vidicon 2 can be detected by the photoelectric conversion element 9 placed at the focal point of the short focal length lens 7, and the photoelectric conversion element 9 placed at the focal point of the long focal length lens 8 can be detected. The element 10 can detect the average brightness of the central portion of the captured image obtained by the vidicon 2.

The detection output signals of both photoelectric conversion elements 9 and 10 are input to a comparison circuit 11. The comparison circuit 11 compares the human power signals as described below, and controls the semiconductor switch 6 based on the result. That is, in the comparison circuit 11, the overall average luminance detection signal from the photoelectric conversion element 9 and
By comparing the central part average brightness detection signal from the photoelectric conversion element IO, it is determined whether the average brightness of the central part in the image captured by the vidicon 2 is greater than or equal to the overall average brightness of the same image, or if the average brightness of the central part is within a predetermined value. The semiconductor switch 6 is configured to select the first correction circuit 4A for front light in the gamma correction circuit 4 when the brightness is smaller than the overall average brightness.
In addition, when the average brightness of the central portion exceeds the predetermined value and is smaller than the overall average brightness, the semiconductor switch 8 is configured to select the second correction circuit 4B for backlighting in the gamma correction circuit 4. Control.

The above configuration is installed at a predetermined location on the casing of the video camera, and the lenses 7 and 8 are placed near the lens 1.

This configuration was chosen because the main subject is located in the center of the image captured by the vidicon 2, and the high-brightness subjects are located around it, which can essentially be considered to be a backlight imaging state. Moreover, the central part can be considered to have intermediate brightness, and the average brightness of the entire image captured by the vidicon 2 and the average brightness of the central part of the same image are compared as explained above. This allows backlight to be accurately determined. In addition, based on this determination result, by appropriately gamma correcting the luminance signal during backlight imaging, it is possible to suppress the brightness of the high-luminance portion of the image captured by the vidicon 2,
Moreover, the intermediate brightness portion, that is, the main subject, can be made relatively bright.

In addition to the above-mentioned example, there are the following methods for detecting the average brightness of the entire image captured by the vidicon 2 and the average brightness of the central portion of the image.

(1) As shown in FIG.
In place of the photoelectric conversion elements 9 and 10, two optical conversion elements 22 and 23 having exactly different light receiving areas are placed. By doing so, the overall average brightness of the image captured by the vidicon 2 can be detected from the photoelectric conversion element f'22, which has a large light-receiving area, and the photoelectric conversion element 23, which has a smaller light-receiving area than the photoelectric conversion element-22.
It is possible to detect the average brightness of the central portion of the image captured by Vision 2.

(2) As shown in FIG. 4, the overall average brightness of the captured image is electronically detected from the composite video signal obtained by the encoder 5 instead of the lenses 7 and 8 and the photoelectric conversion elements 8 and 1O. An overall average brightness detection circuit 24 and a central portion average brightness detection circuit 25 for electronically detecting the average of 1 to 1 degree in the central portion of the captured image are provided. The central portion average brightness detection circuit 25 includes an image crimp circuit 25A, ! l:
The image clipping circuit 25 has a 4-average detection circuit 25B that detects the average brightness of the signal from the image clipping circuit 258. The image processing circuit 25A has a composite image quality of 1. ; Input S l, and only the central part M2 of the video signal (signal indicating no change in brightness along the Kinoshita scanning line) in each IH in the central part layer of the vertical scanning period of 2 is input. is taken out electrically. The signal S3 thus extracted (indicated by the solid line in FIG. 5(B)) is supplied to the average brightness detection circuit 25B, and this circuit
Obtain the average brightness of the central part of the captured image. For example, 1
If shown on the screen, it is as shown in Fig. 6, and one screen has 26
The average brightness of the central portion 26A inside is obtained. In addition, AL
C (Δautomatic Levr41 Control
l) Since the output signal of the circuit is constant, this can be used as the overall average brightness detection signal of the captured image, which is input to the comparison circuit 11 in addition to the above-mentioned overall average brightness detection circuit 24. I can do it.

Moreover, instead of detecting the average brightness of the entire captured image and the average brightness of the central part of the image and comparing the two as described above, for example, in FIG. Brightness 1B] of the outer part of the central part of the captured image (obtained by the central part average brightness detection circuit 25) instead of the detection circuit 24. An outer part average brightness detection circuit that detects uniformity (this circuit consists of an image clipping circuit similar to the central part average brightness detection circuit described above and an average brightness 1 detection circuit that manually inputs 4Lj from this image clipping circuit) The detection signal from the outer part average brightness detection circuit and the detection signal of the central part average brightness detection circuit 25 or 15 are input to the comparison circuit 11. In 11, the two were compared 1. If the average brightness of the central part of the captured image is greater than or equal to the average brightness of the outer part of the captured image, or if the average brightness of the central part is smaller than the average brightness of the outer part within a predetermined value, the j1111 light source in the gamma correction circuit 4 is The first correction circuit 4
The semiconductor switch 6 is controlled to select A, and when the average brightness of the center part exceeds the predetermined value and is smaller than the average brightness of the outer part, the gun corrects the backlight in the correction circuit 4. Backlight can also be determined appropriately by controlling the semiconductor switch 6 to select the second correction circuit 4B for use. Furthermore, below
Optically and electrically photographed objects (captured images) as described in L.
A manual switch is provided at a predetermined location on the casing of the video camera without using a means for detecting the brightness of the subject and a semiconductor switch, and the operator of the video camera determines whether or not the subject is backlit, and responds accordingly. 17 to operate the manual switch 17 to operate the first or second correction circuit 4 of the comma correction circuit 4.
Δ or 4B can also be selected.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, it is possible to obtain a captured image having an image tone that is faithful to the subject over the entire range from low brightness to high brightness during backlight imaging.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the input/output characteristics of a vidicon, FIG. 2 is a block diagram showing an embodiment of the video camera according to the present invention, and FIG. 3 is a diagram showing another embodiment of the video camera according to the present invention. 4 is a block diagram showing the main parts of still another embodiment of the video camera according to the present invention; FIG. 5 is a waveform diagram showing one aspect of the composite video signal according to the present invention; FIG. FIG. 6 is a diagram showing an example of a captured image according to the present invention. l...lens, 2...visicon. 3... Signal separation circuit, 4... Gamma correction circuit. 5...Encoder, 8...Semiconductor switch, ? , 8, 20.21... Lens, 13, 10.22.23... Photoelectric conversion element, 11.
. . . Comparison circuit, 24 . . . Overall average luminance detection circuit, 25 . . . Center portion average luminance detection circuit. Fig. 1 Input Fig. 2 Fig. 3 4A65 Fig. 5 Re---M1 ------- Kazuo Sugi, Tonoko 6 Case, Indication Patent Application No. 59-69927 2, Name of the Invention: Backlight correction circuit in a video camera, relationship with the person who makes the correction case, Watch Applicant (520) Fuji Shasei Film Co., Ltd.-1 Agent 2-chome Toranomon, Minato-ku, Tokyo 105 [9F Akiyama Building, No. 13-22-Telephone: (03) 508-8388, (9067) Patent Attorney Takaaki Nagashima (J□5, 8th edition of the amendment order)

Claims (1)

[Scope of Claims] 1) A frontlighting characteristic changing circuit having frontlighting input/output characteristics and at least one input/output characteristic having an input/output characteristic in which only the output of an intermediate input region is relatively large compared to the input/output characteristics. Characteristic changing means having a characteristic changing circuit for backlighting; and selecting means for selecting one of the plurality of characteristic changing circuits of the characteristic changing means and supplying a luminance signal to it. Backlight correction circuit for video cameras. 2. The backlight correction circuit for a video camera according to claim 1, wherein the selection means includes a switch that allows one of the plurality of characteristic changing circuits to be selected by manual switching. backlight correction circuit. 3) In the backlight correction circuit for a video camera according to claim 1, the selection means includes: a detection means for detecting the overall average brightness and the average brightness of the central part of the subject; Comparing the average brightness detection signal and the central part average brightness detection signal, it is determined whether the average brightness of the central part of the subject is greater than or equal to the overall average brightness, or if the average brightness of the central part is within a predetermined value, When the brightness is smaller than the brightness, the characteristic changing circuit for front lighting in the characteristic changing means is selected, and when the average brightness of the central portion exceeds the predetermined value and is smaller than the overall average brightness, the characteristic changing circuit in the characteristic changing means is selected. A backlight correction circuit for a video camera, comprising a control means for selecting the backlight characteristic changing circuit. 4) In the backlight correction circuit for a video camera according to claim 3, the detection means includes two lens systems having different focal lengths, and the overall average node detection signal and the central partial average brightness detection signal. A backlight correction circuit for a video camera, characterized in that two light-receiving elements having the same light-receiving area are disposed at the focal points of the two lens systems, respectively. 5) In the backlight supplementary circuit in the video camera (J) according to claim 3, the +ii+ detection means comprises two lens systems having the same focal length, and the overall 4iP
-J brightness detection signal and the central border; [;
A video camera characterized in that two light-receiving elements having different light-receiving areas are arranged at the focal points of the two lens systems, respectively, and have different light-receiving areas so as to obtain a detection signal in a uniform manner. Backlight supplement 1 [circuit. G) In the backlight correction circuit for a video camera according to claim 3, the detection stage' detects the overall average brightness and the average brightness of the central part of the subject number by calculating the video signal. A backlight correction circuit for a video camera characterized by having two circuits for electrically detecting the citrus fruit. 7) A backlight correction circuit for a video camera according to claim 3. In the video camera, the detection means has an automatic exposure adjustment means that adjusts the overall average intensity detection signal.(J) Backlight compensation circuit. In the backlight correction circuit for a video camera according to item 1, the selection stage +j includes detection means for detecting the average brightness of the center part of the subject and the average brightness of the row side parts thereof, and the average brightness of the center part from the lower detection stage. Comparison between the brightness detection signal and the average brightness detection signal on the evening side When the luminance is within a predetermined 1h, the outer 1i
-Even brightness nail-, the characteristic changing circuit for front lighting in the characteristic changing means is selected, and when the average brightness of the center portion exceeds the predetermined value and is smaller than the average brightness of the outside A backlight correction circuit for a video camera, comprising control means for selecting the characteristic change g1 circuit for backlight in the characteristic change means.