JP2990733B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image pickup apparatus, and more particularly to light quantity control.

(Prior Art) FIG. 5 shows a conventional example of a two-panel video camera circuit using two CCDs. In the figure, an iris drive circuit 21 for controlling the diaphragm 3 selects a maximum value among R, B, and G Ch signals at the same point in a NAM (non-additive mixing) circuit 18 by using an output signal of the amplifier 8. Detection circuit (Def) 4 for selected signal
The detection and smoothing are performed in step 1, and the aperture 3 is controlled so that the smoothed signal level becomes the set reference value. In this average detection method, the average of the brightness of the entire screen is set to the optimum brightness. It is a method of controlling so that the detection voltage of the screen where the highlight part and the black part are evenly controlled only by controlling the aperture so that it becomes a constant reference value, for example, a full-color screen is photographed In this case, there is a disadvantage that the output of the image sensor is reduced and the S / N ratio is deteriorated. In addition, there is a method called peak detection. In the case of peak detection, the output of the image sensor can be increased in a single color screen, but the aperture control is performed by the maximum peak value regardless of the size of the area. In order to perform, even if the high-luminance part is a small area, aperture control is performed by being subtracted from the luminance level of the high-luminance part of the small area,
There has been a problem that the signal level of the low-luminance part in the wide area becomes low, the entire screen becomes dark, and the S / N ratio also deteriorates.

(Problems to be Solved by the Invention) The present invention improves the S / N ratio when shooting a screen of a single color or when the screen is mostly low in brightness and has a very high brightness portion in part. It is an object of the present invention to solve the problem described above even when there is a very high luminance portion in a part without the whole screen being darkened more than necessary by the effect of the aperture.

(Means for Solving the Problems) In order to achieve the above object, an image pickup apparatus according to the present invention includes a photographing lens, an image pickup unit that receives light transmitted through the photographing lens and outputs a video signal, and an image pickup unit. Amplifying means for amplifying a video signal having a predetermined level or higher with a high gain, and amplifying a video signal having a predetermined level or less with a lower gain than the gain; Light amount control means for controlling the amount of light to be emitted, and the light amount control means is controlled in accordance with the output from the amplification means.

(Operation) According to the above configuration, non-linear amplification is performed such that a video signal having a predetermined level or higher is amplified with a high gain, and a video signal having a predetermined level or lower is amplified with a low gain. Then, the amount of light incident on the imaging means is controlled according to the amplified output signal.

For example, even if there is a highlight area having a small area in the screen, the aperture is narrowed down by the influence of the highlight area, and the entire screen is not darkened more than necessary. Also, for subjects with low contrast, the operating point can be given as high as possible within the dynamic range of the CCD.
A screen with a good S / N ratio can be obtained.

(Embodiment) FIG. 1 shows a block diagram of an embodiment in which the present invention is applied to a two-panel video camera using two CCDs. In the present invention, in FIG. 1, the output signal of the amplifier 8 is selected by the NAM circuit 18 to select the maximum intensity signal in the R, B, and G color channels, and the selected maximum intensity signal is converted by the nonlinear correction circuit 19. Amplify,
The output signal of the non-linear correction circuit 19 is averagely detected by a detection circuit (Det) 20, and the iris drive circuit 21 controls the aperture by the average detected signal.

The nonlinear correction circuit 19 has input / output characteristics as shown in FIG. 3, increases the amplification factor of an input signal within a certain signal level range, and increases the amplification factor for an input signal below the lower limit of the range. FIG. 2 shows an example of a circuit for setting the output signal to a low level and clipping the output above a certain signal level to suppress the maximum value of the output signal strength.

The detection circuit (Det) 20 detects and averages the output signal of the non-linear correction circuit 19, and outputs a full-screen average detection voltage Vav. The average detection voltage Vav of the entire screen is the iris drive circuit 21
The aperture is controlled so that the detection voltage Vav becomes a predetermined value. As described above, since the non-linear correction circuit 19 clips a certain luminance level or higher, even if there is a very bright portion in the screen, the aperture is stopped down for that reason, and the whole is not darkened more than necessary.

This will be described in more detail. Input voltage Vin to the non-linear correction circuit 19, when Vin <of E _1, the collector voltage of the transistor Q ₄
V _M is given by the following equation.

On the other hand, when the Vin ≧ E _1, the transistor Q ₂ passes, in this case, the collector voltage V _M of the transistor Q ₄ are expressed as follows.

Further, the output voltage V _out from the nonlinear correction circuit 19 is represented by the following equation.

V _out = V _M +0.6 (where V _M <When _{E 3) V out = V 3} ( provided that when V _M <E ₃₎ in the characteristic diagram shown in FIG. 3, the imaging element output Ten
0%. For example, the CCD dynamic range is 60
If it is 0 mV, 100% equivalent is set to 200 mV so as not to impair the reproduction of the highlighted portion. In the example shown in FIG. 3, the gain is fixed at 1 for up to 40% input, about 3.8 for 40% to 90% input, and 224% for 90% input or more. When taking a gray scale chart with a gradation ratio of 40: 1, gamma of 0.45, and an average reflectance of 24%, if the image sensor output for white with an reflectance of 83% was adjusted to 100%, the conventional average detection With this method, the output of the image sensor when capturing a full-color chart was 24%. On the other hand, in the present embodiment, if a full-screen one-color chart is photographed with the image sensor output adjusted to 100% in the same manner as described above, the image sensor output becomes 40% and the ratio of about 4 dBS / N Will be improved.

The overall circuit of the video camera will be described with reference to FIG. 1 is a lens, 2 is an infrared cut filter,
Reference numeral 3 denotes an aperture, and 4 denotes a green (G) transmission prism, which transmits only green light. 5 is a magenta transmission prism,
Blocks only green light. A G-CCD 6 detects a G signal from all pixels. Reference numeral 7 denotes an R, B-CCD in which R transmission filters and B transmission filters are alternately arranged in a parallel lattice on the front surface, and R, B signal outputs are obtained in a dot-sequential manner. The G, R, and B signals detected by the CCDs 6 and 7 are converted to a well-known CDS circuit (Corr
(Elation Double Sampling) 8 individually reduces noise, and becomes G, R, B video signals. Thereafter, the G, R, and B video signals are further removed of noise by a low-pass filter (LPF) circuit 9, amplified to an appropriate intensity by an AGC (auto gain control) circuit 10, and a black level is kept at a constant potential by a clamp circuit 11. Fix (clamp) and measure the stability of the black level of the video signal. Reference numeral 12 denotes a white balance circuit which performs white balance adjustment by adjusting gains of R and B channels.

13 is a pedestal adjustment circuit that adjusts the black level of the video signal by correcting the black level rise due to the variation of each element and the flare of the optical system. When the signal is 0, the output signal is 0
Adjust so that With this circuit, the black level can be corrected during backlight by changing the bias voltage according to the backlight state. The bias voltage used for the black level correction is calculated by a function Fped (ΔE) using the difference ΔE between the average detection voltage Vav and the average detection voltage Va at the lower center of the screen in the arithmetic circuit 26 as a variable.
Is calculated by

Reference numeral 14 denotes a gamma correction circuit, which in this embodiment corrects the gamma to 0.45 in accordance with the characteristics of the receiver.

Reference numeral 15 denotes a twenty-first correction circuit which compresses the gradation of a high-luminance part to expand the dynamic range.

Reference numeral 16 denotes a matrix circuit which forms a luminance signal and a dye signal from the R, B, and G video signals. The color difference signal is balanced modulated to become a color signal, mixed with a luminance signal to which a synchronization signal is added,
It becomes a composite video signal.

Reference numeral 18 denotes a NAM circuit as shown in FIG. 4, which inputs the output signal of the amplifier circuit 8 to each of the R, B, and G channels, and outputs a signal having the maximum value among the R, B, and G signals.

Reference numeral 20 denotes a detection circuit (Def) which detects and averages the output signal of the non-linear correction circuit 19 and sends the full-screen average detection voltage Vav to the iris drive circuit 21.

An A / D circuit 22 converts an analog signal of Def20 into a digital signal and inputs the digital signal to the arithmetic circuit 26. Reference numeral 23 denotes an analog switch which is controlled by a control signal from the pulse generation circuit 36 and passes only a luminance signal at the lower center of the photographing screen. The detection circuit 24 detects the luminance signal at the lower center of the screen that has passed through the analog switch 23, and outputs an average detection voltage Va at the lower center. The A / D circuit 25 converts the signal Va into a digital signal and inputs the digital signal to the arithmetic circuit 26.

The arithmetic circuit 26 calculates the difference ΔE between the detection voltages Vav and Va, and when ΔE is larger than a predetermined value, calculates the aperture correction signal.
The digital signal is sent to a D / A circuit 28 and converted into an analog signal of a digital signal. Then, the digital signal is added to an adding circuit 29 to open the aperture 3 so that the subject can be seen with appropriate brightness. Also, AGC circuit 1
0 The correction signal is supplied to the D / A circuit 32, the pedestal adjustment circuit 13 is supplied to the D / A circuit 30, and the correction signal is supplied to the D / A circuit 31.
To perform various types of backlight correction control.

(Effects of the Invention) As described above, according to the present invention, a video signal having a predetermined level or higher is amplified with a high gain, and a video signal having a predetermined level or lower is incident on an imaging unit in accordance with a signal amplified with a low gain. By controlling the amount of light, images with a good S / N ratio can be obtained regardless of the contrast ratio of the screen. That is, even if there is a highlight portion in a part of the screen, the aperture is not narrowed down more than necessary. Even when shooting a screen with no contrast, such as a full-screen one-color screen, the aperture is controlled to an appropriate output level within the range where the image sensor output does not saturate, so the S / N ratio is controlled. You can always get good images.

[Brief description of the drawings]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram of a nonlinear correction circuit, FIG. 3 is a characteristic curve of the nonlinear correction circuit, FIG. 4 is a NAM circuit diagram, and FIG. FIG. 1 ... Lens, 2 ... Infrared cut filter, 3 ... Aperture, 4 ... G transmission prism, 5 ... Magenta transmission prism, 6 ... G-CCD, 7 ... R, B-CCD, 8 ... …amplifier,
9 LPF, 10 AGC, 11 clamp circuit, 12 white balance circuit, 13 pedestal adjustment circuit, 14
... Gamma correction circuit, 15 ... 21 correction circuit, 16 ... Matrix circuit, 17 ... MOD, 18 ... NAM, 19 ... Non-linear correction circuit, 20 ... Detection circuit (Def), 21 ... Iris drive Circuit, 22 A / D circuit, 23 Analog switch, 24 Def, 25
…… A / D circuit, 26 …… Calculation circuit, 27 …… CCD drive circuit, 28
... D / A circuit, 29 ... Addition circuit, 30 ... D / A circuit, 31 ...
D / A circuit, 32 D / A circuit, 33 Adder circuit, 34 NA
M, 35: Gain switching circuit, 36: Pulse generation circuit, 37
...... Def.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/238

Claims (3)

(57) [Claims] An imaging means for receiving a light transmitted through the imaging lens and outputting a video signal; and a high gain for a video signal having a predetermined level or more among the video signals output from the imaging means. Amplifying means for amplifying the image signal at a predetermined level or less, and amplifying the image signal with a gain lower than the gain, and a light amount controlling means for controlling the amount of light incident on the imaging means, and an output from the amplifying means. An image pickup apparatus, wherein the light amount control means is controlled in accordance with the condition. 2. The image pickup apparatus according to claim 1, wherein said light amount control means is controlled in accordance with an average value of the output of said amplification means. 3. An image pickup apparatus according to claim 1, wherein said light amount control means is an aperture mechanism.