JP2990732B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image pickup apparatus, and more particularly to correction at the time of photographing.

(Prior Art) In a video camera, when the average luminance of the object scene is high, the aperture is usually stopped down. Therefore, when the subject is backlit, the main subject is underexposed and becomes black. In order to prevent this, the aperture is adjusted to the main subject during backlighting.
Even in such a case, there is a problem that light from the background enters the subject due to light reflection on the lens surface, the average luminance of the main subject increases, the subject becomes whitish, and sharpness is lost. For example, as shown in FIG. 9A, when a black subject is photographed by backlight, the center of the screen where the main subject is located is black, and the surrounding background is a bright field state.
Flare occurs due to the internal reflection of the optical system, and the luminance in the subject image increases, and the luminance level of the subject is changed from the actual luminance level (black level) Vd shown in FIG. In addition, Vf increases by flare. In correcting such a phenomenon, there has been a problem that satisfactory screen reproducibility cannot be achieved simply by opening the aperture in accordance with the luminance of the main subject.

(Problems to be Solved by the Invention) It is an object of the present invention to eliminate an increase in luminance level due to a flare in backlight photography and to improve the reproducibility of a subject.

(Means for Solving the Problems) In order to achieve the above object, an image pickup apparatus according to the present invention comprises: a photographing lens; an image pickup unit for receiving a light transmitted through the photographing lens to generate a video signal; An adjusting unit that adjusts a signal black level; a detecting unit that detects a luminance difference between a main subject in a field and a background; and a method of adjusting a black level by the adjusting unit according to a detection result of the detecting unit. An imaging apparatus, comprising: control means for controlling.

(Operation) According to the above configuration, imaging is performed by the imaging unit, a video signal is generated, and the black level of the video signal is adjusted. Then, the luminance difference between the main subject in the scene and the background is detected,
The adjustment method of the black level adjustment is switched according to the detection result. In this way, the difference in brightness between the main part and the background is used as a standard for adjusting the black signal level, and the black signal level is adjusted based on the difference in luminance between the main subject and the background, so that harmony is always achieved. Image 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. First, the pedestal adjustment circuit 13 as a main part of the present invention will be described. The pedestal adjustment circuit 13 is for amplifying a video signal obtained by the imaging device, and is inserted after performing black level clamp, white balance adjustment, and the like.Specifically,
A bias voltage is superimposed on the input signal, and adjustment is performed so that the output signal becomes 0 when the input signal is normally 0. FIG. 2 shows an example of the circuit. In the figure, reference numerals 3 and 4 denote OP amplifiers, and this circuit adjusts a zero point of an input video signal by externally inputting a control voltage Vped to a reference voltage Vref. The adjustment is performed so that the black level of the video signal is substantially equal to the level of the blanking signal, and is fixed thereafter. In the present invention, the black level at the time of backlight is corrected by changing this Vped according to the backlight state. The Vped used for the black level correction is output from the arithmetic circuit 26. The arithmetic circuit 26 calculates a function Fped (ΔE) using a difference ΔE between the average detection voltage Vav of the entire screen of the video signal and the average detection voltage Va at the lower center of the screen as a variable, and converts the analog signal into an analog signal by the D / A circuit 30. Is entered. That is, the superimposed voltage Vped due to flare is given by Vped = Fped (ΔE). Offset voltage Vr of pedestal adjustment circuit 13
When Vped is subtracted from ef, the offset voltage decreases by Vped,
Accordingly, the output voltage of the hemister adjustment circuit 13 also decreases by the superimposed voltage Vped due to flare.

Next, general examples will be described. In this embodiment, in addition to the above-described correction, backlight correction for the diaphragm and knee correction (gradation compression) at the time of backlight are also performed. In FIG. 1, reference numeral 1 denotes a lens, and 2 denotes an infrared cut filter, which is insensitive to human eyes, generates only noise, and cuts infrared light which is disturbing for photographing. Reference numeral 3 denotes an aperture, and 4 denotes a G transmission prism that transmits only green (G) light. Reference numeral 5 denotes a magenta transmission prism, which transmits the magenta light transmitted through the G transmission prism 4. Reference numeral 6 denotes a G-CCD, in which light transmitted through the G transmitting prism 4 is incident, and a G luminance signal is detected in all pixels. Reference numeral 7 denotes an R, B-CCD, in which the light transmitted through the magenta transmitting prism 5 is incident, and two lights of red (R) and blue (B) are detected by individually corresponding pixels, and R and B are formed as separate signals. Output. The G, R, and B signals detected by the CCDs 6 and 7 are converted to a well-known CDS circuit (Correlation Double Sampling).
In step 8, the noise is reduced individually to produce G, R, and B video signals.
Thereafter, the G, R, and B video signals are further removed of noise by an LPF (low-pass filter) circuit 9, amplified to an appropriate intensity by an AGC (auto gain control) circuit 10, and clamped.
Clamped at 11. 12 is a white balance circuit, R,
The white balance is adjusted by adjusting the gain of the B channel.

Reference numeral 13 denotes a pedestal adjustment circuit which adjusts the black level of the video signal so as to be a predetermined reference (blank elimination level). Specifically, a bias voltage is superimposed on the input signal,
Normally, when the input signal is 0, adjustment is performed so that the output signal becomes 0.

The gamma correction circuit 14 is a circuit that corrects a gamma value in accordance with the characteristics of the receiver, and in this embodiment, corrects the gamma to 0.45.

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 dye 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 non-additive mixing (NAM) circuit as shown in FIG. 4, which receives the output signal of the CDS circuit 8 for each of the R, B, and G channels and outputs the signal of the maximum value among the R, B, and G signals. I do.

Numeral 19 is a non-linear correction circuit which has input / output characteristics as shown in FIG. 5, increases the amplification factor of an input signal within a certain luminance level range, emphasizes highlights, and clips at a certain luminance level or higher. And a circuit for suppressing the maximum value of the output signal strength.

The detection circuit (Def) 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
To the iris drive circuit 21 and the detection voltage
The aperture is controlled so that Vav approaches 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 3 is narrowed down by the pulling of the portion, and the phenomenon that the entire screen becomes dark is prevented. Can come off.

Reference numeral 22 denotes an A / D circuit which converts an analog signal of the full-screen average detection voltage Vav, which is an output of the detection circuit 20, 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 the output signal of the nonlinear correction circuit 17 corresponding to the lower center of the photographing screen.

The detection circuit 24 detects the output signal of the non-linear correction circuit 17 corresponding to the lower center of the screen passing through the analog switch 23,
The lower center average detection voltage Va is output.

The A / D circuit 25 converts the signal Va into a digital signal and inputs the digital signal to the arithmetic circuit 26.

As described above, the arithmetic circuit 26 detects the detection voltages Vav and V
The aperture correction signal for backlight correction obtained from the difference (ΔE) a is supplied to the D / A circuit 28, and the AGC circuit 10 correction signal is supplied to the D / A circuit 32.
Then, the pedestal adjustment circuit 13 correction signal is output to the D / A circuit 30 and the knee correction circuit 15 correction signal is output to the D / A circuit 31.

36 is a pulse generating circuit, FIG. 6 shows an embodiment thereof, and FIG. 7 shows a signal diagram. Horizontal sync signal HD with counter 36A
When the count reaches a predetermined count, the flip-flop 36D is inverted with the carry signal, and the output signal C is set to “H”.
Level. The counter 36A and the flip-flop 36D are reset by the input of the vertical synchronization signal VD, and the output signal C is reset.
Is set to “L”, and a control signal C synchronized with the vertical synchronization signal as shown in the figure is transmitted. Mono multi 36B is horizontal sync signal H
Synchronized with D, the central part between one pulse generates a control signal D of "H" level, the mono multi 36C is synchronized with the horizontal synchronizing signal HD, and the central part between one pulse is a little wider than the signal A. A control signal E which becomes "H" level is generated. The adder 36E adds the control signal C and the control signal D, and generates a control signal A corresponding to WindowA (see FIG. 8) which becomes "H" level when both signals are at "H" level. The adder 36F adds the control signal C and the control signal D, and generates a control signal B corresponding to WindowB (see FIG. 8) which becomes "H" level when both signals are at "H" level.

The control signal A is sent to the analog switch 23, and when the control signal A is at the "H" level, the analog switch 23 is turned on, and the output signal of the nonlinear correction circuit 19 corresponding to the WindowA area is passed. Selection of WindowA and B is manually performed by the camera user depending on the subject. Therefore, the selected Window
A or WindowB defines the lower center of the screen.

Reference numeral 34 denotes a NAM circuit similar to 18, which receives the output signal of the knee correction circuit 15 for each of the R, B, and G channels and outputs the signal of the maximum value among the R, B, and G signals.

Numeral 35 denotes a gain switch, which determines whether the input signal is WindowA or WindowB. When WindowA is selected, the gain of the AGC circuit 10 is made larger than when WindowB is selected. As a result, when Window A is selected, the main subject image at the lower center of the screen is captured brighter than when Window B is selected.

A detection circuit (Def) 37 detects the video signal amplified by the gain switch 35. The AGC circuit 10 is controlled by the detected signal.

In the above embodiment, the present invention is applied to a two-panel video camera. However, the present invention can of course be applied to a single-panel or three-panel video camera.

(Effects of the Invention) As described above, according to the present invention, the adjustment method of the black level adjustment is switched according to the luminance difference between the main subject in the field and the background. Therefore, since the appropriate black level adjustment is performed according to the situation of the object scene, the reproducibility of the black level is improved even in a shooting situation having a large luminance difference.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a pedestal adjustment circuit diagram, FIG. 3 is a characteristic curve of a knee correction circuit, and FIG.
The figure shows the NAM circuit diagram, FIG. 5 shows the characteristic curve of the nonlinear correction circuit,
FIG. 6 is a diagram of a pulse generating circuit, FIG. 7 is a signal diagram of the pulse generating circuit, FIG. 8 is a diagram for determining a frame of a screen, and FIG. 9 is a diagram for explaining signal changes due to flare. 1 ... lens, 2 ... infrared cut filter, 3 ... aperture, 4 ... G transmission prism, 5 ... magenta transmission prism, 6 ... G-CCD, 7 ... R, B-CCD, 8 ... … CDS, 9…
... LPF, 10 ... AGC, 11 ... Clamp circuit, 12 ... White balance circuit, 13 ... Pedestal adjustment circuit, 14 ... Gamma correction circuit, 15 ... Knee 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.

Claims (1)

(57) [Claims] A photographing lens; an image pickup unit for receiving a light transmitted through the photographing lens to generate a video signal; an adjusting unit for adjusting the black level of the video signal; An imaging apparatus comprising: a detection unit that detects a luminance difference; and a control unit that controls a method of adjusting a black level by the adjustment unit in accordance with a detection result of the detection unit.