JP3337896B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device,
The present invention relates to a 1-field all-pixel reading type television camera or a high-vision type camera having a short horizontal retrace period and having a large floating capacitance of a transfer electrode.
Improvement of technology for correcting non-uniformity (hereinafter, referred to as dark shading) of a video signal in a dark area in a screen, which is remarkable when a device (hereinafter, referred to as a CCD) type imaging device is used. It is about.

[0002]

2. Description of the Related Art Conventionally, in a three-panel color television camera using a CCD type imaging device, a portion of a video signal output from a CCD having a large change in the level of dark shading generally takes a horizontal blanking period. The video period has just begun. This tendency is remarkable in a television camera using a Frame Interline Transfer (hereinafter abbreviated as FIT) type CCD having a large floating capacitance of a vertical transfer electrode. Further, the horizontal retrace period in the progressive scanning method, that is, the one-field all-pixel reading method, is 6 μS.
In the following television cameras, the dark shading is remarkably remarkable in the above-mentioned portions. Also, this tendency is due to the fact that the stray capacitance of the vertical transfer electrode is relatively small.
Even a television camera using an ine transfer (hereinafter abbreviated as IT) type CCD becomes remarkable if the television camera has a horizontal retrace period of 4 μS or less such as a high-definition television. Further, in a high-definition camera, this tendency is particularly remarkable under the condition that the characteristics of the FIT type CCD image sensor are driven to be stable.

A video signal on which a shading waveform output from a CCD at the time of shading is superimposed has, for example, a waveform of a dark shading portion having a horizontal gradient as shown in the waveform of FIG. When the video period starts from the retrace period, it gradually falls, then steeply, changes gradually, and then becomes almost a straight line.

For this reason, conventionally, as an imaging apparatus having a dark shading correction function, for example, there is a block configuration shown in FIG. This imaging apparatus will be described with reference to FIG. 3. 1, 2 and 3 are separated into red (r), green (g) and blue (b) color components by a color separation optical system through a lens 11. The imaging element captures the captured image light, converts the light into a video signal, and outputs the video signal. Reference numeral 6 denotes a first signal processing unit that performs predetermined signal processing, for example, sampling processing and signal level amplification processing, on the video signals output from the imaging elements 1, 2, and 3, and outputs the processed video signals. is there. Each output signal V from the first signal processing unit 6
ir, Vig, and Vib are video signals Vpr, Vpg, and Vpb whose amplitudes are made uniform by the resistors R7 to R12.

On the other hand, in a circuit for generating a correction waveform for correcting shading, a timing generator 14 outputs a horizontal synchronizing signal (HD pulse signal) for synchronizing each part in a horizontal operation cycle, and a horizontal retrace signal. A pre-blanking signal (PRE.BL signal) having a pulse waveform slightly smaller than the width of the period is generated. The HD pulse signal is input to the sawtooth waveform generation circuit 4 and also to the switch SW1. In addition, PRE. The BL signal is also input to the sawtooth waveform generation circuit 4 and also to the calculus circuit 25.

As shown in FIG. 8, the saw-tooth waveform generating circuit 4 opens and closes the analog switch integrated circuit IC1 with the HD pulse signal (FIG. 9 (b)), so that the operational amplifier A1 changes the reference voltage E1, The HSAW signal ((n) in FIG. 9) having a horizontal sawtooth waveform determined by the E2, the integration capacitance C1, and the resistor R1 is generated. The HSAW 'signal having a horizontal sawtooth waveform (FIG. 9 (p)), which is opened and closed by the BL signal (FIG. 9 (h)) and becomes a ground potential during a period slightly shorter than the horizontal retrace period.
Is generated and output.

[0007] The HSAW 'signal is input to the switch SW1 like the HD pulse signal, one of them is selected and output, and then input to the differentiating circuit 25. This differentiation circuit 25
Will be described with reference to FIG.

The HD pulse signal or the HSAW 'signal input to the differentiating circuit 25 is differentiated by C2 and R3 with a predetermined time constant, and further inverted and amplified by the operational amplifier A2 ((c) of FIG. 7). Or (f)) and input to the analog switch integrated circuit IC3. The output of the analog switch integrated circuit IC3 is PRE. BL
According to the switching timing by the signal, the period slightly shorter than the horizontal flyback period is set to the reference potential, and the other is the differentiated and inverted waveform, that is, the dark shading correction signal ((d) in FIG. 7 or ((G) a waveform signal indicated by a solid line).

The dark shading correction signal output from the differentiating circuit 25 is input to the mixing circuits 8, 9, and 10 via resistors for each color component. Mixing circuit 8,
9 and 10, the above described video signals Vpr, Vpg, Vp
b, respectively, and mixes each video signal with the dark shading correction signal. This mixing cancels the dark shading waveform component superimposed on each video signal and the dark shading correction signal having the same absolute value level and the opposite waveform direction, thereby canceling each other. , 10 output video signals with reduced dark shading waveform components. Then, the second signal processing unit 7 to which the video signals output from the mixing circuits 8, 9, and 10 are input performs processes such as gain control and gamma correction.

[0010]

In the above-described prior art, in a one-field all-pixel reading type television camera, high-vision camera, or the like, the waveform of the dark shading component is, for example, as shown in FIG. As shown in FIG. 7A, the waveform becomes more remarkable than FIG. 7A, and the waveform which can be corrected without any problem by the conventional technique cannot be approximated to the waveform of the dark shading component.

Further, as shown in FIG. 5A, as a waveform of the dark shading component, depending on the variation of the CCD element, its characteristic curve is changed to an S-shaped when the video period starts from the horizontal retrace period. Some things may be difficult.

The present invention generates a dark shading correction waveform as shown in FIG. 4 (a ') or FIG. 5 (a ") by a simple circuit and sequentially scans (one field all pixels). An object of the present invention is to improve the reproduction of dark areas and the operability of a CCD high-definition color television camera having a short horizontal retrace period, such as a (readout) camera or a high-vision camera.

[0013]

According to the present invention, in order to solve the above-mentioned problems, a circuit for generating a dark shading correction signal includes an HD pulse signal or an HSAW 'signal.
A predetermined signal waveform synchronized with a horizontal synchronizing signal such as a signal is differentiated by a time constant of か ら to の of a horizontal flyback period, and the differentiated signal is shorter than the time constant of the differentiating means. Integrate with a time constant, and integrate the integrated signal
The video signal is mixed by a mixing circuit for each video signal.

Further, according to the present invention, in a circuit for generating a dark shading correction signal, a predetermined signal waveform synchronized with a horizontal synchronizing signal such as an HD pulse signal or an HSAW 'signal is changed from 1/2 to 1 of a horizontal blanking period. / 4 is differentiated with a time constant, and the differentiated signal is integrated with a time constant shorter than the time constant of the differentiating means, and the integrated signal is set to a constant level within a predetermined period within the horizontal retrace period. ,And,
Integrate with a time constant shorter than the time constant of the differentiating means, mix the processed signal with the signal integrated before the process, and mix the mixed signal for each video signal. This is mixed with a video signal by a circuit.

According to the present invention, as the video signal output,
The non-uniformity of the dark portion of the video signal in the screen can be corrected with higher accuracy, and the reproducibility of the dark portion of the subject is further improved.

Further, since the integrated waveform is used as the correction signal, it is possible to prevent the ringing component of the horizontal synchronizing signal pulse from being mixed during the video period.

Further, even if the horizontal synchronizing signal pulse is made shorter than the horizontal retrace period, a dark shading correction signal in which an S-shape is drawn after the horizontal retrace period can be easily generated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit configuration example of a calculus circuit 5 according to the present invention. An imaging device using this circuit can be realized by replacing the differentiation circuit 25 of the imaging device shown in FIG. Note that the description of each block configuration shown in FIG. 3 is the same as that of the above-described conventional technology, and thus will be omitted here.

In FIG. 1, the HD pulse signal or the HSAW 'signal input to the calculus circuit 5 includes C2 and R3.
, A predetermined time constant, for example, 水平 of the horizontal retrace period
The waveform is differentiated by a time constant of a period from to 反 転, and further integrated and inverted and amplified by the operational amplifiers A2, C3 and R4 with a time constant shorter than the time of the differentiation ((c) in FIG. 4).
Or (f)) and the analog switch integrated circuit I
Input to C3. The output of the analog switch integrated circuit IC3 is PRE. Due to the switching timing by the BL signal, a period slightly shorter than the horizontal blanking period is set to the reference potential, and the other is the integrated and inverted waveform, that is, the dark shading correction signal ((d ′ in FIG. 4). ) Or (g ′) as a solid-state waveform signal), and is output to the subsequent stage.

By integrating the differentiated waveform as described above, it is a waveform of a dark shading component generated in a progressive scanning (one-field all-pixel reading) camera, a high-vision camera, and the like. ') When the video period starts from the horizontal retrace period as shown in ()), it gradually falls, then steeply, becomes even more gentle, and then becomes almost linear. A shading correction signal can be generated, and the reproducibility of a dark portion of a subject is further improved.

Next, another embodiment of a calculus circuit according to the present invention will be described with reference to FIGS. FIG. 2 is a circuit configuration example of the calculus circuit 5 ′ according to the present invention. An imaging device using this circuit can be realized by replacing the differentiation circuit 25 of the imaging device shown in FIG. 3 with a calculus circuit 5 ', like the calculus circuit 5 described above.

In FIG. 2, the HD pulse signal or HSAW 'signal input to the calculus circuit 5' is represented by C2 and R
3, a predetermined time constant, for example, 1 / of the horizontal retrace period
The waveform is differentiated by the time constant of the period from 2 to 1/4 and further integrated and inverted and amplified by the operational amplifiers A2, C3 and R4 with the time constant shorter than that at the time of the above differentiation, and is supplied to the analog switch integrated circuit IC3. Is entered. From the analog switch integrated circuit IC3, PRE. Due to the switching timing by the BL signal, a period slightly shorter than the horizontal flyback period is set to the reference potential, and the other period is the integrated and inverted waveform Vc1 ((d ′) or (g ′) in FIG. 5). ) Is output, the mixing circuit 15 and the resistor R5
Is input to one end of

The signal input to the resistor R5 is integrated with the resistor R5 by the operational amplifiers A3, C4 and R6 with a time constant shorter than that at the time of the differentiation and inverted and amplified.
c2 ((i) or (l) in FIG. 5) and input to the mixing circuit 15.

In the mixing circuit 15, the input waveform Vc1
And the waveform Vc2. The added and mixed waveform ((k) or (m) in FIG. 5) becomes a dark shading correction signal and is output to the subsequent stage.

By integrating the differentiated waveform as described above, further integrating the integrated waveform again, and adding and mixing the once-integrated waveform and the twice-integrated waveform, the sequential scanning (all over one field) is performed. This is a waveform of a dark shading component generated by a (pixel reading) system camera, a high-definition camera, or the like. When the video period starts from a horizontal retrace period as shown in FIG. A dark shading correction signal that is more similar to the waveform can be generated, and the reproducibility of the dark part of the subject is further improved.

[0026]

According to the present invention, a correction waveform having a higher effect of improving the dark shading can be obtained simply by adding a small-scale integration circuit to the conventional dark shading correction waveform generating circuit. Can be generated. In addition, by performing the integration, the amplitude of the correction waveform in the retrace period can be further reduced, and the circuit configuration relating to generation and mixing of the correction waveform can be simplified. further,
The non-uniformity of the dark portion of the video signal in the screen can be corrected with higher accuracy, and the reproducibility of the dark portion of the subject can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a calculus circuit according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a calculus circuit according to another embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a block configuration of an imaging apparatus that performs dark shading correction according to the related art.

FIG. 4 is a signal waveform diagram for explaining the operation of one embodiment of the present invention.

FIG. 5 is a signal waveform diagram for explaining the operation of another embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration example of a conventional differentiation circuit that generates a dark shading correction signal.

FIG. 7 is a signal waveform diagram illustrating an operation of a differentiating circuit that generates a conventional dark shading correction signal.

FIG. 8 is a diagram showing a configuration example of a sawtooth waveform generation circuit.

FIG. 9 is a view for explaining a phase relationship between waveforms on which a dark shading correction signal is generated.

[Explanation of symbols]

1, 2, 3D imaging device, 4 sawtooth waveform generation circuit,
5, 5 ′ calculus circuit, 6 first signal processing unit,
7 second signal processing unit, 8, 9, 10 mixing circuit,
11 lens, 12 color separation optical system, 13 shutter, 14 timing generator, 15 mixing circuit,
A2, A3 Operational amplifier, SW1 switch, IC
3 Analog switch integrated circuit

Claims (3)

(57) [Claims] 1. An image pickup apparatus comprising an image pickup device and outputting a video signal on which a shading waveform is superimposed from the image pickup device, wherein a horizontal synchronizing signal or a predetermined signal waveform synchronized with the horizontal synchronizing signal is converted into a horizontal flyback period. 1/2 to 1/4 of
A differentiating means for differentiating by the time constant of the period, a first integrating means for integrating the signal differentiated by the differentiating means with a time constant shorter than the time constant of the differentiating means, and an integrating means for integrating the signal by the first integrating means. Means for mixing the video signal with the video signal,
An imaging device, which outputs a video signal in which the shading waveform has been corrected. 2. An image pickup apparatus comprising an image pickup device and outputting a video signal on which a shading waveform is superimposed from the image pickup device, wherein a horizontal synchronizing signal or a predetermined signal waveform synchronized with the horizontal synchronizing signal is converted into a horizontal flyback period. 1/2 to 1/4 of
A differentiating means for differentiating by the time constant of the period, a first integrating means for integrating the signal differentiated by the differentiating means with a time constant shorter than the time constant of the differentiating means, and an integrating means for integrating the signal by the first integrating means. A second integrating means for integrating the signal obtained during a predetermined period of the horizontal retrace period with a time constant shorter than the time constant of the differentiating means, and a signal integrated by the second integrating means. And a means for mixing the signal mixed by the first mixing means with the video signal, and mixing the shading waveform with the video signal. An imaging device for outputting a corrected video signal. 3. The imaging device according to claim 1, wherein the predetermined signal waveform synchronized with the horizontal synchronization signal is a saw-tooth waveform.