JP4533176B2 - Imaging apparatus, clamp control method, and program - Google Patents

Description

  The present invention relates to an imaging apparatus, a clamp control method, and a program, and in particular, an imaging apparatus that extracts a stored charge from a two-dimensional imaging element by one-dimensional scanning and outputs a video signal, and clamp control applied to the imaging apparatus. The present invention relates to a method and a program for causing a computer to execute the clamp control method.

  FIG. 3 is a block diagram illustrating a circuit configuration of a conventional imaging device (see, for example, Patent Document 1).

  In FIG. 3, reference numeral 101 denotes an image pickup device such as a CCD (Charge Coupled Device) that photoelectrically converts an image and outputs an image pickup signal. In addition to the effective pixel region for outputting an imaging signal indicating a subject image, the imaging element 101 is optical black (optical black, hereinafter referred to as “black”) for detecting a dark current included in the output signal of the imaging element 101. OB) area). The signal detected in the OB region is used for control for suppressing a change in the black level of the video signal due to a change in the dark current amount.

  FIG. 4 is a diagram illustrating a configuration of the image sensor 101 having an OB area.

  The image sensor 101 includes an effective pixel unit 1, a vertical OB unit 2, and a horizontal OB unit 3. In the vertical OB unit 2 and the horizontal OB unit 3, each photoelectric conversion unit has the same configuration as the effective pixel unit 1, but a light shielding layer is provided on each photoelectric conversion unit.

  Returning to FIG. 3, reference numeral 102 denotes a PGA circuit, which is a double correlation sampling circuit (S / H circuit) for reducing noise included in the charge accumulated in the image sensor 101 and a gain for adjusting the gain of the video signal. It consists of an adjustment circuit. Reference numeral 103 denotes a clamp circuit, which performs level setting (clamping) on the video signal based on the voltage level (OB level) of the video signal obtained in the OB area of the image sensor 101. An A / D converter (ADC) 104 converts the analog video signal output from the clamp circuit 103 into a digital signal such as 12 bits. A signal processing circuit 105 performs digital signal processing on the digital video signal output from the A / D converter 104.

  Reference numeral 107 denotes a clamp voltage generation circuit, which integrates a video signal obtained in the OB region of the image sensor 101, here the voltage level (OB level) of the Y signal for each horizontal line, and clamp control voltage based on the integration value. Is generated. A clamp pulse generation circuit 106 generates an OB clamp pulse that becomes a high level during a period in which the vertical OB unit 2 and the horizontal OB unit 3 of the image sensor 101 are scanned. The clamp circuit 103 controls the clamp control generated by the clamp voltage generation circuit 107 for the video signal output from the PGA circuit 102 when the OB clamp pulse sent from the clamp pulse generation circuit 106 is at a high level. Set the level with voltage.

  A specific operation of the conventional imaging apparatus having such a configuration will be described with reference to FIG.

  FIG. 5 is a timing chart showing signal waveforms at various parts of the conventional imaging apparatus shown in FIG.

  5A shows a vertical synchronization signal used when taking out accumulated charges from the two-dimensional imaging device 101 by one-dimensional scanning, and FIG. 5B shows horizontal synchronization used when taking out the accumulated charges. (C) shows an output signal obtained from the image sensor 101 (sensor) facing the white reference plate, and (D) shows an OB clamp pulse.

  S1 is an output signal obtained from the image sensor 101 in the vertical OB unit 2, S2 is an output signal obtained from the image sensor 101 in the horizontal OB unit 3, and S3 is an output signal obtained from the image sensor 101 in the effective pixel unit 1. . S4 is a clamp pulse for vertical OB2, and S5 is a clamp pulse for horizontal OB3. Further, S6 indicates one horizontal period, and S7 indicates one frame period. S8 indicates the clamping period of the vertical OB unit 2, and S9 indicates the clamping period of the horizontal OB unit 3.

  In the conventional image pickup apparatus shown in FIG. 3, the video signal output from the image pickup element 101 is input to the PGA circuit 102, where it is amplified with a predetermined gain. The video signal output from the PGA circuit 102 is input to the clamp circuit 103 as an AC video signal from which the DC component has been removed by passing through the capacitor 108. The video signal input to the clamp circuit 103 is output from the clamp voltage generation circuit 107 while the OB clamp pulse (see FIG. 5D) output from the clamp pulse generation circuit 106 is high in the clamp circuit 103. Is clamped by the clamp control voltage.

  The clamped video signal is input to the A / D converter 104 and converted into a digital signal. Thereafter, one of the video signals is subjected to digital signal processing by the signal processing circuit 105, and the other is clamped. Input to the generation circuit 107. The clamp voltage generation circuit 107 integrates the OB level of the Y signal obtained from the image sensor 101 in the OB region of the image sensor 101 for each horizontal line or every preset interval, and the integrated value becomes a constant value. Such a clamp control voltage is generated. That is, a closed loop is formed among the clamp circuit 103, the A / D converter 104, and the clamp voltage generation circuit 107, and as a result, the OB level of the video signal input to the signal processing circuit 105 is constant. Feedback control is performed.

  The clamp of the video signal performed by the conventional imaging device when the dark current is large will be described with reference to FIG.

  FIG. 6 is a timing chart showing signal waveforms at various parts of the image pickup apparatus for explaining a video signal clamping operation performed by the conventional image pickup apparatus when the dark current is large.

In FIG. 6, 4 is the level of the output signal (OB clamp level VOB) to be output from the image sensor 101 in the OB region of the image sensor 101 when the dark current is 0, and 5 is the dark current component. As shown in FIG. 6E, the level of the output signal output from the image sensor 101 in the vertical OB unit 2 and horizontal OB unit 3 is the same as the OB clamp level VOB. The level of the input video signal is adjusted. Thereby, the dark current component contained in the video signal is suppressed.
Japanese Patent Laid-Open No. 2000-125211

  However, in the conventional imaging device in which the imaging device includes both the vertical OB unit 2 and the horizontal OB unit 3, dark horizontal shading as shown in FIG. 7 may exist in the characteristics of the imaging device 101. That is, there may be a potential difference (dark horizontal shading) as indicated by Vsh in the output voltage obtained from the image sensor 101 by scanning each pixel of the image sensor 101 facing the black reference plate in the horizontal direction. This potential difference is a potential difference of an offset component that increases as the screen moves to the right side when the left side of the screen is 0.

  FIG. 8 is a timing chart showing signal waveforms at various parts of the image pickup apparatus for explaining a video signal clamping operation performed by a conventional image pickup apparatus when dark horizontal shading is present. FIG. 8C shows an output signal obtained from the image sensor 101 (sensor) facing the black reference plate.

  As described above, in the conventional imaging device, the level of the output signal output from the imaging device 101 in the vertical OB unit 2 and the horizontal OB unit 3 is the same as the OB clamp level VOB. The level of the input video signal is adjusted. That is, as shown in FIG. 8D, the pulse width of the OB clamp pulse in the vertical OB portion 2 (four pulses on the left side in the example shown in FIG. 8D) is almost the width of the horizontal line. Therefore, most of the output signal levels output from the image sensor 101 shown in FIG. 8C affect the generation of the clamp control voltage (used for integration). Since the clamp control voltage generated in this way is used for clamping performed on the output signal output from the image sensor 101 in the horizontal OB unit 3 immediately after that, the level of the output signal output from the image sensor 101 is As shown in FIG. 8 (E), the input video signal to the signal processing circuit 105 after clamping is subjected to vertical shading in several horizontal lines immediately after entering the effective area 1 as shown in FIG. 6 appears.

  For this reason, in an imaging device that includes both the vertical OB unit 2 and the horizontal OB unit 3 in the imaging device and suppresses dark current components, there is a problem that the upper part of the video screen represented by the obtained video signal is darkened. .

  The present invention has been made in view of such problems, and it is an object of the present invention to provide an imaging apparatus, a clamp control method, and a program that suppress vertical shading and eliminate darkening at the top of a video screen. And

  In order to achieve the above object, according to the first aspect of the present invention, in an image pickup apparatus that extracts a stored charge from a two-dimensional image pickup device by one-dimensional scanning and outputs a video signal, a vertical optical black region and a horizontal The level of the output signal obtained from the imaging device having an optical black region, and when the vertical optical black region and the horizontal optical black region of the imaging device are respectively scanned over one horizontal scanning line. Clamp voltage generation means for integrating and generating a clamp voltage for each horizontal scanning line, and a first period required for horizontal scanning of the vertical optical black region of the image sensor as a pulse width. A plurality of first clamp pulses each having a sequentially reduced pulse width and a second period required for horizontal scanning of the horizontal optical black region of the image sensor Clamp pulse generating means for generating a plurality of second clamp pulses having a pulse width, and according to the first and second clamp pulses generated by the clamp pulse generating means for the output signal from the image sensor There is provided an imaging apparatus comprising: a clamp unit that sets a level with the clamp voltage generated by the clamp voltage generation unit.

  According to a third aspect of the present invention, there is provided an imaging apparatus that takes out accumulated charges by one-dimensional scanning from a two-dimensional imaging element having a vertical optical black area and a horizontal optical black area and outputs a video signal. In the clamp control method to be applied, the level of the output signal obtained from the image sensor when the vertical optical black region and the horizontal optical black region of the image sensor are scanned is integrated over one horizontal scanning line. A clamp voltage generation step for generating a clamp voltage for each horizontal scanning line, and a first period required for horizontal scanning of the vertical optical black region of the image sensor as a pulse width, and the pulse width is sequentially decreased. A plurality of first clamp pulses each having a different pulse width and a second period required for horizontal scanning of the horizontal optical black region of the image sensor. A clamp pulse generation step for generating a plurality of second clamp pulses having a pulse width, and an output signal from the image sensor according to the first and second clamp pulses generated in the clamp pulse generation step And a clamp step for setting a level with the clamp voltage generated in the clamp voltage generation step.

  Furthermore, a program for causing a computer to execute the clamp control method is provided.

  According to the present invention, the level of the output signal obtained from the imaging device when the vertical optical black region and the horizontal optical black region of the imaging device having the vertical optical black region and the horizontal optical black region are respectively scanned. Are integrated over one horizontal scanning line to generate a clamp voltage for each horizontal scanning line. A first period required when the vertical optical black region of the image sensor is scanned horizontally is set as a pulse width, and a plurality of first clamp pulses each having a pulse width obtained by sequentially reducing the pulse width; A plurality of second clamp pulses each having a pulse width corresponding to a second period required for horizontal scanning of the horizontal optical black region of the image sensor is generated. Then, the level is set with the generated clamp voltage in accordance with the generated first and second clamp pulses for the output signal from the image sensor.

  As a result, the fluctuation of the output signal level (vertical shading) due to the influence of dark horizontal shading is suppressed, so that the OB level of the video signal input to the signal processing circuit is kept constant, and darkness at the top of the video screen is reduced. It can be lost.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  Since the configuration of the imaging apparatus according to the embodiment of the present invention is basically the same as the configuration of the conventional imaging apparatus shown in FIG. 3, the description of the imaging apparatus according to the present embodiment is shown in FIG. The configuration of a conventional imaging device is used.

  FIG. 1 is a timing chart showing signal waveforms at various parts of the imaging apparatus for explaining the clamping operation of the video signal performed by the imaging apparatus according to the present embodiment. In this clamping operation, it is assumed that dark horizontal shading exists, and FIG. 1C shows an output signal obtained from the image sensor 101 (sensor) facing the black reference plate.

  In the clamp pulse generation circuit 106 in this embodiment, as shown in FIG. 1D, the width of the OB clamp pulse generated in the vertical OB clamp period is gradually reduced, and at the end of the vertical OB clamp period, The width of the OB clamp pulse generated in the horizontal OB clamp period is set to be the same.

  Thereby, vertical shading (refer to 6 in FIG. 8E) can be suppressed.

  FIG. 2 is a diagram illustrating a relationship between each waveform of the OB clamp pulse generated by the clamp pulse generation circuit 106 according to the present embodiment and each part of the image sensor.

  In FIG. 2, S101 is an OB clamp pulse corresponding to the vertical OB (VOB) unit 2, and includes waveforms VOB0 to VOB9. In FIG. 1D, four pulses are exemplified as the OB clamp pulse corresponding to the vertical OB (VOB) unit 2, but in FIG. 2, 10 pulses are illustrated.

  S102 is an OB clamp pulse corresponding to the effective pixel portion 1 and the horizontal OB (HOB) portion 3, and comprises waveforms 0 to V. S 103 is a horizontal scanning period of the horizontal OB (HOB) unit 3, and S 103 is a horizontal scanning period of the effective pixel unit 1.

  In the OB clamp pulse, first, the pulse waveforms VOB0 to VOB3 located at the upper part of the OB clamp pulse S101 corresponding to the vertical OB (VOB) section 2 are set to a high level over a long period corresponding to one horizontal line. As a result, a large amount of direct current components in the video signal can be clamped.

  In the pulse waveforms VOB4 to VOB9, the pulse width is gradually decreased so as to be the same as the pulse width of the OB clamp pulse S102 corresponding to the effective pixel portion 1 and the horizontal OB (HOB) portion 3.

  In this way, the pulse width is gradually reduced in the pulse waveforms VOB4 to VOB9, and finally the pulse width of the pulse waveform VOB9 is changed to the waveform of the OB clamp pulse S102 corresponding to the effective pixel portion 1 and the horizontal OB (HOB) portion 3. The pulse width is the same as 0 to V. As a result, as shown in FIG. 1E, there is no fluctuation in the output signal level (vertical shading) due to the influence of dark horizontal shading. Therefore, the video signal input to the signal processing circuit 105 in this embodiment is not affected. The OB level is kept constant, and a stable and accurate video signal can be obtained.

[Other Embodiments]
In addition, it comprises a part of the imaging device in the above embodiment and a computer composed of a CPU, a storage medium, an input / output device, etc. May be realized.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention.

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. -RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM, etc. can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) running on the computer based on an instruction of the program code. A case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also included.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes the case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a timing chart which shows the signal waveform in each part of the imaging device for demonstrating the clamp operation | movement of the video signal performed with the imaging device which concerns on this Embodiment. It is a figure which shows the relationship between each waveform of the OB clamp pulse which the clamp pulse generation circuit in this Embodiment produces | generates, and each part of an image pick-up element. It is a block diagram which shows the circuit structure of the conventional imaging device. It is a figure which shows the structure of the image pick-up element provided with the OB area | region. It is a timing chart which shows the signal waveform in each part of the conventional imaging device shown in FIG. It is a timing chart which shows the signal waveform in each part of the imaging device for demonstrating the clamp operation | movement of the video signal performed with the conventional imaging device when dark current is large. It is a figure which shows the characteristic of the image pick-up element in which horizontal shading at dark time exists. It is a timing chart which shows the signal waveform in each part of the imaging device for demonstrating the clamp operation | movement of the video signal performed with the conventional imaging device in case darkness horizontal shading exists.

Explanation of symbols

1 Effective pixel portion 2 Vertical OB portion (vertical optical black region)
3 Horizontal OB (horizontal optical black area)
101 Image sensor 102 PGA circuit 103 Clamp circuit (clamp means)
104 A / D converter (ADC)
105 signal processing circuit 106 clamp pulse generation circuit (clamp pulse generation means)
107 Clamp voltage generation circuit (clamp voltage generation means)
S4 Clamp pulse for vertical OB (first clamp pulse)
S5 Clamp pulse for horizontal OB (second clamp pulse)

Claims (5)

In an imaging apparatus that takes out accumulated charges from a two-dimensional imaging element by one-dimensional scanning and outputs a video signal,
An imaging device having a vertical optical black region and a horizontal optical black region;
When the vertical optical black region and the horizontal optical black region of the image sensor are respectively scanned, the level of the output signal obtained from the image sensor is integrated over one horizontal scan line, and a clamp voltage is set for each horizontal scan line. A clamp voltage generating means for generating;
A first period required when the vertical optical black region of the image sensor is scanned horizontally is set as a pulse width, and a plurality of first clamp pulses each having a pulse width obtained by sequentially reducing the pulse width; A clamp pulse generating means for generating a plurality of second clamp pulses each having a pulse width of a second period required for horizontal scanning of the horizontal optical black region of the image sensor;
Clamping means for setting a level with the clamp voltage generated by the clamp voltage generating means according to the first and second clamp pulses generated by the clamp pulse generating means with respect to the output signal from the image sensor; An imaging apparatus comprising:   The said clamp pulse production | generation means reduces each pulse width of these several 1st clamp pulses in steps toward the said 2nd period from the said 1st period. Imaging device. In a clamp control method applied to an image pickup apparatus that takes out accumulated charges by a one-dimensional scan from a two-dimensional image pickup device having a vertical optical black area and a horizontal optical black area and outputs a video signal.
When the vertical optical black region and the horizontal optical black region of the image sensor are respectively scanned, the level of the output signal obtained from the image sensor is integrated over one horizontal scan line, and a clamp voltage is set for each horizontal scan line. A clamp voltage generation step to generate;
A first period required when the vertical optical black region of the image sensor is scanned horizontally is set as a pulse width, and a plurality of first clamp pulses each having a pulse width obtained by sequentially reducing the pulse width; A clamp pulse generating step for generating a plurality of second clamp pulses each having a pulse width of a second period required when the horizontal optical black region of the image sensor is horizontally scanned;
A clamp step for setting a level with the clamp voltage generated in the clamp voltage generation step in accordance with the first and second clamp pulses generated in the clamp pulse generation step with respect to the output signal from the image sensor. A clamp control method comprising:   4. The clamp pulse generation step according to claim 3, wherein each pulse width of the plurality of first clamp pulses is decreased stepwise from the first period toward the second period. Clamp control method. Causes a computer to execute a clamp control method applied to an image pickup apparatus that extracts a stored charge from a two-dimensional image pickup device having a vertical optical black region and a horizontal optical black region by one-dimensional scanning and outputs a video signal. In the program for
When the vertical optical black region and the horizontal optical black region of the image sensor are respectively scanned, the level of the output signal obtained from the image sensor is integrated over one horizontal scan line, and a clamp voltage is set for each horizontal scan line. A clamp voltage generation step to generate;
A first period required when the vertical optical black region of the image sensor is scanned horizontally is set as a pulse width, and a plurality of first clamp pulses each having a pulse width obtained by sequentially reducing the pulse width; A clamp pulse generating step for generating a plurality of second clamp pulses each having a pulse width of a second period required when the horizontal optical black region of the image sensor is horizontally scanned;
A clamp step for setting a level with the clamp voltage generated in the clamp voltage generation step in accordance with the first and second clamp pulses generated in the clamp pulse generation step with respect to the output signal from the image sensor. A program characterized by having.

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