JP2009005169A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a horizontal band generated in a case of a high luminance object by a CMOS sensor. <P>SOLUTION: The imaging device having a black correction circuit capable of varying a clamping time constant by a CMOS sensor imaging element and an HD unit, controls the clamping time constant to be small when the high luminance object is detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a black level correction circuit of an imaging apparatus.

  An image pickup apparatus using a CMOS sensor instead of a CCD has been put into practical use. The CMOS sensor does not generate vertical smear in the case of a high-brightness object, which is a problem with a CCD because of its structure, but instead causes a band-like level fluctuation in the horizontal direction of the same line. In the present specification, this phenomenon is called lateral smear.

In the present invention, the lateral smear is reduced by changing the OB clamp time constant of the black correction circuit. However, the conventional technique for controlling the OB clamp time constant is to change the clamp time constant in accordance with the change of AGC. Yes (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-205667

  However, in the above prior art, the control of the OB clamp time constant is in units of VD (vertical sync signal), and is not effective for fluctuations in HD (horizontal sync signal) units such as lateral smear to be solved by the present invention. .

  In the present invention, the time constant control of the OB clamp is performed in HD units so that the lateral smear fluctuation can be suppressed.

  An image pickup apparatus according to the present invention is characterized in that in an image pickup apparatus having a CMOS sensor image pickup device and a black correction circuit capable of changing a clamp time constant in HD units, the clamp time constant is controlled to be small when a high-luminance subject is detected. Yes.

  As described above, according to the present invention, in an image pickup apparatus using a CMOS image sensor, the horizontal band (lateral smear) at the time of shooting a high-luminance subject is controlled by controlling the OB clamp time constant according to the subject level. Suppress.

Example 1
Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings.

  The present invention is applied to, for example, an imaging apparatus as shown in FIG. The image pickup apparatus according to the present embodiment inputs an image obtained from the CMOS sensor 101a to the AFE 110a, and performs black level correction 104a using the horizontal OB after the AGC 102a. Thereafter, the signal digitally converted by the ADC 103a is output as a video signal through the signal processing circuit 106a.

  Next, the lateral smear phenomenon of the CMOS sensor will be described with reference to FIG.

  When the high-brightness subject 204 is captured, the CMOS sensor draws a band 203 (lateral smear) in the horizontal direction due to the GND level fluctuation of the same line.

  Since the horizontal smear phenomenon also varies (201) in the horizontal OB portion, the lateral smear variation can be suppressed by reducing the clamp time constant for the line where the high luminance detection circuit 107a detects the high luminance portion.

  When high brightness is detected (206), the OB fluctuation can be absorbed quickly by reducing the clamp time constant. However, since horizontal noise is generated on the screen, it is sufficiently large except for detection of high brightness (205, 207). By using the time constant, the quality of the entire screen is not impaired.

  Further, as shown in FIG. 3, since the horizontal smear depends on the level and width of a high-brightness subject, the method for detecting the level and width of a high-brightness subject is effective for high-brightness detection.

  FIG. 4 shows an example of a high luminance portion detection circuit. By performing threshold detection 404 on the one-pixel delay element 401 and the sum thereof, it can be used for detection of the width and level of a high-luminance subject.

  In addition, since the lateral smear has a larger influence as the AGC gain is higher (low illuminance), the clamp time constant control is not performed when photographing with sufficient illuminance with a low AGC gain.

FIG. 5 shows a control flowchart.
S101a: This control is performed every 1H.
S102a: Clamp time constant control is performed only when the AGC gain is higher than a predetermined value. When the AGC gain is lower than a predetermined value, normal clamping time constant control is performed.
S103a: The level and width of a high-luminance subject are detected. If the threshold is exceeded, set a small clamp time constant. If the threshold is not exceeded, the normal clamping time constant is set.
S104a: A normal clamping time constant is set.

(Example 2)
In the first embodiment, the clamp time constant control is performed using the detection of the high luminance portion as a trigger. In the second embodiment, the fluctuation of the OB portion is used as a trigger for the clamp time constant control.

The present invention is applied to, for example, an imaging apparatus as shown in FIG.
An image obtained from the CMOS sensor 101a is input to the AFE, and black level correction 104b is performed using the horizontal OB after the AGC 110b. Thereafter, the signal digitally converted by the ADC 103b is output as a video signal through the signal processing circuit 106b.

  The OB fluctuation detection circuit 107b detects the OB fluctuation 201 shown in FIG. 2, and when there is a fluctuation, it is assumed that a lateral smear has occurred and sets a small clamping time constant. As in the first embodiment, the lateral smear has a larger effect as the AGC gain is higher (low illuminance), and therefore, the clamp time constant control is not performed when photographing with sufficient illuminance with a low AGC gain.

  In this embodiment, in an imaging apparatus having a CMOS sensor imaging device and a black correction circuit capable of changing a clamp time constant in HD units, an image pickup is characterized in that control is performed to reduce the clamp time constant when a high-luminance subject is detected. Features the device. Further, the imaging apparatus determines whether to perform clamp time constant control according to the AGC gain. Further, the imaging apparatus is characterized by detecting a change in an OB region and controlling a clamp time constant.

  As described above, according to the present embodiment, in the image pickup apparatus using the CMOS image pickup device, the horizontal band (lateral smear) at the time of photographing a high brightness subject is controlled according to the subject level. Suppress with.

1 is a block diagram illustrating a configuration of an imaging apparatus to which the present invention is applied in a first embodiment. It is the conceptual diagram which showed the horizontal smear and clamp time constant control. It is the figure which showed the relationship between the horizontal width of a high-intensity subject and a horizontal smear level. It is an example of a circuit of a high-intensity detection part. It is a flowchart for demonstrating operation | movement of 1st Embodiment. In 2nd Embodiment, it is a block diagram which shows the structure of the imaging device to which this invention is applied. It is a flowchart for demonstrating operation | movement of 2nd Embodiment.

Explanation of symbols

201 OB section change 202 OB area 203 horizontal smear 204 high brightness subject 401 1 pixel delay element 402 horizontal width designation of high brightness subject 403 addition circuit 404 threshold detection circuit

Claims (3)

  An image pickup apparatus having a CMOS sensor image pickup element and a black correction circuit capable of changing a clamp time constant in HD units, wherein control for reducing the clamp time constant is performed when a high-luminance subject is detected.   The imaging apparatus according to claim 1, wherein the imaging apparatus determines whether to perform clamp time constant control according to an AGC gain.   The imaging apparatus according to claim 1, wherein the imaging apparatus detects a change in an OB region and controls a clamp time constant.

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