JP2006165709A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of reducing deterioration in the image quality due to OB level abnormality to the utmost by clamping a signal at a more accurate black level and by a simpler method even on the occurrence of abnormality in an OB level because a signal of an OB part is excluded from a clamp processing object for a period when the OB level abnormality is detected. <P>SOLUTION: The imaging apparatus is provided with: an imaging element provided with a photoelectric conversion means part of which includes a light shield region subjected to light shielding; a control means for controlling the imaging element; a signal processing means for receiving an imaging signal outputted from the imaging element; and a detection means for detecting the abnormality of a signal level for a period corresponding to the light shield region in the imaging signal outputted from the imaging element, and the signal processing means is characterized in to exclude part of the imaging signal outputted from the imaging element from the signal processing object for the period when a detection result of the detection means indicates abnormality. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus using a solid-state imaging device.

  Conventionally, in a solid-state imaging device such as a CCD, an optical black portion (hereinafter referred to as an OB portion) in which photoelectric conversion is not performed regardless of the intensity of incident light is provided by shielding a part of all pixels. Of the output signals of the image sensor, the signal level corresponding to the OB portion is generally used as an optical black level and used as a reference for a clamp circuit at the subsequent stage.

  However, when a high-luminance subject such as the sun exists, a part of the light may leak into the OB portion and be photoelectrically converted, or a charge overflowed by blooming may flow into the OB portion. . In such a case, the signal level of the OB portion is no longer the same as the black level, and a normal image cannot be obtained if clamping is performed based on this.

  As a means for avoiding this, for example, a method of shortening the time during which an abnormal OB level is held by shortening the time constant of the clamp circuit is shown (see Patent Document 1). As another means, a method of detecting an abnormality in the OB level and clamping the horizontal blanking period at the time of abnormality is shown (see Patent Document 2). According to this method, when the OB level is abnormal, the horizontal blanking period that is not affected by the incidence of excessive light quantity due to the high-luminance subject is clamped, so that it is possible to avoid image quality deterioration due to the OB level abnormality. Further, as another means, there is shown a method of detecting an abnormality of the OB level and correcting the reference level of the clamp when the abnormality is detected (see Patent Document 3). According to this method, when the OB level is abnormal, the OB level in which no OB abnormality has occurred spatially or temporally is used as the reference level of the clamp, so that the display quality of the image can be prevented from deteriorating.

  Further, white balance control is well known as one of signal processing of a general imaging apparatus. In image integration type white balance control that does not require an external sensor, conventionally, white balance control has been based on the idea that integrating the color signal components of the entire screen results in an achromatic color. This concept is valid when shooting a general landscape in which various colors are mixed at random, but when shooting a subject with many biased colors such as red and blue, a so-called color failure is caused.

As a means for avoiding this, for example, Patent Document 4 discloses a method of detecting a white portion of a subject and performing white balance control based on the detection result. According to this method, malfunctions of white balance control can be reduced (Patent Document 4).
JP-A-5-130450 Japanese Patent Laid-Open No. 9-247552 JP 2003-143488 A Japanese Patent Laid-Open No. 11-275599

  In the method disclosed in Patent Document 1, the time during which an abnormal OB level is maintained can be shortened by shortening the time constant of the clamp circuit, but a broken image is output even in a short time. After all, it is not preferable. The patent document also shows a method of stopping the clamping operation, but an extra circuit is required for this purpose.

  In the method disclosed in Patent Document 2, it is possible to avoid image quality degradation due to an abnormal OB level by clamping the horizontal blanking period, but there is still a level difference between the original black level OB and the horizontal blanking period. Therefore, the correct black level is not reproduced. For example, when the black level fluctuates due to a temperature change, this level difference appears more prominently.

  In the method disclosed in Patent Document 3, the OB level obtained for each line in the horizontal direction is compared in the same frame, and the maximum value and the minimum value are compared to detect an OB level abnormality. In this method, when the OB level is abnormal over the entire frame, the OB level abnormality cannot be detected, and clamping is performed at the abnormal OB level. When an OB level abnormality is detected, clamping is performed with the minimum value of the OB level in one frame. However, since the minimum value cannot be searched for after all the data of one frame has been captured, Processing is difficult. Of course, calculation time for searching for the maximum and minimum values of the OB level is also required.

  Furthermore, this patent document also shows a method for detecting an OB level abnormality by comparing an OB level average value of a frame in a past period with an OB level of a current frame. An extra memory for storing the OB level of the frame is required, and the calculation of the past OB level average value and the OB level comparison must be performed every frame.

  The present invention has been made in view of such circumstances, and even when the OB level is abnormal, clamping is performed with a more accurate black level and a simpler method, and image quality deterioration due to an abnormal OB level is possible. It is an object of the present invention to provide an imaging apparatus that can reduce as much as possible.

  Further, when there is a high-luminance subject that causes an abnormal OB level, white balance control may be adversely affected. Since the luminance level of the image signal corresponding to the high-luminance subject is saturated or close to that level, the color signal is naturally close to an achromatic color. When a method that detects a white portion of a subject as shown in Patent Document 4 and performs white balance control based on the detection result is used, it may cause a malfunction. Is expensive.

  The present invention has been made in view of such circumstances, and even when there is a high-luminance subject that causes an abnormal OB level, more accurate white detection can be performed and normal white balance control can be performed. An object is to provide an imaging device.

  The image pickup apparatus according to claim 1 is provided with an image pickup element having a light shielding region in which photoelectric conversion means is provided and a part of which is shielded, control means for controlling the image pickup element, and an image pickup signal output from the image pickup element. An image pickup apparatus comprising: a signal processing unit configured to detect a signal level abnormality in a period corresponding to a light-shielding region of the image pickup signal output by the image pickup device; During the period when the detection result of the means is abnormal, a part of the imaging signal output from the imaging device is excluded from the signal processing target.

  The imaging apparatus according to claim 2, wherein the signal processing unit includes a clamping unit that performs a clamping process based on a signal level in a period corresponding to a light shielding region of the imaging element, and the signal processing unit includes: During the period when the detection result is abnormal, the signal of the period corresponding to the light shielding region of the image sensor is excluded from the clamp processing target.

  The image processing apparatus according to claim 3, wherein the signal processing unit obtains a white balance from a result of the white detection unit that obtains a white portion of a subject based on an imaging signal output from the imaging element, and a result of the white detection unit. White balance gain control means for determining a gain, and the signal processing means excludes a signal in a period corresponding to a video area of the image sensor from a white detection target during a period when the detection result of the detection means is abnormal. It is characterized by.

  According to the present invention, when the OB level abnormality is detected, the signal of the OB part during that period is excluded from the clamp processing target. Therefore, even if the OB level is abnormal, the black level is more accurate and It is possible to provide an imaging apparatus that can perform clamping by a simpler method and reduce image quality degradation due to an abnormal OB level as much as possible.

  Further, when an OB level abnormality is detected, the video signal in that period is excluded from the white detection target, so that even when there is a high-luminance subject that causes the OB level abnormality, a more accurate white It is possible to provide an imaging device that performs detection and enables normal white balance control.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of an embodiment of an imaging apparatus according to the present invention. The operation at the time of subject shooting will be described with reference to FIG. The image pickup apparatus of the present invention supplies a lens unit 10, a CCD 11 as an image pickup element, an analog signal processing circuit 12 to which an output signal from the CCD 11 is input, driving of the CCD 11 and timing required for the analog signal processing circuit 12. Timing generation circuit 13, A / D converter 14, digital signal processing circuit 15 that performs various signal processing including an image memory, recording medium 16 for recording image data processed by the digital signal processing circuit 15, digital signal It comprises a display device 17 for displaying image data processed by the processing circuit 15 and a CPU 18 for controlling each circuit or unit.

  In accordance with the brightness of the subject, the CPU 18 controls the aperture of the lens unit 10 to adjust the amount of the subject incident on the CCD 11 and further changes the charge accumulation time of the CCD 11 via the timing generation circuit 13 to control the exposure amount. To do. The CCD 11 converts the subject image formed on the image receiving surface into a signal charge of an amount corresponding to the amount of light and accumulates it. The accumulated signal charges are transferred by transfer pulses input from the timing generation circuit 13, converted into signal voltages by the output circuit, sequentially read out, and output to the analog signal processing circuit 12. The analog signal processing circuit 12 mainly comprises a CDS (correlated double sampling) circuit and a GCA (gain control amplifier), and performs noise removal, video signal amplification, and the like. The output of the analog signal processing circuit 12 is input to the A / D converter 14 and converted into a digital signal. The digital signal processing circuit 15 performs necessary signal processing according to the purpose. In the case of recording an image, the digital signal processing circuit 15 performs necessary processing and then outputs to the recording medium 16 to record image data. When displaying an image, the digital signal processing circuit 15 performs necessary processing, and then a signal is output to the display device 17. The display device 17 is a signal output terminal for outputting to a liquid crystal monitor (LCD) mounted on the imaging device main body or a TV monitor. The CPU 18 performs necessary control for the lens unit 10, the analog signal processing circuit 12, the timing generation circuit 13, the digital signal processing circuit 15, and the display device 17.

  FIG. 2 is a diagram showing details of an internal circuit of the analog signal processing circuit 12. The analog signal processing circuit 12 includes a CDS (correlated double sampling) circuit 20, a GCA (gain control amplifier) circuit 21, a clamp circuit 22, and an OB abnormality detection circuit 23. The signal passing through the CDS and GCA is clamped and output by the clamp circuit 22 with the OB level as a reference.

  FIG. 3 is a diagram showing a part related to the OB calculation in the digital signal processing circuit 15. In the imaging apparatus of the present invention, in order to reproduce a more accurate black level, clamping processing is performed in two stages of so-called analog clamping and digital clamping. The analog clamp here refers to the clamp circuit 22, and the digital clamp refers to the OB arithmetic circuit 30. The imaging signal output from the analog signal processing circuit 12 is clamped to a predetermined level by the clamp circuit 22 with the OB level as a reference. Further, the imaging signal converted into a digital signal by the A / D converter 14 is input to the OB arithmetic circuit 30 and the OB integration circuit 31.

  FIG. 4 is an image diagram showing the image pickup signals input to the OB arithmetic circuit 30 and the OB integration circuit 31 in a visually easy-to-understand manner. An OB integration region 40 shown in the figure is a portion corresponding to the OB portion of the image sensor. The imaging signal corresponding to the OB portion, that is, the OB level is clamped to a predetermined level by the clamp circuit 22, and the OB integration circuit 31 integrates the OB level of the input imaging signal. The OB operation circuit 30 receives the integration result of the OB integration circuit 31, and performs an operation on the imaging signal based on the result, specifically, subtraction of the OB level (digital clamp). For example, the OB integration circuit 31 averages all the OB levels in one frame, and the OB calculation circuit 30 subtracts the OB level from the imaging signal of one frame. This determines the black level of the image.

  Here, the operation in the case where the sun is present in a part of the screen as shown in FIG. 5 will be described. In the vicinity of the sun, light leakage and blooming occur due to the intense light quantity, and the OB level of the OB abnormal region 50 shown in the figure is no longer different from the black level. The OB abnormality detection circuit 23 monitors the OB level for each horizontal line, and outputs a detection signal to the clamp circuit 22 during a period when the OB level is abnormal. Based on the abnormality detection signal, the clamp circuit 22 clamps the horizontal blanking period in which the horizontal line is not affected by the excessive light amount. Thereby, it is possible to avoid abnormal image quality degradation such as blackout. This operation is the same as that described in Patent Document 2, for example. The imaging signal output from the clamp circuit 22 is converted into a digital signal by the A / D converter 14 and input to the OB arithmetic circuit 30 and the OB integration circuit 31. In the imaging apparatus of the present invention, so-called digital clamp processing is performed by the OB arithmetic circuit 30 in order to reproduce a more accurate black level. The detection result of the OB abnormality detection circuit 23 is also input to the OB integration circuit 31, and during the period when the OB level is abnormal, the OB integration is performed by excluding it. As a specific OB integration method, for example, during the period when the OB level is abnormal, the OB level of the normal horizontal line immediately before is held. Alternatively, a period during which the OB level is abnormal may be replaced with a specified value. Furthermore, the average value of the OB level for one frame may be calculated excluding the period when the OB level is abnormal. Based on the OB integration result obtained as described above, the OB operation circuit 30 performs subtraction of the OB integration value, so-called digital clamp processing.

  As described above, according to the present invention, when the OB level abnormality is detected, the signal of the OB part during that period is excluded from the clamp processing target, so even if the OB level is abnormal, it is more accurate. Therefore, it is possible to provide an imaging apparatus that can perform clamping with a simple black level and a simpler method and reduce image quality degradation due to abnormal OB level as much as possible.

  Another embodiment using the OB level abnormality detection result will be described below.

  FIG. 6 is a diagram simply showing a part related to white balance control in the digital signal processing circuit 15. The imaging signal input to the white detection means 71 is divided into several spatially fine blocks (for example, 64 blocks of 8 × 8) in order to detect the white portion of the subject. The white detecting means 71 obtains a color difference signal of each block, and determines that the block is white (achromatic color) if the value is within a certain range. The information of the color difference signal of the block determined to be white is passed to the white balance control means 70. The white balance control means 70 calculates a gain for white balance based on the information, and performs white balance control. Do.

  Here, the operation in the case where the sun is present in a part of the screen as shown in FIG. 7 will be described. As described with reference to FIG. 5, the OB abnormality detection circuit 23 detects an OB level abnormality and outputs a detection signal to the clamp circuit 22. Based on the abnormality detection signal, the clamp circuit 22 clamps the horizontal blanking period in which the horizontal line is not affected by the excessive light amount. The imaging signal output from the clamp circuit 22 is converted into a digital signal by the A / D converter 14 and input to the white balance control means 70 and the white detection means 71. The detection result of the OB abnormality detection circuit 23 is also input to the white detection means 71. When there is a high-brightness subject that causes an OB level abnormality, the luminance signal is saturated or close to the portion corresponding to the high-brightness subject in the imaging signal. Naturally it will be achromatic. Thereby, in order to prevent malfunction due to white detection, a block including that period is excluded from white detection during a period when the OB level is abnormal. Specifically, among the 64 blocks shown in FIG. 7, blocks 9 to 16 include the OB abnormality detection area 80, so that white detection is performed ignoring the blocks.

  As described above, according to the present invention, when an OB level abnormality is detected, the signal of the video portion in that period is excluded from the white detection target, so that there is a high-luminance subject that causes the OB level abnormality. Even in such a case, it is possible to provide an imaging device that performs more accurate white detection and enables normal white balance control.

1 is a configuration block diagram illustrating an embodiment of an imaging apparatus of the present invention. It is a figure which shows the detail of the analog signal processing circuit of the imaging device of this invention. It is a figure which shows the part regarding OB calculation of the imaging device of this invention. It is an image figure of the imaging signal of the imaging device of this invention. It is an image figure of an imaging signal when OB abnormality is detected. It is a figure which shows the part regarding the white balance control of the imaging device of this invention. It is explanatory drawing which shows an example of the block in the white detection of the imaging device of this invention.

Explanation of symbols

10 Lens unit 11 CCD
12 Analog signal processing circuit 13 Timing generation circuit 14 A / D converter 15 Digital signal processing circuit 16 Recording medium 17 Display device 18 CPU
20 CDS (correlated double sampling)
21 GCA (gain control amplifier)
22 Clamp circuit 23 OB abnormality detection circuit 30 OB arithmetic circuit (digital clamp)
31 OB integration circuit 40 OB integration area 50 OB abnormality area 60 white balance control means 61 white detection means 70 OB abnormality detection area

Claims (3)

An image sensor having a light-shielding region provided with photoelectric conversion means and part of which is shielded;
Control means for controlling the image sensor;
A signal processing means for inputting an imaging signal output from the imaging element;
An image pickup apparatus comprising: a detection unit that detects an abnormality in a signal level in a period corresponding to a light shielding region among image pickup signals output from the image pickup element;
The image processing apparatus, wherein the signal processing means excludes a part of an image pickup signal output from the image pickup device from a signal processing target during a period in which the detection result of the detection means is abnormal. The signal processing means includes a clamping means for performing a clamping process based on a signal level in a period corresponding to a light shielding region of the image sensor,
The imaging apparatus according to claim 1, wherein the signal processing unit excludes a signal of a period corresponding to a light shielding region of the imaging element from a clamp processing target during a period in which the detection result of the detection unit is abnormal. The signal processing means includes a white detection means for obtaining a white portion of a subject based on an imaging signal output from the imaging device, and a white balance gain control means for determining a gain for white balance from a result of the white detection means. With
The imaging apparatus according to claim 1, wherein the signal processing unit excludes a signal of a period corresponding to a video region of the imaging element from a white detection target during a period in which the detection result of the detection unit is abnormal.

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