JP2007295082A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus with an inexpensive circuit configuration and reduced power consumption, capable of realizing a smear reduction effect during imaging and displaying a moving picture, without giving a sense of incongruity to a user by having only to revise an interleaving rate. <P>SOLUTION: The imaging apparatus provided with an imaging element 1, capable of carrying out reading by revising the interleaving rate in the vertical direction; a clock generator 5 connected to a driving means of the imaging element 1 and capable of outputting an optional clock frequency, in response to the setting from a controller; and a signal processing means 4, including the controller and a smear component detection means for processing an output signal from the imaging element 1 and detecting smear components contained in the output signal from the imaging element 1, includes a control function of controlling revision of the interleaving rate and revision of the output clock frequency from the clock generator 5, when a change takes place in the presence/absence of the detection of the smear components. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus using a CCD, such as a digital camera or a digital still camera, which reduces smear generated during moving image capturing.

In recent years, cameras equipped with a solid-state image sensor such as a digital still camera often use an IT type (interline transfer system) CCD as the image sensor. However, compared to FIT (frame interline transfer method) CCDs, IT-type CCDs, when shooting high-intensity subjects such as the sun, generate strip-like bright lines in the vertical direction of the high-intensity subjects. The level of smearing components is poor and may cause problems.
A smear is a multiple reflection of light to the photodiode that constitutes the light-receiving part of the solid-state image sensor and reaches the vertical transfer path, or the charge generated by the photodiode diffuses into the vertical transfer path, or incident light is The generated smear component charges are generated by mixing the signal charges of other pixels in the charge transfer through the vertical transfer path by passing through the light shielding film on the vertical transfer path and reaching the vertical transfer path. It is a false signal.

When shooting still images, close the mechanical shutter at the end of the exposure period to shut off the incident light to the solid-state image sensor, and then sweep out the vertical transfer path at high speed to sweep out smear components accumulated in the vertical transfer path during the exposure period Thereafter, the signal charge is read from the photodiode to the vertical transfer path. By doing so, it can be prevented from being affected by smear.
However, to capture a moving image, display the captured image on a monitor, and record a captured image on a recording medium, in order to capture the subject image continuously on the imaging surface of the solid-state imaging device The mechanical shutter cannot be closed. Accordingly, light is always incident on the imaging surface of the solid-state imaging device and smear is generated, and it has been difficult to reduce smear while capturing a moving image.

As described above, various techniques have been proposed in the past in order to reduce smear during moving image capturing in which light is always incident on the imaging surface of a solid-state imaging device and smear occurs (for example, patents). References 1 to 5).
Patent Document 1 detects a smear component included in an imaging signal output from a solid-state imaging device in a moving image monitor for displaying a moving image or a moving image recording mode for recording a moving image on a recording medium. The pixel thinning amount in the moving image shooting mode is changed according to the smear component level, and the solid-state imaging device is driven at high speed to transfer the signal charge of the vertical transfer path at high speed according to the change in the pixel thinning amount. This technology is disclosed.

Patent Documents 2 to 4 disclose techniques for suppressing generated smear components and dark current components by performing subtraction processing or discharging in a subsequent signal processing circuit or imaging device. And a special signal processing circuit is required, which may increase the cost of the device.
Patent Document 5 discloses a technique for switching between driving of an image pickup element during thin-film reading or thinning-out reading depending on whether smear components are generated during moving image shooting. Further, paragraph 0055 of Patent Document 5 discloses a technique for switching from the addition readout mode to the thinning readout mode when the number of electronic shutters exceeds a predetermined number (when the shutter speed becomes more than a fixed value).
JP 2003-234964 A JP 2005-39727 A JP 2000-299817 A JP 2002-271699 A JP 2003-189183 A

However, regarding the technique of Patent Document 1, first, if the thinning amount is frequently changed, the update rate of the output image is frequently changed, so that the user feels uncomfortable.
In addition, in order to be able to change the thinning amount finely and smoothly and to gradually bring out the effect of reducing smear, it is necessary to prepare a number of readout lines for the image sensor independently, which is difficult in manufacturing the image sensor. In addition, the circuit for driving the image sensor is also complicated.
Conversely, if the amount of thinning is too discrete, smearing may occur when the amount of thinning is small, and hunting may occur when the smear is below the measurement limit when the amount of thinning is large. .

In addition, in relation to Patent Document 5, whether the amount of smear components generated does not change and the appropriate signal amount is added even if the mode is switched from the addition readout mode to the thinning readout mode under the same subject luminance condition. Since it is common to set the same level regardless of whether or not, the signal-to-smear ratio does not change as a result, so it is considered meaningless.
Therefore, an object of the present invention is to reduce the smear reduction effect during moving image capturing and display in consideration of the above-described situation, by changing the thinning rate, and without causing discomfort to the user. An object of the present invention is to provide an imaging device that has a configuration and can be realized with reduced power consumption.

  In order to solve the above-described problem, the invention according to claim 1 is an image sensor that can read by changing the thinning rate in the vertical direction, and is connected to a drive unit of the image sensor, and from the controller. A clock generator that can output an arbitrary clock frequency in accordance with the setting of the image sensor, a smear component detection unit that processes an output signal of the image sensor and detects a smear component included in the output signal of the image sensor And an image pickup apparatus including a signal processing unit including the controller, wherein the change of the decimation rate and the change of the output clock frequency of the clock generator are controlled together when a change occurs in the presence or absence of the smear component detection. Means are provided.

According to a second aspect of the present invention, when the smear component is detected from a state in which the smear component is not detected, the control means performs the change of the thinning rate in advance, and the smear component is detected. When the smear component is not detected from the existing state, the output clock frequency of the clock generator is changed in advance.
According to a third aspect of the present invention, in the case where a display device for displaying a captured image is provided, the switching timing of the output clock frequency of the clock generator is such that the update period of the image displayed on the display device is It is controlled to be constant.

According to a fourth aspect of the present invention, when an interface for displaying a captured image on an external display device is provided, the output clock frequency switching timing of the clock generator is an image displayed on the display device. The update period is controlled to be constant.
According to a fifth aspect of the present invention, when the moving image shooting mode is provided, the output clock frequency switching timing of the clock generator is such that the image update cycle is constant even when moving image recording is performed. It is characterized by being controlled.

  According to the present invention, it is possible to suppress smear smoothly by simultaneously switching the thinning rate and the drive frequency of the image sensor depending on whether smear occurs, and it is also possible to suppress power consumed by the image pickup apparatus. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block circuit diagram illustrating an example of a general circuit for realizing control of an imaging apparatus according to the present invention.
The subject is imaged on the CCD 1 surface through an imaging lens (not shown). In the CCD 1, the received light is photoelectrically converted and sent to a conversion unit 2 that includes correlated double sampling (CDS) for image noise removal, automatic gain control (AGC), analog / digital (A / D) conversion, and the like.
The timing generator (TG) 3 is an IC necessary for driving the CCD 1. The imaging signal sent to the CDS / AGC / A / D converter 2 is subjected to correlated double sampling in the CDS unit, multiplied by a necessary gain by the AGC circuit, and sequentially converted into digital data by the A / D converter. , And sent to a DSP (data signal processing) unit 4.

The DSP unit 4 also determines whether or not smear components are generated in the captured image. How to actually determine whether smear has occurred will be described later. The clock generator (CLK_GEN) 5 is an IC that can output an arbitrary frequency using the first oscillation circuit (OSC) 6 as a source oscillation. The output frequency is set by setting from the DSP unit 4.
The digital data sent to the DSP unit 4 is subjected to interpolation processing, edge enhancement processing, AWB (auto white balance) processing, RGB-YUV conversion, and the like by the DSP unit 4 and then sent to the SDRAM 7 and the ROM 14.

For monitoring, the data in the SDRAM 7 is sent again to the DSP unit 4 and converted into a predetermined format by the video encoder, and then from the D / A conversion output unit, the display device (generally an LCD) 8 built in the camera or the external display I / F (generally television output) 9. It is assumed that the video encoder unit (not shown) uses the second oscillation circuit (OSC) 10 different from the imaging system as the original oscillation and operates asynchronously with the imaging system.
When recording a moving image, the scale factor is calculated for compression, compressed by a JPEG unit (not shown) in the DSP unit 4, and sent to the memory card interface (memory card I / F) 11 to be stored in the memory card. To be recorded. The above is the configuration of a general digital still camera and the signal flow.

FIG. 2 is a schematic diagram showing how smear appears in an image when a subject is photographed. Next, the actual operation will be described. First, how to determine whether a smear component is born and how smear has occurred will be described.
FIG. 2 shows how smear appears in an image when a subject as shown on the left is photographed. Since the image of FIG. 2 is represented by an image on the CCD 1 (FIG. 1), the top and bottom of the image is reversed.

A circle 16 in the captured image 15 is a high-luminance subject such as a spotlight, and a hatched portion 17 represents an OB (Optical Black) area arranged on the CCD (imaging device) 1.
The pixels in the OB region 17 are covered with an aluminum light-shielding film so that light does not enter the photodiode (not shown), so that signal charges are not normally output from the pixels in the OB region 17. It becomes almost “0”.
All other images shown on the right side of the captured image 15 represent the state of the vertical transfer path over time. One screen represents a state in which 1/90 seconds have elapsed before reaching the right one state. In this example, transfer of one screen is completed in 1/30 seconds (3/90 seconds).

Now, let t = 0 be the moment when the signal charge corresponding to the image captured from the smear-free state is read out to the vertical transfer path. Next, when the charge is read out to the vertical transfer path, vertical transfer for one horizontal line is performed, and the lowermost stage of the imaging unit including the OB portion is sent to a horizontal transfer path (not shown) by vertical transfer.
The charges sent to the horizontal transfer path are sequentially sent to an output amplifier (not shown), and sent to the CDS section 2 (FIG. 1) at the next stage as an output of the CCD 1. By repeating this operation for the number of vertical stages, the charge for one screen is read out.
In this way, it takes time to horizontally transfer the number of horizontal pixels × 1 pixel before the charge for one horizontal line is output. Meanwhile, a smear component is generated in the vertical transfer path by the high brightness subject 16 described above. As a result, a so-called smear appears in the image as if the tail of the high-brightness subject 16 is pulled in the direction opposite to the vertical transfer direction as shown in the drawing described after 1/90 seconds.

When reading for one screen is completed after 1/30 seconds (3/90 seconds), the next frame is read. At this time, as apparent from FIG. 2, since the smear component generated during the transfer of the previous frame remains in the vertical transfer path, this time the smear component is added to the signal charge in the direction of vertical transfer from the high brightness subject 16. Will be.
In this way, a smear that appears as if the tail of the high-brightness subject 16 is pulled up and down is formed. In addition, the smear component outputs a signal based on the same amount of smear component as that of the effective region even in the vertical OB region provided above and below the effective pixel whose normal output should be “0”. Therefore, whether or not smear has occurred can be detected by determining whether or not the amount of output signal in the vertical OB area is “0”.

  In this example, the output of the OB area 17 is almost “0”. However, since the output may not be “0” due to factors different from smear such as dark current, there is a certain difference with respect to other vertical OB areas. If it is determined whether the signal amount is larger than the value, it is possible to detect the presence or absence of smear more accurately. In addition, you can easily know how much smear level is by comparing with the surrounding area. As described above, the smear detection function is achieved.

FIG. 3 is a timing chart showing the control timing of the present invention. Next, how to control the smear detection using this smear detection function will be described.
The row of CCD output in FIG. 3 represents a period for reading out one screen of the CCD 1 (FIG. 1), and the display output represents, for example, the screen update rate of an LCD (liquid crystal display). The same number added to each means the same screen content.
As is apparent from FIG. 3, there is a delay between the CCD output and the display output. This is because a predetermined process is performed while reading the signal of the CCD 1, and it is sequentially stored in the SDRAM 7 (FIG. 1), and when one screen is accumulated, the image data is sent to the video encoder.

FIG. 4 is a schematic diagram showing an example of the storage area of the SDRAM. The SDRAM 7 is actually controlled so that at least two areas A and B for storing the above-described image data are prepared, and the screen is not interrupted while switching the areas. FIG. 4 shows this state. In FIG. 4A, the image data accumulated in A is sent from B, and in FIG. 4B, the image data accumulated in B is sent from A.
Returning to FIG. 3, the third row represents the change in the output frequency of the clock generator 5 (FIG. 1), and the fourth row represents the thinning rate of the CCD 1. Assume that smear is detected when an image of the output 1 of the CCD 1 is read out.
Then, in the pause period of VD (vertical synchronization signal) after reading the frame, the driving mode of TG3 (FIG. 1) is changed so as to increase the thinning rate, and at the same time, the output frequency of the clock generator 5 is halved. To be controlled.
In this way, since the reading cycle of the CCD 1 does not change, the smear level does not change (the image remains “1” before and after the thinning rate and the clock generator 5 is switched). Thereafter, by gradually increasing the output frequency of the clock generator 5, it is possible to obtain an image in which the influence of smear is gradually reduced.

FIG. 5 is a diagram showing an image displayed on the display device when the output frequency of the clock generator is controlled. FIG. 5 shows an image of an image displayed on the display device when the above control is performed.
In FIGS. 5A to 5I, the white portion 12 is a high-brightness subject, and this region has a uniform luminance. A shaded portion 13 means smear. Smear affects the size of the screen per screen height.
Therefore, for example, if the smear is the image (1) in FIG. 3 is (A) in FIG. 5, (2) in FIG. 3 is (B) in FIG. 5, and (3) in FIG. (C)... (6) in FIG. 3 gradually becomes a problem-free level from the larger size per screen height as (F) in FIG. It goes without saying that (G) → (H) → (I) can be achieved if the same control is continued.
In the above-described example, the output frequency of the clock generator 5 is set to 12 MHz, which is half of the output frequency at the moment when the thinning rate is switched, but may be 15 MHz.

FIG. 6 is a timing chart showing a first comparative example with respect to FIG. FIG. 7 is a timing chart showing a second comparative example with respect to FIG. 6 is intended to reduce smear only by changing the thinning rate, and FIG. 7 is intended to reduce smear only by changing the output frequency of the clock generator 5.
In the case of the comparative example of FIG. 6, the image 1 from the CCD 1 (FIG. 1) and the image 2 from the CCD 1 are images as shown in FIGS. Thus, since the smear changes greatly, the user feels uncomfortable while looking at the screen.
Further, in the case of such a system with a large change, hunting may occur. Specifically, if the smear disappears in the image 2 of the CCD 1 or the smear component falls below the detection limit of the smear detection means, the image of the CCD 1 becomes 1 when the thinning rate is returned, and this time the smear Components are detected and the decimation rate is increased. Repeating this control will cause smears to appear and disappear, which can be very uncomfortable.

Also, from the viewpoint of power consumption, FIG. 6 shows no significant change in power consumption before and after smear reduction control. However, in the case of FIG. 7, since it is necessary to increase the output frequency of the clock generator 5 (FIG. 1) in order to reduce smear, if smear reduction control is performed, power consumption will increase. .
On the other hand, in FIG. 3, at the stage of reducing the smear, the output frequency of the clock generator 5 is lowered from the frequency that is normally used, so that the effect of low power consumption can be obtained.

FIG. 8 is a timing chart showing the number of times the same image is displayed on the display device. In FIG. 8, in order to further improve the display quality, the number of times the same image is displayed on the display device (FIG. 1) (display update rate) is set so that the VD cycle on the CCD 1 (FIG. 1) side is for smear reduction control. Even if it changes, the example at the time of making it not change is shown.
As described above, when the same image is displayed on the display device (FIG. 1) or an external display device, or when the moving image shooting mode is provided, the number of times (display update rate) is the display update rate or Since the control is performed so that the frame rate at the time of moving image recording is kept constant, the display quality is improved.

FIG. 9 is a timing chart showing a case where the smear reduction control is returned to the normal drive. In this case, contrary to the case of FIG. 3, it is better to first lower the output frequency of the clock generator 5 (FIG. 1) and then lower the thinning rate.
This is because it is disadvantageous from the viewpoint of power consumption because it is necessary to increase the output frequency of the clock generator 5 in order to reduce the smear level change by the clock generator 5 after reducing the thinning rate. .
As described above, when the smear reduction control is returned to the normal control, the frequency switching of the clock generator 5 is performed prior to the change of the thinning rate, so that the power consumed by the imaging apparatus can be suppressed. .

FIG. 2 is a block circuit diagram illustrating, as an example, a general circuit for realizing control of the imaging apparatus according to the present invention. It is the schematic showing how a smear appears in an image, when a subject is photoed. It is a timing chart which shows the control timing of this invention. It is the schematic which shows the example of the storage area of SDRAM. It is a figure which shows the image of the image displayed on a display apparatus when controlling the output frequency of a clock generator. It is a timing chart which shows the 1st comparative example with respect to FIG. It is a timing chart which shows the 2nd comparative example with respect to FIG. It is a timing chart which shows the frequency | count of displaying the same image on a display apparatus. It is a timing chart which shows the case where it returns to normal drive from smear reduction control.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image pick-up element (CCD), 2 Conversion part, 3 Timing generator (TG), 4 Signal processing means (DSP part, controller), 5 Clock generator (CLK-GEN), 7 SDRAM, 8 Display apparatus (LCD), 9 External Display I / F (generally TV output), 11 Memory card interface (memory card I / F), 12 White part (high brightness subject), 13 Shaded part (smear), 15 Captured image, 16 Circle, 17 shaded area (OB area) in the captured image

Claims (5)

  An image sensor that can read out by changing the thinning rate in the vertical direction, and a clock generator that is connected to the drive unit of the image sensor and can output an arbitrary clock frequency according to the setting from the controller An image pickup apparatus comprising: a smear component detection unit that processes an output signal of the image pickup device and detects a smear component included in the output signal of the image pickup device; and a signal processing unit that includes the controller. An image pickup apparatus comprising: control means for controlling the change of the decimation rate and the change of the output clock frequency of the clock generator when there is a change in the presence or absence of detection.   When the smear component is detected from the state where the smear component is not detected, the control means performs the change of the thinning rate in advance, and the smear component is not detected from the state where the smear component is detected The imaging apparatus according to claim 1, wherein the output clock frequency of the clock generator is changed in advance.   When a display device for displaying a captured image is provided, the switching timing of the output clock frequency of the clock generator is controlled so that the update period of the image displayed on the display device is constant. The imaging apparatus according to claim 1, wherein:   When an interface for displaying captured images on an external display device is provided, the output clock frequency switching timing of the clock generator is controlled so that the update period of the image displayed on the display device is constant. The imaging apparatus according to claim 1, wherein:   The switching timing of the output clock frequency of the clock generator is controlled so that an image update cycle is constant even when recording a moving image when the moving image shooting mode is provided. Item 2. The imaging device according to Item 1.

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