JP2008016961A - Imaging apparatus and read control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus for performing high speed feedback control for automatic focus at a frame rate or over while a preview image is displayed. <P>SOLUTION: An electronic camera 10 includes: a CMOS sensor 14 including a plurality of electronic shutters and capable of exposing each of regions corresponding to respective electronic shutters; a TG section 20 for reading image data for display from a prescribed region and reading image data for feedback more than once during reading of one frame from one or more regions from which the image data for display are not read; and a contrast data extract section 22, a CPU 24, and a lens drive section 26 for performing the feedback control in accordance with reading of the image data for feedback by the TG section 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging device and a reading control method for an image captured by the imaging device.

  Digital cameras have been increasing in number of pixels year by year, and are often provided with an image sensor having several million pixels. For this reason, it takes a long time to read a signal of one frame, and it is difficult to increase the frame rate.

  The autofocus function performed by the imaging apparatus is generally a method in which the lens is moved, the increase / decrease in the contrast amount of the image accompanying the movement of the lens is determined, and the moving direction of the lens is determined. Since the feedback control is to determine whether or not the lens moving direction is appropriate using an image reflecting the lens movement, the higher the frame rate, the faster the feedback control can be performed. The faster the frame rate, the faster autofocus can be performed.

  Even in systems other than autofocus that perform feedback control using image data as an evaluation value, the rate at which the evaluation value is acquired often affects the speed of control and becomes important.

  In a digital still camera, in order to increase the frame rate during preview, reading is performed by thinning out from the image sensor during preview, and all pixels are read when an image is actually captured. However, in autofocus, higher speed is required.

  Japanese Patent Application Laid-Open No. 2004-133867 describes a method of reading only a part of an image sensor area to obtain an evaluation value at high speed and shortening the time until autofocus is focused.

Patent Document 2 describes a method of reading out image data from a plurality of channels and acquiring all-pixel read data at the center of the image while performing thinning-out reading.
JP 2004-88703 A JP 2005-86246 A

  However, with the technique described in Patent Document 1, it is possible to shorten the time until autofocusing is achieved, but it is not possible to display a preview image during the autofocus operation.

  With the technique described in Patent Document 2, preview display can be performed during the autofocus operation, but the autofocus feedback cycle cannot be increased beyond the frame rate of the preview display.

  In view of the above background, an object of the present invention is to provide an imaging apparatus that performs feedback control of autofocus at a speed higher than the frame rate while a preview image is displayed while maintaining a simple configuration.

  An imaging apparatus according to the present invention includes a plurality of electronic shutters, an image sensor that can be exposed for each area corresponding to each electronic shutter, and display image data from a predetermined area, and display image data for display. A reading control unit that reads image data for feedback a plurality of times during reading of one frame from one or a plurality of areas where reading is not performed, and according to reading of the image data for feedback by the reading control unit And a feedback control unit that performs feedback control using the image data.

  In this way, the image display frame rate is obtained by performing feedback control by reading the image data for feedback a plurality of times in the imaging of one frame from the area where the image data for display is not read out while reading out the image data for display. Feedback control with a faster cycle becomes possible.

  In the imaging apparatus of the present invention, the readout control unit is configured to read the feedback image data from the same region.

  As described above, by acquiring the feedback image a plurality of times from the same region, it is possible to appropriately obtain the rate at which the feedback image data has been changed by the feedback control.

  In the image pickup apparatus of the present invention, the read control unit has a configuration in which image data read from a plurality of areas where display image data is not read is added to obtain image data for feedback.

  By adding the image data read from a plurality of areas in this way, the value of the image data for feedback can be increased, so that feedback control is appropriately performed using image data with a small value obtained in a short exposure time. Yes. Thereby, the exposure time for acquiring the image data for feedback can be shortened, and feedback control can be performed at higher speed.

  In the imaging apparatus of the present invention, the feedback control unit performs autofocus control.

  With this configuration, the optimum position of the focus lens can be searched at high speed.

  The readout control method of the present invention is a readout control method of image data of an imaging apparatus having an image sensor that has a plurality of electronic shutters and can be exposed for each area corresponding to each electronic shutter. A display image reading step for reading display image data, a feedback image reading step for reading feedback image data from one or a plurality of areas where reading of the display image data is not performed, and the reading step A feedback control step for performing feedback control using the image data in response to reading of the image data for feedback by a plurality of times, and performing the feedback image reading step and the feedback control step a plurality of times during the reading of one frame. It has a configuration to perform.

  In this way, the image display frame rate is obtained by performing feedback control by reading the image data for feedback a plurality of times in the imaging of one frame from the area where the image data for display is not read out while reading out the image data for display. Feedback control with a faster cycle becomes possible.

  According to the present invention, it is possible to perform feedback control at a cycle faster than the frame rate of image display by reading feedback image data a plurality of times and performing feedback control in imaging of one frame.

  Hereinafter, an imaging device according to an embodiment of the present invention will be described with reference to the drawings. Hereinafter, an electronic camera will be described as an example of the imaging device.

  FIG. 1 is a diagram showing a configuration of an electronic camera 10 according to an embodiment of the present invention. The electronic camera 10 according to the embodiment includes a lens 12, a CMOS sensor 14, an image signal processing unit 16, and an output control unit 18. The lens 12 forms an image of the subject on the CMOS sensor 14. The CMOS sensor 14 is driven according to a sensor drive pulse generated by a timing generator unit (hereinafter referred to as “TG unit”) 20 and photoelectrically converts incident light. The CMOS sensor 14 is an image sensor for line sequential exposure. The CMOS sensor 14 has an electronic shutter for each line, and can perform exposure for each line. Which line the CMOS sensor 14 performs exposure is controlled by a sensor driving pulse generated by the TG unit 20. The TG unit 20 corresponds to a read control unit of the present invention. The CMOS sensor 14 inputs a digital image signal obtained by photoelectric conversion to the image signal processing unit 16.

  The image signal processing unit 16 processes the digital image signal input from the CMOS sensor 14 and inputs the signal to the output control unit 18. The output control unit 18 adds a synchronization signal to the image signal input from the image signal processing unit 16 and outputs it.

  The electronic camera 10 also includes a contrast data extraction unit 22, a CPU 24, and a lens driving unit 26. The contrast data extraction unit 22 receives the digital image signal from the CMOS sensor 14 and extracts the contrast data from the digital image signal. The CPU 24 calculates the moving direction of the focused lens based on the contrast data extracted by the contrast data extraction unit 22. The CPU 24 transmits a driving signal to the lens driving unit 26 based on the calculation result, and controls the lens 12. The contrast data extraction unit 22, the CPU 24, and the lens driving unit 26 constitute a feedback control unit of the present invention.

  Next, an image data reading operation by the CMOS sensor 14 of the electronic camera 10 will be described.

  FIG. 2A and FIG. 2B are diagrams showing the order of reading from the CMOS sensor 14. FIG. 2A shows the reading order during normal monitoring, and FIG. 2B shows the reading order when reading image data for feedback. In the following description, the image data for feedback is referred to as “evaluation value”. During normal monitoring, reading is performed from the upper part of the screen toward the lower part as shown in FIG. At the time of preview, a half-thinning scan is performed.

  FIG. 3A is a diagram illustrating a read example of 1/2 thinning scan. In the half-thinning scan, as shown in FIG. 3A, after reading two lines of the RG line and the GB line, the next two lines are skipped and the next two lines are read.

  Next, reading when the electronic camera 10 reads the evaluation value will be described. As shown in FIG. 2B, reading is performed from the upper part of the screen toward the lower part of the screen, and after reading the lower part of the screen, the central part of the screen is read again. In the readout A at the upper part of the screen shown in FIG. 2A, readout is performed by the same method as the normal 1/2 thinning-out operation shown in FIG. In the readout B at the center of the screen in FIG. 2B, the evaluation value is read out in addition to the display image data read out by the normal thinning operation.

  FIG. 3B is a diagram for explaining in detail the reading of the evaluation value in the reading B at the center of the image shown in FIG. After reading image data for display from two lines (for example, N line and N + 1 line) of RG line and GB line, evaluation is performed from two lines of next RG line and GB line (for example, N + 2 line, N + 3 line). Read the value. The image data for display is read from the subsequent RG line and GB line (N + 4 line, N + 5 line). As described above, in the reading B, the evaluation value is read from the line skipped in reading the display image data.

  Subsequently, in the readout C at the bottom of the screen shown in FIG. 2B, readout is performed by the same method as the normal thinning operation shown in FIG.

  After reading out the lower part of the screen, the central part of the screen is read again as indicated by the readout D in the central part of the screen in FIG. In the reading D, only the evaluation values shown in FIG. 3B are read, and display image data is not read.

  FIG. 4A and FIG. 4B are diagrams illustrating image data read timing. Since the CMOS sensor 14 is a sequential exposure sensor, the relationship between exposure and readout of each line in normal monitoring differs from line to line as shown in FIG. The time zone is shifting sequentially.

  FIG. 4B shows the read timing when reading the evaluation value. The first to sixth lines corresponding to the upper part of the screen are exposed in the same manner as in the normal monitoring shown in FIG. In the Nth to N + 7th lines corresponding to the center of the screen, the electronic shutter is cut twice in the N + 2 line, N + 3 line, N + 6 line, and N + 7 line from which the evaluation value is read, and the exposure time zone is divided into two. The first exposure time zone corresponds to readout B shown in FIG. 2B, and the second exposure time zone corresponds to readout D. Thereby, two image data with different exposure time zones can be acquired at the center of the screen.

  Next, feedback control of the electronic camera 10 will be described. The electronic camera 10 performs feedback control according to the reading of the evaluation value. That is, when reading is performed twice as shown in FIG. 4B, autofocus control is performed to move the lens based on the read evaluation value after reading the first evaluation value, and the lens is moved. The second evaluation value is read in the moved state.

  FIG. 5A is a diagram illustrating timing of conventional autofocus feedback control, and FIG. 5B is a diagram illustrating timing of autofocus feedback control according to the present embodiment. The pulse waveform shown at the top of each figure indicates the readout timing of one frame, that is, the frame rate.

  Conventionally, as shown in FIG. 5A, after obtaining the evaluation value A-1, the lens operation direction is determined based on the obtained evaluation value, and the drive pulse B-1 is output. Since the result of movement by the drive pulse B-1 can be acquired as the evaluation value A-2 in the next frame, the lens operation direction is determined based on the evaluation value A-2, and the drive pulse B-2 is output. As shown in FIG. 5A, this feedback is performed in the same cycle as the frame rate.

  In the present embodiment, as shown in FIG. 5B, after obtaining the evaluation value C-1, the lens operation direction is determined based on the obtained evaluation value, and the drive pulse D-1 is output. Since the result of movement by the drive pulse D-1 can be obtained as the evaluation value C-2 during reading of the same frame, the lens operation direction is determined using the evaluation value C-2, and the drive pulse D-2 is output. . As shown in FIG. 5B, this feedback can be performed with a period twice as long as the frame, and is twice as long as the conventional feedback control.

  Since the electronic camera 10 of the present embodiment acquires two image data with different exposure time zones at the center of the screen, feedback control can be performed twice in monitoring of one frame. Therefore, control such as autofocus can be performed at high speed regardless of the frame rate of the display image.

  Although the imaging apparatus of the present invention has been described in detail with reference to the embodiment, the present invention is not limited to the above-described embodiment.

  Although the exposure time of the display image data can be extended to the length of one frame, since the evaluation value is read twice, the exposure time cannot be extended to the length of one frame. In autofocus, control is performed by looking at the contrast of the image. However, when only horizontal contrast is used, it is also possible to integrate the image data in the vertical direction to increase the sensitivity and obtain the evaluation value.

In the above-described embodiment, the method of dividing the reading of the evaluation value at the center of the screen into two times has been described, but the method may be divided into three or more times. In this case, the feedback period is
Frame rate x number of divisions (1)
As the number of divisions increases, feedback can be executed at high speed.

  In addition, as shown in FIG. 3B, the description has been given of the configuration in which the image data for display is read and the evaluation value is read out, and the evaluation value is read out twice from the same line. May be read from different lines.

  FIG. 6 shows an example in which the evaluation values are read from different lines. The first evaluation value is read from the N + 2 line, N + 3 line, N + 10 line, and N + 11 line, and the second evaluation value is read from the N + 6 line, N + 7 line, N + 14 line, and N + 15 line. By reading the evaluation values from the different lines in this way, the reading time of each evaluation value can be made longer than ½ frame. In addition, if different lines for reading evaluation values are more than a certain distance, they are not suitable for use as an evaluation value for feedback control, so a plurality of different lines for reading evaluation values should be included within a predetermined range. Is preferred.

  In the embodiment described above, 1/2 thinning is used as an example for thinning readout, but other thinnings such as 1/4 thinning and 1/8 thinning can be realized by the same method.

  In the embodiment described above, the autofocus feedback control has been described as an example. However, the feedback control is not limited to autofocus, and can be used according to the application.

  The electronic camera and the image sensor according to the present invention are useful as a digital camera or the like because autofocus control can be performed at high speed.

Block diagram of an electronic camera according to an embodiment of the present invention The figure which shows the reading order from the CMOS sensor at the time of normal monitoring The figure which shows the reading order at the time of reading the image data for feedback The figure which shows the read-out example of 1/2 thinning scan The figure which shows the reading order in the case of reading the image data for feedback in detail The figure which shows the read-out timing of the image data in normal monitoring The figure which shows the read-out timing when reading an evaluation value The figure which shows the timing of the conventional autofocus feedback control The figure which shows the timing of the feedback control of the autofocus of this Embodiment Explanatory drawing of multiple division reading in the embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electronic camera 12 Lens 14 CMOS sensor 16 Image signal processing part 18 Output control part 20 TG part 22 Contrast data extraction part 24 CPU
26 Lens drive unit

Claims (5)

An image sensor that has a plurality of electronic shutters and can be exposed for each area corresponding to each electronic shutter;
Reading out image data for display from a predetermined area and reading out image data for feedback multiple times during reading of one frame from one or a plurality of areas in which image data for display is not read out A control unit;
A feedback control unit that performs feedback control using the image data in response to reading of image data for feedback by the read control unit;
An imaging apparatus comprising:   The imaging apparatus according to claim 1, wherein the read control unit reads the image data for feedback from the same region.   The imaging apparatus according to claim 1, wherein the reading control unit adds image data read from a plurality of areas where reading of image data for display is not performed to obtain image data for feedback.   The imaging apparatus according to claim 1, wherein the feedback control unit performs autofocus control. An image data readout control method for an image pickup apparatus having an image pickup device having a plurality of electronic shutters and capable of exposing each region corresponding to each electronic shutter,
A display image reading step for reading display image data from a predetermined area;
A feedback image reading step for reading image data for feedback from one or a plurality of areas where reading of image data for display is not performed;
A feedback control step of performing feedback control using the image data in response to reading of the image data for feedback in the reading step;
With
A readout control method, wherein the feedback image readout step and the feedback control step are performed a plurality of times during readout of one frame.

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