JP2006195023A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately focus for a subject of any pattern at a low cost and at high speed without increasing a circuit scale by highly accurately detecting the horizontal/vertical high frequency components of a subject image. <P>SOLUTION: A high frequency component detection circuit 6 extracts high frequency components from an image signal scanned and read in horizontal and vertical directions by a solid-state imaging device 3. A CPU 8 performs AF control by moving a lens 1 via a lens drive circuit 2 so that the value of high frequency components obtained by mixing these high frequency components obtains a peak value. This makes it possible to highly accurately detect the horizontal/vertical high frequency components of a subject image at a low cost without increasing the circuit scale. Accordingly, the subject of any pattern can be highly accurately focused at high speed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus that obtains an image signal by forming an image of a subject on a solid-state imaging device using a lens, and more particularly to autofocus (AF) control for automatically focusing an image formed by the lens.

  2. Description of the Related Art Conventionally, in an imaging apparatus such as a still video camera, an image of a subject is formed on a solid-state image sensor by a lens, and thereby an image signal corresponding to the formed image is accumulated in pixels constituting the solid-state image sensor. Therefore, in the conventional AF control, an image signal is read from the pixel of the solid-state imaging device corresponding to the ranging unit in the screen of one frame, and a high-frequency component is detected from the obtained image signal using a high-pass filter. The focus position of the lens is obtained by moving the lens and obtaining the peak value of the high-frequency component value (or its integral value) as shown in FIG.

However, in the conventional AF control described above, since the scanning of the image signal from the image sensor is normally performed in the horizontal direction, the high-frequency component in the horizontal direction of the subject image can be detected with high precision, whereas in the vertical direction. It is difficult to detect high-frequency components with high accuracy. Therefore, for example, a subject with a horizontal stripe pattern has a problem that it is difficult to focus. As one means for solving this, the output image from the solid-state image sensor is temporarily stored in the image memory, and the image signal is read out from the image memory by bi-directional scanning in the horizontal and vertical directions. A method of detecting high-frequency components in the direction with high accuracy has been proposed (see Patent Document 1).
JP-A-5-137046 (page 4-5, FIG. 1)

  However, the above-described method using the image memory can detect the high-frequency component in the vertical direction with high accuracy, but requires an image memory, resulting in an increase in circuit scale and cost. In addition, since the image signal read from the image sensor is written in the image memory by horizontal scanning, the image signal is read from the image memory by horizontal / vertical bidirectional scanning and AF control is performed. There is a concern that it will take longer, and this concern becomes more prominent as the range of measurement increases.

  The present invention has been devised in view of the above circumstances, and the object of the present invention is to detect high-frequency components in the horizontal and vertical directions of a subject image with high accuracy without increasing the circuit scale and at low cost. An object of the present invention is to provide an imaging apparatus capable of obtaining high-speed and high-precision focusing on a subject having any pattern.

  In order to achieve the above-mentioned object, the present invention achieves the above-described purpose by an image sensor that photoelectrically converts an image of a subject imaged by a lens and stores it as an image signal, a lens driving unit that moves the lens, and an image sensor that is stored in the image sensor. From the reading means for scanning and reading the image signal in the horizontal direction and the vertical direction, the high frequency component extraction means for extracting the high frequency component of the read image signal, and the image signal read by scanning in the horizontal direction Mixing means for mixing the extracted high-frequency component and the high-frequency component extracted from the image signal read out by scanning in the vertical direction, and the mixed high-frequency component value or the integrated value of the high-frequency component has a peak. And a focusing control means for controlling and moving the lens driving means to a position.

  The present invention also provides an image sensor that photoelectrically converts an image of a subject imaged by a lens and stores it as an image signal, a lens driving unit that moves the lens, and an image signal stored in the image sensor. Reading means for scanning and reading in the vertical and vertical directions, high-frequency component extraction means for extracting high-frequency components of the read image signal, and high-frequency extracted from the image signal read by scanning in the horizontal direction Comparing means for comparing a component and a high-frequency component extracted from the image signal read out by scanning in the vertical direction, and a scanning direction for reading out the image signal from the image sensor according to the comparison result is set to a horizontal direction or a vertical direction A scanning direction determining means for determining whether or not a high frequency component value of an image signal read out from the image sensor in the determined scanning direction or an integrated value thereof is a peak value. Characterized by comprising a focus control means for moving and controlling said lens drive means to a position.

  As described above, in the present invention, the high frequency component is extracted from the image signal read out by scanning in the horizontal direction and the vertical direction from the image sensor, and the position where the high frequency component value obtained by mixing these high frequency components or the integrated value thereof becomes a peak. The high-frequency component of the image signal read out by moving the lens to the AF control or initially scanning the image sensor in the horizontal direction and the vertical direction is compared. Therefore, it is not necessary to use an image memory by reading out an image signal from the image sensor in the scanning direction in which the image is obtained and performing AF control. Therefore, the horizontal / vertical direction of the subject image can be reduced without increasing the circuit scale of the apparatus and at a low cost. Bidirectional high-frequency components can be detected with high accuracy, and accurate focusing can be obtained for any pattern of subjects. In addition, since it is not necessary to scan the image sensor in the horizontal direction and write the image signal read into the image memory, and then scan the image memory in the horizontal and vertical directions to read out the image signal. The processing time can be shortened, and high-speed and high-precision focusing can be obtained for any subject.

  According to the present invention, the high frequency component is extracted from the image signal read out by scanning in the horizontal direction and the vertical direction from the image sensor, and the high frequency component value obtained by mixing these high frequency components or the integrated value thereof obtains the peak value. The high-frequency component of the image signal read out by scanning the image sensor at the beginning in the horizontal direction and the vertical direction is compared, and thereafter, for example, high-frequency component with a high level is obtained. By reading out the image signal from the image sensor in the direction and performing AF control, it is possible to eliminate the need to use an image memory. Therefore, it can be applied to any pattern subject without increasing the circuit scale of the apparatus. High-speed and high-precision focusing can be obtained at low cost.

  The purpose is to detect the high-frequency components in the horizontal and vertical directions of the subject image with high accuracy without increasing the circuit scale and to obtain high-speed and high-precision focusing for any pattern subject. The high-frequency component is extracted from the image signal read by scanning in the horizontal and vertical directions from the image sensor, and the lens is moved so that the high-frequency component value obtained by mixing these high-frequency components or the integrated value thereof has a peak value. By performing AF control, or by comparing the high-frequency components of the image signal initially read by scanning in the horizontal and vertical directions from the image sensor, for example, imaging is performed in the scanning direction in which a high-frequency component having a high level is obtained thereafter. This was realized by reading the image signal from the element and performing AF control.

  FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to the first embodiment of the present invention. The imaging apparatus includes a lens 1 that forms an image of a subject on a solid-state imaging device 3, a lens driving circuit 2 that moves the lens 1, a solid-state imaging device 3 that photoelectrically converts an image of the subject and stores it as an image signal, and digitally converts an analog image signal. An A / D conversion circuit 4 for converting to an image signal, a signal processing circuit 5 for performing various processes on the image signal, a high-frequency component detection circuit 6 for detecting a high-frequency component from the image signal, an image readout scanning direction and readout timing of the solid-state imaging device 3 And a timing control circuit 7 for controlling the CPU, and a CPU 8 for performing individual control such as imaging operation and AF control and control of the entire apparatus.

  Next, the AF control operation of this embodiment will be described. An image of a subject is formed on the solid-state image sensor 3 by the lens 1, and an image signal corresponding to the formed image is accumulated in the pixels of the image sensor 3. An image signal corresponding to the formed image is read from the pixels of the solid-state imaging device 3 by the timing control circuit 7 and output to the A / D conversion circuit 4. At that time, under the control of the CPU 8, the timing control circuit 7 first scans and reads the image signal from each pixel of the solid-state imaging device 3 as shown in FIG. As shown in FIG. 2, the scanning direction of the image signal is switched so as to scan and read in the vertical direction.

  FIG. 3 is a timing chart for explaining an operation in which an image signal is read from the solid-state imaging device 3 by the timing control circuit 7. The image signal is read out from the solid-state imaging device 3 by horizontal scanning readout and vertical scanning readout that are switched alternately every frame divided by the vertical synchronization signal 100.

  The A / D conversion circuit 4 digitizes the image signal read out as described above and outputs it to the signal processing circuit 5 and the high frequency component detection circuit 6. The high frequency component detection circuit 6 detects and extracts the high frequency components of the image signal read out in the horizontal scan and the image signal read out in the vertical scan, and outputs the obtained high frequency component to the CPU 8. The CPU 8 holds the high-frequency component of the image signal read out in the horizontal scan and the high-frequency component of the image signal read out in the vertical scan in a memory such as a built-in RAM and mixes them by adding these high-frequency components. At this time, the CPU 8 controls the lens driving circuit 2 to move the lens 1 at the timing shown in FIG. 3, and monitors the level change of the mixed high frequency component, and the peak of the high frequency component value (or its integrated value). By moving the lens 1 to the position where the level comes out, the lens 1 is brought to the in-focus position.

  By the way, in order to perform the AF control described above, the range of pixels from which the image signal is read from the solid-state image sensor 3 is read from all the pixels of the solid-state image sensor 3 as shown in FIG. There are two methods of reading out image signals only from pixels within the distance measurement frame as shown in B).

  According to the present embodiment, the image signal is read from the solid-state imaging device 3 in both the horizontal scanning direction and the vertical scanning direction, and the peak of the high-frequency component value (or its integrated value) of the obtained image signal is obtained. Since the lens 1 is moved to the position and AF control is performed, not only the horizontal high-frequency component of the subject image but also the vertical high-frequency component can be detected with high accuracy. For example, a subject having a horizontal stripe pattern is photographed. In this case, it is possible to focus accurately, and it is not difficult to focus by the pattern of the subject, and smooth AF control can always be performed.

  In this embodiment, since the high-frequency component of the image signal obtained by the horizontal / vertical bidirectional scanning is held in a memory such as the RAM of the CPU 8 and AF control is performed, the circuit scale is large and expensive as in the prior art. Since it is not necessary to use an image memory, the above effect can be realized at low cost without increasing the circuit scale of the apparatus.

  Furthermore, in this embodiment, since the high-frequency component is only stored in a memory such as a RAM, the processing does not take time, and high-speed AF control with good responsiveness can be performed. In particular, as shown in FIG. 4B, in the method of reading the image signal only from the pixels in the distance measurement frame, the pixel reading range is limited, so that higher-speed processing can be performed and AF control is performed at higher speed. Can do. As shown in FIG. 4A, in the method of reading image signals from all pixels, the processing speed decreases because there are many target image signals for AF control, but the accuracy of AF control is improved by the amount of target image signals. be able to.

  FIG. 5 is a timing chart showing image signal readout scanning direction switching timing in the imaging apparatus according to the second embodiment of the present invention. However, since the configuration of this example is the same as that of the first embodiment described above, the configuration operation of each unit having the same configuration is omitted, and the characteristic part of the operation will be described below.

  Next, the AF control of this embodiment will be described. Initially, horizontal scanning readout of an image signal is performed for one frame from the solid-state imaging device 3, and vertical scanning readout is performed for the next frame. At that time, the CPU 8 compares the level of the high-frequency component of the image signal read out by horizontal scanning and the level of the high-frequency component of the image signal read out by vertical scanning, and determines the subsequent reading scanning direction as a higher level direction. For example, if the high-frequency component level of the image signal read out by vertical scanning is higher, the image signal is read out from the solid-state imaging device 3 by vertical scanning and the high-frequency component value (or its integrated value) obtained thereby is peaked. The lens 1 is moved to a position where AF is performed, and AF control is performed.

  In the present embodiment as well, in order to perform AF control as in the first embodiment, the range of pixels from which image signals are read from the solid-state image sensor 3 is read from all the pixels of the solid-state image sensor 3 or is measured. There are two methods of reading out image signals only from pixels within the distance frame.

  According to the present embodiment, the image signal is read from the solid-state imaging device 3 in the scanning direction in which the level of the high-frequency component of the image signal is higher. For example, when the subject has a horizontal stripe pattern, the image signal is read from the solid-state imaging device 3 in the vertical scanning direction, and the lens 1 is moved to a position where the peak of the high-frequency component obtained thereby can be obtained. Therefore, there is an effect similar to that of the first embodiment. In particular, in the present embodiment, since the AF control can be performed without mixing the high frequency components obtained by reading by bidirectional scanning, the burden on the CPU 8 can be reduced.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect.

1 is a block diagram illustrating a configuration of an imaging apparatus according to a first embodiment of the present invention. It is the figure which showed the scanning direction at the time of reading an image signal from the solid-state imaging device shown in FIG. 2 is a timing chart showing scanning direction switching timing when an image signal is read from the solid-state imaging device shown in FIG. 1. 2 is a timing chart showing a range in which an image signal is read from the solid-state imaging device shown in FIG. 6 is a timing chart illustrating image signal readout scanning direction switching timing in an imaging apparatus according to a second embodiment of the present invention. It is a characteristic view explaining the conventional AF control method using the high frequency component extracted from the image signal read from the solid-state image sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lens, 2 ... Lens drive circuit, 3 ... Solid-state image sensor, 4 ... A / D conversion circuit, 6 ... High frequency component detection circuit, 7 ... Timing control circuit, 8 ... CPU.

Claims (8)

An image sensor that photoelectrically converts an image of a subject imaged by a lens and stores it as an image signal;
Lens driving means for moving the lens;
Reading means that scans and reads out the image signal accumulated in the image sensor in the horizontal direction and the vertical direction;
High-frequency component extraction means for extracting a high-frequency component of the read image signal;
Mixing means for mixing the high-frequency component extracted from the image signal read by scanning in the horizontal direction and the high-frequency component extracted from the image signal read by scanning in the vertical direction;
A focusing control means for controlling and moving the lens driving means to a position where the mixed high-frequency component value or its integrated value reaches a peak;
An imaging apparatus comprising:   2. The image pickup apparatus according to claim 1, wherein, when reading out an image signal from the image pickup device, the reading unit alternately switches the reading scanning direction between the horizontal direction and the vertical direction for each frame.   The image pickup apparatus according to claim 1, wherein the reading unit reads the image signal from all pixels of the image pickup device.   The imaging apparatus according to claim 1, wherein the reading unit reads the image signal from pixels in a predetermined range of the imaging element. An image sensor that photoelectrically converts an image of a subject imaged by a lens and stores it as an image signal;
Lens driving means for moving the lens;
Reading means that scans and reads out the image signal accumulated in the image sensor in the horizontal direction and the vertical direction;
High-frequency component extraction means for extracting a high-frequency component of the read image signal;
Comparison means for comparing the high-frequency component extracted from the image signal read in the horizontal direction with the high-frequency component extracted from the image signal read in the vertical direction;
A scanning direction determining means for determining whether a scanning direction for reading an image signal from the imaging element is a horizontal direction or a vertical direction based on the comparison result;
A focusing control means for controlling and moving the lens driving means to a position where the high-frequency component value of the image signal read out from the image sensor in the determined scanning direction or the integral value thereof reaches a peak;
An imaging apparatus comprising:   The reading means initially reads the image signal from the image pickup device in the determined scanning direction after alternately performing horizontal reading and vertical reading of the image signal for each frame from the image pickup device. The imaging apparatus according to claim 5, wherein:   The imaging apparatus according to claim 5, wherein the reading unit reads the image signal from all pixels of the imaging element. The imaging apparatus according to claim 5, wherein the reading unit reads the image signal from pixels in a predetermined range of the imaging element.

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