JP2005175976A - Autofocus system of an image pickup apparatus using an image pickup device having a multilayer photodiode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an optimum focusing position for all photodiodes at different positions in the depth direction of an electronic still camera using an image pickup device of a type having a plurality of photodiodes per pixel in the depth direction. An autofocus system for an image pickup apparatus capable of being provided is provided.
The photoelectric conversion value of the photodiodes of all layers in the depth direction of the type of image sensor having a plurality of photodiodes per pixel in the depth direction is added to the signals of all layers in the depth direction. Evaluate with the signal.
[Selection] Figure 1

Description

  The present invention relates to a focus detection device such as an electronic still camera, and in particular, an improvement of a focus device such as an electronic still camera using an image pickup device having a plurality of photodiodes per pixel in the depth direction. About.

  In an electronic still camera or the like having a two-dimensional imaging device, a method of detecting the sharpness of the screen from the video signal of the subject image, controlling the focus position so as to maximize the sharpness, and focusing is adopted. Yes.

In this case, the evaluation of the sharpness generally uses the intensity of the high frequency component of the video signal extracted by the band pass filter or the blur width detection intensity of the video signal extracted by the differentiation circuit. When shooting a normal subject, the intensity of these high-frequency components and the blur width detection intensity are small when the subject is out of focus, increase as the subject is in focus, and reach the maximum value when the subject is completely in focus. . The lens searches for and stops the position where the sharpness is maximized (see Patent Document 1).
JP 2003-255216 A

  However, on the other hand, in order to detect the in-focus position by detecting the position where the sharpness becomes maximum with an electronic still camera or the like using an image pickup device of a type having a plurality of photodiodes per pixel in the depth direction, It is designed to detect different color components with multiple photodiodes with different depths, but because of this structure, the focus position detected by each photodiode in the depth direction is different. End up.

  In addition, since there is a difference in intensity between the outputs of the photodiodes having different depth directions, it is impossible to accurately calculate the in-focus position.

  The present invention has been made in view of the above-described problems, and is a photo having different positions in the depth direction of an electronic still camera using an image sensor having a plurality of photodiodes per pixel in the depth direction. An object of the present invention is to provide an autofocus system for an imaging apparatus capable of detecting an in-focus position optimal for all of the diodes.

  In order to solve the above-described problems, the present invention detects the sharpness of a screen from an imaging device having a plurality of photodiodes per pixel in the depth direction, and a video signal of a subject image of the imaging device, and the sharpness is In an autofocus system of an image pickup apparatus having a focusing system that controls a focus position to achieve a maximum focus, there are a plurality in the depth direction in order to detect the sharpness in a sharpness detection region. It is characterized in that the output values of the photodiodes in all the layers of the photodiode are evaluated.

  According to the present invention, in a focusing device of an electronic still camera using an imaging device of a type having a plurality of photodiodes per pixel in the depth direction, in order to detect the sharpness, all the different depth directions are detected. Since the focus position is detected by adding and evaluating the output values of the photodiodes, the focus detection signal becomes large, and at the same time, the focus position that is centered on the different photodiodes in the depth direction is extracted. It is possible to detect the optimum in-focus position for all the photodiodes at different positions in the depth direction.

BEST MODE FOR CARRYING OUT THE INVENTION

  Examples of the present invention will be described below.

  Below, the 1st Example of this invention is described based on FIGS. 1-4.

  FIG. 1 is a circuit block diagram of an electronic camera embodying the present invention. Reference numeral 2 denotes a lens device for photographing, and reference numeral 3 denotes an image pickup device having a plurality of photodiodes per pixel in the depth direction. In this embodiment, blue, green and green are formed from a shallow portion in the depth direction per pixel. It has a three-layer photodiode that is sensitive to red.

  Reference numeral 4 denotes an A / D conversion device that converts an electrical signal imaged and photoelectrically converted on the image pickup device 3 into a digital signal, which corresponds to outputs from the blue, green, and red photodiodes of the image pickup device 3, respectively. It has three A / D conversion devices.

  Reference numeral 5 denotes a memory device that temporarily records an A / D-converted image signal. The memory device corresponds to the three A / D converters 4 and has three memory devices. 6 is a signal processing circuit for processing the image signal stored in the memory, 7 is a memory device for temporarily storing the image signal processed by the signal processing circuit 6, and 8 is a signal for focus detection from the signal processing circuit 6. The focus calculation circuit detects the sharpness of the screen and discriminates the in-focus state. Here, the high-frequency component of the image extracted by the band-pass filter is evaluated.

  Reference numeral 9 denotes a control device that controls the entire camera 1, which controls all of the reading of the image of the image sensor, A / D conversion, recording in the memory, control of the signal processing circuit, and the like.

  A lens control device 10 controls the lens 2 to the in-focus state based on the result of the in-focus state determined by the focus calculation circuit 8. Reference numeral 11 denotes a lens driving device including a motor that receives a signal from the lens control device 9 and drives the lens device 2. An image recording control device 12 is responsible for receiving an image created by the signal processing circuit 6 and recording it in the recording device 13. A recording device 13 records a final image.

  As shown in FIG. 2, the image pickup element 3 includes a plurality of photodiodes in the height direction at a portion corresponding to one pixel. In this embodiment, the image pickup element 3 has three layers of photodiodes. 31 is a photodiode layer for detecting the green component, 32 is a photodiode layer for detecting the blue component, and 33 is a photodiode layer for detecting the red component.

  The operation of the camera with the above configuration will be described.

  In S1, the start of AF is instructed. Normally, there are SW1 that is turned on when a release button (not shown) is half-pressed and SW2 that is fully pressed to generate a release timing. First, the photographer turns on SW1 to trigger AF (S2).

  When SW1 is pressed (ON state), the camera control device 9 instructs the start of imaging (S3).

  The image sensor 3 captures the subject image condensed through the lens 2 with the photodiode 32 and photoelectrically converts the captured light beam. The photoelectrically converted image signal is A / D converted in accordance with an instruction from the control device 8 (S5), sequentially stored in the memory 5 (S6), and the signal processing circuit 6 inputs a signal necessary for focus calculation to the focus calculation circuit 8. (S7).

  At this time, the focus calculation circuit 8 receives the image signals of all layers among the three signals having different depth directions of the image sensor 3 (S4).

  The focus calculation circuit 8 passes the received signal through a bandpass filter in the focus calculation circuit 8 to extract a high frequency component (S8), and evaluates the sharpness of the high frequency component (S9). Next, the control device 9 instructs the lens control device 10 to drive the lens (S10). The driving direction of the lens may be either a close direction or an infinite direction.

  The lens driving device 11 moves the lens 2 in accordance with an instruction from the lens control device 10 (S11).

  When the driving of the lens 2 is completed, the imaging device 3 performs imaging again in accordance with an instruction from the control device 9 (S3).

  When the imaging is completed, the sharpness of the image is re-evaluated again in the same manner as described above (S4 to S10).

  If the sharpness of the image is increased as a result of the reevaluation, the lens is driven again in the same direction (S11). If the sharpness of the image is decreased as a result of the reevaluation, the lens is driven in the opposite direction to the previous time ( S11). This process is repeated to find a position where the sharpness reaches a peak, and the autofocus operation ends. This is the principle of so-called mountain climbing AF.

  When the in-focus state is reached, the control device 9 displays the in-focus state on the display device of the camera (not shown) (S12), and when the in-focus state is reached, the camera waits for the photographer to turn on the release button SW2 (not shown). (S13).

  If SW2 is not turned on, the camera refers to SW1 again (S14), and if SW1 is turned off, the camera returns to standby (S17).

  If it is detected in step S13 that SW2 is turned on, the control device 9 instructs the camera to capture an image, and the image sensor 3 captures a subject image condensed through the lens 2, and photoelectrically converts the captured light beam (S16).

  The photoelectrically converted image signal is A / D converted in accordance with an instruction from the control device 8 (S18) and sequentially stored in the memory 5 (S19).

  The image signal stored in the memory 5 is subjected to image processing by the signal processing circuit 6 (S20) and stored in the memory device 7.

  The image signal stored in the memory device 7 is stored in the recording device 13 via the image recording control device 12 (S21).

  In the above description, the embodiment of the present invention has been described using the hill-climbing AF, but the autofocus evaluation method may be another method.

  Therefore, in the first embodiment, it is possible to evaluate the photoelectrically converted values of the photodiodes of all the layers in the depth direction of the type of imaging device having a plurality of photodiodes per pixel in the depth direction. .

  Here, the concept of pins and positions in each layer will be described.

  FIG. 4 shows the relationship of the sharpness of each layer of an image sensor of a type having a plurality of photodiodes per pixel, the horizontal axis represents distance, and the vertical axis represents sharpness.

  In the figure, a, b, and c are sharpness differences evaluated by three photodiodes having different depth directions of an image pickup device having a plurality of photodiodes per pixel in the depth direction. As is clear from this figure, the positions of the sharpness peaks are shifted in the three photodiodes each having a different distance from the lens in the optical axis direction.

  However, in this embodiment, the sharpness is evaluated by evaluating a signal obtained by adding the signals of all layers in the depth direction, and the added signal is d in FIG. As is apparent from FIG. 4, since the signals of all layers are added together and evaluated, the signal level becomes high, and an in-focus result that is moderate for all layers can be obtained.

It is a circuit block diagram of the electronic camera of Example 1 which concerns on this invention. It is a tomographic conceptual diagram of one pixel of the image sensor according to the first embodiment of the present invention. The flowchart of the first embodiment according to the present invention shows how the camera moves. FIG. 6 illustrates a focus detection state of each photodiode per pixel according to the first embodiment of the present invention. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic camera 2 Lens apparatus 3 Image pick-up element 4 A / D converter 5 Memory apparatus 6 Signal processing circuit 7 Memory apparatus 8 Focus calculation circuit 9 Control apparatus 10 Lens control apparatus 11 Lens drive apparatus 12 Image recording control apparatus 13 Recording apparatus

Claims (1)

An image sensor having a plurality of photodiodes per pixel in the depth direction, and detecting the sharpness of the screen from the image signal of the subject image of the image sensor, and controlling the focus position so that the sharpness is maximized; In an autofocus system of an imaging apparatus having a focusing system for focusing,
An autofocus system for an imaging apparatus, characterized in that, in a sharpness detection region, in order to detect sharpness, output values of photodiodes in all layers of the plurality of photodiodes existing in the depth direction are evaluated.

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