JP2005003933A - Automatic focusing device for electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing device for an electronic camera capable of always performing an appropriate AF control even in the case the brightness of an object drastically changes when taking a moving picture. <P>SOLUTION: A main pixel frame and a sub pixel frame having different levels of sensitivity are outputted by a CCD 10. Whether or not the main pixel frame taken from the CCD 10 is saturated is discriminated by a main/sub pixel brightness decision part 161, and a gate circuit 164 is controlled through a frame designation part 163 based on the discrimination result, and when not saturated, image data in the focus area of the main pixel frame is guided to a high frequency component extraction part 165, on the other hand, when saturated, image data in the focus area in the sub pixel frame is guided to the part 165. The high frequency components of the inputted image data are extracted by the part 165, and the absolute value of the extracted high frequency components is integrated and an AF evaluation value is calculated by an AF evaluation value calculation part 166. When taking the moving picture, the AF control is performed by the AF control part 167 based on the AF evaluation value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic focus adjustment apparatus for an electronic camera, and more particularly to a technique for automatic focus adjustment at the time of moving image shooting using image pickup elements having elements with different sensitivities.
[0002]
[Prior art]
Conventionally, a high-speed AF mode in which only a part of the image signal in the imaging range of the image sensor is read out at high speed and automatic focus adjustment (AF) is performed based on the read-out image signal is provided. An electronic still camera has been proposed that performs AF control in a short time (Patent Document 1).
[0003]
In the AF control, an absolute value of the high frequency component of the image signal read from the image sensor is integrated to obtain an evaluation value (AF evaluation value), and the focus lens is moved so that the AF evaluation value is maximized. Done.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-298685
[0005]
[Problems to be solved by the invention]
However, even if the AF control is performed in the high-speed AF mode described in Patent Document 1, if high-luminance subject light is incident on the image sensor, the pixels of the image sensor are saturated. There is a problem that a satisfactory AF evaluation value cannot be obtained and good AF control cannot be performed.
[0006]
In particular, when a subject is suddenly brightened due to a scene change or the like during moving image shooting, and the pixel of the image sensor is saturated, after that, exposure control is properly performed until the pixel saturation of the image sensor is canceled. Good AF control cannot be performed. In general, the responsiveness of the exposure control at the time of moving image shooting is set to be slow with respect to the change in the brightness of the subject, and the exposure control does not follow the change in the brightness for a short time. This is because if the exposure control is made to follow a sudden change in the brightness of the subject, the brightness of the main subject of the moving image to be reproduced fluctuates within a short time and becomes unsightly.
[0007]
The present invention has been made in view of such circumstances, and provides an automatic focusing device for an electronic camera that can always perform appropriate AF control even when the brightness of a subject changes suddenly during moving image shooting. For the purpose.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is characterized in that a large number of high-sensitivity main pixels and sub-pixels having lower sensitivity than the main pixels are arranged according to a predetermined arrangement form. It has an image pickup means that can take out the photoelectrically converted signals, and based on the evaluation value indicating the sharpness of the image calculated by using the signal taken from the image pickup means, the shooting lens is combined. In the automatic focusing device for an electronic camera that moves to a focal position, a determination unit that determines whether or not a main pixel frame of main / sub-pixel frames captured from the imaging unit is saturated; When it is determined that the main pixel frame is not saturated, the main pixel frame is selected. When it is determined that the main pixel frame is saturated, the sub pixel frame is selected. / Subpixel frame selection means; evaluation value calculation means for calculating the evaluation value from the image signal of the main pixel frame or the subpixel frame selected by the main / subpixel frame selection means; And a control means for controlling the lens moving means so that the evaluation value always maintains a maximum based on the evaluation value calculated by the evaluation value calculating means. It is a feature.
[0009]
That is, when performing AF control during moving image shooting, the AF control is basically performed based on an evaluation value indicating the sharpness of an image calculated from the main pixel frame. This is because the main pixel has better S / N than the sub-pixel. On the other hand, when the brightness of the subject suddenly changes brightly (for example, when going from indoors to the outdoors) and the main pixel frame is saturated, AF control is performed based on the evaluation value calculated from the subpixel frame. Do. This is because even if the main pixel frame is saturated, the sub-pixel frame with low sensitivity is often not saturated. Thereby, even when the brightness of the subject changes sharply, an appropriate evaluation value can be calculated, and appropriate AF control can always be performed during moving image shooting.
[0010]
According to a second aspect of the present invention, in the automatic focus adjustment apparatus for an electronic camera according to the first aspect, the determination means saturates more than a certain number of pixels in a predetermined focus area in the entire screen of the main pixel frame. It is characterized by determining whether or not.
[0011]
According to a third aspect of the present invention, in the automatic focus adjustment apparatus for an electronic camera according to the first or second aspect, the evaluation value calculation means includes a main pixel frame or a sub-pixel frame selected by the main / sub-pixel frame selection means. A high frequency component of a subject is extracted from an image signal in a predetermined focus area, and the evaluation value is calculated by integrating absolute values of the high frequency component.
[0012]
That is, the evaluation value is calculated from an image signal of a predetermined focus area (for example, the center of the screen) in one frame. This is because, in general, framing is often performed so that the main subject to be photographed enters the center of the screen. Accordingly, whether or not the main pixel frame is saturated is also determined based on whether or not a certain number of pixels in a predetermined focus area in the main pixel frame is saturated. The number of fixed pixels is preferably determined in consideration of an evaluation value calculated when the fixed number of pixels is saturated and an evaluation value calculated from a sub-pixel frame with a poor S / N. .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of an automatic focusing device for an electronic camera according to the present invention will be described below in detail with reference to the accompanying drawings.
[0014]
[Image sensor structure]
First, the structure of the image sensor applied to the electronic camera according to the present invention will be described. FIG. 1 is a schematic plan view showing an example of a CCD solid-state imaging device (hereinafter referred to as CCD) used in an electronic camera according to the present invention.
[0015]
As shown in the figure, the CCD 10 is a two-dimensional imaging device (image sensor) in which a large number of light receiving cells 20 are arranged at a constant arrangement period in the horizontal direction (row direction) and the vertical direction (column direction). The illustrated configuration is a pixel array called a honeycomb array, in which the center points of the geometric shapes of the light receiving cells 20 are shifted by half the pixel pitch (1/2 pitch) every other row direction and column direction. It has become. That is, in the rows (or columns) of the light receiving cells 20 adjacent to each other, the cell arrangement in one row (or column) is in the row direction (or column direction) with respect to the cell arrangement in the other row (or column). The structure is arranged so as to be relatively shifted by about ½ of the arrangement interval.
[0016]
Each light receiving cell 20 includes two photodiode regions 21 and 22 having different sensitivities. The first photodiode region 21 has a relatively large area and constitutes a main photosensitive portion (hereinafter referred to as “main pixel”) having high sensitivity. The second photodiode region 22 has a relatively small area and constitutes a subordinate photosensitive portion (hereinafter referred to as “sub-pixel”) having low sensitivity.
[0017]
For each light receiving cell 20, color filters of the same color are arranged in the main pixel 21 and the sub-pixel 22. That is, one primary color filter of RGB is assigned to each light receiving cell 20. As shown in FIG. 1, the BRBR... Row is arranged in the next stage of the GGGG... Row in the horizontal direction, the GGGG... Row is arranged in the next stage, and the RBRB. Further, in the column direction, the GGGG column, the BRBR column, the GGGG column, and the RBRB column are repeated in a cyclic manner.
[0018]
A vertical transfer path (VCCD) 30 is formed on the right side of the light receiving cell 20. The vertical transfer path 30 extends in the vertical direction by meandering in a zigzag manner in the vicinity of each column of the light receiving cells 20 and avoiding the light receiving cells 20.
[0019]
On the vertical transfer path 30, transfer electrodes 31, 32, 33, and 34 necessary for four-phase driving (φ1, φ2, φ3, φ4) are arranged. The transfer electrodes 31 to 34 are provided close to each row of the light receiving cells 20 so as to meander while avoiding the opening of the light receiving cells 20 and extend in the horizontal direction in FIG. For example, when the transfer electrode is formed of two-layer polysilicon, the first transfer electrode 31 to which the pulse voltage φ1 is applied and the third transfer electrode 33 to which the pulse voltage φ3 is applied are the first polysilicon layer. The second transfer electrode 32 to which the pulse voltage φ2 is applied and the fourth transfer electrode 34 to which the pulse voltage φ4 is applied are formed of a second polysilicon layer.
[0020]
In FIG. 1, a VCCD driving circuit 42 that applies a pulse voltage to the transfer electrodes 31 to 34 is disposed on the right side of the imaging area 40 in which the light receiving cells 20 are arranged. A horizontal transfer path (HCCD) 44 that transfers the signal charges transferred from the vertical transfer path 30 in the horizontal direction is provided below the imaging area 40 (at the lower end side of the vertical transfer path 30).
[0021]
The horizontal transfer path 44 is composed of a two-phase drive transfer CCD, and the last stage (the leftmost stage in FIG. 1) of the horizontal transfer path 44 is connected to the output unit 46. The output unit 46 includes an output amplifier, performs charge detection of the input signal charge, and outputs it to the output terminal 48 as a signal voltage. In this way, the signal photoelectrically converted by each light receiving cell 20 is output as a dot-sequential signal sequence.
[0022]
FIG. 2 is a graph showing the photoelectric conversion characteristics of the main pixel 21 and the sub-pixel 22. The horizontal axis represents the amount of incident light, and the vertical axis represents the image data value (QL value) after A / D conversion. In this example, 12-bit data is illustrated, but the number of bits is not limited to this.
[0023]
As shown in the figure, the sensitivity ratio between the main pixel 21 and the sub-pixel 22 is 1: 1 / a (where a> 1, a = 16 in this example). The output of the main pixel 21 gradually increases in proportion to the amount of incident light, and when the amount of incident light is “c”, the output reaches a saturation value (QL value = 4095). Thereafter, even if the amount of incident light increases, the output of the main pixel 21 becomes constant. This “c” will be referred to as the saturation light amount of the main pixel 21.
[0024]
On the other hand, the sensitivity of the sub-pixel 22 is 1 / a of the sensitivity of the main pixel 21, and is saturated at a QL value = 4095 / b when the incident light quantity is α × c (where b> 1, α = a / b, in this example b = 4, α = 4). “Α × c” at this time is referred to as the saturation light amount of the sub-pixel 22.
[0025]
In this way, by combining the main pixel 21 and the sub-pixel 22 having different sensitivities and saturations, the dynamic range of the image sensor can be expanded α times compared to the configuration of only the main pixel. In this example, the dynamic range is expanded about four times with a sensitivity ratio of 1/16 and a saturation ratio of 1/4. When the maximum dynamic range when only the main pixel 21 is used is 100%, in this example, the dynamic range is expanded to about 400% at the maximum by utilizing the sub-pixel 22.
[0026]
[Configuration example of electronic camera]
Next, an electronic camera equipped with the above-described wide dynamic range imaging CCD 10 will be described.
[0027]
FIG. 3 is a block diagram of the electronic camera according to the present embodiment. The electronic camera 100 can shoot a still image and a moving image by switching between a still image mode and a moving image mode by a mode switching unit (not shown). By synthesizing, it is possible to shoot with a dynamic range specified in advance (for example, 200%, 300%, 400%), and when shooting a moving image, a signal of only the main pixel is used for moving image recording. Note that FIG. 3 mainly illustrates blocks that function in the moving image mode.
[0028]
The photographing optical system 110 of the electronic camera 100 includes a photographing lens and a diaphragm, and a driving unit thereof. The photographing lens (focus lens) and the diaphragm are controlled to be output from the focus / aperture adjustment unit 120 to each driving unit. Focus control and aperture control are performed by the signal. Details of this control will be described later.
[0029]
The light that has passed through the photographing optical system 110 enters the CCD 10. A large number of photosensors (light receiving elements) are two-dimensionally arranged on the light receiving surface of the CCD 10, and red (R), green (G), and blue (B) primary color filters corresponding to each photosensor are predetermined. Arranged in array form.
[0030]
The subject image formed on the light receiving surface of the CCD 10 is converted into a signal charge in an amount corresponding to the amount of incident light by each sensor on the CCD 10.
[0031]
The signal charge accumulated in this way is read out to the shift register by a read gate pulse applied from a CCD drive circuit (not shown), and sequentially read out as a voltage signal corresponding to the signal charge by a register transfer pulse. The CCD 10 has a so-called electronic shutter function that can sweep out the signal charge accumulated by the shutter gate pulse output from the exposure time control unit 130, thereby controlling the charge accumulation time (exposure time). .
[0032]
From the CCD 10, the signal accumulated in the photosensor of the main pixel (signal of the main pixel frame) and the signal accumulated in the photosensor of the subpixel (signal of the subpixel frame) are sequentially read out as voltage signals. These main pixel frame signal and sub-pixel frame signal are applied to the A / D converter 140 where they are converted into digital signals. Note that the signals of the main pixel frame and the sub-pixel frame include signals of odd fields or even fields in the case of signals of two fields and one frame composed of odd fields and even fields.
[0033]
The main / sub-pixel image data (dot sequential R, G, B signals) converted into digital signals by the A / D converter 140 is applied to the signal processing unit 150 and the AF / exposure control unit 160.
[0034]
The signal processing unit 150 includes a synchronization circuit, a white balance adjustment circuit, a dynamic enlargement processing circuit (main / sub-pixel synthesis processing circuit), a gamma correction circuit, a luminance / color difference signal (YC signal) generation circuit, a compression / decompression circuit, and the like. Each of the circuits executes signal processing corresponding to the input image data of the main / sub-pixel frame, and is output to the image output unit 170 as an image file and recorded.
[0035]
The main / sub-pixel combination processing circuit multiplies image data of the main pixel and sub-pixel by appropriate coefficients at the time of still image shooting and adds these multiplication values to expand the dynamic range. Since only the image data of the main pixel is sometimes recorded, the dynamic range expansion process is not performed.
[0036]
The AF / exposure control unit 160 performs AF control and exposure control. Mainly, the main / sub-pixel luminance determination unit 161, the exposure control unit 162, the frame designation unit 163, the gate circuit 164, the high-frequency component extraction unit 165, and the AF evaluation. A value calculation unit 166 and an AF control unit 167 are included.
[0037]
The main / sub-pixel luminance determination unit 161 obtains information on the brightness of the subject based on the image data of main / sub-pixel frames sequentially input from the A / D converter 140 and sends this information to the exposure control unit 162. The exposure control unit 162 adjusts the exposure time via the exposure time control unit 130 based on the brightness information of the subject input from the main / sub-pixel luminance determination unit 161, or shoots via the focus / aperture adjustment unit 120. The diaphragm in the optical system 110 is adjusted.
[0038]
That is, for example, when the maximum value of the main pixel and the sub-pixel is input as the brightness information of the subject, the exposure control unit 162 is when the maximum value of the main pixel is other than a saturation value (QL value is 4095 in this example). The exposure time or aperture value is determined so that the maximum value of the main pixel becomes the optimum value of the maximum main pixel set in advance. On the other hand, when the maximum value of the main pixel is a saturation value, Based on the maximum value and the sensitivity ratio between the main pixel and the sub-pixel, the exposure time or aperture value is determined so that the maximum value of the main pixel becomes the optimum value of the maximum main pixel set in advance. The exposure is controlled by the determined exposure time or aperture value. The exposure control may be performed using only the image data of the sub-pixel frame that is not saturated, although the S / N is not good.
[0039]
Further, the main / sub-pixel luminance determination unit 161 is based on the image data of the main / sub-pixel frame sequentially input from the A / D converter 140, and is in a predetermined focus area (for example, the screen center) of the main pixel frame. It is determined whether or not a certain number of pixels is saturated, and the determination result is output to the frame designation unit 163. The frame designation unit 163 outputs a command indicating which of the main / subpixel frames to be input to the gate circuit 164 is to be selected. That is, when a certain number of pixels within a predetermined focus area of the main / sub-pixel frame is saturated, a command for selecting the sub-pixel frame is output, and in other cases, the main pixel frame is selected. Output a command.
[0040]
The gate circuit 164 selects image data of one of the main / sub-pixel frame image data sequentially input from the A / D converter 140 based on a command input from the frame designating unit 163, and Only the image data of a predetermined focus area among the image data of the selected frame is passed and sent to the high frequency component extraction unit 165.
[0041]
The high frequency component extraction unit 165 extracts a predetermined high frequency component from the input image data, and outputs the extracted high frequency component to the AF evaluation value calculation unit 166. Note that the high frequency component can be extracted by, for example, obtaining a difference between image data of adjacent pixels.
[0042]
The AF evaluation value calculation unit 166 integrates the absolute values of the high frequency components input from the high frequency component extraction unit 165, and outputs the integrated value (referred to as an AF evaluation value) to the AF control unit 167. The AF control unit 167 moves the focus lens via the focus / aperture adjustment unit 120 so that the AF evaluation value input from the AF evaluation value calculation unit 166 is maximized.
[0043]
Here, an outline of AF control using the AF evaluation value will be described.
[0044]
As shown in FIG. 4, in the AF control at the time of still image shooting, for example, the focus lens is moved from the closest end to the infinity, and the AF evaluation value is sampled for each predetermined lens position. Then, a curve passing through a plurality of AF evaluation values including a maximum AF evaluation value among a plurality of sampled AF evaluation values is obtained, and a lens position at which this curve becomes a maximum is obtained. AF control is performed by moving the focus lens to the lens position thus obtained.
[0045]
On the other hand, in the AF control during moving image shooting, the focus lens is moved so that the AF evaluation value always maintains the maximum. Details of the AF control at the time of moving image shooting will be described later.
[0046]
Next, the operation of the AF / exposure control unit 160 will be described.
[0047]
FIG. 5 shows an overall flowchart of AF / exposure control in the AF / exposure control unit 160.
[0048]
First, exposure control during moving image shooting is performed (step S100). In this exposure control, when the maximum value of the main pixel of the main / sub-pixel frame is other than the saturation value, the exposure time is determined so that the maximum value becomes a preset optimum value. To do.
[0049]
If the maximum value of the main pixel is Gmain, the optimum value of the maximum main pixel is Gopt, and the previous exposure time is Told, a new exposure time Tnew is calculated by the following equation.
[0050]
[Expression 1]
Tnew = Told × (Gopt / Gmain)
If the exposure time during moving image shooting is controlled by this exposure time Tnew, the maximum value Gmain of the pixels of the main pixel frame obtained at that time can be set to the optimum value Gopt.
[0051]
On the other hand, when the image data of the main pixel frame is saturated, the maximum value of the subpixel in the subpixel frame is read. Then, if the maximum value of the subpixel is Gsub, the sensitivity ratio of the main pixel and the subpixel is Ggain, the optimum value of the maximum main pixel is Gopt, and the previous exposure time is Told, a new exposure time Tnew is calculated by the following equation. To do.
[0052]
[Expression 2]
Tnew = Told × (Gopt × Ggain) / Gsub
If the exposure time during moving image shooting is controlled by this exposure time Tnew, the image data of the main pixel frame obtained at that time is not saturated, and the maximum value Gmain of the pixels of the main pixel frame can be set to the optimum value Gopt. it can.
[0053]
The exposure control method at the time of moving image shooting is not limited to the above-described embodiment, and the exposure control may be performed based only on the image data of the sub-pixel frame.
[0054]
Next, of the main image frame and the sub-pixel frame, a frame to be used at the time of AF control for moving image shooting is determined (step S200).
[0055]
That is, as shown in the flowchart of FIG. 6, it is determined whether or not a predetermined number of pixels or more in a predetermined focus area of the main pixel frame is saturated based on the image data of the main pixel frame (step S202). If it is determined that it is not saturated, the image data of the main pixel frame is used for AF control (step S204). If it is determined that it is saturated, the image data of the sub-image frame is used for AF control. (Step S206).
[0056]
When a frame to be used for AF control is determined as described above, an AF search is subsequently performed (step S300).
[0057]
In the first AF control during moving image shooting, the focus lens is moved in a certain direction (for example, the infinity side) and the AF evaluation value is sampled. If the AF evaluation value becomes larger than that at the previous sampling, it is determined that the maximum of the AF evaluation value exists on the infinity side, and the focus lens is continuously moved to the infinity side. On the other hand, if the AF evaluation value is smaller than that at the previous sampling, it is determined that there is a maximum AF evaluation value in the reverse direction (closest side), and the focus lens is moved to the close side.
[0058]
After determining the moving direction of the focus lens in this way, the focus lens is moved in the determined direction, and the AF evaluation value is sampled. When the AF evaluation value is initially smaller than the previous sampling time Then, it is determined that the AF evaluation value exceeds the maximum, and the focus lens is returned by one step in the reverse direction. As a result, the focus lens can be moved to the lens position where the AF evaluation value is maximized.
[0059]
Next, AF control is described in which the AF evaluation value is always kept at a maximum after the focus lens is moved to the lens position where the AF evaluation value becomes a maximum as described above.
[0060]
As shown in the flowchart of FIG. 7, an AF evaluation value is calculated (step S302). The calculation of the AF evaluation value is performed based on the image data in the focus area of the frame determined in step S200.
[0061]
Subsequently, it is determined whether or not the AF evaluation value calculated in step S302 has changed by a certain value or more with respect to the AF evaluation value used for the current focus lens position control (step S304). If the newly calculated AF evaluation value has not changed by a certain value or more, there is no change in the shooting scene and there is no need to redo AF control.
[0062]
On the other hand, when the newly calculated AF evaluation value has changed by a certain value or more, it is necessary to perform AF control again, so the focus lens is moved one step in a certain direction (for example, the closest side) (step S306). The AF evaluation value is calculated again at the moving position (step S308).
[0063]
Next, it is determined whether or not the AF evaluation value calculated in step S308 is larger than the AF evaluation value calculated in step S302 (step S310). When the AF evaluation value becomes large, it is determined that the maximum of the AF evaluation value exists on the near side from the current lens position, and the focus lens is continuously moved one step to the close side (step S312), and the movement position is determined. Then, the AF evaluation value is calculated again (step S314).
[0064]
Subsequently, it is determined whether or not the AF evaluation value has become larger than the previously calculated AF evaluation value (step S316). If the AF evaluation value has increased, the process returns to step S312, and steps S312, S314, If it is determined that the AF evaluation value has decreased, the focus lens is returned by one step to the infinity side opposite to the closest side (step S318). This is because the focus lens has been moved beyond the lens position where the AF evaluation value is maximized.
[0065]
The focus lens is moved to the lens position where the AF evaluation value is maximized as described above, and the current AF evaluation value subjected to the AF control is calculated (step S320).
[0066]
On the other hand, when it is determined in step S310 that the AF evaluation value calculated in step S308 is smaller than the AF evaluation value calculated in step S302, the AF evaluation value has a maximum on the infinity side of the current lens position. Then, the focus lens is moved to the infinity side (step S322), and the AF evaluation value is calculated again at the moving position (step S324).
[0067]
Subsequently, it is determined whether or not the AF evaluation value is larger than the previously calculated AF evaluation value (step S326). When the AF evaluation value becomes large, the process returns to step S322, and steps S322, S324, If it is determined that the AF evaluation value has decreased, the focus lens is returned to the closest side in the direction opposite to the infinity side by one step (step S328).
[0068]
The focus lens is moved to the lens position where the AF evaluation value is maximized as described above, and the current AF evaluation value subjected to the AF control is calculated (step S320).
[0069]
In this way, the lens position of the focus lens is controlled so that the AF evaluation value always maintains the maximum during moving image shooting.
[0070]
FIG. 8 is a conceptual diagram of main / sub-pixel frames used for AF control. As shown in the figure, basically, AF control is performed based on the image data of the main pixel frame (the upper frame in FIG. 8). AF control is performed based on image data of a pixel frame (lower frame in FIG. 8). Further, FIG. 8 shows a case where the exposure time is controlled using the image data of the sub-pixel frame.
[0071]
【The invention's effect】
As described above, according to the present invention, when the main pixel frame of the main / sub-pixel frames having different sensitivities captured from the imaging unit is saturated, the main pixel frame is based on the non-saturated sub-pixel frame. Since an evaluation value indicating the sharpness of the image is calculated and AF control is performed based on the evaluation value, proper AF control can always be performed even when the brightness of the subject changes drastically during moving image shooting. . If the main pixel frame is not saturated, the evaluation value is calculated based on the main pixel frame having a better S / N than the sub-pixel frame.
[Brief description of the drawings]
FIG. 1 is a schematic plan view showing an example of a CCD used to implement the present invention.
FIG. 2 is a graph showing photoelectric conversion characteristics of main pixels and sub-pixels.
FIG. 3 is a block diagram of an electronic camera including an automatic focusing device according to the present invention.
FIG. 4 is a graph showing a relationship between a lens position and an AF evaluation value used for explaining AF control based on an AF evaluation value;
FIG. 5 is an overall flowchart of AF / exposure control.
FIG. 6 is a flowchart showing a method for determining main / sub-pixel frames used during AF control of moving image shooting;
FIG. 7 is a flowchart illustrating an example of AF control during moving image shooting.
FIG. 8 is a conceptual diagram of main / sub-pixel frames used for AF control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... CCD, 20 ... Light receiving cell, 21 ... Main pixel, 22 ... Subpixel, 100 ... Electronic camera, 110 ... Imaging optical system, 120 ... Focus / aperture adjustment part, 130 ... Exposure time control part, 150 ... Signal processing part , 160: AF / exposure control unit, 161: main / sub-pixel luminance determination unit, 162: exposure control unit, 163 ... frame designation unit, 164 ... gate circuit, 165 ... high frequency component extraction unit, 166 ... AF evaluation value calculation unit 167: AF control unit

Claims (3)

An imaging means capable of taking out a signal photoelectrically converted by the main pixel and the sub-pixel, wherein a large number of high-sensitivity main pixels and sub-pixels having a lower sensitivity than the main pixel are arranged according to a predetermined arrangement form. In an automatic focus adjustment device for an electronic camera that moves an imaging lens to a focus position during moving image shooting based on an evaluation value indicating the sharpness of an image calculated using a signal captured from the imaging unit,
Discriminating means for discriminating whether or not a main pixel frame of the main / sub-pixel frames captured from the imaging means is saturated;
When it is determined by the determining means that the main pixel frame is not saturated, the main pixel frame is selected, and when it is determined that the main pixel frame is saturated, a main pixel frame is selected. / Subpixel frame selection means;
Evaluation value calculating means for calculating the evaluation value from the image signal of the main pixel frame or the sub pixel frame selected by the main / sub pixel frame selecting means;
Lens moving means for moving the photographing lens for focus adjustment;
Control means for controlling the lens moving means so that the evaluation value always maintains a maximum based on the evaluation value calculated by the evaluation value calculating means;
An automatic focusing apparatus for an electronic camera, comprising: 2. The automatic focus adjustment of an electronic camera according to claim 1, wherein the determination unit determines whether or not a predetermined number of pixels or more in a predetermined focus area in the entire screen of the main pixel frame is saturated. apparatus. The evaluation value calculating means extracts a high frequency component of a subject from an image signal in a predetermined focus area of the main pixel frame or the sub pixel frame selected by the main / sub pixel frame selecting means, and 3. The automatic focus adjustment apparatus for an electronic camera according to claim 1, wherein the evaluation value is calculated by integrating absolute values.

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