JP2006267261A - Automatic focusing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing device which carries out the automatic focusing processing of a target object in a photographed picture. <P>SOLUTION: The automatic focusing device is equipped with: a first band pass filter 60 which extracts the first automatic focusing data being the components of a high frequency band from the luminance signal of pixels in a range where the level of a color difference signal specifies the object, out of the pixels for displaying one frame; a second band pass filter 61 which extracts the second automatic focusing data being the components of the high frequency band from the luminance signal of the pixels for displaying one frame; an automatic focusing data choosing part 62 which chooses the first or second automatic focusing data by comparing the first automatic focusing data with a threshold for establishing that the object is a preset object; and a focus evaluation value generating part 63 which generates a focus evaluation value used for controlling a lens position from the chosen first or second automatic focusing data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an autofocus device applied to an electronic imaging device such as a video camera.

  2. Description of the Related Art In recent years, an electronic imaging device such as a video camera that has been widely used is provided with an autofocus control function that automatically focuses when a lens is directed toward a subject.

  One method for performing autofocus control is hill climbing control. The hill-climbing control is the extraction of the high-frequency component whose luminance value changes drastically between adjacent frames from the luminance signal obtained by the image sensor, and the position of the focus lens so that the focus evaluation value obtained from that component is maximized. Means to adjust. The focus evaluation value is a value obtained by detecting the amplitude of the high-frequency component of the extracted luminance value and converting it to a digital signal, and integrating it over a certain period, such as one field or one frame. It is. The focus evaluation value obtained in this way is considered to represent the focused state of the subject. This is because the high-frequency component of the luminance value reflects a place where the image changes drastically, and it is considered that the edge which is the contour portion of the subject is naturally included. When the focus evaluation value obtained from this high-frequency component is the highest, the lens is correctly focused and the edge that is the contour portion of the subject is clearly formed. On the other hand, as the focus shift increases, the focus evaluation value decreases, and the edge of the image lacks sharpness and the outline becomes blurred. Therefore, by examining the change in the focus evaluation value of the high-frequency component contained in the video luminance signal, it is possible to know whether the focus state is approaching or is moving away from the focus state.

  A conventional imaging device with an autofocus function is shown in FIG. In the conventional imaging apparatus 100 with an autofocus function, first, a subject is photographed so that subject light is incident from the lens 200 and converted into an electrical signal by the CCD 300. Among the converted electrical signals, the luminance signal (Y) is extracted by the signal processing unit 400 and transmitted to the autofocus area extraction unit 501 of the autofocus device 500, and the imaging screen set in advance by the autofocus area setting unit 502 Only the luminance signal (Y) corresponding to the inner autofocus area is transmitted to the band pass filter 503. In the band pass filter 503, only high frequency components equal to or higher than a preset value are extracted from the received luminance signal (Y), and a focus evaluation value generation unit 504 generates a focus evaluation value. The maximum value of the generated focus evaluation value for each frame is determined by the focus evaluation value maximum value determination unit 505 and transmitted to the lens drive control unit 600. The lens drive control unit 600 performs drive control of the lens position so that the received focus evaluation value is maximized. Through the above processing, an in-focus image can be obtained.

An autofocus device using this conventional device is described in Patent Document 1.
Japanese Patent No. 2668160

  However, in this imaging apparatus 100 with an autofocus function, when a high-frequency component other than the subject is present in the autofocus area, the high-frequency band portion is focused and an image focused on the desired subject can be obtained. There was a problem that I could not.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an autofocus device in which an autofocus process is performed on a target subject in a captured image.

  In order to achieve the above object, an autofocus device of the present invention forms an image of subject light by a lens system and outputs a predetermined signal out of luminance signals of an image signal obtained by photoelectrically converting the imaged subject light by an image sensor. The high-frequency component of the luminance signal in the focus area is extracted, and the position of the lens system is moved and adjusted to the focus position so that the focus evaluation value is maximized according to this high-frequency component. A detection unit that detects pixels within a preset color range from the pixels of the image signal, a first extraction unit that extracts luminance signals of all pixels in the focus area, and the focus area. And a second extraction unit that extracts only the luminance signal of the pixel detected by the detection unit, and a high-frequency component of the luminance signal extracted by the first extraction unit is extracted as the first focus data. A filter, a second filter for extracting a high frequency component of the luminance signal extracted by the second extraction unit as second focus data, and first and second focus data are supplied, and the second focus data is preset. A position of a lens system, comprising: a selection unit that selects second focus data only when higher than a threshold; and a focus evaluation value generation unit that generates a focus evaluation value from the selected first focus data or second focus data. It is characterized in that the movement is adjusted.

  The level range of the color difference signal specified for creating the first autofocus data is for specifying the subject. For example, in the case of a person, the range of the skin color level is set.

  According to the autofocus device of the present invention, since the subject to be extracted is extracted from the photographed image using the color difference signal level and the autofocus process is performed, an image focused on the desired subject is obtained. be able to.

  An embodiment in which the autofocus device of the present invention is applied to an imaging device 1 with an autofocus function will be described with reference to FIG.

  The imaging device 1 with an autofocus function of the present embodiment includes a lens 2, a CCD 3 (Charge-Coupled Devices), a signal processing unit 4, an autofocus device 5, and a lens drive control unit 6.

  The lens 2 enters imaging light. The CCD 3 converts the imaging light incident from the lens 2 into an electrical signal. The signal processing unit 4 separates the electric signal converted by the CCD 3 into a luminance signal (Y) and a color difference signal (RY, BY), and transmits them to the autofocus device 5 respectively.

  The autofocus device 5 includes a subject detection range setting unit 51, a color difference signal comparison unit 52, a switch 53, a DC signal generation unit 55, an autofocus area setting unit 57, a first autofocus area extraction unit 58, Second autofocus area extraction unit 59, first bandpass filter 60, second bandpass filter 61, autofocus data selection unit 62, focus evaluation value generation unit 63, and focus evaluation value maximum value determination unit 64 And have.

  The subject detection range setting unit 51 holds a subject detection range, which is a color difference signal area for detecting a subject input in advance by a user. For example, if the subject detection range is focused on a person's face, the subject detection range is set to a skin color.

  The color difference signal comparison unit 52 compares the color difference signals (R−Y, B−Y) received from the signal processing unit 4 with the skin color detection level of the subject detection range received from the subject detection range setting unit 51, and the color difference signal It is determined whether (R−Y, BY) is within the subject detection range. After the determination, the color difference signal comparison unit 52 transmits the determination result to the switch 53.

  The switch 53 switches to the luminance signal (Y) side transmitted from the signal processing unit 4 if the color difference signal is within the subject detection range as a result of the comparison in the color difference signal comparison unit 52, and the first autofocus area extraction unit 58. Transmits a luminance signal (Y). Also, if the color difference signal is outside the subject detection range, switching to the DC signal generation unit 55 side, and causing the first autofocus area extraction unit 58 to transmit the fixed signal generated by the DC signal generation unit 55, thereby out of the subject detection range. The luminance signal (Y) is cut off.

  The autofocus area setting unit 57 holds data indicating an autofocus area that is a range within a shooting screen that is input in advance by the user and performs autofocus processing, and this data is stored in the first autofocus area extraction unit 58 as necessary. And transmitted to the second autofocus area extraction unit 61.

  The first autofocus area extraction unit 58 receives the luminance signal (Y) within the subject detection range or the fixed signal from the direct current signal generation unit 55, and the subject corresponding to the autofocus area received from the autofocus area setting unit 57. A luminance signal (Y) within the detection range is extracted.

  The second autofocus area extraction unit 59 receives all the luminance signals (Y) transmitted from the signal processing unit 4, and receives the luminance signal (Y) corresponding to the autofocus area received from the autofocus area setting unit 57. Extract.

  The first band pass filter 60 further extracts only a high frequency component from the received luminance signal (Y) within the subject detection range, creates the extracted signal as first autofocus data, and transmits it to the autofocus data selection unit 62. .

  The second band pass filter 61 extracts only a high frequency component from the received luminance signal (Y), creates the extracted signal as second autofocus data, and transmits it to the autofocus data selection unit 62.

  The autofocus data selection unit 62 holds a threshold value input in advance by the user, and selects one of the first autofocus data and the second autofocus data based on this threshold value.

  The focus evaluation value creation unit 63 creates a focus evaluation value from the autofocus data selected by the autofocus data selection unit 62.

  The focus evaluation value maximum value determination unit 64 determines the maximum value for each frame from the focus evaluation value created by the focus evaluation value creation unit 63.

  The lens drive control unit 6 drives and controls the position of the lens 2 so that the focus evaluation value determined by the focus evaluation value maximum value determination unit 64 is maximized.

  Next, the operation of this embodiment will be described with reference to the flowchart of FIG.

  First, imaging is performed by the user, and imaging light is incident from the lens 2 (S1). The incident imaging light is converted into an electric signal by the CCD 3 for each pixel constituting one frame, and the converted electric signal is converted into a luminance signal (Y) and a color difference signal (RY, BY) by the signal processing unit 4. (S2). The color difference signals (R−Y, B−Y) of the separated electrical signals are transmitted to the color difference signal comparison unit 52 of the autofocus device 5 and the skin color detection in the subject detection range transmitted from the subject detection range setting unit 51. Compared with level. By comparing, it is determined whether or not the color difference signal is within the subject detection range (S3).

  The result of the determination is transmitted to the switch 53, and the switch 53 is a terminal on the luminance signal (Y) side transmitted from the signal processing unit 4 if the received color difference signals (RY, BY) are within the subject detection range. 54, the luminance signal (Y) within the subject detection range is transmitted to the first autofocus area extracting unit 58 (S4). If the color difference signals (R−Y, B−Y) are out of the subject detection range, they are switched to and connected to the terminal 56 on the DC signal generation unit 55 side, and the fixed signal from the DC signal generation unit 55 is the first auto. The luminance signal (Y) outside the subject detection range is blocked by being transmitted to the focus area extraction unit 58 (S5).

  When the luminance signal (Y) within the subject detection range is received by the first autofocus area extraction unit 58, the luminance signal (Y corresponding to the autofocus area in the imaging screen set by the autofocus area setting unit 57) ) Is transmitted to the first band pass filter 60 (S6). In the first band pass filter 60, only a high frequency component equal to or higher than a preset value is extracted from the received luminance signal (Y), and the extracted signal is transmitted to the auto focus data selection unit 62 as first auto focus data. (S7).

  On the other hand, the second autofocus area extraction unit 59 receives all the luminance signals (Y) transmitted from the signal processing unit 4 (S8), and the autofocus area in the imaging screen set by the autofocus area setting unit 57. Only the luminance signal (Y) corresponding to is transmitted to the second bandpass filter 61 (S9). In the second band pass filter 61, only a high frequency component equal to or higher than a preset value is extracted from the received luminance signal (Y), and the extracted signal is transmitted to the auto focus data selection unit 62 as second auto focus data. (S10).

  The autofocus data selection unit 62 determines whether or not first autofocus data has been created based on whether or not the color difference signals (RY, BY) are within the subject detection range (S11). When the color difference signals (RY, BY) are within the subject detection range and the first autofocus data is created, the stored threshold value is compared with the luminance level of the first autofocus data. Thus, one is selected from the first autofocus data and the second autofocus data (S12). At this time, the second autofocus data is selected when the first autofocus data is lower than the threshold value determined as the subject, such as at the start of shooting, and the first autofocus data is selected when the target value is higher than the threshold value and determined as the subject. Is done. The selected autofocus data is transmitted to the focus evaluation value creation unit. On the other hand, when it is determined that the color difference signals (RY, BY) are outside the subject detection range and the first autofocus data has not been created, the second autofocus data is transmitted to the focus evaluation value creation unit. (S13).

  A focus evaluation value creating unit 63 creates a focus evaluation value from the selected first autofocus data or second autofocus data (S14). The maximum value of the generated focus evaluation value for each frame is determined by the focus evaluation value maximum value determination unit 64 (S15) and transmitted to the lens drive control unit 6. In the lens drive control unit 6, the position of the lens 2 is drive-controlled so that the received focus evaluation value is maximized (S16), and the in-focus state is obtained.

  With the above processing, in the hill-climbing autofocus device, when the skin color of the skin color detection area is lower than the threshold value, the auto focus process is performed with the evaluation value obtained from the luminance signal of the entire focus area, and the skin color of the skin color detection area is set to the threshold value. When it is higher, autofocus processing is performed with the evaluation value obtained from the luminance signal in the focus area and higher than the threshold (only the flesh color part), so an image focused on the desired subject can be obtained with high accuracy Can do.

1 is a block diagram showing an embodiment in which an autofocus device of the present invention is applied to an imaging device with an autofocus function. It is a flowchart which shows operation | movement of one Embodiment which applied the autofocus apparatus of this invention to the imaging device with an autofocus function. It is a block diagram which shows the conventional imaging device with an autofocus function.

Explanation of symbols

1 Imaging device with autofocus function 2 Lens 3 CCD
DESCRIPTION OF SYMBOLS 4 Signal processing part 5 Autofocus apparatus 6 Lens drive control part 51 Subject detection range setting part 52 Color difference signal comparison part 53 Switch 54 Terminal on the luminance signal side transmitted from CCD 55 DC signal generation part 56 Terminal on the DC signal generation part side 57 auto focus area setting unit 58 first auto focus area extracting unit 59 second auto focus area extracting unit 60 first band pass filter 61 second band pass filter 62 auto focus data selecting unit 63 focus evaluation value creating unit 64 focus evaluation value Maximum value judgment part

Claims (1)

The subject light is imaged by the lens system, and the high-frequency component of the luminance signal in a predetermined focus area is extracted from the luminance signal of the image signal obtained by photoelectrically converting the imaged subject light by the image sensor. In the autofocus device that adjusts the position of the lens system to the in-focus position so that the focus evaluation value is maximized according to the component,
A detection unit for detecting a pixel within a preset color range from pixels of the photoelectrically converted image signal;
A first extraction unit for extracting luminance signals of all pixels in the focus area;
A second extraction unit that extracts only a luminance signal of a pixel within the focus area and detected by the detection unit;
A first filter that extracts, as first focus data, a high frequency component of the luminance signal extracted by the first extraction unit;
A second filter for extracting a high frequency component of the luminance signal extracted by the second extraction unit as second focus data;
A selection unit that selects the second focus data only when the first and second focus data are supplied and the second focus data is higher than a preset threshold;
A focus evaluation value creating unit that creates the focus evaluation value from the selected first focus data or the second focus data;
An autofocus device characterized in that the position of the lens system is moved and adjusted.

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