JP2005055746A - Imaging apparatus, focusing control method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which can appropriately focus to any object including a high luminous part. <P>SOLUTION: An evaluation region image to be used for AF control is extracted from a photographed image, and such a pixel having the pixel value of the G color component exceeding a prescribed threshold in the evaluation region image is defined as a high luminance G pixel. If the number of high luminance G pixels is equal to or more than a prescribed number, the object is detected as high luminance. When the object is detected as high luminance, a focus evaluation value is calculated by dividing the sum of the difference in the pixel value between the high luminance G pixels and proximity G pixels located in the proximity of the high luminance G pixel by the integration times of the difference and by the number of the high luminance G pixels to obtain focus evaluation value. Then the lens position giving the maximum focus evaluation value is determined as the focused position. For example, when the focus evaluation value reaches the maximum, the gradient of changes in the pixel value is steep as shown by the curve Cv1, which makes the edge of the high luminance part clear. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for determining the arrangement of an optical system of an imaging apparatus.

  2. Description of the Related Art Conventionally, in an imaging apparatus that acquires an image using an imaging element such as a CCD, such as a digital still camera (hereinafter simply referred to as “digital camera”) or a video camera, a technique called a hill-climbing method is an autofocus control. Has been applied. The hill-climbing method is a method in which an evaluation value (such as the amount of high-frequency components in an image) is acquired at each driving stage while driving the lens, and the lens is moved to a position having the highest evaluation value.

  By the way, when shooting a subject with the sun in the daytime or shooting a subject with a point light source at night, the amount of high-frequency components in the image is used as the evaluation value, and hill-climbing autofocus control is used. If this is done, the evaluation value may be higher at a lens position different from the target in-focus position. For this reason, when photographing a subject in which a point light source is present, there has been a problem that a phenomenon in which the subject cannot be properly focused (hereinafter referred to as “false focus”) occurs.

  For such a problem, a target area for calculating an evaluation value (hereinafter referred to as a “focus evaluation area”) is divided into a plurality of divided areas, and an evaluation value for each divided area is calculated. As the high frequency component increases for the divided area, the evaluation value for the in-focus evaluation area is obtained by adding the evaluation values for all the divided areas while reducing the weighting, thereby appropriately focusing on the subject. A technique capable of performing the above has been proposed (for example, Patent Document 1).

Prior art documents relating to such technology include the following.
JP-A-8-321985

  The technique proposed in the background art works effectively for achieving proper focusing when a high-luminance light source exists locally, such as when the subject includes the sun. However, when a high-intensity light source is present everywhere, such as when the night view is a subject, the high-intensity light source is included in most of the divided areas, and weighting is applied to most of the focus evaluation area. Therefore, it becomes impossible to perform proper focusing.

  Therefore, for example, it is conceivable to focus properly by dividing the focus evaluation area finely and suppressing the number of divided areas including a high-intensity light source as much as possible. When driving, the area of the high-intensity light source that occupies the image changes greatly according to the change in the defocus amount, so that the image related to the high-intensity light source enters and exits between the divided areas. There arises a problem that scorching occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an imaging apparatus that can appropriately focus on any subject including a high-luminance portion.

  In order to solve the above-described problems, the invention of claim 1 is directed to an imaging unit that inputs an image composed of a plurality of pixels while driving a photographing lens in the optical axis direction, and a calculation calculated based on the image. An image pickup apparatus having a drive unit that drives a photographing lens to a focus position based on a focus evaluation value, the extraction unit extracting an evaluation region image related to a predetermined evaluation region from the image, and the evaluation region image The position of the photographic lens that maximizes the contrast between a high-luminance pixel having a pixel value equal to or greater than the first threshold and a neighboring pixel located in the vicinity of the high-luminance pixel is determined as the in-focus position. 1 determination means.

  The invention according to claim 2 is the imaging apparatus according to claim 1, wherein the evaluation area image is focused based on an average value of contrast between the high luminance pixel and the neighboring pixel. Evaluation value calculation means for calculating an evaluation value is provided.

  The invention according to claim 3 is the imaging apparatus according to claim 2, wherein, for the evaluation area image, a difference sum that is a sum of differences in pixel values between the high-intensity pixels and the neighboring pixels. A difference sum value calculating means for calculating a value, a number calculating means for calculating an integration number value that is the number of integrations of the difference by the difference sum value calculating means, and a value obtained by dividing the difference sum value by the integration number value. Average value calculating means for calculating the average value.

  According to a fourth aspect of the invention, there is provided the imaging apparatus according to the second or third aspect, wherein the occupancy value calculating means calculates a high luminance occupancy value indicating an occupancy state of the high luminance pixels in the evaluation area image. The evaluation value calculation means calculates the focus evaluation value based on a value obtained by dividing the average value by the high-luminance occupation value.

  The invention according to claim 5 is the imaging apparatus according to any one of claims 1 to 4, wherein the in-focus position is determined based on a contrast between each pixel included in the evaluation region image. And determining the in-focus position by the first determination unit when the number of pixels having a pixel value equal to or greater than the second threshold is less than a predetermined amount in the evaluation area image. And a control means for controlling the focus position to be determined by the second determination means.

  The invention according to claim 6 is a program for causing the imaging apparatus to function as the imaging apparatus according to any one of claims 1 to 5 when executed by a computer included in the imaging apparatus.

  According to a seventh aspect of the present invention, there is provided imaging means for inputting an image composed of a plurality of pixels while driving the imaging lens in the optical axis direction, and imaging based on a focus evaluation value calculated based on the image. A focus control method in an imaging apparatus including a driving unit that drives a lens to a focus position, wherein an evaluation area image related to a predetermined evaluation area is extracted from the image, Determining a position of the photographing lens that maximizes a contrast between a high-luminance pixel having a pixel value equal to or greater than a threshold value and a neighboring pixel located in the vicinity of the high-luminance pixel as the in-focus position. It is characterized by that.

  According to the first to fifth aspects of the present invention, the position of the photographic lens that maximizes the contrast between the high-luminance pixel and its neighboring pixels is focused to achieve a focused state with respect to the subject. Since the position is determined, it is possible to appropriately focus on any subject including the high luminance part.

  According to the second aspect of the present invention, the focus evaluation value is calculated based on the average value of the contrast between the high-luminance pixel and its neighboring pixels. On the other hand, it is possible to focus more appropriately.

  According to the third aspect of the present invention, the focus evaluation is performed based on a value obtained by dividing the sum of the pixel value differences between the high-luminance pixel and its neighboring pixels by the number of times of difference accumulation. Since the value is calculated, it is possible to appropriately and accurately focus on any subject including the high luminance part.

  According to the fourth aspect of the present invention, based on the value calculated by dividing the average value of the contrast between the high-luminance pixel and its neighboring pixels by the value indicating the occupation state of the high-luminance pixel. Thus, since the focus evaluation value is calculated, it is possible to focus on any subject including the high luminance portion more appropriately and with high accuracy.

  According to the fifth aspect of the present invention, when the number of high-luminance pixels is less than a predetermined amount, the focusing of the photographing lens is simply based on the contrast between the pixels included in the image corresponding to the evaluation area. Since the position is determined, it is possible to properly focus even on a subject that does not include a high brightness portion.

  Further, according to the invention described in claim 6, it is possible to achieve the same effects as the invention described in claims 1-6.

  Further, according to the invention described in claim 7, the same effect as that of the invention described in claim 1 can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Principal configuration of imaging device>
1, 2, and 3 are diagrams showing a main configuration of an imaging apparatus (here, a digital camera) 1 according to an embodiment of the present invention. FIG. 1 is a cross-sectional view as viewed from above, FIG. Is a sectional view seen from the side, and FIG. 3 corresponds to a rear view. These figures do not necessarily conform to the triangulation method, and are mainly intended to conceptually illustrate the main configuration of the imaging apparatus 1.

  As shown in FIGS. 1 and 2, a zoom lens (also referred to as “photographing lens”) 301 is provided on the front surface of the imaging apparatus 1, and the zoom lens 301 realizes an autofocus (AF) control operation to be described later. Therefore, a focus lens that can change the lens position is provided.

  A CCD color area sensor (hereinafter abbreviated as “CCD”) 303 is provided behind the zoom lens 301. In addition, a grip portion GR for a user to hold the imaging device 1 is provided on the front surface of the imaging device 1.

  As shown in FIG. 1, the imaging apparatus 1 can wear a recording medium such as a memory card MC from the side, and record an image acquired by the imaging apparatus 1 on the memory card MC. Can do. Further, the power source battery E formed by connecting four AA batteries E1 to E4 in series can be stored as a drive source.

  As shown in FIG. 2, the imaging apparatus 1 includes a zoom motor M1 for changing the zoom ratio of the zoom lens 301 and driving the lens between the storage position and the shooting position, and autofocus. An AF motor M2 is provided for realizing in-focus driving of the zoom lens 301 by the (AF) operation.

  As shown in FIGS. 2 and 3, a pop-up built-in flash 5 and a shutter start button (hereinafter abbreviated as “shutter button”) 9 are provided on the upper surface of the imaging apparatus 1.

  Further, as shown in FIG. 3, an LCD display unit (hereinafter abbreviated as “LCD”) 10 for performing monitor display of images, reproduction display of recorded images, and the like is provided at the approximate center of the back surface of the imaging apparatus 1. An EVF 11 for framing is provided on the upper back of the imaging apparatus 1. In addition, a display selection switch 12 is provided at the lower right side of the back surface of the imaging apparatus 1, and it is switched between the LCD 10 and the EVF 20 that the live view display at the time of framing is performed depending on the selection state by the display selection switch 12. It is done.

  Further, on the left side of the rear surface of the image pickup apparatus 1, a power / mode switch 25 for switching between “shooting mode”, “power OFF”, and “playback mode” is provided. “Shooting mode” is a mode for shooting a subject, “Power OFF” is a state setting for turning off the power of the imaging apparatus 1, and “Playback mode” is a memory card. This is a mode for reproducing and displaying a captured image stored in the MC or the like on the LCD 10 or the like.

  A single-shot / continuous-shooting mode switch 13 for switching between a “single-shot mode” and a “continuous-shooting mode” is provided on the lower left side of the back side of the imaging apparatus 1. The “single shooting mode” is a mode for shooting a single frame image, and the “continuous shooting mode” is for shooting images of a plurality of frames continuously in time. Mode.

  Further, a quadruple switch 31 is provided on the right side of the back surface of the imaging apparatus 1. The quadruple switch 31 has up, down, left and right buttons U, D, L, and R, and when the left and right buttons L and R are pressed, the zoom motor M1 is driven to perform zooming.

<Functional configuration of imaging device>
FIG. 4 is a block diagram showing a functional configuration of the imaging apparatus 1 according to the embodiment of the present invention.

  The CCD 303 converts the optical image of the subject formed by the zoom lens 301 into R (red). Photoelectrically converted into an image signal of G (green) and B (blue) color components (a signal composed of a signal sequence of pixel signals received by each pixel) and output. That is, the CCD 303 functions as an imaging unit that inputs an image composed of a plurality of pixels.

  The timing generator (hereinafter abbreviated as “TG”) 314 generates various timing pulses for controlling the driving of the CCD 303, and drives the CCD 303 based on the reference clock transmitted from the timing control circuit 202. Generate a control signal. The TG 314 generates a clock signal such as a timing signal for integration start / end (exposure start / end) and a light reception signal read control signal (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.) of each pixel, and the CCD 303 Output to. Therefore, for example, the exposure amount of the CCD 303, that is, the charge accumulation time of the CCD 303 corresponding to the shutter speed can be adjusted.

  The exposure control in the digital camera 1 is performed by adjusting the charge accumulation time of the aperture stop 302 and the CCD 303 corresponding to the shutter speed. Here, when the subject brightness is low and an appropriate shutter speed cannot be set, improper exposure due to insufficient exposure can be corrected by adjusting the level of the image signal output from the CCD 303. That is, when the brightness is low, exposure control is performed by combining the shutter speed and gain adjustment. The level adjustment of the image signal is performed by adjusting the gain of the AGC circuit in the signal processing circuit 313.

  The signal processing circuit 313 performs predetermined analog signal processing on the image signal (analog signal) output from the CCD 303. The signal processing circuit 313 includes a CDS (correlated double sampling) circuit and an AGC (auto gain control) circuit. The CDS circuit reduces noise of the image signal and adjusts the gain of the AGC circuit to adjust the image. Adjust the signal level.

  The A / D converter 205 converts each pixel signal of the image signal output from the signal processing circuit 313 into, for example, a 12-bit digital signal. The A / D converter 205 converts each pixel signal (analog signal) into a 12-bit digital signal based on an A / D conversion clock input from the timing control circuit 202. The timing control circuit 202 that generates a clock for the TG 314 and the A / D converter 205 is controlled by a reference clock in the overall control unit 211.

  The black level correction circuit 206 corrects the black level of the pixel signal A / D converted by the A / D converter 205 to a reference black level, and outputs the corrected signal to the white balance (WB) circuit 207.

  The WB circuit 207 performs level conversion of pixel data of R, G, and B color components. The WB circuit 207 converts the pixel data levels of the R, G, and B color components based on the level conversion table set by the overall control unit 211, and outputs the converted data to the γ correction circuit 208. Note that the conversion coefficient (characteristic gradient) of each color component in the level conversion table is set for each image by the overall control unit 211.

  The γ correction circuit 208 corrects the γ characteristic of the pixel data and outputs the corrected data to the image memory 209.

  The image memory 209 is a memory that stores pixel data input from the γ correction circuit 208. The image memory 209 has a storage capacity necessary for various image processing. In the image memory 209, an area for storing image data for AF control (image area for AF), an area for storing image data for automatic exposure (AE) control (image area for AE), a live view on the LCD 10, etc. And an area for storing image data for displaying a reproduced image (display image area), an area for storing RAW data related to a captured image (main image) at the time of actual shooting (RAW image area), and a memory card MC An area (main image area) for storing a captured image (main image) for recording is set as needed according to the operating state of the camera.

  For example, the LV / AF / AE image generation unit of the overall control unit 211 may arbitrarily select an in-focus evaluation area AFe (640 × 240 pixel image G corresponding to all pixels of the CCD 303 as shown in FIG. Image data (evaluation area image) related to (an area of 80 × 24 pixels that can be set as a position) is extracted and generated. That is, the LV / AF / AE image generation unit functions as a means for extracting an evaluation area image related to a predetermined focus evaluation area AFe from an image input by the CCD 303. The AF image area has a capacity capable of storing the extracted image data.

  The AE image area is an AE control image generated by adding pixel values of 16 pixels for each of R, G, and B in the LV / AF / AE image generation unit of the overall control unit 211 ( 40 × 240 pixels). The image data can be stored. Further, the display image area is an image for live view display whose size is compressed so as to match the number of pixels such as the LCD 10 in the LV / AF / AE image generation unit of the overall control unit 211 (for example, 320 And a capacity capable of storing image data corresponding to (× 120 pixels).

  In the shooting mode, each pixel data of an image captured by the CCD 303 every 1/30 (seconds) is subjected to predetermined signal processing from the A / D converter 205 by the γ correction circuit 208 in the shooting standby state, The image is transferred to the LV / AF / AE image generation unit in the overall control unit 211. In the LV / AF / AE image generation unit, the images processed for AF and AE control are temporarily stored in the AF image area and AE image area in the image memory 209, respectively. In addition, an image for live view display (an image for LV display) is transferred to the display image area as needed and temporarily stored.

  The data stored in the display image area includes the LCD I / F block in the overall control unit 211 when display on the LCD 10 is selected, and the overall control unit when display on the EVF 11 is selected. The data is transferred to the EVFI / F block 211 and output to the LCD 10 or EVF 11 (live view display). Thereby, the user can visually recognize the subject image.

  In the playback mode, an image read from the memory card MC loaded in the memory card slot 17 is temporarily stored in the image memory 209 via the card I / F block in the overall control unit 211 and the playback image generation unit. Are stored in the display image area, transferred to the LCD I / F block or EVFI / F block in the overall control unit 211, and after necessary image processing is performed, a reproduced image is displayed on the LCD 10 or EVF 11. .

  The card I / F block in the overall control unit 211 is an interface block for writing image data to the memory card MC and reading image data from the memory card MC.

  The RTC 219 is a clock circuit for managing the shooting date and time, and is driven by another power source (not shown).

  The operation unit 250 is provided with the various switches and buttons described above.

  The shutter button 9 can detect a half-pressed state (hereinafter referred to as “state S1”) and a pressed-in state (hereinafter referred to as “state S2”) as used in a silver halide camera or the like. It is a switch.

  When the shutter button 9 is pressed halfway in the shooting standby state in the shooting mode to enter the state S1, an AF operation is performed under the control of the overall control unit 211. Specifically, when the shutter button 9 is in the state S1, the zoom lens 301 starts lens driving for AF by the AF motor M2, and the overall control unit 211 evaluates the contrast of the image in the image memory 209, The zoom lens 301 (specifically, the focus lens) is driven to a lens position (focus position) where the contrast is highest. That is, while driving the photographing lens in the optical axis direction, the CCD 303 inputs an image composed of a plurality of pixels, and the AF motor M2 calculates an evaluation value (focus evaluation value described later) calculated based on the image. ) Functions as means for driving the photographic lens to the in-focus position.

  Further, under the control of the overall control unit 211, in the state S1, the brightness level of the image data in the image memory 209 is determined, whereby the shutter speed and the aperture value are determined, and the WB correction value in the WB circuit 207 is determined. Also decide.

  Further, when the shutter button 9 is fully pressed and a shooting instruction is issued from the state S1 to the state S2, a main shooting for storing an image in the memory card MC is performed.

  The overall control unit 211 includes a microcomputer (CPU), a ROM, a RAM, and the like, and organically controls driving of each unit of the imaging device 1 to comprehensively control shooting operations and the like of the imaging device 1. . Various controls and functions in the overall control unit 211 are realized by reading a program stored in the ROM into the CPU.

  In addition, the overall control unit 211 sets a value (exposure control value) for controlling exposure such as a shutter speed and an aperture value (exposure control value) and a part for determining the luminance of the subject (brightness determination unit) and actual exposure control. A part for setting a value (exposure amount setting unit) is provided as its function. Each value (shutter speed, aperture, etc.) included in the exposure control value can be arbitrarily changed by operating the operation unit 250 or the like. At the time of flash photography, the exposure control value includes the light emission amount of the built-in flash 5.

  Furthermore, the overall control unit 211 includes a recorded image generation unit that generates thumbnail images and compressed images in order to perform processing (recording processing) for recording captured images on the memory card MC. In addition, a reproduction image generation unit that generates an image for reproducing and displaying an image recorded on the memory card MC on the LCD 10 or the EVF 11 is also provided as its function.

  The recorded image generation unit reads out image data from the image memory 209 and generates a thumbnail image and a compressed image to be recorded in the memory card MC. The recorded image generation unit performs predetermined compression processing by JPEG method such as two-dimensional DCT conversion and Huffman coding on the image data read from the image memory 209 to generate compressed image data, and the compressed image data is stored in the image memory 209. Temporarily stored in the main image area. The image data stored in the main image area in the image memory 209 is transferred to the card I / F of the overall control unit 211 and finally recorded on the memory card MC.

  When a shooting instruction based on the full depression of the shutter button 9 is given in the shooting mode, the overall control unit 211 follows the set compression rate with respect to the image data captured in the RAW image area of the image memory 209 after the shooting instruction. By performing JPEG compression processing, compressed image data is generated, thumbnail images are generated, and tag information (frame number, exposure value, shutter speed, compression rate, shooting date, on / off of flash at shooting) is generated. Both image data are recorded on the memory card MC together with data, scene information, image determination result and other information.

  When the reproduction mode is selected and set based on the switching operation of the power / mode changeover switch 25, the image data with the largest frame number in the memory card MC is read out and decompressed by the reproduction image generation unit. After being stored in the display image area in the image memory 209 and transferred to the LCD I / F block (or EVFI / F block) in the overall control unit 211, the image having the largest frame number is displayed on the LCD 10 or EVF 11. That is, the most recently captured image is displayed. When the upper button U of the quad switch 31 is pressed, only one image with a large frame number is displayed in sequence, and when the lower button D is pressed, only one image with a small frame number is displayed in sequence. The

  The light control circuit 304 controls the light emission amount of the built-in flash 5 in flash photography to a predetermined light emission amount under the control of the overall control unit 211. In flash photography, the reflected light of the flash light from the subject is received by the light control sensor 305 simultaneously with the start of exposure, and when the amount of received light reaches a predetermined light emission amount, a light emission stop signal is output from the light adjustment circuit 304, In response to the light emission stop signal, the flash control circuit 217 forcibly stops the light emission of the built-in flash 5 under the control of the overall control unit 211. By such an operation, the light emission amount of the built-in flash 5 is controlled to a predetermined light emission amount.

  The aperture motor driving circuit 216 controls the driving of the aperture motor M3 under the control of the overall control unit 211, thereby controlling the opening / closing drive of the aperture 302 and changing the aperture value. The AF motor driving circuit 214 controls the driving of the focus lens included in the zoom lens 301 by controlling the driving of the AF motor M2 under the control of the overall control unit 211. Further, the zoom motor drive circuit 215 controls the lens drive of the zoom lens 301 by controlling the drive of the zoom motor M1 under the control of the overall control unit 211.

<About AF control>
6 and 7 are flowcharts illustrating the operation flow of AF control, and FIG. 8 is a timing chart illustrating the operation of AF control.

  In FIG. 8, the exposure of the CCD 303 and the reading of the image data from the CCD 303 are sequentially performed from the top in correspondence with the numbers (exposure frame numbers) indicating the exposure timings for sequentially acquiring images after the start of the AF control operation. , High-luminance object detection and focus evaluation value calculation, information acquisition of the lens position of the zoom lens 301 (specifically, the focus lens), determination of the focus position of the focus lens, lens drive command for driving the zoom lens 301, The timing of driving the focus lens is also shown.

  The operation flow of the AF control shown in FIGS. 6 and 7 will be described below with reference to FIG.

  The operation flow shown in FIGS. 6 and 7 is controlled by the overall control unit 211. When the user enters the state S1 by pressing the shutter button 9, the operation flow is started, and the process proceeds to step S1.

  In step S1, it is determined whether or not it is the exposure timing of the first frame after the state S1 is reached (that is, the timing when the exposure frame number is 1). Here, if it is the exposure timing of the first frame, the process proceeds to step S11, and if it is not the exposure timing of the first frame, the process proceeds to step S2.

  In step S11, a command to drive the focus lens to the most extended side, so-called far end is generated, and the process returns to step S1.

  In step S2, it is determined whether it is the exposure timing of the second frame after the state S1 is reached. Here, if it is the exposure timing of the second frame, the process proceeds to step S21, and if it is not the exposure timing of the second frame, the process proceeds to step S3.

  In step S21, the image data of the previous frame (that is, the first frame) is read from the CCD 303 while driving the focus lens to the far end, and the process returns to step S1. That is, at the exposure timing of the second frame, the process of step S21 is repeated and the focus lens is driven to the far end. In other words, at the exposure timing of the second frame, the drive to the far end of the focus lens is awaited.

  In step S3, it is determined whether it is the exposure timing of the third frame after the state S1 is reached. Here, if it is the exposure timing of the third frame, the process proceeds to step S31, and if it is not the exposure timing of the third frame, the process proceeds to step S4.

  In step S31, image data of the previous frame (that is, the second frame) is read from the CCD 303, and the process proceeds to step S32.

  In step S32, high brightness subject detection is performed to detect whether or not the main subject (main subject) has high brightness, and the process proceeds to step S33. Here, the evaluation area image is extracted from the image data (image data of the first frame) exposed at the exposure timing of the first frame and read from the CCD 303 at the exposure timing of the second frame. For the G pixel in the evaluation area image, if the number of pixels having a pixel value equal to or greater than the threshold TH1 is equal to or greater than the threshold TH2, the main subject includes many high-luminance subjects. Detect that there is. Here, since gradation representation is performed with 12 bits, for example, threshold TH1 = 1023, threshold TH2 = 100, and the like are applied.

  That is, here, when the number of pixels having a pixel value equal to or greater than the predetermined threshold TH1 is equal to or greater than a predetermined amount in the evaluation area image under the control of the overall control unit 211, the main subject is of high brightness. Detect.

  In step S33, a command to drive the focus lens to the retracting side, so-called near end side, is generated, and the process proceeds to step S34.

  In step S34, information related to the lens position of the focus lens is acquired, and the process returns to step S1.

  That is, here, as shown in FIG. 8, at the exposure timing of the third frame (that is, the timing at which the exposure frame No. is 3), the CCD 303 performs the exposure of the third frame and the two frames from the CCD 303. Reading of eye image data, detection of high-intensity subject based on image data of the first frame, acquisition of position information of the focus lens at the exposure timing of the third frame, and generation of a drive command to the near end of the focus lens are performed in parallel Done.

  In step S4, it is determined whether or not it is the exposure timing of the fourth frame after the state S1 is reached. Here, if it is the exposure timing of the fourth frame, the process proceeds to step S41, and if it is not the exposure timing of the fourth frame, the process proceeds to step S5.

  In step S41, the image data of the previous frame (that is, the third frame) is read from the CCD 303, and the process proceeds to step S42.

  In step S42, information related to the lens position of the focus lens is acquired, and the process returns to step S1.

  That is, here, as shown in FIG. 8, at the exposure timing of the fourth frame (that is, the timing at which the exposure frame No. is 4), the CCD 303 performs the exposure of the fourth frame and the three frames from the CCD 303. Reading of eye image data, acquisition of position information of the focus lens at the exposure timing of the fourth frame, and lens driving from the far end to the near end of the focus lens are performed in parallel.

  In step S5, it is determined whether it is the exposure timing of the 5th to 20th frames after the state S1 is reached. Here, if it is the exposure timing of the 5th to 20th frames, the process proceeds to step S51, and if it is not the exposure timing of the 5th to 20th frames, the process proceeds to step S6.

  In step S51, the image data of the previous frame (that is, the 4th to 19th frames) is read from the CCD 303, and the process proceeds to step S52.

  In step S52, a focus evaluation value corresponding to the image of each frame is calculated based on the evaluation area image extracted from the image data of the 3rd to 18th frames read from the CCD 303, and the process proceeds to step S53.

  Here, the calculation method of the focus evaluation value is switched between the case where it is detected in step S32 that the main subject has high luminance and the case where it is not. Specifically, when the main subject is detected to have high brightness, a method for calculating a focus evaluation value for a high brightness subject (focus evaluation value calculation method for a high brightness subject) described later is executed. When the main subject is not detected to have high brightness, the evaluation area image corresponding to the focus evaluation area AFe set for the image (640 × 240 pixels) of each frame is determined between the pixels. The sum of absolute values of pixel value differences is calculated as a focus evaluation value (a general focus evaluation value calculation method).

  That is, the general control unit 211 functions as a means for determining a focus position using a focus evaluation value calculation method for a high-luminance subject (also referred to as “first determination means”) and general focus. It has a function as means for determining a focus position (also referred to as “second determination means”) based on the contrast between each pixel included in the evaluation area image using the evaluation value calculation method.

  If the overall control unit 211 does not detect that the main subject has high brightness, the overall determination unit 211 prohibits the determination of the in-focus position by the first determining unit, and the in-focus position by the second determining unit. It functions as a means for controlling to determine.

  In step S53, information related to the lens position of the focus lens is acquired, and the process returns to step S1.

  That is, here, as shown in FIG. 8, at the exposure timing of the 5th to 20th frames (that is, the timing when the exposure frame No. is 5 to 20), the exposure of the 5th to 20th frames is performed in the CCD 303, respectively. In addition, readout of the image data of the 4th to 19th frames from the CCD 303, calculation of the focus evaluation value based on the image data of the 3rd to 18th frames, and the position information of the focus lens at the exposure timing of the 5th to 20th frames. Acquisition and lens driving from the far end to the near end of the focus lens are performed in parallel.

  Here, the calculated focus evaluation value and the position information of the corresponding lens position are stored in the RAM in association with each other. Specifically, the focus evaluation value based on the image data of the 3rd to 18th frames and the lens position information at the exposure timing of the 3rd to 18th frames are stored in association with each other.

  In step S6, it is determined whether or not it is the exposure timing of the 21st frame after the state S1 is reached. Here, if it is the exposure timing of the 21st frame, the process proceeds to step S61, and if it is not the exposure timing of the 21st frame, the process proceeds to step S7 in FIG.

  In step S61, image data of the previous frame (that is, the 20th frame) is read from the CCD 303, and the process proceeds to step S62.

  In step S62, a focus evaluation value corresponding to the image of each frame is calculated based on the evaluation area image extracted from the image data of the 19th frame read from the CCD 303, and the process returns to step S1. Here, the calculated 19th frame focus evaluation value and the corresponding lens position information at the exposure timing of the 19th frame are stored in the RAM in association with each other.

  That is, here, as shown in FIG. 8, at the exposure timing of the 21st frame (that is, the timing at which the exposure frame No. is 21), the exposure of the 21st frame is performed in the CCD 303 and the 20th frame from the CCD 303 is obtained. Reading of the eye image data and calculation of the focus evaluation value based on the image data of the 19th frame are performed in parallel.

  In step S7, it is determined whether or not it is the 22nd frame exposure timing after the state S1 is reached. Here, if it is the exposure timing of the 22nd frame, the process proceeds to step S71, and if it is not the exposure timing of the 22nd frame, the process proceeds to step S8.

  In step S71, a focus evaluation value corresponding to the 20th frame image is calculated based on the evaluation area image extracted from the 20th frame image data read from the CCD 303, and the process proceeds to step S72. Here, the calculated focus evaluation value of the 20th frame and the lens position information at the exposure timing of the corresponding 20th frame are stored in the RAM in association with each other.

  In step S72, the focus position of the zoom lens 301 is determined based on the focus evaluation values calculated in steps S52, S62, and S71, and the process proceeds to step S73.

  Here, out of the focus evaluation values calculated in steps S52, S62, and S71, the lens position x2 corresponding to the maximum focus evaluation value y2 is detected, and the total including the lens positions x1 and x3 before and after that is detected. The focus position is determined based on the three focus evaluation values y1, y2, y3 and the lens positions x1, x2, x3. FIG. 9 is a diagram schematically illustrating the relationship between the lens positions x1, x2, and x3 and the corresponding focus evaluation values y1, y2, and y3. Specifically, the focus position can be calculated and determined by substituting the focus evaluation values y1, y2, y3 and the lens positions x1, x2, x3 into the following expression (1).

[Focus position] = {y1 × (x3 ² −x2 ² ) + y2 × (x1 ² −x3 ² ) + y3 × (x2 ² −x1 ² )} / 2 {y1 × (x3−x2) + y2 × (x1− x3) + y3 * (x2-x1)} (1).

  In step S73, a command for driving the zoom lens 301 (specifically, the focus lens) to the in-focus position determined in step S72 is generated, and the process returns to step S1.

  That is, as shown in FIG. 8, at the exposure timing of the 22nd frame (that is, the timing when the exposure frame No. is 22), the calculation of the focus evaluation value based on the image data of the 20th frame, and the 3-20th frame Determination of the in-focus position based on the in-focus evaluation value calculated for the eye image data and generation of a drive command to the in-focus position of the focus lens are sequentially performed.

  In step S8, it is determined whether it is the exposure timing of the 23rd frame after the state S1 is reached. Here, if it is the exposure timing of the 23rd frame, the process proceeds to step S81, and if it is not the exposure timing of the 23rd frame, the operation flow of the AF control is ended.

  In step S81, the focus lens is driven to the in-focus position in response to the drive command in step S73, and the process returns to step S1. That is, as shown in FIG. 8, at the exposure timing of the 23rd frame (that is, the timing when the exposure frame No. is 23), the focus lens is driven to the in-focus position, and during that time, the drive of the focus lens is completed. It will be in a state to wait.

  The AF control operation for realizing the in-focus state with respect to the subject is executed by the operation flow including steps S1 to S81.

<Focus evaluation value calculation method for high brightness subject>
As described above, when the main subject is detected to have high brightness, the overall control unit 211 calculates each focus evaluation value by the focus evaluation value calculation method for the high brightness subject.

  Hereinafter, a focus evaluation value calculation method for high-luminance subjects (calculation method indicated by STEP 1 to STEP 5 below) will be described.

<< STEP1 >>
First, for the evaluation area image corresponding to the focus evaluation area AFe, the pixel of the G color component (G pixel) whose pixel value is the threshold value TH3 = 1023 (here, TH1 = TH3), that is, the pixel value is saturated. The G pixel (hereinafter referred to as “high luminance G pixel”) and the G pixel arranged closest to the high luminance G pixel in the horizontal and vertical directions, that is, in the vicinity of the high luminance G pixel The absolute value (hereinafter referred to as “contrast value”) D1 of the difference in pixel value between the G pixel (hereinafter referred to as “neighboring G pixel”) to be calculated is calculated. Note that when focusing only on the G pixel, it can be said that the high-luminance G pixel and the neighboring G pixel are adjacent to each other. Therefore, the neighboring G pixel is also referred to as a G pixel adjacent to the high-luminance G pixel (adjacent G pixel). it can.

FIG. 10 is a diagram schematically illustrating a part of the evaluation area image. As shown in FIG. 10, the evaluation area image is an image in which pixels of RGB color components are regularly arranged corresponding to a so-called Bayer arrangement in the light receiving unit of the CCD 303. The pixels corresponding to the RGB color components are also referred to as R pixels, G pixels, and B pixels, respectively. For the G pixel, a sign (number) represented by including i and j (i and j are arbitrary natural numbers) is attached to the lower right of the sign of G representing the position of the G pixel. This indicates the position in the horizontal and vertical directions of each G pixel in the evaluation area image. Here, the sign such as G _{i, j} indicates the pixel value of each G pixel.

Here, the contrast value D1 for one G pixel having the pixel value G _{i, j} is calculated as follows, for example.

<< STEP 1-1 >>
When G _{i, j} > TH3, the absolute value of the pixel value difference between the pixels indicated by the pixel G _{i, j} and the pixel G _{i−1, j} (between the high-luminance G pixel and the neighboring G pixel) DH (= | G _{i , j} −G _{i−1, j} |) is calculated (hereinafter also referred to as “pixel difference value”). At this time, if DH> 0, the count number of the non-zero pixel difference value N1 is incremented by one. That is, N1 is incremented by 1 so that N1 = N1 + 1.

<< STEP 1-2 >>
When G _{i, j} > TH3, the absolute value (pixel difference value) DV ₁ (= | G _{i, j} −G) of the pixel value difference between the pixels indicated by G _{i, j} and G _{i, j−1. i, j-1} │) is calculated. At this time, if DV ₁ > 0, the count number of the number N1 of non-zero pixel difference values is incremented by one. That is, N1 is incremented by 1 so that N1 = N1 + 1.

<< STEP 1-3 >>
When G _{i, j} > TH3, the absolute value (pixel difference value) DV ₂ (= | G _{i, j} −G) of the pixel value difference between the pixels indicated by G _{i, j} and G _{i, j + 1. i, j + 1} |) is calculated. At this time, if DV ₂ > 0, the count number of the non-zero pixel difference value N1 is incremented by one. That is, N1 is incremented by 1 so that N1 = N1 + 1.

<< STEP 1-4 >>
The contrast value D1 is calculated according to the following formula (2).

D1 = DH + DV ₁ + DV ₂ (2).

<< STEP2 >>
In the evaluation area image, the contrast value D1 calculated for the G pixel in which the pixel value is saturated is integrated to calculate the sum of the pixel value differences (difference sum value) S1.

  At this time, the number N1 of non-zero pixel difference values is also calculated for all the pixels in the evaluation area image. In other words, in the evaluation area image, the number N1 of pixel difference values other than 0, that is, the number N1 of pixel difference values other than 0 (hereinafter referred to as “effective integration number”) N1 is calculated.

<< STEP3 >>
In the evaluation area image, the number of G pixels with saturated pixel values (hereinafter referred to as “saturated G pixel number”) F1 is calculated.

<< STEP4 >>
By dividing the difference sum value S1 by the effective integration number N1 and normalizing, the evaluation value VAL1 shown in the following equation (3) is calculated.

  Evaluation value VAL1 = S1 / N1 (3).

<< STEP5 >>
By dividing the evaluation value VAL1 by the saturation G pixel number F1 and normalizing, the evaluation value VAL2 shown in the following equation (4) is calculated, and the evaluation value VAL2 is set as the focus evaluation value.

  Evaluation value VAL2 = VAL1 / F1 (4).

  That is, here, the overall control unit 211 sets the average value of contrast between the high luminance G pixel and the neighboring G pixel in the vicinity of the high luminance G pixel (in this case, the evaluation value VAL1) for the evaluation region image. Based on this, it functions as a means for calculating a focus evaluation value. Specifically, the overall control unit 211 sets a difference sum value S1 that is a sum of pixel value differences between a high luminance G pixel and a neighboring G pixel in the vicinity of the high luminance G pixel for the evaluation region image. It functions as a means for calculating, functions as a means for calculating the effective integration number N1 of the difference, and further functions as a means for calculating a value obtained by dividing the difference sum value S1 by the effective integration number N1 as the evaluation value VAL1.

  Further, the overall control unit 211 determines the number of pixels (saturated G pixels) F1 of G pixels (high luminance G pixels) whose pixel values are saturated, that is, high luminance pixels (here, high luminance G pixels) in the evaluation region image. ) Between the high luminance G pixel and a neighboring G pixel in the vicinity of the high luminance G pixel. Functions as a means for calculating a focus evaluation value VAL2 based on a value obtained by dividing the average value of the contrast (here, the evaluation value VAL1) by the high luminance occupation value (here, the number of saturated G pixels F1).

<Effect of the focus evaluation value calculation method for high-luminance subjects>
When the high-brightness subject is the main subject, as in a general focus evaluation value calculation method, the pixels between the pixels included in the evaluation region image extracted from the image of each frame (640 × 240 pixels) are simply used. When the sum of the absolute values of the pixel value differences is calculated as the focus evaluation value, the high-luminance portion is blurred and greatly expanded or contracted during the driving of the zoom lens 301 (specifically, the focus lens). Since the boundary between the high-intensity part and the other part enters and exits from the evaluation area image, the curve indicating the relationship between the focus evaluation value and the lens position is disturbed, or the lens position that is not actually in focus The focus evaluation value may be the maximum value.

  Also, due to other factors such as camera shake and subject blurring, the boundary between the high brightness part and the other part enters and exits from the evaluation area image, so the curve indicating the relationship between the focus evaluation value and the lens position is disturbed, The focus evaluation value for the lens position that is not actually in focus may be the maximum value. As a result, the subject including the high luminance part cannot be focused properly.

  Therefore, in this embodiment, proper focusing is realized by using a focus evaluation value calculation method for a high-luminance subject. Hereinafter, the reason for using the focus evaluation value calculation method for a high-luminance subject and its advantages and effects will be described.

  The evaluation value VAL1 obtained by dividing the difference sum value S1 by the effective integration number N1 is an average value of pixel values between the high luminance G pixel and the neighboring G pixel in the vicinity thereof, that is, the high luminance G pixel and its The average value of the gradient of the change in the pixel value between the neighboring G pixels in the vicinity (actually, the average value of the absolute value of the gradient of the change in the pixel value) is shown.

  In general, for an image acquired by the CCD 303, the boundary edge between the high-luminance portion and the low-luminance portion becomes clearer as the lens position is closer to the in-focus position, and the slope of the change in the pixel value becomes steeper. .

  FIG. 11 is a schematic diagram illustrating a luminance difference between a high luminance portion (high luminance G pixel) and a low luminance portion (neighboring G pixel). In FIG. 11, the change in the pixel value relating to the G pixel on one horizontal line in the evaluation area image is shown, and the horizontal axis shows the position of the pixel on the horizontal line (horizontal pixel position) in the image data. The vertical axis represents the pixel value. The relationship between the pixel value and the horizontal pixel position when the lens position of the focus lens is at the in-focus position is indicated by a curve Cv1, and the relationship between the pixel value and the horizontal pixel position when the lens position is not in the in-focus position is shown. This is illustrated by the curve Cv2.

  As shown in FIG. 11, the closer the lens position is to the in-focus position, the greater the slope of the change in pixel value between the high luminance G pixel and the neighboring G pixel located in the vicinity thereof. Therefore, the larger the evaluation value VAL1 indicating the average value of the change in the pixel value between the high-luminance G pixel and the neighboring G pixel, the closer the lens position is to the in-focus position. Based on the determination of the focus position, it is possible to appropriately focus on the subject including the high luminance portion.

  In other words, here, the overall control unit 211 has a zoom that maximizes the contrast between a high luminance G pixel having a pixel value equal to or greater than the predetermined threshold TH3 and a neighboring G pixel located in the vicinity of the high luminance G pixel. It functions as means for determining the position of the lens 301 (specifically, the focus lens) as the in-focus position.

  In general, the smaller the high-luminance portion in the evaluation area image, the closer the lens position is to the in-focus position. Therefore, in the present embodiment, the evaluation value VAL1 is further divided by the saturated G pixel number F1 to calculate the focus evaluation value VAL2. Therefore, the focus evaluation value VAL2 increases as the high luminance portion decreases, that is, as the saturation G pixel number F1 decreases, and thus the peak of the focus evaluation value VAL2 becomes clearer. As a result, it is possible to focus more appropriately and with high accuracy.

  FIG. 12 is a diagram showing the relationship between the lens position of the focus lens and the focus evaluation value when a main subject is a high brightness subject whose focus position is near the near end. In FIG. 12, for comparison, a curve Cv3 indicating the relationship between the lens position and the focus evaluation value in the case of using the focus evaluation value calculation method for a high-luminance subject according to the embodiment of the present invention. The curve Cv4 which shows the relationship between the lens position at the time of using the conventional general focus evaluation value calculation method and a focus evaluation value is shown. A curve Cv4 shows a state in which false focusing occurs.

  As shown in FIG. 12, the curve Cv3 has the lens position of the focus lens where the focus evaluation value is maximized similarly to the curve Cv4, and detects the lens position corresponding to the maximum value of the focus evaluation value. As described above, the in-focus position can be determined based on the total three focus evaluation values including the lens positions before and after the lens position and the corresponding lens positions, as described above. Therefore, it is possible to appropriately focus on the high-luminance portion that is the main subject.

  As described above, in the imaging apparatus 1 according to the embodiment of the present invention, when the main subject has high luminance, the contrast between the high luminance G pixel and the neighboring G pixel located in the vicinity thereof is maximum. The position of the zoom lens 301 (specifically, the focus lens) is determined as the focus position. As a result, it is possible to appropriately focus on any subject including the high luminance part.

  Also, a value obtained by dividing the total sum of the pixel values between the high-luminance G pixel and the neighboring G pixel located in the vicinity thereof by the number of times of difference accumulation (here, the evaluation value VAL1), that is, the high-luminance G pixel. And the average value of the contrast between the neighboring G pixels located in the vicinity thereof and the focus evaluation value are calculated. As a result, it is possible to focus on any subject including the high brightness portion with high accuracy and more appropriately.

  Further, an average value of contrast between the high luminance G pixel and a neighboring G pixel located in the vicinity thereof (here, the evaluation value VAL1) is a value indicating the occupation state of the high luminance G pixel in the evaluation region image (here. Then, a value (here, evaluation value VAL2) calculated by dividing by the high luminance G pixel number F1) is calculated as the focus evaluation value. As a result, it is possible to focus on any subject including the high luminance portion more appropriately and with high accuracy.

  Further, when the main subject is not detected to have high luminance (when the high luminance pixel is less than a predetermined amount in the evaluation region image), each pixel included in the evaluation region image extracted from the image of each frame The sum of the absolute values of the pixel value differences between them is calculated as the focus evaluation value. As a result, it is possible to appropriately focus even on a subject that includes no or only a high luminance part.

<Others>
As mentioned above, although embodiment of this invention was described, this invention is not limited to the thing of the content demonstrated above.

  For example, in the above-described embodiment, the application target of the present invention is the imaging device, but this imaging device includes all devices having an imaging function such as a mobile phone with a camera.

  In the above-described embodiment, the focus position is determined using the evaluation value VAL2 as the focus evaluation value. However, the present invention is not limited to this, and the focus position is determined using the evaluation value VAL1 as the focus evaluation value. You may do it.

  Even in such a configuration, as described above, as the evaluation value VAL1 indicating the average value of the gradient of the change in the pixel value between the high luminance G pixel and the neighboring G pixel located in the vicinity thereof increases, Since the lens position is close to the in-focus position, the subject including the high-intensity portion can be appropriately focused by determining the in-focus position using the evaluation value VAL1 as the in-focus evaluation value.

  In the embodiment described above, the threshold value TH3 (also referred to as “first threshold value”) and the threshold value TH1 (also referred to as “second threshold value”) are both equal to 1023. However, the present invention is not limited to this. For example, the threshold value TH1 may be smaller than the threshold value TH3, and conversely, the threshold value TH3 may be smaller than the threshold value TH1.

  In the above-described embodiment, the high-luminance occupation value is the saturated G pixel number F1, but is not limited thereto. For example, the high-luminance G pixel number is the same for all the pixels in the evaluation region image. It may be the area ratio occupied by the high-luminance G pixel obtained by dividing.

  In the above-described embodiment, the contrast includes both a difference and a ratio of values representing brightness, such as a difference in pixel values and a ratio of pixel values.

It is an upper section showing the important section composition of the imaging device concerning the embodiment of the present invention. It is a side sectional view showing the important section composition of the imaging device concerning the embodiment of the present invention. It is a rear view which shows the principal part structure of the imaging device which concerns on embodiment of this invention. It is a block diagram which shows the function structure of the imaging device which concerns on embodiment of this invention. It is a figure for demonstrating the focus evaluation area | region set with respect to an image. It is a flowchart which shows the operation | movement flow of AF control. It is a flowchart which shows the operation | movement flow of AF control. It is a timing chart for demonstrating AF control operation | movement. It is a figure for demonstrating the calculation method of a focus position. It is a figure which illustrates typically a part of evaluation field picture. It is a schematic diagram which shows the luminance difference of a high-intensity pixel and a neighboring pixel. It is a figure which shows the relationship between a lens position and a focus evaluation value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 209 Image memory 211 Overall control part 214 AF motor drive circuit 301 Zoom lens 303 CCD
M2 AF motor

Claims (7)

Imaging means for inputting an image composed of a plurality of pixels while driving the photographic lens in the optical axis direction, and driving for driving the photographic lens to a focus position based on a focus evaluation value calculated based on the image An imaging device having means,
Extracting means for extracting an evaluation area image related to a predetermined evaluation area from the image;
For the evaluation area image, the in-focus position of the photographing lens that maximizes the contrast between a high-luminance pixel having a pixel value equal to or greater than a first threshold and a neighboring pixel located in the vicinity of the high-luminance pixel First determining means for determining the position;
An imaging apparatus comprising: The imaging apparatus according to claim 1,
Evaluation value calculation means for calculating a focus evaluation value based on an average value of contrast between the high-luminance pixel and the neighboring pixel for the evaluation region image,
An imaging apparatus comprising: The imaging apparatus according to claim 2,
For the evaluation area image, a difference sum value calculation means for calculating a difference sum value that is a sum of differences of pixel values between the high-intensity pixels and the neighboring pixels;
Number of times calculation means for calculating the number of times of accumulation that is the number of times of accumulation of the difference by the difference total value calculation means;
An average value calculating means for calculating a value obtained by dividing the difference sum value by the cumulative number value as the average value;
An imaging apparatus comprising: The imaging apparatus according to claim 2 or 3, wherein
Occupancy value calculating means for calculating a high luminance occupation value indicating an occupation state of the high luminance pixels in the evaluation area image;
Further comprising
The evaluation value calculating means is
The imaging apparatus, wherein the focus evaluation value is calculated based on a value obtained by dividing the average value by the high luminance occupation value. The imaging apparatus according to any one of claims 1 to 4,
Second determining means for determining the in-focus position based on the contrast between the pixels included in the evaluation area image;
In the evaluation area image, when the number of pixels having a pixel value equal to or greater than a second threshold is less than a predetermined amount, the determination of the in-focus position by the first determination unit is prohibited, and the second determination unit Control means for controlling to determine the in-focus position;
An image pickup apparatus further comprising:   A program for causing the imaging device to function as the imaging device according to any one of claims 1 to 5 when executed by a computer included in the imaging device. Imaging means for inputting an image composed of a plurality of pixels while driving the photographic lens in the optical axis direction, and driving for driving the photographic lens to a focus position based on a focus evaluation value calculated based on the image A focusing control method in an imaging apparatus having means,
Extracting an evaluation area image related to a predetermined evaluation area from the image;
For the evaluation area image, the focus of the position of the photographic lens where the contrast between a high-luminance pixel having a pixel value equal to or greater than a first threshold and a neighboring pixel located in the vicinity of the high-luminance pixel is maximized. Determining as a position;
A focusing control method comprising:

Images