JP2006023339A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of more accurately determining whether it is a night scene. <P>SOLUTION: A digital camera 1A is equipped with a determining means for judging based on image data whether or not a photographic scene is a night-time scene. The determination means determines that the photographic scene is the night-time scene, when a high luminance part exists in a 1st part (AF area AR or the like) being the center part of a framing area FR and a low luminance part exists in a 2nd part (hatched part MR or the like) in the framing area. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for discriminating a scene of a captured image in an imaging apparatus, and more particularly to a technique for discriminating whether or not it is a night scene.

  In an imaging apparatus such as a digital camera, a scene of a captured image may be determined and appropriate shooting conditions may be determined according to the scene.

  For example, in Patent Document 1, when the average brightness of the object scene is small and the ratio of the high brightness area in the object scene is large, the shooting scene is determined as a night scene, and the camera shooting mode is set to the night scene mode. The technology to set is described.

JP 2003-315866 A

  However, in the above technique, when there are a large number of point light sources, the average luminance of the measurement target region may increase, and as a result, the night scene is not a night scene. May be erroneously determined.

  Accordingly, an object of the present invention is to provide an imaging apparatus capable of determining whether or not a night scene is more accurately.

  In order to solve the above-mentioned problems, the invention of claim 1 is an imaging apparatus, wherein an imaging means for converting a light image obtained by the imaging optical system into image data, and a shooting scene based on the image data is a night scene. Determination means for determining whether or not the high-luminance portion is present in the first portion that is the central portion of the framing region and the second portion other than the first portion of the framing region. When a low-luminance part exists in this part, it is determined that the shooting scene is a night scene.

  According to a second aspect of the present invention, in the imaging apparatus according to the first aspect of the invention, the second portion is a peripheral portion of the framing region.

  According to a third aspect of the present invention, in the imaging apparatus according to the first aspect of the present invention, the second portion is an upper edge side peripheral portion of the framing region.

  According to a fourth aspect of the present invention, in the imaging apparatus according to the first aspect of the invention, the second portion includes a left end side peripheral portion, a right end side peripheral portion, and an upper end side peripheral portion of the framing region. It is characterized by that.

  According to a fifth aspect of the present invention, in the imaging device according to any one of the first to fourth aspects, the determination unit is configured to detect when a predetermined number or more of high-luminance pixels are present in the first portion or a high-luminance pixel. , It is determined that a high-luminance portion is present in the first portion when a predetermined ratio or more is present in the first portion.

  According to a sixth aspect of the present invention, in the imaging device according to the fifth aspect of the invention, the determination means determines whether or not a predetermined number or more of high-luminance pixels are present in the first portion, or whether the high-luminance pixels are the first Whether or not there is a predetermined ratio or more in the portion is determined using AF image data that is not thinned image data, and whether or not the low luminance portion exists in the second portion is thinned image data. The determination is made using AE image data.

  According to a seventh aspect of the present invention, in the imaging apparatus according to any one of the first to sixth aspects, the determination means has a predetermined average luminance among a plurality of segmented regions located in the second portion. It is characterized in that it is determined that a low-luminance portion exists in the second portion when there are a predetermined percentage or more of low-luminance segment areas that are less than or equal to a value or when there are a predetermined number or more of the low-luminance segment areas.

  According to an eighth aspect of the present invention, in the imaging apparatus according to any one of the first to seventh aspects, when it is determined that the shooting scene is not a night scene, the AF operation is performed by the first method, and the shooting scene is a night scene. An AF control means for performing an AF operation using a second method different from the first method when it is determined that the scene is a scene is further provided.

  According to a ninth aspect of the present invention, in the imaging apparatus according to the eighth aspect of the invention, the second method is to move the focus lens toward the near side after moving the focus lens to the infinity end. The method is characterized in that an AF evaluation value at each lens position is acquired, and a lens position at which the AF evaluation value is optimized is detected as an in-focus position.

  According to a tenth aspect of the present invention, in the imaging apparatus according to the eighth or ninth aspect, the AF evaluation value in the AF operation by the second method is the high luminance pixel and the high luminance in the first portion. To the normalized value by dividing the integrated value of the pixel value difference with the non-high luminance pixel adjacent to the pixel by the number of non-high luminance pixels adjacent to the high luminance pixel in the first portion It is calculated based on.

  According to an eleventh aspect of the present invention, in the imaging apparatus according to the tenth aspect, the AF evaluation value is based on a value obtained by further dividing the normalized value by the number of high-luminance pixels in the first portion. It is characterized by being calculated.

  According to a twelfth aspect of the present invention, in the image pickup apparatus according to any one of the first to eleventh aspects of the invention, when it is determined that the shooting scene is a night scene, the shooting conditions of the image pickup apparatus are the conditions for the night scene. Further, it is characterized by further comprising an imaging condition setting means for setting to.

  According to the invention described in claims 1 to 12, the high-luminance portion exists in the first portion that is the central portion of the framing region, and the second portion other than the first portion in the framing region. When the low luminance portion exists, it is determined that the shooting scene is a night scene, so that a more accurate night scene determination is possible.

  In particular, according to the third aspect of the invention, since the presence / absence of the low-luminance portion is determined in the peripheral portion on the upper end side corresponding to the night sky portion, night scene determination can be performed more accurately.

  According to the invention described in claim 5, since the presence / absence of the high luminance part is determined based on the number or existence ratio of the high luminance pixels in the first part, the average of the first part is determined. Compared with the case where the presence / absence of a high-luminance portion is determined using luminance, more accurate night scene determination is possible.

  Furthermore, according to the invention described in claim 6, since the number of high-luminance pixels is determined based on AF image data that is not a thinned image, the number of high-luminance pixels is more accurately recognized. be able to. Further, since it is determined whether or not the block is a low-intensity block based on the AE image data that is a thinned image, the night scene determination is efficiently performed by reducing the number of pixels to be calculated in calculating the average luminance. It can be carried out.

  According to the eighth aspect of the invention, it is possible to optimize the AF operation during night scene photography.

  Furthermore, according to the invention described in claim 10, it is possible to improve the accuracy of the AF operation.

  In addition, according to the twelfth aspect of the present invention, it is possible to optimize shooting conditions during night scene shooting.

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

<Hardware configuration>
The hardware configuration of the digital camera 1A will be described with reference to FIGS. FIG. 1 is a front view of the digital camera 1A as viewed from the front. 2 is a cross-sectional view of the digital camera 1A at the position DD in FIG. FIG. 3 is a rear view of the digital camera 1A as viewed from the back.

  A photographing lens 110 is provided in front of the digital camera 1A. The photographing lens 110 acquires a light image for photographing (light image of a subject) and forms an image on a light receiving surface of a CCD 120 (Charge Coupled Device) that is an image sensor.

  Also, inside the lens barrel 111 of the photographing lens 110, the zoom lens 112 for changing the focal angle and changing the angle of view of the light image for photographing, and the focus state of the light image for photographing are changed. A focus lens 113 is provided. Each of the zoom lens 112 and the focus lens 113 is actually composed of one or a plurality of lens elements or the like, but is schematically shown here.

  The zoom lens 112 and the focus lens 113 are connected to an encoder (not shown). As a result, the digital camera 1A can detect the positions (representative positions) of the zoom lens 112 and the focus lens 113 in the optical axis OA direction. The zoom lens 112 and the focus lens 113 are connected to a zoom motor M1 (FIG. 4) and a focus motor M3 (FIG. 4), respectively. As a result, the digital camera 1A can drive the zoom lens 112 and the focus lens 113 in the direction of the optical axis OA. That is, the digital camera 1A is configured to be capable of optical zoom and focus control by driving an optical system. The taking lens 110 also includes a stop 114 for changing the amount of light incident on the CCD 120. The diaphragm 114 is provided between the zoom lens 112 and the focus lens 113. The diaphragm 114 is connected to the diaphragm motor M2 (FIG. 4). Thus, the digital camera 1A can change the aperture diameter for exposure control.

  On the top surface of the digital camera 1A, a shutter start button 150 (hereinafter referred to as a shutter button) for giving a shooting start instruction to the digital camera 1A, a mode setting dial 160 for setting an operation mode of the digital camera 1A, A pop-up flash 170 that emits light during flash photography is provided.

  The shutter button 150 is a push button switch that can distinguish between a half-pressed state S1 and a fully-pressed state S2. When the digital camera 1A detects that the shutter button 150 is half-pressed S1, the digital camera 1A starts a shooting preparation operation such as AF (autofocus) control. Further, when the digital camera 1A detects that the shutter button 150 has been fully pressed S2, the digital camera 1A starts the main photographing operation.

  The mode setting dial 160 includes a “still image shooting mode” for shooting a still image of a subject, a “movie shooting mode” for shooting a movie of a subject, and a “playback mode” of playing back and displaying a stored image. This is a rotary switch for switching the operation mode of the digital camera 1A.

  On the back surface of the digital camera 1A, a liquid crystal display (LCD) 180 that performs live view display of captured images and playback display of recorded images is provided. Further, an electronic view finder (EVF) 190 for displaying a live view of the photographed image is provided above the back surface of the LCD 180. Also, on the back side, a cross switch 205 is provided for performing zooming at the time of shooting and frame advancement at the time of image reproduction. This cross switch 205 is provided with four push buttons UP, DN, LF, and RT on the top, bottom, left, and right. Zooming to the telephoto side is achieved by pressing the upper button UP, and zooming to the wide angle side is performed by pressing the lower button DN. (Hereinafter, telephoto is described as tele, and wide angle as wide). Further, an enter button 200 is provided on the back of the digital camera 1A and in the center of the cross switch 205.

<Functional configuration>
Next, the functional configuration of the digital camera 1A will be described with reference to the block diagram of FIG.

  A photographing optical image acquired by the photographing lens 110 including the zoom lens 112, the focus lens 113, and the diaphragm 114 is formed on the light receiving surface of the CCD 120.

  The CCD 120 photoelectrically converts a light image for photographing into an image signal having R (red), G (green), and B (blue) color components, and outputs the image signal to the signal processing unit 210. The image signal is a signal sequence of pixel signals corresponding to the amount of light received by the light receiving elements (pixels) constituting the CCD 120.

  The signal processing unit 210 performs predetermined analog signal processing on the image signal input from the CCD 120. The signal processing unit 210 includes a correlated double sampling (CDS) circuit and an automatic gain control (AGC) circuit. The CDS circuit reduces sampling noise of the image signal. The AGC circuit adjusts the signal level of the image signal. The gain control in the AGC circuit is also used to increase the level of the image signal when proper exposure cannot be obtained by adjusting the aperture diameter of the aperture 114 and the exposure time of the CCD 120.

  The A / D conversion unit 220 converts the digital image signal having the analog image signal input from the signal processing unit 210 and outputs the digital image signal to the image processing unit 230 as image data. As a result, digital color image data having a predetermined number of gradations (here, 256 levels) is generated for each of the R, G, and B components.

  The operations of the CCD 120, the signal processing unit 210, and the A / D conversion unit 220 are performed in synchronization with a reference clock input from the timing control circuit 240. The timing control circuit 240 generates a reference clock based on a control signal input from the overall control unit 250.

  The image processing unit 230 includes a black level correction circuit 231, a white balance (WB) circuit 232, a γ correction circuit 233, and an image memory 234.

  The black level correction circuit 231 corrects the black level of the image data input from the A / D conversion unit 220 to a predetermined black level.

  The WB circuit 232 performs level conversion of R, G, and B color components of the image data. The level conversion is performed using a level conversion table input from the overall control unit 250. This level conversion table is set for each captured image by the overall control unit 250.

  The γ correction circuit 233 performs gradation conversion of the image data input from the WB circuit 232. The gradation conversion is performed based on a predetermined level conversion table.

  The image memory 234 temporarily stores the image data input from the γ correction circuit 233. The image memory 234 has a storage capacity capable of storing image data for the total number of pixels.

  The digital camera 1A includes a zoom motor control unit 260, an aperture motor control unit 270, and a focus motor control unit 280. The zoom motor control unit 260, the aperture motor control unit 270, and the focus motor control unit 280 are based on the zoom control signal, the aperture control signal, and the focus control signal input from the overall control unit 250, respectively. Drive power is supplied to M2 and focus motor M3. As a result, the overall control unit 250 can change the zoom magnification, the aperture diameter, and the focus state of the photographing lens 110.

  The digital camera 1A also includes a lens position detection unit 290 including an encoder for detecting the positions of the zoom lens 112 and the focus lens 113. The lens position detection unit 290 outputs the detected positions of the zoom lens 112 and the focus lens 113 to the overall control unit 250.

  Further, the digital camera 1A includes a flash circuit 310 and a pop-up flash 170. The flash circuit 310 supplies power for flash emission to the pop-up flash 170 in response to a flash control signal input from the overall control unit 250.

  The digital camera 1 </ b> A includes an operation unit 320. The operation unit 320 includes the shutter button 150, the mode setting dial 160, and the determination button 200 described above. The overall control unit 250 detects the states of these operation members and reflects them in the operation of the digital camera 1A.

  The digital camera 1 </ b> A includes an EVFVRAM 330 and an LCDVRAM 340 that serve as buffer memories for images displayed on the EVF 190 and the LCD 180. The EVFVRAM 330 and the LCDVRAM 340 have storage capacities capable of storing image data having the same number of pixels as the EVF 190 and the LCD 180, respectively.

  The digital camera 1A also includes a card interface 350, a memory card 360, and a communication I / F 370. The memory card 360 is a non-volatile memory that stores captured image data. The card interface 350 is an interface for writing image data to the memory card 360 and reading image data from the memory card 360. The communication I / F 370 is an interface for performing communication with an external device connected to the digital camera 1A.

  In the shooting standby state in the shooting mode, the image signals generated at predetermined time intervals in the CCD 120 are processed by the processing circuits 231 to 234 of the signal processing unit 210, the A / D conversion unit 220, and the image processing unit 230. Later, it is temporarily stored in the image memory 234 as image data. The image data is read by the overall control unit 250 and converted into image data having the same number of pixels as the EVF 190 and the LCD 180. Further, the converted image data is transferred to the EVFVRAM 330 and the LCDVRAM 340 and displayed on the EVF 190 and the LCD 180 as a live view. Thereby, the photographer can visually recognize the subject image. In the playback mode, the image data stored in the memory card 360 is read by the overall control unit 250 via the card interface 350 and subjected to predetermined image processing. The image data subjected to the image processing is converted into image data having the same number of pixels as the EVF 190 and the LCD 180 and transferred to the EVFVRAM 330 and the LCDVRAM 340. This image data is reproduced and displayed on the EVF 190 and the LCD 180.

  The overall control unit 250 is a microcomputer including at least a CPU 251, a RAM 252, and a ROM 253, and comprehensively controls the operation of each component of the digital camera 1 </ b> A according to a program PG stored in the ROM 253. 4, functions realized by the CPU 251, the RAM 252, and the ROM 253 are schematically expressed as a night scene determination unit 254, an AF control unit 255, an AE control unit 256, and a shooting condition setting unit 257. ing.

  The night view determination unit 254 determines whether the shooting scene is a night view scene based on the image data. The AF control unit 255 performs autofocus control (automatic focus control) based on the AF evaluation value (focus evaluation value), and the AE control unit 256 performs automatic exposure control based on the AE evaluation value. The shooting condition setting unit 257 sets shooting conditions (aperture value, shutter speed, image processing content, etc.) according to the shooting scene.

  The digital camera 1 </ b> A further includes an AF evaluation value calculation unit 236, a high luminance pixel detection unit 237, and a block luminance calculation unit 238. The processing by these units will be described below.

<AF>
Next, the AF process will be described.

  FIG. 5 is a diagram showing an image MG1 for automatic focusing control (AF control). This image MG1 is an image composed of a part of all the pixels of the CCD 120. For example, when the CCD 120 has a total number of pixels of 2560 × 1920, the image MG1 is a central strip region CR (2560 × 240 pixels) that is a strip region located at the center in the vertical direction read from the CCD 120. The pixel is composed of 320 × 240 pixels located at the center in the horizontal direction.

  The AF evaluation value calculation unit 236 (FIG. 4) focuses on a region corresponding to the image MG1 in the framing region (that is, the entire captured image) FR (in other words, a region corresponding to the central portion in the framing region FR). An AF evaluation value is calculated based on the pixel value of each pixel in the AF area AR, which is used as an area (hereinafter also referred to as “AF area”) AR. Here, the contrast value C is used as the AF evaluation value. Specifically, the AF evaluation value calculation unit 236 calculates the absolute difference between the target pixel and a pixel (for example, a pixel adjacent in the horizontal direction) located in the vicinity of the target pixel and having a certain positional relationship with the target pixel. The difference calculation results are cumulatively added. This cumulative addition is repeated until all the pixels included in the AF area AR are selected as the target pixel. Thus, the contrast value C for the AF area AR is obtained, and the obtained contrast value C is output to the overall control unit 250.

  The AF (autofocus) control unit 255 of the overall control unit 250 determines the degree of focus based on the contrast value C of the AF area AR, and moves the focus lens to the focus position.

<AE>
Further, the AE process will be described.

  FIG. 6 is a diagram showing an image MG2 for automatic exposure control (AE control). This image MG2 is a thinned image configured by thinning out a part of all the pixels of the CCD 120. For example, the image MG2 is generated as image data having 320 × 240 pixels by being thinned by 1/8 in the horizontal direction and the vertical direction in the CCD 120 having the total number of pixels of 2560 × 1920. This image MG2 is a rough image showing the entire subject to be photographed (in other words, the entire framing area).

  The block luminance calculation unit 238 calculates an AE evaluation value for automatic exposure control using the inside of the image MG2. The block luminance calculation unit 238 divides (divides) the image data (image MG2) output from the A / D conversion unit 220 into, for example, 300 blocks (= (20 × 15) blocks), and each block (divided area) Multi-segment photometry is performed to calculate photometric data for each time. For example, the block luminance calculation unit 238 calculates the average value of the pixel values of the G color component as the subject luminance and outputs it to the overall control unit 250. Alternatively, the Y component may be calculated as a composite value of all components of the R color component, the G color component, and the B color component, and the average value of the pixel values of the Y component may be calculated as the subject luminance.

  Further, the AE control unit 256 of the overall control unit 250 calculates an exposure control value (aperture value, shutter speed, gain) based on the input subject luminance value and controls each unit to realize AE. .

  The digital camera 1A can acquire the images MG1 and MG2 almost simultaneously. In order to show the positional relationship between the images MG1 and MG2 in the framing region FR, a region corresponding to the AF area AR (image MG1) in FIG. 5 in the image MG2 in FIG. 6 is indicated by a broken line.

<Night scene judgment>
Next, determination of whether or not the shooting scene in the digital camera 1A is a night scene (hereinafter also simply referred to as “night scene determination”) will be described. Here, a case where night scene determination is performed using the above-described two images MG1 and MG2 is illustrated. This night view determination is performed by the night view determination unit 254.

  In a night view scene, there is a general tendency that the point light source portion of the night view is distributed in the center of the screen and the end side of the screen is dark. The processing described below pays attention to such a property, and uses such a property to determine whether or not it is a night view more accurately.

  Specifically, the night view determination unit 254 (1) a condition CA that there are a predetermined number (N) or more of “high luminance pixels” in the image MG1 (that is, the AF area AR), and (2) a peripheral edge in the image MG2. When both conditions of the condition CB that a predetermined number (M) or more of “low-intensity blocks” are present among the peripheral blocks present in the partial MR are satisfied, it is determined to be a night scene. Below, each condition is demonstrated.

  First, the condition CA will be described. When a predetermined number (N) or more of high-luminance pixels are present in the image MG1 (that is, the AF area AR), it is determined that a high-luminance portion exists in the center portion of the screen. More specifically, the high luminance pixel detection unit 237 determines and detects a pixel having a pixel value (Y component, G component, or the like) equal to or higher than a threshold TH1 (for example, 250) as a “high luminance pixel”. The night view determination unit 254 determines that the condition CA is satisfied when N or more detected high-luminance pixels exist in the AF area AR. When the threshold value TH1 is set to the maximum value MAX (for example, 255), “high luminance pixel” is synonymous with “overflow pixel (described later)”.

  Next, the condition CB will be described. The night view determination unit 254 determines 92 blocks (hatched portions in FIG. 6) existing in the peripheral portion MR of the screen among 20 × 15 (total 300) blocks BL (i, j) in the image MG2. Select as target. More specifically, the night view determination unit 254 selects a peripheral portion MR composed of three block groups of an upper end side peripheral block group BG1, a left end side peripheral block group BG2, and a right end side peripheral block group BG3 as a determination target. To do. The upper end side peripheral block group BG1 exists in the upper end side peripheral portion, and the uppermost block BL (1, 1) to BL (20, 1) 20 blocks and the lower block BL (1, 2). ) To BL (20, 2), a total of 40 blocks including 20 blocks. Further, the left end side peripheral block group BG2 exists in the left end side peripheral portion, and 13 blocks BL (1, 3) to BL (1, 15) in the leftmost column and the right side block BL (2, 3). ) To BL (2,15), and a total of 26 blocks. Similarly, the right end side peripheral block group BG3 exists in the right end side peripheral edge portion, and the rightmost block BL (20, 3) to BL (20, 15) has 13 blocks and the left side block BL (19, 19). 3) is a block group composed of a total of 26 blocks including 13 blocks of BL (19, 15).

  The night scene determination unit 254 determines a block whose average luminance is equal to or less than a predetermined threshold value TH2 (for example, 20) from among the above 92 blocks to be determined as a “low luminance block (also referred to as a low luminance division region)”. Calculate the number of luminance blocks. If there are M or more low-luminance blocks, it is assumed that the low-luminance portion exists in the peripheral portion of the image. In addition, what is necessary is just to use the value calculated by the block brightness calculating part 238 for the average brightness | luminance of each block.

  The night scene determination unit 254 determines that the shooting scene is a night scene when both of the above conditions CA and CB are satisfied.

  When it is determined that the scene is a night scene, the AF method suitable for the night scene is adopted, and the shooting condition is set to a condition suitable for the night scene (condition for shooting the night scene). Such an operation will be described in detail later.

  According to the night view determination as described above, it is possible to determine whether or not the night view scene is more accurate.

  In particular, since it is determined whether or not there is a low-luminance portion in the peripheral portion of the framing region FR, more specifically, the 92 blocks, it is possible to improve night scene determination accuracy. In addition, the 92 blocks include a peripheral portion on the upper end side corresponding to the “night sky” portion at the time of night scene shooting. And since the presence or absence of a low-intensity part is determined in the peripheral part including such an upper end side peripheral part, night scene determination can be performed more accurately.

  Further, the number of high-luminance pixels is determined based on AF image data (in other words, AF image data that is not thinned-out image data) having the same number of pixels (resolution) as the actual captured image in the AF area AR. Therefore, the number of high-luminance pixels can be recognized more accurately.

  Furthermore, since it is determined whether or not the block is a low-intensity block based on the AE image data that is a thinned-out image of the actual captured image, the number of pixels to be calculated can be efficiently reduced in calculating the average luminance. It becomes possible to perform night view judgment.

<Operation>
The photographing operation of the digital camera 1A will be described with reference to the flowcharts of FIGS.

  First, in step SP10 (FIG. 7), it is determined whether or not the shutter button 150 is in the half-pressed state S1. If it is confirmed that it is in the half-pressed state S1, the process proceeds to step SP20 and subsequent steps in order to perform an AF operation or the like.

  In steps SP20 to SP50, it is determined whether or not the shooting scene is a night scene. If it is determined that the shooting scene is not a night scene, an AF operation is performed by the method MA (step SP60), and the shooting scene is a night scene. If it is determined that, AF operation is performed by another method MB (step SP70). The methods MA and MB are common in that both are AF (so-called hill-climbing method) using image data, but differ in the presence or absence of initial micro-driving, the lens position moving method, and the like.

  Thereafter, the AF operation is continued until the shutter button 150 is fully pressed S2, and when the shutter button 150 is fully pressed S2, shooting conditions for the main shooting are set (step SP90), and the main shooting is performed. An operation is performed (step SP100).

  Specifically, in step SP20, the night scene determination unit 254 acquires the number of “high luminance pixels” detected by the high luminance pixel detection unit 237, and displays the number of high luminance pixels in the center of the screen. It is determined whether or not a high luminance part exists. When there are N or more high-luminance pixels detected by the high-luminance pixel detection unit 237 in the AF area AR, the night scene determination unit 254 determines that the high-luminance part exists in the center of the screen, and the night scene It is determined that one of the conditions for determining that the scene is a scene (also referred to as “night scene determination condition”) is satisfied. In the branching process of step SP30, when it is determined that one requirement of the night view determination condition is satisfied, the process proceeds to step SP40, and when it is determined that the requirement is not satisfied, the process proceeds to step SP60.

  In step SP40, the night scene determination unit 254 has a low luminance at the screen periphery based on the number of low luminance blocks among the 92 blocks to be determined based on the block luminance calculated by the block luminance calculation unit 238. It is determined whether or not a part exists. Specifically, when the number of low-luminance blocks is M or more, it is determined that a low-luminance portion is present at the peripheral edge portion of the screen, and it is determined that another requirement for night scene determination conditions is also satisfied. In the branching process of step SP50, when it is determined that the second requirement regarding the night view determination condition is also satisfied, the process proceeds to step SP70, and when it is determined that the requirement is not satisfied, the process proceeds to step SP60. .

  Next, the AF operation (step SP60) by the technique MA will be described with reference to the flowchart of FIG.

  In step SP61, a minute lens driving routine is executed, and the lens driving direction of the focus lens 113 is determined. Specifically, as shown in FIG. 10, the AF control unit 255 moves the position of the focus lens 113 from the initial lens position to the near side by a predetermined amount. Then, the AF evaluation value before moving the lens and the AF evaluation value after moving the lens are compared, and the focus lens 113 is moved in a direction in which the AF evaluation value becomes a more appropriate value (for example, a direction in which the contrast value C becomes larger). It is estimated that the in-focus position exists, and the direction in which the AF evaluation value becomes a more appropriate value is determined as the lens driving direction.

  In the next step SP62, the AF evaluation value at each lens position is acquired while moving the focus lens 113 by a predetermined amount ΔX toward the lens driving direction determined in step SP61. This movement operation of the focus lens 113 is repeated until the change curve of the AF evaluation value reaches a maximum (see FIG. 10).

  Then, several points near the maximum value, for example, (X (n-1), Y (n-1)), (X (n), Y (n)), (X (n + 1), Y (n + 1)) The lens position (focus position) at which the AF evaluation value reaches a peak is obtained by quadratic interpolation approximation calculation (step SP63). Thereafter, in step SP64, the focus lens 113 is moved to the in-focus position obtained in step SP63.

  As described above, the AF operation by the method MA is performed.

  Next, the AF operation (step SP70) using the technique MB will be described with reference to the flowchart of FIG. In this method MB, the AF operation is performed on the assumption that the shooting scene is a night scene. In the method MB, after the focus lens 113 is once moved to the infinity end, the AF evaluation value at each lens position is acquired while the focus lens 113 is moved toward the near side, and the AF evaluation value is optimized. This is a method for detecting the lens position as the in-focus position.

  Specifically, first, in step SP71, the lens position of the focus lens 113 is moved to the infinity end (see also FIG. 11).

  In the next step SP72, the AF evaluation value at each lens position is acquired while moving the focus lens 113 by a predetermined amount ΔX toward the near side. This movement operation of the focus lens 113 is repeated until the change curve of the AF evaluation value becomes maximum.

  Then, using the data of several points (for example, three points) near the maximum value, the lens position (focus position) at which the AF evaluation value reaches a peak is obtained by secondary interpolation approximation calculation (step SP73). The focus lens 113 is moved to the position (step SP74). The processing of steps SP73 and SP74 is the same as that of steps SP63 and 64.

  As described above, the AF operation by the method MB is performed.

  In photographing night scenes, there is a property that a subject often exists relatively far away. In the above process, the focus lens 113 is moved from the infinity end toward the near side using this property. According to this, since the determination operation of the lens driving direction as shown in step SP61 of the technique MA is not necessary, a higher-speed AF operation can be performed. Further, since it is possible to avoid pseudo-focusing as described below, it is possible to perform a more accurate AF operation.

  FIG. 11 illustrates a situation where a pseudo peak exists. For example, a relatively large point light source in a blurred state enters or exits the AF area AR (FIG. 5) due to camera shake or the like, and is closer to the original focus position as shown in FIG. May show a pseudo peak. If the method MA is used during night scene shooting, depending on the initial position of the lens, it may be affected by this pseudo peak, and the original in-focus position for the subject may not be reached.

  On the other hand, when the method MB is used, since the focus lens 113 is first moved to the infinity end, the detection of the pseudo peak as described above is avoided, and the focus is adjusted to the original in-focus position. The lens 113 can be moved.

  As described above, when it is determined that the shooting scene is a night scene, since the AF operation using the technique MB is performed, it is possible to perform a faster and more accurate AF operation.

  Here, the contrast value C is adopted as the AF evaluation value, and the case where the degree of focusing increases as the value increases is illustrated. However, the present invention is not limited to this, and conversely the value decreases. An AF evaluation value may be used so that the degree of focus increases as the time increases. In the latter case, for example, in steps SP62 and SP72, the movement operation of the focus lens 113 may be repeated until the AF evaluation value becomes minimum.

  If it is determined in step SP80 that the shutter button 150 has been fully pressed S2 after the above-described AF operation has been performed, shooting conditions for actual shooting are set (step SP90).

  Specifically, the setting of the shooting condition is changed according to whether or not the shooting scene is a night scene.

  If it is determined in steps SP20 to SP50 that the shooting scene is a night scene, the shooting conditions are set for shooting a night scene. More specifically, the aperture is opened, the shutter speed is made shorter than normal shooting, and the exposure control parameter is set to a value for night scene shooting. Also, there is a property that noise is likely to occur during night scene shooting. Therefore, it is set that noise reduction should be turned on and image processing to remove noise should be performed. Thereby, it is possible to obtain a captured image in which noise is suppressed. According to the setting operation as described above, when the shooting scene is a night scene, it is possible to obtain a shot image with more appropriate shooting conditions.

  On the other hand, if it is determined that the shooting scene is not a night scene, the shooting conditions are set to those for normal shooting. Specifically, exposure control parameters are set according to a standard program diagram, and noise reduction is turned off.

  Thereafter, a main photographing operation is performed, and a photographed image (main photographed image) relating to a desired subject is acquired (step SP100).

<AF evaluation value>
In the above embodiment, the case where the contrast value C obtained by integrating the difference values of adjacent pixels for all the pixels in the AF area AR is used as the AF evaluation value is described. However, the present invention is not limited to this. As AF evaluation values at the time of shooting, for example, evaluation values V1 and V2 described later may be used. If the value V1 or the value V2 is used as the AF evaluation value, it is possible to improve the accuracy of the AF operation during night scene shooting.

  FIG. 12 is a diagram illustrating a change in the position of the subject brightness in the vicinity of the point light source when the point light source of the night view is captured. In FIG. 12, the horizontal axis represents a position in a predetermined direction (for example, the horizontal direction) in the screen, and the vertical axis represents subject luminance (or pixel value). The three curves CL1, CL2, and CL3 in FIG. 12 are diagrams showing subject brightness at different degrees of focus. Of the three curves CL1, CL2 and CL3, the curve CL1 is a curve indicating the change in the position of the subject brightness when the degree of focus is relatively low, and the curve CL2 is the subject when the degree of focus is relatively high. A curve indicating a change in the position of the luminance, and a curve CL3 is a curve indicating the change in the position of the subject luminance when the degree of focus is higher. As shown in FIG. 12, the curve near the edge rises steeply (or falls) as the degree of focus increases. The pixel value after A / D conversion can only take a value up to the maximum value MAX (for example, 255), the pixel value overflows in the vicinity of the center position CX of the point light source, and at the maximum value MAX during A / D conversion. It will be clipped. Hereinafter, a pixel in which the subject luminance has overflowed is also referred to as an “overflow pixel”, and a pixel that has not overflowed is also referred to as a “non-overflow pixel”. In FIG. 12, overflow pixels are indicated by black circles, and non-overflow pixels are indicated by white circles.

  Here, the case where the inclination degree of the pixel value at the edge portion is calculated and used as the AF evaluation value is illustrated. Specifically, when the high-brightness pixel and the non-high-brightness pixel are adjacent to each other (here, when the overflow pixel and the non-overflow pixel are adjacent to each other), the difference value between the two pixel values (more accurately (The absolute value of the difference value) is calculated.

  For example, for the curves CL1, CL2, CL3, the difference values DV1, DV2, DV3 are respectively acquired at the rising portions. A relationship of DV1 <DV2 <DV3 exists between these difference values DV1, DV2, and DV3, and the difference value increases as the degree of focusing increases. Thus, the difference value is a value that reflects the degree of inclination of the pixel value at the edge portion. Here, a value based on the difference value is used as the AF evaluation value.

  More specifically, when one of the target pixel and its neighboring pixels is an overflow pixel and the other is a non-overflow pixel, a difference value between the pixel values of the two pixels is obtained. Then, the difference value is accumulated while sequentially changing the target pixel to another pixel in the AF area AR, and the same operation is repeated until all the pixels in the AF area AR are set as the target pixel. The integrated value of the difference value is obtained. Further, as will be described later, normalization is performed by dividing the integrated value by the number of times of integration (count number). Thereby, a stable evaluation value can be obtained.

  Hereinafter, the case where the AF evaluation value is calculated using the pixel value of the G pixel (green component pixel) will be described in more detail with reference to FIG. However, the present invention is not limited to this, and pixel values of other component pixels (for example, R pixels or B pixels) may be used, or Y component pixel values (as synthesized values of R, G, and B components) ( (Luminance component pixel value) may be used.

  FIG. 13 is a diagram showing a part of the pixel array of the CCD 120 extracted. Here, the relationship between adjacent pixels adjacent in three directions is considered for each target pixel.

  Specifically, first, the horizontal direction is considered. When only one of the target pixel G (i, j) and the adjacent pixel G (i-1, j) adjacent to the left side is an overflow pixel, the pixel value PV (i, j) of both pixels A difference value (specifically, a difference absolute value, that is, | PV (i, j) −PV (i−1, j) |) is calculated from the pixel value PV (i−1, j) and integrated as a value DH. I will do it. This operation is repeated until all the pixels in the AF area AR are set as the target pixel. At this time, the number of times of integration, in other words, the number of times that only one of the target pixel and the adjacent pixel is determined to be an overflow pixel is also counted as the value NH.

  Similarly, when only one of the target pixel G (i, j) and the adjacent pixel G (i, j-1) adjacent to the upper left is an overflow pixel, the pixel value PV ( i, j) and a difference value between pixel values PV (i, j-1) (specifically, a difference absolute value, i.e., | PV (i, j) -PV (i, j-1) |) is calculated. The value DU is accumulated. This operation is repeated until all the pixels in the AF area AR are set as the target pixel. At this time, the number of times of accumulation, in other words, the number of times that only one of the target pixel and the adjacent pixel is determined to be an overflow pixel is also counted as the value NU.

  Similarly, when only one of the target pixel G (i, j) and the adjacent pixel G (i, j + 1) adjacent to the lower left side is an overflow pixel, the pixel values PV (i, j, j) and a difference value between pixel values PV (i, j + 1) (specifically, a difference absolute value, that is, | PV (i, j) −PV (i, j + 1) |) is calculated and integrated as a value DL. To go. This operation is repeated until all the pixels in the AF area AR are set as the target pixel. At this time, the number of times of accumulation, in other words, the number of times that only one of the target pixel and the adjacent pixel is determined to be an overflow pixel is also counted as the value NL.

  Then, a value VS (= DH + DU + DL) obtained by further adding the integrated values DH, DU, DL in each of the three directions is obtained, and an addition value NA (= NH + NU + NL) of the count numbers NH, NU, NL is obtained.

  Thereafter, a value V1 (= VS / NA) obtained by dividing the total value VS by the total count number NA is obtained. If the value V1 normalized by dividing the total value VS, which is an integrated value of the difference values, is used as the AF evaluation value, a more accurate AF operation can be performed. This is because, compared with the case where the total value VS is used as an AF evaluation value as it is, it is less affected by the fluctuation of the number of point light sources that enter and exit the AF area AR.

  Further, it is more preferable to obtain a value V2 (= V1 / NF) obtained by further dividing this value V1 by the number NF of overflow pixels in the AF area AR, and to use this value V2 as an AF evaluation value. As shown in FIG. 14, the area of the light image C1 of the point light source in the focused state is smaller than the area of the light image C2 of the point light source in the out-of-focus state. In other words, the smaller the number of overflow pixels NF in the AF area AR, the closer to the in-focus state. For this reason, the value V2 obtained by dividing the value V1 by the overflow pixel number NF has a degree of increase when approaching the in-focus state larger than the value V1. Therefore, by using this value V2 as the AF evaluation value, it is possible to more accurately determine the peak position of the AF evaluation value and perform a more accurate AF operation.

  In addition, although the case where the difference value about the adjacent part of the overflow pixel and the non-overflow pixel is obtained is illustrated here, the present invention is not limited to this. For example, after setting the threshold TH1 in the high luminance pixel determination to a value (for example, 250) smaller than the maximum value MAX (here, 255), the high luminance pixel determination is performed, and the adjacent portion between the high luminance pixel and the non-high luminance pixel A difference value or the like may be obtained.

<Others>
In the above-described embodiment, the night scene determination unit 254 determines whether or not the high-luminance portion exists in the center of the screen, depending on whether or not there are a predetermined number (N) or more of high-luminance pixels in the AF area AR. However, it is not limited to this.

  For example, it may be determined that a high-luminance portion exists in the center of the screen when high-luminance pixels are present in the AF area AR at a predetermined ratio (for example, 5%) or more.

  Alternatively, when the average brightness of the AF area AR is higher than a predetermined threshold instead of the number of high brightness pixels, it may be determined that the high brightness portion exists in the center of the screen.

  However, according to the determination using the existence number or the occupation ratio of high-luminance pixels, it is possible to more accurately determine the presence / absence of a point light source than in the case of determination using average luminance. It is possible to more accurately determine whether the scene is a night scene.

  Furthermore, in the above embodiment, when there are a predetermined number (M) or more of low-luminance blocks among the peripheral blocks in the image MG2, it is determined that the low-luminance portion exists in the peripheral portion of the screen. However, it is not limited to this.

  For example, when a low-luminance block is present in a predetermined ratio (for example, 50%) or more among the peripheral blocks in the image MG2, it may be determined that a low-luminance portion exists in the peripheral portion of the screen.

  Alternatively, instead of determining whether or not each segmented area (block) is a low-luminance block (low-luminance segmented area), the average luminance of the plurality of peripheral blocks shaded in FIG. 6 is a predetermined threshold value. It may be determined that there is a low-luminance part in the peripheral part of the screen depending on whether or not it is below. However, it is more accurate to determine whether each divided region is a low-luminance divided region than to use the average luminance of the entire plurality of peripheral blocks hatched in FIG. It is possible to determine the presence / absence of the existence.

  Moreover, although the case where it was determined whether the low-intensity part exists in the peripheral part (shaded part) MR of FIG. 6 was illustrated in the said embodiment, it is not limited to this. For example, instead of such determination, as shown in FIG. 15, the block group BG1 existing in the upper edge portion MU (shaded portion) of the framing region FR is used, and the low luminance portion is added to the upper edge portion MU. It may be determined whether or not there exists. Even in this case, it is possible to accurately determine the night view by determining the presence or absence of the low brightness portion in the upper edge portion MU corresponding to the “night sky” portion at the time of night view shooting.

  Furthermore, in the above-described embodiment, as illustrated in FIG. 7, the case where the shooting condition is set (step SP90) after it is determined that the shutter button 150 has been fully pressed (step SP80) is illustrated. It is not limited to. For example, the shooting conditions may be changed before the shutter button 150 is fully pressed S2. Specifically, the setting operation in step SP90 may be performed between the night scene determination operation in steps SP20 to SP50 and the determination operation in step SP80 (for example, immediately before step SP80).

It is a front view of digital camera 1A. It is sectional drawing of the digital camera 1A in the position of DD of FIG. It is a rear view of the digital camera 1A. It is a functional block diagram of digital camera 1A. It is a figure which shows image MG1 for AF control. It is a figure which shows image MG2 for AE control. It is a flowchart which shows operation | movement of 1 A of digital cameras. It is a flowchart which shows AF operation by technique MA. It is a flowchart which shows AF operation by method MB. It is a conceptual diagram which shows AF operation by technique MA. It is a conceptual diagram which shows AF operation by method MB. It is a figure which shows the position change of the object brightness | luminance near the point light source of a night view. It is a figure which shows the pixel arrangement | sequence (part) of CCD. It is a figure which shows the magnitude | size of the point light source at the time of focusing and the non-focusing. It is a figure which shows the block (partition area | region) used for determination of a low-intensity part.

Explanation of symbols

1A digital camera 112 zoom lens 113 focus lens 120 CCD
150 Shutter button AR AF area MG1 AF image MG2 AE image

Claims (12)

An imaging device comprising:
Imaging means for converting a light image by the photographing optical system into image data;
Determination means for determining whether or not the shooting scene is a night scene based on the image data;
With
In the case where the high-luminance portion exists in the first portion that is the central portion of the framing region and the low-luminance portion exists in the second portion other than the first portion of the framing region, An image pickup apparatus that determines that a shooting scene is a night scene. The imaging device according to claim 1,
2. The imaging apparatus according to claim 1, wherein the second portion is a peripheral portion of the framing region. The imaging device according to claim 1,
2. The imaging apparatus according to claim 1, wherein the second portion is a peripheral portion on an upper end side of the framing region. The imaging device according to claim 1,
2. The imaging apparatus according to claim 1, wherein the second portion includes a left end side peripheral portion, a right end side peripheral portion, and an upper end side peripheral portion of the framing region. In the imaging device according to any one of claims 1 to 4,
The determination means includes a high-luminance portion in the first portion when a predetermined number or more of high-luminance pixels are present in the first portion or when a high-luminance pixel is present in a predetermined ratio or more in the first portion. An imaging device characterized in that it is determined to exist. The imaging apparatus according to claim 5,
The determination means determines whether or not a predetermined number or more of high-luminance pixels are present in the first portion or whether or not high-luminance pixels are present in a predetermined ratio or more in the first portion. An image pickup apparatus comprising: determining using image data, and determining whether or not a low-luminance portion is present in the second portion using image data for AE that is thinned image data. The imaging apparatus according to any one of claims 1 to 6,
The determination means includes a plurality of divided areas located in the second portion when a low luminance divided area having an average luminance equal to or lower than a predetermined value is present in a predetermined ratio or more or a predetermined number of low luminance divided areas are present. And determining that a low-luminance portion is present in the second portion. In the imaging device in any one of Claims 1-7,
When it is determined that the shooting scene is not a night scene, the first method performs AF operation. When it is determined that the shooting scene is a night scene, the AF operation is performed using a second method different from the first method. AF control means,
An image pickup apparatus further comprising: The imaging device according to claim 8,
In the second method, after the focus lens is once moved to the infinity end, the AF evaluation value at each lens position is acquired while the focus lens is moved toward the near side, and the AF evaluation value is optimized. An imaging apparatus characterized in that it is a method for detecting a lens position to be detected as a focus position. In the imaging device according to claim 8 or 9,
The AF evaluation value in the AF operation according to the second method is the integrated value of the difference value of the pixel value between the high luminance pixel in the first portion and the non-high luminance pixel adjacent to the high luminance pixel. An image pickup apparatus that is calculated based on a normalized value by dividing by the number of non-high brightness pixels adjacent to a high brightness pixel in one portion. The imaging device according to claim 10.
The AF evaluation value is calculated based on a value obtained by further dividing the normalized value by the number of high-luminance pixels in the first portion. The imaging apparatus according to any one of claims 1 to 11,
When it is determined that the shooting scene is a night scene, shooting condition setting means for setting the shooting condition of the imaging device to the condition for the night scene,
An image pickup apparatus further comprising:

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