JP2007208405A - Imaging apparatus, imaging system, and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus, an imaging system, and an imaging method capable of obtaining parameters for D-range compression speedily and capable of performing D-range compression without losing useful information that an original image has. <P>SOLUTION: The imaging apparatus, the imaging system, and the imaging method can obtain parameters for D-range compression speedily and perform D-range compression, without losing useful information that an original image has by calculating parameters for the D-range compression, based on object luminance information when capturing the original image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus, an image pickup system, and an image pickup method, and more particularly, to an image pickup apparatus, an image pickup system, and an image pickup method that change dynamic range compression characteristics depending on the luminance of a subject.

  Due to the recent trend toward downsizing and increasing the number of pixels in an image sensor, the pixel size of the image sensor continues to be reduced, and accordingly, the illuminance range (so-called dynamic range: hereinafter referred to as D range) that can be imaged by the image sensor. ) Becomes narrower and has a great influence on image quality. Therefore, a wide D range of the image sensor is desired.

  In order to solve this problem, images with different exposure amounts are shot a plurality of times, and a screen portion of an appropriate level is selected from the plurality of screens and combined to create an image with a wider D range than the individual screens. An image pickup apparatus to be combined (see, for example, Patent Document 1) and a charge-voltage converter that converts photoelectric conversion signal charges of the image sensor into signal voltages, and the charge-voltage converter includes a plurality of capacitors having different voltage dependencies. , An image pickup device whose D range is variable (see, for example, Patent Document 2), and a plurality of capacitors for holding the signal charge of the photodiode, and the signal charge obtained by one exposure is represented by a capacitance value. A method of expanding the D range by switching a plurality of times to read out and adding the read signals (for example, see Patent Document 3) has been proposed.

  Also, in a logarithmic conversion type image sensor that converts photocurrent into logarithmically compressed voltage using the sub-threshold characteristics of MOSFET, depending on the original output characteristics of the solid-state image sensor, that is, incident light quantity, by giving a specific reset voltage to the MOSFET A logarithmic conversion type imaging device (hereinafter referred to as a linear log characteristic) that can automatically switch between a linear operation state in which an electrical signal is linearly converted and output and the logarithmic operation state described above (hereinafter referred to as linear log characteristics). (Referred to as Patent Document 4).

  However, the D range of the device that transmits, stores, and displays the captured image is finite, and even if a wide D range image is obtained by the method proposed in Patent Documents 1 to 4 described above, it can be obtained. It is difficult to handle all of the information provided. Therefore, processing that matches the D range of the device that transmits, stores, and displays the image (hereinafter referred to as tone reproduction processing) while retaining useful information of the wide D range image obtained by the above-described method or the like. Say) is required.

As an example of gradation reproduction processing, a plurality of blurred images are created from captured images (original images), a synthesized blurred image is created from the obtained plurality of blurred images, and an original image is generated based on the synthesized blurred image. There is a method of performing D range compression. In that case, processing parameters for creating a plurality of blurred images when compressing the D range according to the scene discrimination result of the original image or the shooting information attached to the original image There has been proposed a method (for example, Patent Document 5) in which processing parameters for creating a synthetic blurred image are variable.
Japanese Patent Publication No. 7-97841 JP 2000-165755 A JP 2000-165754 A JP 2002-77733 A JP 2001-298619 A

  However, in the method proposed in Patent Document 5, when scene discrimination processing is performed from an original image, processing to the image increases for discrimination, and it takes a very long time to obtain a scene discrimination result. Even when shooting information attached to the original image is used, information such as the default shooting scene classification, presence or absence of flash emission at shooting, shooting magnification, main subject position, photographer's intention and preference In addition, in the sense that the parameters for D range compression are calculated using the image data of the original image, this is the same as the case of scene discrimination, and much time is required until the parameters for D range compression are obtained. The problem of needing the same is the same.

  The present invention has been made in view of the above circumstances, and can obtain parameters for D-range compression at high speed, and can perform D-range compression without impairing useful information of the original image. An object is to provide an apparatus, an imaging system, and an imaging method.

  The object of the present invention can be achieved by the following constitution.

1. Imaging means for capturing an image of a subject;
In an imaging device comprising subject brightness detection means for detecting the brightness of a subject,
Dynamic range compression means for compressing the dynamic range of the image captured by the imaging means;
An imaging apparatus comprising: a dynamic range compression characteristic control unit that controls a compression characteristic of the dynamic range compression unit based on a detection result of the subject luminance detection unit.

  2. The subject luminance detecting means detects the luminance of a plurality of areas of the subject, and controls the compression characteristics of the dynamic range compressing means based on the detected maximum and minimum values of the subject luminance. The imaging apparatus according to 1.

  3. The subject brightness detecting means detects brightness in at least two ranges of the subject, and controls the compression characteristics of the dynamic range compressing means based on the detected magnitude relationship of the subject brightness. The imaging device described.

4). Imaging means for capturing an image of a subject;
In an imaging system comprising subject brightness detection means for detecting the brightness of a subject,
Dynamic range compression means for compressing the dynamic range of the image captured by the imaging means;
An imaging system comprising: a dynamic range compression characteristic control unit that controls a compression characteristic of the dynamic range compression unit based on a detection result of the subject luminance detection unit.

5). An imaging process for capturing an image of a subject;
A subject brightness detection step for detecting brightness of a plurality of ranges or areas of the subject;
A dynamic range compression characteristic calculation step for calculating a compression characteristic when compressing the dynamic range of the image captured in the imaging step based on the detection result in the subject luminance detection step;
An imaging method comprising: a dynamic range compression step of compressing a dynamic range of an image captured in the imaging step using the compression characteristic calculated in the dynamic range compression characteristic calculation step.

  According to the present invention, the parameters for D range compression can be obtained at high speed by calculating the parameters for D range compression based on the subject luminance information at the time of capturing the original image. An imaging apparatus, an imaging system, and an imaging method that can perform D-range compression without impairing useful information can be provided.

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

  First, a digital camera which is an example of an imaging apparatus according to the present invention will be described with reference to FIGS.

  1A and 1B are schematic external views of a digital camera. FIG. 1A is a front view and FIG. 1B is a rear view.

  In FIG. 1A, an interchangeable lens 20 is attached to the front surface of the body 10 of the digital camera 1. A release button 101, which is an operation member for imaging, is installed on the upper surface of the body 10, and an AF that operates in the first stage of pressing the release button 101 inside the body 10 is below the release button 101. A switch 101a and a two-stage switch constituting the release switch 101b that operates in the second stage of pressing the release button are arranged. A flash 102 is built in the upper part of the body 10 and a mode setting dial 112 for setting the operation mode of the digital camera 1 is arranged.

  In FIG. 1 (b), on the back of the body 10, a power switch 111 for turning on / off the power of the digital camera 1, a change dial 113 for changing various setting conditions of the camera, up / down / left / right and center five switches A jog dial 115 for performing various settings in each operation mode of the digital camera 1, a finder eyepiece 121a, and an image display means 131 for displaying recorded images and various information are arranged.

  FIG. 2 is a block diagram showing an example of a circuit of the digital camera 1 shown in FIG. In the figure, the same parts as those in FIG.

  The camera control means 150 that controls the digital camera 1 includes a CPU (central processing unit) 151, a work memory 152, a storage unit 153, a data memory 154, and the like, and programs stored in the storage unit 153 are stored in the work memory 152. And each unit of the digital camera 1 is centrally controlled according to the program. The data memory 154 stores various data such as photometry and AF.

  The camera control means 150 receives inputs from operation members such as the power switch 111, the mode setting dial 112, the change dial 113, the jog dial 115, the AF switch 101a, the release switch 101b, and the photometric module 122 on the optical viewfinder 121. The photometry operation is controlled by communicating with the AF module 144, the AF operation is controlled by communicating with the AF module 144, the reflex mirror 141 and the sub mirror 142 are driven via the mirror driving unit 143, and the shutter driving unit 146 is used. The shutter 145 is controlled, the flash 102 is controlled, and the imaging operation is controlled by communicating with the imaging control unit 161. The captured image and various types of information are displayed on the image display unit 131, and the infinder display unit 132 is displayed. Displays various information. The camera control means 150 and the photometry module 122 function as subject brightness detection means in the present invention.

  The camera control means 150 also includes a personal computer or a portable information terminal provided outside the digital camera 1 via an external interface (I / F) 185, captured image data, control signals for the digital camera 1, and the like. Exchange.

  Further, the camera control means 150 communicates between the body 10 and the interchangeable lens 20 on the mount (body side) 171 and the mount (lens side) 271 provided on the mount (body side) 171. Through the BL communication means (lens side) 272 provided, via the lens interface 251 of the interchangeable lens 20, a lens control means 241 for controlling the focus and zoom of the lens 211, and an aperture control means 222 for controlling the diaphragm 221. The entire interchangeable lens 20 is controlled by communicating with the lens information storage means 231 storing the unique information of the interchangeable lens 20.

  An image formed on the image sensor 162 by the lens 211 of the interchangeable lens 20 is photoelectrically converted by the image sensor 162, amplified by an amplifier 163, and converted into digital data by a front end processor (hereinafter referred to as FEP) 164. After being converted, pre-processing such as black level correction and fixed pattern noise (hereinafter referred to as FPN) correction is performed, predetermined image processing is performed by the image processing means 165, and once recorded in the image memory 181 Finally, it is recorded on the memory card 182. These operations are controlled by the imaging control unit 161 under the control of the camera control unit 150. The imaging control unit 161, the amplifier 163, the FEP 164, and the image processing unit 165 constitute an imaging circuit 160.

  The image pickup device 162 is preferably an image pickup device having a wide D range as disclosed in, for example, Patent Documents 2 to 4, but is not limited thereto, and is a CCD (Charge Coupled Device) having linear photoelectric conversion characteristics. It may be a normal imaging device such as a type or a CMOS (complementary metal oxide semiconductor) type. The imaging element 162 and the imaging circuit 160 function as imaging means in the present invention.

  Next, an example of a photometric area in the photometric module 122 which is a main part of the subject luminance detecting means in the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram in which the imaging range of the imaging device, the photometry area of the photometry module, and the AF area of the AF module are optically superimposed on the object scene.

  The photometric area of the photometric module 122 includes a photometric area A0 that covers almost the entire inner side of the imaging range 162z of the image sensor 162, and a photometric area A1 to A13 in which the inner side is divided into a plurality of (here, 13) photometry. A total of 14 photometric areas. The camera control unit 150 performs BEX (Brightness value) of each photometric area as multi-divided photometric data from the output of each area of the multi-divided photometric element mounted on the photometric module 122 by performing an APEX (Additive system of Photographic Exposure) calculation. 14 Bv values (Bv (0) to Bv (13)) as values or 14 Ev values (Ev (0) to Ev (13)) as Ev (Exposure value) values are calculated. Here, the camera control means 150 and the photometry module 122 function as subject brightness detection means in the present invention. Details of the photometric calculation are described in, for example, “Japanese Patent Laid-Open No. 2005-192139”, and the description thereof is omitted here.

  On the other hand, the AF area is composed of three AF areas: an AF area 144C looking at the center of the object scene, and AF areas 144L and 144R looking right and left. Based on the AF data of these three AF areas output from the AF module 144, the camera control unit 150 determines, for example, the subject in the AF area indicating the closest distance as the main subject, and the lens via the lens control unit 241. 211 is driven to focus on the main subject described above to obtain a focus signal.

  In the above description, three AF areas and 14 photometry areas are provided and the position of the main subject is determined by AF operation. However, both the AF area and photometry area are of course not limited to this example. The configuration can be freely changed as long as it is not contrary to the purpose. The determination of the AF area to which the main subject belongs is not limited to being determined by the AF operation, and may be determined by a method such as manual selection by the photographer.

  Next, a first embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a circuit block diagram showing the image processing means 165 and its peripheral part in the first embodiment of the present invention.

  First, in FIG. 2, when the AF switch 101 a is turned on, multi-division photometry operation is performed by the photometry module 122, and AF operation is performed by the AF module 144. Next, when the release switch 101b is turned on, the reflex mirror 141 and the sub mirror 142 are mirrored up, the shutter 145 is opened, and the subject image is formed on the image sensor 162 by the lens 211 of the interchangeable lens 20, and image pickup is performed. Imaging is performed by the element 162. Here, the multi-segment photometry operation by the photometry module 122 functions as a subject luminance detection process in the present invention, and the image capture operation by the image sensor 162 functions as an image capture process in the present invention.

In the present embodiment, the photometric operation is performed by the photometric module 122. However, the present invention is not limited to this. For example, the photometric operation may be performed by a so-called video AE using an image of an image sensor. In this case, for example, the image is divided into horizontal m × vertical n blocks (m and n are positive integers), and the average luminance Iv (ij) of each block is obtained from the average value of the pixel values of each block. here,
Iv (ij) = log2 (average pixel value of block (ij))
It is. This Iv (ij) may be handled in the same manner as the Bv value or Ev value described above and used for calculation of compression characteristics.

  In FIG. 4, image data 162k imaged by the image sensor 162 is amplified by an amplifier 163, and then converted by FEP 164 into digital image data 164a that has undergone preprocessing such as black level correction and FPN correction. Input to the processing means 165. The input digital image data 164a is subjected to white balance processing by the WB unit 501, and then subjected to color interpolation processing by the color interpolation unit 502 and color correction processing by the color correction unit 503, and the corrected image data 503a of the present invention. Is input to a D range compression unit 504 functioning as a dynamic range compression means. Each process performed by the WB unit 501, the color interpolation unit 502, and the color correction unit 503 may be a general well-known process.

  On the other hand, the D range compression parameter is calculated by the camera control means 150 based on the output of the photometry module 122 by a method described later with reference to FIG. 5, and is output to the D range compression unit 504 as the D range compression characteristic control signal 150a. . Here, the camera control means 150 functions as a dynamic range compression characteristic control means in the present invention.

  The corrected image data 503a input to the D-range compression unit 504 is subjected to D-range compression processing described later in FIG. 5 according to the D-range compression characteristic control season 150a output from the camera control unit 150. The gamma correction is performed by the gamma correction unit 505 as the range compressed data 504a, the color space correction is performed by the color space conversion unit 506, and the compressed data is compressed by the JPEG compression unit 507 at an appropriate compression ratio and output to the imaging control unit 161 as the image signal 165a. Is done. Each process in the gamma correction unit 505 and the color space conversion unit 506 may be a general well-known process. Here, the D range compression unit 504 functions as dynamic range compression means in the present invention.

  The image signal 165 a input to the imaging control unit 161 is once recorded in the image memory 181 by the imaging control unit 161 under the control of the camera control unit 150, and finally recorded on the memory card 182.

  Next, the D range compression processing performed by the D range compression unit 504 illustrated in FIG. 4 will be described with reference to FIG. FIG. 5 is a flowchart showing the flow of the operation of the D range compression process performed by the D range compression unit 504.

  In step S101, an illumination image is extracted from the corrected image data 503a. Generally, the image I is represented as a product of the illumination image L and the reflectance image R.

I = LR
As for the extraction method of the illumination image L, a method of extracting only a low frequency component from the image I using a low-pass filter or a method of extracting an illumination component using a median filter, an epsilon filter or the like (for example, Harashima et al., “Ε-separation nonlinear” Digital filters and their applications, ”The Journal of the Institute of Electronics, Information and Communication Engineers (A), Vol. J65-A, No. 4, pp. 297-304, (Apr. 1982)) etc. are used as appropriate.

  In step S102, the reflectance image R is obtained by dividing the image I by the illumination image L.

R = I / L
In step S103, a compression rate c, which is a compression parameter of the illumination image L, is calculated based on the above-described multi-division photometry data by a method described later in FIG. 6, and the illumination image L is compressed in step S104. If the illumination image after compression processing is L ′,
L ′ = n · L ^c
It is. Here, n is a normalization term.

  In step S105, the illumination image L ′ after the compression processing and the reflectance image R are multiplied to obtain a D-range compressed image I ′, and the operation ends.

I '= L' · R
Here, step S103 functions as a dynamic range compression characteristic calculation step in the present invention, and step S104 functions as a dynamic range compression step in the present invention.

  Next, “illumination image compression parameter calculation” performed in step S103 of FIG. 5 will be described with reference to FIG. FIG. 6 is a schematic diagram of a graph illustrating a method for obtaining the compression rate c that is a compression parameter of the illumination image L.

  6A, the right side of the graph is the image data I captured on the horizontal axis, the vertical axis is the illumination image L extracted from the image data I, and the left side of the graph is the illumination image on the vertical axis. L is a compressed illumination image L ′ on the horizontal axis. Here, in the exposure control of the digital camera 1, the aperture value and the shutter speed are controlled so that the image data of the area that gives the maximum luminance Bvmax in the multi-segment photometry data becomes the maximum value of the output of the image sensor 162. . For the sake of simplicity, the illumination image L extracted from the image data I is assumed to be proportional to the image data I.

  First, consider a case in which the width D1 (= Bvmax1-Bvmin1) of the maximum value Bvmax1 and the minimum value Bvmin1 of the subject brightness is wide in multi-segment photometry data. According to the exposure control method of the digital camera 1 described above, the image data of the photometry area that gives the maximum value Bvmax1 of multi-division photometry becomes the maximum value of the output of the image sensor 162. Since it becomes the value L2, the illumination image extracted from the image data of the photometry area that gives the minimum value Bvmin1 of multi-division photometry becomes a very small value L11, and the image is darkly crushed.

  In this case, when considering a compression characteristic curve CC1 that converts the illumination image value L11 into an illumination image value L1 ′ having an appropriate brightness and converts the maximum value L2 of the illumination image into L2 ′, a darkly crushed image Is converted into an image with appropriate brightness, and the image of the brightest part is also reproduced without being crushed white. At this time, the compression characteristic curve CC1 passing through the points (L11, L1 ') and the points (L2, L2') in the graph on the left side of FIG. 6A is expressed by the following equation.

L ′ = n1 · L ^c1
Here, n1 is a normalization term, and c1 is a compression rate.

  Similarly, when the width D2 (= Bvmax2−Bvmin2) of the maximum value (Bvmax2) and the minimum value (Bvmin2) of the subject brightness is narrow in the multi-division photometry data, the photometry area that gives the minimum value (Bvmin2) of multi-division photometry The illumination image extracted from the image data is a large illumination image value L21 as compared to the above-described minimum value Bvmin1. In this case, as described above, a compression characteristic curve CC2 is considered that converts the illumination image L21 into an illumination image value L1 ′ of appropriate brightness and converts the maximum value L2 of the illumination image into L2 ′. The compression characteristic curve CC2 is expressed by the following formula.

L ′ = n2 · L ^c2
Here, n2 is a normalization term, c2 is a compression ratio, and C1 <C2.

  The relationship between the illumination image L described above and the illumination image L ′ after compression is shown in FIG. 6B is the same as the graph on the left side of FIG. 6A, and shows a compression characteristic curve CC1 when the width D of the maximum value Bvmax and minimum value Bvmin of the subject brightness is wide, and a compression characteristic curve CC2 when it is narrow. Is illustrated. As described above, the compression characteristic of the illumination image in the coordinate space of FIG. 6B is set to a compression characteristic curve (CC1 in the figure) having a stronger curvature as the maximum value D and the minimum value D of the subject luminance are wider. The narrower the width D, the closer to the linear compression characteristic curve (CC2 in the figure), and the D range compression characteristic is controlled by this compression characteristic curve.

  In this way, the compression ratio c, which is the compression parameter of the illumination image L, is obtained from the original image as in the conventional manner by obtaining the subject luminance maximum value Bvmax and the minimum value Bvnin width D based on the multi-segment photometry data. Since the calculation of the compression ratio c can be performed at a very high speed as compared with the case of performing the scene determination process, the illumination image compression process can be performed at a high speed and a D range compressed image with appropriate brightness can be obtained. Further, the relationship between the compression rate c and the maximum value Bvmax and the minimum value Bvnin width D of the subject brightness is obtained in advance and stored in the form of a lookup table or the like, and the compression rate c is read from the table whenever necessary. It is also possible to further speed up the processing by omitting the calculation of the compression rate c.

  In the example described above, the compression processing of the illumination image is performed by the image processing means 165 in the digital camera 1 which is the imaging device according to the present invention. However, the present invention is not limited to this, and for example, a personal computer outside the digital camera 1 ( PC) or the like. By using a PC, it is possible to perform more detailed compression processing of an illumination image. Here, the digital camera 1, the PC, and the like constitute an imaging system according to the present invention.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a flowchart showing a method for determining the compression rate c in the second embodiment of the present invention. Here, for example, the center of the screen, that is, the central area (A7) of the photometric element 122a shown in FIG. 3 is set as the main subject area, and the other is set as the background area, and the main subject luminance Bvmain and the background luminance (for example, The average luminance of the background area) Bvsub is obtained, and the compression rate c of the illumination image is determined therefrom. The main subject area is not limited to the central area (A7), and may be an area designated by the photographer, for example, or a focus area obtained from the result of the AF operation as described with reference to FIG. May be.

  In FIG. 7, in step S201, the luminance Bvmain of the main subject is obtained from the photometric data in the A7 area of multi-division photometry, and in step S202, the background luminance Bvsub is calculated from the average value of the photometric data in areas other than A7 of multi-division photometry. Desired. In step S203, in a front light scene where the difference ΔBv (= Bvmain−Bvsub) between the main subject brightness Bvmain and the background brightness Bvsub is greater than or equal to 0 (zero), that is, the main subject brightness is greater than or equal to the background brightness. It is confirmed whether or not there is. If it is a front light scene (step S203; YES), the compression rate c of the illumination image is set to a small value (c1) in step S204, and the operation ends. As a result, the inclination becomes flat over the entire compression characteristic, and the gradation of the entire image is ensured.

  If the scene is not a follow light scene (step S203; NO), in step S205, the difference between the main subject brightness Bvmain and the background brightness Bvsub (Bvmain−Bvsub) is determined from the backlight determination value TH (where TH is a negative number). It is confirmed whether or not the scene is a strong backlight scene that is smaller or equal, that is, the main subject brightness is much darker than the background brightness. If it is a strong backlight scene (step S205; YES), the compression rate c of the illumination image is set to a large value (c3) in step S206, and the operation is terminated. As a result, the slope of the compression characteristic of the low-luminance portion increases, and the gradation of the low-luminance portion including the low-luminance subject, that is, the main subject is ensured. The backlight determination value TH may be a predetermined value, or may be a value set by a photographer, for example.

  If the scene is neither a direct-light scene nor a strong backlight scene, that is, a weak backlight scene where the main subject brightness is slightly darker than the background brightness (step S205; NO), the compression rate c of the illumination image is intermediate in step S207. The operation is terminated by setting the value (c2). Here, c1 <c2 <c3. As a result, in the case of a weak backlight scene, the compression characteristic is intermediate between a follow scene and a strong backlight scene.

FIG. 8 shows the relationship between the illumination image L using the compression rate c of the illumination image determined by the method described above as a parameter and the illumination image L ′ after compression. As described above, in this example, the main subject luminance and the background luminance are compared, and the D-range compression characteristic is controlled so that the compression rate of the illumination image decreases as the main subject luminance increases and increases as the background luminance increases. In particular, the D-range compression characteristics are controlled in multiple stages from the main subject luminance and the background luminance into the following scenes: a front light scene, a strong backlight scene, and a weak backlight scene. Therefore, as shown in FIG. 8, the curve of the compression characteristic in the case of the following light scene is CC1 (L ′ = n1 · L ^c1 ), which has a flat inclination over the entire compression characteristic, and the gradation of the entire image is improved. It is secured. The curve of the compression characteristic in the case of a strong backlight scene is CC3 (L ′ = n3 · L ^c3 ), and the inclination on the low luminance side is large, and the low luminance part of the low luminance part including the main object is low. Tonality is secured. The compression characteristic curve in the case of the weak backlight scene is CC2 (L ′ = n2 · L ^c2 ), which is an intermediate characteristic between the follow scene and the strong backlight scene.

  Here, the relationship between the main subject brightness and the background brightness in the image has been described as being classified into three scenes: a follow scene, a weak backlight scene, and a strong backlight scene. However, the present invention is not limited to this. Alternatively, a more detailed classification may be performed, or the classification of the subject may be changed, for example, the first main subject, the second main subject, or the background.

  Next, a third embodiment of the present invention will be described. Here, D range compression is performed by applying a method called the Gostasby method. The Gostasby method is basically a method of photographing a screen with different exposure amounts a plurality of times and obtaining an appropriate image using the plurality of images, as shown in Patent Document 1, for example, “A Gostasby, “Fusion of Multi-Exposure Images”, Image and Vision Computing, vol. 23, 2005, pp. 611-618 ”.

  In the third embodiment, one image taken by the linear log sensor described in Patent Document 4 is used instead of the plurality of images having different exposure amounts described above. Hereinafter, this embodiment will be described with reference to FIG. FIG. 9 is a schematic diagram showing a method for obtaining a plurality of images from one image taken by the linear log sensor. FIG. 9A is a graph showing the photoelectric conversion characteristics of the linear log sensor, and FIG. Is a graph showing a method for creating a plurality of images, and the horizontal axis represents the subject brightness, and the vertical axis represents the pixel value of the image sensor linearly.

  In FIG. 9A, the photoelectric conversion characteristics of the linear log sensor are a linear characteristic (characteristic 901 in the figure) for a low-luminance subject and a logarithmic characteristic (characteristic 902 in the figure) for a high-luminance object. About the image image | photographed with the linear log sensor, the part of the logarithmic characteristic 902 is expanded to the linear characteristic 903 by calculation, and the image I of a linear characteristic is obtained. On the other hand, photometric data Bv (1) to Bv (N) (N = 13 in the example of FIG. 3) of each photometric area in multi-division photometry are obtained by the method described in FIG.

  Next, in FIG. 9B, the photometric data Bv (1) to Bv (N) become appropriate pixel values (for example, 128 when the maximum pixel value is 8 bits) from the linear characteristic image I. The images I1 to IN with the tilt corrected are generated by calculation. For example, if the photometric data of the area is bright (for example, in the case of Bv1), an image I1 with a slanted inclination is obtained. In the case of the image I1, the entire image is reproduced without being crushed white, but the image has a low contrast. Further, when the photometric data of the area is dark (for example, in the case of Bv3), an image I3 having a tilt is obtained. In the case of the image I3, all bright portions of the image are crushed white, but the contrast of the low luminance portion is high. When the photometric data of the area is between Bv1 and Bv3 (for example, Bv2), an image I2 between the image I1 and the image I3 is obtained.

  The D range compression characteristic is determined using the plurality of images I1 to IN thus obtained. Since the subsequent operation follows the same method as described in the above-mentioned paper, only a brief description will be given. First, each of the plurality of images I1 to IN is divided into m × n blocks (m and n are positive integers), and entropy E that is a scale indicating the contrast of the image is obtained in each block. If the entropy of the color image of block (j, k) is Ec (jk),

Here, p _i represents the occurrence probability of the pixel value i in the block, and r, g, and b represent R (red) pixel, G (green) pixel, and B (blue) pixel, respectively.

Next, an image giving the maximum contrast is selected for each block. Here, the image number I _jk of the image that gives the maximum contrast is the number of the image that gives the maximum entropy among the N images for the block (j, k). Since the m × n images selected in this way are unnatural at the joints as they are, a natural image is obtained by performing a process called blending. The output image O (x, y) at this time is

It becomes. Here, W _jk is a weight represented by (Equation 3), and I _jk (x, y) is a pixel value of an image that gives the maximum entropy for the block (j, k).

Here, G _jk (x, y) is a Gaussian expressed by (Equation 4).

Here, (x _jk , y _jk ) is the coordinates of the central pixel of the block, and σ is the standard deviation.

  According to the present embodiment, a plurality of images are created from a single image captured by a linear log sensor based on the detection result of the photometric means, and the created plurality of images are divided into an arbitrary number of blocks. By selecting a high-contrast image for each block, the D-range characteristics can be controlled, and by blending, the D-range can be compressed well and quickly, and a natural image can be obtained. .

  As described above, according to the present invention, the parameters for D range compression can be obtained at high speed by calculating the parameters for D range compression based on the subject luminance information at the time of capturing the original image. In addition, it is possible to provide an imaging apparatus, an imaging system, and an imaging method that can perform D-range compression without impairing useful information of an original image.

  It should be noted that the detailed configuration and detailed operation of each component constituting the imaging apparatus, imaging system, and imaging method according to the present invention can be changed as appropriate without departing from the spirit of the present invention.

1 is a schematic external view of a digital camera that is an example of an imaging apparatus according to the present invention. It is a block diagram which shows an example of the circuit of the digital camera shown in FIG. It is a schematic diagram which shows the relationship between an imaging range, a photometry area, and AF area. 1 is a circuit block diagram showing an image processing means and its peripheral part in a first embodiment of the present invention. It is a flowchart which shows the flow of operation | movement of D range compression processing. It is a schematic diagram of the graph which shows the method of calculating | requiring the compression characteristic of an illumination image. It is a flowchart which shows the determination method of the compression rate in the 2nd Embodiment of this invention. It is a graph which shows the relationship between the illumination image in the 2nd Embodiment of this invention, and the illumination image after compression. It is a schematic diagram which shows the method of obtaining a some image from one image image | photographed with the linear log sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital camera 10 Body 112 Mode setting dial 122 Photometry module 131 Image display means 141 Reflex mirror 142 Sub mirror 144 AF module 145 Shutter 150 Camera control means 151 CPU (central processing unit)
152 Work memory 153 Storage unit 154 Data memory 160 Imaging circuit 161 Imaging control means 162 Imaging element 163 Amplifier 164 Front-end processor (FEP)
165 Image processing means 504 D-range compression unit 181 Image memory 182 Memory card 20 Interchangeable lens 211 Lens 221 Aperture

Claims (5)

Imaging means for capturing an image of a subject;
In an imaging device comprising subject brightness detection means for detecting the brightness of a subject,
Dynamic range compression means for compressing the dynamic range of the image captured by the imaging means;
An imaging apparatus comprising: a dynamic range compression characteristic control unit that controls a compression characteristic of the dynamic range compression unit based on a detection result of the subject luminance detection unit. The subject luminance detecting means detects the luminance of a plurality of areas of the subject, and controls the compression characteristics of the dynamic range compressing means based on the detected maximum and minimum values of the subject luminance. The imaging device according to claim 1. The subject brightness detection means detects brightness in at least two ranges of the subject, and controls compression characteristics of the dynamic range compression means based on the detected magnitude relationship of the subject brightness. The imaging apparatus according to 1. Imaging means for capturing an image of a subject;
In an imaging system comprising subject brightness detection means for detecting the brightness of a subject,
Dynamic range compression means for compressing the dynamic range of the image captured by the imaging means;
An imaging system comprising: a dynamic range compression characteristic control unit that controls a compression characteristic of the dynamic range compression unit based on a detection result of the subject luminance detection unit. An imaging process for capturing an image of a subject;
A subject brightness detection step for detecting brightness of a plurality of ranges or areas of the subject;
A dynamic range compression characteristic calculation step for calculating a compression characteristic when compressing the dynamic range of the image captured in the imaging step based on the detection result in the subject luminance detection step;
An imaging method comprising: a dynamic range compression step of compressing a dynamic range of an image captured in the imaging step using the compression characteristic calculated in the dynamic range compression characteristic calculation step.

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