JP2008131530A - Image pickup device, image processing apparatus and method, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pickup device and an image processing apparatus having a simple configuration for carrying out gradation correction in accordance with a subject luminance level of an image. <P>SOLUTION: In a configuration for correcting an image photographed under exposure control adjusting a luminance level of a main subject in an image pickup device, for example, data corresponding to the subject luminance of the photographed image are selected from gradation correction characteristic data as many as a limited number corresponding to luminance, and gradation correction is performed thereon. Specifically, correction processing is performed by applying gradation correction characteristics which are set in accordance with a region including the average luminance of the main subject in the photographed image. In such a configuration, correction processing can be speedily and efficiently carried out without expanding circuit scale of a digital signal processor (DSP) in the image pickup device, for example. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, an image processing apparatus, a method, and a computer program, and more particularly to an imaging apparatus, an image processing apparatus, a method, and a computer program that perform correction processing of a captured image.

  More specifically, the present invention relates to an imaging apparatus, an image processing apparatus, a method, and a computer program that perform correction processing on an image captured by performing exposure control for reducing overexposure and blackout of a subject in the imaging apparatus.

  For example, an imaging apparatus such as a digital still camera is generally provided with an AE (automatic exposure) function for automatically adjusting an exposure amount. Exposure control is performed by measuring the amount of light in the field of view and adjusting the aperture of the lens, the amount of electronic shutter, and the gain of the electrical signal output from the image sensor based on the photometric result.

  There are two types of photometry using a dedicated sensor and one using an output signal of an image sensor. As a method of measuring the amount of light, the whole surface average metering method that measures the average brightness of the entire screen, the center-weighted metering method that focuses on the brightness of the center part of the screen, and the area divided into each area There are a multi-division photometry method for measuring the average luminance in a spot and a spot photometry method for measuring the luminance at an arbitrary position in the screen.

  Further, as a prior art disclosing a method for improving photometric performance, there is, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2003-158673). This patent document 1 discloses a method of generating a histogram indicating the frequency of a pixel with respect to a luminance level from a captured image, detecting a feature of the captured image based on the generated histogram, and correcting an exposure control amount according to the feature. is doing.

  This exposure control method is based on controlling the main subject on the screen to the optimum exposure amount, and the exposure amount is reduced to reduce the degree of exposure in special images where a lot of overexposure or underexposure occurs. By correcting this, the dynamic range of luminance reproduction is expanded. However, since there is no limitation on the amount of correction, there is a possibility of overcorrection depending on the image. Further, if the correction is too large, overexposure and underexposure are reduced, but there is a problem that the exposure amount of the main subject is greatly deviated from the optimum value.

Also, in an image shot with exposure control to reduce overexposure and underexposure, the luminance distribution of the subject may deviate from the original luminance distribution. This correction processing, that is, pixel value conversion is performed. May be required. When performing this image correction process, it is desirable to selectively execute an optimal conversion process according to various images. However, in an apparatus that requires downsizing and speeding up of the process, such as an imaging apparatus, there are many It is not preferable to execute a process that requires the above calculation or to store a large number of conversion tables, which increases the size of the apparatus and increases the cost.
JP 2003-158673 A

  The present invention solves the above-described problems, for example, and performs a correction process for an image captured by performing exposure control to reduce overexposure and underexposure of a subject in an imaging apparatus, with a simple configuration. An object is to provide an imaging apparatus, an image processing apparatus and method, and a computer program that can be executed quickly.

The first aspect of the present invention is:
In an imaging device that performs image shooting processing,
A digital signal processing unit that executes correction processing of a captured image in the imaging apparatus;
The digital signal processor is
An imaging apparatus having a configuration for selecting a gradation correction characteristic to be applied according to the average luminance of a photographed image and generating a corrected image by executing a gradation correction process using the selected gradation correction characteristic It is in.

  Furthermore, in an embodiment of the imaging apparatus of the present invention, the digital signal processing unit holds gradation correction characteristic data corresponding to a luminance region divided according to luminance, and includes a luminance that includes the average luminance of the subject of the photographed image. It has a configuration in which an area is determined, and a correction image is generated by executing gradation correction processing based on a gradation correction characteristic set corresponding to a luminance area including the subject average luminance of the photographed image. .

  Furthermore, in an embodiment of the imaging apparatus of the present invention, the imaging apparatus further includes a control unit that executes automatic exposure control, and the control unit is configured to perform a subject operation based on image data acquired by the imaging apparatus. The average luminance and the luminance distribution range of the subject are calculated, and the optimum average luminance level of the subject is determined based on the calculated subject luminance distribution range and the required number of gradations corresponding to the subject. The exposure control is performed so as to have a level, and the digital signal processing unit is configured to perform a correction process of a captured image based on the exposure control of the control unit.

  Furthermore, in an embodiment of the imaging apparatus of the present invention, the control unit determines a main subject from acquired image data of the imaging device, calculates an average luminance and a luminance distribution range of the main subject, and calculates the calculated main subject luminance distribution Based on the range and the required number of gradations corresponding to the main subject, the optimum average luminance level of the main subject is determined, and exposure control is performed so that the main subject in the captured image has the optimum average luminance level. The digital signal processing unit selects a gradation correction characteristic to be applied according to the average luminance of the main subject included in the captured image, and executes a gradation correction process using the selected gradation correction characteristic to generate a corrected image. It has the structure which performs this.

Furthermore, in one embodiment of the imaging apparatus of the present invention, the control unit includes:
Average brightness of subject = Y _M ,
Luminance distribution range of subject = a × Y _{M to} b × Y _M (0 ≦ a ≦ 1, 1 ≦ b),
The overexposure threshold, which is the brightness threshold (threshold level) for determining overexposure,
Overexposure threshold _{= T} H,
Necessary number of gradations for subject = M,
When
M / (b−a) ≦ Y _M <T _H / b... Formula A,
So as to satisfy the above formulas A, a configuration of determining the optimal average luminance level Y _M of the subject, the subject in the captured image to perform exposure control to have the best average luminance level Y _M, the digital signal processing The unit is configured to execute a correction process of a captured image based on the exposure control of the control unit.

Furthermore, in an embodiment of the imaging apparatus of the present invention, the control unit includes an overexposure area [S _H ], which is an area of an overexposure pixel included in acquired image data of the image pickup apparatus, and an area of a blackout pixel. The blackout area [S _L ] is calculated, the above-mentioned optimum average luminance is satisfied so that the formula A is satisfied and the sum of the overexposure area [S _H ] and the blackout area [S _L ] becomes the minimum value. The exposure control is performed to set the level [Y _M ].

  Furthermore, in an embodiment of the imaging apparatus of the present invention, the digital signal processing unit is configured to execute gradation correction processing for setting the average luminance level of the subject of the captured image to the optimum value of the luminance distribution of the corrected image. It is characterized by that.

Furthermore, in an embodiment of the imaging apparatus of the present invention, the digital signal processing unit may include a representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of one or more k luminance regions divided according to luminance. ) And a gain (Y _n / Y _M ) based on the subject average luminance Y _M of the photographed image, and then the gradation correction generated based on the representative luminance value Y _n corresponding to the luminance region It is characterized by having a configuration for executing gradation correction processing based on characteristics.

Furthermore, in one embodiment of the imaging apparatus of the present invention, the digital signal processing unit is based on representative luminance values Y _n (where 1 ≦ n ≦ k) corresponding to each of k luminance regions divided according to luminance. It holds the generated tone correction characteristic f _n as, corresponding to the subject the average brightness of the photographed image Y _M 2 one representative luminance sandwiching the luminance level is present value Y _n and Y _{m (provided} that 1 ≦ m ≦ k) A new gradation correction characteristic f _nm is generated based on the two gradation correction characteristics f _n and f _m, and a gradation correction process using the generated gradation correction characteristic f _nm is executed. Features.

Furthermore, in an embodiment of the imaging apparatus of the present invention, the digital signal processing unit includes two representative brightness values Y _n and Y _m that sandwich a brightness level where the subject average brightness Y _M of the captured image exists. in output value graph corresponding to the gradation correction characteristic _{f n} and _{f m,} and calculating a curved line dividing the distance between the input values axis on a percentage of _{(Y M -Y n) :( Y} m -Y M) , by setting the curve as new tone correction characteristic f _nm, and having an arrangement for executing the tone correction process according to the gradation correction characteristic f _nm set.

Further, in the imaging apparatus according to an embodiment of the present invention, the digital signal processing unit, the luminance level of the subject the average luminance Y _M of the captured image exists, the representative luminance value Y ₁ corresponding to the pre-set minimum brightness regions In the following cases, Y _M : (Y ₁ −Y _M) based on the input / output value graph corresponding to the gradation correction characteristic f ₁ corresponding to the representative luminance value Y ₁ and the linear data with the input value = 0. ) is calculated curve is divided into the ratio of, by setting the curve as a new gradation correction characteristics f _01, that has a configuration for executing the tone correction process according to the gradation correction characteristic f ₀₁ set Features.

Furthermore, in an embodiment of the imaging apparatus according to the present invention, the digital signal processing unit is configured such that the luminance level at which the subject average luminance Y _M of the captured image exists corresponds to a preset maximum luminance region Y _k. If larger, (Y _M −Y _k ): (based on the input / output value graph corresponding to the gradation correction characteristic f _k corresponding to the representative luminance value Y _k and the linear data with the input value = Y _MAX. calculating a curved line dividing the ratio of Y _{MAX -Y M),} by setting the curve as a new gradation correction characteristic f _{kk + 1,} executes the tone correction process according to the gradation correction characteristic f _{kk + 1} set It has the structure.

Furthermore, the second aspect of the present invention provides
An image processing device,
An image signal processing unit for performing image correction processing;
The image signal processor is
An image having a configuration in which a gradation correction characteristic to be applied is selected according to the average luminance of the object to be corrected, and a correction image is generated by executing a gradation correction process using the selected gradation correction characteristic. In the processing unit.

  Furthermore, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit holds gradation correction characteristic data corresponding to a luminance region divided according to luminance, and includes subject average luminance of the correction target image. And determining a luminance area to be corrected, and generating a corrected image by executing gradation correction processing based on a gradation correction characteristic set corresponding to the luminance area including the subject average luminance of the correction target image. Features.

  Furthermore, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit selects a gradation correction characteristic to be applied according to the average luminance of the main subject included in the correction target image, and selects the selected gradation correction. The present invention is characterized in that a corrected image is generated by executing gradation correction processing based on characteristics.

  Furthermore, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit executes a gradation correction process for setting the average luminance level of the subject of the correction target image to the optimum value of the luminance distribution of the correction image. It is characterized by being.

Furthermore, in one embodiment of the image processing apparatus of the present invention, the image signal processing unit includes representative luminance values Y _n (where 1 ≦ n ≦ 1) corresponding to each of one or more k luminance regions divided according to luminance. k) and a gain (Y _n / Y _M ) based on the subject average luminance Y _M of the correction target image are multiplied by the correction target image, and then generated based on the representative luminance value Y _n corresponding to the luminance region. It is characterized by having a configuration for executing gradation correction processing based on gradation correction characteristics.

Furthermore, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit calculates a representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of k luminance regions divided according to luminance. The gradation correction characteristic f _n generated as a reference is held, and the two representative luminance values Y _n and Y _m (where 1 ≦ m ≦ k) sandwich the luminance level where the subject average luminance Y _M of the correction target image exists. A new gradation correction characteristic f _nm is generated based on the corresponding two gradation correction characteristics f _n and f _m, and a gradation correction process using the generated gradation correction characteristic f _nm is executed. It is characterized by that.

Furthermore, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit corresponds to two representative luminance values Y _n and Y _m sandwiching a luminance level where the subject average luminance Y _M of the correction target image exists. in the two output values graph corresponding to the gradation correction characteristic _{f n} and _{f m,} the curved line dividing the distance between the input values axis on a percentage of _{(Y M -Y n) :( Y} m -Y M) It is characterized by having a configuration for calculating, setting the curve as a new gradation correction characteristic f _nm , and executing a gradation correction process using the set gradation correction characteristic f _nm .

Further, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit corrects the subject the average luminance Y luminance _{level M} is present in the target image, the representative luminance value corresponding to a preset minimum luminance regions If Y ₁ or less, based on the input / output value graph corresponding to the gradation correction characteristic f ₁ corresponding to the representative luminance value Y ₁ and the linear data with the input value = 0, Y _M : (Y ₁ − calculating a curved line dividing the ratio of Y _M), by setting the curve as a new gradation correction characteristics f _01, has a configuration for executing the tone correction process according to the gradation correction characteristic f ₀₁ set It is characterized by that.

Further, in an embodiment of the image processing apparatus of the present invention, the image signal processing unit corrects the subject the average luminance Y luminance _{level M} is present in the target image, the representative luminance value corresponding to a preset maximum luminance regions If it is larger than Y _k , (Y _M −Y _k ) based on the input / output value graph corresponding to the gradation correction characteristic f _k corresponding to the representative luminance value Y _k and the linear data with the input value = Y _MAX. : _(Y MAX -Y _M) to calculate a curved line dividing the percentage of, by setting the curve as a new gradation correction characteristic _{f kk + 1,} the gradation correction process of applying the gradation correction characteristic _{f kk + 1} set It has the structure to perform.

Furthermore, the third aspect of the present invention provides
An image processing method for executing image correction processing in an image processing apparatus,
The image signal processor
A gradation correction characteristic to be applied is selected according to the subject average luminance of the correction target image, and a gradation correction process using the selected gradation correction characteristic is executed, and an image correction step for generating a corrected image is executed. In the image processing method.

  Furthermore, in an embodiment of the image processing method of the present invention, the image correction step holds gradation correction characteristic data corresponding to a luminance region divided according to luminance, and includes subject average luminance of the correction target image. A step of determining a luminance region and generating a corrected image by executing a gradation correction process based on a gradation correction characteristic set corresponding to the luminance region including the subject average luminance of the photographed image. To do.

  Furthermore, in an embodiment of the image processing method of the present invention, the image correction step selects a gradation correction characteristic to be applied according to the average luminance of the main subject included in the correction target image, and selects the selected gradation correction characteristic. This is a step for generating a corrected image by executing the gradation correction processing according to the above.

  Furthermore, in an embodiment of the image processing method of the present invention, the image correction step is a step of executing a gradation correction process for setting the average luminance level of the subject of the correction target image to the optimum value of the luminance distribution of the correction image. It is characterized by being.

Furthermore, in an embodiment of the image processing method of the present invention, the image correction step includes the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of one or more k luminance regions divided according to luminance. ) And a gain (Y _n / Y _M ) based on the subject average luminance Y _M of the correction target image, and then the floor generated by using the representative luminance value Y _n corresponding to the luminance region as a reference. It is a step for executing gradation correction processing based on tone correction characteristics.

Furthermore, in an embodiment of the image processing method according to the present invention, the image correction step is based on representative luminance values Y _n (where 1 ≦ n ≦ k) corresponding to each of k luminance regions divided according to luminance. It holds the generated tone correction characteristic f _n as, corresponding to the subject the average of the correction target image luminance Y _M 2 one representative luminance sandwiching the luminance level is present value Y _n and Y _{m (provided} that 1 ≦ m ≦ k) A step of generating a new gradation correction characteristic f _nm based on the two gradation correction characteristics f _n and f _m to be executed, and executing a gradation correction process using the generated gradation correction characteristic f _nm. It is characterized by.

Furthermore, in an embodiment of the image processing method of the present invention, the image correction step includes 2 corresponding to two representative brightness values Y _n and Y _m sandwiching a brightness level where the subject average brightness Y _M of the correction target image exists. In the input / output value graph corresponding to the two tone correction characteristics f _n and f _m , a curve is calculated that divides the distance in the input value axis direction into a ratio of (Y _M −Y _n ) :( Y _m −Y _M ). and, by setting the curve as a new gradation correction characteristic f _nm, characterized in that it is a step of performing a tone correction processing using the gradation correction characteristic f _nm set.

Furthermore, in an embodiment of the image processing method according to the present invention, the image correction step includes a representative luminance value Y corresponding to a preset minimum luminance region where the luminance level at which the subject average luminance Y _M of the correction target image exists. If it is ₁ or less, Y _M : (Y ₁ -Y) based on the input / output value graph corresponding to the gradation correction characteristic f ₁ corresponding to the representative luminance value Y ₁ and the linear data with the input value = 0. _M ) is a step of calculating a curve to be divided into proportions, setting the curve as a new gradation correction characteristic f ₀₁ , and executing a gradation correction process using the set gradation correction characteristic f _01. It is characterized by.

Furthermore, in an embodiment of the image processing method according to the present invention, the image correction step includes a representative luminance value Y corresponding to a preset maximum luminance region where the luminance level at which the subject average luminance Y _M of the correction target image exists. _{When it is} larger than _k , based on the input / output value graph corresponding to the gradation correction characteristic f _k corresponding to the representative luminance value Y _k and the linear data with the input value = Y _MAX , (Y _M −Y _k ): calculating a curved line dividing the ratio of (Y _{MAX -Y M),} by setting the curve as a new gradation correction characteristic f _{kk + 1,} perform the tone correction processing using the gradation correction characteristic f _{kk + 1} set It is a step to perform.

Furthermore, the fourth aspect of the present invention provides
A computer program for executing image correction processing in an image processing apparatus,
Image correction that causes the image signal processing unit to select a gradation correction characteristic to be applied in accordance with the average luminance of the subject of the correction target image, and to execute a gradation correction process using the selected gradation correction characteristic to generate a corrected image. A computer program characterized by causing a step to be executed.

  The computer program of the present invention is, for example, a storage medium or communication medium provided in a computer-readable format to a general-purpose computer system capable of executing various program codes, such as a CD, FD, MO, etc. Or a computer program that can be provided by a communication medium such as a network. By providing such a program in a computer-readable format, processing corresponding to the program is realized on the computer system.

  Other objects, features, and advantages of the present invention will become apparent from a more detailed description based on embodiments of the present invention described later and the accompanying drawings. In this specification, the system is a logical set configuration of a plurality of devices, and is not limited to one in which the devices of each configuration are in the same casing.

  According to the configuration of one embodiment of the present invention, for example, in a configuration in which a captured image is corrected by performing exposure control such that a main subject has an optimal average luminance level, a limited number of floors are used. Tone correction is performed by selecting data corresponding to the main subject luminance from the tone correction characteristic data. Specifically, for example, the gradation correction characteristic set corresponding to the area including the average luminance of the main subject of the photographed image is selectively applied to perform the correction process. With this configuration, for example, optimal image correction according to an image can be performed without complicating the circuit scale of a digital signal processing unit (DSP) in the imaging apparatus, and correction processing can be executed quickly and efficiently. .

The details of the imaging apparatus, image processing apparatus and method, and computer program of the present invention will be described below with reference to the drawings. The description will be made sequentially for the following items.
1. 1. Overview of overall configuration of imaging apparatus and imaging process 2. Automatic exposure control processing 3. Simplified configuration for realizing gradation correction processing Image processing apparatus configuration for performing image correction

[1. Overview of overall configuration of imaging device and imaging process]
First, with reference to FIG. 1 and FIG. 2, an overall configuration of the imaging apparatus of the present invention and an outline of imaging processing will be described. FIG. 1 is a diagram showing an appearance of an image pickup apparatus (digital camera) 10 as an embodiment of the image pickup apparatus of the present invention. 1A is a top view of the imaging apparatus 10, FIG. 1B is a front view, and FIG. 1C is a rear view. (A) The lens portion of the top view is shown as a cross-sectional view.

  The imaging apparatus 10 includes a power switch 11, trigger means for setting image capture timing, that is, a release switch 12 that functions as a shutter, a monitor 13 that displays an image (through image) photographed by the imaging apparatus, operation information, and the like, an imaging element An imager 14 (for example, a CCD), an operation button 15 for inputting various operation information, a viewfinder 16 for confirming an image (through image) acquired by the imaging device, a focus lens 17 driven in focus adjustment, A zoom lens 18 driven during zoom adjustment, a mode dial 19 for setting a shooting mode, a focus lens motor (M1) 21 for driving the focus lens 17, and a zoom lens motor (M2 for driving the zoom lens 18) 22) Exposure Aperture blade 25 which is driven when your, diaphragm driver 26 to drive the diaphragm blades, and a strobe light emitting means 31.

  The subject image is displayed on the viewfinder 16 and the monitor 13. The viewfinder 16 and the monitor 13 are configured by, for example, an LCD, and a subject image through the lens is displayed as a moving image. This moving image is called a through image. The user confirms the viewfinder 16 or the monitor 13, confirms the target subject to be photographed, and presses the release switch 12 as a shutter, whereby the image recording process is executed.

  With reference to FIG. 2, an internal configuration of an image pickup apparatus (digital camera) 100 according to an embodiment of the present invention will be described. As shown in FIG. 2, the imaging apparatus 100 includes a lens unit 101, a CCD 102, a timing signal generation circuit (TG) 103, a sampling hold gain control (S / H · GC: Sampling Hold Gain Control) circuit, and the like. Analog signal processing unit 104, A / D converter 105, digital signal processing unit (DSP) 106, monitor 107, viewfinder 108, recording device 109, detection unit 110, shutter and other operation unit 115, shutter determination Unit 116 and control unit 120.

  The CCD 102 converts the imaging light of the subject imaged on the light receiving surface via the lens unit 101 into an electrical signal for each pixel, and outputs an image signal. The image signal accumulated by the CCD 102 is supplied to the analog signal processing unit 104 at a predetermined timing (image update period), and the analog signal processing unit 104 performs analog signal processing such as noise removal and gain control. As these processing circuits, the analog signal processing unit 104 includes a sampling hold gain control (S / H · GC) circuit.

  The timing signal generation circuit 103 generates various drive pulses necessary for the CCD 102 to read out image signals for each screen and an electronic shutter pulse for controlling the accumulation time of charges accumulated in the CCD 102. Various pulses generated from the timing signal generation circuit 103 are supplied to the CCD 102 and used as timing signals for image signal imaging processing and output processing. The timing signal generation circuit 103 controls the shutter speed of the electronic shutter configured in the operation unit 115 in accordance with a control command from the control unit 120.

  An analog signal processing unit 104 having a sampling hold gain control (S / H · GC) circuit performs analog processing such as sampling processing and amplification processing on the image signal supplied from the CCD 102. The analog image signal output from the S / H • GC circuit is supplied to the A / D converter 105. The amplification degree of the image signal supplied from the CCD 102 is controlled by the control unit 120.

  The A / D converter 105 samples the analog image signal supplied from the analog signal processing unit 104 at a predetermined sampling rate, and converts it into a digital image signal. The digital image signal output from the A / D converter 105 is supplied to the digital signal processing unit (DSP) 106 and also to the recording device 109 in the RAW image recording mode.

  A digital signal processing unit (DSP) 106 generates a digital video signal such as an NTSC format or a format required for a recording medium from the digital image signal supplied from the A / D converter 105, and outputs the digital video signal to the outside. A digital signal processing unit (DSP) 106 generates a display image signal from the digital image signal and supplies it to the monitor 107 and the viewfinder 108 during framing. The digital signal processing unit (DSP) 106 generates a single still image signal from the digital image signal and compresses the digital image signal and supplies the still image signal to the recording device 109. In these signal processes, tone correction is performed based on the exposure control result information, which will be described later in detail.

  The monitor 107 and the viewfinder 108 are electronic display devices composed of, for example, a liquid crystal panel, and display image signals are input from the digital signal processing unit (DSP) 106 during framing, and the image signals are displayed.

  The recording device 109 records an image signal on a storage medium such as a memory card at the time of capturing a still image, but the operation differs depending on the image recording mode. In the normal image recording mode, the still image signal supplied from the digital signal processing unit (DSP) 106 is recorded, and in the RAW image recording mode, the RAW image signal supplied from the A / D converter 105 is recorded. In the RAW image recording mode, a still image signal supplied from the digital signal processing unit (DSP) 106 may be recorded together with the RAW image signal.

  The detection unit 110 generates various detection signals necessary for autofocus (AF), automatic exposure (AE), and the like from the video signal supplied from the digital signal processing unit (DSP) 106. Various detection signals are read by the control unit 120, for example, for each frame. The control unit 120 includes a CPU 121 and a memory 122, and controls the lens unit 101 and the like so that an appropriate image can be taken based on the read various detection signals.

  Specific detection signals detected by the detection unit 110 include, for example, detection signals related to autofocus and detection signals related to automatic exposure control. The detection unit 110 detects a luminance edge component in an AF detection area set at a predetermined position on the captured image as a detection signal related to autofocus, and outputs a contrast value obtained by integrating the edge components. . The detection unit 110 also outputs to the control unit 120 the average luminance and luminance distribution range of the main subject and the area of the overexposure portion and the underexposure portion in the entire image as detection signals relating to automatic exposure control.

  The control unit 120 performs exposure control so that overexposure and blackout are minimized to the extent that the gradation of the main subject can be sufficiently obtained from these data. Details regarding this exposure control will be described later. The various detection signals are obtained by the detection unit 110. However, instead of the detection unit 110, a separate optical sensor may be provided for detection. Using the detection unit or optical sensor as a constituent element of the control unit 120, the control unit performs detection processing, that is, calculation processing of the average luminance and luminance distribution range of the main subject and the area of the whiteout portion and the area of the blackout portion in the entire image It is good also as a structure which performs.

  The operation unit 115 includes, for example, a shutter release switch. The shutter release switch is, for example, a momentary press switch operated by a user. This shutter release switch switches between three states: a state where the switch is not pressed at all (off), a state where the switch is fully pressed (full press), and a state where the switch is pressed halfway (half press). Function is provided. The three pressed states (off, half-pressed, and fully-pressed) of the shutter release switch are determined by the shutter determination unit 116, and the determination information is supplied to the control unit 120.

  The lens unit 101 includes a zoom lens 131, a focus lens 132, an aperture blade 133, and an aperture blade drive unit 134 that drives the aperture blade 133. In addition to these, the lens unit 101 includes, for example, an infrared cut filter that cuts infrared light of incident light, an optical system such as a shutter blade that blocks incident light, a zoom lens driving unit that drives the zoom lens 131, and the like. A focus lens driving unit for driving the focus lens, a shutter driving unit for driving the shutter blades, and the like are also provided.

  The zoom lens 131 in the lens unit 101 is provided at a position where its optical axis coincides with a vertical line extending from the approximate center of the light receiving surface of the CCD 102. The zoom lens 131 is provided so as to be linearly movable back and forth on the optical axis, and changes the imaging magnification of the image formed on the light receiving surface of the CCD 102 according to the movement position. The movement position of the zoom lens 131 is controlled by the control unit 120 via the zoom lens driving unit.

  The focus lens 132 in the lens unit 101 is provided at a position where its optical axis coincides with a vertical line extending from the approximate center of the light receiving surface of the CCD 102. The focus lens 132 is provided so as to be linearly movable back and forth on the optical axis, and changes the focal position of the image formed on the light receiving surface on the CCD 102 according to the movement position. The movement position of the focus lens 132 is controlled by the control unit 120 via the focus lens driving unit.

  The diaphragm blade 133 adjusts the amount of imaging light imaged on the light receiving surface of the CCD 102. The aperture blade 133 forms a hole around the optical axis of the optical system of the lens unit 101, and controls the amount of light by changing the hole diameter. That is, the aperture blade 133 controls the aperture value (F value) of the camera. The aperture diameter of the aperture blade 133 is controlled by the control unit 120 via the aperture drive unit 134.

  The control unit 120 controls each unit of the imaging device 100. For example, framing process control (off), autofocus process control (half press), and still image recording control (full press) are performed based on the pressed state of the shutter release switch that constitutes the operation unit 115.

  The framing process is a process of displaying an image captured by the CCD 102 on the monitor 107 or the viewfinder 108 so that the user can confirm the position of the subject in the screen and the composition of the screen before shooting. . At the time of this framing process, the CCD 102 performs an imaging process for one screen at a constant image update cycle (for example, every 1/30 seconds), and an image signal obtained by imaging is output. For this reason, the images displayed on the monitor 107 and the viewfinder 108 are also updated at regular intervals (for example, every 1/30 seconds), and the user can check the displayed captured image with a moving image. Since the number of pixels of the monitor 107 and the viewfinder 108 is usually smaller than the number of pixels of the CCD 102, the output signal of the CCD 102 is thinned and output during framing processing, thereby reducing the load of image processing and making a smooth moving image monitor 107. Or the viewfinder 108. This framing process is performed when the imaging apparatus 100 itself is ready to shoot and the shutter release switch is in an off state, that is, when the user is not pressing the shutter release switch.

  The autofocus process is a process for automatically setting the focus of a subject image to be captured of a still image. That is, the autofocus process is a process of automatically adjusting the moving position of the focus lens 132 and adjusting the focus of the captured image. When the shutter release switch is half-pressed during the framing process, the image capturing apparatus 100 starts an autofocus process for detecting the in-focus position based on the captured image.

  Specifically, during the autofocus process, the control unit 120 acquires the contrast value at each position from the detection unit 110 while moving the focus lens 132, and determines whether the contrast value increases or decreases with respect to each movement position of the focus lens 132. . Then, the control unit 120 determines the degree of focus of the image with respect to the movement position of the focus lens 132 from the increase / decrease of the contrast value, and moves the focus lens 132 to a position with the highest degree of focus.

  Further, in the imaging apparatus 100, during the autofocus process, settings of the aperture of the aperture blade 133 and the electronic shutter speed at the time of recording a still image, that is, the settings of the aperture value (F value) and shutter speed of the camera are also performed. It can be carried out. However, when setting a special camera aperture value (F value), shutter speed, and the like during autofocus, the F value and shutter speed during still image recording are reset after autofocus processing.

  The still image shooting process is a process of capturing a subject image for one screen and recording the subject image for one screen on a medium. When the control unit 120 of the imaging apparatus 100 detects that the shutter release switch of the operation unit 115 is fully pressed after completing the autofocus process, the movement position of the focus lens 132 and the opening degree of the aperture blade 133 are detected. The electronic shutter time and the S / H · GC gain of the analog signal processing unit 104 are set, and a still image for one screen is captured by the CCD 102. The captured still image is converted into a digital image signal by the A / D converter 105, stored in a medium as a RAW image signal, and subjected to processing such as compression by the digital signal processing unit (DSP) 106 or the like. Saved to media.

[2. About automatic exposure control processing]
Next, automatic exposure control processing executed in the imaging apparatus of the present invention will be described.
In the automatic exposure control process, the components shown in FIG. 2 are controlled so that the captured subject image has an optimal exposure during the framing process and the autofocus process. In particular,
(A) setting the aperture of the aperture blade 133;
(B) setting of the electronic shutter speed of the CCD 102;
(C) setting of the amplification degree (gain value) set in the sampling hold gain control (S / H · GC) circuit of the analog signal processing unit 104;
These settings are determined for optimal exposure control.

  Each of these settings is executed under the control of the control unit 120 in accordance with the exposure control parameter stored in the internal memory 122 of the control unit 120. The exposure control based on the exposure control parameter is, for example, a table showing the aperture frequency of the aperture blade 133, the electronic shutter speed amount, the amplification level of the image signal, etc. for each value of the exposure control parameter, or these data from the exposure control parameter. This is performed using an arithmetic expression for calculating.

The control unit 120 controls the exposure in the direction of brightening the image when the value of the exposure control parameter increases, and controls the exposure in the direction of darkening the image when the value of the exposure control parameter decreases. That is, the control unit 120
(1) If the exposure control parameter increases,
(1a) Increasing the aperture of the aperture blade 133 (opening the aperture blade 133),
(1b) Decreasing the electronic shutter speed (increasing the exposure time of the CCD 102),
(1c) Increasing the degree of amplification of the image signal output from the CCD 102 (increasing the gain of the S / H • GC circuit in the analog signal processing unit 104)
Control in the direction.

Conversely, the control unit 120
(2) If the exposure control parameter decreases,
(2a) Decreasing the aperture of the diaphragm blade 133 (closing the diaphragm blade 133),
(2b) Increasing the electronic shutter speed (decreasing the exposure time of the CCD 102),
(2c) Decreasing the amplification degree of the image signal output from the CCD 102 (reducing the gain of the S / H • GC circuit in the analog signal processing unit 104)
Control in the direction.

  The exposure control parameters stored in the internal memory 122 of the control unit 120 are based on the average luminance and luminance distribution range of the main subject detected by the detection unit 110 and the area of the overexposure portion and the underexposure portion in the entire image. For example, the correction is sequentially performed for each frame.

Various methods can be applied as the main subject detection processing mode. For example,
* A method that uses the center of the screen as the main subject.
* A method to divide the screen into multiple areas and estimate the main subject from the luminance distribution.
* A method to estimate the main subject from the histogram of the image,
* A method for the user to specify the main subject,
These various methods are applicable. Further, the configuration may be such that the main subject is not specified and the entire screen is determined as the main subject.

The average luminance of the main subject in the output data of the A / D converter 105 is
Average luminance = Y _M
The luminance distribution range of the main subject
Luminance distribution range = a × Y _{M to} b × Y _M (0 ≦ a ≦ 1, 1 ≦ b),
Luminance threshold (threshold level) for judging overexposure and underexposure,
Overexposure threshold = _{T H}
Blackout threshold = _TL
And

FIG. 3 shows an example of a histogram (frequency distribution) showing the relationship between each of the above values and the luminance distribution of the image in a certain sample image data. In FIG. 3, the horizontal axis represents the luminance level, and the vertical axis represents the frequency of luminance corresponding to the number of pixels having each luminance. From the left to the horizontal axis of the brightness level,
Blackout threshold [ _TL ],
Minimum luminance [a × Y _M ] in the luminance distribution range of the main subject,
Maximum luminance [b × Y _M ] in the luminance distribution range of the main subject,
Overexposure threshold _[T H]
Each of these luminance values is shown.

Let M be the number of gradations required to satisfactorily reproduce a subject in the luminance distribution range (a × Y _{M to} b × Y _M ). M is determined according to the assumed main subject type and noise level. An example of setting the number of gradations necessary for subject expression will be described with reference to FIG. The memory of the control unit 120 of the imaging apparatus stores a necessary gradation number determination table as shown in FIG. 4, for example, and the control unit 120 obtains the necessary gradation number M from the image information and table acquired in the imaging apparatus. The required gradation number M is determined based on the above.

  The required number of gradations M may be configured to apply fixed data, but may be changed depending on [subject type], [shooting mode], [subject size], [subject importance], and these conditions. It is good.

  1) When the required gradation number M is changed depending on the type of subject, a necessary gradation number determination table corresponding to the type of subject as shown in FIG. 4A is applied. For example, when the subject is a person, the subject is sensitive to the tone of the skin color, and the importance of the background other than the person is likely to be low. Setting M to be large with emphasis on. For example, when the face recognition process is executed by the image pickup apparatus and the face is recognized from the image acquired by the image pickup apparatus, the necessary gradation number M is set to be increased.

  2) When changing the required number of gradations M depending on the shooting mode, a table in which the required number of gradations M corresponding to the modes that can be set in the imaging apparatus is applied as shown in FIG. Accordingly, the required number of gradations M is determined. For example, in the portrait mode, since the subject is likely to be a person, M is increased.

  3) When the required gradation number M is changed depending on the size of the subject, a necessary gradation number determination table corresponding to the size of the subject as shown in FIG. 4 (3) is applied. The larger the subject is, the easier it is to recognize the gradation change, and the importance of the background other than the subject is likely to be low. Therefore, the larger the subject, the larger M is. Note that the size of the subject is, for example, the size of the person area occupied in the photographed image. By providing the above-described face recognition processing configuration in the imaging apparatus, the area occupied by the person is calculated to obtain the size of the subject. Can do.

  4) When changing the required number of gradations M according to the importance of the subject, a necessary gradation number determination table corresponding to the importance of the subject is applied as shown in FIG. In the case where the main subject is emphasized and it is not necessary to consider much other than that, the necessary number of gradations M is set large. With such a setting, there is a high possibility that the background will be blown out, but the gradation expression of the main subject is improved. The importance level information is input by the user via the operation unit, and the control unit 120 determines the necessary gradation number M based on the input information and the table shown in FIG.

  As described above, the required number of gradations M is applied to [subject type], [shooting mode], [subject size], [subject importance], at least one of these conditions, or in combination. It is possible to adopt a configuration that is determined as follows. The user may set various conditions regarding the subject, that is, whether or not the subject is a person, the size of the subject, and the importance of the subject. For example, it may be configured to set whether or not the subject is a person or to set the importance of the subject and control the value of M accordingly.

In this way, the control unit 120 determines the number of gradations M necessary to satisfactorily reproduce the subject in the luminance distribution range (a × Y _{M to} b × Y _M ). In order to secure this necessary number of gradations,
It is sufficient that the luminance distribution range [a × Y _{M to} b × Y _M ] of the subject is equal to or greater than the required number of gradations [M]. That is,
b × Y _M −a × Y _M ≧ M (Formula 1)
It is sufficient if the above formula is satisfied.
At this time, if the condition of the above (Equation 1) is satisfied and the minimum luminance of the subject is set so as not to be blackened ( _TL or more), the main subject is not blackened. In order to prevent the main subject from being overexposed,
_{b × Y M <T H ···} ( Equation 2)
It is sufficient if the above formula is satisfied.

From these Formula 1 and Formula 2,
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
If the exposure control parameters are controlled so as to satisfy the above formula 3, the constituent pixels of the main subject are not overexposed, and sufficient gradation can be secured for the main subject.

In the whole image,
The area of the overexposed portion, that is, the area of the portion where the luminance is T _H or higher is represented by S _H ,
Area i.e. the luminance of dark portions is the area of the T _L following parts as S _L,
The allowable values of S _H and S _L are R _H and R _L.
If the exposure is controlled so that S _H and S _L are minimized within a range satisfying the above [Equation 3], an image with the widest dynamic range can be obtained while ensuring the gradation of the main subject.

The processing for each specific case of various images will be described.
(Case 1: overexposure area _{(S H)} only allowable value _{(R H)} is greater than)
For example, when the overexposure area (S _H ) is larger than the allowable value (R _H ) and the blackout area (S _L ) is equal to or smaller than the allowable value (R _L ) (S _H > R _H , S _L ≦ R _L ), Equation 3, i.e.
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The exposure control parameter is changed so that the main subject average luminance (Y _M ) decreases within a range that satisfies the above formula. That is, as a whole, the brightness is lowered and the overexposed area is reduced.

(Case 2: When only the blackout area (S _L ) is larger than the allowable value (R _L ))
Overexposure area _{(S H)} is allowable value _{(R H)} underexposure area _{(S L)} only allowable value or less _{(R L)} is greater than _{(S H ≦ R H, S} L> R L) when the above Equation 3, i.e.
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The exposure control parameter is changed so that the main subject average luminance (Y _M ) increases within a range that satisfies the above formula. That is, the luminance is increased as a whole to reduce the black area.

(Case 3: When the overexposure area (S _H ) and the underexposure area (S _L ) are less than the allowable values)
Overexposure area _(S H), underexposure area _{(S L)} following both tolerance _{(S H ≦ R H, S} L ≦ R L) but may not change the exposure control parameter when the overexposure area (S _H), may change the exposure control parameters so as to further reduce the larger of underexposure area (S _L), in order to better the S / N ratio, the range of the [formula 3] The exposure control parameter may be changed so that the main subject average luminance (Y _M ) increases within the range.

(Case 4: When the overexposure area (S _H ) and the underexposure area (S _L ) are larger than the allowable values)
When both the whiteout area (S _H ) and the blackout area (S _L ) are larger than the allowable values (S _H > R _H , S _L > R _L ), the one that is farther away than the allowable value is reduced. Change the exposure control parameters.
For example, an image with a prominent whiteout, specifically,
_{S H -R H> S L -R} L,
When the above relational expression holds, the above [Expression 3], that is,
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The exposure control parameter is changed so that the main subject average luminance (Y _M ) decreases within a range that satisfies the above formula. That is, the overall brightness is reduced to make the overexposure unremarkable.

On the other hand, an image where blackout is conspicuous, specifically,
_{S H -R H <S L -R} L,
When the above relational expression holds, the above [Expression 3], that is,
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The exposure control parameter is changed so that the main subject average luminance (Y _M ) increases within a range that satisfies the above formula. That is, the overall brightness is increased to eliminate the blackout.

In the case of (case 4), comparison expressions to be applied _{(S H -R H> S L} -R L, S H -R H <S L -R L) may be weighted both sides in. That is,
_{(S H} -R H) and _(S L _-R L)
, Apply weighting parameters c and d,
c × (S _H −R _H ) and d × (S _L −R _L )
The comparison processing may be performed by calculating a value to which the above weighting parameter is applied.

For example, if you want to focus on reducing whiteout,
Set the weighting parameters c and d
c> d,
If you value low blackout,
c <d
And
Which one is emphasized can be determined by, for example, the entire luminance distribution. There is a method that emphasizes overexposure when the image is biased to high luminance, and emphasizes underexposure when it is the reverse. In the comparison formula, ratios (S _H / R _H , S _L / R _L ) may be used instead of the differences.

  Hereinafter, a specific processing sequence of exposure control processing executed by the imaging apparatus according to the embodiment of the present invention will be described with reference to a flowchart shown in FIG. In the imaging apparatus, when the power is turned on and the operation is started, the exposure control process is started from the following step S101.

  In step S <b> 101, the control unit 120 performs exposure control based on the exposure control parameters held in the internal memory 122. In the internal memory 122, for example, exposure control parameters preset in a nonvolatile memory or the like are stored at the start of the flow control shown in FIG. In addition, after the flow control is looped once or more, the new exposure control parameter obtained by the processing in step S104 in the previous loop is stored in the internal memory 122.

Note that the exposure control parameters are as described above.
(A) a set value of the aperture of the diaphragm blade 133,
(B) Electronic shutter speed setting value,
(C) Amplification degree of the image signal output from the CCD 102, that is, a set value of a gain of the S / H · GC circuit,
With these values, the control unit 120 controls the exposure in the direction of brightening the image when the value of the exposure control parameter increases, and controls the exposure in the direction of darkening the image when the value of the exposure control parameter decreases. .

Specifically, the control unit 120
(1) If the exposure control parameter increases,
(1a) Increasing the aperture of the aperture blade 133 (opening the aperture blade 133),
(1b) Decreasing the electronic shutter speed (increasing the exposure time of the CCD 102),
(1c) Increasing the degree of amplification of the image signal output from the CCD 102 (increasing the gain of the S / H • GC circuit in the analog signal processing unit 104)
Control in the direction
(2) If the exposure control parameter decreases,
(2a) Decreasing the aperture of the diaphragm blade 133 (closing the diaphragm blade 133),
(2b) Increasing the electronic shutter speed (decreasing the exposure time of the CCD 102),
(2c) Decreasing the amplification degree of the image signal output from the CCD 102 (reducing the gain of the S / H • GC circuit in the analog signal processing unit 104)
Control in the direction.

In step S102, the main subject in the screen is detected. As described above, there are various detection methods. That is,
* A method that uses the center of the screen as the main subject.
* A method to divide the screen into multiple areas and estimate the main subject from the luminance distribution.
* A method to estimate the main subject from the histogram of the image,
* A method for the user to specify the main subject,
These various methods are applicable. Further, the configuration may be such that the main subject is not specified and the entire screen is determined as the main subject.

In step S103, the average luminance [Y _M ] of the main subject identified in step S102, the luminance distribution range [a × Y _{M to} b × Y _M (0 ≦ a ≦ 1, 1 ≦ b)], and the white of the entire screen The jump area [S _H ] and the black crush area [S _L ] are obtained. These calculation processes may be executed by the detection unit 110 as described above, and the calculation result may be input to the control unit 120, or these values may be calculated using a dedicated optical sensor. It is good also as a structure. Moreover, it is good also as a structure which performs these processes in a control part by making a detection part and an optical sensor into a constituent element of a control part.

In step S104, [Equation 3] described above, that is,
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The brightness control range shown in FIG. As described above, M is the number of gradations necessary for satisfactorily reproducing an object in the luminance distribution range (a × Y _{M to} b × Y _M ). M is determined according to the assumed main subject type and noise level.

In step S105, the exposure control parameter is changed from the overexposure area [S _H ] and the underexposure area [S _L ], and is stored in the internal memory 122 of the control unit 120. Details of the processing in step S105 will be described later.
The control unit 120 performs the processing from step S101 to step S105 for each frame, for example, and starts the processing from step S101 again when performing processing for the next frame.

The details of the process in step 105, that is, the process of changing the exposure control parameter from the overexposure area [S _H ] and the underexposure area [S _L ] and storing them in the internal memory 122 of the control unit 120 are shown in the flowchart of FIG. Will be described with reference to FIG. The flow shown in FIG. 6 is an exposure control parameter determination process executed as a process of the control unit 120.

In step S201, the overexposure area [S _H ] is compared with its allowable value [R _H ]. If S _H ≦ R _H , the process proceeds to step S202, and if S _H > R _H , the process proceeds to step S203.
In step S202, the blackout area [S _L ] is compared with its allowable value [R _L ]. If S _L ≦ R _L , the process proceeds to step S204, and if S _L > R _L , it is determined that the image should be brightened. The process moves to step S206.
In step S203, the blackout area [S _L ] and its allowable value [R _L ] are compared, and if S _L ≦ R _L , it is determined that it is better to darken the image, the process proceeds to step S207, and if S _L > R _L. The process moves to step S205.
In step S204, the overexposure area [S _H ] and the underexposure area [S _L ] are compared. If S _H > S _L , it is determined that the image should be dark, and the process proceeds to step S207. If S _H <S _L If it is determined that the image should be brightened, the process proceeds to step S206. If S _H = S _L , the process ends.

Step overexposed area in S205 _{[S H]} and its allowable value blackout area the difference _{(S H} -R H) of _{[R H] [S L]} and the allowable value _{[R L]} of the difference _(S L -R _L ) and if S _H -R _H > S _L -R _L , it is determined that the image should be darkened, and the process proceeds to step S207. If S _H -R _H <S _L -R _L , the image is brightened. If it is determined that it is better, the process proceeds to step S206, and if S _H −R _H = S _L −R _L , the process ends.

In step S206, the exposure control parameter is increased to brighten the image, and the process ends. In this case, specifically, the control unit 120 increases the exposure control parameter,
(1a) Increasing the aperture of the aperture blade 133 (opening the aperture blade 133),
(1b) Decreasing the electronic shutter speed (increasing the exposure time of the CCD 102),
(1c) Increasing the degree of amplification of the image signal output from the CCD 102 (increasing the gain of the S / H • GC circuit in the analog signal processing unit 104)
The exposure control in such a direction is executed.

In step S207, the exposure control parameter is decreased to darken the image, and the process ends. In this case, specifically, the control unit 120
(2a) Decreasing the aperture of the diaphragm blade 133 (closing the diaphragm blade 133),
(2b) Increasing the electronic shutter speed (decreasing the exposure time of the CCD 102),
(2c) Decreasing the amplification degree of the image signal output from the CCD 102 (reducing the gain of the S / H • GC circuit in the analog signal processing unit 104)
The exposure control in such a direction is executed.

The luminance distribution range of the main subject, i.e.
Luminance distribution range = a × Y _{M to} b × Y _M (0 ≦ a ≦ 1, 1 ≦ b),
Is a luminance range that is to be reproduced particularly well in the image. In the above-described embodiments, the luminance distribution range of the main subject has been processed. For example, the luminance distribution range of the image including the main subject and its surroundings It is good also as composition to do. However, it is necessary to set an optimal value for the necessary number of gradations [M] according to the setting of the luminance distribution range.

  Image data obtained by executing the exposure control of the present invention will be described in comparison with image data obtained by a conventional exposure control method. Hereinafter, description will be made sequentially for each type of image.

(Processing example 1. When the dynamic range of the subject is small)
First, an image captured by the conventional exposure control when the dynamic range of the subject is small is compared with an image captured by applying the exposure control of the present invention. FIG.
(A) a histogram showing the luminance distribution of an image taken by conventional exposure control;
(B) a histogram showing the luminance distribution of an image taken by applying the exposure control of the present invention;
It is.
Note that the image data shown in (b) corresponds to the output image of the A / D converter 105 in the imaging apparatus of the present invention. A digital signal processing unit (DSP) 106 appropriately performs correction processing on the output image of the A / D converter 105 to obtain a final output image. The correction process executed in the digital signal processing unit (DSP) 106 will be described later.

In the conventional image shown in FIG. 7A, the average luminance [Y _M ] of the main subject is controlled near the center of the luminance level. In this case, in the conventional method in FIG. 7A, the data of the high luminance part, that is, the high luminance data of the luminance region 301 shown in FIG. 7A does not exist, and the dynamic range of the A / D converter 105 is wasted. Yes.

On the other hand, in FIG. 7B showing the luminance distribution of an image shot by performing exposure control according to the present invention, data exists between the blackout threshold value [T _L ] and the overexposure threshold value [T _H ]. Image data that effectively uses the dynamic range of the A / D converter 105 is obtained.

This case corresponds to the case 3 described above. That is, as described above, (Case 3: overexposure area (S _H), underexposure area (S _L) both when the allowable value or less), the it is not necessary to change the exposure control parameters, white The exposure control parameter may be changed so that the larger one of the skipped area (S _H ) and the blacked-out area (S _L ) is smaller, and in order to improve the S / N ratio, the above [Equation 3] The exposure control parameter may be changed so that the main subject average luminance (Y _M ) increases within the range of.

In this processing example, the exposure control parameter is changed so that the main subject average luminance (Y _M ) is increased. As a result, as shown in FIG. 7B, data exists between the blackout threshold value [T _L ] and the overexposure threshold value [T _H ], and image data that effectively uses the dynamic range of the A / D converter 105. Is obtained.

(Processing example 2. When the dynamic range of the subject is large)
Next, an image captured by the conventional exposure control when the dynamic range of the subject is large is compared with an image captured by applying the exposure control of the present invention. FIG.
(A) a histogram showing the luminance distribution of an image taken by conventional exposure control;
(B) a histogram showing the luminance distribution of an image taken by applying the exposure control of the present invention;
It is.

The example shown in FIG. 8 is an example in the case where the dynamic range of the subject is large, particularly when the subject is greatly widened on the high luminance side, and the overexposed area of the entire image cannot be less than the allowable value. In the conventional method, the average luminance [Y _M ] of the main subject is controlled near the center of the luminance level.

In the luminance distribution histogram of the image obtained by the exposure control of the conventional method shown in FIG. 8A, the number of pixels exceeding the overexposure threshold [T _H ] is increased in the overexposure area, that is, the luminance level. In the luminance distribution histogram of the image obtained by executing the exposure control according to the present invention shown in (b), the overexposure area, that is, the number of pixels exceeding the overexposure threshold [T _H ] in the luminance level is significantly reduced. .
In FIG. 8, the image data shown in (b) corresponds to the output image of the A / D converter 105, and the digital signal processing unit (DSP) 106 performs further correction processing to generate a final image. Output. This process will be described later.

The case shown in FIG. 8 corresponds to the case 1 described above. In other words, the exposure control according to the present invention corresponds to the processing when only the overexposed area (S _H ) is larger than the allowable value (R _H ). Overexposure area _{(S H)} is allowable value _{(R H)} greater than underexposure area _{(S L)} is allowable value _{(R L)} or less _{(S H> R H, S} L ≦ R L) when the above-described Equation 3, ie
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The exposure control parameter is changed so that the main subject average luminance (Y _M ) decreases within a range that satisfies the above formula. As a result, the overall brightness can be reduced to reduce the overexposure area, and an image with a brightness distribution as shown in FIG. 8B, that is, image data with a reduced overexposure pixel area can be obtained.

As described above, by applying the exposure control method according to the present invention, the dynamic range of the A / D converter 105 can be utilized to the maximum extent. However, since the average luminance [Y _M ] of the main subject is adjusted in the above-described process, if the adjusted image is output as it is, the image has an average luminance different from the average luminance of the original subject. It may end up.

  Therefore, in the imaging apparatus of the present invention, in order to obtain an optimum image in the final output image, the digital signal processing unit (DSP) 106 performs gradation correction so that the luminance of the main subject is optimized. The gradation correction characteristic is basically determined by the average luminance of the main subject, and more preferable luminance reproduction can be realized by further optimization according to the luminance distribution of the image.

For example, an example of gradation correction when the average luminance of the main subject is corrected to the center of the luminance level will be described with reference to FIG.
FIG. 9 shows an example in which the average luminance [Y _M ] of the main subject is controlled to a value larger than the center value in the exposure control according to the present invention, like the image data described with reference to FIG. Is shown. FIG. 9 shows graphs (a), (b), and (c). Each graph is the following data.
FIG. 9A is a luminance distribution histogram of an image photographed by the exposure control process of the present invention. This corresponds to FIG. 7B and corresponds to an image output from the A / D converter 105.
FIG. 9B is a conversion table for gradation correction applied for performing gradation correction so that the luminance of the main subject is optimized in the digital signal processing unit (DSP) 106. The digital signal processing unit (DSP) 106 holds such a gradation correction conversion table in a memory, and executes a gradation correction process using the conversion table.
FIG. 9C is a luminance distribution histogram of the corrected image data obtained as a result of executing the gradation correction process to which the gradation correction table shown in FIG. 9B is applied.

  The digital signal processing unit (DSP) 106 inputs image data having the luminance distribution shown in FIG. 9A from the A / D converter 105 and applies the conversion table for gradation correction shown in FIG. 9B. The gradation correction process is executed to generate and output image data having a luminance distribution shown in FIG.

The example shown in FIG. 9 shows an example of correction processing when the exposure control according to the present invention described with reference to FIG. 7, that is, the average luminance [Y _M ] of the main subject is controlled to a value larger than the center value. ing. FIG. 9A is a luminance distribution histogram of an image photographed by the exposure control processing of the present invention, which corresponds to FIG. 7B and corresponds to an image output from the A / D converter 105. If it is output as it is, the main subject as a whole becomes an image having a brightness that is too bright. The digital signal processing unit (DSP) 106 executes a gradation correction process to which the gradation distribution conversion table shown in FIG. 9B is applied to the luminance distribution image, and the luminance distribution shown in FIG. Generate and output image data with.

In the gradation correction conversion table shown in FIG. 9B, the horizontal axis represents the input luminance level, and the vertical axis represents the output luminance level. For example, the average luminance [Y _M ] = P1 shown in FIG. 9A is converted into the output luminance [P2] in the conversion table.

By the luminance level conversion processing by this conversion table, the average luminance [Y _M ] = P1 of the main subject shown in FIG. 9A is the optimum value of the output luminance of the output image as shown in FIG. For example, it is almost converted to the center value. Further, by the conversion of the conversion table, many gradations are assigned to the luminance distribution range of the main subject.

  The conversion table shown in FIG. 9B includes a region Q2 having an inclination of approximately 45 degrees and regions Q1 and Q3 having an inclination smaller than 45 degrees. In the region Q2 where the inclination is approximately 45 degrees, the input luminance value and the output luminance value correspond to one to one, but in the regions Q1 and Q3 where the inclination is small, the input luminance value range is compressed and the luminance range is reduced. Output. By this conversion table conversion, a large number of gradations are assigned to the luminance distribution range of the main subject, and the assignment of gradations in other low-luminance areas and high-luminance areas is reduced.

In the corrected image converted by this conversion table, as shown in FIG. 9C, the average luminance [Y _M2 ] = P2 of the main subject comes to be positioned at the approximate center of the luminance range of the output image. An optimal output image can be obtained.

FIG. 10 also shows an example in which gradation correction is performed in the digital signal processing unit (DSP) 106 so that the luminance of the main subject is optimized, as in FIG. Also in FIG.
(A) Luminance distribution histogram of an image photographed by the exposure control processing of the present invention (b) Tone correction conversion table applied in the digital signal processor (DSP) 106 (c) Tone correction shown in (b) Luminance distribution histogram of post-correction image data obtained as a result of executing a tone correction process using a table. These data are shown.

  However, the conversion table shown in FIG. 10B is a table that performs conversion processing different from the conversion table shown in FIG. A digital signal processing unit (DSP) 106 stores various conversion tables for gradation correction in a memory, and selects and applies an optimum conversion table to execute gradation correction processing.

Similarly to FIG. 9, the image obtained as a result of the exposure control shown in FIG. 10A (the output image of the A / D converter 105) also has the average luminance [Y _M ] of the subject from the central value of the luminance distribution of the entire image. Control to a large value. Therefore, the operation of setting the average luminance [Y _M ] of the subject at the center of the luminance distribution of the entire image is executed using the conversion table shown in FIG. 10B. The conversion described with reference to FIG. It is the same as the processing.

  In the example shown in FIG. 10, there is a portion where the frequency is very small in the luminance distribution of the image obtained as a result of the exposure control shown in FIG. This is a luminance region 321 shown in FIG. Since it is apparent that assigning a large number of gradations to this area is a waste as a result, a conversion process is performed in which the number of gradations in this luminance area is reduced and a larger number of gradations are assigned to a portion having a higher frequency.

  The conversion table applied to perform such conversion processing is the conversion table shown in FIG. 10B, and FIG. 10B in which the slope of the region corresponding to the luminance region 321 shown in FIG. The conversion table shown below is applied. In the portion where the slope is small, the output luminance range is smaller than the input luminance range, and gradation allocation is less.

In the corrected image converted by the conversion table, as shown in FIG. 10C, the average luminance [Y _M2 ] of the main subject comes to be located at the approximate center of the luminance range of the output image, and The brightness range of the portion with less frequency is narrowed, and an optimum output image suitable for the image is obtained.

  The digital signal processing unit (DSP) 106 executes gradation correction processing to which a conversion table for gradation correction is applied. In addition to performing conversion processing according to an image, gradation correction characteristics (conversion characteristics) ) Is not uniform over the entire screen, but a correction characteristic (conversion characteristic) changed for each pixel or for each block may be applied.

  In this way, the digital signal processing unit (DSP) 106 performs gradation correction according to the luminance level and luminance distribution determined by the exposure control, thereby making the maximum use of the dynamic range of the A / D converter 105 and finally. Brightness reproduction in the image can be optimized.

[3. Simplified configuration for tone correction processing]
As described above, the digital signal processing unit (DSP) 106 performs optimum gradation correction in consideration of the average luminance [Y _M ] and luminance distribution of the main subject. For example, a gradation correction process using a conversion table for gradation correction is executed. However, as described with reference to FIGS. 9 and 10, it is necessary to use different gradation correction characteristics according to the respective luminance distributions in order to realize the optimum conversion processing corresponding to the input image data. It becomes. For example, it is necessary to prepare a large number of gradation correction conversion tables corresponding to various images, select an optimum table from these tables, and perform gradation correction.

However, in order to reduce the size of the imaging apparatus, it is desired that the circuit scale of the digital signal processing circuit (DSP) 106 in the imaging apparatus is realized as small as possible. Therefore, a circuit for executing the gradation correction process, a complicated process, and a configuration that requires a large number of conversion tables are not preferable. That is, it is required to perform quick processing with a simpler configuration. In the following, an image correction processing configuration that meets such mounting requirements will be described. Specifically, gradation correction is not optimized in all cases, but gradation correction characteristics corresponding to some representative subject average luminances [Y _M ] are prepared, and the actual correction target image The gradation correction characteristic to be used is selected according to the subject average luminance [Y _M ]. Hereinafter, three embodiments of the gradation correction processing configuration according to the present invention will be described in order.

(3-1. Example 1 of gradation correction processing configuration)
A first embodiment for simplifying the gradation correction processing will be described with reference to FIGS. As shown in FIG. 11, in this processing example, any one of three types of gradation correction processing is selected and executed. This is gradation correction processing using one of the conversion tables shown in FIGS. 11 (1), (2), and (3). 11 (1), (2), and (3) are the same as the conversion tables shown in FIGS. 9 (b) and 10 (b), the horizontal axis represents the luminance value of the input image, and the vertical axis represents the output. Corresponds to the brightness value of the image. FIG. 11 (4) shows the position of the subject average luminance [Y _M ] of the image to be corrected input to the digital signal processing circuit (DSP) 106 in the imaging apparatus.

In this processing example, as shown in FIG. 11 (4), the luminance level range of the subject average luminance [Y _M ] of the correction target image is divided into three regions (regions 1, 2, and 3), and each region is divided. Representative values Y ₁ , Y ₂ , and Y ₃ are determined, and gradation correction processing corresponding to the levels is executed. The three gradation correction characteristics corresponding to each area are the gradation correction characteristics of the conversion table shown in FIGS. 11 (1), (2), and (3), that is, f ₁ , f ₂ , and f ₃ .

In this processing example, when the luminance level of the subject average luminance [Y _M ] of the correction target image is in the region 1, the pixel value (luminance value) to which the gradation correction characteristic [f ₁ ] of FIG. ) When gradation correction processing as conversion is executed and the luminance level of the subject average luminance [Y _M ] of the correction target image is in the region 2, the gradation correction characteristic [f ₂ ] in FIG. When gradation correction processing as applied pixel value (luminance value) conversion is executed and the luminance level of the subject average luminance [Y _M ] of the correction target image is in the region 3, the gradation shown in FIG. A gradation correction process is performed as a pixel value (luminance value) conversion to which the correction characteristic [f ₃ ] is applied. As described above, one of the three gradation correction characteristics is selected and correction processing is performed. In this case, only three conversion tables need be provided as conversion tables.

As shown in FIG. 11 (4), three regions 1, 2, and 3 are set between the luminance levels Low to High, and representative values Y ₁ , Y ₂ , and Y ₃ corresponding to the regions are determined. Although the range of each region may be equal, in this example, the central portion is set narrow. This is because the subject average luminance [Y _M ] is often near the center, and is rarely near the maximum and minimum values. The representative values Y _{1 to} Y ₃ in each region can be arbitrarily set in each region. In the example shown in the figure, representative values Y _{1 to} Y ₃ of each region are set at positions close to the center value of the luminance level range in each region. That representative value Y ₁ in the area 1 is near the maximum value in the area, the representative value Y ₂ in region 2 near the center value of the region, the representative value Y ₃ in the region 3 are respectively set in the vicinity of the minimum value in the region Yes. The reason for this will be described in the following description of FIG.

  A method for performing gradation correction using the gradation correction characteristics shown in FIG. 11 is shown in FIG. 12A and 12E show the luminance distribution of the output signal of the AD converter 105, and FIG. 12A shows the exposure control process described above with reference to FIGS. Calculate the average luminance and luminance distribution range, determine the optimum average luminance level of the subject based on the calculated subject luminance distribution range and the required number of gradations corresponding to the subject, and set the subject in the captured image to the optimum average luminance level. FIG. 12E is a histogram showing the luminance distribution of an image obtained by performing exposure control according to the conventional method.

FIG. 12A shows a case where the average luminance [Y _M ] of the main subject is included in the area 1 of the area set in FIG. Note that a method similar to the method described below can be applied even when it is included in another region. First, in order to match the average luminance [Y _M ] of the main subject shown in FIG. 12A with a representative value [Y ₁ ] set in advance as a representative value in the region 1, the entire image is multiplied by (Y ₁ / Y _M ). Apply the gain.

FIG. 12B shows a result obtained by multiplying the entire image by a gain of (Y ₁ / Y _M ) times. The gradation correction process is executed by applying the gradation correction characteristic f ₁ corresponding to the region 1 set in FIG. 11 to this. That is, the gradation correction process is executed by the conversion table having the gradation correction characteristic f ₁ shown in FIG. FIG. 12D shows a histogram showing the luminance distribution of the output image obtained as a result of this correction processing.

In the luminance distribution shown in FIG. 12D of the output image thus obtained, the luminance is increased as a whole when the gain (Y ₁ / Y _M ) from FIG. 12A to FIG. 12B is applied. In FIG. 12E, the overexposed portion increases by shifting to higher luminance, and the dynamic range becomes narrower than in the case of performing optimum gradation correction without applying gain. The dynamic range is clearly wider than that. That is, in FIG. 12E, many overexposed pixels exist in the high-luminance portion. However, in the exposure control described above, by performing exposure control that reduces overexposure, shooting is performed as shown in FIG. An image having the luminance distribution shown in FIG. 12A is obtained. In the luminance distribution shown in FIG. 12A, the overexposed portion shown in FIG. 12E is set to have a pixel value that does not become overexposed. In the image of FIG. 12B obtained by applying the gain (Y ₁ / Y _M ) to this image, whiteout does not occur as shown in FIG. 12E, and FIG. In the corrected image of FIG. 12D obtained by executing the gradation correction processing on the image shown in FIG. 12C using the conversion table having the gradation correction characteristic f ₁ shown in FIG. e) compared to e), the dynamic range There the image data can be generated and output.

12A to 12B, that is, when gain (Y ₁ / Y _M ) is applied to the correction target image, if the gain is smaller than 1, the gradation of the main subject is reduced, and the gain When is larger than 1, the overexposed part is increased. Therefore, when the average luminance [Y _M ] of the main subject is smaller than the center value of the luminance distribution of the correction target image, that is, when it is dark, the risk of increasing overexposure is not so great, and the gain (Y ₁ / Y _M ) is set to 1 or more, and the gain (Y ₁ / Y _M ) is set to 1 or less in order to prevent overexposure when the average luminance [Y _M ] of the main subject is larger than the center value, that is, when it is bright. Good to do. That is, it is desirable to set the representative value of each region to a value close to the central value of the entire luminance level range in each region. This is the reason why the representative values Y ₁ , Y ₂ , and Y ₃ of the regions ₁ , ₂ , and ₃ are biased to the center position in FIG. 11.

That is, in FIG. 11, when the average luminance [Y _M ] of the main subject is in the region 1, that is, when the average luminance of the main subject is dark, the gain (Y ₁ / Y _M ) is represented to be 1 or more. When the value Y ₁ is set to the high luminance part in the region 1 and the average luminance [Y _M ] of the main subject is in the region 3, that is, when the average luminance of the main subject is bright, the gain (Y ₁ / Y _M ) Is set to a low luminance portion in the region 3 so that the value is ₃ or less. When the average luminance of the main subject is dark due to the gradation correction, in many cases, the gain (Y ₁ / Y _M ) is set to 1 or more, and a correction process for further increasing the gradation is realized. When the average luminance is bright, in many cases, the gain (Y ₁ / Y _M ) is set to 1 or less, and gradation conversion processing that prevents overexposure is realized. It should be noted that the average luminance [Y _M ] of the main subject is corrected so as to be set at substantially the center position of the luminance distribution of the output image in any of the areas 1, 2 and 3 shown in FIG. .

  A specific tone correction processing sequence according to the first embodiment of the tone correction processing configuration will be described with reference to the flowchart shown in FIG. The digital signal processing unit (DSP) 106 in the imaging apparatus 100 shown in FIG. 2 executes the processing according to the flowchart shown in FIG.

In step S301, it is determined which of the luminance areas 1 to 3 described with reference to FIG. 11 is the average luminance [Y _M ] of the main subject. If YES in step S304, the process advances to step S306.

When the average luminance [Y _M ] of the main subject is in the luminance region 1, the process proceeds to step S302, and in step S302, the image signal to be corrected is multiplied by (Y ₁ / Y _M ) times and the process proceeds to step S303. . This process corresponds to the process from FIG. 12A to FIG. Step S303 In applying the gradation correction characteristic f ₁ to the image signal, by performing the tone correction processing, and ends the process to obtain a corrected image. The gradation correction characteristic f ₁ is a correction characteristic shown in FIG. In this process, gradation correction is performed on the image corresponding to FIG. 12B by applying the conversion table shown in FIG. 12C to obtain a corrected image corresponding to FIG. It corresponds to processing. The corrected image generated in this way is output to, for example, the monitor 107 and the viewfinder 108 shown in FIG.

When the average luminance [Y _M ] of the main subject is in the luminance region 2, the process proceeds to step S304, and in step S304, the image signal to be corrected is multiplied by (Y ₂ / Y _M ) times and the process proceeds to step S305. . Step S305 In applying the gradation correction characteristic f ₂ to the image signal, by performing the tone correction processing, and ends the process to obtain a corrected image. Gradation correction characteristic _{f 2} is a correction characteristic shown in FIG. 11 (2).

When the average luminance [Y _M ] of the main subject is in the luminance region 3, the process proceeds to step S306, and in step S306, the image signal to be corrected is multiplied by (Y ₃ / Y _M ) times and the process proceeds to step S307. . Step S307 In applying the gradation correction characteristic f ₃ into an image signal, by performing the tone correction processing, and ends the process to obtain a corrected image. Gradation correction characteristic _{f 3} is a correction characteristic shown in FIG. 11 (3).

As described above, in this embodiment, the representative value Y _{1 of} each area depends on whether the average luminance [Y _M ] of the main subject is in the luminance area 1, 2 or 3 shown in FIG. 11 (4). , Y ₂ , Y ₃ is applied, and the gradation correction characteristics f ₁ , f ₂ , f ₃ corresponding to each of the regions ₁ , ₂ , ₃ are selectively applied to adjust the gradation. Perform correction. That is, the conversion table to be applied is only the conversion table shown in FIGS. 11 (1), (2), and (3), and the average luminance [Y _M ] of the main subject is the luminance region 1 shown in FIG. 11 (4). Only one of the three patterns of image correction processing is executed depending on whether the digital signal processing unit 2 or 3 is present, and the processing of the digital signal processing unit (DSP) 106 is simplified, enabling rapid processing.

(3-2. Second Embodiment of Tone Correction Processing Configuration)
A second embodiment for simplifying the gradation correction processing will be described with reference to FIG. In this processing example, the step of multiplying the gain in the first embodiment described above is omitted. Also in the present processing example, as in the previous processing example, each region 1, depending on whether the average luminance [Y _M ] of the main subject is in the luminance region 1, 2, 3 shown in FIG. The gradation correction is performed by selectively applying the gradation correction characteristics f ₁ , f ₂ , and f ₃ corresponding to 2 and 3 respectively.

FIG. 14A shows the luminance distribution of the output signal of the AD converter 105. FIG. 14A shows an example in which the average luminance [Y _M ] of the main subject is included in the region 1 of the three regions shown in FIG. 11 (4). Even in the case of being included in other areas, the same method as described below can be applied.

Tone correction is performed by selectively applying, for example, the tone correction characteristics f ₁ , f ₂ , and f ₃ shown in FIGS. 11 (1) to (3) to the image shown in FIG. 14 (a). In this case, the gradation correction characteristic f ₁ shown in FIG. 11 (1) corresponding to the region ₁ is applied. This is the gradation correction characteristic f ₁ shown in FIG.

An output image is obtained by applying the conversion table having the gradation correction characteristic f ₁ shown in FIG. The histogram showing the luminance value distribution of the output image is the data shown in FIG. In the luminance distribution of FIG. 14C obtained in this way, the gradation correction result of the average luminance [Y _M ] of the main subject deviates from the optimum value, but the overexposed portion does not increase as in the first example. The dynamic range of the input can be fully utilized.

The conversion table applied in the second embodiment is a table having different gradation correction characteristics f ₁ , f ₂ , and f ₃ corresponding to the areas 1 to ₃ , and these gradation correction characteristics f ₁ , in generating the _f 2, _{f 3} becomes necessary to determine the representative value _Y 1 to Y ₃ in the regions 1-3 shown in FIG. 11 (4) as a reference value. The representative value Y ₁ to Y ₃ is can be set at an arbitrary position of each region, in order to reduce the deviation of the gradation correction result of Y _M is as in Example 1 described above The representative values Y _{1 to} Y 3 of the areas 1 to ₃ are preferably set near the center of each area. That is, the conversion table having the gradation correction characteristics f ₁ , f ₂ , and f ₃ is preferably set based on the representative values Y _{1 to} Y ₃ set near the center of each region. For example, the representative value Y ₁ has a near one-to-one input-output relationships to Y _3, the farther away the luminance level from representative value Y ₁ to Y _3, and generates a conversion table to be processed mode for compressing the gradation .

Further, in the exposure control described above, the average luminance [Y _M ] of the main subject is expressed by Equation 3, that is,
M / (b−a) ≦ Y _M <T _H / b (Expression 3)
The exposure control parameter is controlled so as to satisfy the above expression 3, and photographing is performed. However, when the values of the representative values Y _{1 to} Y 3 of the respective areas 1 to ₃ are set in advance, the three One of the representative values Y _{1 to} Y ₃ is selected within the range of the above expression 3, and exposure control is performed so as to control the average luminance [Y _M ] of the main subject at or near the selected value. If shooting is performed in this manner, the degree of freedom of exposure control is reduced. However, in the captured image, for example, if the average luminance [Y _M ] of the main subject is set substantially equal to the representative value Y ₁ , FIG. Y _M and Y ₁ shown in) is set to a position substantially overlapping, it is possible to reduce the deviation of the gradation based on the gradation correction in case of executing the applied conversion process a conversion table.

  A specific processing sequence of the second embodiment will be described with reference to a flowchart shown in FIG. The flowchart shown in FIG. 15 is obtained by omitting the steps (steps S302, S304, and S306) for multiplying the gain of the flowchart shown in FIG. 13 described as the processing sequence of the first embodiment. The digital signal processing unit (DSP) 106 in the imaging apparatus 100 shown in FIG. 2 executes the processing according to the flowchart shown in FIG.

In step S351, it is determined which of the luminance areas 1 to 3 described with reference to FIG. 11 is the average luminance [Y _M ] of the main subject. If it is in area 1, it is moved to step S352. If YES in step S353, the process advances to step S354.

When the average luminance [Y _M ] of the main subject is in the luminance region 1, the process proceeds to step S 352, the gradation correction characteristic f ₁ is applied to the image signal, gradation correction processing is executed, and a corrected image is obtained. The process ends. The gradation correction characteristic f ₁ is a correction characteristic shown in FIG. In this process, gradation correction is performed on the image corresponding to FIG. 14A by applying the conversion table shown in FIG. 14B to obtain a corrected image corresponding to FIG. It corresponds to processing. The corrected image generated in this way is output to, for example, the monitor 107 and the viewfinder 108 shown in FIG.

If the average luminance [Y _M ] of the main subject is in the luminance region 2, the process proceeds to step S 353, the gradation correction characteristic f ₂ is applied to the image signal, gradation correction processing is executed, and a corrected image is obtained. The process ends. Gradation correction characteristic _{f 2} is, for example, a correction characteristic shown in FIG. 11 (2).

When the average luminance [Y _M ] of the main subject is in the luminance region 3, the process proceeds to step S354, the gradation correction characteristic f ₃ is applied to the image signal, gradation correction processing is executed, and a corrected image is obtained. The process ends. Gradation correction characteristic _{f 3} is a correction characteristic shown in FIG. 11 (3).

As described above, in this embodiment, each of the regions 1, 2, and 3 depends on whether the average luminance [Y _M ] of the main subject is in any of the luminance regions 1, 2, and 3 shown in FIG. The gradation correction is executed by selectively applying the gradation correction characteristics f ₁ , f ₂ , and f ₃ corresponding to. That is, the conversion table to be applied is only the conversion table shown in FIGS. 11 (1), (2), and (3), for example, and the average luminance [Y _M ] of the main subject is the luminance region 1 shown in FIG. 11 (4). , 2, and 3, only one of the three patterns of image correction processing is executed, and the processing of the digital signal processing unit (DSP) 106 is simplified to enable rapid processing.

(3-3. Third Embodiment of Tone Correction Processing Configuration)
A third embodiment for simplifying the gradation correction processing will be described with reference to FIGS. In the third embodiment of the simplification of the gradation correction processing, the step of applying the gain (FIGS. 12A to 12B) in the first embodiment described above is omitted and, for example, a conversion table is applied. The gradation correction characteristics to be applied for performing the gradation correction processing are the three gradation correction characteristics f ₁ , f ₂ , f corresponding to the luminance regions 1, 2 and 3 described above with reference to FIG. ₃ is further used to generate new gradation correction characteristics different from these gradation correction characteristics and apply the generated new gradation correction characteristics to execute gradation conversion.

For example, when the average luminance [Y _M ] of the main subject is between the representative value [Y ₁ ] of the luminance area ₁ and the representative value [Y ₂ ] of the luminance area 2 described with reference to FIG. gradation correction characteristic f ₁ corresponding to 1 and region _2, f ₂ instead of executing the applied tone corrected during the gradation correction characteristic f _1, f ₂ corresponding to each of the areas 1 and 2 performing tone correction generates a new tone correction characteristic f ₁₂ with the correction characteristic. In the process of generating the new gradation correction characteristic, a characteristic curve is generated so that the output corresponding to the input [Y _M ] is approximately the center value of the luminance distribution of the output image.

The present processing example is the same as the _first and _second embodiments in that the _three gradation correction characteristics f ₁ , f ₂ , and f ₃ corresponding to the luminance regions 1, 2, and 3 are stored in advance. in these three gradation correction characteristic _{f 1,} f 2, _{f 3} only instead of utilizing these three gradation correction characteristic _{f 1,} f 2, further from _{f 3,} a new correction characteristic Generate and apply a correction characteristic curve.

An example of a method for generating a new gradation correction characteristic will be described with reference to FIG. When the average luminance [Y _M ] of the main subject is between the representative value [Y ₁ ] of the luminance region ₁ and the representative value [Y ₂ ] of the luminance region 2 shown in FIG. 11 (4), it corresponds to each region. create a gradation correction characteristic _f 1, the distance of the input value axis direction between _{f 2} is _{(Y M -Y 1) :( Y} 2 curve _{f 12} made on the proportion of -Y _M), the gradation of this curve The gradation correction characteristic is applied to the conversion.

Further, when the average luminance [Y _M ] of the main subject is between the representative value [Y ₂ ] of the luminance region ₂ and the representative value [Y ₃ ] of the luminance region 3 shown in FIG. create distance between the input values axis direction between the corresponding gradation correction characteristic _f 2, _{f 3} is the _{(Y M -Y 2) :( Y} 3 -Y M) curve _{f 23} made on the proportion of the curve The gradation correction characteristic is applied to gradation conversion.

When the average luminance [Y _M ] of the main subject is smaller than the representative value [Y ₁ ] of the luminance region 1 shown in FIG. 11 (4) (shown as Y _M ′ in FIG. 16), the input value = 0 The distance in the input value axis direction between the straight line and the gradation correction characteristic f ₁ is a ratio of (Y _M −0) :( Y ₁ −Y _M ), that is, Y _M : (Y ₁ −Y _M ). A curve f ₀₁ is created, and this curve is used as a gradation correction characteristic applied to gradation conversion.

Similarly, when the average luminance [Y _M ] of the main subject is larger than the representative value [Y ₃ ] of the luminance region 3 shown in FIG. 11 (4), the gradation correction characteristic f ₃ corresponding to the region ₃ and the input value = A curve f _{34 in} which the distance in the input value axis direction between the maximum values Y _MAX is a ratio of (Y _M −Y ₃ ) :( Y _MAX −Y _M ) is created, and this curve is applied to the gradation conversion. It is a tone correction characteristic.

An example in which gradation conversion is performed using the gradation correction characteristics obtained in this way is shown in FIG. FIG. 17A shows a luminance distribution of an image to be corrected, that is, an output image signal of the AD converter 105. FIG. 17A shows a case where the average luminance [Y _M ] of the main subject is smaller than the representative value [Y ₁ ] of the luminance region 1 shown in FIG. 11 (4). In other cases, the process is the same as the process described below.

The gradation correction characteristic f ₁ set corresponding to the representative value [Y ₁ ] of the luminance region 1 shown in FIG. 11 (4) in the correction target image having the luminance distribution shown in FIG. A new gradation correction characteristic f ₀₁ is generated from the 0 line and applied. As described with reference to FIG. 16, the gradation correction characteristic f ₀₁ has a distance in the input value axis direction between the straight line of the input value = 0 and the gradation correction characteristic f ₁ (Y _M −0) :( Y ₁ −Y _M ), that is, a curve f ₀₁ that has a ratio of Y _M : (Y ₁ −Y _M ). This curve is a gradation correction characteristic applied to gradation conversion. This gradation correction characteristic f ₀₁ becomes a curve shown in FIG.

A luminance distribution histogram of an image obtained by applying the newly generated gradation correction characteristic f ₀₁ and executing the gradation conversion processing of the image having the luminance distribution shown in FIG. 17A is shown in FIG. It becomes. In the luminance distribution of FIG. 17C obtained in this way, the overexposed portion does not increase as in the first example, so that the input dynamic range can be fully utilized, and the Y _{M value} as in the second example can be obtained. The gradation correction result does not deviate from the optimum value.

  Here, a specific processing sequence of the third example will be described with reference to a flowchart shown in FIG. The digital signal processing unit (DSP) 106 in the imaging apparatus 100 shown in FIG. 2 executes the processing according to the flowchart shown in FIG.

In step S401, the average luminance of the main object _{[Y M],} determines the magnitude of 11 preset representative luminance values corresponding to the luminance area 1, 2, 3 shown in (4) _Y 1 ~Y ₃ .

If Y _M ≦ _{Y 1} in step _S402, if _Y 1 <Y _M ≦ Y ₂ in step _S404, if _Y 2 <Y _M ≦ Y ₃ in step _S406, if Y 3 _{<Y M} The process proceeds to step S408.

When the average luminance [Y _M ] of the main subject is less than or equal to the preset representative luminance value Y ₁ corresponding to the luminance area 1 shown in FIG. 11 (4), that is, Y _M ≦ Y ₁ , the process proceeds to step S402. move on. At step S402, and generates a new tone correction characteristic _{f 01} between the straight line and the gradation correction characteristic _{f 1} of the input value = 0 the process proceeds to step S403. As described with reference to FIG. 16, the gradation correction characteristic f ₀₁ generated in step S403 has a distance in the input value axis direction between the straight line of the input value = 0 and the gradation correction characteristic f ₁ (Y _M −0): (Y ₁ −Y _M ), that is, a curve f ₀₁ that has a ratio of Y _M : (Y ₁ −Y _M ).

In step S403, by applying the gradation correction characteristic _{f 01} generated in step S402, it executes a luminance value conversion processing of the input image. This process is the process described with reference to FIG.

Further, the average luminance [Y _M ] of the main subject is set to a preset representative luminance value Y ₁ corresponding to the luminance area 1 shown in FIG. 11 (4) and a preset representative luminance value corresponding to the luminance area 2. If it is between Y ₂ , that is, if Y ₁ <Y _M ≦ Y ₂ , the process proceeds to step S404. In step S404, the process proceeds to step S405 and generates a new tone correction characteristic _{f 12} between the gradation correction characteristic _{f 1} and the gradation correction characteristic _{f 2.} As described with reference to FIG. 16, the gradation correction characteristic f ₁₂ generated in step S404 has a distance in the input value axis direction between the gradation correction characteristics f ₁ and f ₂ corresponding to each region (Y _M -Y ₁₎ is a curve _{f 12} made on the proportion of _:( Y 2 -Y _M).

In step S405, by applying the gradation correction characteristic _{f 12} generated in step S404, it executes a luminance value conversion processing of the input image.

In addition, the average luminance [Y _M ] of the main subject is set to a predetermined representative luminance value Y ₂ corresponding to the luminance region 2 shown in FIG. 11 (4) and a predetermined representative luminance value corresponding to the luminance region 3. If it is between Y ₃ , that is, if Y ₂ <Y _M ≦ Y ₃ , the process proceeds to step S406. In step S406, the process proceeds to step S407 to generate new gradation correction characteristic _{f 23} between the gradation correction characteristic _{f 2} and the gradation correction characteristic _{f 3.} As described with reference to FIG. 16, the gradation correction characteristic f ₂₃ generated in step S406 has a distance in the input value axis direction between the gradation correction characteristics f ₂ and f ₃ corresponding to each region (Y a _M -Y _{2) :(} Y 3 curve _{f 23} made on the proportion of -Y _M).

In step S407, by applying the gradation correction characteristic _{f 23} generated in step S406, it executes a luminance value conversion processing of the input image.

Further, when the average luminance [Y _M ] of the main subject is larger than the preset representative luminance value Y ₃ corresponding to the luminance area 3 shown in FIG. 11 (4), that is, Y ₃ <Y _M. The process proceeds to step S408. In step S408, the process proceeds to step S409 and generates a new tone correction characteristic _{f 34} between the straight line of the input value = maximum value gradation correction characteristic _{f 3} (MAX). As described with reference to FIG. 16, the gradation correction characteristic f ₃₄ generated in step S408 is the input value axis direction between the gradation correction characteristic f ₃ corresponding to the region ₃ and the input value = maximum value Y _MAX. Is a curve f ₃₄ having a ratio of (Y _M −Y ₃ ) :( Y _MAX −Y _M ).

At step S409, the by applying the gradation correction characteristic _{f 34} generated in step S408, it executes a luminance value conversion processing of the input image.

  In the first to third embodiments described above, the case where the luminance level range is divided into three regions has been described. However, the number of divided regions is not limited to three, and various division numbers can be set. For example, by increasing the number of divisions, optimal conversion processing can be performed without shifting the characteristics of the original image. In the above-described embodiment, the gradation correction characteristics corresponding to each area have been described as having a one-to-one correspondence. However, a plurality of applicable gradation correction characteristics are associated with one area and are processed. A configuration may be adopted in which conversion is appropriately selected according to the characteristics of the image. For example, if the gradation correction characteristics to be applied are selected according to the luminance distribution of the subject, further optimal conversion can be performed.

  As described in the first to third embodiments, the luminance in the final image is obtained while maximizing the dynamic range of the AD converter 105 by performing gradation correction according to the luminance level and luminance distribution determined by the exposure control. The reproduction can be optimized. Further, by applying simplification of the gradation correction process, the digital signal processing circuit (DSP) 106 can be realized with a smaller circuit scale.

[4. Configuration of image processing apparatus that executes image correction]
The value of the average luminance [Y _M ] of the main subject determined by the exposure control is also recorded in the RAW image recorded in the RAW image recording mode. When developing a RAW image by applying a developing program of an image reproducing device or a computer, an optimum luminance reproduction image is obtained by performing gradation correction in accordance with the value of the average luminance [Y _M ] of the main subject. Is obtained. For example, in an image processing apparatus such as a PC, correction similar to gradation correction in the digital signal processing unit (DSP) 106 can be executed. In this gradation correction processing, the above-mentioned [3. The simplified processing corresponding to each of the first to third embodiments described in the item “About simplified configuration for realizing gradation correction processing” can be applied. It is also possible to perform image analysis in an image reproduction apparatus or a development program of a computer, and to perform further optimum gradation correction.

  As an example of applying the exposure control and gradation correction described above, the following system can be realized. The exposure control described above and the simplified gradation correction are applied to the imaging apparatus, and the optimum gradation correction that is not simplified is applied to the RAW development program. As a result, it is possible to realize an imaging apparatus that can capture an image with a wider dynamic range than the conventional one, while minimizing an increase in circuit scale.

  On the other hand, since the RAW image file obtained by the image pickup device is not affected by the simplification of gradation correction, it is possible to develop a wider dynamic range by applying more optimal gradation correction characteristics with the RAW development program. And an image that achieves optimum luminance reproduction.

This average brightness of the main subject in the above description as Y _M but has to perform the exposure control and tone correction so as to optimize, other values may perform the process defined as Y _M. For example, Y _M may be used as the spot-like luminance of a portion that is particularly important.

  Note that the digital signal processing circuit (DSP) 106, the image reproduction apparatus for developing the RAW recorded image data, and the development program of the computer conventionally include gradation correction such as gamma correction in addition to the gradation correction. The gradation correction characteristics are determined in consideration of these gradation correction characteristics.

  For example, when simple gradation correction based on an input image is executed in an image processing apparatus such as a PC, a plurality of gradation corrections set corresponding to the luminance regions described with reference to FIGS. A conversion table having characteristics is stored in a memory, and gradation conversion processing is performed by selectively applying these conversion tables.

  For example, an image processing apparatus such as a PC has an image signal processing unit that executes image correction processing, and the image signal processing unit selects gradation correction characteristics to be applied according to the average luminance of the main subject of the correction target image. Then, a correction image is generated by executing a gradation correction process using the selected gradation correction characteristic. That is, the image signal processing unit holds the gradation correction characteristic data corresponding to the luminance region divided according to the luminance as described above with reference to FIG. 11, and includes the subject average luminance of the correction target image. A luminance area is determined, and a correction image is generated by executing a gradation correction process based on a gradation correction characteristic set corresponding to the luminance area including the subject average luminance of the correction target image. For example, as described above with reference to FIGS. 11 to 18, a gradation correction process is performed in which the average luminance level of the subject of the correction target image is set to approximately the center of the luminance distribution of the correction image.

The image signal processing unit performs a correction process to which any of the above-described [Embodiments 1 to 3 of the gradation correction process configuration] is applied. When the processing according to the first embodiment is executed, the image signal processing unit performs representative luminance values Y _n (where 1 ≦ n ≦ k) corresponding to each of one or more k luminance regions divided according to luminance. And a gain (Y _n / Y _M ) based on the average luminance Y _M of the correction target image is multiplied by the correction target image, and then the gradation generated based on the representative luminance value Y _n corresponding to the luminance region A gradation correction process using correction characteristics is executed. When executing the process according to the second embodiment, the process without the process of multiplying the gain is executed.

Further, when the process according to the third embodiment of the gradation correction process configuration described above is executed, the following process is performed. The image signal processing unit of the image processing apparatus has a gradation correction characteristic f _n generated based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of k luminance regions divided according to luminance. And two gradation correction characteristics f _n corresponding to two representative luminance values Y _n and Y _m (where 1 ≦ m ≦ k) sandwiching a luminance level where the subject average luminance Y _M of the correction target image exists. generating new gradation correction characteristic f _nm based on the f _m, it executes the generated tone correction processing applying gradation compensation characteristic f _nm was. When performing this processing, the image signal processing unit, as described above with reference to FIG. 16, has two representative luminance values Y _n sandwiching the luminance level where the subject average luminance Y _M of the correction target image exists. In the input / output value graph corresponding to the two gradation correction characteristics f _n and f _m corresponding to Y _m and Y _m , the distance in the input value axis direction is expressed as (Y _M −Y _n ) :( Y _m −Y _M ). calculating a curved line dividing the percentage, by setting the curve as a new gradation correction characteristic f _nm, it executes the tone correction process according to the gradation correction characteristic f _nm set.

Incidentally, in this process, the luminance level of the subject the average luminance Y _M of the correction target image is present, if the representative luminance value Y ₁ below corresponding to the preset minimum luminance regions, corresponding to the representative luminance value Y ₁ Based on the input / output value graph corresponding to the gradation correction characteristic f ₁ and the linear data with the input value = 0, a curve divided into the ratio of Y _M : (Y ₁ −Y _M ) is calculated, and the curve set as a new gradation correction characteristic f _01, executes the tone correction process according to the gradation correction characteristic f ₀₁ set, the subject average luminance Y luminance _{level M} is present in the correction target image, advance If the set is greater than the maximum brightness corresponding to the area representative luminance values Y _k, the linear data input and output value graph, an input value = Y _MAX corresponding to the gradation correction characteristic f _k corresponding to the representative luminance value Y _k And (Y _M − Y _k) calculates _{:( Y} MAX curved line dividing the percentage of -Y _M), by setting the curve as a new gradation correction characteristic _{f kk + 1,} was applied to the gradation correction characteristic _{f kk + 1} set gradation Execute correction processing.

  In the imaging apparatus 100 shown in FIG. 2, the output data of the A / D converter 105 is data corresponding to the color filter of the CCD 102. For example, in the case of the primary color filter, it is composed of RGB signals instead of luminance signals. This method can be applied by generating an appropriate signal from For example, the exposure control can be applied to a luminance signal synthesized from RGB signals. Alternatively, exposure control can be applied using the G signal instead of the luminance signal.

  Although the above-described embodiment is a digital still camera, the present invention can also be applied to a digital video camera. The image pickup device is a CCD, but other image pickup devices such as a CMOS may be used.

  In the imaging apparatus or the image processing apparatus according to an embodiment of the present invention, a circuit scale is obtained because a limited number of gradation correction characteristic data is applied and optimum gradation correction is performed by simplified processing. It is possible to generate and output a high-quality image having a wider dynamic range than before, while minimizing the increase in image quality. For example, since the RAW image obtained by the imaging apparatus is not affected by the simplification of the gradation correction characteristics, it is possible to obtain a better image by applying more optimal gradation correction characteristics in the RAW development program. I can do it.

  In the imaging device according to an embodiment of the present invention, a luminance control range in which the gradation of the subject can be sufficiently obtained is obtained from the average luminance of the main subject and the luminance distribution range, and overexposure and blackout are minimized within the range. By performing exposure control in such a manner and further performing gradation correction based on the exposure control result information in the digital signal processing circuit or RAW development processing program, it is possible to optimize the luminance reproduction in the final image. By setting the brightness control range in this way, it is possible to prevent excessive correction of exposure and the like and to prevent erroneous control of exposure control. In exposure control, the first is to make the best use of the dynamic range of the image sensor. In order to correct the brightness reproduction of the final image through signal processing, images with a wider dynamic range than before can be captured. I can do it.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiments without departing from the gist of the present invention. In other words, the present invention has been disclosed in the form of exemplification, and should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims should be taken into consideration.

  The series of processing described in the specification can be executed by hardware, software, or a combined configuration of both. When executing processing by software, the program recording the processing sequence is installed in a memory in a computer incorporated in dedicated hardware and executed, or the program is executed on a general-purpose computer capable of executing various processing. It can be installed and run.

  For example, the program can be recorded in advance on a hard disk or ROM (Read Only Memory) as a recording medium. Alternatively, the program is temporarily or permanently stored on a removable recording medium such as a flexible disk, a CD-ROM (Compact Disc Read Only Memory), an MO (Magneto optical) disk, a DVD (Digital Versatile Disc), a magnetic disk, or a semiconductor memory. It can be stored (recorded). Such a removable recording medium can be provided as so-called package software.

  The program is installed on the computer from the removable recording medium as described above, or is wirelessly transferred from the download site to the computer, or is wired to the computer via a network such as a LAN (Local Area Network) or the Internet. The computer can receive the program transferred in this manner and install it on a recording medium such as a built-in hard disk.

  Note that the various processes described in the specification are not only executed in time series according to the description, but may be executed in parallel or individually according to the processing capability of the apparatus that executes the processes or as necessary. Further, in this specification, the system is a logical set configuration of a plurality of devices, and the devices of each configuration are not limited to being in the same casing.

  As described above, according to the configuration of one embodiment of the present invention, for example, a configuration for correcting an image captured by executing exposure control such that a main subject in the captured image has an optimum average luminance level. The tone correction is performed by selecting data corresponding to the main subject brightness from the limited number of tone correction characteristic data. Specifically, for example, the gradation correction characteristic set corresponding to the area including the average luminance of the main subject of the photographed image is selectively applied to perform the correction process. With this configuration, for example, an optimal image correction according to an image can be performed without complicating the circuit scale of a digital signal processing unit (DSP) in the imaging device, and an imaging device that performs correction processing quickly and efficiently, An image processing apparatus can be provided.

It is a figure explaining the external appearance structural example of the imaging device which concerns on one Example of this invention. It is a figure explaining the hardware structural example of the imaging device which concerns on one Example of this invention. It is a figure explaining an example of the histogram (frequency distribution) which shows the relationship between the luminance value corresponding to an image and a subject, and luminance distribution in sample image data. It is a figure explaining the example of a setting of the number of gradations required for object expression. It is a figure which shows the flowchart explaining the specific process sequence of the exposure control process which the imaging device which concerns on one Example of this invention performs. A processing sequence in which the exposure control parameter is changed from the overexposure area [S _H ] and the underexposure area [S _L ] executed by the imaging apparatus according to an embodiment of the present invention and stored in the internal memory 122 of the control unit 120 will be described. It is a figure which shows the flowchart to do. It is a figure which compares and verifies the image image | photographed by the conventional exposure control in case the dynamic range of a to-be-photographed object is small, and the image image | photographed applying the exposure control of this invention. It is a figure which compares and verifies the image image | photographed by the conventional exposure control in case the dynamic range of a to-be-photographed object is large, and the image image | photographed by applying the exposure control of this invention. It is a figure explaining the gradation correction example which correct | amends the average brightness | luminance of a to-be-photographed object to the center of a luminance level in a digital signal processing part (DSP). It is a figure explaining the example of a gradation correction performed in a digital signal processing part (DSP). It is a figure explaining the process of the 1st Example of simplification of a gradation correction process. It is a figure explaining the process of the 1st Example of simplification of a gradation correction process. It is a figure which shows the flowchart explaining the process sequence of 1st Example of simplification of a gradation correction process. It is a figure explaining the process of the 2nd Example of simplification of a gradation correction process. It is a figure which shows the flowchart explaining the process sequence of the 2nd Example of simplification of a gradation correction process. It is a figure explaining the process of the 3rd Example of simplification of a gradation correction process. It is a figure explaining the process of the 3rd Example of simplification of a gradation correction process. It is a figure which shows the flowchart explaining the process sequence of the 3rd Example of simplification of a gradation correction process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Imaging device 11 Power switch 12 Release switch 13 Monitor 14 Imager 15 Operation button 16 Viewfinder 17 Focus lens 18 Zoom lens 19 Mode dial 21 Focus lens motor (M1)
22 Zoom lens motor (M2)
Reference Signs List 25 Aperture blade 26 Aperture drive unit 31 Strobe light emitting means 100 Imaging device 101 Lens unit 102 Imaging element 103 Timing generator (TA)
104 Analog Signal Processing Unit 105 A / D Converter 106 Digital Signal Processing Unit 107 Monitor 108 Viewfinder 109 Recording Device 110 Detection Unit 115 Operation Unit 116 Shutter Determination Unit 120 System Controller 121 CPU
122 Memory 131 Zoom Lens 132 Focus Lens 133 Aperture Blade 134 Aperture Blade Drive Unit

Claims (31)

In an imaging device that performs image shooting processing,
A digital signal processing unit that executes correction processing of a captured image in the imaging apparatus;
The digital signal processor is
An imaging apparatus having a configuration for selecting a gradation correction characteristic to be applied in accordance with the average luminance of a photographed image and generating a correction image by executing a gradation correction process using the selected gradation correction characteristic . The digital signal processor is
The gradation correction characteristic data corresponding to the brightness area divided according to the brightness is retained, the brightness area including the average brightness of the subject of the photographed image is determined, and the brightness area including the average brightness of the subject of the photographed image is determined. The image pickup apparatus according to claim 1, wherein the image pickup apparatus has a configuration for generating a corrected image by executing a gradation correction process using a set gradation correction characteristic. The imaging device further includes:
A control unit for performing automatic exposure control;
The controller is
The average luminance and luminance distribution range of the subject are calculated based on the image data acquired by the imaging device, and the optimum average luminance level of the subject is calculated based on the calculated subject luminance distribution range and the required number of gradations corresponding to the subject. And performing exposure control so that the subject in the captured image has the optimum average luminance level,
The digital signal processor is
The imaging apparatus according to claim 1, wherein the imaging apparatus is configured to perform correction processing of a captured image based on exposure control of the control unit. The controller is
The main subject is determined from the acquired image data of the imaging device, the average luminance and the luminance distribution range of the main subject are calculated, and the main subject is calculated based on the calculated main subject luminance distribution range and the required number of gradations corresponding to the main subject. Is determined to determine the optimum average brightness level, and exposure control is performed so that the main subject in the captured image has the optimum average brightness level.
The digital signal processor is
The gradation correction characteristic to be applied is selected according to the average luminance of the main subject included in the photographed image, and the correction image is generated by executing the gradation correction process using the selected gradation correction characteristic. The imaging apparatus according to claim 3. The controller is
Average brightness of subject = Y _M ,
Luminance distribution range of subject = a × Y _{M to} b × Y _M (0 ≦ a ≦ 1, 1 ≦ b),
The overexposure threshold, which is the brightness threshold (threshold level) for determining overexposure,
Overexposure threshold _{= T} H,
Necessary number of gradations for subject = M,
When
M / (b−a) ≦ Y _M <T _H / b... Formula A,
So as to satisfy the above formulas A, a configuration of determining the optimal average luminance level Y _M of the object, executes exposure control so that the subject in the captured image has the best average luminance level Y _M,
The digital signal processor is
The imaging apparatus according to claim 3, wherein the imaging apparatus is configured to perform a correction process of a captured image based on exposure control of the control unit. The controller is
Calculating an overexposure area [S _H ], which is an area of an overexposure pixel, and an underexposure area [S _L ], which is an area of an underexposure pixel, included in the acquired image data of the imaging device;
Exposure control for setting the optimum average luminance level [Y _M ] so that the formula A is satisfied and the sum of the overexposure area [S _H ] and the underexposure area [S _L ] is minimized. The imaging apparatus according to claim 5, wherein the imaging apparatus is configured to perform. The digital signal processor is
The imaging apparatus according to claim 1, wherein a gradation correction process is performed to set an average luminance level of a subject of a captured image to an optimum value of a luminance distribution of the corrected image. The digital signal processor is
A gain (Y _n / Y) based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of one or more k luminance regions divided according to luminance and the subject average luminance Y _M of the captured image. after multiplied by _M) to the captured image, claim characterized by having a configuration that executes gradation correction process by the gradation correction characteristic produced based on the representative luminance value Y _n corresponding to the luminance area 1 The imaging device described in 1. The digital signal processor is
The gradation correction characteristic f _n generated based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of the k luminance regions divided according to the luminance is held, and the subject average luminance of the photographed image New gradation correction based on two gradation correction characteristics f _n and f _m corresponding to two representative luminance values Y _n and Y _m (where 1 ≦ m ≦ k) sandwiching a luminance level where Y _M exists The imaging apparatus according to claim 1, wherein the imaging device has a configuration in which a characteristic f _nm is generated and a gradation correction process using the generated gradation correction characteristic f _nm is executed. The digital signal processor is
In an input / output value graph corresponding to two gradation correction characteristics f _n and f _m corresponding to two representative luminance values Y _n and Y _m sandwiching a luminance level where the subject average luminance Y _M of the photographed image exists A curve that divides the distance in the value axis direction into a ratio of (Y _M −Y _n ) :( Y _m −Y _M ) is calculated, and the curve is set as a new gradation correction characteristic f _nm. The imaging apparatus according to claim 9, wherein the imaging apparatus has a configuration for executing gradation correction processing to which the tone correction characteristic f _nm is applied. The digital signal processor is
Luminance level object average luminance Y _M of the captured image exists, if it is the representative luminance value Y ₁ below corresponds to a preset lowest luminance area, the gradation correction characteristic f ₁ corresponding to the representative luminance value Y ₁ Based on the corresponding input / output value graph and the straight line data with the input value = 0, a curve that is divided into a ratio of Y _M : (Y ₁ −Y _M ) is calculated, and the curve is converted into a new gradation correction characteristic. is set as f _01, the imaging apparatus according to claim 9, characterized in that it has a structure for executing the tone correction process according to the gradation correction characteristic f ₀₁ set. The digital signal processor is
If the brightness level of the subject the average luminance Y _M of the photographed image is present it is greater than the representative luminance value Y _k corresponding to preset maximum brightness regions, corresponding to the gradation correction characteristic f _k corresponding to the representative luminance value Y _k Based on the input / output value graph to be calculated and the straight line data with the input value = Y _MAX , a curve that is divided into the ratio of (Y _M −Y _k ) :( Y _MAX −Y _M ) is calculated, and the curve is newly set. gradation correction characteristic is set as f _{kk + 1,} the imaging apparatus according to claim 9, characterized in that it has a structure for executing the applied tone correction processing gradation correction characteristic f _{kk + 1} set. An image processing device,
An image signal processing unit for performing image correction processing;
The image signal processor is
An image having a configuration in which a gradation correction characteristic to be applied is selected according to the average luminance of the object to be corrected, and a correction image is generated by executing a gradation correction process using the selected gradation correction characteristic. Processing equipment. The image signal processor is
Stores tone correction characteristic data corresponding to the luminance area divided according to the luminance, determines the luminance area that includes the average luminance of the subject of the correction target image, and corresponds to the luminance region that includes the average luminance of the subject of the correction target image The image processing apparatus according to claim 13, wherein the correction processing is generated by executing a gradation correction process using the gradation correction characteristic set as described above. The image signal processor is
Selecting a gradation correction characteristic to be applied according to the average luminance of the main subject included in the correction target image, and performing a gradation correction process using the selected gradation correction characteristic to generate a corrected image. The image processing apparatus according to claim 13, characterized in that: The image signal processor is
The image processing apparatus according to claim 13, wherein gradation correction processing is performed to set an average luminance level of a subject of the correction target image to an optimum value of the luminance distribution of the correction image. The image signal processor is
A gain (Y _n //) based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of one or more k luminance regions divided according to luminance and the subject average luminance Y _M of the correction target image. Y _M ) is multiplied by a correction target image, and then gradation correction processing is performed using gradation correction characteristics generated with reference to a representative luminance value Y _n corresponding to the luminance region. Item 14. The image processing apparatus according to Item 13. The image signal processor is
The gradation correction characteristic f _n generated based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of the k luminance regions divided according to the luminance is held, and the subject average of the correction target image New gradation based on two gradation correction characteristics f _n and f _m corresponding to two representative luminance values Y _n and Y _m (where 1 ≦ m ≦ k) sandwiching a luminance level where luminance Y _M exists. the image processing apparatus according to claim 13 in which the correction characteristic f _nm generates, characterized in that it has a configuration for executing the generated tone correction processing applying gradation compensation characteristic f _nm was. The image signal processor is
In the input / output value graph corresponding to the two gradation correction characteristics f _n and f _m corresponding to the two representative luminance values Y _n and Y _m across the luminance level where the subject average luminance Y _M of the correction target image exists, A curve that divides the distance in the input value axis direction into a ratio of (Y _M −Y _n ) :( Y _m −Y _M ) is calculated, and the curve is set as a new gradation correction characteristic f _nm . The image processing apparatus according to claim 18, wherein the image processing apparatus has a configuration for executing a gradation correction process to which a gradation correction characteristic f _nm is applied. The image signal processor is
When the correction object average luminance Y luminance _{level M} is present in the target image is representative luminance value Y ₁ below corresponds to a preset lowest luminance area, the gradation correction characteristic f ₁ corresponding to the representative luminance value Y ₁ Based on the input / output value graph corresponding to, and the straight line data with the input value = 0, a curve divided into the ratio of Y _M : (Y ₁ −Y _M ) is calculated, and the curve is subjected to new gradation correction. set as characteristics f _01, the image processing apparatus according to claim 18, characterized in that it has a structure for executing the tone correction process according to the gradation correction characteristic f ₀₁ set. The image signal processor is
Subject the average luminance Y luminance _{level M} is present in the correction target image is greater than the representative luminance value Y _k corresponding to a preset maximum luminance regions, the gradation correction characteristic f _k corresponding to the representative luminance value Y _k Based on the corresponding input / output value graph and the straight line data with the input value = Y _MAX , a curve that is divided into the ratio of (Y _M −Y _k ) :( Y _MAX −Y _M ) is calculated. is set as a new gradation correction characteristic f _{kk + 1,} the image processing apparatus according to claim 18, characterized in that it has a structure for executing the tone correction process according to the gradation correction characteristic f _{kk + 1} set. An image processing method for executing image correction processing in an image processing apparatus,
The image signal processor
A gradation correction characteristic to be applied is selected according to the subject average luminance of the correction target image, and a gradation correction process using the selected gradation correction characteristic is executed, and an image correction step for generating a corrected image is executed. An image processing method. The image correction step includes
The gradation correction characteristic data corresponding to the brightness area divided according to the brightness is retained, the brightness area including the average brightness of the subject of the correction target image is determined, and the brightness area including the average brightness of the subject of the photographed image is supported. 23. The image processing method according to claim 22, wherein the corrected image is generated by executing a gradation correction process using the gradation correction characteristic set in the step. The image correction step includes
Selecting a gradation correction characteristic to be applied according to the average luminance of the main subject included in the correction target image, and executing a gradation correction process using the selected gradation correction characteristic to generate a corrected image. The image processing method according to claim 22, characterized in that: The image correction step includes
23. The image processing method according to claim 22, wherein the image processing method is a step of executing gradation correction processing for setting an average luminance level of a subject of the correction target image to an optimum value of the luminance distribution of the correction image. The image correction step includes
A gain (Y _n //) based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of one or more k luminance regions divided according to luminance and the subject average luminance Y _M of the correction target image. Y _M ) is multiplied by the correction target image, and then gradation correction processing is performed using gradation correction characteristics generated with reference to a representative luminance value Y _n corresponding to the luminance region. Item 22. The image processing method according to Item 22. The image correction step includes
The gradation correction characteristic f _n generated based on the representative luminance value Y _n (where 1 ≦ n ≦ k) corresponding to each of the k luminance regions divided according to the luminance is held, and the subject average of the correction target image New gradation based on two gradation correction characteristics f _n and f _m corresponding to two representative luminance values Y _n and Y _m (where 1 ≦ m ≦ k) sandwiching a luminance level where luminance Y _M exists. the image processing method according to claim 22, wherein the correction characteristic f _nm generates a step of performing the generated gradation correction characteristic tone correction processing applying f _nm. The image correction step includes
In the input / output value graph corresponding to the two gradation correction characteristics f _n and f _m corresponding to the two representative luminance values Y _n and Y _m across the luminance level where the subject average luminance Y _M of the correction target image exists, A curve that divides the distance in the input value axis direction into a ratio of (Y _M −Y _n ) :( Y _m −Y _M ) is calculated, and the curve is set as a new gradation correction characteristic f _nm . 28. The image processing method according to claim 27, wherein the image processing method is a step of executing a gradation correction process to which a gradation correction characteristic _fnm is applied. The image correction step includes
When the correction object average luminance Y luminance _{level M} is present in the target image is representative luminance value Y ₁ below corresponds to a preset lowest luminance area, the gradation correction characteristic f ₁ corresponding to the representative luminance value Y ₁ Based on the input / output value graph corresponding to, and the straight line data with the input value = 0, a curve divided into the ratio of Y _M : (Y ₁ −Y _M ) is calculated, and the curve is subjected to new gradation correction. set as characteristics f _01, an image processing method according to claim 27, characterized in that the step of performing a tone correction processing using the gradation correction characteristic f ₀₁ set. The image correction step includes
Subject the average luminance Y luminance _{level M} is present in the correction target image is greater than the representative luminance value Y _k corresponding to a preset maximum luminance regions, the gradation correction characteristic f _k corresponding to the representative luminance value Y _k Based on the corresponding input / output value graph and the straight line data with the input value = Y _MAX , a curve that is divided into the ratio of (Y _M −Y _k ) :( Y _MAX −Y _M ) is calculated. 28. The image processing method according to claim 27, wherein the image processing method is a step of executing gradation correction processing that is set as a new gradation correction characteristic _{fkk + 1} and to which the set gradation correction characteristic _{fkk + 1} is applied. A computer program for executing image correction processing in an image processing apparatus,
Image correction that causes the image signal processing unit to select a gradation correction characteristic to be applied in accordance with the average luminance of the subject of the correction target image, and to execute a gradation correction process using the selected gradation correction characteristic to generate a corrected image. A computer program for executing a step.