JP5251203B2 - Image processing apparatus and image processing program - Google Patents

Description

  The present invention relates to an image processing technique for correcting peripheral dimming.

In recent years, electronic cameras using solid-state image sensors have been widely used. However, due to the characteristics of the photographic lens used in the electronic camera, there is a problem of peripheral dimming in which the amount of light at the peripheral portion falls concentrically with respect to the center of the optical axis of the captured image. This peripheral dimming changes depending on the incident angle of light incident on the solid-state image sensor, the diameters of the front lens and rear lens of the photographing lens, the aperture diameter, the distance from the lens and the aperture to the image sensor, and the like. In particular, in the case of a zoom lens, the peripheral dimming state differs depending on the zoom position, and it is difficult to eliminate the peripheral dimming only by the lens design. Therefore, in order to eliminate unevenness in the amount of light due to peripheral dimming, a technique for correcting the unevenness in the amount of light by performing image processing after shooting is known. For example, a method may be considered in which a plurality of correction tables are stored in advance in the memory of the electronic camera for each shooting condition for the shooting lens to be used, and the peripheral dimming is corrected by reading the correction table corresponding to the shooting condition during shooting. (For example, refer to Patent Document 1).
JP 2006-270919 A

  However, the conventional peripheral dimming correction technology needs to have a correction table corresponding to the shooting lens to be used for each shooting lens, and when a new shooting lens is used, the correction table of the electronic camera has to be updated. .

  Although it is conceivable to perform processing for calculating the peripheral light attenuation shape corresponding to the new photographing lens in the electronic camera, it is difficult to perform processing for calculating the complex light attenuation shape in the electronic camera. Alternatively, it may be possible to simplify the processing by using a correction table for each of various peripheral dimming shapes, but there is a problem that the memory capacity increases.

  An object of the present invention is to provide an image processing apparatus and an image processing program capable of performing peripheral light attenuation correction at high speed without the need for performing complicated calculations.

An image processing apparatus according to the present invention is an image processing apparatus that performs peripheral dimming correction of an image shot through a lens optical system, and each image is based on a plurality of shooting conditions including lens information of the lens optical system. A storage unit that stores in advance a coefficient of a prediction formula for calculating a predicted value of peripheral dimming shape information of the lens optical system at a high level for each of the plurality of shooting conditions, and a plurality of lens information including lens information at the time of image shooting An imaging condition acquisition unit for acquiring the imaging condition, and a coefficient of the prediction formula corresponding to each imaging condition acquired by the imaging condition acquisition unit is read from the storage unit, and peripheral dimming is performed for each image height by the prediction formula Any one of an image correction unit that obtains a gain value for correcting the image and corrects an image photographed through the lens optical system based on the gain value, and a plurality of correction degrees with different degrees of correction of the peripheral dimming shape. To select one It has a section, a vignetting compensation gain table creation unit for creating a vignetting compensation gain table from the gain value based on the correction degree selected by the operation unit, the image correcting unit, the peripheral An image captured through the lens optical system is corrected with a correction gain of a dimming correction gain table.

Preferably, the coefficient of the prediction formula stored in the storage unit is calculated in advance by multivariate analysis using actual measurement values measured for a plurality of photographing conditions including lens information of a plurality of lens optical systems. It is characterized by that.
In particular, the coefficient of the prediction formula stored in the storage unit is stored in advance in the storage unit in association with the shooting conditions, image data shot by a plurality of shooting conditions including lens information of a plurality of lens optical systems. A process for reading out the image data from the storage unit and actually measuring an output level for each image height for each photographing condition, and multivariate analysis using actually measured values for a plurality of photographing conditions for each image height. It is obtained by a learning process including a process for calculating a coefficient, and is stored in the storage unit for each image height as a coefficient table.

  Preferably, the multivariate analysis is a multiple regression analysis.

  Preferably, the prediction formula is a linear formula.

  Preferably, the subject luminance is calculated using the image corrected by the image correction unit.

An image processing program according to the present invention is an image processing program for performing peripheral dimming correction of an image shot through a lens optical system, and each image based on a plurality of shooting conditions including lens information of the lens optical system. A storage procedure for pre-recording a coefficient of a prediction formula for calculating a predicted value of peripheral dimming shape information of the lens optical system at a high level in correspondence with each of the plurality of shooting conditions, and lens information at the time of image shooting An imaging condition acquisition procedure for acquiring a plurality of imaging conditions including, and a coefficient of the prediction formula corresponding to each of the imaging conditions acquired by the imaging condition acquisition unit is read from the storage unit, and a peripheral for each image height by the prediction formula obtains a gain value to correct the dimming, the image correction procedure that corrects a captured image through the lens optical system based on the gain value, the degree of correction of vignetting shape of different correction degree Has an operation procedure for selecting the Zureka one, a vignetting compensation gain table creation process of creating a vignetting compensation gain table from the gain value based on the correction degree selected by the operation procedure, The image correction procedure includes a process of correcting an image photographed through the lens optical system with a correction gain of the peripheral light attenuation correction gain table.

  According to the present invention, it is not necessary to perform complicated calculations, and peripheral light attenuation correction can be performed at high speed.

  Hereinafter, embodiments of an image processing apparatus and an image processing program according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
The electronic camera 100 according to the first embodiment includes the function of the image processing apparatus and the function of the image processing program according to the present invention. First, the configuration of the electronic camera 100 will be described.
[Configuration of Electronic Camera 100]
FIG. 1 is a block diagram illustrating a configuration of an electronic camera 100 according to the present embodiment. The electronic camera 100 includes a camera body 101 and a photographing lens 102. The photographing lens 102 is a single-lens reflex camera that is connected to the camera body 101 via the lens mount 103 and can exchange the photographing lens 102.

  The photographing lens 102 includes a lens optical system 104, a diaphragm 105, an encoder 106, and a ROM 107.

  Although only the front lens 104a and the rear lens 104b are drawn, the lens optical system 104 is actually composed of a plurality of lenses.

  The encoder 106 detects the lens position of the lens optical system 104 and outputs it to the camera body 101 side. The ROM 107 stores lens information of the photographing lens 102 in advance. The stored lens information includes, for example, the model number of the photographing lens 102, the focal length, the lens system of the front lens 104a and the rear lens 104b.

  The camera body 101 includes a mechanical shutter 108, an image sensor 109, an A / D conversion unit 110, a gain control unit 111, a signal processing unit 112, a storage unit 113, a display unit 114, a mirror unit 115, Viewfinder 116, AE sensor 117, AF sensor 118, CPU (central processing unit) 119, aperture control unit 120, lens control unit 121, shutter control unit 122, operation unit 123, and peripheral reduction An optical table calculation unit 124 and a coefficient table 125 are included. The mirror unit 115 includes a main mirror 115a, a sub mirror 115b, and a rotation mechanism 115c.

The electronic camera 100 is controlled according to a program stored in advance in the CPU 119. The photographer uses the electronic camera 100 by operating the operation buttons (power button, release button, zoom button, setting button, etc.) of the operation unit 123. Operation information of the operation unit 123 is input to the CPU 119, and the CPU 119 controls each unit of the electronic camera 100 according to the operation information. In this embodiment, for easy understanding, the aperture control unit 120, the lens control unit 121, the shutter control unit 122, and the peripheral light attenuation table calculation unit 124 are drawn as blocks different from the CPU 119. However, the processing block performed by the CPU 119 may be included in the CPU 119.
[Operation of Electronic Camera 100]
Next, the operation of the electronic camera 100 according to this embodiment will be described. In FIG. 1, subject light that enters through the lens optical system 104 of the photographing lens 102 and the diaphragm 105 enters the mirror unit 115 of the camera body 101.

  The subject light incident on the mirror unit 115 is reflected by the main mirror 115a and incident on the viewfinder 116 and the AE sensor 117, and is reflected by the sub mirror 115b and incident on the AF sensor 118. The photographer looks into the viewfinder 116 and determines the shooting composition.

  The AE sensor 117 performs photometry of a predetermined area and outputs a photometric value to the CPU 119. The AF sensor 118 is a dedicated sensor for performing a phase difference detection type focal position, and a sensor signal is output to the CPU 119. The mirror unit 115 can be flipped up by the rotation mechanism 115c. When the release button of the operation unit 123 is pressed during shooting, the shutter control unit 122 jumps up the mirror unit 115 and mechanical shutter 108 according to a command from the CPU 119. Control to open. In this way, the subject light incident through the photographing lens 102 is imaged on the imaging surface of the image sensor 109.

  The CPU 119 obtains the aperture value and shutter speed at which the optimum exposure is obtained from the photometric value output from the AE sensor 117 according to the shooting mode, and issues a command to the aperture controller 120 and the shutter controller 122.

  The diaphragm control unit 120 varies the diaphragm 105 on the photographing lens 102 side in accordance with a command from the CPU 119. The shutter control unit 122 varies the shutter speed of the mechanical shutter 108 in accordance with a command from the CPU 119.

  Further, the CPU 119 calculates a defocus amount from the output signal of the AF sensor 118, obtains a focal position, and issues a command to the lens control unit 121. The lens control unit 121 changes the position of the focus lens of the lens optical system 104 on the photographing lens 102 side in accordance with a command from the CPU 119. The lens control unit 121 changes the position of the zoom lens of the lens optical system 104 on the photographing lens 102 side in accordance with a command from the CPU 119 even when the photographer operates the zoom button of the operation unit 123.

  The imaging element 109 has an imaging surface composed of a plurality of pixels arranged in a two-dimensional matrix, and subject light imaged on the imaging surface is converted into an electric signal by a photoelectric conversion unit of each pixel. The data is output to the A / D converter 110.

  The A / D conversion unit 110 converts the analog electric signal photoelectrically converted by the image sensor 109 into digital image data for each pixel, and outputs the digital image data to the gain control unit 111.

  The gain control unit 111 performs gain control of the image data output from the A / D conversion unit 110 and outputs the gain to the signal processing unit 112. The gain control will be described in detail later.

  The signal processing unit 112 performs color conversion processing, γ correction processing of the image adjusted to an appropriate level by the gain control unit 111, or image compression processing according to the JPEG standard, and the like, and then stores the final captured image in the storage unit 113. It memorize | stores or displays a picked-up image on the display part 114. FIG.

The peripheral dimming table calculation unit 124 obtains peripheral dimming shape information by a multivariate analytical expression using the coefficients stored in the coefficient table 125 according to the photographing conditions, and a correction gain for correcting the peripheral dimming Calculate the table. Note that the calculation of the coefficient by the multivariate analysis and the calculation of the correction gain table will be described in detail later.
[Ambient dimming]
Here, peripheral dimming will be described with reference to FIG. FIG. 2A illustrates a state of the imaging surface 200 of the imaging element 109 when there is peripheral light reduction. Peripheral dimming is a phenomenon in which the amount of light in the peripheral portion of the image 200 drops and darkens concentrically with respect to the optical axis center L0 of the image captured by the image sensor 109 due to the characteristics of the photographing lens 102 used in the electronic camera 100. is there. In FIG. 2, for the sake of easy understanding, the change in the amount of light is depicted in a staircase pattern. However, in actuality, it changes smoothly within the gradation range of the image.

  The graph of FIG. 2B is a graph showing a change in output level (peripheral dimming characteristic 201) when the imaging surface 200 of the imaging element 109 is cut along a diagonal line (two-dot chain line A-A ′). In the graph of FIG. 2B, the horizontal axis indicates the image height, and the vertical axis indicates the output level. Here, assuming that the image height r at the optical axis center L0 of the imaging surface 109 of the image sensor 109 is 0 mm and the output level is 1.0, for each equidistant position (image height) extending concentrically from the optical axis center L0. When the change of the output level is drawn, it becomes like a peripheral dimming characteristic 201, and the output level decreases as the peripheral portion of the imaging surface 200 is reached.

For example, as shown in FIG. 3, the peripheral dimming shape includes an incident angle of light incident on the image sensor 109, a diameter L1 of the front lens 104a of the photographing lens 102, a diameter L2 of the rear lens 104b, and an aperture 105. It depends on the aperture diameter S, the distance d1 from the front lens 104a to the image sensor 109, the distance d2 from the aperture 105 to the image sensor 109, the distance d3 from the rear lens 104b to the image sensor 109, and the like. Further, when the photographing lens 102 is a zoom lens, the shape of the peripheral dimming changes according to the zoom position. In FIG. 3, the diameter L1 and distance d1 of the front lens 104a and the diameter L2 and distance d3 of the rear lens 104b are the design diameters and distances of the lens optical system 104 composed of a plurality of lenses. It is shown and not an actual measurement.
[Ambient dim correction]
Here, the image processing for performing the peripheral light reduction correction performed by the electronic camera 100 according to the present embodiment is divided into image processing outside the electronic camera 100 and image processing inside the electronic camera 100. First, image processing outside the electronic camera 100 will be described.
[Image processing performed outside the electronic camera 100]
The coefficient table 125 includes a plurality of prediction formula coefficients for calculating predicted values of peripheral dimming shape information of the lens optical system 104 at each image height based on a plurality of imaging conditions including lens information of the lens optical system 104. Each shooting condition is stored in advance corresponding to each shooting condition. Next, a method for calculating the coefficient of the prediction formula will be described.

  The coefficient of the prediction formula stored in advance in the coefficient table 125 is calculated by an image processing program of these apparatuses using a personal computer or the like as an image processing apparatus instead of the electronic camera 100. In this embodiment, the multivariate analysis formula is used as the prediction formula. However, another multivariate analysis method such as a least square method may be used. In addition, the calculated coefficient of the multivariate analytical expression is stored in the coefficient table 125 when the electronic camera 100 is manufactured.

  Next, the learning process for calculating the coefficients of the multivariate analytical expression will be described using the flowchart of FIG. It is assumed that image data already taken under various shooting conditions is stored in a storage medium of a personal computer corresponding to the shooting conditions. The imaging conditions used in this embodiment include lens information such as an aperture value obtained from the ROM 107 of the photographing lens 102, camera control information such as an F value obtained from the CPU 119, and the like. For example, as described with reference to FIG. 3, an aperture value, a pupil position, a focal length, and the like relating to a lens diameter and an aperture diameter that are optically formed on the imaging lens 102 are used as imaging conditions. As shown in FIG. 5, an angle θ formed by the imaging surface of the image sensor 109 and the optical axis may be used as the imaging condition.

  (Step S101) An image processing program is launched on a personal computer or the like, and learning processing is started.

  (Step S102) The image data for each shooting condition stored in the storage medium is read, and the light amount distribution reaching the imaging surface, that is, the output level for each image height is measured for each shooting condition.

  (Step S103) A multiple regression analysis is performed using measured values for each of a plurality of photographing conditions for each image height. Multiple regression analysis is a common technique in multivariate analysis, and can be easily obtained using application software on a personal computer. The graph of FIG. 6 is an example of a result of performing multiple regression analysis when an image height r = 18 mm using about 30 photographing lenses. In FIG. 6, the horizontal axis indicates the prediction result based on the lens information, and the vertical axis indicates the actual measurement value. As shown in FIG. 2, the vertical axis and the horizontal axis indicate values when the output level when the image height r = 0 at the center of the imaging surface 200 is 1.0. In the case of multivariate analysis, weighted analysis may be performed for each photographing lens.

  As shown in the graph of FIG. 6, a deviation occurs between the actual measurement value and the prediction result due to the influence of noise or the like, but it can be approximated by a straight line 251 of a linear function. Similar analysis is performed for a plurality of image heights such as an image height r = 12 mm and an image height r = 6 mm.

(Step S104) A multiple regression equation is obtained for each image height from the result of the multiple regression analysis. As a result, the coefficient of the polynomial that minimizes the residual with respect to all the imaging conditions (in this embodiment, the coefficient including the slope and the intercept is referred to) is obtained. Here, an example of a multiple regression equation is shown in (Equation 1).
y = a1 · x1 + a2 · x2 + a3 · x3 + ... + an · xn + b (Formula 1)
In (Expression 1), y is an objective variable (corresponding to an output level), x1, x2, x3,..., Xn are explanatory variables (corresponding to photographing conditions such as an aperture value and an aperture value), a1, a2 , A3,..., An are inclinations, and b is an intercept.

  (Step S105) The calculated coefficient is stored in the coefficient table 125 of the electronic camera 100 for each image height.

  (Step S106) The learning process of the image processing program by a personal computer or the like is terminated.

Through the learning process described above, the coefficient of the multiple regression equation for calculating the output level (peripheral dimming shape information) for each image height is obtained and stored in the coefficient table 125 of the electronic camera 100.
[Image processing performed in electronic camera 100]
In the electronic camera 100, the peripheral light attenuation level for each image height is calculated using the coefficient of the multiple regression equation stored in the coefficient table 125 at the time of photographing. For example, the surrounding dimming level at each image height position under the photographing condition is obtained by inputting the photographing condition when photographing with the electronic camera 100 into the explanatory variable of the multiple regression equation of (Equation 1) and performing calculation. . Note that, as shown in (Expression 1), the multiple regression equation is a linear function equation and is a simple multiplication and addition equation, so the processing load of the electronic camera 100 is small and high-speed processing is possible.

  Next, image processing when photographing with the electronic camera 100 will be described with reference to the flowchart of FIG. 7 is operated by a program stored in advance in the CPU 119 in FIG.

  (Step S201) The power button of the operation unit 123 is pressed to turn on the electronic camera 100. When the release button of the operation unit 123 is pressed, the photographing process is started.

  (Step S <b> 202) An image formed on the imaging surface of the imaging element 109 via the photographing lens 102 is input to the gain control unit 111 via the A / D conversion unit 110.

  (Step S203) The peripheral dimming table calculation unit 124 acquires imaging conditions. For example, lens information such as an aperture value is input from the ROM 107 of the photographing lens 102, and camera control information such as an F value is input from the CPU 119 that performs aperture control. Although the peripheral light attenuation table calculation unit 124 is drawn so as to read lens information directly from the ROM 107 of the photographing lens 102, it may be read via the CPU 119 in the same manner as the camera control information.

  (Step S204) The peripheral dimming table calculation unit 124 inputs the imaging conditions input in step S203 to the explanatory variable of the multiple regression equation of (Expression 1), and obtains output levels at a plurality of image height positions. As a result, the peripheral dimming shape is known.

  (Step S205) The peripheral dimming table calculation unit 124 creates a peripheral dimming correction gain table from the peripheral dimming shape information obtained in step S204. The peripheral dimming correction gain table is a correction gain table for making a flat characteristic by multiplying an output level that decreases concentrically by a predetermined gain with an output level of image height r = 0 as a reference. Note that the output level obtained in step S204 is a discrete value having, for example, about three image height positions, and therefore does not indicate the output level at all image height positions. Therefore, interpolation is performed with an approximate pattern based on a simple quadratic function to obtain peripheral dimming shape information at each image height position, and a correction gain table is created.

  Here, a method of creating a correction gain table will be described with reference to FIG. FIG. 8 is a graph showing the image height r (mm) on the horizontal axis and the output level on the vertical axis, and corresponds to the graph of FIG. FIG. 8A illustrates a state where the output levels obtained in step S204 are three points z1 (r = 6), z2 (r = 12), and z3 (r = 18). The peripheral dimming characteristic 201 is represented by four discrete points from z0 to z3 obtained by adding z0 of image height r = 0.

In FIG. 8A, the peripheral dimming characteristic 201 can be approximated by (Equation 2).
z = a · r ^ 2 + b · r + 1 (Formula 2)
Here, it is assumed that a plurality of combinations of the coefficients a and b in (Expression 2) are stored in the coefficient table 125 in advance. Then, the actual peripheral dimming characteristics are obtained from the four levels of z0 (r = 0), z1 (r = 6), z2 (r = 12), and z3 (r = 18) as the output level obtained in step S204. The coefficients a and b of the approximate expression (expression 2) close to 201 are selected from the coefficient table 125 to approximate the peripheral dimming characteristic 201.

  In this embodiment, instead of approximating the peripheral dimming characteristic 201, a correction gain characteristic 202 for flattening the peripheral dimming characteristic 201 is obtained as shown in FIG.

In FIG. 8B, the correction gain characteristic 202 can be approximated by (Equation 3).
g = c · r ^ 2 + d · r + 1 (Formula 3)
Here, it is assumed that a plurality of combinations of the coefficients c and d in (Equation 3) are stored in the coefficient table 125 in advance. Then, the peripheral dimming characteristic 201 is obtained from the change in the output level at four points z0 (r = 0), z1 (r = 6), z2 (r = 12), and z3 (r = 18) obtained in step S204. Correction gains g0 (r = 0), g1 (r = 6), g2 (r = 12), and g3 (r = 18) that are corrected to be flat are obtained. Further, a combination of the coefficients c and d of the approximate expression (Expression 3) that approximates the correction gain characteristic 202 from these discrete values is selected from the coefficient table 125, and other than the four points of the image height r = 0, 6, 12, and 18. A peripheral light reduction correction gain table for determining a correction gain at the image height position of the image is created.

  (Step S206) The gain control unit 111 performs correction processing for each image height of the captured image based on the peripheral light attenuation correction gain table. Since the gain for each image height differs concentrically, the processing can be simplified by converting the pixel array arranged in a two-dimensional matrix into a concentric pixel array using a lookup table and multiplying it by a correction gain. can do.

  (Step S207) The image whose peripheral light is corrected by the gain control unit 111 is subjected to color interpolation processing, γ correction processing, and the like by the signal processing unit 112, and then subjected to image compression processing and stored in the storage unit 113. The captured image is displayed on the display unit 114 as necessary.

  (Step S208) The photographing process is terminated.

  As described above, since the electronic camera 100 according to the present embodiment includes the image processing apparatus and the image processing program for correcting the peripheral dimming level, it is not necessary to perform complicated calculations, and the electronic camera 100 can perform high-speed processing. Peripheral dimming correction can be performed with high accuracy. Even if the correction value for the peripheral dimming correction of the mounted lens is not stored in advance in the lens or camera, it can be used by using general-purpose lens information such as optical information of the mounted lens. It is possible to obtain dimming shape information and perform appropriate peripheral dimming correction.

  Note that an image processing apparatus and an image processing program in the electronic camera 100 that perform peripheral light attenuation correction include at least a CPU 119, a peripheral light attenuation table calculation unit 124, a coefficient table 125, and a gain control unit 111. This can be realized by processing according to the flowchart of FIG. The learning process performed outside the electronic camera 100 can be realized by executing an image processing program according to the flowchart of FIG. 4 on a personal computer or the like.

  In the present embodiment, the case where the image captured by the image sensor 109 is subjected to the peripheral light reduction correction using the RAW data after A / D conversion by the A / D conversion unit 110 has been described. Image data that has been subjected to correction processing, γ correction processing, or the like, or image data that has been compressed according to the JPEG standard, or the like may be used. However, when an image after gradation conversion such as γ correction is used, the image data after the image data is once returned to a linear value by inverse γ correction is used. The image data after returning to the linear value may be used in place of the output image data of the A / D converter 110 in FIG. Then, γ correction, color correction processing, and the like are performed again after the peripheral light reduction correction, and a JPEG compression process is performed as necessary to obtain an image after peripheral light attenuation correction. In this case, it is assumed that shooting conditions are stored as information of the EXIF standard for each shot image, and when reading out image data to be corrected for peripheral light reduction, the shooting conditions at the time of shooting the image are also read and read. By calculating a multivariate analysis formula according to the shooting conditions that have been issued, it is possible to obtain peripheral dimming shape information of the image, and to create a peripheral dimming correction gain table to correct the peripheral dimming it can.

  As described above, the peripheral dimming correction is performed by executing the processing according to the flowchart of FIG. 7 using an image processing program such as a personal computer on an image captured by the electronic camera 100 instead of in the electronic camera 100. be able to.

(Second Embodiment)
Next, an electronic camera 100 according to the second embodiment will be described. The electronic camera 100 according to the second embodiment includes the function of the image processing apparatus and the function of the image processing program according to the present invention.

  The electronic camera 100 according to the present embodiment can select the degree of correction of the peripheral dimming shape. For example, in FIG. 8 described in the first embodiment, the correction gain characteristic 202 for correcting the peripheral dimming characteristic 201 to be flat is obtained. However, as shown in FIG. 9, the correction gain characteristic 202 is weaker than the correction gain characteristic 202. A gain characteristic 203 or a correction gain characteristic 204 stronger than the correction gain characteristic 202 can be selectively obtained.

  For example, the photographer uses the operation unit 123 to select the peripheral dimming correction degree from four levels of “strong”, “medium”, “weak”, and “none”. When the photographer selects “strong”, the peripheral dimming shape is corrected using the correction gain characteristic 204 of FIG. 9, and when the photographer selects “medium”, the correction gain characteristic 202 of FIG. 9 is used. When the peripheral dimming shape is corrected and the photographer selects “weak”, the peripheral dimming shape is corrected using the correction gain characteristic 203 of FIG. 9, and when the photographer selects “none”, the peripheral dimming shape is corrected. The CPU 119 controls not to correct the light shape.

  As described above, in the present embodiment, the peripheral dimming characteristic is not necessarily corrected to be flat, but a correction degree according to the photographer's preference can be selected, so in addition to the effects of the first embodiment. Various shootings are possible.

(Third embodiment)
Next, an electronic camera 100 according to a third embodiment will be described. In the present embodiment, the peripheral dimming that occurs in the output of the AE sensor 117 is corrected. For example, the imaging surface 200 in FIG. 2 described in the first embodiment is considered to be replaced with the light receiving surface of the AE sensor 117. In this case, on the light receiving surface of the AE sensor 117, similarly to the imaging surface 200 of the imaging element 109, a peripheral dimming shape is formed concentrically for each image height from the center of the optical axis. As a result, for example, when partial photometry is performed in the peripheral portion of the light receiving surface of the AE sensor 117, there is a problem that appropriate photometry cannot be performed due to peripheral dimming.

  Therefore, in the present embodiment, the CPU 119 that has received the output signal of the AE sensor 117 in FIG. 1, as in the first embodiment, the gain control unit 111, the peripheral light attenuation table calculation unit 124, the coefficient table 125, By performing the same processing as the image processing apparatus and the image processing program configured as described above, the peripheral light reduction generated on the light receiving surface of the AE sensor 117 is corrected.

  As described above, since the electronic camera 100 according to the present embodiment includes the image processing apparatus and the image processing program for correcting the peripheral light attenuation level on the light receiving surface of the AE sensor 117, the electronic camera 100 does not need to perform complicated calculations. However, it is possible to perform high-speed processing and accurately correct the peripheral dimming shape, and even when a new lens is attached, appropriate peripheral dimming correction can be performed from a combination of photographing conditions. As a result, appropriate exposure control can be performed.

  As described above in each embodiment, the electronic camera 100 using the image processing apparatus and the image processing program according to the present invention uses the multivariate analysis formulas for the peripheral dimming shape information under various shooting conditions in advance. Since the coefficients of the multivariate analysis formula predicted in the above are stored, the peripheral dimming shape information corresponding to the photographing conditions can be obtained by a simple calculation formula, and the peripheral dimming shape can be corrected with high accuracy. In particular, even when a new lens is attached, it is possible to obtain optimum peripheral dimming shape information from a combination of photographing conditions and perform peripheral dimming correction on the photographed image.

  In each embodiment, the learning process executed by the image processing apparatus and the image processing program outside the electronic camera 100 performs multivariate analysis for each image height using a plurality of shooting conditions including lens information and camera control information. However, the learning process may be performed by adding the image height as a variable for multivariate analysis. In this case, the coefficient of the multivariate analytical expression including the image height is obtained, not the coefficient of the multivariate analytical expression for each image height, so the peripheral dimming shape information can be obtained at one time and should be stored. Since the number of coefficients is also reduced, the processing speed can be increased and the storage capacity can be reduced.

1 is a block diagram of an electronic camera 100 according to each embodiment. It is explanatory drawing for demonstrating a periphery dimming shape. It is explanatory drawing which shows an example of the imaging | photography conditions relevant to a peripheral light reduction. It is a flowchart which shows the flow of a learning process. It is explanatory drawing which shows a mode in case an angle is used as a parameter. It is explanatory drawing which shows the relationship between the prediction result by imaging | photography condition, and a measured value. It is a flowchart which shows the flow of an imaging | photography process. It is explanatory drawing which shows an example of a peripheral light attenuation characteristic and a correction gain characteristic. It is explanatory drawing which shows an example of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Electronic camera 101 ... Camera body 102 ... Shooting lens 103 ... Lens mount 104 ... Lens optical system 105 ... Aperture 106 ... Encoder 107 ... ROM
104a, front lens 104b, rear lens 108, mechanical shutter 109, image sensor 110, A / D conversion unit 111, gain control unit 112, signal processing unit 113 ... Storage unit 114 ... Display unit 115 ... Mirror unit 116 ... Viewfinder 117 ... AE sensor 118 ... AF sensor 119 ... CPU
DESCRIPTION OF SYMBOLS 120 ... Diaphragm control part 121 ... Lens control part 122 ... Shutter control part 123 ... Operation part 124 ... Peripheral light reduction table calculation part 125 ... Coefficient table 115a ... Main mirror 115b ... Submirror 115c ... Rotation mechanism

Claims (7)

An image processing apparatus that performs peripheral dimming correction of an image shot through a lens optical system,
Based on a plurality of imaging conditions including lens information of the lens optical system, a coefficient of a prediction formula for calculating a predicted value of peripheral dimming shape information of the lens optical system at each image height is associated with each of the plurality of imaging conditions. A storage unit stored in advance,
A shooting condition acquisition unit for acquiring a plurality of shooting conditions including lens information at the time of image shooting;
The coefficient of the prediction formula corresponding to each imaging condition acquired by the imaging condition acquisition unit is read from the storage unit, a gain value for correcting peripheral light attenuation is obtained for each image height by the prediction formula, and the gain value is calculated. An image correction unit that corrects an image captured through the lens optical system,
An operation unit that selects any one of a plurality of correction degrees with different degrees of correction of the peripheral dimming shape ;
A peripheral dimming correction gain table creating unit that creates a peripheral dimming correction gain table from the gain value based on the correction degree selected by the operation unit ;
The image processing apparatus, wherein the image correction unit corrects an image captured through the lens optical system with a correction gain of the peripheral light attenuation correction gain table. The image processing apparatus according to claim 1.
The coefficient of the prediction formula stored in the storage unit is
An image processing apparatus characterized in that it is calculated in advance by multivariate analysis using measured values measured for a plurality of photographing conditions including lens information of a plurality of lens optical systems. The image processing apparatus according to claim 2,
The coefficient of the prediction formula stored in the storage unit is
A process of storing in advance in the storage unit image data photographed according to a plurality of photographing conditions including lens information of a plurality of lens optical systems, corresponding to the photographing conditions;
A process of reading the image data from the storage unit and actually measuring an output level for each image height for each shooting condition;
It is obtained by a learning process including a process for calculating coefficients by multivariate analysis using measured values for a plurality of photographing conditions for each image height, and is stored in the storage unit as a coefficient table for each image height. An image processing apparatus. The image processing apparatus according to claim 2 or 3,
The image processing apparatus according to claim 1, wherein the multivariate analysis is a multiple regression analysis. In the image processing device according to any one of claims 1 to 4,
The image processing apparatus according to claim 1, wherein the prediction formula is a linear formula. In the image processing device according to any one of claims 1 to 5,
An image processing apparatus that calculates subject luminance using an image corrected by the image correction unit. An image processing program for performing peripheral light reduction correction of an image taken through a lens optical system,
Based on a plurality of imaging conditions including lens information of the lens optical system, a coefficient of a prediction formula for calculating a predicted value of peripheral dimming shape information of the lens optical system at each image height is associated with each of the plurality of imaging conditions. Storage procedure to be recorded in advance in the storage unit,
Shooting condition acquisition procedure for acquiring a plurality of shooting conditions including lens information at the time of image shooting,
The coefficient of the prediction formula corresponding to each imaging condition acquired by the imaging condition acquisition unit is read from the storage unit, a gain value for correcting peripheral light attenuation is obtained for each image height by the prediction formula, and the gain value is calculated. An image correction procedure for correcting an image shot through the lens optical system,
An operation procedure for selecting any one of a plurality of correction degrees having different degrees of correction of the peripheral dimming shape ;
A peripheral dimming correction gain table creating procedure for creating a peripheral dimming correction gain table from the gain value based on the correction degree selected by the operation procedure ,
The image processing program is characterized in that the image correction procedure performs a process of correcting an image photographed through the lens optical system with a correction gain of the peripheral light attenuation correction gain table.