JP4804327B2 - Electronic camera - Google Patents

Description

  The present invention relates to an electronic camera, and more particularly to an electronic camera that corrects, for example, luminance shading generated on an imaging surface.

  An example of a conventional camera of this type is disclosed in Patent Document 1. According to this prior art, a surface light source with uniform brightness is photographed in a state where a zoom position and an aperture diameter at which the influence of shading is maximized are set in the camera manufacturing process. The captured image is converted into a thumbnail image by the reduction process, and the maximum value of Y data forming the converted thumbnail image is detected.

Next, a coefficient for making the Y data the same value as the detected maximum value is calculated for each pixel. The calculated coefficient is stored in the ROM as two-dimensional shading correction data corresponding to the position of each pixel. Such processing is executed corresponding to a plurality of zoom positions and a plurality of aperture diameters, and shading correction data obtained thereby is also stored in the ROM.
JP 2006-253970 A [H04N 5/243, 1/401]

    The prior art assumes a shading characteristic in which the brightness decreases as it spreads radially from the center of the screen. However, some shading characteristics show a characteristic in which the luminance only at one end in the horizontal direction of the screen drops or a characteristic in which the luminance only at one end in the vertical direction of the screen falls. If such a shading characteristic is corrected by the same method as in the prior art, a trace of shading correction appears at one end in the horizontal direction or one end in the vertical direction due to an error in the correction data value, and the appearance of the corrected image may be deteriorated. is there.

    Therefore, a main object of the present invention is to provide an electronic camera capable of improving the appearance of an image subjected to luminance shading correction.

The electronic camera according to the first aspect of the present invention (10: reference numeral corresponding to the embodiment; the same applies hereinafter) has an imaging surface on which an optical image representing a subject is irradiated, and outputs a subject image generated on the imaging surface. An imaging unit (16), a correction unit (24) for correcting the luminance of the subject image output from the imaging unit with reference to the luminance correction value, and a luminance shading pattern on the imaging surface corresponding to the first position on the imaging surface A discriminating means (S9) for discriminating whether or not the specific pattern to be reduced corresponds, and when the discrimination result of the discriminating means is affirmative, the luminance corresponding to the second position of the imaging surface symmetrical to the first position is reduced. The first selection means (S15, S17, S19, S21) for selecting the first correction value having the reduction characteristic as the luminance correction value, and the predetermined second correction value when the discrimination result of the discrimination means is negative. Second selection means (S23) for selecting the value is provided.

  The imaging means has an imaging surface on which an optical image representing the scene is irradiated, and outputs an object scene image generated on the imaging surface. The luminance of the object scene image output from the imaging unit is corrected by the correction unit with reference to the luminance correction value. The determination unit determines whether or not the luminance shading pattern on the imaging surface corresponds to a specific pattern in which the luminance corresponding to the first position on the imaging surface is reduced. If the determination result of the determination unit is affirmative, the first correction value having a reduction characteristic for reducing the luminance corresponding to the second position of the imaging surface symmetrical to the first position is obtained by the first selection unit. Selected as. If the determination result of the determination unit is negative, the predetermined second correction value is selected as the luminance correction value by the second selection unit.

  Therefore, when the luminance corresponding to the first position on the imaging surface is reduced, the luminance of the object scene image is corrected so that the luminance corresponding to the second position on the imaging surface symmetrical to the first position is reduced. . The corrected object scene image is an image with reduced luminance at both the first position and the second position. Thereby, the appearance of the image subjected to the shading correction can be improved.

Furthermore, the first correction value further has an increase characteristic that increases the luminance corresponding to the first position. By increasing the luminance at the first position, it is possible to suppress the reduction width of the luminance at the second position.

The electronic camera according to the invention of claim 2 is dependent on claim 1 , and the first correction value is obtained by correcting each of the luminance after correction at the first position and the luminance after correction at the second position before correction at the first position. The characteristic which makes it correspond with the average value of the brightness | luminance before correction | amendment in a brightness | luminance and a 2nd place value is shown.

An electronic camera according to a third aspect of the invention is dependent on any one of the first and second aspects, wherein the first position is a band-like position extending in the vertical direction at one horizontal end of the imaging surface, and the second position is the imaging surface. This is a band-like position extending in the vertical direction at the other end in the horizontal direction.

An electronic camera according to a fourth aspect of the invention is dependent on any one of the first and second aspects, wherein the first position is a band-like position extending in the horizontal direction at one vertical end of the imaging surface, and the second position is the imaging surface. This is a band-like position extending in the horizontal direction at the other end in the vertical direction.

An electronic camera according to a fifth aspect of the invention is dependent on any one of the first and second aspects, wherein the first position is one of the four corners forming the imaging surface, and the second position is the four corners forming the imaging surface. The position is diagonal to the first position.

An electronic camera according to a sixth aspect of the invention is dependent on any one of the first to fifth aspects, and further includes first correction means (S51) for correcting the luminance correction value according to the change of the optical zoom magnification.

An electronic camera according to a seventh aspect of the invention is dependent on any one of the first to sixth aspects, and further includes second correction means (S53) for correcting the luminance correction value according to the exposure amount of the imaging surface.

  According to the present invention, when the luminance corresponding to the first position on the imaging surface is reduced, the luminance of the object scene image is reduced so that the luminance corresponding to the second position on the imaging surface symmetrical to the first position is reduced. Is corrected. The corrected object scene image is an image with reduced luminance at both the first position and the second position. Thereby, the appearance of the image subjected to the shading correction can be improved.

  The above object, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

  Referring to FIG. 1, a digital camera 10 of this embodiment includes a zoom lens 12 and an aperture unit 14. The optical image of the object scene is irradiated on the imaging surface of the image sensor 16 through the zoom lens 12 and the aperture unit 14. On the imaging surface, charges representing the object scene image are generated by photoelectric conversion. The imaging surface is covered with a color filter (not shown) having a primary color Bayer array, and the charges generated in each of the plurality of pixels formed on the imaging surface are R (Red), G (Green) or B (Blue) color information.

  When the camera mode is selected by the key input device 44, the CPU 42 initializes imaging conditions. Specifically, the lens position data indicating the tele end is set in the driver 18a, the aperture amount data indicating the fully open aperture amount is set in the driver 18b, the exposure time data indicating the initial exposure time is set in the driver 18c, The white balance adjustment gain stored in the flash memory 42m is set in the white balance adjustment circuit 22.

  When the initialization of the imaging conditions is completed, the CPU 42 sets the luminance shading correction gain curve stored in the flash memory 42m in the luminance shading correction circuit 24. In this embodiment, the gain curve will be described as including a “straight line”.

  When the setting of the gain curve is completed, the CPU 42 instructs the driver 18c to repeat pre-exposure and thinning-out reading so as to execute through image processing. The driver 18c executes pre-exposure according to the set exposure time data every time a timing signal is generated, and reads a part of the charge generated thereby from the imaging surface in a raster scanning manner. As a result, a low-resolution raw image signal representing the object scene is repeatedly output from the image sensor 16.

  The raw image signal of each frame output from the image sensor 16 is subjected to a series of processes of correlated double sampling, automatic gain adjustment, and A / D conversion by the CDS / AGC / AD circuit 20. The raw image data output from the CDS / AGC / AD circuit 20 is further subjected to white balance adjustment processing by the white balance adjustment circuit 22 and luminance shading correction processing by the luminance shading correction circuit 24. The white balance adjustment is executed with reference to the white balance adjustment gain set by the CPU. The luminance shading correction process is also executed with reference to the gain curve set by the CPU. The raw image data subjected to these processes is written into the SDRAM 32 via the memory control circuit 30.

  The post-processing circuit 34 reads the raw image data stored in the SDRAM 32 through the memory control circuit 30, performs a series of processes of color separation, gamma correction, and YUV conversion on the read raw image data, and outputs an image in the YUV format. Data is written to the SDRAM 32 through the memory control circuit 30. The LCD driver 28 reads the image data stored in the SDRAM 32 through the memory control circuit 30 and drives the LCD monitor 28 based on the read image data. As a result, a real-time moving image representing the object scene, that is, a through image is displayed on the monitor screen.

  When the zoom key 44z on the key input device 44 is operated, the CPU 42 sets the corresponding lens position data in the driver 18a. The zoom lens 12 is moved in the designated direction by the driver 18a, whereby the magnification of the through image displayed on the LCD monitor 28 is changed.

  The luminance evaluation circuit 36 evaluates the brightness of the object scene based on the Y data created by the post-processing circuit 34, and gives an evaluation result, that is, a luminance evaluation value to the CPU 42. The CPU 42 adjusts the exposure amount through the through image AE process, and adjusts the white balance through the through image WB adjustment process.

  In the through image AE process, the CPU 42 calculates an appropriate aperture amount and an appropriate exposure time based on the given luminance evaluation value, and indicates the aperture amount data indicating the calculated appropriate aperture amount and the calculated appropriate exposure time. Exposure time data is applied to drivers 18b and 18c, respectively. The driver 18b sets the aperture amount of the aperture unit 14 to a value according to the given aperture amount data, and the driver 18c executes pre-exposure according to the exposure time data. As a result, the brightness of the through image displayed on the LCD monitor 30 is appropriately adjusted.

  In the through-image WB adjustment processing, the CPU 42 takes in the color evaluation values of R, G, and B from the white balance adjustment circuit 22, calculates an appropriate white balance adjustment gain based on the taken-in color evaluation values, Then, the calculated white balance adjustment gain is given to the white balance adjustment circuit 22. As a result, the white balance of the through image is appropriately adjusted.

  When the shutter button 44s on the key input device 44 is half-pressed, the recorded image AE process and the recorded image WB adjustment process are executed by the CPU 42. The recorded image AE process is stricter than the through image AE process, and the recorded image WB adjustment process is also stricter than the through image WB adjustment process. As a result, the aperture amount, exposure time, and white balance adjustment gain are accurately adjusted. Subsequently, the CPU 42 corrects the gain curve set in the luminance shading correction circuit 24 based on the current zoom magnification and the current exposure amount.

  Referring to FIG. 10, in the range where the EV value defining the exposure amount is “0.0” or less, a correction coefficient K1 indicating “C” (C> 1.0) is multiplied by the gain curve. In the range where the EV value exceeds “0.0”, the correction coefficient K1 decreases to “1.0” as the EV value increases. Referring to FIG. 11, when the zoom lens 12 exists at any position from the center of the movement range to the wide end, a correction coefficient K2 indicating “1.0” is multiplied by the gain curve. When the zoom lens 12 exists at any position from the center of the moving range to the tele end, the correction coefficient K2 indicates a value exceeding “1.0”. By such correction processing, the luminance shading is accurately corrected.

  When the shutter button 44s is fully pressed, the CPU 42 instructs the driver 18c to execute main exposure and all-pixel reading in order to execute a recording process. The driver 18c performs main exposure on the imaging surface in accordance with the appropriate exposure period obtained by the AE process for recorded images, and reads out all charges generated thereby from the imaging surface in a raster scanning manner. As a result, one frame of raw image signal having high resolution is output from the image sensor 16.

  The output raw image signal is processed in the same manner as described above. As a result, high-resolution image data corresponding to the YUV format is secured in the SDRAM 32. When executing the recording process, the CPU 42 gives a processing command to the I / F 38 as well. The I / F 38 reads the high-resolution image data secured in the SDRAM 32 through the memory control circuit 30 and records the read image data on the recording medium 40 in a file format.

  The luminance shading correction circuit 24 is configured as shown in FIG. The R data, G data, and B data forming the raw image data output from the CDS / AGC / AD circuit 20 are supplied to the amplifiers 24a, 24b, and 24c, respectively. The gain curve given from the CPU 42 is stored in a register 24h provided in the gain setting circuit 24g.

  The gain setting circuit 24g specifies the position of the pixel data currently output from the CDS / AGC / AD circuit 20 based on the pixel position information given from the driver 18c, and registers the gain value corresponding to the specified position. The gains Kr, Kg, and Kb that are extracted from the gain curve stored in 24h and define the extracted gain values are supplied to the amplifiers 24a to 24c, respectively. The amplifier 24a amplifies the R data with reference to the coefficient Kr, the amplifier 24b amplifies the G data with reference to the coefficient Kg, and the amplifier 24c amplifies the B data with reference to the coefficient Kb. As a result, R data, G data, and B data with corrected luminance shading are obtained.

  Evaluation areas B0 to B4 are allocated to the imaging surface in the manner shown in FIG. 3 in association with the luminance shading correction process. The evaluation area B0 is assigned to the center of the imaging surface, and the evaluation areas B1 to B4 are respectively assigned to the four corners of the imaging surface. Evaluation area B1 is located in the upper left, evaluation area B2 is located in the upper right, evaluation area B3 is located in the lower left, and evaluation area B4 is located in the lower right.

  The integrating circuit 24d integrates R data belonging to the evaluation area B * (*: 0 to 4, the same applies hereinafter) to calculate an integrated value Ir (*), and the integrating circuit 24e integrates G data belonging to the evaluation area B *. Then, the integrated value Ig (*) is calculated, and the integrating circuit 24f calculates the integrated value Ib (*) by integrating the B data belonging to the evaluation area B *. The calculated integrated values Ir (*), Ig (*) and Ib (*) are given to the CPU.

  The gain curve for shading correction stored in the flash memory 42m is determined by the CPU 42 in the following manner when a predetermined operation is performed in the adjustment process before shipping the digital camera 10.

  First, the imaging process is executed in a state where the imaging conditions are initialized and the imaging surface captures a light source (special scene) having uniform brightness. The image sensor 16 outputs a raw image signal of one frame having a low resolution, and integrated values Ir (*), Ig (*) and Ib (*) based on this are calculated by the integrating circuits 24d, 24e and 24f. . The process of determining the luminance shading pattern that occurs on the imaging surface is executed based on the calculated integrated values Ir (*), Ig (*), and Ib (*).

In the pattern discrimination process, the integrated value Iy (*) is calculated by a predetermined calculation with respect to the integrated values Ir (*), Ig (*), and Ib (*). The calculated integrated value Iy (*) corresponds to the integrated value of the luminance of the partial images belonging to the evaluation area B *. Subsequently, the luminance parameter value P1 in the evaluation area B1 is calculated with reference to Equation 1, the luminance parameter value P2 in the evaluation area B2 is calculated with reference to Equation 2, and the luminance in the evaluation area B3 with reference to Equation 3. The parameter value P3 is calculated, and the luminance parameter value P4 in the evaluation area B4 is calculated with reference to Equation 4. The calculated luminance parameters P0 to P4 are described in the luminance parameter table 32t on the SDRAM 32. Due to the log operation according to Equations 1 to 4, the difference in numerical values between the evaluation areas appears remarkably.
[Equation 1]
P1 = log ₁₀ {Iy (1) / Iy (0)} / log ₁₀ 2
[Equation 2]
P2 = log ₁₀ {Iy (2) / Iy (0)} / log ₁₀ 2
[Equation 3]
P3 = log ₁₀ {Iy (3) / Iy (0)} / log ₁₀ 2
[Equation 4]
P4 = log ₁₀ {Iy (4) / Iy (0)} / log ₁₀ 2
Among the calculated luminance parameters P0 to P4, the luminance parameters P1 to P4 are sorted in descending order of numerical values, and then redefined in descending order of numerical values by other codes “L1” to “L4”. For example, when the numerical value decreases in the order of P1, P3, P2, and P4, the luminance parameter P1 is redefined as the luminance parameter L1, the luminance parameter P3 is redefined as the luminance parameter L2, and the luminance parameter P2 is the luminance parameter. L3 is redefined, and the luminance parameter P4 is redefined as the luminance parameter L4.

  The redefined luminance parameters L1 to L4 are checked against each of the rules 1 to 8 shown in Table 1. Rules 1 to 8 are all defined by numerical conditions and position conditions. When the luminance parameters L1 to L4 satisfy both the numerical condition and the position condition that define the attention rule, the pattern assigned to the attention rule is determined as the luminance shading pattern. In the determination process, the average value ave of the luminance parameters L1 to L4 is also referred to.

  Referring to Table 1 and FIG. 5, the luminance parameters L1 to L4 satisfy the numerical condition of L1 <L2 <ave <L3 <L4, and the luminance parameters L1 and L2 are in the evaluation areas B1 and B3 on the left side of the imaging surface. If it corresponds, the pattern A1 is determined as a luminance shading pattern. When the luminance parameters L1 to L4 satisfy the numerical condition of L1 <L2 <ave <L3 <L4 and the luminance parameters L1 and L2 correspond to the evaluation areas B2 and B4 on the right side of the imaging surface, the pattern A2 is a luminance shading pattern Is determined.

  When the luminance parameters L1 to L4 satisfy the numerical condition of L1 <L2 <ave <L3 <L4, and the luminance parameters L1 and L2 correspond to the evaluation areas B1 and B2 on the upper side of the imaging surface, the pattern B1 is a luminance shading pattern Is determined. When the luminance parameters L1 to L4 satisfy the numerical condition of L1 <L2 <ave <L3 <L4 and the luminance parameters L1 and L2 correspond to the evaluation areas B3 and B4 below the imaging surface, the pattern B2 is luminance shading Discriminated as a pattern.

  When the luminance parameters L1 to L4 satisfy the numerical conditions of L1 <ave <L2 <L3 <L4 and the luminance parameters L1 and L4 correspond to the evaluation areas B1 and B4 on the imaging surface, the pattern C1 is a luminance shading pattern. Determined. When the luminance parameters L1 to L4 satisfy the numerical condition of L1 <ave <L2 <L3 <L4, and the luminance parameters L1 and L4 correspond to the evaluation areas B2 and B3 on the imaging surface, the pattern C2 is a luminance shading pattern Determined.

  When the luminance parameters L1 to L4 satisfy the numerical condition of L1 <ave <L2 <L3 <L4 and the luminance parameters L1 and L4 correspond to the evaluation areas B3 and B2 on the imaging surface, the pattern C3 is used as the luminance shading pattern. Determined. When the luminance parameters L1 to L4 satisfy the numerical condition of L1 <ave <L2 <L3 <L4, and the luminance parameters L1 and L4 correspond to the evaluation areas B4 and B1 on the imaging surface, respectively, the pattern C4 is a luminance shading pattern Determined.

  The flash memory 42m stores gain tables 42t1 to 42t3 shown in FIGS. According to FIG. 6, the numerical value range indicated by the difference value “L4−L1” between the luminance parameters L1 and L4 is “less than 0.2”, “0.2 to 0.3”, “0.3 to 0.5”. ”,“ 0.5 to 0.6 ”and“ 0.6 or more ”, and is divided into L1 and L2 side end portions (joint band connecting two evaluation areas corresponding to the luminance parameters L1 and L2). , And gain values of L3 to L4 side end portions (joint band connecting two evaluation areas corresponding to the luminance parameters L3 and L4) are assigned to each of the five divided ranges.

  The gain values at the L1 and L2 side end portions are positive values, and increase as the difference value “L4−L1” increases. On the other hand, the gain value at the L3 to L4 side end is a negative value, and decreases as the difference value “L4−L1” increases. Furthermore, the absolute value of the gain value at the L1-L2 side end is larger than the absolute value of the gain value at the L3-L4 side end.

  Each of the five divided ranges on the gain table 42t1 includes a gain value at one end in the parallel direction (one end of the imaging surface in a direction parallel to the above-described coupling band) and the other end in the parallel direction (the above-described coupling band). The gain value of the other end of the imaging surface in the direction parallel to the image is also assigned. However, these gain values all indicate “0”.

  According to FIG. 7, the numerical value range indicated by the difference value “L4−L2” between the luminance parameter values L2 and L4 is “less than 0.3”, “0.3 to 0.5”, “0.5 to 0. Divided into four ranges of “6” and “0.6 or more”, the gain value of the L2 area (evaluation area corresponding to the luminance parameter L2) and the gain value of the L4 area (evaluation area corresponding to the luminance parameter L4) are four. Assigned to each of the two split ranges. The gain value in the L2 area is a positive value and increases as the difference value “L4−L2” increases. On the other hand, the gain value in the L4 area is “0” or a negative value, and decreases as the difference value “L4−L2” increases. Furthermore, the absolute value of the gain value in the L2 area is larger than the absolute value of the gain value in the L4 area. The gain value described in the gain table 42t2 is half or less than the gain value described in the gain table 42t1.

  The gain table 42t3 illustrated in FIG. 8 is the same as the gain table 42t2 illustrated in FIG. 7 except that the luminance parameter value L3 is noticed instead of the luminance parameter value L2, and thus a duplicate description is omitted.

  When the pattern A1, A2, B1, or B2 is determined as the luminance shading pattern, four gain values corresponding to the difference value “L4-L1” are read from the gain table 42t1 shown in FIG. When any one of the patterns C1 to C4 is determined as the luminance shading pattern, two gain values corresponding to the difference value “L4-L2” are read from the gain table 42t2 illustrated in FIG. Two gain values corresponding to L4-L3 "are read from the gain table 42t3 shown in FIG.

  A gain curve that conforms to the pattern A1, A2, B1, or B2 is created based on the four gain values read from the gain table 42t1. Specifically, the gain curve that changes the gain value of the L1-L2 side end and the gain value of the L3-L4 side end and changes to indicate “0” at the substantially center, and the parallel direction one end A gain curve connected by a straight line connecting the gain value and the gain value at the other end in the parallel direction is created by interpolation calculation.

  A gain curve that conforms to the pattern C1, C2, C3, or C4 is created based on the two gain values read from the gain table 42t2 and the two gain values read from the gain table 42t3. Specifically, a gain curve that connects the gain value of the L2 area and the gain value of the L4 area and changes so as to show “0” at the center, and the gain value of the L3 area and the gain value of the L4 area are connected. In addition, a gain curve that changes so as to indicate “0” in the approximate center is created by interpolation.

In the gain curve thus created, the luminance levels at both ends subjected to luminance correction are the luminance level at one end (bright side) before correction, and the luminance level at the other end (dark side) before correction. The characteristic which agree | coincides with the average value of is shown. The created gain curve is stored in the flash memory 42m. If the luminance shading pattern does not correspond to any of the above-described patterns A1 to A2, B1 to B2, and C1 to C4, a predetermined gain curve is stored in the flash memory 42m.

  The pattern A1 is determined when the luminance on the left side of the imaging surface falls as shown in FIG. At this time, the gain curve corresponding to the horizontal direction changes in an S shape, and the gain curve corresponding to the vertical direction becomes a straight line indicating “0”. The pattern A2 is determined when the luminance on the right side of the imaging surface falls as shown in FIG. At this time, the gain curve corresponding to the horizontal direction changes in an inverted S shape, and the gain curve corresponding to the vertical direction is a straight line indicating “0”.

  The pattern B1 is discriminated when the luminance on the upper side of the imaging surface falls as shown in FIG. At this time, the gain curve corresponding to the vertical direction changes in an inverted S shape, and the gain curve corresponding to the horizontal direction is a straight line indicating “0”. The pattern B2 is determined when the luminance on the lower side of the imaging surface falls as shown in FIG. At this time, the gain curve corresponding to the vertical direction changes in an S shape, and the gain curve corresponding to the horizontal direction is a straight line indicating “0”.

  The pattern C1 is discriminated when the upper left luminance of the imaging surface falls as shown in FIG. At this time, the gain curve corresponding to the horizontal direction changes to an S shape, and the gain curve corresponding to the vertical direction changes to an inverted S shape. The pattern C2 is discriminated when the luminance at the upper right of the imaging surface falls as shown in FIG. At this time, both the gain curve corresponding to the horizontal direction and the gain curve corresponding to the vertical direction change in an inverted S shape.

  The pattern C3 is discriminated when the lower left luminance of the imaging surface falls as shown in FIG. At this time, both the gain curve corresponding to the horizontal direction and the gain curve corresponding to the vertical direction change in an S shape. The pattern C4 is discriminated when the lower right luminance of the imaging surface falls as shown in FIG. At this time, the gain curve corresponding to the horizontal direction changes to an inverted S shape, and the gain curve corresponding to the vertical direction changes to an S shape.

  Therefore, for example, when luminance shading occurs on the right side of the imaging surface shown in FIG. 12A and the luminance changes as shown in FIG. 12B, the gain curve shown in FIG. Created corresponding to the direction. The luminance corrected using such a gain curve changes as shown in FIG. As a result, the reduction in luminance on the right side of the imaging surface is alleviated, while the luminance is reduced on the left side of the imaging surface. That is, luminance reduction occurs at both ends in the horizontal direction of the imaging surface. The luminance levels at both ends in the horizontal direction after correction indicate an average value of the luminance level at one end (bright side) in the horizontal direction before correction and the luminance level at the other end (dark side) in the horizontal direction before correction.

  Similarly, the luminance shading shown in FIG. 13 (A) is corrected as shown in FIG. 13 (D), the luminance shading shown in FIG. 13 (B) is corrected as shown in FIG. 13 (E), and FIG. The luminance shading shown in (C) is corrected as shown in FIG. Thus, by generating the equivalent luminance reduction at a symmetrical position, it is possible to improve the appearance of the image subjected to the shading correction.

  When a default operation is performed in the adjustment process, the CPU 42 executes a process according to the flowchart shown in FIG. A control program corresponding to this flowchart is stored in the flash memory 42m.

  First, the imaging conditions are initialized in step S1, the settings of the luminance shading correction circuit 24 are initialized in step S3, and the imaging process is executed in step S5. The gain curve set in the register 24h by the initialization shows a straight line (gain value: 0) in both the vertical direction and the horizontal direction. Through the imaging process, one frame of raw image data having a low resolution is created. In step S 7, integrated values Ir (*), Ig (*) and Ib (*) based on this raw image data are taken from the luminance shading correction circuit 24. In step S9, the luminance shading pattern is determined based on the integrated values Ir (*), Ig (*), and Ib (*).

  If the determined luminance shading pattern is the pattern A1, A2, B1, or B2, the process proceeds from step S11 to step S15, and four gain values are extracted from the gain table 42t1 shown in FIG. If the determined luminance shading pattern is the pattern C1, C2, C3 or C4, the process proceeds from step S13 to step S17, and two gain values are obtained from each of the gain table 42t2 shown in FIG. 7 and the gain table 42t3 shown in FIG. Extract.

  When the process of step S15 or S17 is completed, the process proceeds to step S19, and a gain curve that matches the pattern determined in step S9 is created. The created gain curve changes in the manner shown in any of FIGS. 9 (A) to 9 (H). In step S21, the gain curve created in this way is stored in the flash memory 42m, and then the process ends.

  If the determined luminance shading pattern is not one of the patterns A1, A2, B1, B2 and C1 to C4, the predetermined gain curve is stored in the flash memory 42m in step S23, and the process is terminated.

  When the camera mode is selected at the use stage of the user, the CPU 42 executes processing according to the flowcharts shown in FIGS. A control program corresponding to this flowchart is stored in the flash memory 42m.

  First, in step S31, imaging conditions are initialized. In step S33, the gain curve stored in the flash memory 42m is set in the luminance shading correction circuit 24. When the setting is completed, through image processing is executed in step S35. As a result, a through image is displayed on the LCD monitor 28.

  In step S37, it is determined whether or not the shutter button 44s has been half-pressed. If “NO” here, a through image AE process is executed in a step S39, and a through image WB adjustment process is executed in a step S41. As a result, the brightness and white balance of the through image displayed on the LCD monitor 28 are appropriately adjusted. In step S43, it is determined whether or not the zoom key 44z has been operated. If NO, the process returns to step S37. If YES, the zoom lens 12 is moved in the optical axis direction in step S45, and then the process returns to step S37.

  If YES is determined in the step S37, the recorded image AE process is executed in a step S47, and the recorded image WB adjustment process is executed in a step S49. In step S51, the gain curve set in the luminance shading correction circuit 24 is corrected based on the current zoom magnification (see FIG. 10). In step S53, the gain curve set in the luminance shading correction circuit 24 is corrected based on the EV value defining the current exposure amount (see FIG. 11). In step S55, it is determined whether or not the shutter button 44s has been fully pressed. In step S57, it is determined whether or not the operation of the shutter button 44s has been released. If “YES” in the step S55, the process returns to the step S35 through a recording process, and if “YES” in the step S57, the process returns to the step S37 as it is.

  As can be seen from the above description, the image sensor 16 has an imaging surface on which an optical image representing the object scene is irradiated, and outputs an object scene image generated on the image pickup surface. The luminance of the object scene image output from the image sensor 16 is corrected by the luminance shading correction circuit 24 with reference to a gain curve (luminance correction value) set by the CPU 42. When a predetermined operation is performed in the adjustment process, the CPU 42 selects any one of the specific patterns (A1 to A2, B1 to B2, C1 to C4) in which the luminance shading pattern on the imaging surface decreases in luminance corresponding to the first position on the imaging surface. It is determined whether or not this is true (S9). If the determination result is affirmative, the CPU 42 selects a gain curve (first correction value) having a reduction characteristic for reducing the luminance corresponding to the second position on the imaging surface symmetrical to the first position (S15). , S17, S19, S21). If the determination result is negative, a predetermined gain curve (second correction value) is selected by the CPU 42 (S23).

  Therefore, when the luminance corresponding to the first position on the imaging surface is reduced, the luminance of the object scene image is corrected so that the luminance corresponding to the second position on the imaging surface symmetrical to the first position is reduced. . The corrected object scene image is an image with reduced luminance at both the first position and the second position. Thereby, the appearance of the image subjected to the shading correction can be improved.

  In this embodiment, the luminance shading correction circuit 24 is provided with amplifiers 24a, 24b and 24c corresponding to R data, G data and B data, respectively, but the amplifiers 24a and 24c are provided in the white balance adjustment circuit 22. It may be integrated with the amplifier for R data and the amplifier for B data.

  In this embodiment, the gain curve is corrected when the shutter button 44s is half-pressed. In addition, the gain curve is corrected before the shutter button 44s is half-pressed. It may be.

  Further, in this embodiment, the luminance reduction caused by the luminance shading is alleviated by correction according to the gain curve, but the process for mitigating the luminance reduction may be omitted. However, in that case, it is necessary to make the reduction width of the luminance on the opposite side larger than the reduction width of this embodiment.

It is a block diagram which shows the structure of one Example of this invention. It is a block diagram which shows an example of a structure of the luminance shading correction circuit of FIG. 1 Example. FIG. 5 is an illustrative view showing one portion of an operation of an integrating circuit provided in the embodiment in FIG. 2; It is an illustration figure which shows an example of the brightness | luminance parameter table referred by CPU of FIG. 1 Example. It is an illustration figure which shows the brightness | luminance shading pattern assumed in this Example. It is an illustration figure which shows an example of the gain table referred by CPU of FIG. 1 Example. It is an illustration figure which shows another example of the gain table referred by CPU of FIG. 1 Example. It is an illustration figure which shows another example of the gain table referred by CPU of FIG. 1 Example. (A) is an illustrative view showing a distribution state of luminance shading corresponding to the pattern A1 and a gain curve for correcting the distribution state, and (B) shows a distribution state of luminance shading corresponding to the pattern A2 and a gain curve for correcting the distribution state. (C) is an illustrative view showing a distribution state of luminance shading corresponding to the pattern B1 and a gain curve for correcting this, and (D) is a distribution state of luminance shading corresponding to the pattern B2 and this. (E) is an illustrative view showing a luminance shading distribution state corresponding to the pattern C1 and a gain curve for correcting this, and (F) is a luminance diagram corresponding to the pattern C2. It is an illustration figure which shows the distribution state of a shading, and the gain curve which correct | amends this, (G) is the brightness | luminance shader corresponding to the pattern C3. It is an illustrative view showing a gain curve to correct this and distribution of ring, (H) is an illustrative view showing a gain curve to correct this and distribution of luminance shading corresponding to the pattern C4. It is a graph which shows the relationship between the correction coefficient K1 of a gain curve, and EV value. It is a graph which shows the relationship between the correction coefficient K2 of a gain curve, and zoom magnification. (A) is an illustrative view showing an example of an imaging surface, (B) is a waveform diagram showing an example of luminance change before correction in the horizontal direction, and (C) is an example of change in gain curve in the horizontal direction. (D) is a waveform diagram showing an example of a luminance change after correction in the horizontal direction. (A) is an illustrative view showing an example of the luminance distribution before correction, (B) is an illustrative view showing another example of the luminance distribution before correction, and (C) is another diagram of the luminance distribution before correction. It is an illustration figure which shows an example, (D) is an illustration figure which shows an example of the luminance distribution after correction | amendment, (E) is an illustration figure which shows another example of the luminance distribution after correction | amendment, (F) is It is an illustration figure which shows another example of the luminance distribution after correction | amendment. It is a flowchart which shows a part of operation | movement of CPU applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU applied to the FIG. 1 Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 12 ... Zoom lens 16 ... Image sensor 24 ... Luminance shading correction circuit 34 ... Post-processing circuit 42 ... CPU

Claims (7)

An imaging unit having an imaging surface on which an optical image representing a subject is irradiated, and outputting a subject image generated on the imaging surface;
Correction means for correcting the luminance of the subject image output from the imaging means with reference to a luminance correction value;
Determining means for determining whether or not the luminance shading pattern of the imaging surface corresponds to a specific pattern in which the luminance corresponding to the first position of the imaging surface is reduced;
When the determination result of the determination means is affirmative, a first correction value having a reduction characteristic for reducing the luminance corresponding to the second position of the imaging surface that is symmetrical to the first position is selected as the luminance correction value. First selection means, and second selection means for selecting a predetermined second correction value as the luminance correction value when the determination result of the determination means is negative,
The electronic camera , wherein the first correction value further has an increase characteristic that increases a luminance corresponding to the first position . The first correction value is the luminance after correction at the first position and the luminance after correction at the second position. The luminance before correction at the first position and the luminance before correction at the second position. The electronic camera according to claim 1 , wherein the electronic camera exhibits a characteristic that matches an average value. The first position is a belt-like position extending in a vertical direction at one horizontal end of the imaging surface, and the second position is a belt-like position extending in a vertical direction at the other horizontal end of the imaging surface. The electronic camera according to any one of 1 to 2 . The first position is a belt-like position extending in a horizontal direction at one vertical end of the imaging surface, and the second position is a belt-like position extending in a horizontal direction at the other vertical end of the imaging surface. The electronic camera according to any one of 1 to 2 . 3. The first position according to claim 1, wherein the first position is one of four corners forming the imaging surface, and the second position is a position diagonal to the first position among the four corners forming the imaging surface . An electronic camera according to any one of the above. Further comprising an electronic camera according to any one of claims 1 to 5 the first correction means for correcting in accordance with the luminance correction value to change the optical zoom magnification. Further comprising an electronic camera according to any one of claims 1 to 6 the second correction means for correcting in accordance with the luminance correction value for the exposure amount of the imaging surface.

Images