JP2010021915A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera capable of executing proper shading correction in accordance with a picked-up scene. <P>SOLUTION: The digital camera includes: an imaging section for imaging a subject and generating the data of the image; an evaluation value calculating section for dividing an imaging screen into a plurality of areas and calculating an evaluation value for each area based on the image data generated by the imaging section; a determination section for determining whether or not shading correction is performed for each area based on the evaluation value calculated by the evaluation value calculating section; and a shading correction section for executing shading correction for areas determined to be subjected to shading correction by the determination section and not executing shading correction for areas determined not to be subjected to shading correction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a digital camera that images a subject and generates image data.

  2. Description of the Related Art Conventionally, a digital camera that corrects a light amount drop (shading) around an image is known.

For example, the digital camera of Patent Document 1 divides an image into a plurality of blocks, and performs shading correction for each pixel based on light amount correction data set for each block.
JP 2001-275029 A

  However, the above-described digital camera uniformly performs shading correction on the captured image. Therefore, there is a possibility that appropriate shading correction according to the imaging scene is not necessarily performed. For example, a high brightness subject in the image may be saturated. In addition, an entirely dark image such as a night view becomes bright overall, and the user may feel uncomfortable. Furthermore, noise may be noticeable in an image having an edge.

  Therefore, an object of the digital camera of the present invention is to perform an appropriate shading correction according to an imaging scene.

  The digital camera of the present invention includes an imaging unit that captures a subject and generates image data, and an imaging screen that is divided into a plurality of areas, and is evaluated for each area based on the image data generated by the imaging unit. An evaluation value calculation unit that calculates a value, a determination unit that determines whether or not to perform shading correction for each area based on the evaluation value calculated by the evaluation value calculation unit, and shading correction by the determination unit A shading correction unit that performs shading correction on an area determined to be performed and does not perform shading correction on an area determined not to perform shading correction.

  Preferably, the image processing apparatus further includes a memory that stores in advance a shading correction value corresponding to each area, and the determination unit calculates the evaluation value calculated by the evaluation value calculation unit and the shading correction stored in the memory. It may be determined whether shading correction is performed for each area by comparing the values.

  Preferably, the determination unit may determine whether to perform shading correction for each area by comparing the evaluation value calculated by the evaluation value calculation unit with a threshold value.

  Preferably, the image processing apparatus further includes an edge detection unit that detects an edge for each area based on the image data generated by the imaging unit, and the determination unit detects the edge by the edge detection unit. Alternatively, it may be determined that the shading correction is not performed on the area where the edge is not detected.

  Preferably, the image processing apparatus further includes an edge amount calculation unit that calculates an edge amount for each area based on the data of the image generated by the imaging unit, and the determination unit includes an area located at the center of the image. The ratio between the evaluation value and the evaluation value of the area located around the image approximates the reciprocal of the shading correction value corresponding to the area located around the image, and is located around the image. It may be determined that the shading correction is performed when the edge amount of the area to be processed is equal to or smaller than the threshold value.

  In addition, preferably, it further includes a photometry unit that measures the luminance of the subject, and a gain value calculation unit that calculates a gain value corresponding to the luminance measured by the photometry unit, and the shading correction unit includes the gain value Shading correction may be performed based on the gain value calculated by the calculation unit.

  Preferably, an average value calculation unit that calculates an average value of the evaluation values of all areas included in the image generated by the imaging unit, and a gain value corresponding to the average value calculated by the average value calculation unit And a shading correction unit that performs shading correction based on the gain value calculated by the gain value calculation unit.

  According to the digital camera of the present invention, it is possible to perform appropriate shading correction according to the imaging scene.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a digital camera 1 according to an embodiment of the present invention. As shown in FIG. 1, the digital camera 1 includes an imaging lens 2, an imaging device 3, an A / D conversion unit 4, an image processing unit 5, a buffer memory 6, a memory 7, a control unit 8, a display unit 9, a recording I / O. An F unit 10, a recording medium 11, an operation unit 12, and a bus 13 are provided.

  The imaging lens 2 forms a subject image on the imaging surface of the imaging element 3. The image sensor 3 photoelectrically converts a subject image formed by a light beam that has passed through the imaging lens 2 and outputs an analog image signal corresponding to each of R, G, and B colors. Here, in the imaging mode, the imaging device 3 captures a recording image (main image) when a release button described later is fully pressed. Further, the imaging device 3 captures a through image by thinning-out reading at predetermined intervals even during standby for imaging. The output of the image sensor 3 is connected to the A / D converter 4. The A / D conversion unit 4 performs A / D conversion of the output signal of the image sensor 3.

  The image processing unit 5 performs various types of image processing (white balance adjustment, shading correction, color interpolation, gradation conversion processing, contour enhancement processing, etc.) on the data output from the A / D conversion unit 4. The image processing unit 5 also executes a process of compressing the image data in the JPEG format before recording the image data on the recording medium 11 and a process of decompressing and restoring the compressed data. The buffer memory 6 temporarily records image data in the pre-process and post-process of the image processing by the image processing unit 5.

  The memory 7 has a shading correction table 7a for correcting a light amount drop around the image. Details of the shading correction table 7a will be described later. The control unit 8 is a processor that performs overall control of the digital camera 1 in accordance with a predetermined sequence program. The control unit 8 performs various calculations required at the time of imaging, calculation of shading correction values described later, and the like.

  The display unit 9 displays various images under the control of the control unit 8. Various images displayed on the display unit 9 include a main image, a through image, an image recorded on the recording medium 11, a menu screen, and the like. The recording I / F unit 10 is formed with a connector for connecting the recording medium 11. Then, the recording I / F unit 10 executes data writing / reading with respect to the recording medium 11 connected to the connector. The operation unit 12 includes a release button, an operation button, and the like. The release button receives an input of a release instruction from the user. The operation button receives an operation input on the menu screen or the like from the user. The state of the operation unit 12 is detected by the control unit 8.

  The image processing unit 5, the buffer memory 6, the memory 7, the control unit 8, and the recording I / F unit 10 are connected to each other via a bus 13. The output of the A / D conversion unit 4 is connected to the image processing unit 5 via the bus 13. The outputs of the image processing unit 5 and the recording I / F unit 10 are connected to the display unit 9 via the bus 13.

  FIG. 2 is a flowchart showing the operation of the control unit 8 at the time of imaging in the digital camera 1. An example in which an image is divided into 35 areas will be described below.

  In step S1, the control unit 8 starts an imaging mode. For example, the control unit 8 controls the imaging device 3 to start capturing a through image.

  In step S2, the control unit 8 performs an exposure calculation. For example, the control unit 8 calculates a Bv value (subject brightness) based on the data of the through image captured in step S1. Then, the control unit 8 sets the Bv value, the imaging sensitivity and the exposure mode set on the menu screen via the operation buttons (for example, the program priority exposure mode, the aperture priority exposure mode, the shutter speed priority exposure mode, etc.). The shutter speed and aperture value are calculated based on the imaging conditions.

  In step S3, the control unit 8 determines whether or not the release button has been fully pressed. If the release button is fully pressed (YES), the process proceeds to step S4. On the other hand, if the release button is not fully pressed (NO), the process waits until the release button is fully pressed.

  In step S4, the control unit 8 captures the main image. An example of the main image captured in step S4 is shown in FIG.

  Here, the shading correction table 7a will be described. The shading correction table 7a stores a shading correction value corresponding to each area. An example of the shading correction table 7a is shown in FIG. In the following, the luminance of any area is Yn, the luminance of the area located in the center of the image is Y, the shading correction value corresponding to any of the above areas is Gn, and the area located in the central part of the image corresponds to Let G be the shading correction value. When a uniform luminance surface is imaged, the ratio of Y and Yn (Yn / Y) and the ratio of Gn and G (G / Gn) coincide.

  By the way, the image captured by the digital camera 1 is not limited to a uniform luminance surface, for example, an image having a high-luminance subject in the periphery, a dark image such as a night scene, a landscape with a flat upper side and an edge on the lower side. There are various images. If shading correction is uniformly performed on various image data in this way, if there is a high-luminance subject in the vicinity, the high-luminance subject may be saturated. Also, an overall dark image such as a night view is generally brighter and the user may feel uncomfortable. Further, noise may be conspicuous in a portion having an edge. Note that if the noise reduction processing is strengthened to suppress this noise, there is a problem that details are lost.

  Therefore, the digital camera 1 of the present embodiment performs the following processing to perform appropriate shading correction according to the imaging scene.

  In step S5, the control unit 8 calculates the luminance for each area for all areas included in the main image captured in step S4.

  In step S6, the control unit 8 calculates a gain value corresponding to the brightness of the entire image. The relationship between the brightness of the entire image and the gain value is recorded in the memory 7 in advance. FIG. 5 is a diagram illustrating the relationship between the brightness of the entire image and the gain value. For example, the control unit 8 divides the total luminance for each area calculated in step S5 by the total number of areas 35, calculates the average value of the luminance of all the areas, and sets the brightness of the entire image. Then, the control unit 8 calculates a gain value based on the relationship recorded in the memory 7. Note that the control unit 8 may use the Bv value calculated in step S2 as the brightness of the entire image.

  In step S7, the control unit 8 reads the shading correction values for all areas from the shading correction table 7a. Then, the control unit 8 compares the luminance calculated in step S5 with the read shading correction value for each area. For example, the control unit 8 determines whether or not the following expression is satisfied for each area. Note that Th is a threshold value.

| Yn / YG / Gn | ≦ Th
In step S8, the control unit 8 sets a flag A for determining whether or not to perform shading correction for each area based on the result determined in step S7. For example, if the above equation is satisfied, the control unit 8 determines to perform shading correction and sets the flag A to 1. On the other hand, if the above equation is not satisfied, the control unit 8 determines that the shading correction is not performed, and sets the flag A to 0. Thereby, a possibility that the high-intensity subject in the image is saturated can be reduced. An example in which the flag A is set for each area is shown in FIG.

  In step S9, the control unit 8 calculates an edge amount for each area for all areas included in the main image captured in step S4. For example, the control unit 8 calculates the edge amount based on the difference between the luminance of each pixel included in the area and the luminance of the pixel adjacent to the pixel.

  In step S10, the control unit 8 determines for each area whether or not the edge amount calculated in step S9 is equal to or less than a threshold value.

  In step S11, the control unit 8 sets, for each area, a flag B indicating whether or not to perform shading correction based on the result determined in step S10. For example, if the edge amount is less than or equal to the threshold, the control unit 8 determines that shading correction is to be performed, and sets the flag B to 1. This is because an area with a small edge amount is flat and smooth, and shading is conspicuous.

  On the other hand, when the edge amount is larger than the threshold value, the control unit 8 determines that the shading correction is not performed, and sets the flag B to 0. In areas where the amount of edges is large, shading is inconspicuous due to irregularities. Another reason is not to increase the noise multiplied by the shading correction value. An example in which the flag B is set for each area is shown in FIG.

  In step S12, the control unit 8 sets a final flag C for determining whether to perform shading correction for each area based on the flag A set in step S8 and the flag B set in step S11. For example, the control unit 8 determines that shading correction is performed for an area where the flag A is 1 and the flag B is 1, and sets the flag C to 1. On the other hand, the control unit 8 determines that no shading correction is performed in an area where the flag A is 0 or the flag B is 0, and sets the flag C to 0. An example in which the flag C is set for each area is shown in FIG.

  In step S13, the control unit 8 reads the shading correction values for all areas from the shading correction table 7a. And the control part 8 changes the read shading correction value for every area based on the gain value calculated by step S6. When the shading correction value after change is G′n, G′n is expressed by the following equation.

G′n = (Gn−1) × (gain value) +1
Thereby, the shading correction value can be changed according to the brightness of the entire image. For example, as shown in FIG. 5, the gain value approaches 0 as the entire image becomes darker, so the shading correction value becomes smaller. Therefore, for example, when a dark night scene is imaged as a whole, the entire scene is not bright and the night scene atmosphere is not impaired.

  In step S14, the control unit 8 recalculates the shading correction value of an area at the boundary between the area where shading correction is performed and the area where shading correction is not performed (hereinafter referred to as a boundary area). For example, the control unit 8 extracts an area where the flag C of the adjacent area is 1 from the areas where the flag C set in step S12 is 0, and sets it as a boundary area. Then, for each boundary area, the control unit 8 calculates an average value of the shading correction value of the boundary area changed in step S13 and the shading correction value “1” when no shading correction is performed. If the shading correction value of the boundary area after recalculation is G ″ n, G ″ n is expressed by the following equation.

G ″ n = (G′n + 1) / 2
Thereby, since the shading correction value of the boundary area is smoothed, the boundary between the area where the shading correction is performed and the area where the shading correction is not performed becomes inconspicuous.

  In step S15, the control unit 8 creates a final shading correction table. For example, the control unit 8 sets the shading correction value changed in step S13 for the area where the flag C set in step S12 is 1. Further, the control unit 8 sets the shading correction value recalculated in step S14 for the boundary area extracted in step S14. Then, the control unit 8 sets “1” for an area other than the above, that is, an area where the flag C is 0 and the flag C of the adjacent area is 0. An example of the final shading correction table is shown in FIG.

  In step S16, the control unit 8 controls the image processing unit 5 to perform various types of image processing on the main image data captured in step S4, and based on the final shading correction table created in step S15. Multiply the shading correction value corresponding to each area.

  In step S17, the control unit 8 records the data of the main image processed in step S16 on the recording medium 11.

  As described above, according to the digital camera of this embodiment, it is determined whether or not to perform shading correction for each area. Then, the shading correction is performed on the area determined to perform the shading correction, and the shading correction is not performed on the area determined not to perform the shading correction. Therefore, appropriate shading correction according to the imaging scene can be performed.

  In step S8, the flag A is set by comparing the luminance calculated in step S5 with the shading correction value. However, the present invention is not limited to this. For example, the control unit 8 determines for each area whether or not the luminance calculated in step S5 is equal to or less than a threshold value. If the brightness calculated in step S5 is equal to or less than the threshold, the flag A is set to 1. On the other hand, if the luminance calculated in step S5 is greater than the threshold, the flag A may be set to 0. Further, it may be determined for each area whether or not the Bv value calculated in step S2 is equal to or less than a threshold value, and the flag A may be set in the same manner as described above.

  In the above embodiment, the control unit 8 calculates the Bv value based on the data of the through image. However, the present invention is not limited to this. For example, the digital camera 1 includes a photometric sensor that measures the luminance of a subject. Then, the control unit 8 may calculate the Bv value based on the output of the photometric sensor.

  In step S14, the control unit 8 uses the shading correction value of the boundary area, but the present invention is not limited to this. For example, the control unit 8 may use the shading correction value changed in step S13 in the area adjacent to the boundary area and having the flag C set to 1 in step S12, instead of the shading correction value in the boundary area. good.

  In the above embodiment, an example in which shading correction is performed on the main image captured in step S4 has been described. However, the present invention is not limited to this. For example, the control unit 8 may perform shading correction on the image recorded on the recording medium 11. In this case, the control unit 8 reads the model name from the image file recorded on the recording medium 11. If it is determined that the image is captured by a digital camera of the same model as the digital camera 1, the processing from step S5 to step S17 may be performed based on the image data recorded on the recording medium 11. .

  In the above embodiment, the control unit 8 performs the shading correction by controlling the image processing unit 5 in step S <b> 16, but is not limited thereto. For example, when the imaging device 3 is a CMOS (Complementary Metal Oxide Semiconductor) image sensor, the exposure time can be set in advance for each pixel. Therefore, when the image pickup device 3 is a CMOS image sensor, the control unit 8 performs the processing from step S5 to step S15 based on the data of the through image immediately before the release button is fully pressed in step S3. A typical shading correction table. Then, the control unit 8 sets the exposure time of each pixel based on this final shading correction table. Thereafter, when the release button is fully pressed in step S3, the control unit 8 may read an analog image signal from the image sensor 3 for each set exposure time. In this case, in step S16, the control unit 8 controls the image processing unit 5 and does not perform shading correction. Therefore, it is possible to reduce noise corresponding to the shading correction value.

  In the above embodiment, one shading correction is set for each area, but the present invention is not limited to this. For example, shading correction values corresponding to R, G, and B colors may be set for each area. The shading correction value may be set based on a value obtained by individual adjustment of the digital camera 1, a center value of manufacturing variation, a value obtained from the imaging lens 2 and a lens barrel setting value (not shown), and the like.

It is a block diagram which shows the structure of the digital camera 1 in embodiment of this invention. 4 is a flowchart illustrating an operation of the control unit 8 at the time of imaging in the digital camera 1. It is a figure which shows the example of the main image imaged in step S4. It is a figure which shows the example of the shading correction table 7a. It is a figure which shows the relationship between the brightness of the whole image, and a gain value. It is a figure which shows the example which set the flag for every area, and a figure which shows the final shading correction table.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Imaging device, 4 ... A / D conversion part, 5 ... Image processing part, 7 ... Memory, 7a ... Shading correction table, 8 ... Control part

Claims (7)

An imaging unit that images a subject and generates image data;
An evaluation value calculation unit that divides an imaging screen into a plurality of areas and calculates an evaluation value for each area based on data of the image generated by the imaging unit;
A determination unit for determining whether to perform shading correction for each area based on the evaluation value calculated by the evaluation value calculation unit;
A digital camera comprising: a shading correction unit that performs shading correction on an area that is determined to be subjected to shading correction by the determination unit, and that does not perform shading correction on an area that is determined not to perform shading correction. The digital camera according to claim 1, wherein
A memory for storing in advance a shading correction value corresponding to each area;
The determination unit determines whether to perform shading correction for each area by comparing the evaluation value calculated by the evaluation value calculation unit and the shading correction value stored in the memory. A featured digital camera. The digital camera according to claim 1, wherein
The determination unit determines whether to perform shading correction for each area by comparing the evaluation value calculated by the evaluation value calculation unit with a threshold value. The digital camera according to claim 1, wherein
Based on the data of the image generated by the imaging unit, further comprising an edge detection unit for detecting an edge for each area,
The digital camera according to claim 1, wherein the determination unit performs shading correction on an area where the edge is detected by the edge detection unit, and determines not to perform shading correction on an area where the edge is not detected. The digital camera according to claim 1, wherein
An edge amount calculation unit that calculates an edge amount for each area based on the image data generated by the imaging unit;
The determination unit is configured such that a ratio between the evaluation value of the area located at the center of the image and the evaluation value of the area located around the image corresponds to the shading correction value corresponding to the area located around the image. The digital camera is characterized in that shading correction is determined to be performed when the edge amount of an area that is close to the reciprocal of the image and is located around the image is equal to or smaller than a threshold value. The digital camera according to any one of claims 1 to 3,
A metering unit for metering the luminance of the subject;
A gain value calculation unit that calculates a gain value corresponding to the luminance measured by the photometry unit;
The digital camera according to claim 1, wherein the shading correction unit performs shading correction based on the gain value calculated by the gain value calculation unit. The digital camera according to any one of claims 1 to 3,
An average value calculating unit that calculates an average value of the evaluation values of all areas included in the image generated by the imaging unit;
A gain value calculation unit that calculates a gain value according to the average value calculated by the average value calculation unit;
The digital camera according to claim 1, wherein the shading correction unit performs shading correction based on the gain value calculated by the gain value calculation unit.

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