JP5652488B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus.

A conventional imaging device is known that converts a captured image in accordance with the following gamma conversion.
Y = aX ^ γ + b [1]
However, X is a pixel value of the captured image, Y is a pixel value after conversion, a and b are constants, γ is a gamma value that determines gamma characteristics, and ^ is a power operator.

  Patent Document 1 discloses a technique for keeping the average brightness of an image after gamma conversion constant by changing the exposure condition of the imaging device in accordance with the switching of the gamma value.

JP 2002-84455 A

  Incidentally, an image correction technique for selectively brightening a dark area of image data, such as D-Lighting (registered trademark), is known. This type of image correction is a process performed separately from the above-described gamma conversion.

  An object of the present invention is to provide a technique for adaptively enhancing the appearance of image data in accordance with the image correction for brightening the dark area.

An imaging apparatus according to an example of the present invention includes a photometry unit, an exposure calculation unit, an imaging unit, and an image processing unit. The photometry unit measures the subject. The exposure calculation unit sets the exposure condition and determines the charge accumulation time based on the photometry result of the photometry unit . The imaging unit images a subject according to the exposure condition and generates image data. The image processing unit includes a second image processing for performing brightness enhancing correction of the dark region of the image represented by the first image processing and image data subjected to gradation conversion and color space conversion on the image data generated by the imaging unit And a second mode in which only the first image processing is performed without performing the second image processing, and one of the first mode and the second mode is set by a user's prior reservation setting. Do. Further, the exposure calculation unit sets the exposure condition when the user sets to perform the second mode, and performs the second mode when the user sets the exposure condition to perform the first mode. The exposure conditions are set lower than when the user makes a reservation setting.
An imaging device according to another example of the present invention includes a photometry unit, an exposure calculation unit, an imaging unit, and an image processing unit. The photometry unit measures the subject. The exposure calculation unit sets the exposure condition and determines the photographing sensitivity based on the photometry result of the photometry unit. The imaging unit images a subject according to the exposure condition and generates image data. The image processing unit includes: first image processing that performs gradation conversion and color space conversion on the image data generated by the imaging unit; and second image processing that performs brightness improvement correction of a dark area of the image indicated by the image data. And a second mode in which only the first image processing is performed without performing the second image processing, and one of the first mode and the second mode is set by a user's prior reservation setting. Do. Further, the exposure calculation unit sets the exposure condition when the user sets to perform the second mode, and performs the second mode when the user sets the exposure condition to perform the first mode. The exposure conditions are set lower than when the user makes a reservation setting.

  In the present invention, the exposure condition at the time of shooting is changed corresponding to the correction setting for improving the brightness in the dark area. As a result, it is possible to obtain a good-looking image data by balancing the gradation of the dark area where the brightness is improved by the image correction and the gradation of the bright area mainly determined by the exposure condition.

2 is a block diagram illustrating a configuration of an imaging apparatus 11. FIG. 4 is a flowchart for explaining the operation of the imaging apparatus 11. It is a figure which shows an example of parameter Lpw. It is a figure which shows an example of parameter fg [YL (x, y)]. It is a flowchart explaining operation | movement of photometry and exposure calculation. It is a figure which shows the field division of division | segmentation photometry. It is a figure which shows an example of the setting table of k1-k4.

[1] Description of Configuration of Imaging Device 11 FIG. 1 is a block diagram showing the configuration of the imaging device 11.

  In FIG. 1, a photographing lens 12 is attached to the imaging device 11. The photographing lens 12 is provided with a diaphragm 12a. In the image space of the taking lens 12, a shutter 13a and an image sensor 13 are arranged. The operation of the image sensor 13 is controlled by the output pulse of the timing generator 22b. The image data generated by the imaging device 13 is temporarily stored in the buffer memory 17 via the signal processing unit 15 (including a gain adjustment unit corresponding to imaging sensitivity) and the A / D conversion unit 16. The buffer memory 17 is connected to the bus 18. An image processing unit 19, a card interface 20, a microprocessor 22, a compression / decompression unit 23, and an image display unit 24 are connected to the bus 18. The card interface 20 records image data on a removable memory card 21. The microprocessor 22 is connected to a switch group 22a, a timing generator 22b, and a photometric sensor 22c of the imaging device 11. Further, the microprocessor 22 also controls the aperture 12a and the shutter 13a. The image display unit 24 displays an image or the like on a monitor screen 25 provided on the back surface of the imaging device 11.

[2] Description of Imaging Operation FIG. 2 is a flowchart illustrating the operation of the imaging device 11. Hereinafter, this operation will be described along the step numbers shown in FIG.

  Step S1: The microprocessor 22 performs photometry and exposure calculation, and determines subject exposure conditions (aperture value, charge accumulation time, imaging sensitivity, etc.). This operation will be described in detail later.

  Step S2: The microprocessor 22 detects the shutter release depression by the user via the switch group 22a.

  Here, when the depression of the shutter release is not detected, the microprocessor 22 returns the operation to step S1.

  On the other hand, when it is detected that the shutter release is depressed, the microprocessor 22 shifts the operation to step S3.

  Step S3: The microprocessor 22 drives the aperture 12a, the shutter 13a, the timing generator 22b, etc., and performs imaging according to the exposure conditions (aperture value, charge accumulation time) set in Step S1. The signal processing unit 15 amplifies the image data read from the image sensor 13 by applying an imaging gain corresponding to the imaging sensitivity. The amplified image data is A / D converted by the A / D converter 16 and then temporarily recorded in the buffer memory 17.

  Step S4: The image processing unit 19 performs normal image processing such as gradation conversion (gamma conversion) and color space conversion on the image data in the buffer memory 17.

  Step S5: The user can make a reservation setting in advance for image correction to be performed on the image data by operating the switch group 22a. As one of the image corrections, an image correction for improving brightness in a dark area is prepared like D-lighting. The microprocessor 22 refers to the correction setting data for the image correction and determines whether or not to improve the brightness of the dark area.

  Here, when not performing the brightness improvement of a dark part area | region, the microprocessor 22 transfers operation | movement to step S12.

  On the other hand, when improving the brightness of the dark area, the microprocessor 22 shifts the operation to step S6.

  Step S6: The image processing unit 19 performs the following smoothing process on the luminance component Y (x, y) of the image data to obtain a smoothed image YL (x, y).

  (X, y) in the above expression is a coordinate value indicating the position of the processing pixel. (i, j) is a relative coordinate value of a neighboring pixel reflected in the smoothing process. r is a radius value indicating the selection range of the neighboring pixels. Lpw is a weighted ratio of neighboring pixels as shown in FIG. From the pixel value of the smoothed image YL (x, y) obtained in this way, it is possible to know in which area the pixel position (x, y) of the image data is located.

  Step S7: The microprocessor 22 refers to the correction setting data for the image correction, and determines whether to increase the brightness of the dark part region.

  Here, when the lightness improvement of the dark part region is performed weakly, the microprocessor 22 shifts the operation to step S8.

  On the other hand, in the case where the brightness improvement in the dark area is to be performed with a higher intensity, the microprocessor 22 shifts the operation to step S9.

  Step S8: The microprocessor 22 selects the weak parameter fg from the two types of parameters fg as shown in FIG.

  The parameter fg decreases monotonously and approaches 1 as the neighborhood range including the pixel position (x, y) of the image data becomes brighter (the value of the smoothed image YL (x, y) increases). Conversely, the darker the neighborhood (the smaller the value of the smoothed image YL (x, y)), the greater the value of the parameter fg.

  After setting the parameter fg, the microprocessor 22 shifts the operation to step S10.

  Step S9: The microprocessor 22 selects the stronger parameter fg from the two types of parameters fg as shown in FIG.

  This strong parameter fg takes a larger value than the weak parameter fg set in step S8.

  After setting the strong parameter fg, the microprocessor 22 shifts the operation to step S10.

Step S10: The image processing unit 19 substitutes the value of the smoothed image YL (x, y) obtained in step S6 for the set parameter fg to obtain the gain map GM (x, y).
GM (x, y) = fg [YL (x, y)] ... [2]
Step S11: The image processing unit 19 performs gradation correction on the signal component RGB of the image data in the buffer memory 17 using the gain map GM (x, y) as shown in the following equation, and the image after gradation correction Data RcGcBc is obtained.
Rc (x, y) = R (x, y) · GM (x, y)
Gc (x, y) = G (x, y) · GM (x, y)
Bc (x, y) = B (x, y) · GM (x, y)
By such image correction, the dark area of the image data is corrected brightly.

  Step S12: The card interface 20 compresses and stores the image data in the memory card 21.

[3] Description of photometry and exposure calculation FIG. 5 is a flowchart for explaining the operation (photometry and exposure calculation) of step S1 described above.

  Hereinafter, this operation will be described along the step numbers shown in FIG.

  Step S31: The microprocessor 22 acquires correction setting data for the image correction (steps S5 to S11 described above) reserved for the image data after imaging.

  Step S32: The photometric sensor 22c divides the object scene into five areas shown in FIG. 6 and performs photometry. The microprocessor 22 acquires five divided photometric values Bv [1] to Bv [5] as a result of the divided photometry.

  Note that the photometry section is not limited to the five divisions shown in FIG. Actually, the photometric section may be determined in accordance with the specifications of the photometric sensor 22c.

Step S33: The microprocessor 22 substitutes the divided photometric values Bv [1] to Bv [5] into the following formula to obtain the average photometric value Bv _MEAN , the bright part photometric value Bv _MAX , and the central part photometric value Bvc.
Bv _MEAN = (Bv [1] + Bv [2] + Bv [3] + Bv [4] + Bv [5]) / 5
Bv _MAX = MAX [Bv [1], Bv [2], Bv [3], Bv [4], Bv [5])
Bvc = Bv [1]
Step S34: The microprocessor 22 calculates the exposure control value Bv _CNTL by substituting the value obtained in Step S33 into the equation [3].
Bv _CNTL = k1 · Bv _MEAN + k2 · Bv _MAX + k3 · Bvc + k4 ... [3]
In addition, the values of the reflection ratios k1 to k3 and the offset value k4 in the expression [3] are determined so as to follow the following rules.
(1) When the brightness of the dark area is improved in the image data after imaging, the offset value k4 is relatively increased compared to the case where it is not performed.
(2) When the brightness of the dark area is improved in the image data after imaging, the reflection ratio k2 of the bright area photometric value Bv _MAX is increased as compared with the case where it is not performed.
(3) The offset value k4 is increased as the lightness improvement amount in the dark area increases.
(4) The reflection ratio k2 of the bright portion photometric value Bv _MAX is increased as the lightness improvement amount in the dark region is larger.
(5) However, when the average photometric value Bv _MEAN is low (for example, Bv4 or less), the reflection ratio k1 of the average photometric value Bv _MEAN is increased, and the reflection ratio k2 of the bright part photometric value Bv _MAX is decreased. Further, the offset value k4 is set to zero.

  FIG. 7 is a diagram illustrating an example of a setting table of values k1 to k4 according to this rule.

  When designing such a setting table, if the values k1 to k4 are adjusted according to the rules (1) to (5) so that the gradation reproduction of the image data after image correction is improved in various shooting scenes. Good.

Step S35: The microprocessor 22 performs a known exposure calculation based on the exposure control value Bv _CNTL calculated in Step S34, and determines an exposure condition (aperture value, charge accumulation time, imaging sensitivity, etc.). After the above-described operation, the microprocessor 22 ends the photometry and exposure calculation routines, and returns the operation to step S2 of the main routine (FIG. 2).

[4] Effects of this Embodiment In this embodiment, when the brightness of the dark area is improved in the image data after imaging, the exposure condition at the time of shooting is adaptively changed. As a result, it is possible to obtain image data with good gradation reproducibility by balancing the gradation reproduction of the dark area due to the lightness improvement and the gradation reproduction of the bright area due to the exposure condition.

In particular, in the present embodiment, the offset value k4 of the exposure control value Bv _CNTL is lowered when the brightness of the dark area is not improved after imaging. In this case, the exposure control value Bv _CNTL itself is lowered, and the exposure condition during photographing is complementarily increased. As a result, the image data is photographed brightly as a whole, and the lack of gradation in the dark area can be compensated.

On the contrary, when the brightness of the dark area is improved, the offset value k4 of the exposure control value Bv _CNTL is increased. In this case, the exposure control value Bv _CNTL itself is increased, and the exposure condition during photographing is complementarily lowered. As a result, it is possible to improve the brightness of the dark area by image correction and to improve the lack of gradation (such as whiteout) in the bright area by using a lower exposure condition.

Furthermore, in this embodiment, when the brightness improvement of the dark area is not performed, the reflection ratio k2 of the bright area photometric value Bv _MAX is reduced. In this case, the exposure condition is determined with a comparative emphasis on the dark area. As a result, the dark area of the image data is photographed brightly, and the lack of gradation in the dark area can be compensated.

On the contrary, when improving the brightness of the dark area, the reflection ratio k2 of the bright area photometric value Bv _MAX is increased. In this case, the exposure condition is determined with emphasis on the bright area. As a result, while the brightness of the dark area is improved by image correction, the lack of gradation (such as overexposure) of the bright area is improved by the exposure condition that emphasizes the bright area.

  In the present embodiment, the exposure value is lowered by changing the offset value k4 as the brightness improvement amount in the dark area increases. As a result, the exposure condition becomes lower as the brightness of the dark area is increased more strongly, and the lack of gradation (such as whiteout) in the bright area can be further improved.

Furthermore, in the present embodiment, the reflection ratio k2 of the bright part photometric value Bv _MAX is increased as the brightness improvement amount in the dark part region is increased. In this case, the exposure condition is determined with more emphasis on the bright area. As a result, the higher the lightness of the dark area, the higher the lightness, and the more the exposure condition is focused on the bright area, and the lack of gradation (such as whiteout) in the bright area can be further improved.

<< Additional items of embodiment >>
In the above-described embodiment, the value of the exposure control value Bv _CNTL is changed. However, the present invention is not limited to this. For example, the exposure correction setting value may be changed in accordance with the correction setting for improving the brightness of the dark area.

  In the above-described embodiment, the maximum value of the divided photometric values is used as the bright part photometric value. However, the present invention is not limited to this. For example, as the bright part photometric value, the average value of the top several places of the divided photometric value may be used.

  Furthermore, in the above-described embodiment, the image correction using the parameter fg has been described. However, the present invention is not limited to this image correction. For example, the brightness enhancement technique described in US Pat. No. 5,991,456 may be used.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the above-described embodiments are merely examples in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the scope of claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the present invention is a technique that can be used for an imaging apparatus or the like.

DESCRIPTION OF SYMBOLS 11 ... Imaging device, 12 ... Shooting lens, 12a ... Aperture, 13 ... Imaging element, 13a ... Shutter, 15 ... Signal processing part, 16 ... A / D conversion part, 17 ... Buffer memory, 18 ... Bus, 19 ... Image processing , 20 ... card interface, 21 ... memory card, 22 ... microprocessor, 22a ... switch group, 22b ... timing generator, 22c ... photometric sensor, 23 ... compression / expansion part, 24 ... image display part, 25 ... monitor screen

Claims (5)

A metering unit for metering the subject;
An exposure calculation unit that sets an exposure condition and determines a charge accumulation time based on a photometric result of the photometry unit;
An imaging unit that images the subject according to the exposure condition and generates image data;
Implementing a second image processing for performing brightness enhancing correction of the dark region of the image represented by the image data and the first image processing for performing tone conversion and color space conversion to the image data generated by said image pickup unit The first mode to be performed and the second mode to perform only the first image processing without performing the second image processing, and any one of the first mode and the second mode is set by a user's prior reservation setting. An image processing unit for performing
The exposure calculating unit sets the exposure condition when the user sets the reservation to perform the second mode, and sets the exposure condition when the user sets the exposure condition to perform the first mode. The imaging apparatus , wherein the exposure condition is set lower than when the reservation is set by a user to perform a mode . A metering unit for metering the subject;
Based on the photometric result of the photometric unit, an exposure calculation unit that sets the exposure condition and determines the photographing sensitivity ;
An imaging unit that images the subject according to the exposure condition and generates image data;
Implementing a second image processing for performing brightness enhancing correction of the dark region of the image represented by the image data and the first image processing for performing tone conversion and color space conversion to the image data generated by said image pickup unit The first mode to be performed and the second mode to perform only the first image processing without performing the second image processing, and any one of the first mode and the second mode is set in advance by a user. An image processing unit for performing
The exposure calculating unit sets the exposure condition when the user sets the reservation to perform the second mode, and sets the exposure condition when the user sets the exposure condition to perform the first mode. The imaging apparatus , wherein the exposure condition is set lower than when the reservation is set by a user to perform a mode . In the imaging device according to claim 1 or 2,
The metering unit divides the subject into a plurality of locations and performs split metering,
In the divided photometric value, the exposure calculation unit is set when the reservation is set by the user to perform the first mode , compared with the case where the reservation is set by the user to perform the second mode. An imaging apparatus, wherein the exposure condition is set by increasing a reflection ratio of a photometric value in a bright place. The imaging apparatus according to any one of claims 1 to 3,
The exposure apparatus sets the exposure condition lower as the correction setting increases the brightness improvement amount in the dark area. The imaging apparatus according to any one of claims 1 to 4,
The metering unit divides the subject into a plurality of locations and performs split metering,
The exposure calculation unit sets the exposure condition by increasing a reflection ratio of a photometric value of a bright part in the divided photometric value as the correction setting having a large brightness improvement amount in the dark area is set. apparatus.

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