JP2018029225A - Image processing apparatus and imaging device - Google Patents

Abstract

Kind Code: A1 A brightness correction suitable for a shooting scene is performed. In a digital camera, an arbitrary portion of the screen can be selected when performing correction regarding peripheral brightness, and a selected portion located on a line passing through the optical axis corresponding to the selected portion of the screen is provided. A correction coefficient for a correction target pixel determined according to an image area can be adjusted. After the correction pixels corresponding to the selected area are adjusted, the peripheral brightness is corrected based on the correction coefficient of the selected area. [Selection drawing] Fig. 2

Description

  The present invention relates to an imaging apparatus such as a camera, and more particularly, to a process for correcting a decrease in the amount of light around an image caused by lens characteristics or the like.

  In a digital camera or the like, the amount of light decreases at the periphery of the captured image due to the characteristics of the photographing lens. Therefore, shading correction (hereinafter also referred to as peripheral light amount reduction correction) is performed on the obtained image signal, and gain correction is performed on pixels in the light amount reduction portion.

  The degree of decrease in the amount of ambient light differs depending not only on the optical characteristics of the taking lens used but also on the shooting conditions. Therefore, the image is divided into a plurality of blocks, a series of correction coefficients that differ depending on the aperture value and zoom magnification are stored in the memory for each block, and shading is performed by selecting a correction coefficient corresponding to the aperture value, zoom magnification, etc. at the time of shooting. Correction is performed (see Patent Document 1). Further, when the same correction coefficient is multiplied to different color filters of the image pickup device, pseudo color may occur due to color modulation. In order to suppress this, shading correction is performed using a correction coefficient corresponding to each color filter (see Patent Document 2).

  Further, depending on the shooting scene, the shading correction may increase the luminance level more than necessary and increase noise. In order to prevent this, it is determined whether or not it is a shooting scene in which the decrease in the amount of peripheral light is inconspicuous, and if it is inconspicuous, the gain is suppressed. For example, the captured image is divided into a plurality of blocks, luminance values and color information are detected for each block, and shading correction is performed on the blue area corresponding to the sky where the peripheral light amount decrease is conspicuous, while the peripheral light amount decrease is not conspicuous When a green area such as trees is detected, shading correction is not performed (see Patent Document 3).

JP 2003-110936 A JP 2000-41179 A JP 2006-148791 A

  The subject composition at the time of shooting varies, and even if the shooting scene is determined based on the camera characteristics, exposure conditions, or color information, the shooting scene may not be properly determined. When the reduction correction is performed, the image quality at the periphery of the captured image is reduced, such as noise increase and saturation, and an image preferred by the user cannot be obtained.

  Therefore, it is possible to perform appropriate brightness / light quantity correction (peripheral light quantity reduction correction, etc.) for various shooting scenes, and to obtain an image that the user likes.

  The image processing apparatus of the present invention can be incorporated into a computer or an imaging apparatus. For example, the image processing apparatus can be selected from a plurality of image areas determined by dividing a captured image in accordance with a user's selection operation, or an arbitrary image processing apparatus. Brightness correction is performed on a selection unit that selects a specific image region from the region and a correction target pixel that is determined according to the image region selected by the selection unit.

  As the correction relating to the brightness, the brightness of the correction target pixel of the photographed image may be corrected according to the characteristics of the imaging device or the contents designated by the user. For example, the correction means can correct the decrease in the amount of light based on the characteristics of the photographing optical system or a correction coefficient determined according to a user instruction. However, the correction includes a correction for increasing the pixel luminance in an image region having a relatively low luminance and a correction for decreasing the pixel luminance in an image region having a relatively high luminance.

  For example, the correction unit executes any one of the gain, the offset, and the combination of the gain and the offset for the correction target pixel determined according to the image region selected by the selection unit.

  Note that the “plurality of image regions” here represents the image portion that the user wants to perform the peripheral light amount reduction correction around the region or the region. For example, it is possible to configure the first area including the upper left corner portion of the photographed image, the second area including the upper right corner portion, the third area including the lower right corner portion, and the fourth area including the lower left corner portion. Alternatively, any other location is possible.

  Regarding selection of an image area, for example, when a monitor using a touch panel is used, it is possible to select a point and specify a range by touching an arbitrary area in which an image is displayed. Further, on a computer, a point and a range may be specified using a pointing device such as a mouse.

  When a predetermined image area is selected, a correction target pixel is determined according to the area. The pixel in the selected image region and its surrounding pixels may be set as the correction target pixel, and the pixel in the selected image region may be set as the correction target pixel. The correction target pixel is a plurality of pixels determined in advance according to the selected image area, and is determined for each specified area. In addition, in the case of a selection method that is not a predesignated image area, for example, an arbitrary designated area such as a touch panel, it is set accordingly.

  It is also possible to provide an adjustment unit that can adjust the correction coefficient of the adjustment target pixel determined in the selected image area in accordance with the user's adjustment operation. For example, the adjustment unit can adjust the correction coefficient of the adjustment target pixel determined along the line from the image center of the captured image and the optical center (optical axis position) of the captured image in accordance with the user's adjustment operation. be able to. Or you may adjust a correction coefficient for every area | region.

  Note that the image center is, for example, the center of the effective pixel of the image sensor. Although the optical center may coincide with the image center, when using a sensor shift type camera shake correction mechanism, a lens drive type camera shake correction mechanism, or the like, the optical center deviates from the image center.

  For example, the adjustment unit corrects the correction coefficient of the correction target pixel other than the adjustment target pixel by interpolation using the correction coefficient of the adjustment target pixel located on a concentric circle equidistant from the correction target pixel and the image center. Is possible.

  An image processing method according to another aspect of the present invention selects a specific image area from a plurality of image areas or arbitrary areas defined in a captured image in accordance with a user's selection operation, and selects the selected image area The correction relating to the brightness is performed on the correction target pixel determined according to the above. For example, the light amount reduction is corrected based on a correction coefficient determined according to the characteristics of the photographing optical system or a user instruction.

  According to the present invention, it is possible to perform correction related to brightness suitable for a shooting scene.

It is a block diagram of the digital camera which is this embodiment. It is a flowchart of a shading correction process. It is the figure which showed the selection screen of the correction | amendment object area | region. It is the figure which showed the interpolation of the correction coefficient in a picked-up image. It is the figure which showed interpolation of the correction coefficient in case the image center does not correspond with the optical center.

  Below, the digital camera which is this embodiment is demonstrated with reference to drawings.

  FIG. 1 is a block diagram of a digital camera according to the present embodiment.

  Here, the digital camera 100 is configured as a mirrorless digital camera, and shoots and reproduces recorded images according to user input operations on the operation member 104 including a mode dial, a release button, a cross button, an execution button, and the like. Mode setting is performed. A lens barrel 102 that houses the taking lens 107 is detachably attached to the front side of the camera, and an LCD 106 is provided on the back side of the camera.

  A signal processing unit 101 including a CPU, a RAM, and the like performs overall camera operation control such as exposure control, recording operation, and reproduction display operation in response to button operations on the operation member 104 such as a release button. In addition, an image processing unit 132 and a correction unit 134 that perform image signal processing and the like are provided. The camera operation control program is stored in a recording medium such as a ROM (not shown).

  The photographic lens 107 forms light on the image sensor 111 such as a CCD or CMOS sensor when light from the subject is incident, and thereby a subject image is formed on the image sensor 111. On the light receiving surface of the image sensor 111, a color filter array (not shown) such as R, G, and B is arranged.

  In the case of through image display, pixel signals for one field or one frame are output from the image sensor 111 at a predetermined time interval (for example, 1/60 seconds or 1/30 seconds) in accordance with a drive signal from the timing generator (TG) 120. Read out. The read pixel signal is amplified and digitized by the AFE circuit 130 and then sent to the image processing unit 132 of the signal processing unit 101.

  The image signal processing unit 132 performs color interpolation processing, color conversion processing, white balance adjustment processing, and the like on the pixel signal. Accordingly, R, G, and B pixel values are obtained for each pixel, and a color image signal is generated. The generated color image signal is temporarily stored in the image memory 103. The signal processing unit 101 drives the LCD 106 based on the color image signal, thereby displaying a real-time moving image.

  When the release button is pressed halfway, a contrast AF process is executed based on the pixel signal read from the image sensor 111. The signal processing unit 101 controls the lens driving unit 136 to drive the photographing lens 107 and detects a focus position where the contrast value reaches a peak. In addition to the contrast AF process, the brightness of the subject image is detected based on the pixel signal read from the image sensor 111, and the exposure value is calculated.

  Further, when the release button is fully pressed, the exposure control unit 138 controls the exposure by driving a shutter, a diaphragm, etc. (not shown) based on the exposure value. Thereby, a pixel signal for one frame is read from the image sensor 111.

  The image signal processing unit 132 generates still image data based on the read pixel signal for one frame. Still image data is recorded on a recording medium 105 such as a memory card in a compressed state or in an uncompressed state. When the playback mode is set, the selected recorded image is displayed on the LCD 106.

  The correction unit 134 performs a shading correction process on the generated R, G, and B color image signals. That is, the gain correction is performed so as to compensate for a decrease in the amount of light in the peripheral portion of the photographed image due to the lens characteristics of the attached photographing lens 107 and the like. However, R, G, B color image signals may be generated after shading correction. The lens memory 108 of the lens barrel 102 or a non-volatile memory (not shown) attached to the signal processing unit stores data relating to lens design values (or measurement values, adjustment values, etc.).

  In the present embodiment, it is possible to perform shading correction targeting an image portion desired by the user by an input operation by the user, and it is possible to adjust the degree of shading correction by the user. Hereinafter, it explains in full detail using FIGS.

  FIG. 2 is a flowchart of the shading correction process. FIG. 3 is a diagram showing a selection screen for a correction target area. FIG. 4 is a diagram illustrating interpolation of correction coefficients in a captured image.

  When the user selects the reproduction mode and reproduces a predetermined recorded image and then selects the shading correction manual setting mode, a selection screen shown in FIG. 3 is displayed (S101). FIG. 3 shows a screen when a captured image RI showing a mountain is reproduced and displayed. In the upper left corner, upper right corner, lower right corner, and lower left corner of the screen, character information R1 to R4 of “upper left”, “upper right”, “lower right”, and [lower left] are displayed, respectively. By operating, the inversion area RF can be moved between the character information R1 to R4, and the screen corner portion can be selected.

  The decrease in the amount of light in the peripheral area of the image, particularly in the vicinity of the four corners of the image due to the lens characteristics, may or may not be noticeable depending on the shooting scene. For example, when a subject such as a person or a building is present around the field of view (frame), the reduction in the amount of light is not noticeable. On the other hand, when photographing a blue sky or the like, a decrease in the amount of light around the image is conspicuous. Therefore, when the lower half of the photographed image is a building such as a building and the upper half is a composition like a blue sky, the decrease in the amount of peripheral light in the upper left and the upper right becomes noticeable, but the decrease in the amount of peripheral light in the lower left and lower right is so noticeable. Absent.

  If correction for a decrease in peripheral light amount is performed uniformly on such a captured image, the impression does not change so much in the lower left corner portion and lower right corner portion of the image, and only noise increases. Further, in the case of a photographed image by room illumination, if illumination enters any one of the four corners of the image, the portion becomes overexposed by the light amount reduction correction, and the image quality is deteriorated and the impression is deteriorated.

  In the present embodiment, the user individually selects the upper left, upper right, lower left, and lower right corner portions of the image while viewing the captured image, and performs peripheral light amount reduction correction based on the selected corner portions. Specifically, the corner portion of the captured image is such that shading correction is performed on the portion of the captured image that can be determined to have a noticeable decrease in light intensity, and shading correction is not performed on the portion that can be determined to be inconspicuous. Select. For example, in the case of a captured image RI as shown in FIG. 3, the user can select only the upper right corner portion of the screen as a correction target.

  When the user selects a screen corner by operating the cross button and operates the execution button, the screen corner of the inversion area RF is selected and set as a correction target area (S102, S103). The user can select one or a plurality of screen corner portions. However, the selection of the screen corner portion here merely determines the target area to be subjected to shading correction, and does not cause the user to determine the pixel area to be actually corrected, and will be described later. In addition, shading correction is not performed only on the corners of the screen.

  When the screen corner portion is selected by the user, it is determined whether or not a correction coefficient adjustment operation has been performed by the user (S104). The user can adjust the value of the correction coefficient for the selected screen corner by operating the cross button or the like.

  A correction coefficient for a discrete image height is stored in advance for a predetermined pixel because of the limitation of the data capacity of the lens data to be stored. The correction coefficient is calculated for each pixel by interpolating the correction coefficient. Here, the pixels whose correction coefficients can be adjusted are defined as pixels on the diagonal lines S1 and S2 shown in FIG. 4, and the upper left corner and upper right corner along the diagonal lines S1 and S2 from the image center C coincident with the optical axis. The values of the correction coefficients can be adjusted (changed) separately for the lines T1 to T4 that face in the direction of the lower left corner and the lower right corner. The user can arbitrarily set the correction coefficient. Although not shown, since the correction coefficient is data with respect to the image height, the correction coefficient is not limited to diagonal, and any point can be taken as long as it is on a line passing through the center of the optical axis. That is, any point in the screen can be specified.

  When the correction coefficient is adjusted by the user's adjustment operation (S105), it is determined whether an operation for executing shading correction (here, pressing of the execution button) has been performed (S106). If it is determined that an operation for performing shading correction has been performed, shading correction is performed on the pixels that are to be subjected to shading correction (S107). When an operation for shifting to another mode or the like is performed, the process ends (S108).

  For the pixels on the diagonal lines S1 and S2, the peripheral light amount decrease correction is performed based on the adjusted correction coefficient. For pixels that are not on the diagonal lines S1 and S2, the correction coefficients of the pixels that are on concentric circles having the same distance from the image center (optical axis) C relative to the pixels on the diagonal lines S1 and S2 are calculated on the diagonal lines S1 and S2. Therefore, it is obtained by performing linear interpolation using a correction coefficient of pixels on concentric circles.

  For example, when the user selects the upper left corner portion and the upper right corner portion of the captured image RI as correction targets and adjusts the correction coefficient with respect to the lines T1 and T2, the pixels PK1 and PK2 having the same image height from the image center C are concentric. The correction coefficient of the pixel PJ having the same image height along the line is obtained by linear interpolation using the correction coefficients of the pixels PK1 and PK2. Correction coefficients are obtained by the same linear interpolation for the pixels not on the other diagonal lines S1 and S2. However, you may obtain | require by interpolation calculations other than linear interpolation.

  When the peripheral light amount reduction correction based on the interpolation is performed, the gain correction is performed for pixels other than the screen corner portion selected by the user, but this does not cause an unnatural difference in the light amount in the captured image. . That is, it is possible to perform the peripheral light amount decrease correction with the screen corner selected by the user as the center. For example, when the user selects only the upper left corner portion and the upper right corner portion of the photographed image RI, the pixels in the areas A1, A2, and A4 shown in FIG. A relatively large gain correction is applied to the pixels on the lines T1 and T2 (particularly corner portions) at the corner portion R2.

  As described above, according to the present embodiment, when the peripheral light amount reduction correction is performed based on the correction coefficient, the user can select the screen corner portion to be corrected, and the diagonal line corresponding to the selected screen corner portion can be selected. The correction coefficient of the pixel located on the line can be adjusted. When the screen corner is selected and the correction coefficient is adjusted, the peripheral light amount reduction correction is performed based on the correction coefficient of the selected area.

  Since the user actually sees the captured image and decides the corner of the screen where the peripheral light amount reduction correction is performed, it is possible to appropriately identify and correct the portion that needs to be corrected for the shooting scene, and to the selected area Since the correction coefficient can be adjusted, the degree of correction can be adjusted to the user's preference.

  Instead of directly adjusting the value of the correction coefficient, the correction ratio may be adjusted. However, the correction ratio is a value that adjusts the degree to which the correction coefficient is reflected in the pixel value. When the correction ratio is 100%, the correction coefficient value is used as it is, and the correction coefficient value decreases as the correction ratio value decreases. To do. If an upper limit is set, a correction ratio such as 120% may be set.

  In the present embodiment, the image center is regarded as the optical center, that is, the optical axis, but in the case of a captured image in which the image center and the optical center do not coincide with each other by a camera shake mechanism or the like, pixels on a line passing through the optical center are determined. A pixel whose correction coefficient can be adjusted.

  FIG. 5 is a diagram showing interpolation of correction coefficients when the image center does not coincide with the optical center. Correction coefficients can be adjusted for pixels on two diagonal lines S′1 and S′2 passing through the optical center C and parallel to the diagonal lines S1 and S2, and the lines S′1 and S′2. For the pixel PJ ′ that is not above, the correction coefficient is obtained by the interpolation process described above. Although not shown, the line segment can be a line segment connecting any one of the four corners of the screen to the optical axis, and the correction coefficient can be adjusted for the pixels on the line segment. Furthermore, as long as the line segment passes through the optical axis, an arbitrary line segment may be set.

  In this embodiment, the correction coefficient of another pixel is obtained by interpolation based on the correction coefficient of the pixel along the line passing through the optical center, but the pixel located in the image area selected by the user is determined as the correction target pixel. And the peripheral light amount decrease correction may be performed on the pixel. Further, instead of adjusting and correcting a predetermined correction coefficient according to the characteristics of the photographing optical system, the correction coefficient or the correction ratio value may be set as it is by a user input operation or the like.

  The image portion selected by the user is not limited to the four corner portions of the screen, and may be an arbitrary region within the screen. Furthermore, the user may select a specific area from an arbitrary area on the screen. In this case, the adjustment coefficient that can be adjusted is a pixel that is on the line from the optical center to the area under the photographing conditions. It is possible to perform correction for a light amount decrease that is not limited to the peripheral portion of the screen.

  Further, the user may select only the correction target area without adjusting the correction coefficient. Even in this case, correction for the light amount reduction centered on the image portion desired by the user is performed, and appropriate correction according to the user preference can be performed. As correction for the light amount reduction, offset processing other than gain processing is also possible, and gain processing and offset processing may be combined.

  In this embodiment, the digital camera is configured to perform the peripheral light amount decrease correction. However, a computer such as a PC may be incorporated in the image editing software to correct the light amount decrease.

100 Digital camera (photographing device)
101 Signal processing unit (selection unit, adjustment unit)
132 Image signal processing unit 134 Correction unit

Claims (7)

A selection means for selecting a specific image area from a plurality of image areas determined by dividing a captured image, or an arbitrary area;
An image processing apparatus comprising: correction means for performing correction relating to brightness on a correction target pixel determined according to an image region selected by the selection means.   The image processing apparatus according to claim 1, further comprising an adjustment unit that can adjust a correction coefficient of a pixel to be adjusted that is determined in the selected image region. The adjustment means is capable of adjusting a correction coefficient of an adjustment target pixel determined along an image center or an optical center of a captured image;
The adjustment unit corrects the correction coefficient of the correction target pixel other than the adjustment target pixel by interpolation using the correction coefficient of the adjustment target pixel located on the concentric circle equidistant from the correction target pixel and the image center or the optical center. The image processing apparatus according to claim 2.   The plurality of image regions include a first region including an upper left corner portion of the photographed image, a second region including an upper right corner portion, a third region including a lower right corner portion, and a fourth region including a lower left corner portion. The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus.   2. The correction unit performs any one of a gain, an offset, and a combination of a gain and an offset on a correction target pixel determined according to an image region selected by the selection unit. 5. The image processing apparatus according to any one of 4 to 4.   An imaging apparatus comprising the image processing apparatus according to claim 1. Select a specific image area from a plurality of image areas defined by dividing the captured image or from any area,
An image processing method comprising performing correction relating to brightness on a correction target pixel determined according to a selected image area.

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