JP5970871B2 - Electronic camera - Google Patents

Description

  The present invention relates to an electronic camera.

  2. Description of the Related Art Conventionally, in an electronic camera, a technique is generally known in which shooting is performed by determining an appropriate exposure amount according to the brightness of a subject and adjusting a shutter speed based on a program diagram (for example, Patent Document 1).

Japanese Patent No. 4586463

  However, in the above-described conventional technique, when exposure adjustment is performed to increase the imaging sensitivity indicating the sensitivity of the image sensor in the case of shooting at low brightness such as at night, noise components ( (Hereinafter referred to as “noise”). Therefore, a technique for performing image processing for removing noise on a photographed image is conventionally known. However, the above-described technology for removing noise causes a new problem that image quality deterioration such as roughness and unevenness of the entire screen is likely to occur, and there is a possibility that an image preferable for viewing cannot be obtained. Further, since it is difficult to perform image processing for changing the imaging sensitivity level on the image after shooting, it is desirable to carefully select the imaging sensitivity level.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an electronic camera that obtains a favorable image for viewing even when shooting under low luminance.

In one embodiment of the present invention, an electronic camera captures noise from an image sensor that captures light from a subject and generates image data, a light emitting unit that emits light that illuminates the subject, and image data generated by the image sensor. Based on the noise removal processing unit to be removed in the first processing, the correction processing unit to correct the image data from which noise has been removed in the noise removal processing unit in the second processing, the brightness of the subject and the presence or absence of light emission from the light emitting unit And a setting unit that sets the first process and the second process, and the correction processing unit corrects image quality degradation based on noise removal of the image data from which noise has been removed by the noise removal processing unit .

As another aspect of the present invention, there are the following.
An electronic camera according to a first technique includes an imaging device, a subject luminance detection unit, a first setting unit, a second setting unit, a noise removal processing unit, and a correction processing unit. The imaging element captures an image of a subject and generates an image. The subject brightness detection unit detects the subject brightness. When the subject brightness is lower than a preset reference value, the first setting unit sets a setting mode that supplements shooting under the low brightness. The second setting unit includes a first parameter for removing noise of the image data generated according to the setting value of the setting mode, and a second parameter for correcting image quality degradation caused by noise removal. Set. The noise removal processing unit removes noise in the image data of the recording image generated by the image sensor under the setting mode based on the first parameter. The correction processing unit corrects the image quality deterioration of the image data of the recording image based on the second parameter.
The electronic camera according to the second technique includes an imaging device, a first setting unit, a second setting unit, a noise removal processing unit, and a correction processing unit. The imaging element captures an image of a subject and generates an image. The first setting unit sets, by user input, a setting mode for supplementing shooting under a luminance lower than the reference value set in advance. The second setting unit includes a first parameter for removing noise of the image data generated according to the setting value of the setting mode, and a second parameter for correcting image quality degradation caused by noise removal. Set. The noise removal processing unit removes noise in the image data of the recording image generated by the image sensor under the setting mode based on the first parameter. The correction processing unit corrects the image quality deterioration of the image data of the recording image based on the second parameter.

The third technique is an imaging sensitivity priority mode in which the setting mode in the first or second technique prioritizes setting of the imaging sensitivity indicating the sensitivity of the imaging element. The set value is a value indicating the level of imaging sensitivity.

In a fourth technique , in the first or second technique , the setting mode is a gradation compression priority mode that prioritizes a process of expanding the dynamic range by compressing the pixel value of the image data. Setting value is a value indicating the level of gradation compression.

In the fifth technique , in any one of the first to fourth techniques , the first parameter is a parameter related to dark current correction. The second parameter includes a parameter related to at least one correction among contrast correction, contour correction, saturation correction, and gradation compression correction.

A sixth technique is the one of the first to fifth techniques , further comprising a flash light emitting unit. The flash light emitting unit emits flash light toward the subject. The second setting unit sets the first parameter and the second parameter according to the flash emission amount.

  The electronic camera of the present invention can obtain a favorable image for viewing even when shooting under low luminance.

Side view showing a configuration example of a main part of the electronic camera 1 The figure which shows the internal structural example of the electronic camera 1 and the flash apparatus 150 which are shown in FIG. The figure which shows an example of the table used in imaging sensitivity priority mode The figure which shows an example of the table used in gradation compression priority mode The figure explaining setting mode selection processing The flowchart which shows an example of imaging | photography operation | movement of the electronic camera 1 The figure which shows an example of the table used by 2nd Embodiment. The flowchart which shows an example of imaging | photography operation | movement of the electronic camera 1 of 2nd Embodiment.

(First embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a side view illustrating a configuration example of a main part of the electronic camera 1. The electronic camera 1 is, for example, a single-lens reflex type electronic camera, and includes a camera body 100 and a photographing lens unit 50. The taking lens unit 50 is detachably attached to a lens mount 100 a formed on the front surface of the camera body 100 in order to guide subject light to the camera body 100. The camera body 100 and the photographic lens unit 50 are electrically connected via a contact point of the lens mount 100a when the photographic lens unit 50 is mounted.

  Further, a flash device 150 for irradiating the subject with irradiation light is detachably attached to a hot shoe (connection terminal) 150 a formed on the upper surface of the camera body 100. The camera body 100 and the flash device 150 are electrically connected via a contact of a hot shoe (connecting terminal) 150a when the flash device 150 is mounted.

  The taking lens unit 50 includes a lens system 51 and a diaphragm 52. The lens system 51 includes a plurality of lenses including a focus lens for focusing on a subject and a zoom lens for zooming the subject image. Here, for convenience of explanation, it is illustrated with one lens. The diaphragm 52 adjusts the amount of incident light by opening and closing the diaphragm blades.

  The camera body 100 includes a quick return mirror 101, a sub mirror 101a, a diffusion screen 102, a condenser lens 103, a penta roof prism 104, a photometric prism 105, a photometric lens 106, a photometric sensor 107, an eyepiece lens 108, a focus detection unit 110, and a mechanical type. A shutter 111 and an image sensor 10 are provided.

  The quick return mirror 101 is rotatably provided on an optical axis OA (Optical Axis) indicated by a one-dot chain line in the drawing. When photographing a subject, the quick return mirror 101 is retracted to a position indicated by a dotted line in the figure by rotation. At this time, the sub mirror 101a is folded. Thereby, the subject light incident on the camera body 100 from the subject is guided to the image sensor 10.

  On the other hand, when the subject is not photographed, the quick return mirror 101 is disposed at an oblique position with respect to the optical axis OA. In this case, the quick return mirror 101 reflects the subject light incident on the camera body 100 via the lens system 51 and guides it to the diffusion screen 102 and also guides it to the sub mirror 101a.

  The diffusion screen 102 diffuses the subject light guided by the quick return mirror 101 and guides the diffused subject light to the penta roof prism 104 via the condenser lens 103. The penta roof prism 104 reflects subject light and guides it to the photometric prism 105 and guides it to the eyepiece 108. The photometric prism 105 guides subject light to the photometric sensor 107 via the photometric lens 106.

  The eyepiece 108 forms the subject light guided by the penta roof prism 104 as a subject image. A photographer (user) can determine the composition of the subject by looking at the image of the subject formed by the eyepiece 108 via an optical viewfinder (not shown).

  The photometric sensor 107 detects subject luminance (subject brightness) and subject color information. Specifically, the photometric sensor 107 has an imaging region that selectively reads out image signals (output signals) of pixels arranged in two dimensions, and measures subject light in the imaging region.

  Alternatively, the photometric sensor 107 measures the reflected light from the subject at the time of preliminary light emission for flash photography in the imaging region. Here, the photometric sensor 107 has, for example, a complementary metal oxide semiconductor (CMOS) type image sensor that can read an arbitrary line by XY addressing. In the image pickup area of the image pickup element, three types of color filters of red (R), green (G), and blue (B) are arranged in a Bayer array as an example in order to detect the color of the subject image. .

  In the present embodiment, the size of the imaging area of the image sensor of the photometric sensor 107 and the size of the imaging area of the image sensor 10 are the same. However, the image sensor 10 has a higher resolution than the image sensor of the photometric sensor 107.

  The image signal output from the image sensor of the photometric sensor 107 is subjected to gain adjustment, A / D conversion, and the like in the photometric sensor 107, and is stored in a RAM (Random Access Memory) 13 or a CPU (Central Processing Unit) 18 to be described later. It is temporarily recorded in a memory (not shown).

  The release button 109 accepts instruction inputs for a half-press operation (start of shooting preparation operation such as automatic exposure (AE) and autofocus (AF)) and a full-press operation (start of shooting operation).

  The focus detection unit 110 detects the focus state of the lens system 51 by performing, for example, phase difference focus detection. The electronic camera 1 may detect the focus state of the lens system 51 by performing contrast-type focus detection based on the luminance and color information of the subject detected by the image sensor 10 or the photometric sensor 107. Alternatively, focus detection by a phase difference method may be performed using an AF sensor arranged in the image sensor 10.

  The mechanical shutter 111 includes an openable / closable shutter curtain, and switches between a light-blocking state in which incident light to the image sensor 10 is blocked and a non-light-blocking state in which the incident light reaches the image sensor 10 by opening and closing the shutter curtain.

  The image sensor 10 captures an image of a subject and generates an image. The image sensor 10 is, for example, a CMOS type color image sensor. The image sensor and the image sensor 10 of the photometric sensor 107 may be a CCD (Charge Coupled Device) type color image sensor.

  The light receiving surface of the image sensor 10 includes an imaging region for capturing an image and an optical black region (hereinafter referred to as “OB region”). In the OB region, the light receiving element is covered with a light shielding member such as aluminum and a dark current component signal (hereinafter referred to as “dark signal”) is output.

  FIG. 2 is a diagram illustrating an internal configuration example of the electronic camera 1 and the flash device 150 illustrated in FIG. As described above, the electronic camera 1 includes the camera body 100 and the taking lens unit 50.

  2, illustration of the diffusing screen 102, the condenser lens 103, the penta roof prism 104, the eyepiece lens 108, and the mechanical shutter 111 shown in FIG. 1 is omitted for convenience of explanation.

  The camera body 100 includes a quick return mirror 101, a sub mirror 101a, a photometric prism 105, a photometric lens 106, a photometric sensor 107, a focus detection unit 110, an image sensor 10, a signal processing unit 11, and an image. A processing unit 12, a RAM 13, a flash memory 14, a recording interface unit (hereinafter referred to as "recording I / F unit") 15, a display monitor 16, an operation unit 17, a release button 109, a CPU 18, The bus 19 includes a lens mount 100a and a hot shoe 150a.

  Among these, the signal processing unit 11, the image processing unit 12, the RAM 13, the flash memory 14, the recording I / F unit 15, the display monitor 16, and the CPU 18 are connected to each other via a bus 19. In addition, the image sensor 10, the photometric sensor 107, the operation unit 17, the release button 109, the focus detection unit 110, and the hot shoe 150 a are connected to the CPU 18.

  The signal processing unit 11 is a circuit that performs signal processing on an image signal generated by the image sensor 10. A timing generator (not shown) sends a drive signal to each of the image sensor 10 and the signal processing unit 11 according to an instruction from the CPU 18 and controls the drive timing of both.

  The signal processing unit 11 performs gain adjustment and A / D conversion of the image signal. The image signal output from the signal processing unit 11 is temporarily recorded in the RAM 13 as image data. The type of image data is image data such as a recording image (hereinafter referred to as “main image”), a composition confirmation through image, or a dark image described later.

  The image processing unit 12 reads the image data recorded in the RAM 13 and performs various image processing (for example, white balance processing) on the image data of the main image, for example. The RAM 13 is a volatile memory. The flash memory 14 is a non-volatile memory that stores a program for controlling the electronic camera 1 in advance.

  The recording I / F unit 15 is formed with a connector (not shown) for connecting a detachable recording medium 30. In response to an instruction from the CPU 18, the recording I / F unit 15 accesses the recording medium 30 connected to the connector and performs recording processing of the main image. The recording medium 30 is, for example, a non-volatile memory card. FIG. 2 shows the recording medium 30 after being connected to the connector.

  The display monitor 16 is composed of, for example, a liquid crystal display medium. The display monitor 16 displays various images, an operation menu of the electronic camera 1 and the like according to instructions from the CPU 18.

  The operation unit 17 includes a command dial for command selection, a power button, and the like (not shown). In addition, the operation unit 17 accepts an instruction input for operating the electronic camera 1.

  The CPU 18 is a processor that performs overall control of the electronic camera 1. The CPU 18 controls each unit of the electronic camera 1 by executing a program stored in advance in the flash memory 14. Based on the output signal of the photometric sensor 107, the CPU 18 determines whether or not the subject brightness in the imaging range is low brightness (low illuminance) such as nighttime, dim light, sunset, or indoors.

  The CPU 18 determines whether or not the subject brightness is low depending on whether or not the brightness (or lightness) of the image signal output from the photometric sensor 107 is below a reference value. This reference value may be an actually measured value based on an experiment or the like in advance. Alternatively, the CPU 18 may determine whether or not the subject brightness is low based on whether or not the brightness of the through image generated by the image sensor 10 is lower than the reference value.

  More specifically, as an example, the CPU 18 determines whether or not the luminance of the image signal output from the photometric sensor 107 (or the image sensor 10) is lower than a reference value, and determines the average luminance of each pixel in the entire area of the image. Judgment is made based on whether the value falls below the reference value. Alternatively, the CPU 18 may determine whether or not the subject brightness is low by multi-division metering described later.

  The CPU 18 also functions as a first setting unit 18a, a second setting unit 18b, a shooting scene estimation unit 18c, a noise removal processing unit 18d, and a correction processing unit 18e.

  When the subject luminance is lower than a preset reference value, the first setting unit 18a sets a setting mode that supplements shooting under the low luminance. Or the 1st setting part 18a may set the setting mode for supplementing imaging | photography under low luminance via the operation part 17 by a user input. The electronic camera 1 of the present embodiment includes two types of setting modes, an imaging sensitivity priority mode and a gradation compression priority mode, as setting modes for supplementing shooting under low luminance.

  The imaging sensitivity priority mode is a mode that prioritizes setting of imaging sensitivity (hereinafter also referred to as “ISO sensitivity”). In this imaging sensitivity priority mode, it is possible to obtain a favorable image for viewing by giving priority to the setting of imaging sensitivity in shooting under low luminance.

  For example, as an application example of the imaging sensitivity priority mode, there is a case where a person, an animal, or another subject is to be reproduced with appropriate brightness at the time of shooting at night. In this case, in the imaging sensitivity priority mode, when there is a limit only by adjusting the exposure, the imaging sensitivity of the image sensor 10 is preferentially determined, and the first and second parameters are determined in order to obtain an appropriate image.

  The gradation compression priority mode is a mode in which priority is given to processing for expanding the dynamic range by performing gradation compression on pixel values of image data. In this gradation compression priority mode, an image preferable for viewing can be acquired by giving priority to the process of compressing the gradation and expanding the dynamic range in photographing under low luminance. In the gradation compression priority mode, the ISO sensitivity should be taken at the current set value (for example, ISO sensitivity: 1600), but the image is taken one step lower (for example, ISO sensitivity: 800), and correction processing described later is performed. In this case, deterioration of image quality may be suppressed. Thereby, in the gradation compression priority mode, generation of noise can be suppressed as much as the ISO sensitivity is lowered.

  For example, as an application example of the gradation compression priority mode, there is a case where there is a backlit person. In this case, in the gradation compression priority mode, since the light source is the sun or the like and the gradation having a luminance difference of a predetermined level or more is corrected, the gradation correction value is preferentially determined, and a more appropriate image is obtained. Determine the first and second parameters.

  The second setting unit 18b includes a first parameter for removing noise of the image data generated according to the setting value of the setting mode, and a first parameter for correcting image quality degradation caused by noise removal. Set two parameters.

  Specifically, the first parameter is a parameter related to dark current correction. The second parameter includes a parameter related to at least one correction among contrast correction, contour correction, saturation correction, and gradation compression correction. Therefore, for example, in the gradation compression priority mode, the second parameter may be only a parameter related to gradation compression correction.

  The shooting scene estimation unit 18c analyzes the image and estimates the shooting scene. For example, the shooting scene estimation unit 18c estimates a shooting scene as a landscape based on the luminance distribution of the sky, the sea, etc. included in the subject image, the RGB signal distribution, and the color temperature. The shooting scene estimation unit 18c analyzes the image by a known face detection process to detect a face such as a person, and estimates the type of shooting scene as a person. Note that, as an additional function, the shooting scene estimation unit 18c may accept the type of shooting scene by user input.

  The noise removal processing unit 18d removes noise in the image data of the main image generated by the image sensor 10 in the imaging sensitivity priority mode or the gradation compression priority mode based on the first parameter. Since the first parameter is a parameter related to dark current correction, the noise removal processing unit 18d can remove noise of image data caused by dark current. Here, the electronic camera 1 of the present embodiment includes a plurality of noise reduction (hereinafter referred to as “NR”) modes in addition to the setting mode in order to remove noise of image data.

  In the first NR mode, normally, immediately after the main image is captured, the electronic camera 1 captures a dark image with the same exposure time as the main image while the image sensor 10 is shielded from light. In the first NR mode, the noise removal processing unit 18d performs correction processing for subtracting the image data of the dark image from the image data of the main image. This correction process removes (suppresses) noise such as dark current noise generated in the image sensor 10 and minute scratches (for example, scratches) due to pixel defects inherent to the image sensor.

  In the second NR mode, the noise removal processing unit 18d optically separates the incident light by applying a low-pass filter, thereby blurring an image of a component having a spatial frequency smaller than the pixel pitch of the sensor. . Thereby, light can be efficiently guided to each pixel of RGB by the sensor, and generation of false colors can be suppressed. Further, in the second NR mode, it is possible to add a setting for the noise removal processing unit 18d to perform correction processing such as averaging processing and smoothing processing between adjacent pixels. By this correction processing, noise such as dark current noise generated in the image sensor 10 is further suppressed.

  The correction processing unit 18e corrects the image quality deterioration of the image data of the main image based on the second parameter. Here, since the second parameter is a parameter related to at least one correction among contrast correction, contour correction, saturation correction, and gradation compression correction, the correction processing unit 18e is a screen newly generated by noise removal. Image quality deterioration such as overall roughness and unevenness can be suppressed by the above correction processing. Note that the image processing unit 12 may have the functions of the noise removal processing unit 18d and the correction processing unit 18e.

  FIG. 3 is a diagram illustrating an example of a table used in the imaging sensitivity priority mode. FIG. 4 is a diagram illustrating an example of a table used in the gradation compression priority mode. These tables are recorded in the flash memory 14 in advance as look-up tables (hereinafter referred to as “LUT”).

  In the LUT 1 illustrated in FIG. 3, the first parameter and the second parameter are associated with the setting value in the imaging sensitivity priority mode. In the LUT 2 shown in FIG. 4, the first parameter and the second parameter are associated with the set value in the gradation compression priority mode.

  In FIG. 3, each ISO sensitivity setting value is associated with a first parameter indicating noise removal and a plurality of second parameters indicating contrast correction, contour correction, saturation correction, and the like. Similarly, in FIG. 4, each tone compression setting value corresponds to a first parameter indicating noise removal and a plurality of second parameters indicating contrast correction, contour correction, saturation correction, and the like. It is attached.

  In FIGS. 3 and 4, the descriptions of strong, slightly strong, medium, slightly weak, and weak are correction processing within a range of five levels according to each setting value (ISO sensitivity or gradation compression). This indicates that noise removal processing is performed. In the present embodiment, classification into five levels is an example, and for example, classification into three levels may be performed.

  Here, in FIG. 3, the correction processing unit 18e increases the contrast as the ISO sensitivity setting value decreases. Here, increasing the contrast means, for example, increasing a difference in luminance between a bright part and a dark part in the image.

  Further, the correction processing unit 18e performs a process of increasing the saturation as the ISO sensitivity setting value decreases. Here, to increase the saturation means, for example, that the color signal in the image is adjusted so that the orange color of the main image becomes bright when the shooting scene is estimated to be “evening scene”. That is, in the present embodiment, the degree of color signal adjustment is expressed by the intensity of saturation.

  Further, the correction processing unit 18e performs a process of enhancing the contour as the ISO sensitivity setting value is lowered. Here, the process of emphasizing the outline performs an unsharp mask process which is a kind of the outline emphasis process. In the unsharp mask process, the image is first blurred, and the difference between the blurred image and the original image is obtained. In the unsharp mask process, the edge enhancement process is performed by adjusting this difference and adding it to the original image. Specifically, the correction processing unit 18e performs image processing that increases the contrast of the contour portion by unsharp mask processing to make the contour portion clear.

  Conventionally, noise is likely to occur in shooting with increased ISO sensitivity, and noise is more noticeable when contour enhancement is applied. For this reason, the conventional electronic camera has a problem that the image cannot be emphasized so much that the image lacks resolution. However, in the present embodiment, the contour emphasis is applied according to the ISO sensitivity, so that the above problem can be improved.

  Further, the noise removal processing unit 18d weakens the degree of noise removal as the ISO sensitivity setting value decreases. Here, the higher the ISO sensitivity, the higher the level increase (dark current offset) due to dark current. Therefore, in this embodiment, for the convenience of explanation, the level increase due to the dark current for each ISO sensitivity is divided into five stages. Therefore, the item of noise removal in FIGS. 3 and 4 represents the degree of removal of the level increase in five levels: strong, slightly strong, medium, slightly weak, and weak.

  More specifically, in the first NR mode, the noise removal processing unit 18d compares the average value of the dark current with a predetermined threshold value, and if the average value of the dark current is larger than the predetermined threshold value, Correction processing for subtracting the image data of the dark image from the image data is performed. That is, in the first NR mode, the predetermined threshold is associated with five levels of strong, slightly strong, medium, slightly weak, and weak. Therefore, when the first parameter indicating noise removal is “strong”, the noise removal processing unit 18d performs correction by setting the lowest value among the above five levels as a threshold value in order to make the noise removal strength the strongest. Perform processing.

  In the second NR mode, correction processing such as averaging processing and smoothing processing between adjacent pixels is divided into five levels (strong, slightly strong, medium, slightly weak, and weak). Here, for example, when “strong” is selected, the noise removal processing unit 18d maximizes the strength of the correction processing among the five levels. On the other hand, when “weak” is selected, the noise removal processing unit 18d makes the strength of the correction processing the weakest among the five levels. In the present embodiment, one of the first NR mode and the second NR mode may be performed, or may be used in combination.

  In FIG. 4, the correction processing unit 18e increases the contrast as the gradation compression setting value decreases. Further, the correction processing unit 18e performs a process of increasing the saturation as the gradation compression setting value decreases. In addition, the correction processing unit 18e performs a process of enhancing the outline as the gradation compression setting value decreases. Further, the noise removal processing unit 18d weakens the degree of noise removal as the gradation compression setting value decreases.

  Here, in FIG. 3 and FIG. 4, the degree of noise removal is divided into five stages. However, in this embodiment, for example, correction processing is not performed for the “strong” level as much as correction processing is performed. Compared to the case of the above, the feature is that the degree of noise removal can be set lower. The reason why it can be set lower is that image quality deterioration due to noise removal can be suppressed accordingly.

  Returning to the description of FIG. 2, the flash device 150 includes a light emitting unit 150b and a light emission control circuit 150c. The light emitting unit 150b is a circuit that converts electrical energy charged in the capacitor into light energy. The light emitting unit 150b is provided with, for example, a xenon tube, and emits light by discharging the xenon tube.

  Note that the light emitting unit 150b may use, for example, an LED (light emitting diode) as a light source. The light emission control circuit 150c receives light emission information indicating the light emission amount and the like of the light emission unit 150b from the CPU 18, and causes the light emission unit 150b to perform preliminary light emission and main light emission based on the received light emission information.

  Next, an example of the photographing operation of the electronic camera 1 will be described. Here, the user can select and input setting modes such as the imaging sensitivity priority mode and the gradation compression priority mode of the present embodiment via the operation unit 17. Note that the processing of the following flowchart (hereinafter referred to as “flow processing”) assumes a shooting scene such as night, dim, sunset, backlit, or dark subject in a room.

  FIG. 5 is a diagram for explaining setting mode selection processing. FIG. 5A shows an initial screen of the setting mode displayed on the display monitor 16. FIG. 5B shows a screen for selectively inputting the setting value of the imaging sensitivity priority mode. FIG. 5C shows a screen for selectively inputting the setting value of the gradation compression priority mode.

  Here, as illustrated in FIG. 5A, the CPU 18 receives a selection input from the user via the operation unit 17 for any one of the imaging sensitivity priority mode, the gradation compression priority mode, and the AUTO mode. The AUTO mode is a mode for selecting either the imaging sensitivity priority mode or the gradation compression priority mode by internal processing on the electronic camera 1 side.

  For example, when the imaging sensitivity priority mode is selected and input, the CPU 18 displays a screen for selecting and inputting the setting value of the imaging sensitivity priority mode on the display monitor 16 (see FIG. 5B). The CPU 18 receives a set value of ISO sensitivity via the operation unit 17. When the gradation compression priority mode is selected and input, the CPU 18 displays a screen for selecting and inputting the setting value of the gradation compression priority mode on the display monitor 16 (see FIG. 5C). The CPU 18 receives a setting value for gradation compression processing via the operation unit 17.

  Here, a phenomenon is known in which a dark portion gradation of image data is darkened by photographing a subject having a large luminance difference. Therefore, in the gradation compression process, the gradation is compressed by increasing the gain of the dark portion gradation, and the blackening of the dark portion gradation is improved. In FIG. 5C, the gradation compression processing level is divided into five levels, which corresponds to the dark portion gradation gain level. In this way, when the setting mode selection process ends, the CPU 18 starts an actual photographing operation.

  FIG. 6 is a flowchart illustrating an example of the photographing operation of the electronic camera 1. Here, in order to make the explanation easy to understand, first, an example in which the AUTO mode is selected and input and flash photography is not considered will be exemplified. When the setting mode selection processing ends, the CPU 18 starts the processing of the flow shown in FIG. Here, the CPU 18 displays a through image on the display monitor 16.

  Step S101: The CPU 18 determines whether or not there is an instruction input for a half-press operation. Specifically, when release button 109 does not accept an instruction input for a half-press operation (step S101: No), CPU 18 repeats step S101. On the other hand, when the release button 109 receives an instruction input for a half-press operation (step S101: Yes), the CPU 18 proceeds to the process of step S102.

  Step S102: The CPU 18 performs photometry processing and distance measurement processing. Specifically, the CPU 18 performs subject luminance detection processing as photometry processing. That is, the CPU 18 instructs the photometric sensor 107 to perform subject luminance detection processing, whereby the output signal of the photometric sensor 107 is temporarily recorded in the RAM 13. Here, the image processing unit 12 performs multi-division photometry that divides the photographing screen into a plurality of areas (blocks) and detects photometric values for each area. For example, the image processing unit 12 performs multi-division photometry by converting image data of RGB signals into image data of luminance signals (Y signals) and color difference signals (Cr, Cb signals) (YC conversion) for each divided area. To do. Alternatively, an optimal exposure value may be calculated using the output RGB signal. Furthermore, distance information from the camera to the subject may be received from the lens and added to the calculation.

  In addition, as a distance measurement process, the CPU 18 instructs the focus detection unit 110 to perform phase difference type focus detection and detect the focus state of the lens system 51.

  Step S103: The shooting scene estimation unit 18c of the CPU 18 performs shooting scene estimation processing. Specifically, the shooting scene estimation unit 18c determines whether or not the subject brightness is lower than a preset reference value based on the result of multi-segment photometry. For example, the shooting scene estimation unit 18c can estimate that the shooting scene is a night scene if almost the entire screen excluding the light source has a luminance lower than the reference value.

  In addition, the shooting scene estimation unit 18c integrates luminance values (photometric values) for each of a plurality of regions (blocks) based on the result of multi-segment photometry. Further, the shooting scene estimation unit 18c calculates a luminance difference between the blocks. The shooting scene estimation unit 18c analyzes the color information in the screen. The shooting scene estimation unit 18c estimates a shooting scene based on the luminance difference and the color information. For example, in the shooting screen, when the gradation is smoothly changed and the orange color is dominant, the shooting scene estimation unit 18c estimates that the shooting scene is a sunset scene.

  Further, the shooting scene estimation unit 18c detects not only the subject brightness of the entire shooting screen but also the face by face detection processing, and determines whether or not the subject brightness of the face in the shooting screen is dark (low brightness). May be determined. The shooting scene estimation unit 18c may estimate a shooting scene by analyzing a through image. And CPU18 transfers to the process of step S104.

  Step S104: The first setting unit 18a of the CPU 18 performs setting mode and setting value setting processing. Specifically, for example, when the shooting scene is a night view, the first setting unit 18a sets the imaging sensitivity priority mode. The first setting unit 18a refers to the LUT 1 illustrated in FIG. Then, for example, the ISO sensitivity is set to 6400 based on the current subject brightness. Furthermore, the second setting unit 18b of the CPU 18 refers to the LUT 1 and sets the first parameter setting value indicating noise removal corresponding to the ISO sensitivity and the second parameter setting indicating contrast correction, contour correction, and saturation correction. Set the value. And CPU18 transfers to the process of step S105.

  Step S105: The CPU 18 performs shooting condition setting processing. For example, in the case of the imaging sensitivity priority mode, shooting conditions such as an aperture value and a shutter speed are set based on the ISO sensitivity. And CPU18 transfers to the process of step S106.

  Step S106: The CPU 18 determines whether or not a full-press operation instruction is input. Specifically, if the release button 109 does not accept an instruction input for full-press operation even after a predetermined time has elapsed (step S106: No), the CPU 18 once cancels the processing after the half-press operation, and in step S101. Return to processing. Thereby, CPU18 repeats the process of step S101-step S105 again. On the other hand, when the release button 109 receives an instruction input for a full-press operation (step S106: Yes), the CPU 18 proceeds to the process of step S107.

  Step S107: The CPU 18 performs a photographing process for the main image. Specifically, the CPU 18 causes the quick return mirror 101 to jump up and open the shutter curtain of the mechanical shutter 111. Subsequently, the CPU 18 drives the image sensor 10 based on the shooting conditions set in the process of step S105. The signal processing unit 11 performs gain adjustment, A / D conversion, and the like of the image signal. At this time, the signal processing unit 11 adjusts the gain of the image signal based on the ISO sensitivity set in the process of step S104. The image signal output from the signal processing unit 11 is temporarily recorded as image data in the RAM 13.

  Next, the CPU 18 performs a dark image photographing process. Specifically, in order to acquire a dark image, the CPU 18 closes the shutter curtain of the mechanical shutter 111 and then drives the image sensor 10 based on the shooting conditions for the main image. The dark signal output from the signal processing unit 11 is temporarily recorded as image data of a dark image in the RAM 13. Note that the CPU 18 may acquire the dark image prior to the actual image capturing process. When acquiring the main image and the dark image, the CPU 18 proceeds to the process of step S108.

  Step S108: The noise removal processing unit 18d of the CPU 18 performs noise removal processing. Specifically, the noise removal processing unit 18d reads out the image data of the main image and the image data of the dark image from the RAM 13 and performs subtraction processing in the first NR mode. That is, when the ISO sensitivity is 6400 with reference to LUT1, the noise removal processing unit 18d performs a correction process corresponding to the setting value (strong) of the noise removal parameter.

  Furthermore, the noise removal processing unit 18d performs the correction process such as the averaging process and the smoothing process between adjacent pixels, with the highest intensity among the five stages.

  Subsequently, the noise removal processing unit 18 d records the image data of the main image after the noise removal in the RAM 13. And CPU18 transfers to the process of step S109.

  Step S109: The correction processing unit 18e of the CPU 18 performs a correction process for correcting the image quality deterioration of the image data of the main image. Specifically, the correction processing unit 18e first reads out the image data of the main image after noise removal from the RAM 13. Then, the correction processing unit 18e performs contrast correction, contour correction, and saturation correction on the image data of the main image based on the setting value of the second parameter set in the process of step S104.

  Subsequently, the CPU 18 performs a recording process. Specifically, the CPU 18 records the corrected image data on the recording medium 30 via the recording I / F unit 15. Then, the CPU 18 ends the processing of the flow shown in FIG.

  In the processing of the flow shown in FIG. 6, when the imaging sensitivity priority mode or the gradation compression priority mode is selected by the user input, the CPU 18 does not need to estimate the shooting scene. Is skipped and the process of step S104 is performed.

  As described above, the electronic camera 1 according to the first embodiment not only removes the noise described above, but also causes rough or unevenness of the entire screen, which is newly generated by removing the noise, with respect to an image acquired by shooting under low luminance. Such image quality deterioration is suppressed by the above correction processing. For example, in the imaging sensitivity priority mode, when the ISO sensitivity level is raised to a desirable limit for viewing, the electronic camera 1 performs image processing such as reducing the adjustment of contrast, contour, and saturation accordingly. Can be suppressed.

  Alternatively, in the gradation compression priority mode, in order not to raise the ISO sensitivity level to the limit value, the electronic camera 1 performs processing such as strengthening gradation compression processing. As a result, blackout in the dark portion gradation is improved and the subject has appropriate brightness, so that the electronic camera 1 can suppress image quality deterioration.

  Therefore, the electronic camera 1 of the present embodiment can obtain a favorable image for viewing even when shooting under low luminance.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the first embodiment of the present invention and the second embodiment of the present invention, the same elements are denoted by the same reference numerals and description thereof is omitted.

  That is, the configuration of the electronic camera 1 according to the second embodiment is the same as that of the electronic camera 1 according to the first embodiment shown in FIGS. 1 and 2 and is different in that flash photography is taken into consideration. For this reason, in the second embodiment, a new table considering flash photography will be described.

  FIG. 7 is a diagram illustrating an example of a table used in the second embodiment. The second embodiment is characterized in that flash light emission is properly used for a case where a main subject is a person and a landscape in photographing under low luminance. That is, when the landscape is the main subject, the flash does not reach the main subject.

  The table shown in FIG. 7 is recorded in advance in the flash memory 14 as LUT3 and LUT4. Actually, the electronic camera 1 of the second embodiment is not limited to the LUT 3 and the LUT 4, and the LUT for each ISO sensitivity is recorded in the flash memory 14 in advance.

  In LUT3 and LUT4, the first parameter and the second parameter are associated with the set value in the imaging sensitivity priority mode, respectively. Further, a set value for flash emission is added to LUT3 and LUT4.

  As an example, the LUT 3 illustrated in FIG. 7A illustrates a case where the main subject is a landscape in the imaging sensitivity priority mode (ISO sensitivity: 6400). In addition, the LUT 4 illustrated in FIG. 7B illustrates the case where the main subject is a person in the imaging sensitivity priority mode (ISO sensitivity: 6400). LUT3 and LUT4 have the same setting values for contrast correction, contour correction, saturation correction, and noise removal. In LUT3, since the flash emission is set to OFF, the setting value for gradation compression is set to “strong”. On the other hand, in the LUT 4, since the flash emission is set to ON, the gradation compression setting value is set to “weak”.

  That is, when the main subject is landscape at the time of shooting under low luminance, the first setting unit 18a sets the setting value of the imaging sensitivity of the imaging device 10 with priority over the upper limit for obtaining a preferable image. Then, the second setting unit 18b sets the parameters for contrast correction, contour correction, and saturation correction to “weak”, and sets gradation compression to “strong”. Further, the second setting unit 18b turns off flash emission. With this setting, the electronic camera 1 can acquire a preferable image for viewing.

  In addition, when the main subject is a person (or animal) at the time of shooting under low luminance, the first setting unit 18a sets the imaging sensitivity setting value of the imaging element 10 in preference to the upper limit for obtaining a preferable image. To do. Then, the second setting unit 18b sets parameters for contrast correction, contour correction, and saturation correction to “weak”, and also sets gradation compression to “weak”. Further, the second setting unit 18b turns on flash emission. In other words, the second setting unit 18b uses the flash emission together to make the degree of gradation compression weaker than in the case of landscape, thereby reducing the influence on the image. Thereby, the electronic camera 1 can acquire a preferable image for viewing.

  Next, an example of the photographing operation of the electronic camera 1 in the second embodiment will be described.

  FIG. 8 is a flowchart illustrating an example of the photographing operation of the electronic camera 1 according to the second embodiment. Note that the operation of the electronic camera 1 of the second embodiment is common to the operation of the electronic camera 1 of the first embodiment, except that there is no operation corresponding to steps S203, S204, S209, and S210. Therefore, the contents common to the operation of the electronic camera 1 of the first embodiment will be described in a simplified manner.

  Step S201: The CPU 18 determines whether or not a half-press operation instruction is input. When the release button 109 does not accept an instruction input for a half-press operation (step S201: No), the CPU 18 repeats step S201. On the other hand, when the release button 109 receives an instruction input for a half-press operation (step S201: Yes), the CPU 18 proceeds to the process of step S202.

  Step S202: The CPU 18 performs photometry processing and distance measurement processing.

  Step S203: The CPU 18 determines the presence or absence of flash emission based on the subject brightness. When flash emission is required (step S203: Yes), the CPU 18 proceeds to the process of step S204. On the other hand, when flash emission is not required (step S203: No), the CPU 18 proceeds to the process of step S205. Note that if a flash light emission instruction is input by a user input, the CPU 18 skips the process of step S203 and proceeds to the process of step S204.

  Step S204: The CPU 18 performs a light emission amount calculation process by preliminary light emission. Specifically, the CPU 18 transmits preliminary light emission information to the light emission control circuit 150 c of the flash device 150. The light emission control circuit 150c causes the light emitting unit 150b to perform preliminary light emission based on the light emission information. Here, the flash of preliminary light emitted from the light emitting unit 150b illuminates the subject. The reflected light from the subject is output as an image signal by the photometric sensor 107. The CPU 18 calculates the main light emission amount based on the image signal. And CPU18 transfers to the process of step S205.

  Step S205: The shooting scene estimation unit 18c performs shooting scene estimation processing. For example, it is assumed that the shooting scene estimation unit 18c estimates a shooting scene of a person shooting at night as an example.

  Step S206: The first setting unit 18a performs setting mode and setting value setting processing. Specifically, the first setting unit 18a sets the imaging sensitivity priority mode when, for example, the shooting scene is a person shooting at night. Then, the first setting unit 18a refers to the LUT 4 illustrated in FIG. Then, the first setting unit 18a sets the ISO sensitivity to 6400, for example, based on the current subject brightness.

  The second setting unit 18b refers to the LUT 4 and sets the first parameter setting value indicating noise removal corresponding to the ISO sensitivity and the second value indicating contrast correction, contour correction, saturation correction, and gradation compression correction. Set the parameter value.

  Further, the second setting unit 18b sets the flash emission to ON. In this case, the first setting unit 18a sets the first parameter and the second setting unit 18b sets the second parameter according to the amount of flash emission. As a result, the electronic camera 1 of the second embodiment can apply the noise removal and the above correction process to shooting with flashing light.

  Step S207: The CPU 18 performs shooting condition setting processing. For example, in the case of the imaging sensitivity priority mode, shooting conditions such as an aperture value and a shutter speed are set based on the ISO sensitivity.

  Step S208: It is determined whether or not an instruction for full-press operation has been input. Specifically, when the release button 109 does not accept an instruction input for full-press operation even after a predetermined time has elapsed (step S208: No), the CPU 18 once cancels the processing after the half-press operation, and in step S201. Return to processing. On the other hand, when the release button 109 receives an instruction input for a full press operation (step S208: Yes), the CPU 18 proceeds to the process of step S209.

  Step S209: The CPU 18 determines whether or not there is a flash emission instruction. When there is an instruction for flashing (step S209: Yes), the CPU 18 proceeds to the process of step S210. On the other hand, when there is no instruction for flash emission (step S209: No), the CPU 18 proceeds to the process of step S211.

  Step S210: The CPU 18 performs a flash emission process. Specifically, the CPU 18 transmits light emission information of main light emission to the light emission control circuit 150 c of the flash device 150. The light emission control circuit 150c causes the light emitting unit 150b to perform main light emission based on the light emission information. Here, the main flash emitted from the light emitting unit 150b illuminates the subject.

  Step S211: The CPU 18 performs photographing processing of the main image and the dark image in synchronization with the main light emission.

  Step S212: The noise removal processing unit 18d performs noise removal processing.

  Step S213: The correction processing unit 18e performs a correction process for correcting the image quality deterioration of the image data of the main image. Subsequently, the CPU 18 performs a recording process. Then, the CPU 18 ends the process of the flow shown in FIG.

  As described above, the electronic camera 1 according to the second embodiment emits a flash as necessary to perform shooting at low luminance. The electronic camera 1 according to the second embodiment not only removes the noise described above, but also improves the image quality such as roughness and unevenness of the entire screen newly generated by the noise removal. Suppress with correction processing. Here, in the electronic camera 1, the difference in ISO sensitivity may be compensated for by one step lowering (for example, ISO sensitivity: 3200) with respect to the upper limit value of ISO sensitivity (for example, ISO sensitivity: 6400) and flash photography. Alternatively, if the electronic camera 1 cannot shoot with a set value (for example, ISO sensitivity: 12800) that is one step higher than the upper limit value (for example, 6400) of the ISO sensitivity, flash photography can compensate for the difference in ISO sensitivity. Also good. In any case, in the electronic camera 1, image quality degradation can be suppressed by applying the noise removal and correction processing described above.

  Therefore, the electronic camera 1 according to the second embodiment can obtain a favorable image for viewing even when shooting under low luminance.

(Supplementary information)
(1) In the above embodiment, a single-lens reflex type electronic camera is taken as an example, but a compact type electronic camera that does not require lens replacement may be used. In this case, an image sensor used in a compact electronic camera may be used as the photometric sensor 107 described above.

  (2) In the above embodiment, parameters for contrast correction, contour correction, saturation correction, and gradation compression correction are used as the second parameter. However, the present invention is not limited to these parameters. For example, the second parameter may be a parameter such as brightness correction, hue correction, and exposure correction. Note that it is not necessary to use all the parameters, and they may be selectively used according to the situation. Further, when performing gradation compression correction, it may be performed in conjunction with exposure correction.

  (3) In the above embodiment, the multi-division photometry is performed in the image processing unit 12 as an example, but an exposure control unit may be provided separately.

  Note that the image sensor 10 may be used instead of the photometric sensor 107 to measure and output the reflected light from the subject.

DESCRIPTION OF SYMBOLS 1 ... Electronic camera, 107 ... Photometric sensor, 18a ... 1st setting part, 18b ... 2nd setting part, 18d ... Noise removal process part, 18e ... Correction process part

Claims (3)

An image sensor that captures light from a subject to generate image data;
A light emitting unit for emitting light for illuminating the subject;
A noise removal processing unit for removing noise of the image data generated by the image sensor in a first process;
A correction processing unit that corrects the image data from which noise has been removed by the noise removal processing unit in a second process;
A setting unit that sets the first process and the second process based on the brightness of the subject and whether or not the light emitting unit emits light;
Equipped with a,
The correction processing unit is an electronic camera that corrects image quality degradation based on the noise removal of the image data from which noise has been removed by the noise removal processing unit . The correction processing unit, contrast correction, contour correction, color saturation correction, to claim 1 for correcting image degradation of the image data from which noise is removed by the noise removal processing unit by at least one of the gradation compression correction The electronic camera described. The electronic camera according to claim 1, further comprising a detection unit that detects the brightness of the subject.

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