JP2014123902A - Imaging apparatus and imaging apparatus control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly adjust white balance even under a light source having poor color rendering properties in addition to a normal light source.
An imaging unit, a photometric unit that measures light emitted by a light emitting unit that can irradiate the subject when the imaging unit images the subject, and a color that evaluates the color of image data acquired by the imaging unit A white detection unit that detects white by varying a white detection region for extracting a white candidate pixel corresponding to the light emitting unit based on a photometric result obtained by the photometric unit; An imaging apparatus comprising: white balance correction means for performing white balance correction according to a result of white detection by a detection region.
[Selection] Figure 4

Description

  The present invention relates to a white balance control technique at the time of flash photography.

  In order to calculate a white balance coefficient in photographing using a light emitting means such as a strobe, a method as disclosed in Patent Document 1 has been proposed. In Patent Document 1, a light quantity ratio between strobe light and external light is calculated, and a WB coefficient suitable for each light source is mixed according to the light quantity ratio.

JP 2000-308069 A

  However, a light source with poor color rendering properties, such as an LED light source, is located far from the blackbody radiation axis, and thus often does not fall within the white detection range that matches the normal blackbody radiation axis. When there is an LED light source with poor color rendering in an ordinary light environment, it is difficult to set a white detection range that satisfies both the chromaticity on the black body radiation axis and the chromaticity of the LED light source. Even if the white detection range is set in the vicinity of the chromaticity of the LED strobe light, the LED strobe has a light amount smaller than that of the xenon tube and is mixed with external light. Therefore, there is a problem that white of the subject is difficult to be extracted in the color area of the LED strobe light, white detection cannot be performed and appropriate white balance control cannot be performed, and it is difficult to obtain a good image.

  The present invention has been made in view of the above-described problems, and an object thereof is to make it possible to appropriately adjust the white balance even under a light source having a poor color rendering property in addition to a normal light source.

  In order to achieve the above object, an imaging apparatus according to the present invention includes an imaging unit, a photometric unit that measures light emitted from the light emitting unit that can irradiate the subject when the imaging unit images the subject, and chromaticity. In the figure, a white detection area for extracting white candidate pixels corresponding to the light emitting means is varied based on a photometric result obtained by the photometric means, and white detection means for performing white detection, and white detection by the white detection area. And white balance correction means for performing white balance correction according to the result.

  According to another aspect of the present invention, there is provided a control method for an imaging apparatus, comprising: an imaging unit; and a photometric unit that measures light emitted from the light emitting unit that can irradiate the subject when the imaging unit captures an image of the subject. A white detection step of performing white detection by varying a white detection region for extracting a white candidate pixel corresponding to the light emitting unit on the chromaticity diagram based on a photometric result by the photometric unit; A white balance correction step of performing white balance correction in accordance with a result of white detection by the white detection region.

  According to the present invention, it is possible to appropriately adjust the white balance even under a light source having poor color rendering properties in addition to a normal light source.

1 is a block diagram showing a configuration of a camera according to an embodiment of the present invention. The flowchart which shows the WB control value calculation process of this invention Diagram showing white detection range and white point of strobe light The flowchart which showed the flow which takes a still image in the present invention Flowchart explaining the strobe white detection frame setting method Flowchart explaining the outside light / strobe light quantity ratio calculation process in detail Conceptual diagram showing how the white detection range can be varied according to the strobe and external light quantity ratio

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a configuration of an imaging apparatus according to the present embodiment.

  The imaging unit 100 receives a light beam incident on the optical system and outputs an image signal digitized by A / D (analog / digital) conversion. The imaging unit 100 includes a lens group including a focus lens, a shutter, a diaphragm, and an imaging sensor that constitute an optical system. The shutter, the diaphragm, and the focus lens can be controlled by the imaging control circuit 113, respectively. In this embodiment, the imaging sensor is an XY address type, CMOS sensor having a Bayer array of RGB pixels, but is not limited thereto. For example, it may be a CCD (Charge Coupled Device) or a sensor in which complementary color pixels are arranged.

  The light emitting unit 101 is a strobe capable of irradiating a subject as auxiliary light when photographing by the imaging unit 100. In the present embodiment, it is assumed that the LED strobe has a chromaticity relatively distant from the black body radiation axis.

  The image data output from the imaging unit 100 can be stored in the memory 102 at the same time as being input to the image processing unit 200. The image data stored in the memory 102 can be read again, and a CPU (Central Processing Unit) 114 can refer to the image data or input the read image data to the image processing unit 200. In the present embodiment, the CPU 114 measures the brightness of a light-emitting image captured with the light-emitting unit 101 emitting light by the imaging unit 100 and a non-light-emitting image captured with the light-emitting unit 101 not emitting light. It is responsible for photometric means for photometry. Based on the photometric result, white balance correction processing is performed in the subsequent image processing unit 200.

  Image data subjected to image processing by the image processing unit 200 can be written back to the memory 102 or arbitrary data can be written from the CPU 114.

  The display unit 116 can D / A convert the digital image data processed by the image processing unit 200 and stored in the memory 102 to display an image on a display medium such as a liquid crystal display. In addition to image data, arbitrary information can be displayed alone or with an image, and exposure information at the time of shooting can be displayed, and a frame can be displayed in the detected face area. is there.

  The recording unit 115 can store captured image data in a recording medium such as a ROM or an SD card.

  With respect to the processing in the image processing unit 200, portions related to the present embodiment will be described. Reference numeral 103 denotes a WB (white balance) control unit that calculates a white balance correction value (WB correction value) based on information from the image signal stored in the memory 102, and outputs the white balance correction value to the image signal stored in the memory 102. WB correction is performed. A detailed configuration of the WB control unit 103 and a method for calculating the WB correction value will be described later.

  Reference numeral 104 denotes a color conversion MTX (color conversion matrix) circuit that converts color signals RY and BY by applying a color gain so that the image signal corrected by the WB control unit 103 is WB-corrected to be reproduced in an optimum color. It is. Reference numeral 105 denotes an LPF (low-pass filter) circuit that limits the band of the color difference signals RY and BY. Reference numeral 106 denotes a CSUP (Chroma) that suppresses a false color signal in a saturated portion of the image signal band-limited by the LPF circuit 105. (Suppress) circuit. On the other hand, the image signal WB corrected by the WB control unit 103 is also output to the Y (luminance signal) generation circuit 111 to generate the luminance signal Y, and the edge enhancement circuit 112 performs edge processing on the generated luminance signal Y. Emphasis processing is performed.

  The color difference signals RY and BY output from the CSUP circuit 106 and the luminance signal Y output from the edge emphasis circuit 112 are converted into RGB signals by the RGB conversion circuit 107, and the gamma correction circuit 108 converts the gradation signals Y to B and Y. Tone correction is applied. Thereafter, it is converted into a YUV signal by the color luminance conversion circuit 109, further compressed by the JPEG compression circuit 110, written to the memory 102, and recorded as an image signal on the external recording medium or the internal recording medium. Alternatively, it is displayed on the display medium by the display unit 116. Alternatively, it may be output to an external output (not shown).

  Here, a part or all of each of the above-described configurations may be configured as a software module.

  Next, a method for calculating the WB correction value in the WB control unit 103 in FIG. 1 will be described in detail. FIG. 2 is a flowchart of the WB correction value calculation process. This process is mainly performed by the CPU 114 and the WB control unit 103.

First, the image signal stored in the memory 102 is read, and the screen is divided into arbitrary m blocks (step S101). Then, for each block (1 to m), pixel values are added and averaged for each color to calculate a color average value (R [i], G [i], B [i]), and the following equation (1) ) Is used to calculate color evaluation values (Cx [i], Cy [i]) (step S102) to evaluate the color of the image data.
Cx [i] = (R [i] −B [i]) / Y [i] × 1024
Cy [i] = (R [i] + B [i] -2G [i]) / Y [i] × 1024 (1)
However, Y [i] = R [i] + 2G [i] + B [i]

  Next, it is determined whether or not the color evaluation value (Cx [i], Cy [i]) of the i-th block calculated in step S102 is included in the preset white detection range 301 shown in FIG. S103).

  The white detection range 301 is obtained by photographing white under a different light source in advance and plotting the calculated color evaluation value on a chromaticity diagram, that is, corresponding to an area where pixels serving as white candidates exist under each light source. . This white detection range can be set separately depending on the shooting mode. The negative direction of the x coordinate (Cx) in FIG. 3 is a color evaluation value when white of a high color temperature subject is photographed, and the positive direction is a color evaluation value when white of a low color temperature subject is photographed. The y-coordinate (Cy) means the degree of the green component of the light source, and the green (green) component increases as it goes in the negative direction, that is, it indicates a fluorescent lamp. As shown in FIG. 3A, in the case of a xenon tube strobe, the chromaticity is located in a high color temperature portion close to black body radiation. However, the light source of the LED strobe has various chromaticities depending on the type of the LED, and many of them are located at a strong and green place as shown in FIG.

  In such an LED strobe, in an environment that does not include external light, the white distribution only in the LED strobe is distributed in the Green direction, so the white detection range is set to a range that detects the Green direction. (302 in FIG. 3B). In the case where it is determined that the subject is photographed with only the LED strobe with little external light, the white balance control may be performed by moving the white detection area in this way.

  When the calculated color evaluation values (Cx [i], Cy [i]) are included in the white detection range 302 (YES in step S103), it is determined that the block is white. Then, the color average values (R [i], G [i], B [i]) of the block are integrated (step S104). If the calculated color evaluation values (Cx [i], Cy [i]) are not included in the white detection range 302, the process proceeds to step S105 without adding them. The processing of step S103 and step S104 can be expressed by equation (2).

  Here, in the expression (2), if the color evaluation value (Cx [i], Cy [i]) is included in the white detection range (302 in FIG. 3B), Sw [i] is included in 1. If not, Sw [i] is set to 0. Thereby, the process of whether or not to add the color evaluation values (R [i], G [i], B [i]) is substantially performed according to the determination in step S103.

  In step S105, it is determined whether or not the above process has been performed for all blocks. If there is an unprocessed block, the process returns to step S102 to repeat the above process, and if all the blocks have been processed, the process proceeds to step S106. .

In step 106, the first WB correction values (WBCo1_R, WBCo1_G, WBCo1_B) are calculated from the integrated values (sumR, sumG, sumB) of the obtained color evaluation values using the following equation (3).
WBCo1_R = sumY × 1024 / sumR
WBCo1_G = sumY × 1024 / sumG (3)
WBCo1_B = sumY × 1024 / sumB
However, sumY = (sumR + 2 × sumG + sumB) / 4

  FIG. 4 is a flowchart showing a flow of still image shooting in this embodiment.

  In step S201, the display unit 116 is a live view mode in which an image periodically output from the imaging unit 100 is displayed as a live image, and a live image is displayed. When a shooting instruction is issued in step S202, exposure calculation for still image shooting is performed in step S203. (AutoExposure, AE). In step S204, if the subject is dark as a result of performing AE in step S203, the flash emission is determined. If it is determined in step S205 that the flash is emitted, a non-flash image is acquired in step S206.

  In step S207, actual exposure still image shooting is performed. In step S208, a strobe white detection frame is set. Details of the processing in step S208 will be described later. On the other hand, if the flash is not emitted in step S205, the main exposure still image is taken in step S210, and a normal white detection frame for external light is set in step S211. In step S209, a white detection frame is set in the actual detection circuit, and a white detection operation is performed in step S212. The white balance coefficient calculation process described above is performed in step S213, and the development process is performed in step S214.

  FIG. 5 is a flowchart for explaining the strobe white detection frame setting method in step S208 of FIG.

  In FIG. 5, in step S301, the light quantity ratio between the external light and the strobe is calculated. Details will be described later. In step S302, the CxCy value corresponding to the WB coefficient in the strobe non-light emission state at the time of live image display is acquired. In step S303, a CxCy value corresponding to the WB coefficient of the LED strobe measured in advance is acquired. In S304, the movement amount of the white detection frame for the strobe is calculated. FIG. 7 is a conceptual diagram showing how the strobe white detection frame moves in step S304.

The moving method is performed based on the strobe / external light quantity ratio calculated in step S301, thereby making it possible to detect an appropriate white balance.
In the present embodiment, as an example, an example is described in which it is linearly changed according to the strobe light amount ratio.
FIG. 7 is a conceptual diagram showing how the white detection range is varied in accordance with the light quantity ratio between the strobe and the outside light in this embodiment.

The WB coefficient and control value (first white balance control value) for the LED strobe are Cx_swb_led and Cy_swb_led, and the white detection range width for the strobe is SearchAreaCx and SearchAreaCy. At this time, the strobe white search area (white detection area), Cx_ledsearchArea, and Cy_ledsearchArea can be described as the following equation (4).
Cx_ledsearchArea = [Cx_swb_led-SearchAreaCx: Cx_swb_led + SearchAreaCx]
Cy_ledsearchArea = [Cy_swb_led-SearchAreaCy: Cy_swb_led + SearchAreaCy]
(4)

Assuming that the WB control coefficient during live view is (second white balance control value) Cx_lv, Cy_lv, the amount of movement of the white detection frame is Offset_Cx, Offset_Cy, and the strobe / outside light amount ratio is Flash_Ratio as external light. (5).
offsetCx = (Cx_lv-Cx_swb_led) * (1-Flash_Ratio)
offsetCy = (Cy_lv-Cy_swb_led) * (1-Flash_Ratio)
(5)

In this case, the white detection range (white detection region) for the strobe can be described as the following formula (6).
Cx_ledsearchArea = [Cx_swb_led-SearchAreaCx + offsetCx: Cx_swb_led + SearchAreaCx + offsetCx]
Cy_ledsearchArea = [Cy_swb_led-SearchAreaCy + offsetCy: Cy_swb_led + SearchAreaCy + offsetCy]
(6)

  By doing so, the white detection frame of the strobe can be dynamically varied according to the light quantity ratio between the strobe light and the outside light, and appropriate white balance control can be performed.

  In general, light and color have light additivity. Therefore, linear interpolation of the white balance coefficient and white detection range according to the light quantity ratio between outside light and strobe light is an effective method for moving the white detection range. .

  In this embodiment, the movement amount is controlled linearly with respect to the light amount ratio. However, when the strobe light amount ratio has a threshold value and is equal to or greater than the predetermined threshold value, the white detection range for the strobe is set. You may set to the white detection range for external light. It goes without saying that the amount of movement of the white detection range may have nonlinearity such as a look-up table format in accordance with the strobe light amount ratio.

  Of course, the control information of the strobe light emission amount may be used as a white detection range of outside light when the light emission amount is smaller than a certain level. In addition, it goes without saying that the strobe irradiation amount and the strobe external light ratio may be estimated from the subject distance obtained from the result of the automatic focus control device (AutoFocus, AF) and the light emission amount of the strobe.

  FIG. 6 is a flowchart illustrating in detail the external light / strobe light amount ratio calculation process of S301 in FIG. In FIG. 6, in S401, the block integration value when the area is divided into a plurality of blocks from the non-light emitting image acquired in S206 is acquired. In step S402, a block integration value is obtained when the region is divided into a plurality of blocks from the main exposure image acquired in S207.

In step S403, the strobe irradiation amount (FlashY [i]) and the external light irradiation amount (PreY [i]) for each block in the main exposure image are calculated.
Non-luminous image sensitivity (Sv_pre) / F value (Av_pre), exposure time (Tv_pre) and block integration value (Pre_Y), main exposure image sensitivity (Sv_cap) / F value (Av_cap), exposure time (Tv_cap) ) And the block integral value CapY (x, y), the luminance value (PreY ′ [i]) obtained by converting the luminance value of the non-luminous image into the main exposure photographing condition is calculated by the equation (7). . However, values such as Sv_pre are expressed by the following Apex.

  Here, PreY ′ [i] corresponds to the amount of external light at the time of main exposure for each block, and FlashY [i] corresponds to the amount of strobe irradiation at the time of main exposure for each block. In S404, FlashY calculated for each block is multiplied by the weighting table (CenterWight [i]) of the center weight (FlashY_wgt [i]).

  Similarly, the light emission amount of the non-light-emitting image is similarly multiplied by the weight of the center weight (also, equation (8)).

  Thus, the brightness was calculated for each of the light emitting image and the non-light emitting image.

  In step S405, subject area specifying processing is performed. More specifically, from the FlashY_wgt [i] value, the values are sorted in descending order of brightness, leaving the upper 50% area as the effective area, leaving the lower 50% block value as the invalid area, and the FlashY_wgt [i] value as the invalid area. Set to zero. In addition, a median filter is applied to determine dust areas such as noise and minute strobe reflection areas. Similarly, the FlashY_wgt [i] value is set to 0 for the part determined to be a garbage area. The block data calculated in this way can extract a central region and a region having a certain area or more with strong strobe irradiation, and this region can be determined as a main subject region. (Main_TgtTbl [i])

  In step S406, an integrated value (FlashLightVal) of the FlashY [i] value and an integrated value (DayLightVal) of PreY ′ [i] are calculated for the main subject area calculated in step S405. Then, the light quantity ratio (Flash_Ratio) between the external light and the strobe can be calculated by the following formula (9).

  In this embodiment, the main subject area is determined to be as close to the center as possible and the area irradiated with the strobe. However, of course, not only this, but also a method for identifying a face, a method of dividing an image region from information such as color and brightness, and further specifying a main subject region from the image region. Alternatively, the subject region may be specified using a method such as subject recognition that applies an image pattern matching method or the like. In these methods, if the subject region can be specified, only the calculation method of Main_TgtTbl [i] described above is changed, and the light amount ratio between the strobe and the external light in the main region can be calculated in the same manner.

  As described above, in this embodiment, the light quantity ratio between strobe light with poor color rendering properties and external light such as a fluorescent lamp is calculated, and the white detection frame is moved based on this light quantity ratio. This makes it possible to appropriately adjust the white balance even under a light source with poor color rendering properties in addition to the normal light source.

(Other embodiments)
The object of the present invention can also be achieved as follows. That is, a storage medium in which a program code of software in which a procedure for realizing the functions of the above-described embodiments is described is recorded is supplied to the system or apparatus. The computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium and program storing the program code constitute the present invention.

  Examples of the storage medium for supplying the program code include a flexible disk, a hard disk, an optical disk, and a magneto-optical disk. Further, a CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD-R, magnetic tape, nonvolatile memory card, ROM, or the like can also be used.

  Further, by making the program code read by the computer executable, the functions of the above-described embodiments are realized. Furthermore, when the OS (operating system) running on the computer performs part or all of the actual processing based on the instruction of the program code, the functions of the above-described embodiments are realized by the processing. Is also included.

  Furthermore, the following cases are also included. First, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing.

  In addition, the present invention is not limited to devices such as digital cameras, but includes built-in or external connection of imaging devices such as mobile phones, personal computers (laptop type, desktop type, tablet type, etc.), game machines, etc. It can be applied to any device. Therefore, the “imaging device” in this specification is intended to include any electronic device having an imaging function.

Claims (8)

Imaging means;
A photometric means for measuring light emitted by a light emitting means capable of irradiating the subject when the imaging means images the subject;
Color evaluation means for evaluating the color of the image data acquired by the imaging means;
A white detection unit for performing white detection by varying a white detection region for extracting a white candidate pixel corresponding to the light emitting unit based on a photometric result by the photometric unit, from a color evaluation result by the color evaluating unit;
White balance correction means for performing white balance correction according to the result of white detection by the white detection area;
An imaging device comprising: The light metering means calculates the brightness of each of a light emitting image that is shot while the light emitting means is emitting light and a non-light emitting image that is shot when the light emitting means is not emitting light,
The imaging apparatus according to claim 1, wherein the white detection unit sets the white detection region based on a brightness ratio between the light-emitting image and the non-light-emitting image.   The light metering means obtains the brightness of the light-emitting image and the non-light-emitting image by dividing each image into a plurality of regions and weighting and adding the luminance for each region. The imaging device described in 1.   The white detection area is defined in a color space, and a first white balance control value corresponding to light emission by the light emitting means acquired in advance and a second white balance control corresponding to a light source different from the white balance control value. 4. The imaging apparatus according to claim 1, wherein the second white balance control value is calculated from a value and the second white balance control value is a white balance control value calculated from the non-light-emitting image.   The white detection means sets a white detection region for external light when the brightness ratio of the light-emitting image and the non-light-emitting image is smaller than a predetermined value, and when the brightness ratio is larger than the predetermined value, The imaging apparatus according to claim 3, wherein a detection area is set. A method for controlling an imaging apparatus, comprising: an imaging unit; and a photometric unit that measures light emitted by a light emitting unit capable of irradiating the subject when the imaging unit images the subject,
A color evaluation step for evaluating the color of the image data acquired by the imaging means;
A white detection step for performing white detection by varying a white detection region for extracting a white candidate pixel corresponding to the light emitting means from a color evaluation result by the color evaluation step based on a photometry result by the photometry means;
A white balance correction step for performing white balance correction according to a result of white detection by the white detection region;
A method for controlling an imaging apparatus, comprising:   A computer-executable program in which a procedure of a control method for an imaging apparatus according to claim 6 is described.   A computer-readable storage medium storing a program for causing a computer to execute each step of the control method of the imaging apparatus according to claim 6.

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