JP4239219B2 - Auto white balance adjustment method and apparatus - Google Patents

Description

  The present invention relates to an auto white balance adjustment method and apparatus, and more particularly to an auto white balance adjustment technique for performing an appropriate white balance adjustment while leaving a tint atmosphere by a light source under shooting conditions.

  As a conventional automatic white balance adjustment method of this type, there is a method described in Patent Document 1.

  This auto white balance adjustment method is based on the luminance level of a subject and the color information for each divided area obtained by dividing one screen into a plurality of areas (the ratio of integrated values obtained by integrating the R, G, and B signals in each divided area by color). R / G and B / G).

  On the other hand, on the color space of R / G, B / G, a detection frame indicating a color distribution range corresponding to a light source type such as a shade, a blue sky, a fluorescent lamp, and a tungsten light bulb is set, and each of the obtained divided areas is set. The number of divided areas in which color information enters each detection frame is obtained based on the color information. Then, a light source type is determined based on the detected luminance level of the subject and the number of divided areas included in the detection frame, and white balance adjustment is performed based on a white balance correction value suitable for the determined light source type. Yes.

Further, Patent Document 2 performs conversion based on chromatic adaptation on each pixel of an original image from the chromaticity of illumination light at the time of shooting and the chromaticity of light (reference light) as illumination light in an image, A technique for correcting hue is disclosed.
JP 2000-224608 A JP 2001-16607 A

  The color itself originally taken by the camera is desirably color-corrected in accordance with human color vision characteristics (chromatic adaptation). The human visual characteristics are perceived by the visual system estimating the color of the light irradiating the visible image and correcting it to the original color so that it is not affected by changes in the illumination light. (Constant color vision).

  For example, if you look at the same gray as the light source A and the gray light illuminated under the incandescent light bulb at the same time, the gray light illuminated under sunlight or fluorescent light is clearly different for all people. Difference). Physically, the same object (in this case, gray paper) is irradiated with illumination with a different spectral distribution, so the physical color that reflects from the object and enters the human eye after irradiation is different . However, after a few minutes, the gray paper that appears a little yellowish or bluish when you see it appears as a similar gray color. This is chromatic adaptation based on human visual function. It is considered that each of the three types of photoreceptors (cones) in the human retina maintains an almost constant balance by reacting in inverse proportion to the illumination light.

  As is generally experienced, human visual functions are not simple, and they look different depending on conditions. The appearance of “color” is very different. Although it is known that chromatic adaptation to illumination light acts to cancel the change in illumination light, it is clear that in fact, “chromatic adaptation” is not a mechanism for canceling the change in illumination light 100%. is there. This incomplete adaptation means that even if it fully adapts to the illumination light, not everything will look the same as when illuminated with daylight white illumination. In other words, as it is generally felt, just by chromatic adaptation, there is a slight difference in color appearance.

  If the white balance is adjusted according to the degree of color adaptation by the human visual function in this way, a photograph having the same color as the appearance can be taken.

  In conventional cameras, regardless of the color of illumination light, gray objects are perfectly adapted to be corrected to gray, or even when setting a correction amount that leaves color, the color sensitivity ratio of an image sensor such as a CCD is set. In many cases, the affected colors were left behind, and none of them expressed the degree of adaptation to the original visual characteristics.

  The auto white balance adjustment method described in Patent Document 1 uses a correction amount that is empirically set in advance for each light source type, and is not correction with chromatic adaptability that matches the original visual characteristics. Further, in the color correction described in Patent Document 2, the color adaptation is predicted and corrected. However, the light (reference light) used as the illumination light in the image is set by the user, and the shooting situation It does not correspond to the following light source types. Furthermore, Patent Documents 1 and 2 do not have a description that allows the degree of adaptation to be set freely.

  The present invention has been made in view of such circumstances, and can perform white balance adjustment in accordance with the visual characteristics of a person according to the color appearance of the original light source type and the color appearance after color adaptation, It is another object of the present invention to provide an automatic white balance adjustment method and apparatus capable of performing white balance adjustment so as to always leave the same color regardless of the difference between an image sensor and a lens.

In order to achieve the above object, the invention according to claim 1 is directed to an automatic white balance adjustment method for adjusting white balance of R, G, B signals acquired via an image sensor, and to the R, G, B signals. Obtaining color information related to the type of light source under shooting conditions based on the color information corresponding to the color information, color information on the black body locus corresponding to the obtained color temperature, and color after complete adaptation A step of setting color information according to the degree of color adaptation between the information as a target value, and a white balance correction value for the R, G, B signals based on the obtained color information and the set target value a step of determining, on the basis of the white balance correction value the determined R, viewed contains G, and performing white balance adjustment of the B signal, the step of determining the color temperature, 1 Obtaining color information of a plurality of divided areas obtained by dividing a surface into a plurality of areas based on R, G, and B signals in each divided area; and on a color space of the color information of the plurality of divided areas And calculating the color information of the barycentric position in the color space of the set of color information that are mutually approximated by, and relating to the light source type from the light source type having the color information closest to the color information of the calculated barycentric position It is characterized by comprising the step of obtaining color information .

  That is, color information related to the light source type under actual shooting conditions is obtained based on the R, G, and B signals acquired via the image sensor, and the corresponding color temperature is obtained from this color information. Then, color information corresponding to the degree of color adaptation between the color information on the black body locus corresponding to the obtained color temperature and the color information after complete adaptation is set as a target value. The chromatic adaptation is preferably a chromatic adaptation adapted to human visual characteristics. A white balance correction value for the R, G, B signal is determined based on the obtained color information and the set target value, and the R, G, B signal of the R, G, B signal is determined based on the determined white balance correction value. The white balance is adjusted.

  In this way, the color temperature related to the light source type under actual shooting conditions is obtained, and the color information on the black body locus corresponding to this color temperature (appearance of the color of the original light source) from the color information (complete gray) Color information according to the appropriate color adaptability until the color information) is set as a target value, so that white balance adjustment can be performed in accordance with human visual characteristics, and color remains. Also in the setting, the target value is fixed according to the obtained color temperature, so that the white balance can be adjusted so as to always leave the same tint regardless of the difference between the imaging element and the lens.

  In the automatic white balance adjustment method according to claim 1, when the color information for each color temperature on the black body locus is set as a target value, the color adaptation is set to 0%, and the complete gray is set. The step of setting the target value includes setting the target value to 100%, and manually setting an arbitrary color adaptability of 0 to 100%. The step of setting the target value includes the step of setting the manually set color adaptability. The target value is changed according to the degree.

  Since the chromatic adaptation can be arbitrarily set, it is possible to perform white balance adjustment according to a case where there is an individual difference in the chromatic adaptation or when it is desired to leave the color of the light source strongly in the image.

According to a third aspect of the present invention, there is provided an automatic white balance adjustment device for adjusting white balance of R, G, B signals acquired via an image sensor, and a light source under photographing conditions based on the R, G, B signals. Color information acquisition means for acquiring color information relating to the seed, means for obtaining a color temperature corresponding to the acquired color information, color information on a black body locus corresponding to the acquired color temperature, and color after complete adaptation Target value setting means for setting color information according to the degree of color adaptation between information as a target value, and white balance for R, G, B signals based on the acquired color information and the set target value Means for determining a correction value, and means for adjusting white balance of the R, G, B signals based on the determined white balance correction value, and the color temperature acquisition means comprises a plurality of screens for a plurality of screens. D Means for obtaining color information of a plurality of divided areas divided into a based on R, G, B signals in each divided area, and mutually approximating on a color space of the color information of the plurality of divided areas Color information relating to the light source type is obtained from means for calculating color information of the barycentric position in the color space of the set of color information and the light source type having the color information closest to the color information of the calculated barycentric position It is characterized by comprising means .

4. The automatic white balance adjustment apparatus according to claim 3 , wherein the storage unit stores color information for each color temperature on the black body locus, and the color adaptation degree for manually setting the color adaptation degree. Setting means, and the target value setting means reads color information on the corresponding black body locus from the storage means based on the acquired color temperature, and the read color information and the color information after complete adaptation, The color information obtained by interpolating between the two in accordance with the set color adaptation degree is set as a target value.

5. The automatic white balance adjustment apparatus according to claim 3 , wherein color information after color adaptation predicted by a color adaptation prediction formula corresponding to color information for each color temperature on the black body locus is set for each color. Storage means for storing each temperature is provided, and the target value setting means reads out color information after color adaptation from the storage means based on the acquired color temperature, and sets the read color information as a target value. It is characterized by that.

  According to the present invention, color information at the time of perfect adaptation (color information of complete gray) from color information on the black body locus (appearance of the color of the original light source) corresponding to the color temperature related to the light source type under actual shooting conditions. ) Is set as a target value according to an appropriate degree of color adaptation until the white balance adjustment is performed based on the color information related to the light source type under the actual photographing condition and the set target value. As a result, white balance can be adjusted according to human visual characteristics (color adaptation), and one target value is set for each color temperature related to the light source type under actual shooting conditions. The white balance can be adjusted so that the same color is always maintained regardless of the difference between the image sensor and the lens.

  Hereinafter, preferred embodiments of an auto white balance adjusting method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an embodiment of a digital camera to which the present invention is applied.

  The camera 10 is a digital camera having functions for recording and reproducing still images and moving images, and the overall operation of the camera 10 is centrally controlled by a central processing unit (CPU) 12. The CPU 12 functions as a control means for controlling the camera system according to a predetermined program, and performs various calculations such as automatic exposure (AE) calculation, automatic focus adjustment (AF) calculation, white balance (WB) adjustment calculation, etc. Functions as a means.

  A ROM 16 connected to the CPU 12 via the bus 14 stores programs executed by the CPU 12, various data necessary for control, and the like, and an EEPROM 17 stores CCD pixel defect information, various constants / information related to camera operation, and the like. Has been.

  The memory (SDRAM) 18 is used as a program development area and a calculation work area for the CPU 12, and is also used as a temporary storage area for image data and audio data. The VRAM 20 is a temporary storage memory dedicated to image data, and includes an A area 20A and a B area 20B. The memory 18 and the VRAM 20 can be shared.

  The camera 10 is provided with a mode selection switch 22, a shooting button 24, and other operation means 26 such as a menu / OK key, a cross key, and a cancel key. Signals from these various operation units (22 to 26) are input to the CPU 12, and the CPU 12 controls each circuit of the camera 10 based on the input signals. For example, lens driving control, photographing operation control, image processing control, image Data recording / reproduction control, display control of the image display device 28, and the like are performed.

  The mode selection switch 22 is an operation means for switching between the photographing mode and the reproduction mode. When the mode selection switch 22 is operated to connect the movable contact piece 22A to the contact point a, the signal is input to the CPU 12, the camera 10 is set to the photographing mode, and the movable contact piece 22A is connected to the contact point b, the camera 10 is set to a reproduction mode for reproducing recorded images.

  The shooting button 24 is an operation button for inputting an instruction to start shooting, and includes a two-stroke switch having an S1 switch that is turned on when half-pressed and an S2 switch that is turned on when fully pressed.

  The menu / OK key is an operation having both a function as a menu button for instructing to display a menu on the screen of the image display device 28 and a function as an OK button for instructing confirmation and execution of selection contents. Key. The cross key is an operation unit for inputting instructions in four directions, up, down, left, and right, and functions as a button (cursor moving operation means) for selecting an item from the menu screen or instructing selection of various setting items from each menu. To do. The up / down key of the cross key functions as a zoom switch at the time of shooting or a playback zoom switch at the time of playback, and the left / right key functions as a frame advance (forward / reverse feed) button in the playback mode. The cancel key is used when deleting a desired item such as a selection item, canceling an instruction content, or returning to the previous operation state.

  The image display device 28 is composed of a liquid crystal display capable of color display. The image display device 28 can be used as an electronic viewfinder for checking the angle of view at the time of shooting, and is used as a means for reproducing and displaying a recorded image. The image display device 28 is also used as a user interface display screen, and displays information such as menu information, selection items, and setting contents as necessary. Instead of the liquid crystal display, other types of display devices (display means) such as an organic EL can be used.

  The camera 10 has a media socket (media mounting portion) 30, and a recording medium 32 can be mounted on the media socket 30. The form of the recording medium is not particularly limited, and various media such as a semiconductor memory card represented by xD-PictureCard (trademark) and smart media (trademark), a portable small hard disk, a magnetic disk, an optical disk, and a magneto-optical disk are used. be able to.

  The media controller 34 performs necessary signal conversion in order to deliver an input / output signal suitable for the recording medium 32 attached to the media socket 30.

  The camera 10 also includes a USB interface unit 36 as a communication means for connecting to a personal computer or other external device. By connecting the camera 10 and an external device using a USB cable (not shown), it is possible to exchange data with the external device. Of course, the communication method is not limited to USB, and IEEE1394, Bluetooth, or other communication methods may be applied.

  Next, the shooting function of the camera 10 will be described.

  When the shooting mode is selected by the mode selection switch 22, power is supplied to an image pickup unit including a color CCD solid-state image pickup element (hereinafter referred to as CCD) 38, and the camera is ready for shooting.

  The lens unit 40 is an optical unit that includes a photographic lens 42 including a focus lens and an aperture / mechanical shutter 44. The lens unit 40 is electrically driven by a lens driving unit 46 and a diaphragm driving unit 48 controlled by the CPU 12 to perform zoom control, focus control, and iris control.

  The light that has passed through the lens unit 40 is imaged on the light receiving surface of the CCD 38. A large number of photodiodes (light receiving elements) are two-dimensionally arranged on the light receiving surface of the CCD 38, and red (R), green (G), and blue (B) primary color filters corresponding to the respective photodiodes. They are arranged in a predetermined arrangement structure (Bayer, G stripe, etc.). The CCD 38 has an electronic shutter function for controlling the charge accumulation time (shutter speed) of each photodiode. The CPU 12 controls the charge accumulation time in the CCD 38 via the timing generator 50. Instead of the CCD 38, another type of image sensor such as a MOS type may be used.

  The subject image formed on the light receiving surface of the CCD 38 is converted into a signal charge of an amount corresponding to the amount of incident light by each photodiode. The signal charge accumulated in each photodiode is sequentially read out as a voltage signal (image signal) corresponding to the signal charge based on a drive pulse given from the timing generator 50 in accordance with a command from the CPU 12.

  The signal output from the CCD 38 is sent to an analog processing unit (CDS / AMP) 52, where the R, G, B signals for each pixel are sampled and held (correlated double sampling processing), amplified, and then A / Applied to the D converter 54. The dot-sequential R, G, B signals converted into digital signals by the A / D converter 54 are stored in the memory 18 via the image input controller 56.

  The image signal processing circuit 58 processes the R, G, B signals stored in the memory 18 in accordance with a command from the CPU 12. That is, the image signal processing circuit 58 includes a synchronization circuit (a processing circuit that converts a color signal into a simultaneous expression by interpolating a spatial shift of the color signal associated with the color filter array of the single CCD), a white balance correction circuit, It functions as an image processing means including a gamma correction circuit, a contour correction circuit, a luminance / color difference signal generation circuit, etc., and performs predetermined signal processing using the memory 18 in accordance with commands from the CPU 12.

  The RGB image data input to the image signal processing circuit 58 is converted into a luminance signal (Y signal) and a color difference signal (Cr, Cb signal) by the image signal processing circuit 58, and predetermined processing such as gamma correction is performed. Applied. The image data processed by the image signal processing circuit 58 is stored in the VRAM 20.

  When the captured image is output to the image display device 28 on the monitor, the image data is read from the VRAM 20 and sent to the video encoder 60 via the bus 14. The video encoder 60 converts the input image data into a predetermined signal for display (for example, an NTSC color composite video signal) and outputs the signal to the image display device 28.

  Image data representing an image for one frame is rewritten alternately in the A region 20A and the B region 20B by the image signal output from the CCD 38. Of the A area 20A and B area 20B of the VRAM 20, the written image data is read from an area other than the area where the image data is rewritten. In this manner, the image data in the VRAM 20 is periodically rewritten, and a video signal generated from the image data is supplied to the image display device 28, whereby the image being captured is displayed on the image display device 28 in real time. Is done. The photographer can check the shooting angle of view from the video (through movie image) displayed on the image display device 28.

  When the shooting button 24 is pressed halfway and S1 is turned on, the camera 10 starts AE and AF processing. That is, the image signal output from the CCD 38 is input to the AF detection circuit 62 and the AE / AWB detection circuit 64 via the image input controller 56 after A / D conversion.

  The AE / AWB detection circuit 64 includes a circuit that divides one screen into a plurality of areas (for example, 16 × 16) and accumulates RGB signals for each divided area, and provides the accumulated value to the CPU 12. The CPU 12 detects the brightness of the subject (subject brightness) based on the integrated value obtained from the AE / AWB detection circuit 64, and calculates an exposure value (shooting EV value) suitable for shooting. According to the obtained exposure value and a predetermined program diagram, the aperture value and the shutter speed are determined, and the CPU 12 controls the electronic shutter and iris of the CCD 38 according to this to obtain an appropriate exposure amount.

  Further, the AE / AWB detection circuit 64 calculates an average integrated value for each color of the RGB signals for each divided area during automatic white balance adjustment, and provides the calculation result to the CPU 12. The CPU 12 obtains the integrated value of R, the integrated value of B, and the integrated value of G, obtains the ratio of R / G and B / G for each divided area, and R of these R / G and B / G values. The light source type is discriminated based on the distribution in the color space of the / G, B / G axis coordinates, etc., and the gain value (white balance correction value) for the R, G, B signals of the white balance adjustment circuit according to the discriminated light source type ) To correct the signal of each color channel. Details of the white balance adjustment will be described later.

  The AF control in the camera 10 is, for example, a contrast AF that moves a focusing lens (a moving lens that contributes to focus adjustment among the lens optical systems constituting the photographing lens 42) so that the high-frequency component of the G signal of the video signal is maximized. Applies. That is, the AF detection circuit 62 cuts out a signal in a focus target area set in advance in a high-pass filter that passes only a high-frequency component of the G signal, an absolute value processing unit, and a screen (for example, the center of the screen). An area extraction unit and an integration unit that integrates absolute value data in the AF area are configured.

  The integrated value data obtained by the AF detection circuit 62 is notified to the CPU 12. The CPU 12 calculates a focus evaluation value (AF evaluation value) at a plurality of AF detection points while moving the focusing lens by controlling the lens driving unit 46, and determines a lens position where the evaluation value is a maximum as a focus position. To do. Then, the lens driving unit 46 is controlled so as to move the focusing lens to the obtained in-focus position. The calculation of the AF evaluation value is not limited to a mode using the G signal, and a luminance signal (Y signal) may be used.

  The shooting button 24 is half-pressed, AE / AF processing is performed when S1 is turned on, the shooting button 24 is fully pressed, and the shooting operation for recording starts when S2 is turned on. The image data acquired in response to S2 ON is converted into a luminance / color difference signal (Y / C signal) by the image signal processing circuit 58, subjected to predetermined processing such as gamma correction, and then stored in the memory 18. The

  The Y / C signal stored in the memory 18 is compressed according to a predetermined format by the compression / decompression circuit 66 and then recorded on the recording medium 32 via the media controller 34. For example, a still image is recorded in JPEG (Joint Photographic Experts Group) format.

  When the playback mode is selected by the mode selection switch 22, the compressed data of the last image file (last recorded file) recorded on the recording medium 32 is read. When the file related to the last recording is a still image file, the read image compression data is expanded to an uncompressed YC signal via the compression / decompression circuit 66, and the image signal processing circuit 58 and the video encoder 60 are used. After being converted into a display signal, it is output to the image display device 28. Thereby, the image content of the file is displayed on the screen of the image display device 28.

  During single-frame playback of still images (including playback of the first frame of a movie), the file to be played can be switched (forward / reverse frame advance) by operating the right or left key of the four-way controller. it can. The image file at the frame-advanced position is read from the recording medium 32, and still images and moving images are reproduced and displayed on the image display device 28 in the same manner as described above.

  Next, an auto white balance adjustment method according to the present invention will be described.

  FIG. 2 is a flowchart used for explaining the white balance adjustment method according to the present invention.

  First, when the photographing button 24 is pressed, the subject is photographed. The R, G, B signals obtained from the CCD 38 at the time of photographing are temporarily stored in the memory 18. Using the R, G, and B signals stored in the memory 18, an average integrated value for each color of the RGB signals is calculated for each of 256 divided areas in which one screen is divided into 16 × 16, and each divided area is calculated. The ratio of the average integrated values of R, G, and B (that is, the ratio of R / G and B / G) is calculated for each.

  The color information for each of the 256 divided areas thus calculated is distributed on the color space of the R / G and B / G axis coordinates shown in FIG. 3 based on the values of R / G and B / G. Can be represented as 256 points.

  Then, the barycentric position of a set of color information (hereinafter referred to as “catalyst”) that is close to each other out of 256 pieces of color information distributed in the color space of the R / G and B / G axis coordinates is calculated. (Step S10).

  The color temperature of the color information indicated by the center of gravity position of the catamari is detected (step S12). The reason why the color information is catalyzed is that the subject is illuminated by a light source having a certain color temperature. Accordingly, a light source type having color information that most closely approximates the color information of the center of gravity position of the catamaria (for example, blue sky, shade 1 to 4, daylight colors 1 to 4, shown in FIG. 5, sunny, day white 1, 2, white 1, 2 , Warm white 1-4, tungsten 1-4, low tungsten, etc.) can be automatically determined.

  Next, it is determined whether the white balance (WB) mode set in the camera 10 is the auto WB mode or the manual WB mode (step S14). If the manual WB mode is set, the color information on the black body locus corresponding to the color temperature detected in step S12 is acquired (step S16).

  Here, the color information on the black body locus will be described.

  The change of color temperature changes the “human original color appearance”. In principle, “visual appearance of human beings” is a constant color vision under any light source. For example, a gray object adapts to gray. However, in practice, the color of the light source remains and looks no matter how the eyes adapt. The remaining color of the light source also changes depending on the color temperature. In the present invention, white balance adjustment is performed in consideration of this “human original color appearance”.

  FIG. 4 is a graph showing the spectral distribution of black body radiation for each color temperature. The black body radiation spectrum shown in FIG. 4 is used as a reference light source.

The original color of the light source when a gray plate (N gray) is applied to black body radiation spectroscopy can be expressed by the following equation using color matching functions x (λ), y (λ), and z (λ). .
[Equation 1]
X = k∫R (λ) P (λ) x (λ) dλ
Y = k∫G (λ) P (λ) y (λ) dλ
Z = k∫B (λ) P (λ) z (λ) dλ
k = 100 / ∫P (λ) y (λ) dλ
The value obtained by converting the tristimulus values XYZ of the XYZ color system of the CIE (International Lighting Commission) shown in [Equation 1] into an RGB system is defined as “original light source appearance”. That is, the color of the light source itself.

  FIG. 5 is a graph showing the locus of black body color change due to color temperature (black body locus) on R / G and B / G axis coordinates.

  Returning to FIG. 2, in step S16, the color information on the black body locus shown in FIG. 5 and corresponding to the color temperature detected in step S12 (R / G, B / G in FIG. 5). Get coordinate values in color space. Note that the black body locus corresponding to the color temperature shown in FIG. 5 is stored in the EEPROM 17 in advance.

  Subsequently, a target value for white balance adjustment is calculated based on the acquired color information and the color adaptation degree (0 to 100%) input by the user in step S20 (step S18). That is, when color information for each color temperature on the black body locus is set as a target value, the chromatic adaptation is set to 0%, and the complete gray is set to the target value (R / G, B / G coordinates (1, 1)) is set to 100% color adaptation, and the color information for each color temperature on the black body locus (appearance of the original light source) and complete gray according to the color adaptation input by the user The interpolated value is set as the target value. Therefore, the target value calculated in step S18 moves on a straight line between the color information of the color temperature on the black body locus and the complete gray according to the input color adaptation (0 to 100%). Become.

  On the other hand, if it is determined in step S14 that the auto WB mode is set, the color information after the predetermined color adaptation of the color information on the black body locus corresponding to the color temperature detected in step S12 is used as the target value. Set (step S22). That is, the color information after the color adaptation is set as a target value in order to obtain “original appearance of human being” by chromatic adaptation, not the color information itself on the black body locus corresponding to the detected color temperature. The color information after color adaptation at this time can be a value predicted by, for example, a CIE color adaptation prediction formula. The position after the color adaptation shown in FIG. 6 is stored in advance in the EEPROM 17 for each color temperature.

  The color information corresponding to each color temperature on the black body locus shown in FIG. 5 becomes the position shown in FIG. 6 after the chromatic adaptation by applying the chromatic adaptation prediction formula. The coordinates of each color information after this chromatic adaptation are between “appearance of the light source itself” and complete adaptation.

  Referring back to FIG. 2, when the target value is set in step S18 or step S22, the R, G, B signals are then based on the position of the center of gravity of the color information calculated in step S10 and the set target value. A white balance correction value for is calculated (step S24).

That is, as shown in FIG. 7, assuming that the coordinates of the center of gravity position of the R / G, B / G coordinate system are (Xi, Yi) and the coordinates of the target value are (Xj, Yj), the coordinates (Xi, Yi) The white balance gain (WB gain) is obtained so that is at the coordinates (Xj, Yj). Assuming that the WB gain to be obtained is g _r i and g _b i, g _r i and g _b i are as follows:
[Equation 2]
g _r i = Xj / Xi
g _b i = Yj / Yi
Can be expressed as

From the WB gains g _r i and g _b i obtained as described above, R, G, and B gain values (WB correction values) for the R, G, and B signals stored in the memory 18 of FIG. 1 are obtained. The R and B gain values to be applied to the R and B signals can be obtained by multiplying the WB gains g _r i and g _b i by a required gain value to be applied to the G signal. Further, when the required gain value to be added to the G signal is 1, the WB gains g _r i and g _b i are directly used as the R and B gain values to be added to the R and B signals.

  Then, the R, G, B signals stored in the memory 18 are corrected by the R, G, B gain values (WB correction values). Thereby, white balance adjustment is performed (step S26).

  In this way, by adjusting the white balance by setting the color from the “light source appearance” to the full adaptation as the target value, for example, a white balance adjustment that removes redness a little with a tungsten light source is performed. Natural color.

  In this embodiment, the color information related to the light source type is obtained from the barycentric position of the catamari in the color space in which the color information of the plurality of divided areas is distributed. In the R / G and B / G color spaces, the blue sky, shade 1 to 4, daylight colors 1 to 4, clear, day white 1, 2, white 1, 2, warm white 1 as shown in FIG. -4, tungsten 1-4, low detection tungsten and other detection frames indicating the range of color distribution corresponding to the light source type, and based on the color information for each divided area, the color information in each detection frame The number of light sources is determined, the light source type is determined based on the luminance level of the subject and the number of divided areas included in the detection frame, and the center coordinates of the detection frame corresponding to the light source type are obtained as color information related to the light source type in the shooting state You may do it.

FIG. 1 is a block diagram showing an embodiment of a digital camera to which the present invention is applied. FIG. 2 is a flowchart used to explain the auto white balance adjustment method according to the present invention. FIG. 5 is a graph showing an example of the distribution of color information of a plurality of divided areas in the R / G and B / G color spaces. FIG. 4 is a graph showing the spectral distribution of black body radiation for each color temperature. FIG. 5 is a graph showing the locus of black body color change due to color temperature (black body locus) on R / G and B / G axis coordinates. FIG. 6 is a graph showing the position after color adaptation of each color temperature on the black body locus. FIG. 7 is a diagram used to explain how to obtain the white balance gain.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Camera, 12 ... CPU, 16 ... ROM, 17 ... EEPROM, 18 ... Memory, 26 ... Operation means, 32 ... Recording medium, 38 ... Color CCD solid-state image sensor (CCD), 40 ... Lens unit, 42 ... Shooting lens 58 ... Image signal processing circuit

Claims (5)

In an automatic white balance adjustment method for adjusting white balance of R, G, B signals acquired via an image sensor,
Obtaining color information related to a light source type under photographing conditions based on the R, G, B signals, and obtaining a color temperature corresponding to the color information;
Setting, as a target value, color information corresponding to the degree of color adaptation between the color information on the black body locus corresponding to the obtained color temperature and the color information after full adaptation;
Determining a white balance correction value for R, G, B signals based on the obtained color information and the set target value;
Look including the steps of: performing a white balance adjustment of the R, G, B signals based on the white balance correction value the determined,
The step of obtaining the color temperature comprises obtaining color information of a plurality of divided areas obtained by dividing one screen into a plurality of areas based on R, G, and B signals in each divided area, and the plurality of divided areas. Calculating the color information of the barycentric position in the color space of the set of color information that is mutually approximate on the color space, and the color information that most closely approximates the color information of the calculated barycentric position. And obtaining color information relating to the light source type from the light source type .   When the color information for each color temperature on the black body locus is set as a target value, the chromatic adaptation is set to 0%, and when the complete gray is set as the target value, the chromatic adaptation is set to 100%, and an arbitrary value of 0 to 100% is set. The step of setting the target value includes changing the target value according to the manually set color adaptability. Auto white balance adjustment method. In an automatic white balance adjustment device that performs white balance adjustment of R, G, and B signals acquired via an image sensor,
Color information acquisition means for acquiring color information related to a light source type under shooting conditions based on the R, G, B signals;
Means for obtaining a color temperature corresponding to the acquired color information;
Target value setting means for setting, as a target value, color information corresponding to the degree of color adaptation between the color information on the black body locus corresponding to the acquired color temperature and the color information after full adaptation;
Means for determining a white balance correction value for R, G, B signals based on the acquired color information and the set target value;
Means for adjusting white balance of the R, G, B signals based on the determined white balance correction value ;
The color temperature acquisition means includes means for obtaining color information of a plurality of divided areas obtained by dividing one screen into a plurality of areas based on R, G, and B signals in each divided area; Means for calculating color information of the barycentric position in the color space of a set of color information that are mutually approximated on the color space of the color information, and color information that most closely approximates the color information of the calculated barycentric position An automatic white balance adjusting device comprising means for obtaining color information related to the light source type from the light source type . A storage unit that stores color information for each color temperature on the black body locus; and a color adaptation setting unit that manually sets a color adaptation. The target value setting unit is based on the acquired color temperature. The color information on the corresponding black body locus is read from the storage means, and the color information obtained by interpolating between the read color information and the color information after complete adaptation according to the set color adaptation degree is obtained. 4. The automatic white balance adjusting device according to claim 3 , wherein the automatic white balance adjusting device is set as a target value. Storage means for storing color information after color adaptation predicted by a color adaptation prediction formula corresponding to color information for each color temperature on the black body locus for each color temperature, and the target value setting means, the target value setting means 4. The automatic white balance adjustment apparatus according to claim 3 , wherein the color information after color adaptation corresponding to the storage unit is read from the storage unit, and the read color information is set as a target value.

Images