JP2006020165A - Method of setting white balance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify setting for giving a hue to an object image. <P>SOLUTION: A red proper WB gain Rg0 and a blue proper WB gain Bg0 out of three colors for performing proper white balance are multiplied by hue coefficients α and β corresponding to a selected hue to calculate a red correction WB gain Rg1 and a blue correction WB gain Bg1. The red correction WB gain Rg1, the blue correction WB gain Bg1 and a green proper WB gain Gg0 are set in an image signal processing unit to correct white balance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for setting a white balance of a photographing apparatus.

  In a photographing apparatus such as a digital camera, a photographing signal output from an image sensor such as a CCD image sensor is converted into digital image data and recorded on a recording medium such as a memory card. Such a digital camera has a function of adjusting and setting the white balance in order to accurately reproduce the color of the subject without losing the color balance. The loss of color balance is caused by the difference in sensitivity to the wavelength of the image sensor, the difference in the color temperature of the light source, etc. The white balance is adjusted when the white or gray subject is photographed. This is done by adjusting the gain for amplifying the photographic signal or image data so that the blue levels are the same.

  In digital cameras, auto white balance, reset white balance, and preset white balance are known as white balance setting functions. The auto white balance is a method of automatically adjusting and setting a gain so that a correct color is always expressed following a change in color temperature, and is also called an auto tracking white balance.

  Reset white balance is also called one-push white balance. When a subject such as white or gray paper is photographed under a light source used for shooting, the white balance is instructed. The gain of each color is determined so that no color is added to the paper or gray paper. Then, the subsequent shooting is performed under the gain. The preset white balance is adjusted in advance according to the selected light source by the operator selecting from the types of light sources prepared in advance, for example, “daylight”, “incandescent light”, “fluorescent light”, etc. The gain is set.

  Further, Japanese Patent Laid-Open No. 2004-151867 discloses a digital camera having a function of setting a desired color tone by manually increasing / decreasing the gain of each color after setting the white balance with the setting function as described above. According to this, it is possible for the photographer to intentionally break the color balance and to photograph the entire image with a tint. Note that the function called “preset WB” in Patent Document 1 corresponds to the reset white balance.

JP 2002-185972 A

  By the way, when the white balance gain is increased / decreased so that the desired color tone can be obtained with the above-described digital cantilever, as described above, for example, the preset white balance is used to obtain an appropriate white balance. After the above setting is made, the red and blue gains themselves are increased or decreased to achieve a desired color. However, with such a setting method, there is a problem in that it is necessary to increase or decrease the gain while checking the color, and it takes time to perform the color setting operation. Further, when the light source is changed, it is necessary to adjust the gain again. Furthermore, since the gain itself is increased / decreased to set the color tone, the auto white balance in which the gain is changed according to the color temperature of the light source cannot perform shooting with a color tone.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a white balance setting method capable of easily setting a desired color.

  The white balance setting method according to claim 1, wherein a coefficient designated for each color by an external operation and a gain determined to obtain an appropriate white balance for each color are multiplied by corresponding colors. The gain obtained is set as a gain for white balance, and each color component of the captured image is individually amplified.

  3. The white balance setting method according to claim 2, wherein a coefficient is designated by an external operation for other colors except for a specific color, and the white balance is determined to have an appropriate white balance for the specific color. The gain is set as a white balance gain.

  Since the gain determined to achieve the appropriate white balance multiplied by the coefficient specified for each color is used as the gain for white balance, the desired color only needs to be specified according to the color. Since the white balance gain is corrected so as to achieve taste, it is possible to easily set the color in a short time. In addition, since the color tone is not changed by increasing or decreasing the gain itself determined to achieve an appropriate white balance, even if the gain that makes the white balance appropriate follows the change in the color temperature of the light source, the color tone changes. There is no need to reset.

  The front of the digital camera embodying the present invention is shown in FIG. 1, and the back is shown in FIG. On the front surface of the digital camera 10, a photographing lens 11, a strobe light emitting unit 12, an objective window 13 a of an optical viewfinder 13, and a lens barrier 14 are provided. The lens barrier 14 is slidable between a closed position covering the photographing lens 11 and the strobe light emitting unit 12 and an open position where the lens barrier 14 is retracted from the front surface and can be photographed as shown in FIG.

  A CCD image sensor 15 (see FIG. 3) is arranged at the ridge of the taking lens 11. The subject image photographed by the CCD image sensor 15 is displayed on the LCD 16 provided on the back surface of the digital camera 10 as a so-called through image. Further, an eyepiece window 13b of the optical viewfinder 13 is provided on the back surface. In addition to observing a through image displayed on the LCD 16, framing can be performed using the optical finder 13.

  A release button 18 is provided on the upper surface of the digital camera 10. The release button 18 is pressed in two steps. When the release button 18 is lightly pressed to a half-pressed position, various shooting conditions such as automatic exposure adjustment (AE) and automatic focus adjustment (AF) are set. A shooting preparation process is performed. When the shooting preparation process is completed, the setting is held until the release button 18 is released. When the release button 18 is further pushed from the half-pressed position to the full-pressed position, a still image is shot under the shooting conditions set in the shooting preparation process. The photographing signal for one screen obtained by this photographing is converted into image data and recorded on the memory card 22 inserted in the memory card slot 21.

  On the back of the digital camera 10, in addition to the LCD 16, a power button 24 for switching on / off the power, a zoom operation button 25 for zooming the photographing lens 11, a mode button 26 for selecting various modes, selection of a playback image, An operation key 27 for performing various operations such as changing various settings on a setting screen displayed on the LCD 16 is provided.

  The operation mode selected by operating the mode button 26 includes a shooting mode for shooting still images, a playback mode for displaying still images recorded on the memory card 22 on the LCD 16, and a setup mode for setting various settings. . Each of these operation modes can be switched by sliding the mode button 26.

  At the time of shooting in the shooting mode, as a white balance setting mode, either a reset white balance (hereinafter referred to as RWB) mode or an auto white balance (hereinafter referred to as AWB) mode can be selected. When the RWB mode is selected, the white balance is set by instructing white balance setting while shooting an achromatic (white or gray) subject under the light source at the time of shooting. When the AWB mode is selected, the white balance is automatically set based on the subject image being shot and is adjusted following the change in the color temperature of the light source.

  In any of the RWB mode and the AWB mode, it is possible to add color to the captured image. Various colors are easily prepared in advance. For example, warm colors such as when shooting with an incandescent bulb as the light source under the white balance set for daylight, and conversely the daylight color under the white balance set for incandescent lamps Cold colors like when shooting under a light source, neutral colors to make color reproduction accurate without coloring, etc. are available.

  The electrical configuration of the digital camera 10 is shown in FIG. A ROM 31, a RAM 32, and an EEPROM 33 are connected to the CPU 30. In the ROM 31, programs and parameters for executing various sequences are written. The CPU 30 responds to the operation of the release button 18, the zoom operation button 25, the mode button 26, and the operation key 27 and controls each part according to the program in the ROM 31. The RAM 31 is used as a work memory that temporarily stores data necessary for executing a shooting sequence and the like. In the EEPROM 33, a green proper WB gain that is fixedly used for white balance adjustment, and a red color coefficient α and a blue color coefficient β that are used for coloring are recorded in advance, and are read out by the CPU 30.

  Various colors are prepared as described above, and the respective color coefficients α and β corresponding to the colors are recorded in the EEPROM 33. For example, color coefficients α and β each having a value “1” are recorded in the neutral color. In addition, a red color coefficient α larger than “1” and a blue color coefficient β smaller than “1” are recorded for the warm color, and red smaller than “1” is recorded for the warm color. The color coefficient α and the blue color coefficient β larger than “1” are recorded.

  A diaphragm 34 is disposed between the photographing lens 11 and the CCD image sensor 15. A lens motor 36 and an iris motor 37 are connected to the photographing lens 11 and the diaphragm 34. These motors 36 and 37 are controlled via motor drivers 38 and 39 connected to the CPU 30. The lens motor 36 adjusts the focus of the photographing lens 11 in addition to zooming the photographing lens 11 to the wide side or the tele side in conjunction with the operation of the zoom operation button 25. The diaphragm 34 is operated by an iris motor 37 and adjusts the light intensity of the incident light to the CCD image sensor 15.

  The CCD image sensor 15 is controlled based on a timing signal (clock pulse) from a timing generator (TG) 41 controlled by the CPU 30, such as control of charge accumulation time, that is, shutter speed of an electronic shutter, transfer of charges, and the like. The optical subject image photographed through the photographing lens 11 is converted into an electrical photographing signal and output.

  An imaging signal output from the CCD image sensor 15 is input to the analog signal processing unit 42. The analog signal processing unit 42 is composed of a CDS (correlated double sampling) circuit, an amplifier, a color separation circuit, and the like, and after performing noise removal and amplification on the photographic signal, red), green, blue Converted to a photographic signal and output. The A / D converter 43 converts each color photographing signal output from the analog signal processing unit 42 into red, green, and blue image data. The analog signal processing unit 42 and the A / D converter 43 receive the timing signal from the timing generator 41 and operate in synchronization with the output operation of the CCD image sensor 15.

  The image data of each color from the A / D converter 43 is sent to the image input controller 45. The image input controller 45 controls input of image data to the bus 46. The CPU 46, the image input controller 45, and the like are connected to the bus 46, and each unit connected to the bus 46 is controlled by the CPU 30 via the bus 46 and can exchange data with each other. It is possible.

  The AF detection circuit 51 detects the contrast of the image being photographed using the image data from the image input controller 45 for focusing the photographing lens 11 and sends the contrast information to the CPU 30. The CPU 30 refers to the contrast information and drives the lens motor 31 via the motor driver 38 so that the contrast of the image being photographed is maximized, thereby matching the focus of the photographing lens 11 with the subject.

  Based on the image data from the image input controller 45, the AE detection circuit 52 detects the subject brightness of the subject image being shot, and sends the result to the CPU 30 as subject brightness information. The CPU 30 determines an appropriate aperture and shutter speed of the electronic shutter based on the subject luminance information, and performs control so that shooting is performed with these.

  The WB setting circuit 53 obtains red and blue appropriate WB gains for obtaining an appropriate white balance by processing according to the selected white balance setting mode, and adds a color correction to the red and blue corrections. WB gain is calculated. The red and blue correction WB gains obtained by the WB setting circuit 53 and the green proper WB gain read from the EEPROM 33 are set in the image signal processing unit 54. In this example, for green, a predetermined green appropriate WB gain is used as a gain for white balance. However, the appropriate green WB gain and the corrected WB gain may be calculated or changed. .

  The image signal processing unit 54 performs white balance correction processing and gamma correction on the image data. The gain of each color for white balance correction is set by the WB setting circuit 53 described above.

  The YC conversion processing circuit 55 converts red, green and blue image data into image data corresponding to the luminance signal Y and the color difference signals Cr and Cb when recording the image data on the memory card 22. In the reproduction mode, the YC processing circuit 55 converts the image data read from the memory card 22 into red, green, and blue image data.

  The compression / decompression circuit 56 performs data compression for recording image data on the memory card 22 and decompresses the compressed image data read from the memory card 22. The media controller 57 controls writing and reading of data in the memory card 22. The still image data obtained in response to the operation of the release button 18 is processed by the image signal processing unit 54, the YC conversion processing circuit 55, and the compression / decompression processing circuit 56, and then sent to the media controller 57. Is written to the memory card 22.

  In the SDRAM 58, image data to be displayed on the LCD 16 is written. When a through image is displayed in the shooting mode, image data input from the image input controller 45 is processed by the image signal processing circuit 54 and then written to the SDRAM 58 one after another. The LCD driver 59 reads this and reads the LCD 16. To drive.

  In the reproduction mode, after being read from the memory card 22 and decompressed by the compression / decompression unit 24, the image data of each color converted by the YC conversion processing circuit 55 is written into the SDRAM 58, which is displayed on the LCD 58. By being repeatedly read by the driver 59, the image recorded on the memory card 22 is displayed on the LCD 16.

  FIG. 4 shows functional blocks related to white balance of the WB setting circuit 53 and the image signal processing unit 54. The integration means 53a, subtraction means 53b, and gain calculation means 53c of the WB setting circuit 53 calculate an appropriate WB gain in the RWB mode, and the AWB gain determination means 53d calculates an appropriate WB gain in the auto white balance mode.

  In response to the setting instruction in the RWB mode, the integrating means 53a receives the green integrated value Gi, the red integrated value Ri, the blue integrated value Bi, the green OB integrated value Gob, the red OB integrated value Rob, and the blue OB integrated value Bob. Ask for. Each color integrated value Gi, Ri, Bi is obtained by integrating a predetermined number of image data corresponding to the subject image, that is, image data obtained corresponding to the pixels in the effective light receiving surface of the CCD image sensor 15 for each color. .

  On the other hand, each color OB integrated value Gob, Rob, Bob is obtained by integrating a predetermined number of image data obtained for the optical black of the CCD image sensor 15, that is, image data obtained corresponding to the light-receiving element shielded for dark current correction. It is. Note that an integrated value obtained by integrating a predetermined number of image data is used as each color integrated value and each color OB integrated value, but an integrated average value may be used.

As shown in the following equations (1) to (3), the subtracting means 53b is provided with each color integrated value Gi, Ri,
By subtracting Bi and each color OB integrated value Gob, Rob, Bob between corresponding colors, subtracted values Gs, Rs, Bs of each color are obtained.
Gs = Gi-Gob (1)
Rs = Ri-Rob (2)
Bs = Bi-Bob (3)

The gain calculating means 53c uses the subtracted values Gs, Rs, Bs of the respective colors from the subtracting means 53b and the green proper WB gain Gg0 read from the EEPROM 33 and given by the CPU 30, and the following equations (4), ( 5), the red proper WB gain Rg0 and the blue proper WB gain Bg0 are obtained.
Rg1 = Gg0 × Gs / Rs (4)
Bg1 = Gg0 × Gs / Bs (5)

  A combination of the appropriate red balance WB gain Rg0, blue proper WB gain Bg0, and green proper WB gain Gg0 obtained by photographing a white or gray subject and obtained as described above is an appropriate white balance, that is, white or gray. It is a combination for white balance that can prevent the color from being added to the color.

  On the other hand, the AWB gain determination unit 53d performs an appropriate white balance in combination with the appropriate green WB gain Gg0 read from the EEPROM 33 based on the image data of each color obtained by photographing by an appropriate method under the AWB mode. A red proper WB gain Rg0 and a blue proper WB gain Bg0 are determined. The calculation of the red proper WB gain Rg0 and the blue proper WB gain Bg0 is performed every time the color temperature of the light source changes.

  In any mode, various methods can be adopted as a method for determining an appropriate WB gain.

As shown in the following formulas (6) and (7), the gain correction unit 53e converts the red proper WB gain Rg0 and the blue proper WB gain Bg0 from the gain calculation unit 53d in the RWB mode, and the AWB gain in the AWB mode. The red proper WB gain Rg0 and the blue proper WB gain Bg0 from the determining unit 53d are multiplied by the corresponding colors by the red and blue color coefficients α and β, and the red correction WB gain Rg1 and the blue correction WB gain Bg1 are obtained. calculate. The color coefficients α and β corresponding to the color selected by operating the operation key 27 and the like are read from the EEPROM 33 by the CPU 30 and given to the WB setting circuit 53.
Rg1 = α × Rg0 (6)
Bg1 = β × Bg0 (7)

  The red correction WB gain Rg1, the blue correction WB gain Bg1, and the green proper WB gain Gg0 are sent to the image signal processing unit 54, respectively.

  The green multiplication unit 54a of the image signal processing unit 54 multiplies the green image data by the green proper WB gain Gg0. The red multiplier 54b multiplies the red image data by the red correction WB gain Rg1, and the blue multiplier 54c multiplies the blue image data by the blue correction WB gain Bg1. The multiplication results from the color multipliers 54a to 54c are output as image data with white balance corrected and tinted.

  Next, the operation of the above configuration will be described with reference to FIG. When shooting, first select the RWB mode or the AWB mode. For example, when the RWB mode is selected, a white or gray subject, for example, a gray chart is photographed, and the operation key 27 is operated to select and specify the color, and then a white balance setting instruction is issued. To do.

  When a setting instruction is given after the selection of the RWB mode, a photographing signal obtained by photographing with the CCD image sensor 15 is converted into red, green, and blue image data via the analog signal processing circuit 42 and the A / converter 43. After that, it is sent to the WB setting circuit 53 via the image input controller 45. At this time, the photographing signal output from the CCD image sensor 15 includes a photographing signal corresponding to the optical black light receiving element, and the photographing signal is also converted into red, green, and blue photographing signals. Later, the image data is converted into red, green, and blue image data by the A / D converter 43 and sent to the WB setting circuit 53.

  Further, in response to the setting instruction, the CPU 30 reads out the green proper WB gain Gg0 and the color coefficients α and β corresponding to the selected color from the EEPROM 33 and sends them to the WB setting circuit 53.

  The type of image data input to the WB setting circuit 53 is determined based on the input timing and the like, and a predetermined number is integrated for each color by the WB setting circuit 53. Thereby, the green integrated value Gi, the red integrated value Ri, the blue integrated value Bi, the green OB integrated value Gob, the red OB integrated value Rob, and the blue OB integrated value Bob are obtained.

  Next, using each color integrated value Gi, Ri, Bi and each color OB integrated value Gob, Rob, Bob, as shown in the above formulas (1) to (3), OB integration is performed from the integrated value between corresponding colors. Subtracted values Gs, Rs, and Bs for each color obtained by subtracting the values are calculated. Thereafter, the red proper WB gain Rg0 and the blue proper WB gain Bg0 are obtained by the above formulas (4) and (5) using the subtraction values Gs, Rs, Bs and the green proper WB gain Gg0.

  Further, according to the above formulas (6) and (7), the red appropriate WB gain Rg0 is multiplied by the red color coefficient α, the blue appropriate WB gain Bg0 is multiplied by the color coefficient β, and the red correction WB gain Rg1, Blue correction WB gain Bg1 is calculated. Then, the red correction WB gain Rg1 and the blue correction WB gain Bg1 are set in the image signal processing unit 54 together with the green proper WB gain Gg0. The white balance is corrected using the WB gain Gg0.

  Therefore, after the setting instruction in the RWB mode, each red image data obtained by shooting is multiplied by the red correction WB gain Rg1 set as described above by the image signal processing unit 54, and the blue image data is blue. The corrected WB gain Bg1 is multiplied. Further, the green image data is multiplied by a green white balance gain Gg0. A through image is displayed based on the image data obtained in this way. If the release button 18 is pressed to shoot a still image, each color image data subjected to white balance processing is subjected to γ correction processing, and then the YC conversion processing circuit 55 and compression / decompression processing circuit 56 are processed. Is performed and written to the memory card 22.

  For example, when the neutral color is selected, the respective color coefficients α and β having the value “1” are read from the EEPROM 33, and these are multiplied by the appropriate red and blue WB gains Rg0 and Bg0. Thus, the red correction WB gain Rg1 and the blue correction gain Bg1 are calculated. Therefore, as a result, the white balance is corrected with the appropriate WB gain for each color, so that the photographed subject image is not tinted and the subject color is accurately reproduced.

  On the other hand, for example, when a warm color is selected, a red color coefficient α larger than “1” and a blue color coefficient β smaller than “1” are read from the EEPROM 33 and are used. A red correction WB gain Rg1 and a blue correction gain Bg1 are calculated. Since the white balance is corrected using the red correction WB gain Rg1, the blue correction gain Bg1, and the green proper WB gain Gg0, the captured subject image has a weak blue component and a red component. As a result, the image becomes yellowish and reddish overall.

  On the other hand, even when the AWB mode is selected, the color is selected, but the selection of the color can be changed at any timing in the AWB mode. In the case of the AWB mode, the red proper WB gain Rg0 and the blue proper WB gain Bg0 are determined from the image data of each color obtained during shooting, and the colors of the colors selected as the red and blue proper WB gains Rg0 and Bg0. The red color correction WB gain Rg1 and the blue color correction gain Bg1 are calculated by multiplying the taste coefficients α and β and set in the image signal processing unit 54.

  Thereafter, the white balance of the image data is corrected in the same manner as in the RWB mode, and the subject image can be taken with the selected color. Further, in this AWB mode, when the color temperature of the light source changes, the red proper WB gain Rg0 and the blue proper WB gain Bg0 are calculated in response to the change, and the color coefficients α, A red correction WB gain Rg1 and a blue correction gain Bg1 multiplied by β are calculated. Then, the red correction WB gain Rg1, the blue correction gain Bg1, and the green proper WB gain Gg0 are reset in the image signal processing circuit 54. Thereby, even if the white balance is readjusted according to the change in the color temperature of the light source, the color is maintained.

  As described above, the appropriate WB gain is increased / decreased by the color coefficients α and β, and the obtained corrected WB gain is used as the gain for white balance. Therefore, the operator can easily set the white balance with the tint. Can do. In addition, it is possible to shoot with a tint even with auto white balance.

  In the RWB mode, the red proper WB gain and the blue proper WB gain are held until the next setting instruction is made, and are held when the color selection is changed before the setting instruction. The red correct WB gain and the blue correct WB gain may be recalculated using the red correct WB gain and blue correct WB gain. The present invention can also be used in a preset mode in which the user sets the type of light source and uses an appropriate WB gain prepared in advance for the set light source.

  In the above embodiment, a digital camera has been described as an example. However, the present invention is not limited to a digital camera, and may be applied to various photographing devices such as a video camera, a mobile phone with a camera, and the like. Can do. In addition, in the present invention, when performing shooting setting with a tint for a plurality of photographing devices, after adjusting the white balance with the reset white balance for each photographing device, a color coefficient is set for each photographing device. If it does, it can be set as the operation | work which only sets a color coefficient uniformly to each imaging device, and the color setting operation | work can be simplified. .

It is a front perspective view of the digital camera which implemented this invention. It is a rear perspective view of a digital camera. It is explanatory drawing which showed the electrical structure of the digital camera. It shows a functional block related to gain setting. It is a flowchart explaining the procedure of white balance.

Explanation of symbols

10 Digital Camera 15 CCD Image Sensor 53 WB Setting Circuit 54 Image Signal Processing Circuit

Claims (2)

In a white balance setting method for individually amplifying each color component of a captured image obtained from an image sensor,
The gain obtained by multiplying the coefficient specified for each color by an external operation and the gain determined to obtain an appropriate white balance for each color with the corresponding colors is set as the gain for white balance. A white balance setting method characterized by amplifying each color component of a photographed image individually. A coefficient is designated by an external operation for other colors except for a specific color, and a gain determined to obtain an appropriate white balance for the specific color is set as a white balance gain. The white balance setting method according to claim 1.

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