JP2012152314A - White balance adjusting system, endoscope processor, and correction and balance adjustment cap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compute a proper white balance adjustment factor.SOLUTION: An endoscope processor 20 includes a digital signal processor (DSP) 23 and an input unit 27. When a white balance initializing operation is inputted into the input unit 27, the DSP 23 performs white balance initializing processing. The DSP 23 determines whether or not an identification mark is included in an image corresponding to an image signal transmitted from an image pickup element 43, in the white balance initializing processing. When the identification mark is included in the image, the DSP 23 computes R and B gains by using the image signal.

Description

  The present invention relates to a white balance adjustment system that appropriately calculates a white balance adjustment coefficient used for white balance adjustment processing of an image captured by an electronic endoscope.

  An endoscope system having an electronic endoscope is used for observing the inside of the body not irradiated with light. In an endoscope system, an insertion tube is inserted into a body, an illuminated biological tissue or the like is imaged, and the captured subject image can be observed on a monitor.

  A subject image is picked up by a color image pickup device, and an image signal which is an electric signal is generated. Since the color image sensor has different light receiving sensitivity depending on the band of light received, the subject is displayed on the monitor in a color different from the actual color of the subject. It is known that white balance adjustment processing is performed on an image signal in order to bring the color of the subject displayed on the monitor closer to the color of the actual subject (see Patent Document 1).

  The white balance adjustment process is executed by multiplying a specific color signal component such as an R signal component and a B signal component by a white balance adjustment coefficient calculated in advance. In order to execute an appropriate white balance adjustment process, it is necessary to calculate an appropriate white balance adjustment coefficient.

  A white balance adjustment coefficient is calculated so that an image corresponding to an image signal generated by imaging a white subject is white. Therefore, in order to calculate an appropriate white balance adjustment coefficient, it is necessary to image an appropriate white subject.

  A dedicated white balance adjustment cap is used to capture an appropriate white subject. The white balance adjustment cap can be attached to the tip of the insertion tube, and the inner surface is colored white. It is possible to calculate an appropriate white balance adjustment coefficient by photographing the inner surface of the cap colored white with such a white balance adjustment cap attached.

  However, a white object such as white paper or gauze may be used instead of a dedicated adjustment cap. However, in general, paper, gauze, and the like are different from the color temperature suitable for calculating the white balance adjustment coefficient, or the entire surface is not white. It is difficult to calculate an appropriate white balance adjustment coefficient with an image signal obtained by imaging such a substitute subject.

Japanese Patent Laid-Open No. 4-69615

  Accordingly, an object of the present invention is to provide a white balance adjustment system that calculates a white balance adjustment coefficient when a dedicated white balance adjustment cap is used.

  A white balance adjustment system according to the present invention calculates a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at the distal end of an insertion tube of an electronic endoscope. A memory for storing a mark drawn on a photographing surface of a white balance adjustment cap attached to the tip of the insertion tube, an input unit for detecting an input operation for calculating a white balance adjustment coefficient, and an input unit A determination unit that determines whether or not a mark is included in a captured image, which is an image corresponding to an image signal, based on the image signal when a white balance adjustment coefficient calculation is input, and the determination unit adds a mark to the captured image. And a calculation unit that calculates a white balance adjustment coefficient using an image signal when determining that it is included. It is.

  The memory stores the position of a specific area in the captured image, and the determination unit determines whether or not the captured image includes the mark by determining whether or not the partial image in the specific area of the captured image matches the mark. It is preferable to determine whether or not.

  In addition, it is preferable to provide a warning unit that issues a warning when it is determined that the mark is not included in the captured image.

  The first endoscope processor according to the present invention calculates a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at a distal end of an insertion tube of an electronic endoscope. An endoscope processor for receiving an image signal, a memory for storing a mark drawn on a photographing surface of a white balance adjustment cap attached to the tip of an insertion tube, and execution of calculation of a white balance adjustment coefficient An input unit that detects the input operation of the image, and whether or not a mark is included in a captured image that is an image corresponding to the image signal based on the image signal when the input unit calculates the white balance adjustment coefficient. A determination unit for determining, and a calculation unit for calculating a white balance adjustment coefficient using an image signal when the determination unit determines that a mark is included in the captured image; It is characterized in that it comprises.

  The second endoscope processor according to the present invention calculates a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at the distal end of an insertion tube of an electronic endoscope. An endoscope processor that receives mark data corresponding to a mark from an image receiving unit that receives an image signal and a memory that stores a mark drawn on a photographing surface of a white balance adjustment cap attached to the tip of an insertion tube A mark receiving unit, an input unit that detects an input operation for executing the calculation of the white balance adjustment coefficient, and an image corresponding to the image signal based on the image signal when the input unit calculates the white balance adjustment coefficient. A determination unit that determines whether or not a mark is included in a captured image, and an image signal when the determination unit determines that a mark is included in the captured image It is characterized in that it comprises a calculation unit for calculating a white balance adjustment coefficient using.

  The white balance adjustment cap of the present invention is an insertion tube for calculating a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at the distal end of the insertion tube of an electronic endoscope. A white balance adjusting tool that can be attached to the tip of an image pickup device, wherein a mark is drawn on a background colored in an achromatic color on a surface facing the image pickup device when attached to the insertion tube.

  The background is preferably colored white.

  The mark is preferably colored in an achromatic color different from the background.

  The mark is preferably colored black.

  The mark is preferably drawn near the center of the inner surface.

  The mark is preferably annular or circular.

  According to the present invention, the white balance adjustment coefficient is calculated when the imaging surface of the dedicated white balance adjustment tool is imaged. Therefore, appropriate white balance adjustment is possible.

1 is a block diagram schematically showing an internal configuration of an endoscope system including an endoscope processor having a white balance adjustment system to which an embodiment of the present invention is applied. FIG. It is an external view of the white balance adjustment cap of this embodiment. It is a top view of the bottom face of a hollow part. It is a 1st flowchart which shows the white balance initialization process performed by CPU and DSP. It is a 2nd flowchart which shows the white balance initialization process performed by CPU and DSP.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram schematically showing an internal configuration of an endoscope system including an endoscope processor having a white balance adjustment system to which an embodiment of the present invention is applied.

  The endoscope system 10 includes an endoscope processor 20, an electronic endoscope 40, and a monitor 11. The endoscope processor 20 is connected to the electronic endoscope 40 and the monitor 11.

  Illumination light for illuminating the subject is supplied from the endoscope processor 20 to the electronic endoscope 40. The subject irradiated with the illumination light is imaged by the electronic endoscope 40. An image signal generated by imaging of the electronic endoscope 40 is sent to the endoscope processor 20.

  In the endoscope processor 20, predetermined signal processing is performed on the image signal obtained from the electronic endoscope 40. The image signal subjected to the predetermined signal processing is transmitted to the monitor 11, and an image corresponding to the transmitted image signal is displayed on the monitor 11.

  Next, the configuration of the endoscope processor 20 will be described. The endoscope processor 20 includes a light source system 21, an image sensor driver 22, a DSP 23, a nonvolatile memory 24 (memory), a system controller 25, a ROM 26, an input unit 27, and the like.

  Illumination light emitted from the light source system 21 enters a light guide 41 provided in the electronic endoscope 40. The illumination light is transmitted to the tip of the insertion tube 42 by the light guide 41. The transmitted illumination light is applied to the subject in the distal direction of the insertion tube 42.

  An optical image of the reflected light of the subject irradiated with the illumination light is imaged on the light receiving surface of the image sensor 43 by an objective lens (not shown) provided at the distal end of the insertion tube 42. The image sensor 43 is controlled by the image sensor driver 22 so as to generate an image signal of one field every fixed period, for example, 1/60 seconds.

  A plurality of pixels (not shown) are two-dimensionally arranged on the light receiving surface of the image sensor 43. Each pixel is covered with one of RGB color filters (not shown). In each pixel, a pixel signal corresponding to the amount of received light component transmitted through the color filter is generated. The image signal is composed of pixel signals generated in all pixels.

  The generated image signal is subjected to CDS processing and AGC processing in an AFE (not shown) provided in the electronic endoscope 40, and then converted into a digital signal. The image signal converted into the digital signal is transmitted to the DSP 23.

  In the DSP 23, predetermined data processing such as white balance adjustment processing, color interpolation processing, and gamma correction processing is performed on the image signal. Here, the white balance adjustment process will be described in detail.

  As described above, the image signal includes an R pixel signal component, a G pixel signal component, and a B pixel signal component corresponding to the amounts of received light of red light, green light, and blue light. In the white balance adjustment process, the R pixel signal component and the B pixel signal component are multiplied by an R gain (white balance adjustment coefficient) and a B gain (white balance adjustment coefficient), respectively.

  As will be described later, the R gain and the B gain are calculated when the white balance is initialized. The calculated R gain and B gain are stored in the nonvolatile memory 24. When observing the subject, the R gain and the B gain are transmitted to the DSP 23 via the system controller 25 and used for white balance adjustment processing.

  An image signal subjected to predetermined data processing is transmitted to the monitor 11. An image corresponding to the received image signal is displayed on the monitor 11. As described above, the image sensor 43 is driven so as to generate an image signal of one field every 1/60 seconds, and the image signal is transmitted to the monitor 11 every 1/60 seconds. A moving image is displayed on the monitor 11 by switching the image to be displayed every 1/60 seconds.

  Operations of the light source system 21, the image sensor driver 22, and the DSP 23 are controlled by a system controller 25. The operation of each part provided in the endoscope processor 20 is also controlled by the system controller 25. A ROM 26 is connected to the system controller 25, and data necessary for controlling each part is stored in the ROM 26. Data stored in the ROM 26 is read to the system controller 25 as necessary.

  An input unit 27 is connected to the system controller 25. The input unit 27 includes a keyboard (not shown), buttons (not shown), switches (not shown), and the like. An input operation for executing and adjusting various functions provided in the endoscope system 10 is detected by the input unit 27. The detected input operation is transmitted to the system controller 25, and each part of the endoscope processor 20 is controlled by the system controller 25 based on the detected input operation.

  Next, calculation of the R gain and the B gain will be described below. When an input operation for white balance initialization is performed on the input unit 27, white balance initialization processing for calculating R and B gains is executed.

  In order to calculate appropriate R and B gains, it is necessary to photograph a subject that is uniformly colored white. A white balance adjustment cap 30 shown in FIG. 2 is used as a subject that is uniformly colored white. The white balance adjustment cap 30 is formed in a rectangular parallelepiped shape, and a recess 32 is provided on the mounting surface 31.

  The recess 32 is formed so that the inner diameter is longer than the outer diameter of the insertion tube 42 of various electronic endoscopes 40 assumed to be used. A bottom surface 33 parallel to the mounting surface 31 is formed in the recess 32. As shown in FIG. 3, on the bottom surface 33, an annular identification mark 34 colored in black is drawn on a background colored white. The identification mark 34 is drawn at the center of the bottom surface 33. Further, the size of the identification mark 34 is determined to be smaller than the imaging range CA of the electronic endoscope 40 that is assumed to be used.

  In the white balance initialization process, it is determined whether the white balance adjustment cap 30 shown in FIG. 2 is attached to the distal end of the insertion tube 42, and when it is attached, R and B gains are calculated.

  When the execution input of the white balance initialization process is received, the image sensor 43 and the DSP 23 are driven as described above, and a real-time moving image is displayed on the monitor 11. The DSP 23 reads an image signal corresponding to the warning message from the ROM 26 via the system controller 25. In the DSP 23, the warning message is superimposed on the moving image.

  An image signal obtained by superimposing the warning message is transferred to the monitor 11, and a warning message such as “Attach the adjustment cap and project the identification mark in the center of the image” is displayed. The warning message is deleted after a predetermined time.

  After the warning message is displayed, the image sensor 43 and the DSP 23 are driven as described above, and a real-time moving image is displayed on the monitor 11. When a determination execution operation is input to the input unit 27 when a moving image is displayed, it is determined whether or not the white balance adjustment cap 30 is attached using the image signal of the next field.

  Whether or not the white balance adjustment cap 30 is attached is determined by determining that the identification mark 34 is positioned near the center of the imaging range. For determination, the position of the identification mark 34 is read from the ROM 26 to the DSP 23 via the system controller 25.

  If the identification mark 34 is not positioned near the center, a warning message is read from the ROM 26 via the system controller 25 and superimposed on the moving image. When the identification mark 34 is positioned near the center, calculation of R and B gains is started.

  The R and B gains are calculated using the image signal of the next field when it is determined that the identification mark 34 is positioned near the center. When the target image signal is transmitted to the DSP 23, the DSP calculates an average value of the signal intensities of the R, G, and B pixel signal components.

  The R gain is calculated by dividing the average value of the G pixel signal component by the average value of the R pixel signal component (normalization). Similarly, a B gain is calculated by dividing the average value of the G pixel signal component by the average value of the B pixel signal component (normalization). The calculated R and B gains are stored in the nonvolatile memory 24.

  Next, white balance initialization processing executed in the system controller 25 and the DSP 23 will be described with reference to the flowcharts of FIGS. The white balance initialization process is executed by an operation input to the input unit 27 as described above.

  In step S100, the system controller 25 reads out the image signal component corresponding to the above-mentioned warning message that prompts the user to attach the adjustment cap and display the mark, and transmits the image signal component to the DSP 23. The DSP 23 executes a superimpose process for superimposing the warning message on the moving image, and displays the warning message on the moving image. After the warning message is displayed, the process proceeds to step S101.

  In step S101, the system controller 25 causes a timer (not shown) to start measuring time. When the timing is started, the process proceeds to step S102.

  In step S102, the system controller 25 determines whether or not the measurement time of the timer has passed a predetermined display time. If the predetermined display time has not elapsed, the process returns to step S102, and step S102 is repeated until the predetermined display time elapses. If the predetermined display time has elapsed, the process proceeds to step S103. By repeating step S102 until the predetermined display time elapses, the warning message can be displayed for the predetermined display time.

  In step S103, the DSP 23 stops the warning message superimposing process and deletes the warning message from the moving image. After deleting the warning message, the process proceeds to step S104.

  In step S <b> 104, the system controller 25 reads the address of the pixel forming the identification mark 34 from the ROM 26 as data of the identification mark 34 and transmits it to the DSP 23. After reading the data of the identification mark 34, the process proceeds to step S105. The pixel forming the identification mark 34 is a pixel forming the black annular portion described above.

  In step S105, the system controller 25 activates an H counter (not shown) and a V counter (not shown) that count the horizontal synchronization signal and the vertical synchronization signal included in the image signal, and outputs the horizontal synchronization signal and the vertical synchronization signal. Start recognition. After starting the H counter and the V counter, the process proceeds to step S106.

  In step S <b> 106, the system controller 25 determines whether or not a determination execution operation is input to the input unit 27. If the determination execution operation is not input, the process returns to step S106, and step S106 is repeated until the determination execution operation is input. If a discrimination execution operation has been input, the process proceeds to step S107.

  In step S107, the system controller 25 determines whether or not the vertical synchronization signal counted by the V counter is in a reset state, that is, whether or not reception of the last row of pixel signals constituting the image signal has been completed. If it is not in the reset state, the process returns to step S107, and thereafter step S107 is repeated until the reset state is reached. If it is in the reset state, the process proceeds to step S108.

  In step S108, the DSP 23 resets the number of black matches to zero. The black coincidence number is the number of pixels that are black at the same position as the position of the identification mark 34 in the pixel signal component constituting the image signal received from the electronic endoscope 40. After resetting the number of black matches, the process proceeds to step S109.

  As shown in FIG. 5, in step S109, the system controller 25 determines that the horizontal synchronization signal and the vertical synchronization signal counted by the H and V counters are the addresses of any pixels constituting the identification mark 34 read in step S104. It is determined whether or not it coincides with the H and V synchronization signals corresponding to.

  If it matches the address of any pixel, the process proceeds to step S110. If it does not match the addresses of all the pixels, step S110 and step S111 are skipped and the process proceeds to step S112.

  In step S110, the DSP 23 receives the pixel signal at the address corresponding to the horizontal synchronization signal and the vertical synchronization signal in step S109. The DSP 23 determines whether the luminance signal component of the received pixel signal is less than the first threshold value. The first threshold value is set to an appropriate value that can be distinguished from a black pixel.

  If the luminance signal component is less than the first threshold, it is determined that the pixel is black, and the process proceeds to step S111. If the luminance signal component is greater than or equal to the first threshold, step S111 is skipped and the process proceeds to step S112.

  In step S111, the DSP 23 increments +1 to the number of black matches. After the increment, the process proceeds to step S112.

  In step S112, the system controller 25 determines whether or not the vertical synchronization signal counted by the V counter is in a reset state, that is, whether or not the discrimination for all the pixel signals constituting one field image signal has been completed. Determine.

  If not in the reset state, the process returns to step S109. Thereafter, steps S109 to S112 are repeated until the reset state is established in step S112. If it is in the reset state, the process proceeds to step S113.

  In step S113, the DSP 23 determines whether the number of black matches exceeds the second threshold value. The second threshold value is set to a predetermined value that is larger than zero and smaller than the number of pixels that form the identification mark 34.

  If the number of black matches is less than or equal to the second threshold, it is determined that the adjustment cap is not attached or the mark is not reflected in the center, and the process returns to step S100. Thereafter, steps S100 to S113 are repeated until the number of black matches exceeds the second threshold. If the number of black matches exceeds the second threshold, it is determined that the adjustment cap is attached and the mark is reflected in the center, and the process proceeds to step S114.

  In step S114, the DSP 23 calculates an average value for every R pixel signal component, G pixel signal component, and B pixel signal component that form an image signal of one field. When the average value is calculated, the process proceeds to step S115.

  In step S115, the DSP 23 calculates the R gain by dividing the average value of the G pixel signal component by the average value of the R pixel signal component. The DSP 23 calculates the B gain by dividing the average value of the G pixel signal component by the average value of the B pixel signal component. When the R and B gains are calculated, the process proceeds to step S116.

  In step S116, the system controller 25 stores the R and B gains calculated in step S115 in the nonvolatile memory 24. After the R and B gains are stored in the nonvolatile memory 24, the white balance initialization process is terminated.

  As described above, according to the white balance adjustment system of this embodiment, when the identification mark 34 is not imaged, it is possible not to start the calculation of the R and B gains. That is, calculation of the R and B gains can be executed only when the dedicated white balance adjustment cap on which the identification mark 34 is drawn is attached. Therefore, since appropriate R and B gains are calculated, the color reproducibility of the image during normal observation can be improved.

  In the present embodiment, a configuration for determining whether or not the identification mark 34 is included in the captured image by determining whether or not the pixel forming the identification mark 34 stored in the ROM 26 is black. However, it may be determined whether or not the identification mark 34 is included in an image captured by any other known method.

  For example, it may be configured to determine whether or not the shape of the identification mark 34 stored in the ROM 26 matches the shape of the mark included in the captured image by pattern matching. According to a method such as pattern matching, it is not necessary to adjust the position where the identification mark 34 is photographed, and convenience is improved. However, the method as in this embodiment is simple and accurate.

  In the present embodiment, the RGB pixel signal component is generated by the image sensor 43, but other color signal components may be generated. When other color signal components are generated, a white balance adjustment coefficient suitable for the color signal components generated instead of the R and B gains is calculated by the white balance initialization process and used for the white balance process.

  In the present embodiment, the position of the identification mark 34 is stored in the ROM 26 of the endoscope processor 20, but is stored in a ROM (not shown) provided in the electronic endoscope 40. May be. When stored in the electronic endoscope 40, the electronic endoscope 40 is read from the electronic endoscope 40 to the endoscope processor 20 when the white balance initialization process is executed with the electronic endoscope 40 and the endoscope processor 20 connected. You can do it.

  In the present embodiment, a warning message is issued when the white balance initialization process is executed without attaching the white balance adjustment cap 30 and when the alignment of the identification mark 34 is insufficient. . However, even if no warning message is issued, calculation of R and B gains can be prevented from starting when the white balance adjustment cap 30 is not attached.

  Further, in the present embodiment, the background of the identification mark 34 on the bottom surface 33 of the recess 32 of the white balance adjustment cap 30 is configured to be colored white. However, even if the background is colored to an achromatic color other than black, it is appropriate. It is possible to calculate the R and B gains.

  In the present embodiment, the identification mark 34 is black, but may be other colors as long as the color is different from the background. However, when the identification mark 34 is a chromatic color, it is necessary to exclude all pixels constituting the identification mark 34 from the calculation of the R and B gains. When the identification mark 34 is achromatic, it can be used as it is for the calculation of the R and B gains as in this embodiment.

  In this embodiment, the position where the identification mark 34 is determined to be included in the captured image is near the center of the imaging range, but may be any position in the imaging range.

  In the present embodiment, the identification mark 34 is annular, but may have any shape of symbol or character. However, if it is annular or circular, it is possible to obtain a certain discrimination accuracy regardless of the angle of the white balance adjustment cap 30.

10 Endoscope System 20 Endoscope Processor 23 DSP
24 Nonvolatile memory 25 System controller 26 ROM
27 Input unit 30 White balance adjustment cap 33 Bottom surface 34 Identification mark 40 Electronic endoscope 43 Image sensor

Claims (11)

A white balance adjustment system that calculates a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at a distal end of an insertion tube of an electronic endoscope,
A memory for storing a mark drawn on a photographing surface of a white balance adjustment cap attached to a tip of the insertion tube;
An input unit for detecting an input operation for executing the calculation of the white balance adjustment coefficient;
When the white balance adjustment coefficient calculation execution input is input to the input unit, it is determined whether or not the mark is included in a captured image that is an image corresponding to the image signal, based on the image signal. A discriminator;
A white balance adjustment system comprising: a calculation unit that calculates the white balance adjustment coefficient using the image signal when the determination unit determines that the mark is included in the captured image. The memory stores a position of a specific area in the captured image,
The discriminating unit discriminates whether or not the captured image includes the mark by determining whether or not a partial image in a specific region of the captured image matches the mark. The white balance adjustment system according to claim 1.   The white balance adjustment system according to claim 1, further comprising a warning unit that issues a warning when it is determined that the mark is not included in the captured image. An endoscope processor for calculating a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at a distal end of an insertion tube of an electronic endoscope,
An image receiving unit for receiving the image signal;
A memory for storing a mark drawn on a photographing surface of a white balance adjustment cap attached to a tip of the insertion tube;
An input unit for detecting an input operation for executing the calculation of the white balance adjustment coefficient;
When the white balance adjustment coefficient calculation execution input is input to the input unit, it is determined whether or not the mark is included in a captured image that is an image corresponding to the image signal, based on the image signal. A discriminator;
An endoscope processor, comprising: a calculating unit that calculates the white balance adjustment coefficient using the image signal when the determining unit determines that the mark is included in the captured image. An endoscope processor for calculating a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at a distal end of an insertion tube of an electronic endoscope,
An image receiving unit for receiving the image signal;
A mark receiving unit that receives mark data corresponding to the mark from a memory that stores a mark drawn on a photographing surface of a white balance adjustment cap attached to a distal end of the insertion tube;
An input unit for detecting an input operation for executing the calculation of the white balance adjustment coefficient;
When the white balance adjustment coefficient calculation execution input is input to the input unit, it is determined whether or not the mark is included in a captured image that is an image corresponding to the image signal, based on the image signal. A discriminator;
An endoscope processor, comprising: a calculating unit that calculates the white balance adjustment coefficient using the image signal when the determining unit determines that the mark is included in the captured image. A white that can be attached to the distal end of the insertion tube in order to calculate a white balance adjustment coefficient used for white balance adjustment of an image corresponding to an image signal generated by an image sensor provided at the distal end of the insertion tube of the electronic endoscope A balance adjuster,
A white balance adjuster, wherein a mark is drawn on an achromatic background on a surface opposite to the imaging device in a state of being mounted on the insertion tube.   The white balance adjuster according to claim 6, wherein the background is colored white.   The white balance adjuster according to claim 6 or 7, wherein the mark is colored in an achromatic color different from a background.   The white balance adjuster according to claim 8, wherein the mark is colored black.   The white balance adjusting tool according to any one of claims 6 to 9, wherein the mark is drawn near a center of the inner surface.   The white balance adjuster according to any one of claims 6 to 10, wherein the mark is annular or circular.

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