JP2004312366A - White balance control method and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white balance control method and an imaging apparatus capable of realizing white balance correction corresponding to the light source type and reduction in excess correction of an object color in a well-balanced way. <P>SOLUTION: The gain for automatic white balance adjustment is calculated from RGB data outputted from a CCD (a step S210). When the calculated R gain (or B gain) exceeds a G gain by a specified multiple (steps S212, S214), an R gain (or B gain) is clipped at a limit value (steps S216, S220). Information of the specified multiples AR, AB is set to an EEPROM in a camera. A limiter function of the white balance correction has also a function of specifying a lower limit of the gain in addition to the function of specifying the upper limit of the gain. Since the gain clip processing can prevent excess correction of the object color and carry out white balance correction to a degree within a range until clipping is made, a failure such as the occurrence of a low color temperature scene can be avoided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a white balance control method and an imaging apparatus, and more particularly to a white balance control technique suitable for a digital camera, a video camera, and the like.
[0002]
[Prior art]
Japanese Patent Laid-Open No. 2004-133867 provides a color feria scene in which color balance is over-corrected in a color-biased scene, for example, a scene including an object color similar to a tungsten light source, such as a wood-grained desk or wall, resulting in a loss of color. In order to prevent such a situation, there is disclosed a method of controlling the gain for each color signal by setting a limiter region for regulating the gain and changing the limiter region according to the subject luminance.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-78606
[Problems to be solved by the invention]
Conventionally, auto white balance correction for scenes with low color temperature is difficult to distinguish between a wood-like object color such as a desk and a light source color. A broken image may be obtained due to excessive application of balance gain. For example, if you shoot a scene with a wooden desk, pillar, etc. in the background, the color of the desk or pillar will be misjudged as the color of the light source, and excessive white balance correction will occur. turn into.
[0005]
By providing a limiter area at the time of white balance correction as in Patent Document 1, the above-described color feria phenomenon is suppressed, but the white balance correction is not applied in a low color temperature scene or the like. There is.
[0006]
In such scenes, there is a trade-off relationship that takes into account color feria prevention and white balance correction such as low color temperature, and abandons one of them to help either. It is very difficult to do.
[0007]
Also, in the conventional auto white balance correction, the object color is determined as the light source and white balance adjustment is performed.Therefore, if the angle of view is slightly changed during shooting and the desk or column is moved off the screen, The balance correction amount changes greatly, and if the angle of view is changed even a little, a hunting phenomenon in which the color changes may occur.
[0008]
Note that the above-described color feria phenomenon can occur in a similar manner in a green scene similar to a light source color such as a mercury lamp or a metal halide light source (for example, a scene including leafy greens such as grass and leaves).
[0009]
The present invention has been made in view of such circumstances, and a white balance control method and imaging capable of realizing a contradictory matter of appropriate white balance correction corresponding to a light source type and reduction of overcorrection of an object color in a balanced manner. An object is to provide an apparatus.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a white balance control method according to the present invention includes a gain calculation step of calculating a gain for white balance adjustment based on an image signal acquired via an imaging unit, and a color used for white balance adjustment. A limit value setting step for setting a limit value that restricts at least one of an upper limit and a lower limit for another gain, and a gain that is outside the limit value is calculated in the gain calculation step. And a limiter processing step for limiting the gain, and a white balance adjustment step for performing white balance adjustment by correcting the color signal based on the gain determined under the restriction by the restriction value.
[0011]
According to the present invention, the gain for white balance adjustment is calculated based on the image signal obtained by imaging the subject using the imaging means. For example, in the case of an image signal that is color-separated into three primary colors of R (red), G (green), and B (blue), R and B gains based on G may be calculated. Each gain may be calculated.
[0012]
In the present invention, a limit is set for the gain that is finally output. If the calculated gain is within the limit of the limit value, the white balance is corrected based on the gain. On the other hand, when the calculated gain is outside the limit value (when exceeding the upper limit value or below the lower limit value), the gain is clipped at the limit value, and the white balance is corrected by the gain indicated by the limit value. I do.
[0013]
In this way, the gain calculated using the white balance gain calculation algorithm is clipped with a certain limit value, so white balance correction according to the light source color within a certain range (the range until clipping) Is possible, and overcorrection for object colors above or below the scene is also prevented.
[0014]
In order to provide an apparatus that embodies the above method invention, an imaging apparatus according to the present invention includes an imaging unit that converts an optical image of a subject into an electrical signal, and a white signal based on an image signal acquired through the imaging unit. A gain calculating means for calculating a gain for balance adjustment; a limit value setting means for setting a limit value for restricting at least one of an upper limit and a lower limit of a gain used for white balance adjustment; and When a gain out of the limit is calculated, a limiter processing means for limiting the gain by the limit value and a white balance adjustment by correcting the color signal based on the gain determined in the limit by the limit value White balance adjusting means.
[0015]
According to an aspect of the present invention, the limit value setting unit includes a nonvolatile storage unit that stores the limit value.
[0016]
According to another aspect of the present invention, the limit value setting means sets at least an upper limit value of a gain for the B signal so as to prevent overcorrection of white balance in a low color temperature scene. To do.
[0017]
In a low color temperature scene where a large gain can be calculated, when a gain exceeding a predetermined upper limit value is calculated, the white balance can be corrected for a certain range by clipping the gain, and the object color Failure due to overcorrection can be prevented.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a white balance control method and an imaging apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0019]
FIG. 1 is a rear view of a digital camera according to an embodiment of the present invention. As shown in the figure, a finder 2, a multifunction cross key 3, a menu / execution key 4, a cancel key 5, a display key 6, a mode switching lever 7 and a liquid crystal monitor 52 are provided on the back of the camera 1. ing.
[0020]
The cross key 3 is an operation key that can input instructions in four directions, up, down, left, and right, and means for instructing selection of various setting items and change of setting contents on a menu screen displayed on the liquid crystal monitor 52 (cursor moving means). It is also used as a means for instructing magnification adjustment of electronic zoom and sending / returning of playback frames.
[0021]
The menu / execution key 4 is an operation key having both a function as a menu button for instructing display of a menu screen and a function as an OK button for instructing selection confirmation, execution of processing, and the like. For example, when the setup mode is selected, a setup screen is displayed on the liquid crystal monitor 52. On the setup screen, the number of recording pixels (image size), recording image quality (compression rate), ON / OFF selection of the LCD monitor 52 at startup, auto power off time, opening screen display settings, date and time settings, white balance mode Various setting items such as settings are displayed. The user operates the cross key 3 to select an item to be changed from the setup screen or change the setting contents, and then press the menu / execution key 4 to confirm the instruction.
[0022]
The cancel key 5 is used to cancel (cancel) an item selected from the menu or return to the previous operation state. The display key 6 is an operation means for turning on / off the liquid crystal monitor 52 and switching between display / non-display of a reproduction method and a frame number being reproduced.
[0023]
The mode switching lever 7 is an operation unit for switching between “shooting mode” and “reproduction mode”. Further, by rotating the mode dial 8 provided on the upper surface of the camera, a setup mode, a continuous shooting / bracketing mode, a manual shooting mode, an auto shooting mode, a portrait shooting mode, a landscape shooting mode, and a night scene shooting mode can be selected. Any one of the modes can be selected.
[0024]
A shutter button 9 is provided at the center of the mode dial 8. The shutter button 9 is composed of 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. When the shutter button 9 is “half-pressed”, automatic focusing (AF) and automatic exposure control (AE) are activated to lock AF and AE. Shooting operation) is executed.
[0025]
The liquid crystal monitor 52 can be used as an electronic viewfinder for checking the angle of view at the time of shooting, and also displays a preview image of the shot image, a reproduced image read from a memory card (denoted by reference numeral 56 in FIG. 2) loaded in the camera 1, and the like. Can be displayed. The LCD monitor 52 also displays information such as the number of storable frames (shootable time for movies), playback frame number display, presence / absence of strobe light emission, macro mode display, recording image quality (quality) display, and pixel count display. Is displayed. The liquid crystal monitor 52 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 monitor 52, other types of display devices (display means) such as an organic EL can be used.
[0026]
The photographer determines the composition (angle of view) while confirming the real-time image (through image) displayed on the finder 2 or the liquid crystal monitor 52, and presses the shutter button 9 to perform photographing. In FIG. 1, reference numeral 11 denotes a grip portion, and reference numeral 13 denotes a power switch.
[0027]
FIG. 2 is a block diagram of the digital camera according to the present embodiment. The taking lens 10 of the camera 1 may be a single focus lens or a variable focal length such as a zoom lens. The light that has passed through the taking lens 10 and the aperture 12 enters a CCD solid-state image sensor (hereinafter referred to as CCD) 14. A large number of photosensors (light-receiving elements) are two-dimensionally arranged on the light-receiving surface of the CCD 14, and primary color filters of red (R), green (G), and blue (B) corresponding to each photosensor are predetermined. Arranged in array form.
[0028]
The subject image formed on the light receiving surface of the CCD 14 is converted into signal charges of an amount corresponding to the amount of incident light by each sensor on the CCD 14. The signal charges accumulated in this way are read out to the shift register by a read gate pulse applied from the CCD drive circuit 16, and sequentially read out as a voltage signal corresponding to the signal charge by a register transfer pulse. The CCD 14 has a so-called electronic shutter function that can sweep out the accumulated signal charge by a shutter gate pulse and thereby control the charge accumulation time (shutter speed).
[0029]
The voltage signal (image signal) sequentially read out from the CCD 14 is applied to a correlated double sampling circuit (CDS circuit) 18, where the R, G, B signals for each light receiving element (pixel) are sampled and held. It is added to the A / D converter 20. The A / D converter 20 converts the R, G, B signals sequentially added from the CDS circuit 18 into digital signals and outputs them. The CCD drive circuit 16, the CDS circuit 18 and the A / D converter 20 are driven in synchronism with a timing signal applied from the timing generation circuit 22.
[0030]
The R, G, B signals output from the A / D converter 20 are temporarily stored in the memory 24, and then the R, G, B signals stored in the memory 24 are added to the digital signal processing circuit 26. The digital signal processing circuit 26 includes a synchronization circuit 28, a white balance adjustment circuit 30, a gamma correction circuit 32, a luminance / color difference signal (YC signal) creation circuit 34, and a memory 36.
[0031]
The synchronization circuit 28 converts the dot-sequential R, G, B signals read from the memory 24 into simultaneous equations and outputs the R, G, B signals to the white balance adjustment circuit 30 simultaneously. The white balance adjustment circuit 30 includes multipliers 30R, 30G, and 30B for increasing and decreasing the digital values of the R, G, and B signals. The R, G, and B signals are respectively multiplied by the multipliers 30R, 30G, and 30G, respectively. Added to 30B.
[0032]
White balance correction values (gain values) Rg, Gg, and Bg for white balance control from the central processing unit (CPU) 38 are added to other inputs of the multipliers 30R, 30G, and 30B. , 30G, and 30B each multiply two inputs, and output R ′, G ′, and B ′ signals that have undergone white balance adjustment by this multiplication to the gamma correction circuit 32.
[0033]
If the white balance correction values are Rg, Gg, Bg, the signals before correction are R, G, B, and the correction results in the white balance adjustment circuit 30 are R ′, G ′, B ′, the correction results R ′, G ′ and B ′ are the following equations:
[0034]
[Expression 1]
R ′ = Rg × R
G ′ = Gg × G
B ′ = Bg × B
Represented by
[0035]
Details of the white balance correction values Rg, Gg, and Bg applied from the CPU 38 to the white balance adjustment circuit 30 will be described later.
[0036]
The gamma correction circuit 32 changes the input / output characteristics so that the white balance-adjusted R ′, G ′, B ′ signals have the desired gamma characteristics, and outputs them to the YC signal generation circuit 34. The YC signal creation circuit 34 creates a luminance signal Y and chroma signals Cr and Cb from the gamma-corrected R, G and B signals. These luminance signal Y and chroma signals Cr and Cb (YC signal) are stored in the memory 36 in the same memory space as the memory 24.
[0037]
Here, by reading the YC signal in the memory 36 and outputting it to the liquid crystal monitor 52, a moving image or a still image can be displayed on the liquid crystal monitor 52. Further, the YC signal that is shot in response to the S2 switch ON of the shutter button 9 and stored in the memory 36 is compressed by the compression / expansion circuit 54 according to a predetermined format such as JPEG, and then the memory card 56 or other recording medium. To be recorded.
[0038]
Smart media (Solid-State Floppy Disk Card), PC card, compact flash, magnetic disk, optical disk, magneto-optical disk, memory stick, etc. can be applied as a recording medium as means (recording unit) for storing image data, Various media that can be read and written in accordance with an electronic, magnetic, optical, or combination thereof can be used. A signal processing means and an interface corresponding to the medium to be used are applied. A configuration in which a plurality of media can be mounted regardless of different types or the same type of recording media may be adopted. The means for storing the image is not limited to a removable medium that can be attached to and detached from the camera body, but may be a recording medium (internal memory) built in the camera 1.
[0039]
In the reproduction mode, the image data recorded on the memory card 56 is read out, decompressed by the compression / expansion circuit 54, and then output to the liquid crystal monitor 52. In this way, the reproduced image is displayed on the liquid crystal monitor 52.
[0040]
The CPU 38 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, and auto white balance (AWB) calculation. Functions as a means. The memories 24 and 36 are used as a development area for the execution program of the CPU 38 and a calculation work area for the CPU 38.
[0041]
Signals are input to the CPU 38 from the camera operation unit 40 including the mode dial 8 and the shutter button 9. The CPU 38 controls each circuit of the camera 1 based on an input signal from the camera operation unit 40, for example, lens drive control, AE / AF control, AWB control, photographing operation control, charge readout control from the CCD 14, and image processing control. , Read / write control of memory card, display control of LCD monitor, etc.
[0042]
The camera operation unit 40 is not limited to a push-type switch member, dial member, lever switch, or the like, but may be realized by a user interface that selects a desired item from a menu screen. include.
[0043]
In addition, the camera 1 of this example has a strobe device 46, an automatic flash mode in which the strobe device 46 automatically emits light at low brightness in response to an operation of a strobe key (not shown), and a strobe device regardless of subject brightness. 46 is set to a forced light emission mode in which light is emitted from 46, or a light emission inhibition mode in which light emission from the strobe device 46 is prohibited.
[0044]
The CPU 38 controls charging of a main capacitor (not shown), discharge (light emission) timing to a light emitting tube (for example, a xenon tube) and the like according to a strobe mode selected by the user. The CPU 38 performs white balance control according to the setting of the strobe mode.
[0045]
The EEPROM 58 connected to the CPU 38 has target value data necessary for white balance control, limit value (for example, limit multiple values indicating upper and lower gains) data, data necessary for AE / AF control, or individual users. Stores various setting information set in. The EEPROM 58 is a non-volatile storage unit that can rewrite information, and retains information contents even when the power is turned off. The CPU 38 performs calculations and the like with reference to the data in the EEPROM 58 as necessary.
[0046]
The AF control of the camera 1 is, for example, contrast AF that moves the photographing lens 10 so that the high-frequency component of the G signal is maximized, and the lens is driven so that the high-frequency component of the G signal is maximized when the shutter button 9 is half-pressed. The photographing lens 10 is moved to the in-focus position via the unit 42.
[0047]
In the AE control, as shown in FIG. 3, the R, G, and B signals are fetched a plurality of times (up to four times) at predetermined exposures (1) to (4), and these R, G, and B signals are integrated. Subject brightness (shooting EV value) is obtained based on the integrated value.
[0048]
Next, details of the measurement of the photographing EV value will be described.
[0049]
As shown in FIG. 4, one screen is divided into a plurality of areas (for example, 8 × 8), luminance signals obtained from R, G, and B signals are integrated for each divided area, and based on the integrated value. The EV value (EVi) of each divided area is obtained.
Subsequently, as shown in FIG. 4, the EV value of each divided area is weighted corresponding to the shooting mode, and the EV ′ value of the entire screen is calculated by the following equation.
[0050]
[Expression 2]
EV ′ = log ₂ {Σ (W _i × 2 ^EVi ) / ΣW _i }
However, i: 0 to 63 (subscript indicating an 8 × 8 divided area)
W _i : The weighting coefficient for each divided area according to the shooting mode, that is, when the shooting mode is the auto shooting mode or the person shooting mode, the center-weighted metering method is used as shown in the weighting coefficient of FIG. In the landscape shooting mode, as shown in FIG. 4 (B), the photometry method is performed by reducing the weight of the divided areas located on the outermost periphery, and in the night scene shooting mode, as shown in FIG. 4 (C). Average metering method.
[0051]
The EV ′ calculated as described above is further subjected to exposure correction ΔEV corresponding to the shooting mode as shown in the following equation to obtain the shooting EV value.
[0052]
[Equation 3]
EV = EV′−ΔEV
Note that ΔEV is, for example, ΔEV = 0 in the portrait shooting mode, and ΔEV = 0.3 in the landscape shooting mode and the night scene shooting mode.
[0053]
The aperture value and shutter speed at the time of shooting are finally determined based on the shooting EV value obtained as described above.
[0054]
Then, the aperture 12 is driven via the aperture drive unit 44 so that the aperture value determined when the shutter button 9 is fully pressed, and the charge accumulation time is controlled by the electronic shutter so that the determined shutter speed is obtained. .
[0055]
Next, a white balance control method for the camera 1 configured as described above will be described. Note that, when shooting with the flash device 46 emitting light, white balance correction values Rg, Gg, and Bg for performing good white balance with respect to the flash light are added to the white balance adjustment circuit 30. The white balance control when the strobe does not emit light (in the light emission inhibition mode) will be described with reference to the flowchart of FIG.
[0056]
The RGB data for one screen acquired from the CCD 14 in response to the full press of the shutter button 9 (S2 = ON) is stored in the memory 24. The imaging screen is divided into a plurality of areas (for example, 8 × 8), and an integrated value for each color of the R, G, and B signals is calculated for each divided area (step S110). An average value per pixel is calculated from the obtained integrated value for each color, and a ratio R / G between the R signal and the G signal and a ratio B / G between the B signal and the G signal are obtained from the average value (step). S112).
[0057]
Note that the average integrated values of the R, G, and B signals for each divided area are calculated by the integrating circuit 48 shown in FIG. Further, multipliers 50R, 50G, and 50B are provided between the integrating circuit 48 and the CPU 38, and an adjustment gain value for adjusting variation of devices is added to the multipliers 50R, 50G, and 50B. It has become.
[0058]
In this way, the color information (R / G, B / G) obtained for each divided area falls within any detection frame among the detection frames represented by the color coordinates in FIG. Used to determine whether. Note that the detection frames such as the shade-clouding detection frame and the daylight color detection frame in FIG. 6 are frames represented on the color coordinates with the horizontal axis being R / G and the vertical axis being B / G. A range of color distribution such as a light source type is defined for each frame.
[0059]
In FIG. 6, a high color temperature detection frame, a blue sky detection frame, a shade-cloud detection frame, a daylight color detection frame, a green detection frame, a day white-white fluorescent light detection frame divided into six regions, a warm white detection frame, and a skin color detection A tungsten detection frame divided into two regions and a low color temperature detection frame are shown, but the types and number of detection frames, the setting range, etc. are not limited to this example, and various designs are possible. .
[0060]
Using the detection frames shown in FIG. 6, a distribution of 64 points (R / G, B / G) corresponding to each divided area of the imaging screen is obtained, and each detection frame is only related to the points output to each detection frame. And the average coordinates in each detection frame are calculated (step S114 in FIG. 5).
[0061]
Next, the barycentric point of the distribution is calculated by weighting the number in each detection frame and the average coordinates in each detection frame (step S116).
[0062]
If the R / G coordinate of the center of gravity point is Rd, the B / G coordinate of the center of gravity point is Bd, the average R / G and B / G values in each detection frame are Ri and Bi, and the number of detection is Ni, the coordinates of the center of gravity point Is calculated by the following equation.
[0063]
[Expression 4]
Rd = Σ (Ni × Ri) / Ni
Bd = Σ (Ni × Bi) / Ni
A gain for white balance correction is calculated by multiplying the reciprocal from the center of gravity obtained in this way to a target point (for example, a point that becomes gray) (step S118).
[0064]
When the WB gain of R / G is Gr, the WB gain of B / G is Gb, and the target point of (R / G, B / G) is (Tr 1, Tb), the WB gain is calculated by the following equation.
[0065]
[Equation 5]
Gr = Tr / Rd
Gb = Tb / Bd
The target point is not limited to (1, 1), and there is an aspect in which the target point is set according to the scene so as to leave the atmosphere of the light source.
[0066]
FIG. 7 is a flowchart showing the procedure of white balance correction limiter processing (overflow processing for defining the correction upper limit). As described with reference to FIG. 6, when the white balance gain is calculated (step S <b> 210 in FIG. 7), first, the R gain (or B gain) is set to G by looking at the R gain amount and the B gain amount with respect to the G gain. It is determined whether or not the specified multiple quantity is exceeded (steps S212 and S214). The specified multiple value (AR) of the R gain for G and the specified multiple value (AB) of the B gain for G are set in the EEPROM 58. By changing this set value, the restricted area can be varied.
[0067]
In step S212, if the R gain exceeds AR times with respect to the G gain, the R gain is clipped with a value of AR × G gain (step S216). On the other hand, if the R gain does not exceed AR times the G gain in step S212, the calculated R gain value is used as it is (step S218).
[0068]
Similarly, in step S214, if the B gain exceeds AB times the G gain, the B gain is clipped with a value of AB × G gain (step S220). On the other hand, if the B gain does not exceed AB times the G gain in step S214, the calculated B gain value is used as it is (step S222).
[0069]
In addition to the white balance correction upper limit limiting function described with reference to FIG. 7, the camera 1 of this example also has a white balance correction lower limit limiting function.
[0070]
FIG. 8 shows an underflow process procedure for defining the correction lower limit. As described with reference to FIG. 6, when the white balance gain is calculated (step S <b> 310 in FIG. 8), first, the R gain (or B gain) is set to G by looking at the R gain amount and the B gain amount with respect to the G gain. It is determined whether or not it is below a predetermined lower limit multiple quantity (steps S312 and S314). The lower limit multiple value (CR) of the R gain for G and the lower limit multiple value (CB) of the B gain for G are set in the EEPROM 58. By changing this set value, the restricted area can be varied.
[0071]
In step S312, if the R gain is less than CR times the G gain, the R gain is clipped with a value of CR × G gain (step S316). On the other hand, if the R gain is not less than CR times the G gain in step S312, the calculated R gain value is used as it is (step S318).
[0072]
Similarly, in step S314, if the B gain is less than CB times the G gain, the B gain is clipped with a value of CB × G gain (step S320). On the other hand, if the B gain is not less than CB times the G gain in step S314, the calculated B gain value is used as it is (step S322).
[0073]
Since the gain is clipped when the gain that exceeds (or falls below) a certain limit is calculated by the limiter function described with reference to FIGS. 7 and 8, overcorrection of the object color can be prevented. Further, although the gain is clipped at a certain upper limit or lower limit, the white balance is corrected to some extent within the limit range, so that the color does not fail even in a low color temperature scene or the like.
[0074]
For example, as an example of a gain clip value in a low color temperature scene, when the G gain digital value is 88, the upper limit of the B gain is 500, and the lower limit of the R gain is 80.
[0075]
FIG. 9 is a conceptual diagram summarizing the main configuration of the camera 1 according to the embodiment. When the shutter button 9 is pressed, an image signal is extracted from the CCD 14. The signal output from the CCD 14 is converted into a digital signal by the A / D converter 20. A white balance gain is calculated on the basis of the acquired image data, and the final gain value is determined by being limited by the overflow processing unit 62 and the underflow processing unit 63.
[0076]
The balance of each color signal is adjusted by the white balance adjustment circuit 30 according to the determined gain value. The image signal that has been subjected to white balance adjustment by the white balance adjustment circuit 30 is subjected to necessary processing such as gamma conversion by a gamma conversion unit 68, and as a final image, a display unit (liquid crystal monitor 52) or a recording unit (memory card). 56) or the like.
[0077]
In the above-described embodiment, the digital camera that mainly records a still image is exemplified, but the scope of application of the present invention is not limited to this, and an electronic camera such as a digital camera, a video camera, and a DVD camera capable of recording a moving image, or The present invention can also be applied to other imaging devices having an electronic imaging function, such as a mobile phone with camera, a PDA with camera, and a mobile personal computer with camera.
[0078]
【The invention's effect】
As described above, according to the present invention, a limit is set for the gain for white balance adjustment calculated based on the image signal obtained by imaging the subject, and the calculated gain is within the limit value limit. If so, the white balance is corrected based on the gain, and if the calculated gain is outside the limit value limit (when exceeding the upper limit value or below the lower limit value), the gain is set to the limit value. The white balance is corrected using the gain indicated by the limit value, so that it is possible to correct the white balance according to the light source color to some extent and prevent overcorrection in the case of object colors. It is.
[Brief description of the drawings]
FIG. 1 is a rear view of a digital camera according to an embodiment of the present invention. FIG. 2 is a block diagram of the digital camera according to an embodiment of the present invention. FIG. 4 is a diagram used for explaining a photometry method for each photographing mode. FIG. 5 is a flowchart used for explaining an auto white balance control method. FIG. 6 is a detection showing a range of color distribution such as a light source type. FIG. 7 is a flowchart showing a limiter processing (overflow processing) procedure in white balance correction. FIG. 8 is a flowchart showing a limiter processing (underflow processing) procedure in white balance correction. Schematic diagram summarizing the main configuration of the camera according to the embodiment [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Camera, 3 ... Cross key, 4 ... Menu / execution key, 14 ... CCD, 26 ... Digital signal processing circuit, 30 ... White balance adjustment circuit, 38 ... CPU, 48 ... Integration circuit, 52 ... Liquid crystal monitor, 56 ... Memory card

Claims (4)

A gain calculating step of calculating a gain for white balance adjustment based on an image signal acquired via the imaging means;
A limit value setting step for setting a limit value for restricting at least one of the upper limit and the lower limit of the gain used for white balance adjustment;
A limiter processing step of limiting the gain by the limit value when a gain outside the limit value is calculated in the gain calculation step;
A white balance adjustment step of performing white balance adjustment by correcting the color signal based on the gain determined in the limit by the limit value;
A white balance control method comprising: Imaging means for converting an optical image of a subject into an electrical signal;
Gain calculating means for calculating a gain for white balance adjustment based on an image signal acquired via the imaging means;
Limit value setting means for setting a limit value for restricting at least one of the upper limit and the lower limit of the gain used for white balance adjustment;
Limiter processing means for limiting the gain by the limit value when the gain calculation means calculates a gain outside the limit value;
White balance adjustment means for performing white balance adjustment by correcting the color signal based on the gain determined in the restriction by the restriction value;
An imaging apparatus comprising: The imaging apparatus according to claim 2, wherein the limit value setting unit includes a non-volatile storage unit that stores the limit value. 4. The image pickup apparatus according to claim 2, wherein the limit value setting means sets at least an upper limit value of a gain for the B signal so as to prevent overcorrection of white balance in a low color temperature scene.

Images