HK1095237B - Image pickup apparatus and white balance control method - Google Patents

Description

Image pickup apparatus and white balance control method

Technical Field

The present invention relates to an image pickup apparatus, a white balance control method, and a white balance control program.

Background

As is well known, an electronic camera is a type of image pickup apparatus that causes a liquid crystal monitor to display an object image captured with a solid-state image pickup device such as a CCD as a through image (viewfinder image) in an imaging standby state in which a predetermined mode such as a REC mode is set, without taking into account a shutter operation. In such an electronic camera, it is necessary to achieve white balance in order to reproduce the color of an object more accurately. The purpose of white balance is to display a white object in white even if an image is taken under light having different color temperatures. The gain of the image signal output from the solid-state image pickup device is controlled for each of the color components R, G and B in accordance with the imaging environment (light source), whereby white balance can be configured. Therefore, by storing gain values corresponding to expected plural types of imaging environments (light sources) in the memory, or storing correction coefficients of reference gains in the memory, and letting the user set an actual imaging environment (light source), it is possible to obtain a white balance close to the optimum state.

However, this forces the user to perform complicated operations, thereby providing an automatic white balance function capable of automatically obtaining white balance. In order to realize the automatic white balance, it is necessary to determine which part of the captured image is white. To determine this white portion, the output signal (image signal) of the above-described solid-state image pickup device is first subjected to YUV conversion to obtain a color difference signal (Cb signal, Cr signal). With this color difference signal, color information, that is, a Cb value and a Cr value, of all pixels constituting an image is checked. At this time, when the Cb value and Cr value of a certain pixel are included in a predetermined white detection range WS (in a range where white is highly likely), it is determined that the color of the certain pixel is white. The Cb value and the Cr value of all pixels determined to be white are accumulated. Then, the gain of the R component and the gain of the B component are controlled so that the integrated Cb value and the integrated Cr value are both "0" (Cb ═ Cr ═ 0). That is, in the case where white becomes slightly blue (when imaging is performed under high color temperature light), the gain of the R component is increased, and the gain of the B component is decreased. In the case where white becomes slightly red (when imaging is performed under light of a low color temperature), the gain of the R component is reduced, and the gain of the B component is increased.

In this method, when an object appearing white in sunlight (standard light of 5500K) is imaged under a different imaging condition (imaging light), a range in which this color (Cb value, Cr value) changes is set as the white detection range WS, and thus, even if the imaging condition (imaging light) is different, a correct white balance can be automatically obtained.

In addition, an automatic white balance control method has been proposed, by which correct white balance can be automatically obtained when flash illumination is employed (for example, refer to japanese patent laid-open No. 2000 and 308069). The automatic white balance control method includes comparing a brightness of an object obtained by adding a constant to a brightness of the object optically measured before an image is taken with a brightness of the object optically measured during flash illumination imaging, wherein the constant accounts for an increase in the brightness of the object during flash illumination. As a result of this comparison, in the case where the brightness of the object measured optically during the flash illumination is larger, it is determined that this light source is a flash, and the white balance is controlled.

However, in the automatic white balance control method described above, when the type of the light source is a flash lamp, the xenon tube as the light source of the flash lamp has a color temperature of 5500K, which is equal to the color temperature of sunlight. Then, the gain setting of the white balance is performed in the same manner as in the case of sunlight. Therefore, there is no problem in the case where there is no external light or the external light is sunlight. In the case where there is ambient light other than sunlight and this light is irradiated onto an object, if a flash is turned on, a photographed and recorded image is reproduced as an image having an ambient light color because the gain setting of white balance is based on sunlight.

Disclosure of Invention

An object of the present invention is to provide an image pickup apparatus, a white balance control method, and a white balance control program, whereby an image can be recorded with good white balance even if light is used for illumination at the time of imaging.

According to an embodiment of the present invention, an image pickup apparatus includes:

an image pickup device for taking an image of an object and outputting an image signal having a plurality of color components;

a light emitting unit for emitting light;

a first amplification unit configured to amplify the image signal output by the image pickup device for each color component;

a second amplification unit configured to amplify the image signal output by the image pickup device for each color component;

a gain storage unit for storing a plurality of sets of gains for each color component so as to establish different white balances in the course of light emission of the light emitting unit;

a changing unit for sequentially changing the gain group for each color component of the second amplifying unit;

a detection unit that detects a set of gains having color information included in a predetermined white detection range based on the image signal amplified by the second amplification unit, wherein the set of gains of the second amplification unit is changed by the change unit;

a setting unit configured to select a set of gains to be set to the first amplification unit from the set gain storage unit based on the gain detected by the detection unit and set the selected set of gains to the first amplification unit during imaging in which the light emitting unit emits light; and

a control unit that supplies the image signal amplified by the first amplifying unit to a recording device, wherein the first amplifying unit is set with the gain group by the setting unit.

According to another embodiment of the present invention, a white balance control method in an image pickup apparatus including an image pickup device that picks up an image of a subject and outputs an image signal having a plurality of color components, a light emitting unit that emits light, a first amplifying unit that amplifies the image signal output from the image pickup device for each color component, a second amplifying unit that amplifies the image signal output from the image pickup device for each color component, and a storage unit that stores a plurality of sets of gains for each color component to establish white balance during light emission by the light emitting unit, the method includes:

sequentially changing the gain set for each color component of the second amplification unit;

detecting a set of gains having color information included in a predetermined white detection range based on the image signal amplified by the second amplifying unit sequentially changing the set of gains;

selecting a set of gains to be set to the first amplification unit from the storage unit based on the detected set of gains and setting the selected set of gains to the first amplification unit during imaging in which the light emitting unit emits light; and

the image signal amplified by the first amplifying unit in which the gain group is set in the setting step is supplied to a recording device.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention, in which:

fig. 1 is a block diagram showing the structure of an electronic camera in one embodiment of the present invention;

FIG. 2A shows one configuration of a gain table during non-light emission;

FIG. 2B shows a distribution of gain values of the gain table during non-light emission shown in FIG. 2A;

FIG. 3A shows a structure of a gain table during first light emission;

FIG. 3B shows a structure of a gain table during the second light emission;

FIG. 3C shows a distribution of gain values of the gain table during the second illumination shown in FIG. 3B;

FIG. 4A shows one structure of a variable gain table;

FIG. 4B shows a distribution of gain values of the variable gain table shown in FIG. 4A;

fig. 5 shows white detection frame data;

fig. 6 shows EV determination data;

fig. 7 is a flowchart of the operation of the REC procedure mode in this embodiment;

fig. 8 illustrates a specific example of the operation procedure in the REC procedure mode in this embodiment; and

fig. 9 illustrates a white detection method in another embodiment of the present invention.

Detailed Description

An embodiment of the present invention will be described below with reference to the drawings.

Fig. 1 is a block diagram of the configuration of an electronic camera as one embodiment of the present invention. The CCD 25 located behind the lens 20 is driven by a timing signal generator 26 and a vertical driver 27. At the CCD 25, a color filter array of primary colors RGB is provided. In each of R, G and the B light receiving section, an optical image formed on the light receiving surface of the CCD 25 is subjected to charge accumulation and converted into R, G and B signal charges in accordance with the light intensity, and the image after the charge accumulation is output as an analog image signal to the unit circuit 28. The unit circuit 28 includes a CDS unit for removing noise from an input captured image signal and an a/D converter for converting the captured image signal from which the noise is removed into digital image data. The image data output from the unit circuit 28 is sent to the first and second gain controller circuits 21, 22.

The first and second gain controller circuits 21, 22 include R amplifiers 21a, 22a, G amplifiers 21B, 22B, and B amplifiers 21a, 22c for the color components R, G and B, respectively, and the gains of the amplifiers 21a, 22a, 21B, 22B, 21c, 22c are controlled by control signals sent by the control circuit 35. The image signal amplified by the first gain controller circuit 21 is sent to the first color processor circuit 23 for color processing operation. Then, YUV data including the digital luminance signal (Y signal) and the color difference signal (a Cb signal, a Cr signal) is written in a buffer of the DMA controller 29. At the same time, R, G and B image data before the color processing operation are also written in the buffer. The DMA controller 29 transfers the YUV data written to the buffer to a designated area of the DRAM 30 and decompresses the transferred data.

The video encoder 31 generates a video signal based on the YUV data read out from the buffer, and outputs the generated video signal to a display device 32 having an LCD. In this way, when the REC (recording) course mode is set in the image capturing wait state, the captured image is displayed as one course image on the display device 32. In addition, in this state, if the shutter button is pressed to command imaging, one frame of YUV data written in the buffer is sent to the compression/decompression unit 33; carrying out compression treatment; and records the compressed data in the flash memory 34. When set to PLAY mode to perform image reproduction or the like, the image data recorded in the flash memory 34 is sent to the compression/decompression unit 33 through the DMA controller 29; carrying out decompression processing; and reproduces YUV data. In this way, the recorded image can be displayed on the display device 32.

On the other hand, the image signal amplified by the second gain controller circuit 22 is sent to the second color processor circuit 24 for color processing. Then, YUV data including the digital luminance signal (Y signal) and the color difference signal (Cd signal, Cr signal) is sent to the control circuit 35.

The control circuit 35 has a ROM in which programs or data are stored and a working RAM. This control circuit 35 controls the operation of each of the aforementioned components in accordance with a predetermined program, and provides a plurality of functions of the electronic camera, i.e., automatic exposure control (AE) or Automatic White Balance (AWB), corresponding to the status signal sent from the operation unit 36. Various buttons such as a shutter button, a REC process mode, and a PLAY mode selection button are provided at the operation unit 36, and a status signal in accordance with the button operation is sent to the control circuit 35. The flash 37 may be driven to emit auxiliary light during operation of the shutter button (during imaging) as necessary.

The gain storage memory 38 stores the gains set at the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 and the gains set at the R amplifier 22a and the B amplifier 22c of the second gain controller circuit 22 during the auto white balance control of the control circuit 35. That is, the gain storage memory 38 stores the non-emission gain table 381 shown in fig. 2A; gain tables 383 and 384 for setting the first and second light emissions of the gain storage unit shown in fig. 3A and 3B; and a variable gain table 382 serving as a variable gain storage unit shown in fig. 4A.

The table 381 shown in fig. 2A is provided as a table for setting gains to set the gains of the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 during the non-emission period in which the emission of light of the flash 37 is inhibited and during the automatic white balance control by the control circuit 35. This table 381 stores R gain values and B gain values corresponding to gain No. (1) to gain No. (4). (1) Gains to (4) represent values of R gain and B gain that can set a correct white balance when shadow, sunlight, a fluorescent lamp, and an incandescent lamp are used as light sources during imaging. These R and B gain values consist of empirical values. Fig. 2B is a conceptual view showing the distribution of gain values in the non-light emission gain table 381 shown in fig. 2A.

The first light emission gain table 383 shown in fig. 3A is provided for setting the gains of the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 during light emission of the flash 37 and during automatic white balance control using the control circuit 35. The first light emission gain table 383 stores codes indicating the R gain value and the B gain value in the cases of "EV (exposure value) 2 or less", "EV 3 ~ 4" and "EV 5 or more" corresponding to "incandescent lamp", "fluorescent lamp", "shade" and "sunlight" as shown in the figure. The second light emission gain table 384 stores in detail the R gain value and the B gain value represented by codes a1, a2, B1 … … D stored in the first light emission gain table 383 in a digital manner, as shown in fig. 3B and 3C.

The variable gain table 382 shown in fig. 4A and 4B is provided for setting the gains of the R amplifier 22a and the B amplifier 22c of the second gain controller circuit 22 during the automatic white balance control using the control circuit 35. This table stores R gain values and B gain values corresponding to gains No. 1 to 12. Gains No. 1 to 12 represent values of R gain and B gain that can set correct white balance during imaging when shadow a, shadow B, sunlight a, sunlight B, sunlight C, fluorescent lamp a, fluorescent lamp B, fluorescent lamp C, incandescent lamp a, incandescent lamp B, green lamp, and beige lamp are used as light sources. These R-gain and B-gain values also consist of empirical values.

Fig. 4B is a conceptual view showing the distribution of gain values in the variable gain table 382 shown in fig. 4A.

In the non-emission gain table 381 and the variable gain table 382, each of (gain No. 1) and gain No. 1, (gain No. 2) and gain No. 4, (gain No. 3 and gain No. 6, and gain No. 4 and gain No. 9 represents the same R gain value and B gain value.

The ROM or the gain storage memory 38 of the control circuit 35 stores white detection frame data 351 shown in fig. 5 and EV (exposure value) determination data 352 shown in fig. 6.

The operation of the REC process mode in the state where the AWB mode has been set in the present embodiment having the above-described constituent elements will be described below with reference to the flowchart shown in fig. 7.

In the electronic camera, if the REC process mode is set, the control circuit 35 starts processing in accordance with this flowchart based on the relevant program. First, the CCD 25 is driven to capture an image of 1 frame (step S1). Thus acquiring the obtained digital data of 1 frame (step S2); collecting a white detection frame and an EV value (step S3); and performs a step of determining whether the EV corresponds to "dark" (step S4).

The processing in step S4 is executed on the basis of EV determination data 352 shown in fig. 6, which determines whether or not the collected EV value is a value corresponding to "dark" belonging to the EV determination data 352. When the acquired EV value corresponds to a value belonging to "dark" in the EV determination data 352 (yes in step S4), it is assumed that the acquired image data is taken in either one of a case where it is imaged in shadow and a case where it is imaged using sunlight, an incandescent lamp, or a fluorescent lamp as a light source.

In this case, it is determined whether the gain number determined under condition 1 is the gain number 1 or the gain number 2 in the variable gain table 382 (step S5). If the gain No. 1 to gain No. 12 in the variable gain table 382 are cyclically set to the R amplifier 22a and the B amplifier 22c of the second gain controller circuit 22 frame by frame, the gain No. determined under the condition 1 is one gain No. in the table corresponding to the largest number of white pixels in the latest 12 frames (the number of pixels included in the white frame 353 of the white detection frame data 351 shown in fig. 5).

That is, as shown in the specific example in fig. 8 (in fig. 8, the first gain controller circuit 21 is denoted by "# 1" and the second gain controller circuit 22 is denoted by "# 2"). In the state where the EV determination result is "dark", gains No. 1 to No. 12 are cyclically set in the R amplifier 22a and the B amplifier 22c of the second gain controller circuit 22(#2) for each of the frames 1, 2, and 3 … …, the "number of white pixels" of each frame is detected, and the frame number with the largest number of white pixels in the latest 12 frames is determined. If multiple frames have the same maximum number of white pixels, the most recent frame is determined.

As a result of the judgment at step S5, when the gain of variable gain table 382 determined under condition 1 is gain No. 1 or gain No. 2 (step S5: yes), gain No. (1) corresponding to the shade in non-light emission gain table 381 is set as a gain candidate to set the gain at R amplifier 21a and B amplifier 21c of first gain controller circuit 21 (step S6).

As a result of the determination in step S5, when the gain of variable gain table 382 determined under condition 1 is neither No. 1 nor No. 2 (step S5: no), it is determined whether the gain of variable gain table 382 determined under condition 1 is No. 3, 4, 5, 11, or 12 (step S7). When the determination in step S7 is yes, gain No. (2) corresponding to sunlight in non-emission gain table 381 is set as a gain candidate for setting at R amplifier 21a and B amplifier 21c of first gain controller circuit 21 (step S8).

As a result of the determination at step S7, when the gain of variable gain table 382 determined under condition 1 is not any of nos. 3, 4, 5, 11, and 12 (step S7: no), it is determined whether the gain of variable gain table 382 determined under condition 1 is No. 6, 7, or 8 (step S9). When the judgment result of step S9 is yes, gain No. (3) corresponding to the fluorescent lamp in non-emission gain table 381 is set as a gain candidate for setting at the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 (step S10).

That is, in the specific example shown in fig. 8, of gains No. 1, 2, 3, … …, 12 set for 1, 2, 3, … …, 12 frames, the gain No. (100) having the largest number of white pixels is gain No. 7. Therefore, the judgment result in step S9 is yes at the time of frame 13 (time point a), and number (3) corresponding to the fluorescent lamp in non-emission gain table 381 is set as a candidate (step S10).

Further, as a result of the judgment at step S9, when the gain of variable gain table 382 determined under condition 1 is not any of gains No. 6, 7 and 8 (step S9: NO), gain No. (4) corresponding to the fluorescent lamp in non-light emission gain table 381 is set as a gain candidate for setting at R amplifier 21a and B amplifier 21c of first gain controller circuit 21 (step S11).

On the other hand, as a result of the judgment at step S4, when the collected EV value is not a value corresponding to "dark" belonging to the EV judgment data 352 (step S4: NO), it is judged whether the value corresponds to "bright" (step S24). When this EV value belongs to one value of "bright" of the EV determination data 352 (step S24: yes), it is assumed that the acquired image data is captured while using sunlight as a light source. Therefore, in this case, as in the previously described step S8, gain No. (2) corresponding to sunlight in non-emission gain table 381 is set as a gain candidate for setting at the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 (step S25).

However, as a result of the determination at step S14, when the collected EV value is not a value of "Bright" belonging to the EV determination data 352 (step S24: NO), it is determined whether the gain of the variable gain table 382 determined under condition 1 is No. 1 or No. 2 (step S26) as in the previously described step S5. When the gain of variable gain table 382 determined under condition 1 is gain No. 1 or 2 (step S26: yes), gain No. (1) corresponding to the shade in non-emission gain table 381 is set as a gain candidate for setting at R amplifier 21a and B amplifier 21c of first gain controller circuit 21 (step S28).

However, when the gain of variable gain table 382 determined under condition 1 is neither No. 1 nor No. 2 (step S26: NO), gain No. (2) corresponding to sunlight in non-emission gain table 381 is set as a gain candidate for setting at R amplifier 21a and B amplifier 21c of first gain controller circuit 21 (step S28).

Next, it is determined whether those numbers as candidates are the same 32 times consecutively in steps S6, S8, S10, S11, S25, S27, and S28 (step S12). When a negative determination is made (step S12: NO), the process from step S1 is repeated. When an affirmative determination is made (step S12: yes), it is determined whether or not the strobe 37 is to be turned on to emit light (step S13).

When it is determined (during imaging) that it is not necessary to have the strobe 37 emit light while operating the shutter button, or when the user sets the strobe 37 not to emit light at the operation unit 36 (step S13: no), the gain values of this number are set and updated at the R amplifier 21a and the B amplifier 21c of the gain controller circuit 21 (step S13).

That is, in the specific example shown in fig. 8, gain No. (3) is defined as a candidate 32 times in succession at time point B. Then, at the time point B, the judgment result of the step S12 is yes, and the gain No. (2) which is the initial value of the R amplifier 21a and the B amplifier 21c of the gain controller circuit 21 is updated to the gain No. (3). In addition, also at time point C, from time point D at which the scene is assumed to have changed, (2) gain is defined as a candidate for 32 consecutive times. Therefore, also at time C, the determination result in step S12 is yes, and gain No. (3) is updated to gain No. (2).

Then, the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 amplify the R and B color components of the digital image data of the optical image sent from the unit circuit 28 in accordance with the gains set in step S14. This amplification process is performed independently of the selection process shown in fig. 7. Further, as described above, the image signal amplified by the first gain controller circuit 21 is sent to the first color processor circuit 23, and color processing is performed. Then, YUV data including the digital luminance signal (Y signal) and the color difference signal (Cb signal, Cr signal) is written into one buffer of the DMA controller 29. The DMA controller 29 transfers the YUV data written to the buffer to a designated area of the DRAM 30 and decompresses the transferred data. The video encoder 31 generates a video signal based on the YUV data read out from the buffer, and outputs this generated signal to the display device 32 having an LCD.

In this way, when the REC process mode is set in the imaging standby state, setting the white balance in accordance with the light source does not require any complicated operation. In the process of imaging with luminescence, an object image in which a good white balance is established is displayed as a through image on the display device 32. In addition, the through image is displayed on the display device 32 not based on the image data obtained from the second gain controller circuit 22 by setting the gains of the variable gain control table 382 to the second gain controller circuit 22 in the order of No. 1 to No. 12 frame by frame under the condition 1, but based on the image data from the second gain controller circuit 22 whose gain is updated and set at step S13. In this way, the white balance of the through image displayed on the display device 32 does not change frequently.

When the shutter button is pressed to issue an imaging instruction, 1 frame of YUV data stored in the buffer is sent to the compression/decompression unit 33; carrying out compression treatment; and records the compressed data into the flash memory 34. In this way, image data of an object image in which good white balance is established can be recorded in the flash memory 34.

On the other hand, when it is determined that the control circuit 35 needs to cause the flash 37 to emit light during operation of the shutter button (during imaging), or when the user sets forced emission of the flash 37 at the operation unit 36 (step S13: YES), one light source is designated (step S15). That is, as described above, at the time point when the determination result of step S12 is yes, any one of gains No. (1) to No. (4) in the gain table for non-light emission is determined. Among the gains No. (1) to (4) thus obtained, as described above, the gain No. (1) is a gain set at the time of imaging in shadow; (2) the signal gain is a gain set when imaging in sunlight; (3) the sign gain is a gain set when imaging is performed using a fluorescent lamp as a light source; (4) the sign gain is a gain set when an incandescent lamp is used as a light source for imaging. Then, when the judgment result of step S12 is yes, if the determined gain is gain No. (1), the light source is designated as "shadow". When the judgment result of step S12 is yes, if the determined gain is gain No. (2), the light source is designated as "sunlight". When the judgment result of step S12 is yes, if the determined gain is the gain No. (3), the light source is designated as "fluorescent lamp". When the judgment result of step S12 is yes, if the determined gain is the gain No. (4), the light source is designated as "incandescent lamp".

Next, referring to the light emission gain tables 383 and 384, those gain values during stroboscopic light-emitting are set and updated at the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 (step S16).

That is, according to the processing operation of step S15, the light source is specified as any one of "shadow", "sunlight", "fluorescent lamp", and "incandescent lamp". In addition, the EV value is collected in accordance with the processing operation in step S3. Then, in step S16, first, a code corresponding to a specified light source ("shadow", "sunlight", "fluorescent lamp", or "incandescent lamp") and corresponding to the acquired EV value is read out from the first light emission gain table 383 shown in fig. 3A. Further, the R gain value and the B gain value corresponding to the code read out from the first light emission gain table 383 are read out from the second light emission gain table 384, and these gain values are set and updated at the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 (step S16).

That is, in the specific example shown in fig. 8, gain No. (3) is defined as a candidate 32 times in succession at time point B. Therefore, at the time point B, the judgment result of the step S12 is yes, and the light source "fluorescent lamp" corresponding to the gain No. (3) is specified. At this time, for example, when the EV value is EV3 to 4, "B1" is read out from the first light emission gain table 383 shown in fig. 3A on the basis of "EV 3 to 4" of "fluorescent lamp". Further, based on "B1", R gain "125" and B gain "106" are read out from the second light emission gain table 384. Therefore, at the time point B, the gain value of the R amplifier 21 of the first gain controller circuit 21 is set and updated to "125", and the gain value of the B amplifier 21c is set and updated to "106", respectively.

Also at time C, from time D at which a scene is assumed to have changed, gain No. (2) is defined as a candidate for 32 consecutive times. Therefore, at the time point C, the judgment result of step S12 is yes, and the light source "sunlight" corresponding to the gain No. (2) is specified. At this time, even if any one of EV 2 or less, EV3 to 4, and EV 5 or more is set, the code of "sunlight" is set to "D" in the first light emission gain table 383 shown in fig. 3A. In addition, the code "D" represents the R gain "129" and the B gain "72" shown in the second light emission gain table 384 (fig. 3B). Therefore, at the time point C, the gain value of the R amplifier 21a of the first gain controller circuit 21 is set and updated to "129", and the gain value of the B amplifier 21C is set and updated to "25", respectively.

Therefore, the R amplifier 21a and the B amplifier 21c of the first gain controller circuit 21 amplify the R and B color components of the digital image data of the optical image sent from the unit circuit 28 in accordance with the gain set in step S16. Further, as described above, the image signal amplified by the first gain controller circuit 21 is sent to the first color processor circuit 23, and color processing is performed. Then, YUV data including the digital luminance signal (Y signal) and the color difference signal (Cb signal, Cr signal) is written in the buffer of the DMA controller 29. The DMA controller 29 transfers the YUV data written to the buffer to a designated area of the DRAM 30 and decompresses the transferred data. The video encoder 31 generates a video signal based on the YUV data read out from the buffer, and outputs the generated signal to the display device 32.

When the shutter button is pressed to issue an imaging instruction, 1 frame of YUV data stored in the buffer is sent to the compression/decompression unit 33 after the flash 37 emits light; carrying out compression treatment; the compressed data is recorded in the flash memory 34. In this way, the flash memory 34 can record image data of an object image in which white balance is well established in consideration of external light during the emission of the flash 37. That is, during the emission of the flash 37, even in a state where "shadow", "fluorescent lamp", or "incandescent lamp" is illuminating an object as ambient light, instead of "sunlight", the flash memory 34 can record image data of an object image without being affected by any color of the ambient light.

In this embodiment, white detection is performed by CCD 25 for one complete image of 1 frame. However, as shown in fig. 9, the image P of 1 frame is divided into three parts, a middle part Pc, an upper part Pu, and a lower part Pd. Typically the object is located in the middle part Pc. In this way, white detection can be performed by partially detecting one image, for example, by detecting only the upper Pu and the lower Pd, but not the middle Pc.

In addition, in this embodiment, although the EV value itself is used for the EV determination, one EV running average may be obtained, and the obtained average may be used for the EV determination. In this way, stable determination can be made without depending on a short-time change in the EV value.

Further, although this embodiment is described as an electronic camera for recording an image captured at the time when a shutter button is pressed in a state of displaying a through-image, the present invention is not necessarily limited to the above electronic camera, and may be applied to other devices as long as they perform automatic white balance control on a captured image.

Claims (9)

1. An image pickup apparatus comprising:

an image pickup device for taking an image of an object and outputting an image signal having a plurality of color components;

a light emitting unit for emitting light;

a first amplification unit configured to amplify the image signal output by the image pickup device for each color component;

a second amplification unit configured to amplify the image signal output by the image pickup device for each color component;

a gain storage unit for storing a plurality of sets of gains for each color component so as to establish different white balances in the course of light emission of the light emitting unit;

a changing unit for sequentially changing the gain group for each color component of the second amplifying unit;

a detection unit that detects a set of gains having color information included in a predetermined white detection range based on the image signal amplified by the second amplification unit, wherein the set of gains of the second amplification unit is changed by the change unit;

a setting unit configured to select a set of gains to be set to the first amplification unit from the set gain storage unit based on the gain detected by the detection unit and set the selected set of gains to the first amplification unit during imaging in which the light emitting unit emits light; and

a control unit that supplies the image signal amplified by the first amplifying unit to a recording device, wherein the first amplifying unit is set with the gain group by the setting unit.

2. The image pickup apparatus according to claim 1, wherein the setting unit selects a group of gains stored in the gain storage unit as candidates based on the gain group detected by the detection unit, and the setting unit finally selects the gain group that is successively selected as the candidate by a predetermined number of times as the gain group to be set to the first amplification unit when the number of times the same group of gains is successively selected as the candidate reaches the predetermined number of times.

3. The image pickup apparatus according to claim 1, further comprising:

a variable gain storage unit for storing a plurality of sets of gains for each color component to be set to the second amplification unit,

wherein the changing unit changes the gain of each color component by sequentially setting the plurality of sets of gains stored in the variable gain storage unit to the second amplifying unit.

4. The image pickup apparatus according to claim 3, wherein the setting unit selects a group of gains stored in the gain storage unit as candidates based on the group of gains detected by the detection unit, and when a number of times that the same group of gains is successively selected as the candidates reaches a predetermined number of times, the setting unit finally selects the group of gains successively selected as the candidates a predetermined number of times as the group of gains to be set to the first amplification unit.

5. The image pickup apparatus according to claim 3, wherein the variable gain storage unit stores more sets of gains in number than the sets of gains stored in the set gain storage unit.

6. The image pickup apparatus according to claim 5, wherein the setting unit selects a group of gains stored in the gain storage unit as candidates based on the group of gains detected by the detection unit, and when the number of times of successively selecting the same group of gains as the candidates reaches a predetermined number of times, the setting unit finally selects the group of gains successively selected as the candidates by the predetermined number of times as the group of gains to be set to the first amplification unit.

7. The image pickup apparatus according to claim 1, wherein the plurality of sets of gains stored in the set gain storage unit include a plurality of sets of gains for each color component capable of establishing a white balance of an object during lighting of the lighting unit under incandescent light, fluorescent light, shadow, and sunlight.

8. The image pickup apparatus according to claim 7, further comprising:

an exposure amount determining unit that determines an exposure amount when the image pickup device captures an object as an image, wherein

The setting unit selects the gain group to be set to the first amplification unit from the plurality of groups of gains stored in the set gain storage unit based on the exposure amount determined by the exposure amount determination unit and the gain group detected by the detection unit, and sets the selected gain group to the first amplification unit.

9. A white balance control method in an image pickup apparatus including an image pickup device that picks up an image of a subject and outputs an image signal having a plurality of color components, a light emitting unit that emits light, a first amplifying unit that amplifies the image signal output from the image pickup device for each color component, a second amplifying unit that amplifies the image signal output from the image pickup device for each color component, and a storage unit that stores a plurality of sets of gains for each color component to establish white balance during light emission by the light emitting unit, the method comprising:

sequentially changing the gain set for each color component of the second amplification unit;

detecting a set of gains having color information included in a predetermined white detection range based on the image signal amplified by the second amplifying unit sequentially changing the set of gains;

selecting a set of gains to be set to the first amplification unit from the storage unit based on the detected set of gains and setting the selected set of gains to the first amplification unit during imaging in which the light emitting unit emits light; and

the image signal amplified by the first amplifying unit in which the gain group is set in the setting step is supplied to a recording device.