JP4228432B2 - Imaging apparatus and imaging method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image pickup apparatus and an image pickup method capable of achieving good white balance when using a strobe device, for example.
[0002]
[Prior art]
Recently, a number of compact digital cameras, camera-integrated VTRs, and the like have been put into practical use due to the development of electronic image technology and the miniaturization of electronic circuits. These imaging devices are easy to use in terms of ease of image processing and ease of reproduction processing, and are becoming popular in general with the spread of personal computers. In addition, currently popular imaging apparatuses are equipped with a strobe so that they can be used in dark place shooting.
[0003]
These imaging apparatuses are usually provided with an auto white balance control that improves color reproducibility by automatically controlling so that the white portion of the image does not change depending on the color temperature of the light source. When the flash fires, white balance is adjusted to the color temperature of the flash.
[0004]
[Problems to be solved by the invention]
There are various shooting conditions for using a strobe. When the strobe is fired, it is affected by outside light other than the strobe light, or a part where the strobe light does not strike may be generated. Therefore, if the white balance is fixedly adjusted according to the color temperature at which the flash fires, the white balance may shift in areas where the influence of external light having a color temperature different from that of the flash light is strong or where the flash light does not strike. It was.
[0005]
Accordingly, an object of the present invention is to provide an imaging apparatus and an imaging method with good color reproducibility by preventing white balance deviation by adapting the white balance at the time of strobe light emission to the photographing conditions.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the invention of claim 1 includes a white balance means for controlling the white balance of the supplied captured image signal by signal processing ,
Selection means for selecting a forced flash mode in which the flash device always emits light as an operation mode of the flash device and an automatic flash mode in which the flash device emits light in synchronization with an instruction only when outside light is dark,
With
In white balance means,
In forced flash mode,
The brightness of the subject is compared with the first parameter and / or the second parameter that is brighter than the first parameter, and in the range where the brightness of the subject is darker than the first parameter, it corresponds to the color temperature of the strobe device. To control the white balance,
In a range where the brightness of the subject is brighter than the first parameter and darker than the second parameter, the white balance is controlled along the color temperature change that changes from the color temperature of the strobe device to the color temperature of the external light,
In the range where the brightness of the subject is brighter than the second parameter, the white balance is controlled according to a predetermined color temperature between the color temperature of the strobe device and the color temperature of the external light,
In automatic flash mode,
The brightness of the subject is compared with the first parameter and / or the third parameter that is brighter than the second parameter, and in the range where the brightness of the subject is darker than the first parameter, it corresponds to the color temperature of the strobe device. To control the white balance,
In a range where the brightness of the subject is brighter than the first parameter and darker than the third parameter, the white balance is controlled along the color temperature change that changes from the color temperature of the strobe device to the color temperature of the external light,
In the range where the brightness of the subject is brighter than the third parameter, the white balance is controlled almost according to the color temperature of the outside light.
An imaging device.
[0010]
In this invention, the influence of external light at the time of strobe light emission is estimated from the brightness of the subject, and the white balance is controlled according to the color temperature in consideration of the influence of external light. Further, the white balance control method is changed in accordance with whether the strobe operation mode is the forced light emission mode or the automatic light emission mode. As a result, the white balance can be favorably controlled according to the operation mode of the strobe.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a digital camera will be described with reference to the drawings. FIG. 1 shows the overall configuration of an embodiment of the present invention. As shown in FIG. 1, the digital camera has a lens unit 1, a CCD (Charge Coupled Device) 2, a sample hold, an AGC (Automatic Gain Control) and A / D conversion unit 3, a camera signal processing unit 4, a memory controller 5, and a buffer memory. 6, D / A converter 7, LCD (Liquid Crystal Display) 8, DRAM (Dynamic Random Access Memory) 9, interface unit 10, external recording medium 11, CPU 12, operation input unit 13, encoder / decoder 15, strobe device 21 And a non-volatile memory 22.
[0012]
The lens unit 1 includes a zoom, focus, and iris mechanism, a driving circuit thereof, and the like, and the lens unit 1 and the CCD 2 constitute an imaging unit. Control information from the CPU 12 is supplied to the lens unit 1 to perform an automatic iris control operation and an automatic focus control operation. Accordingly, the iris mechanism is opened and closed based on the control information from the CPU 12, and the light quantity of the subject image supplied through the lens is adjusted. A subject image having a predetermined level of light quantity through the lens and iris mechanism is incident on the CCD 2.
[0013]
Although not shown, the CCD 2 has a timing generation circuit and the like, performs exposure for a predetermined time based on control information from the CPU 12, and takes in a subject image supplied via a lens and an iris mechanism as a signal charge. The signal charge output of the CCD 2 is supplied to the sample hold, AGC and A / D converter 3.
[0014]
The output of the CCD 2 is supplied to the sample hold, AGC and A / D converter 3, and a digital image pickup signal of 10 bits per sample is formed in the sample hold, AGC and A / D converter 3. The sample hold, AGC and A / D conversion unit 3 includes a buffer circuit, a CDS (Correlated Double Sampling) circuit, an AGC circuit, an A / D converter, and the like, and forms a digital imaging signal.
[0015]
The camera signal processing unit 4 includes a digital clamp circuit, a luminance signal processing circuit, a color signal processing circuit, a defect compensation circuit, an automatic iris control circuit, an automatic focus control circuit, a white balance adjustment circuit, and the like. In the camera signal processing unit 4, the digital image pickup signal is converted to form a digital image signal in the form of a component signal composed of a luminance signal and a color difference signal, and this digital image signal is supplied to the memory controller 5. Further, a luminance signal level as brightness information of the subject is supplied from the camera signal processing unit 4 to the CPU 12. The brightness information is not limited to the level of the luminance signal, but means the brightness of the subject estimated by combining the amount of light received by the CCD 2, the degree of iris opening, the shutter speed, the AGC control voltage, etc. alone or in combination. To do.
[0016]
FIG. 2 shows an example of the configuration of the main part of the camera signal processing unit. The digital image pickup signal from the sample hold, AGC, and A / D converter 3 described above is supplied to an input terminal 41 shown in FIG. A digital imaging signal is supplied to each of the color signal processing circuit 42 and the luminance signal processing circuit 43 via the input terminal 41.
[0017]
The color signal processing circuit 42 demodulates the three primary color signals (RGB signals) from the digital image pickup signal. The RGB signal demodulated in the color signal processing circuit 42 is supplied to the white balance circuit 45 and also supplied to the CPU 12 through the output terminal 46. A white balance control signal is supplied to the white balance circuit 45 via a terminal 47. The white balance control signal is generated by the CPU 12 using RGB signals. The RGB signal from the white balance circuit 45 is supplied to a matrix conversion circuit (not shown) via the output terminal 48, and a color difference signal is generated.
[0018]
The luminance signal processing circuit 43 includes a contour correction circuit and a level detection circuit. A luminance signal from the luminance signal processing circuit 43 is taken out to the output terminal 49. Further, signal level information is formed in the luminance signal processing circuit 43, and this signal level information is supplied to the CPU 12 via the output terminal 44 as brightness information or part of brightness information.
[0019]
Each component signal of the digital image signal from the camera signal processing unit 4 is supplied to the memory controller 5. A display buffer memory 6 and a bus 14 of the CPU 12 are connected to the memory controller 5. The buffer memory 6 processes the component signal to generate an RGB signal and outputs the RGB signal to the D / A converter 7. An analog signal from the D / A converter 7 is supplied to the LCD 8. Further, the buffer memory 6 outputs RGB signals at a timing that matches the display timing of the LCD 8.
[0020]
In addition, a DRAM 9, a CPU 12, an encoder / decoder 15, an interface unit 10, and a nonvolatile memory 22 are connected to the bus 14. The DRAM 9 is controlled by an address and control information supplied from the memory controller 5 or the CPU 12. Accordingly, a digital image signal supplied via the memory controller 5 is temporarily written in the DRAM 9 when the shutter is pressed. The written digital image signal is read out as necessary and supplied to the encoder / decoder 15 and the like. The nonvolatile memory 22 stores color temperature information of the flash device 21 and white balance control parameters required for white balance control as described later. These pieces of information are read out and supplied to the CPU 12 for white balance control during flash photography.
[0021]
The encoder / decoder 15 compresses (encodes) or expands (decodes) image data based on, for example, JPEG (Joint Photographic Experts Group). Note that this processing may be performed by encoding / decoding processing by software processing of the CPU 12.
[0022]
The interface unit 10 is an interface between the external storage medium 11 and the CPU 12. As the external storage medium, a disk-shaped recording medium such as a floppy disk, a memory card, or the like can be used. Further, an operation signal from the operation input unit 13 is supplied to the CPU 12. The operation input unit 13 includes a shutter button and other various switches operated by the photographer. The operation input unit 13 detects operations of buttons, switches, and the like, and sends the detected signals to the CPU 12 as operation signals.
[0023]
Also, a strobe device 21 is shown in FIG. The strobe device 21 includes a strobe, a strobe discharge circuit, a light emission amount control circuit, and the like, and is configured to emit light in synchronization with the pressing of the shutter button according to control information from the CPU 12. The operation input unit 13 is provided with a switch for setting a shooting mode when the strobe is used. That is, three modes of automatic light emission, forced light emission, and light emission prohibition can be set in association with the strobe device 21. The forced light emission mode is a mode in which the flash is emitted regardless of the brightness of the subject. The automatic light emission mode is a mode in which the strobe light is emitted only when the brightness of the subject is insufficient based on the above-described brightness information such as the signal level information from the camera signal processing unit 4. The light emission prohibition mode is a mode in which the flash is not emitted.
[0024]
The CPU 12 generates a white balance control signal and supplies it to the white balance circuit 45. The present invention can use various known white balance controls. As an example of white balance control, an RGB signal detected as a white portion of an imaging signal is integrated, a ratio (R / G) of an integration value of an R signal and an integration value of a G signal, an integration value of a B signal, and G Considering that the ratio (B / G) of the integral value of the signal is on and near the black body radiation curve 51 shown in FIG. 3, the gain control amplifier provided in the white balance circuit 45 allows the gain of the R signal to be increased. Some control the gain of the B signal.
[0025]
The black body radiation curve 51 shoots a white subject under a light source having a different color temperature, forms an integral value of each color signal of the RGB signal at that time, and calculates the ratio (R / G) and (B / G). As shown by the black body radiation curve 51, when the color temperature is high, in the black body radiation curve 51, B / G is larger than R / G, while when the color temperature is low, black body radiation. In the curve 51, B / G becomes smaller than R / G.
[0026]
The strobe light is bluish, and its color temperature is very high as indicated by 52 in FIG. 3 and is slightly off the black body radiation curve 51. Therefore, during strobe light emission, white balance control is performed so as to decrease the gain of the B signal and increase the gain of the R signal. Further, the video light has a slightly low color temperature of 3200 K ° (Kelvin temperature) as indicated by 53 in FIG. Therefore, when the video light is used, white balance control is performed so that the gain of the G signal is increased and the gain of the R signal is decreased. The CPU 12 generates a white balance control signal for controlling the gains of the B signal and the R signal corresponding to the color temperature of the light source, and supplies the white balance control signal to the terminal 47 of the white balance circuit 45.
[0027]
The white balance control operation when the strobe is used in the embodiment of the present invention will be described with reference to FIG. The vertical axis in FIG. 4 indicates the color temperature, and the horizontal axis indicates the brightness information. As described above, the CPU 12 generates a white balance control signal for the white balance circuit 45 in correspondence with the color temperature.
[0028]
Four ranges X1, X2, X3 and X4 are set by the first, second and third parameters A, B and C (A <B <C) related to the brightness information. When the brightness information is smaller than the first parameter A, that is, in the range X1 where the incident light is small, a white balance control signal is generated corresponding to the color temperature of the strobe device 21 indicated by Ts. Actually, since the strobe device 21 varies in color temperature, the color temperature is measured at the time of assembly, and the measurement result is stored in the nonvolatile memory 22. The parameters A, B, and C are preset and stored in the nonvolatile memory 22. In the range X1 smaller than the parameter A, the strobe light is dominant, and the influence of external light can be ignored. Therefore, the white balance is controlled corresponding to the color temperature Ts of only the strobe light.
[0029]
In the range X2 where the brightness is brighter than the parameter A and smaller than the parameter B, the white balance is controlled along the color temperature change characteristic Tx that changes from the color temperature Ts of the strobe device to the color temperature Ty of the external light. That is, the color temperature on the color temperature change characteristic Tx is determined from the brightness information. Similarly, in the range X3 where the brightness is brighter than the parameter B and smaller than the parameter C, the white balance is similarly controlled along the color temperature change characteristic Tx that changes from the color temperature Ts of the strobe device to the color temperature Ty of the external light. To do. Furthermore, in the range X4 where the brightness is brighter than the parameter C, the white balance is controlled corresponding to the color temperature Ty of the external light. That is, in the range X4, the same auto white balance control as that at the time of shooting without using the strobe is performed.
[0030]
The color temperature change characteristic Tx is obtained when the external light color temperature Ty is lower than the strobe color temperature Ts. On the other hand, if the color temperature Ty ′ of the external light is higher than the color temperature Ts of the strobe, a change characteristic of the color temperature can be obtained as indicated by Tx ′ in FIG.
[0031]
When the operation of the strobe device 21 is in the forced light emission mode, when the brightness information is brighter than the parameter B, the color temperature change characteristic of the strobe and the color temperature Ty of the external light are indicated by the broken line as shown by the broken line. The white balance is controlled corresponding to a predetermined color temperature Tz between the two. When the operation of the strobe device 21 is set to the automatic light emission mode, the white balance is controlled along the color temperature change characteristic Tx indicated by the solid line.
[0032]
The parameter B is set because, in the forced light emission mode, there should be a subject to be photographed in the range irradiated with the strobe light, so the white balance is controlled corresponding to the color temperature close to the color temperature of the strobe light. Because. The parameter C is set in the automatic light emission mode. When the light is bright, the external light is dominant even if the strobe emits light. When the light is brighter than the parameter C, it corresponds to the color temperature of the external light. This is for controlling the white balance.
[0033]
The color temperature change characteristics Tx and Tx ′ described above differ depending on the color temperatures Ty and Ty ′ of the external light even if the color temperature Ts of the strobe device 21 is previously measured and obtained. The color temperatures Ty and Ty ′ of the external light at the time of shooting are obtained by white balance control, and the values of the parameters A, B, and C are preset values, so that the color temperature that connects Ts and Ty or Ty ′ The characteristic Tx or Tx ′ can be obtained by linear approximation.
[0034]
For example, by dividing the ranges X2 and X3 defined by the parameters A and C into N steps at equal intervals and dividing the difference between Ts and Ty by N, the change in color temperature per step can be obtained. Then, the difference between the brightness information at the time of shooting and the parameter A (number of steps) is obtained, the number of steps is multiplied by the change in color temperature per step, and the multiplication result is subtracted from Ts, thereby obtaining the brightness at the time of shooting. The color temperature corresponding to the information is obtained. The color temperature Tz corresponding to the parameter B is similarly calculated. In this case, the difference (number of steps) between the brightness information at the time of shooting and the parameter C may be obtained, the number of steps multiplied by the change in color temperature per step, and the multiplication result may be added to Ty.
[0035]
As shown in FIG. 4, the color temperature at the time of using the strobe is determined in consideration of the influence of external light, and the white balance is controlled in accordance with the determined color temperature. Compared with the white balance control fixed to 1, the white balance can be controlled corresponding to the color temperature close to the actual. Therefore, the white balance of the captured image can be made good. Further, since the white balance can be controlled in accordance with the operation mode (forced light emission mode / automatic light emission mode) of the flash device 21, better white balance control can be performed.
[0036]
FIG. 5 shows a processing procedure of the CPU 12 when performing the above-described white balance control. First, in step S1, it is determined whether or not the operation mode of the flash device 21 is the light emission inhibition mode. If it is in the light emission inhibition mode, the process proceeds to step S6, where the current white balance control signal is processed and the process ends. If it is determined in step S1 that the mode is not the light emission inhibition mode, it is determined in step S2 whether the brightness information is brighter than the parameter A, that is, whether it is the range X1 in FIG.
[0037]
When the brightness information is determined to be smaller than the parameter A (range X1), the strobe light color temperature Ts information stored in the nonvolatile memory 22 is read, and a white balance control signal that matches the color temperature Ts is output. . If the brightness information is determined to be brighter than the parameter A, it is determined whether or not the operation mode of the flash device 21 is set to the automatic light emission mode (step S3).
[0038]
If it is determined in step S3 that the automatic light emission mode is set, it is determined in step S4 whether or not the brightness information is greater than or equal to parameter C, that is, whether or not the range is X4 in FIG. When the brightness information is determined to be equal to or greater than parameter C (range X4), the current white balance control signal is output in step S7, and the process ends. If it is determined in step S4 that the brightness information is not equal to or greater than the parameter C (range X2 or X3), in step S10, the color temperature along the color temperature change characteristic Tx or Tx ′ is determined by the linear approximation described above. A white balance control signal corresponding to the calculated color temperature is output.
[0039]
On the other hand, if it is determined in step S3 that the forced light emission mode is set, it is determined in step S5 whether or not the brightness information is greater than or equal to parameter B (range X3). If so, the brightness information is fixed at parameter B in step S8. In step S10, the color temperature Tz is calculated by the above-described linear approximation, and a white balance control signal corresponding to the color temperature Tz is calculated and output.
[0040]
Note that although one embodiment in which the present invention is applied to a digital camera has been described, the present invention can also be applied to other imaging devices, for example, an imaging device capable of taking a still image, such as a camera-integrated VTR. . Furthermore, the present invention can also be applied to an image pickup apparatus using a solid-state image pickup device other than a CCD, for example, a MOS sensor.
[0041]
【The invention's effect】
According to the present invention, white balance control when using a strobe can be performed in accordance with a color temperature that takes into account the influence of external light. Therefore, white balance can be controlled in accordance with actual shooting conditions. Also, according to the present invention, since the method of white balance control is switched according to the operation mode (forced light emission mode / automatic light emission mode) of the strobe device, even better white balance control can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an embodiment in which the present invention is applied to a digital camera.
FIG. 2 is a block diagram showing a partial configuration of a camera signal processing unit according to an embodiment of the present invention.
FIG. 3 is a schematic diagram for explaining an example of white balance control;
FIG. 4 is a schematic diagram for explaining white balance control when using a strobe in one embodiment of the present invention;
FIG. 5 is a flowchart used for explaining white balance control when using a strobe in one embodiment of the present invention;
[Explanation of symbols]
2 ... CCD, 3 ... sample hold, AGC and A / D converter, 4 ... camera signal processor, 9 ... DRAM, 11 ... external storage medium, 12 ... CPU, DESCRIPTION OF SYMBOLS 13 ... Operation input part, 21 ... Strobe device, 22 ... Nonvolatile memory, 45 ... White balance circuit

Claims (3)

The signal processing, and white balance means for controlling the white balance of the supplied captured image signal,
Selection means for selecting a forced flash mode in which the flash device always emits light as an operation mode of the flash device and an automatic flash mode in which the flash device is flashed in synchronization with the instruction only when the outside light is dark,
With
In the above white balance means,
In the forced flash mode,
The brightness of the subject is compared with the first parameter and / or the second parameter brighter than the first parameter. When the subject brightness is darker than the first parameter, the color temperature of the strobe device The white balance is controlled to correspond to
In the range where the brightness of the subject is brighter than the first parameter and darker than the second parameter, the white balance is controlled according to the color temperature change that changes from the color temperature of the strobe device to the color temperature of the external light. And
In a range where the brightness of the subject is brighter than the second parameter, the white balance is controlled according to a predetermined color temperature between the color temperature of the strobe device and the color temperature of the external light,
In the automatic flash mode,
The brightness of the subject is compared with a third parameter that is brighter than the first parameter and / or the second parameter. When the brightness of the subject is darker than the first parameter, the brightness of the strobe device is Control the white balance to correspond to the color temperature,
In the range where the brightness of the subject is brighter than the first parameter and darker than the third parameter, the white balance is controlled along with the color temperature change that changes from the color temperature of the strobe device to the color temperature of the external light. And
In a range where the brightness of the subject is brighter than the third parameter, the white balance is controlled almost according to the color temperature of the outside light.
Imaging device. The imaging apparatus according to claim 1 , wherein the color temperature of the strobe device is measured in advance, and the measured color temperature information is stored in a nonvolatile memory. The color temperature on the color temperature change that changes from the color temperature of the strobe device to the color temperature of the external light is the color temperature of the strobe device, the color temperature of the external light, and the first, second, and third parameters. The imaging device according to claim 1, wherein the imaging device is calculated by linear approximation.

Images