JP2004274246A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic camera by which an optimal light emission quantity of a stroboscope can be accurately found. <P>SOLUTION: A CCD imager 18 includes a plurality of photodetectors for generating electric charges corresponding to an optical image of a field, and vertical and horizontal transfer registers for transferring the generated charges. A CPU 44 selects a charge transfer mode in which a degree of mixture of charges is low as a distance to an object is short. In relation to the light emission of a stroboscope 50, the charges generated by the CCD imager 18 are read out of the CCD imager 18 according to the selected charge transfer mode. The optimal light emission quantity of the stroboscope 50 is calculated on the basis of thus read charges. The optimal light emission quantity can be accurately calculated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic camera, and more particularly, to an electronic camera that determines an optimal amount of light emission of a strobe based on charges generated by an image sensor in relation to light emission of the strobe.
[0002]
[Prior art]
As a conventional electronic camera of this type, a real-time moving image (through image) of an object scene based on charges generated by an image sensor is displayed on a monitor before a shutter button is operated, and the electronic camera responds to the operation of the shutter button. In some cases, the main light emission amount of the strobe is calculated based on the electric charge generated by the image sensor at the time of the pre-emission of the strobe.
[0003]
[Problems to be solved by the invention]
However, in the related art, the charge generated by the image sensor is the same regardless of whether the through image is output or the main light emission amount is calculated, and further, regardless of the distance to the subject (main subject). The image was output from the image sensor by the transfer method. For this reason, there is a possibility that the main light emission amount cannot be accurately calculated due to charge saturation or variation in the amount of strobe light emission.
[0004]
That is, if the distance to the subject is short, the amount of light emitted from the strobe and reflected by the subject increases, and the charge is saturated in the image sensor. Saturation can be avoided if the light emission amount of the throat is suppressed, but then the light emission amount becomes unstable. Since the calculation of the main light emission amount requires a luminance evaluation value based on the charge obtained in the pre-emission and the pre-emission amount, even if the charge is saturated by the pre-emission or the pre-emission amount becomes unstable, , The calculated main light emission amount deviates from the optimum value.
[0005]
SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an electronic camera capable of accurately determining the optimum light emission amount of a strobe.
[0006]
[Means for Solving the Problems]
An electronic camera according to a first aspect of the present invention provides an image sensor having a plurality of light receiving elements that generate electric charges corresponding to an optical image of an object field and a transfer register that transfers the electric charges. In an electronic camera including a reading unit that reads from an image sensor according to the first transfer method and a display unit that displays an object scene image based on the charge read by the reading unit, a predetermined condition related to strobe light emission is satisfied. Setting means for setting the second transfer method having a lower degree of charge mixing than the first transfer method in the read means instead of the first transfer method; and an image sensor generated by the image sensor when the strobe light is emitted and according to the second transfer method. Calculating means for calculating an optimum flash emission amount based on the charge read from the The features.
[0007]
An electronic camera according to a second aspect of the present invention provides an image sensor having a plurality of light receiving elements for generating electric charges corresponding to an optical image of an object field and a transfer register for transferring electric charges. Means for selecting a low charge transfer method, first light emitting means for emitting a strobe light, and an image sensor in accordance with the charge transfer method selected by the selection means for generating charges generated by the image sensor in connection with light emission of the first light emitting means. And a calculating unit for calculating an optimal flash emission amount based on the charge read by the reading unit.
[0008]
[Action]
In the first aspect, the image sensor includes a plurality of light receiving elements that generate electric charges corresponding to the optical image of the object scene, and a transfer register that transfers the electric charges. The charge generated by the exposure of the image sensor is read out from the image sensor according to the first transfer method, and a field image based on the read charge is displayed. However, when a predetermined condition relating to the light emission of the strobe is satisfied, the second transfer method having a lower charge mixing degree than the first transfer method is set instead of the first transfer method. The optimum flash emission amount is calculated based on the electric charge generated by the image sensor at the time of flash emission and read from the image sensor according to the second transfer method.
[0009]
When the strobe light is emitted, the electric charges are more likely to be saturated than when the strobe light is not emitted. Therefore, in the present invention, the second transfer method having a low charge mixing degree is set when a predetermined condition relating to the light emission of the strobe is satisfied. As a result, the possibility of charge saturation during transfer is reduced, and accurate calculation of the optimal light emission amount becomes possible.
[0010]
Preferably, the predetermined condition includes a light emission condition that a strobe needs to be fired and a distance condition that a distance to a subject is smaller than a threshold. When irradiating a nearby object with the slot light, the possibility of charge saturation increases. In such a case, by setting the second transfer method, the effect of the present invention is remarkably exhibited.
[0011]
Preferably, the strobe emits light at the minimum light emission amount at which the light emission amount is stable in calculating the optimum light emission amount. As a result, it is possible to prevent the calculation accuracy of the optimum light emission amount from being lowered due to the variation in the light emission amount.
[0012]
Preferably, when a charge is generated in the image sensor in association with the strobe light emission at the optimum light emission amount, an image signal based on the charge is recorded on a recording medium. Thereby, the quality of the recorded image can be improved.
[0013]
In the second aspect, the image sensor has a plurality of light receiving elements that generate electric charges corresponding to the optical image of the object scene, and a transfer register that transfers the generated electric charges. As the charge transfer method, a charge transfer method in which the degree of charge mixture is lower as the distance to the subject is shorter is selected. The charge generated by the image sensor in connection with the strobe light emission is read from the image sensor according to the selected charge transfer method. The optimum light emission amount of the strobe is calculated based on the read charges.
[0014]
As the distance to the subject becomes shorter, the amount of light emitted from the strobe and reflected by the subject increases, and the electric charge is more likely to be saturated. Therefore, in the present invention, the degree of charge mixture is changed according to the distance to the subject. As a result, the possibility of charge saturation during transfer is reduced, and accurate calculation of the optimal light emission amount becomes possible.
[0015]
Preferably, when the distance to the subject is greater than or equal to the threshold, the first transfer method having the first degree of mixture is selected, and when the distance to the subject is less than the threshold, the second number of transfer methods having the degree of mixture smaller than the first number is selected. Is selected.
[0016]
When the second transfer method is selected, the strobe emits light with the minimum light emission amount at which the light emission amount is stabilized. As a result, it is possible to prevent the calculation accuracy of the optimum light emission amount from being lowered due to the variation in the light emission amount.
[0017]
If the exposure time of the image sensor is adjusted to include the strobe light emission time, the calculation accuracy is further improved.
[0018]
Preferably, when a charge is generated in the image sensor in association with the strobe light emission at the optimum light emission amount, an image signal based on the charge is recorded on a recording medium. Thereby, the quality of the recorded image can be improved.
[0019]
【The invention's effect】
According to the first aspect, since the second transfer method having a low charge mixing degree is set when a predetermined condition related to light emission of the strobe is satisfied, the possibility of charge saturation during transfer is reduced. Thereby, it is possible to accurately calculate the optimum light emission amount.
[0020]
According to the second aspect, the degree of charge mixture is changed according to the distance to the subject, so that the possibility of charge saturation during transfer is reduced. As a result, the optimum light emission amount can be accurately calculated.
[0021]
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.
[0022]
【Example】
Referring to FIG. 1, a digital camera 10 of this embodiment includes a CCD imager 18 of an interline transfer system. The light receiving surface of the CCD imager 18 is covered with the color filter 14, and the optical image of the object scene is irradiated on the light receiving surface of the CCD imager 18 via the aperture unit 12 and the color filter 14.
[0023]
With reference to FIG. 2, the color filter 14 is a primary color filter in which a red color element (R element), a green color element (G element), and a blue color element (B element) are arranged in a mosaic pattern. In the vertical direction, RG lines in which R elements and G elements are alternately arranged in the horizontal direction, and GB lines in which G elements and B elements are alternately arranged in the horizontal direction are alternately arranged. These color elements correspond one-to-one to the light receiving elements 18a, ie, pixels, formed on the light receiving surface of the CCD imager 18, as shown in FIG. 5 (A), FIG. 6 (A) or FIG. 7 (A). The charge generated by photoelectric conversion in the light receiving element 18a, that is, a pixel signal, has R, G, or B color information.
[0024]
When the camera mode is selected to display a through image of the object scene on the LCD monitor 38, the CPU 44 controls the driver 16 to set the aperture amount Ap in the aperture unit 14, and sets the pre-exposure time Ep (= initial value). ) And the HVpmix mode are set to TG (Timing Generator) 24, and the ASIC 25 is instructed to execute a through image display process.
[0025]
Each time the vertical synchronization signal is generated, the TG 24 performs a pre-exposure on the CCD imager 18 according to the pre-exposure time Ep, and reads out the charges generated by the pre-exposure from the CCD imager 18 according to the HVpmix mode. In the HVpmix mode, pixels indicated by oblique lines in FIG. 5A are to be read, and electric charges generated by the pixels are read from the CCD imager 18 in the manner shown in FIGS. 5B to 5F.
[0026]
Referring to FIG. 5A, two RG lines are read lines in three consecutive lines in the vertical direction, that is, RG line → GB line → RG line in the order of RG line → GB line → RG line, and GB line → RG line → GB line. , Two GB lines are read-out lines in three lines that are continuous in the vertical direction in the order of, that is, the belt B2.
[0027]
Assuming that each of the belts B1 and B2 is a set of a matrix MT of 3 vertical lines × 2 horizontal pixels, first, the charges generated in the even-numbered matrices MT of the belt B1 are read out at the timing shown in FIG. Then, the charges having the same color information are mixed in the vertical transfer register 18b. The mixed charges are transferred in the horizontal direction by the horizontal transfer register 18c as shown in FIG. 5C, and at the timing shown in FIG. 5D with the charges read from the odd-numbered matrices MT of the belt B1. Mixed. In this way, charges for four pixels having the same color information are combined into one.
[0028]
The charges generated in the even-numbered matrices MT of the belt B2 are read out at the timing shown in FIG. 5D, and mixed with each other in the vertical transfer register 18b between charges having the same color information. The mixed charges are transferred in the horizontal direction by the horizontal transfer register 18c as shown in FIG. 5E, and mixed with the charges read from the odd-numbered matrices MT of the belt B2 at the timing shown in FIG. Is done. Therefore, also for the belt B2, charges for four pixels having the same color information are combined into one.
[0029]
That is, the HVpmix mode is a mode in which two charges existing in the horizontal direction and two charges existing in the vertical direction are mixed with each other, and the degree of charge mixture is “4”.
[0030]
The low-resolution raw image signal of each frame output from the CCD imager 18 is subjected to noise removal and level adjustment by the CDS / AGC circuit 20, and is converted into digital data (low-resolution raw image data) by the A / D converter 22. Is converted. When displaying a through image on the monitor 38, the switch SW1 is connected to the terminal S1. Therefore, the low-resolution raw image data output from the A / D converter 22 is provided to the signal processing circuit 26 via the switch SW1, and is converted into low-resolution YUV data by signal processing corresponding to live image display. The low-resolution YUV data output from the signal processing circuit 26 is provided to a buffer control circuit 32 through a reduction zoom process by a zoom circuit 28.
[0031]
Referring to FIG. 4, buffer control circuit 32 includes controllers 321a to 321f to which buffers 322a to 322f for temporarily storing data are individually assigned. Data writing to the SDRAM 36 is performed by the controllers 321a to 321c, and data reading from the SDRAM 36 is performed by the controllers 321d to 321f.
[0032]
The low-resolution YUV data output from the zoom circuit 28 shown in FIG. 1 is provided to the SDRAM control circuit 34 via the controller 321a and the buffer 322a. The SDRAM 36 is mapped in the manner shown in FIG. 3, and the SDRAM control circuit 34 writes the applied low-resolution YUV data to the display image area 36a.
[0033]
The low-resolution YUV data stored in the display image area 36a is read by the SDRAM control circuit 34 and output to the video encoder 38 via the controller 321e and the buffer 322e. The video encoder 38 converts the low-resolution YUV data into a composite image signal, and supplies the converted composite image signal to the LCD monitor 40. As a result, a through image is displayed on the monitor screen.
[0034]
The luminance evaluation circuit 30 integrates the Y data output from the signal processing circuit 26 for each frame period, and provides the CPU 44 with the luminance evaluation value obtained thereby. The CPU 44 updates the pre-exposure time Ep based on the given luminance evaluation value. Thereby, the brightness of the through image output from the LCD monitor 40 is adjusted.
[0035]
When the shutter button 46 is half-pressed, the CPU 44 updates the pre-exposure time Ep to a photometric time in order to accurately measure the brightness of the object scene. It takes two frame periods to execute the pre-exposure according to the updated pre-exposure time Ep and read out the charges based on the pre-exposure. Therefore, the CPU 44 fetches the luminance evaluation value from the luminance evaluation value 30 after counting the vertical synchronization signal twice, and calculates the optimal aperture amount As and the optimal exposure time Es based on the fetched luminance evaluation value. When the calculation is completed, first, the optimum aperture amount As is set in the aperture unit 12. Subsequently, the CPU 44 determines whether or not the strobe 50 needs to emit light, and measures the distance to the subject.
[0036]
When the object scene is dark and the result of the determination that the strobe 50 needs to emit light is obtained, the CPU 44 causes the strobe 50 to pre-emit in response to the full depression of the shutter button 46, and evaluates the brightness based on the pre-emission. The main light emission amount Lm is calculated by performing a predetermined calculation on the value.
[0037]
However, if the distance to the subject is short, the amount of light emitted from the strobe 50 and reflected by the subject by pre-emission increases, and the CCD imager 18 saturates the charge. If the light emission amount of the throat 50 is suppressed, the saturation of the electric charge can be avoided, but the light emission amount becomes unstable. Since the calculation of the main light emission amount requires a luminance evaluation value based on the charge obtained in the pre-light emission and the pre-light emission amount, the calculation is performed even if the charge is saturated or the pre-light emission amount becomes unstable. The main light emission amount deviates from the optimum value.
[0038]
Therefore, in this embodiment, the lower limit of the pre-emission amount is set, and the degree of mixture of electric charges generated by the CCD imager 18 decreases as the distance to the subject decreases.
[0039]
More specifically, if the distance d to the subject exceeds the threshold value TH, it is considered that the electric charge will not be saturated, and the pre-light emission amount Lp is calculated according to Equation 1.
[0040]
(Equation 1)
Lp = MIN * d²
On the other hand, when the distance d to the subject is equal to or less than the threshold value TH, the pre-light emission amount Lp is set to the minimum stable value MIN shown in FIG. The charge transfer mode is changed from the HVpmix mode to the Vpmix mode as needed.
[0041]
Further, the pre-emission time Tp corresponding to the set pre-emission amount Lp is detected with reference to the graph shown in FIG. 8, and the pre-exposure time Ep is updated so that the detected pre-emission time Tp is included. Note that data corresponding to the graph shown in FIG. 8 is stored in the flash memory 52.
[0042]
In the Vpmix mode, pixels indicated by oblique lines in FIG. 6A are to be read, and the charges generated by the pixels are read from the CCD imager 18 in the manner shown in FIGS. 6B to 6E.
[0043]
First, the charge generated on the lower RG line of the belt B1 shown in FIG. 6A is read out to the vertical transfer register 18b and transferred to the horizontal transfer register 18c as shown in FIG. 6B. Next, the charges generated in the upper RG line of the belt B1 are read out to the vertical transfer register 18b and transferred to the horizontal transfer register 18c. The charges are mixed between charges having the same color information as shown in FIG. When the output of the mixed charges is completed, the charges generated on the lower RG line of the belt B2 are read out to the vertical transfer register 18b and transferred to the horizontal transfer register 18c as shown in FIG. Subsequently, the charges generated on the upper RG line of the belt B2 are read out to the vertical transfer register 18b and transferred to the horizontal transfer register 18c. As shown in FIG. 6D, the charges are mixed by charges having the same color information and then output. As described above, in the Vpmix mode, charges of two pixels having the same color information are combined into one.
[0044]
That is, the Vpmix mode is a mode in which two charges existing in the vertical direction are mixed with each other, and the degree of charge mixture is “2”.
[0045]
When the charge transfer mode, the pre-light emission amount Lp, and the pre-exposure period Ep are determined, the CPU 44 causes the strobe 50 to pre-emit in response to the generation of the vertical synchronization signal, and outputs the luminance evaluation value based on the pre-emission to the next vertical synchronization signal The main light emission amount Lm is calculated based on the taken luminance evaluation value. The CPU 44 further sets the optimal exposure time Es to TG24, and makes the strobe 50 emit main light in the next frame. As a result, the CCD imager 18 is subjected to the main exposure in an optimal state.
[0046]
The CPU 44 changes the charge transfer mode of the CCD imager 18 to the individual transfer mode in response to the vertical synchronization signal immediately after the main exposure is completed, and instructs the ASIC 25 to perform a recording process.
[0047]
In the individual transfer mode, as shown in FIG. 7A, all pixels are to be read. The TG 24 reads the charge of the RG line shown in FIG. 7B in the first field, and reads the charge of the GB line shown in FIG. 7C in the second field.
[0048]
The one-frame high-resolution raw image signal output from the CCD imager 18 passes through the CDS / AGC circuit 20 and is converted into high-resolution raw image data by the A / D converter 22. The converted high-resolution raw image data is directly input to the buffer control circuit 32 and supplied to the SDRAM control circuit 34 via the controller 321b and the buffer 322b. The high-resolution raw image data is written by the SDRAM control circuit 34 into the raw image area 36b shown in FIG.
[0049]
Note that while one frame of high-resolution raw image data is taken into the raw image area 36b after the shutter button 46 is operated, the video encoder 38 is turned off, and a black image is displayed on the LCD monitor 40.
[0050]
The high-resolution raw image data stored in the raw image area 36b is read by the SDRAM control circuit 34. The raw image data of the odd field and the high-resolution raw image data of the even field are alternately read line by line, whereby the interlaced scan data is converted into progressive scan data. The converted high-resolution raw image data is output to the terminal S2 shown in FIG. 1 via the controller 321f and the buffer 322f.
[0051]
The switch SW1 is connected to the terminal S2 in response to the recording command, and the high-resolution raw image data output from the controller 321f is provided to the signal processing circuit 26 via the switch SW1. The signal processing circuit 26 performs signal processing corresponding to image recording on the given high-resolution raw image data, thereby generating high-resolution YUV data. The generated high-resolution YUV data is provided to the zoom circuit 28, and is converted into low-resolution YUV data for display by a reduction zoom process.
[0052]
The converted low-resolution YUV data is provided to the SDRAM control circuit 34 via the controller 321a and the buffer 322a shown in FIG. 4, and is written into the display image area 36a of the SDRAM 36 by the SDRAM control circuit 34. The low-resolution YUV data stored in the display image area 36a is provided to the video encoder 38 by the same processing as when outputting a through image. As a result, a freeze image of the subject is displayed on the LCD monitor 40.
[0053]
When the writing of the low-resolution YUV data corresponding to the frozen image into the display image area 36a is completed, the high-resolution raw image data stored in the raw image area 36b is read out again by the SDRAM control circuit 34. Also at this time, the high-resolution raw image data of the odd field and the high-resolution raw image data of the even field are alternately read for each line. The read high-resolution raw image data is supplied to the signal processing circuit 26 in the same manner as described above, and is converted into high-resolution YUV data.
[0054]
The horizontal zoom magnification and the vertical zoom magnification of the zoom circuit 28 are initialized after low-resolution YUV data corresponding to a frozen image is obtained. Therefore, the high-resolution YUV data is output from the zoom circuit 26 without being subjected to zoom processing.
[0055]
The output high-resolution YUV data is provided to the SDRAM control circuit 34 through the controller 321a and the buffer 322a shown in FIG. 4, and is written by the SDRAM control circuit 36 into the JPEG work area 36c shown in FIG. The high-resolution YUV data stored in the JPEG work area 36c is thereafter read by the SDRAM control circuit 34, and applied to the JPEG codec 42 via the controller 321d and the buffer 322d shown in FIG. The JPEG codec 42 performs JPEG compression on the given high-resolution YUV data to generate JPEG data. The generated JPEG data is provided to the SDRAM control circuit 34 via the controller 321c and the buffer 322c shown in FIG. 4, and is written into the compressed image area 36d shown in FIG. 3 by the SDRAM control circuit 34.
[0056]
After the JPEG data is secured in the compressed image area 36d, the CPU 44 accesses the SDRAM 36 through the SDRAM control circuit 34 and reads the JPEG data from the compressed image area 36d. Further, the CPU 44 creates an image file including the read JPEG data, that is, a JPEG file, and records the created JPEG file on the recording medium 48.
[0057]
When the camera mode is selected, the CPU 44 executes processing according to the flowcharts shown in FIGS. The control program corresponding to this flowchart is stored in the flash memory 52.
[0058]
First, the aperture amount Ap is set to the aperture unit 12 in step S1, the pre-exposure time Ep (= initial value) is set to TG24 in step S3, and the HVpmix mode is set to TG24 in step S5. When the setting of the aperture unit 12 and the TG 24 is completed, the ASIC 25 is instructed to perform through image processing in step S7. As a result, a through image is output from the LCD monitor 40. In step S9, it is determined whether or not the shutter button 46 has been half-pressed. If NO, the monitoring AF process is repeatedly executed in step S11. Thereby, the luminance of the through image is appropriately adjusted.
[0059]
When the shutter button 46 is half-pressed, the process proceeds to step S13, and the pre-exposure period Ep set in the TG 24 is updated to a photometric period. When the vertical synchronization signal is generated twice after the update, the process proceeds from step S15 to step S17, and the luminance evaluation value is fetched from the luminance evaluation circuit 30. The captured luminance evaluation value is an evaluation value based on the pre-exposure for photometry. In step S19, the optimum aperture amount As and the optimum exposure time Es are calculated based on the luminance evaluation value.
[0060]
When the calculation is completed, the optimum aperture amount As is set in the aperture unit 12 in step S21. Further, it is determined in step S23 whether or not the strobe 50 needs to emit light, and the distance d to the subject is measured in step S25.
[0061]
In steps S27 and S29, the operation state of the shutter button 46 is determined. When the half-press of the shutter button 46 is released, the process proceeds from step S29 to step S31, and the pre-exposure period Ep set in the TG 24 is initialized. In step S33, the aperture amount Ap is set in the aperture unit 12, and when the setting is completed, the process returns to step S9.
[0062]
When the shutter button 46 has shifted from the half-pressed state to the fully-pressed state, the process proceeds from step S27 to step S35, and the determination result of step S23 is referred to. If the determination result is "light emission unnecessary", the process directly proceeds to step S59. If the determination result is "light emission required", the process proceeds to step S59 via the processes of steps S37 to S57.
[0063]
First, in step S37, the distance d to the subject is compared with a threshold value TH. If it is determined that d ≧ TH, the pre-light emission amount Lp is calculated in accordance with Equation 1 in step S39. On the other hand, if it is determined that d <TH, the pre-flash amount Lp of the strobe 50 is determined to be the minimum stable value MIN in step S41, and the Vpmix mode is set to TG24 in step S43. Upon completion of the process in the step S39 or S43, the process proceeds to a step S45 to detect the pre-emission time Tp at which the pre-emission amount Lp is obtained based on the graph shown in FIG. In step S47, the pre-exposure time Ep set in the TG 24 is updated to the shortest period that includes the pre-emission time Tp.
[0064]
When the charge transfer mode, the pre-light emission amount Lp, and the pre-exposure period Ep are determined in this way, the generation of a vertical synchronization signal is waited in step S49, and the start of pre-exposure is waited in step S50. When the pre-exposure is started, the flash 50 is caused to emit light in the pre-emission amount Lp in step S51. Since the luminance evaluation value based on the pre-emission is obtained in the frame next to the pre-emission, after waiting for the generation of the vertical synchronization signal in step S53, the luminance evaluation value is fetched from the luminance evaluation circuit 30 in step S55. In step S57, the main light emission amount Lm is calculated based on the acquired luminance evaluation value.
[0065]
In step S59, the optimum exposure period Es calculated in step S19 is set to TG24, and thereafter, the process proceeds from step S61 to step S63 in response to the generation of the vertical synchronization signal. In step S63, the determination result regarding the light emission of the strobe 50 is referred to. If the result of the determination is "light emission unnecessary", the process directly proceeds to step S67. However, if the result of the determination is "light emission required", the start of the main exposure is waited for in step S64, and then the strobe 50 is set to the main light emission amount Lm in step S65. The light is emitted, and the process proceeds to step S67. By the light emission processing in step S65, the main exposure is performed on the CCD imager 18 in an optimum state.
[0066]
In step S67, it is determined whether or not a vertical synchronizing signal has been generated. If YES, the individual transfer mode is set to TG24 in step S69, and a recording process is instructed to the ASIC 25 in step S71. The charge generated by the main exposure, that is, the raw image signal is output from the CCD imager 18 according to the individual transfer mode, and is subjected to a recording process by the ASIC 25. As a result, the freeze image is displayed on the LCD monitor 40, and the JPEG file is recorded on the recording medium 48. When the recording process is completed, “YES” is determined in the step S73, and the process returns to the step S1.
[0067]
As can be understood from the above description, the CCD imager 18 includes a plurality of light receiving elements 18a that generate electric charges corresponding to the optical image of the object scene, a vertical transfer register 18b and a horizontal transfer register 18c that transfer the generated electric charges. Having. When a through image is output, the charge transfer mode in which the charge mixture is high is selected. However, when the strobe 50 is pre-emitted, the charge transfer mode in which the charge mixture is low as the distance to the subject is short is selected. .
[0068]
Specifically, when outputting a through image, the HVpmix mode in which the degree of mixture is “4” is selected. When pre-flashing the strobe 50, the HVpmix mode is maintained if the distance d to the subject is equal to or greater than the threshold TH, and the Vpmix mode with a mixing degree of "2" is selected if the distance d to the subject is less than the threshold TH. Is done.
[0069]
The pre-light emission amount Lp of the strobe 50 is determined in a manner according to the selected charge transfer mode. That is, when the HVpmix mode is selected, the pre-light emission amount Lp of the strobe 50 is determined according to Expression 1, and when the Vpmix mode is selected, the pre-light emission amount Lp of the strobe 50 is determined to the minimum stable value MIN.
[0070]
The charges generated by the CCD imager 18 in connection with the pre-emission of the strobe 50 are read out from the CCD imager 18 according to the selected charge transfer mode. The main light emission amount Lm of the strobe 50 is calculated based on the charges thus read.
[0071]
As described above, when the strobe 50 needs to emit light and the distance to the subject is short, the strobe 50 pre-emits light at the minimum stable value MIN, and the charge generated by the pre-emission is transferred in the Vpmix mode. Therefore, the saturation of the charge and the variation of the pre-light emission amount Lp are prevented, and the accurate calculation of the main light emission amount Lm can be performed.
[0072]
In this embodiment, the charge is mixed only in the vertical direction when the distance to the subject is short, but the charge may be completely stopped instead. In this case, the mixing degree is “1”.
[Brief description of the drawings]
FIG. 1 is a block diagram showing one embodiment of the present invention.
FIG. 2 is an illustrative view showing one example of a color filter applied to the embodiment in FIG. 1;
FIG. 3 is an illustrative view showing one example of a mapping state of an SDRAM applied to the embodiment in FIG. 1;
FIG. 4 is a block diagram illustrating an example of a buffer control circuit applied to the embodiment in FIG. 1;
FIG. 5 is a timing chart showing a part of the operation of the CCD imager when reading charges in the HVpmix mode.
FIG. 6 is a timing chart showing a part of the operation of the CCD imager when reading out electric charges in the Vpmix mode.
FIG. 7 is a timing chart showing a part of the operation of the CCD imager when reading out electric charges in the individual transfer mode.
FIG. 8 is a graph showing a relationship between a flash emission time and a light emission amount.
FIG. 9 is a flowchart showing a part of the operation of the embodiment in FIG. 1;
FIG. 10 is a flowchart showing another portion of the operation of the embodiment in FIG. 1;
FIG. 11 is a flowchart showing another portion of the operation of the embodiment in FIG. 1;
FIG. 12 is a flowchart showing yet another portion of the operation of the embodiment in FIG. 1;
[Explanation of symbols]
10 ... Digital camera
18 ... CCD imager
26 ... Signal processing circuit
30 ... Brightness evaluation circuit
32 ... Buffer control circuit
38 Video encoder
42 ... JPEG codec
44 ... CPU
50 ... Strobe

Claims (9)

An image sensor having a plurality of light receiving elements that generate electric charges corresponding to an optical image of the object field and a transfer register that transfers the electric charges,
An electronic camera, comprising: reading means for reading out the charge generated by exposure of the image sensor from the image sensor according to a first transfer method; and display means for displaying a field image based on the charge read by the reading means. ,
Setting means for setting a second transfer method having a lower charge mixing degree than the first transfer method in the reading means when a predetermined condition relating to the light emission of the strobe is satisfied, and the strobe An electronic camera, further comprising: calculating means for calculating an optimal light emission amount of the strobe based on charges generated by the image sensor at the time of light emission and read from the image sensor according to the second transfer method. . The electronic camera according to claim 1, wherein the predetermined condition includes a light emission condition that the strobe needs to emit light and a distance condition that a distance to a subject is smaller than a threshold. 3. The electronic camera according to claim 1, wherein the strobe emits light at a minimum light emission amount at which the light emission amount is stabilized in calculating the optimum light emission amount. 4. The electronic camera according to claim 1, further comprising a recording unit configured to record an image signal based on a charge generated by the image sensor in association with light emission of the strobe according to the optimal light emission amount on a recording medium. 5. . An image sensor having a plurality of light receiving elements that generate electric charges corresponding to an optical image of the object field and a transfer register that transfers the electric charges,
Selection means for selecting a charge transfer method in which the charge mixture degree is lower as the distance to the subject is shorter,
First light emitting means for emitting a strobe light,
Reading means for reading the charge generated by the image sensor in association with the light emission of the first light emitting means from the image sensor according to the charge transfer method selected by the selection means; and reading the charge read by the reading means. An electronic camera, comprising: a calculation unit configured to calculate an optimal light emission amount of the strobe based on the electronic camera. The selecting means selects the first transfer method having the first degree of mixture when the distance to the subject is equal to or greater than a threshold value, and selects the first degree of transfer when the distance to the subject is less than the threshold value. 6. The electronic camera according to claim 5, wherein a second number of second transfer methods smaller than the second transfer method is selected. 7. The electronic camera according to claim 6, wherein the first light emitting means emits the strobe light at a minimum light emission amount at which the light emission amount is stabilized when the second transfer method is selected by the selection means. 8. The electronic camera according to claim 5, further comprising an adjusting unit that adjusts an exposure time of the image sensor so as to include a time when the strobe emits light by the first light emitting unit. 9. A second light emitting unit that emits the strobe light at the optimal light emission amount; and a recording unit that records an image signal based on a charge generated by the image sensor in association with light emission of the second light emitting unit on a recording medium. An electronic camera according to any one of claims 5 to 8.

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