JP4884887B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus using strobe light emission as subject illumination means.

  As a subject illumination means in an imaging device such as a camera, a strobe device is generally used. The strobe device includes a flashmatic method (hereinafter referred to as FM method) and an automatic light control method using a light receiving sensor.

  The FM method is a method in which the amount of light emission is determined in advance from distance information, and is not easily affected by the reflectance of the subject, but is greatly affected by a distance measurement error at a long distance, so it is not suitable for light control at a long distance. On the other hand, the automatic light control method is a method in which light emission is stopped by the integrated amount of reflected light after light emission, and light control can be performed regardless of the distance, but it is greatly affected by the reflectance of the subject. The automatic light control method is disclosed in, for example, Patent Document 1.

From the above, conventionally, it has been difficult to optimally cope from a short distance to a long distance.
If the device has a subject distance measurement function, a flash system suitable for various shooting environments can be realized by combining both the FM method and the automatic light control method.

Patent Document 2 discloses an invention that attempts to cope with a short distance to a long distance by switching between the FM method and the automatic light control method according to the distance measurement data and the focal length.
However, in the invention described in Patent Document 2, there is a problem that complicated control is required to control the two systems, and the point of preventing the influence of subject reflectance in the automatic light control system is not taken into consideration. There is also a problem.
JP-A-3-287149 Japanese Patent Laid-Open No. 3-149535

  The present invention has been made in view of the above circumstances, and is an imaging apparatus that includes a means for obtaining distance information indicating a distance to a subject and an automatic dimming strobe means, from a short distance to a long distance. It is an object of the present invention to provide an imaging apparatus that can cope with the above-described shooting and that is less susceptible to the influence of subject reflectance by comparing the scheduled illumination amount of the preliminary illumination with the actual illumination amount.

To achieve the above object, the present invention provides, in a first aspect, an imaging means for electrically imaging optical means for focusing an optical image of an object, the optical image formed by said optical means, said a distance detecting means for obtaining distance information indicating a distance between the subject and the lighting means for performing lighting for the object, light receiving means for receiving reflected light from the subject illuminated by the illuminating means, from said light receiving means depending on the light reception signal, an automatic illumination stop means for stopping the illumination by said illuminating means, and a control means for controlling said each means, said illuminating a subject prior to the photography, imaging of the subject an imaging apparatus for performing preliminary illumination to obtain data, further, based on the distance information acquired by the distance detecting means, and expected illumination amount determining means for previously determining the expected illumination amount, the An illumination amount comparison means for comparing the actual illumination amount from the start of illumination to the stop of illumination at the time of preparation illumination and the scheduled illumination amount determined in advance by the scheduled illumination amount determination unit, and the illumination amount comparison unit Based on the result of comparison, the reflectance of the subject is estimated, and when it is determined that the estimated reflectance of the subject is high, the automatic light control stop amount set in the automatic illumination stop means at the time of the main photographing Is set higher than the set value during preliminary illumination, and if it is determined that the estimated reflectance of the subject is low, the automatic dimming stop amount set in the automatic illumination stop means during the main photographing is set as the preliminary illumination. Provided is an imaging device characterized in that it is set lower than the set value at the time .

  According to the present invention, it is possible to perform dimming from a short distance to a long distance using only the automatic dimming method, and it is possible to perform dimming corresponding to the reflectance of the subject at short and medium distances. Become. Therefore, it is possible to cope with shooting from a short distance to a long distance without requiring complicated control for controlling the two systems as in the prior art, and it is possible to make the influence of the subject reflectivity difficult.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus (camera) according to the present exemplary embodiment. As shown in FIG. 1, the imaging apparatus of the present embodiment includes a lens 1, a mechanical shutter 2, a CCD (Charge Coupled Device) 3, a CCD signal, a CDS (Correlated Double Sampling) and CDS-A / D unit 4 for A / D (Analog / Digital) conversion, A / D converted digital signal is converted to luminance Y, color difference U, V signal, and the YUV data is JPEG compressed A driver for driving a digital signal processor (DSP) unit 5 for performing digital signal processing, a mechanical unit (lens 1, mechanical shutter 2), and a focus driving unit for driving the lens 1 (including a lens position detecting unit). And a mechanical driving unit 6 having a shutter opening / closing operation unit of the mechanical shutter 2, a CCD driving circuit unit 7 for driving the CCD 3, and a control unit for controlling the entire imaging apparatus. A central processing unit (CPU) 8, a captured image data, and read data from a file are held for a period of time, and a DSP 9 and a memory 9 used as a work memory for the CPU 8 are communicated with the outside of the imaging apparatus. Communication unit 10, a memory card 11 that can be attached to and detached from the imaging device, a display controller that converts a video output signal from the DSP unit 5 into a signal that can be displayed on an LCD (Liquid Crystal Display), and an LCD that actually displays it The display unit 12, the SW (switch) unit 13 for the user who uses the imaging apparatus to perform each operation, the AF (autofocus) unit 14 using the triangulation method, and the flash whose emission start / stop is controlled by the CPU 8. A light emitting unit 15, a main capacitor 16 for strobe light emission (the charge voltage can be detected from the CPU 8), a light receiving optical system, And a strobe light receiving unit 17 including a sensor (a light emission stop signal is sent to the strobe issuing unit 15 when the amount of light received after the start of light reception from the CPU 8 reaches a set value from the CPU 8). .

  FIG. 2 is a program configuration diagram, and the imaging apparatus of the present embodiment executes a main process and a parallel process that is performed in parallel with the main process. The main processing includes SW determination processing, AE (automatic exposure) processing, AF (autofocus) processing, pre-flash processing, light emission amount comparison, main light emission shift processing, and still image recording processing. The parallel processing includes periodic timer interrupt processing and monitoring processing. This parallel processing is started by periodic timer interrupt processing, and reads the state of the SW unit 13 and the like. Each of the above processes is performed at the timing shown in the timing chart of FIG.

  FIG. 3 is a main processing flow during image recording. The image pickup apparatus of the present embodiment can record a moving image and a still image, but the description here is a recording of a still image.

  First, when the camera power is turned on in the recording mode, although not shown, initial processing such as initialization of hardware inside the camera and creation of file information in the card in the memory 9 is performed. Thereafter, the main process during recording shown in FIG. 3 is started.

  In the main process, first, the monitoring state is checked (step S1). If the monitoring state is ON (step S1 / ON), the process proceeds to step S5. If the monitoring state is a stop state (step S1 / stop state), a monitoring start process is performed (step S2). This monitoring start process starts driving of the CCD 3 as the image pickup means and starts a monitoring process (see FIG. 2) of the parallel process. Note that this monitoring start process is also executed when the main process is entered first.

  After the monitoring start process, the CPU 8 checks the charging voltage Vm of the main capacitor 16 (step S3). If the charging voltage Vm is high (step S3 / high), the process proceeds to step S5. If the charging voltage Vm is low (step S3 / low), charging is performed (step S4), and then the process proceeds to step S5.

  The monitoring process in the parallel process shown in FIG. 2 is to execute AE and AWB (auto white balance) tracking processing when displaying a through image of the camera, thereby displaying on the camera display device. The image can always be kept at appropriate brightness and natural color. Specifically, the CPU 8 acquires evaluation values for each AE and AWB, which are evaluated based on the data of the CCD 3 in the DSP unit 5 which is a digital image processing unit, and drives the CCD so that the values become predetermined values. An exposure time is set in the circuit unit 7, and an amplification factor in the CCD 3 of the image pickup signal is set, or an image processing color parameter of the DSP unit 5 is adjusted.

  The parallel processing of the above-described monitoring processing and the above-described SW section state reading processing is executed by a 20 ms periodic timer interrupt.

  In step S5 of FIG. 3, the SW determination process of the main process determines the SW information input in the above-described periodic timer interrupt process every 20 ms, and performs a process corresponding to the operated SW. If there is no valid SW information (step S5 / invalid operation), the loop is repeated to return to the SW determination process of step S5 without performing any process.

  The SW unit 13 shown in FIG. 1 includes a shutter button. During still image shooting, when the first switch of the shutter button (hereinafter abbreviated as SW) is turned on (step S5 / first SW on process), monitoring is stopped (step S6), and image data is captured by AE processing. Is evaluated by the DSP unit 5, and the exposure time value of the CCD and the amplification factor of the CCD 3 set in the CCD driving circuit unit 7 at the time of photographing exposure are determined (step S7).

  If it is determined in step AE processing AE that low brightness is determined and strobe light emission is required, then AF processing is performed (step S8).

  The distance measurement (measurement of the distance to the subject) in the AF process in step S8 is generally, for example, a triangular distance measurement based on a phase difference between subject images formed by two different optical systems as shown in FIG. is there.

  Then, the lens 1 is moved by the mechanical drive unit 6 in accordance with distance measurement data (L data) that is distance information acquired by the distance measurement process to adjust the focus (step S9). Thereafter, the process returns to step S1.

  Here, the case of a normal automatic light control method will be described. When the second SW is turned on, in the normal automatic dimming method, the CPU 8 sets (sets) the default automatic dimming stop amount determined from the F value of the lens 1 and the imaging gain table in the strobe light receiving unit 17 (set). )

  The amount of automatic light control stop is determined to be a value that is approximately the center value Y0 of the dynamic range when a subject with a reference reflectance is imaged through the imaging optical system, signal amplified, image processed, and converted into a digital signal. It is done.

  The reference reflectance is, for example, about 18%, and it is preferable that the reference reflectance is within the dynamic range of the imaging data as much as possible even if there is a subject with reflectance like the natural world above and below the screen.

  Then, the CPU 8 instructs the strobe light emitting unit 15 to emit strobe light, and instructs the strobe light receiving unit 17 to start receiving light.

  The strobe light receiving unit 17 includes a sensor optical system and a sensor (photoelectric conversion element) that receive reflected light from a subject. When the integrated amount of the received photocurrent from this sensor reaches the same value as the automatic light control stop amount described above, a stop signal is sent to the strobe light emitting unit 15 and light emission is stopped.

  However, there are not a few general shooting environments in which the difference in reflectance within the screen is small, and when a scene containing a lot of white is dimmed to the median value of luminance Y0, there is a problem that the image is taken dark gray. On the other hand, when a dark scene is dimmed to the median value of the luminance Y0, there is an adverse effect that an image appears to be white.

  From the above, in this embodiment, prior to still image shooting (main shooting), the strobe is pre-flashed as preliminary illumination to prevent the above-described adverse effects.

That is, in this embodiment, when the second SW is turned on in FIG. 3 (step S5 / second SW on process), the strobe is determined (step S10). When it is determined that there is no strobe (step S10 / none), the process proceeds to step S14. When it is determined that there is a strobe (step S10 / present), pre-emission (step S11), emission amount comparison (step S12), and main emission shift processing (step S13) are sequentially performed, and the process proceeds to step S14. Then, after stopping the monitoring (step S14), a still image recording process is performed (step S15), and the process returns to step S1.
When other SWs other than the first SW and the second SW are turned on (step S5 / other SW on process), processing corresponding to the other SW is performed, and the process returns to step S1.

  Next, the pre-light emission (step S11) and the light emission amount comparison (step S12) shown in FIG. 3 will be described in detail below with reference to FIGS.

<Example 1>
First, as Example 1, each process will be described with reference to FIGS. 4 (a) and 4 (b).
As shown in FIG. 4A, the pre-light emission is set to a default automatic dimming stop amount (step S21), and after the light emission is started (step S22), issuance stop is waited (step S23).
As shown in FIG. 4B, the light emission amount comparison calculates the planned light emission amount G (step S31), and the program has the expected remaining voltage Vp of the main capacitor as a table value by G obtained by the calculation (step S31). S32). The voltage Vm actually remaining in the main capacitor is read (step S33), Vp and Vm are compared, and an automatic dimming stop amount shift value is determined (step S34).

Hereinafter, the light emission amount comparison in FIG. 4B will be described in more detail.
Specifically, the expected remaining voltage Vp of the main capacitor after pre-emission is determined in advance from the distance measurement data (L data).

  The scheduled remaining voltage is a scheduled value of the voltage remaining in the main capacitor after subjecting the subject to the reference reflectance, pre-light emission and automatic light control at the distance L, the photographing F value, and the ISO sensitivity.

For example, the light emission amount G in the case of taking a stroboscope image of a subject having a ISO reflectance of 100, a lens F value of Fno., And a reference reflectance of a distance L [m] is calculated by the following formula 1 (FIG. 4B). Step S31).
G = Fno. × L (Formula 1)

If the ISO sensitivity is different, it is further converted as shown in Equation 2. ΔISO is ISO10
This is the difference in the number of APEX stages from zero.
G = (√2) ΔISO × G (Expression 2)
G is a value indicating the amount of flash emission.

  The expected remaining voltage Vp of the main capacitor can be stored in the program as a table value by G obtained by calculation (FIG. 4B, step S32).

  After the pre-light emission, the calculated Vp is compared with the voltage Vm actually remaining in the main capacitor (FIG. 4B, step S34).

  As a result of comparison, if Vm is substantially the same value as Vp, the reflectance of the object at the distance L is regarded as the same as the reference reflectance, and the automatic dimming stop amount set during the main flash is set to be the same as the set value in the pre-flash. Good to do. On the other hand, when Vm is larger than Vp by a predetermined amount, the average reflectance of the subject is high, so it is preferable to set the automatic light control stop amount set during the main light emission higher than the set value for the pre-light emission. On the other hand, when Vm is smaller than Vp by a predetermined amount, the average reflectance of the subject is lower, so it is preferable to set the automatic light control stop amount set during the main light emission to be lower than the set value in the pre-light emission.

  Note that Vm is smaller than Vp even when the subject is smaller than the angle of view of the photometric area of the strobe light receiving unit. Also in this case, if the amount of automatic light control stop at the time of actual photographing is the same as that at the time of pre-emission, there is a high possibility that the subject will be overexposed. Therefore, as described above, it is preferable that the automatic dimming stop amount is set lower than the set value in the pre-flash.

  As described above, according to Example 1, strobe light control according to the average reflectance of a subject is possible by changing the automatic light control stop amount even in the automatic light control method.

<Example 2>
In Example 1 described above, the subject reflectance is estimated from the residual voltage of the main capacitor. However, the subject reflectance may be estimated based on the time from the start of light emission to the automatic stop at the time of pre-emission. .

Hereinafter, as Example 2, a description will be given with reference to FIGS.
As shown in FIG. 5 (a), the pre-flash is set to a default automatic dimming stop amount (step S41), and after starting the light emission and timing (step S42), issuance stop waiting and timing Tr completion. (Step S43).
As shown in FIG. 5B, the light emission amount comparison is performed by calculating the planned light emission amount G (step S51), and having a predetermined light emission time Tp at the time of pre-emission as a table value by G obtained by the calculation (see FIG. 5B). Step S52). Tr and Tp are compared to determine the automatic light control stop amount shift value (step S53).

Hereinafter, the light emission amount comparison in FIG. 5B will be described in more detail.
Specifically, the scheduled light emission time Tp at the time of pre-light emission is determined in advance from distance measurement data (L data).

  The scheduled light emission time is an estimated calculated value of the time from the start of light emission to the automatic stop when pre-light emission and automatic light control are performed with the subject having the reference reflectance, the distance L, the photographing F value, and the ISO sensitivity.

  For example, the amount of light emission G in the case of taking a stroboscopic shot on a subject having a reference reflectance of ISO sensitivity 100, lens F value Fno., And distance L [m] can be obtained by the above-described equations 1 and 2 (FIG. 5). (B) Step S51).

  The scheduled light emission time Tp at the time of pre-light emission can be held by the program as a table value by G obtained by calculation (FIG. 5B, step S52).

  After the pre-light emission, the calculated Tp is compared with the actual light emission time Tr (FIG. 5B, step S53).

  As a result of the comparison, if Tr is substantially the same value as Tp, the reflectance of the subject at the distance L is regarded as the same as the reference reflectance, and the automatic light control stop amount set at the main light emission is made the same as the set value at the pre-light emission. Good to do. On the other hand, when Tr is larger than Tp by a predetermined amount, the average reflectance of the subject is high, so it is preferable to set the automatic light control stop amount set during the main light emission higher than the set value for the pre-light emission. On the other hand, when Tr is a predetermined amount smaller than Tp, the average reflectance of the subject is low, so it is preferable to set the automatic light control stop amount set during the main light emission to be lower than the set value for the pre-light emission.

  As described above, according to Example 2, even in the automatic light control method, the flash light control according to the average reflectance of the subject can be performed by changing the automatic light control stop amount.

<Example 3>
In the above example, for a subject at a long distance, the error for determining the scheduled illumination amount at the time of pre-emission is large. In addition, if the voltage of the main capacitor is consumed in the preliminary illumination, the reach distance during the main light emission is also shortened. Further, when the subject has low contrast, distance measurement is impossible and distance measurement data may not be obtained. In addition, pre-light emission can be prohibited, but the operation of pre-light emission or not depending on the distance feels unstable from the viewpoint of the user.

  Therefore, although it does not contribute to photometry by pre-emission, it is better to emit a small amount of light, and also to prevent red eyes.

As Example 3, each process will be described with reference to FIGS.
In pre-emission, as shown in FIG. 6A, first, an AF result is determined (step S61). If the AF result is a long distance or cannot be measured (step S61 / long distance or distance measurement is impossible), the automatic light emission stop amount for minute emission is set (step S62), and the process proceeds to step S64. On the other hand, when the AF result is other than long distance and inability to measure distance (step S61 / distance and distance measurement impossible), the default automatic dimming stop amount is set (step S62), and the process proceeds to step S64. And after starting light emission (step S64), it will be on issue stop waiting (step S65).
In the light emission amount comparison, as shown in FIG. 6B, first, the AF result is determined (step S71). If the AF result is a long distance or cannot be measured (step S71 / far distance or distance measurement is impossible), the automatic light control stop amount shift value is determined to be zero (step S76), and the process ends. On the other hand, when the AF result is other than long-distance and distance measurement impossible (step S71 / distance and distance measurement impossible), the planned light emission amount G is calculated (step S72), and the table value by G obtained by the calculation is used as the main table value. The program has the expected remaining voltage Vp of the capacitor (step S73). The voltage Vm actually remaining in the main capacitor is read (step S74), Vp and Vm are compared, and an automatic dimming stop amount shift value is determined (step S75).

Even if the distance is between short distance and long distance, if the subject is small with respect to the reflectance of the subject or the angle of view of the light receiving part of the strobe, the pre-flash amount will be large and sufficient for the main flash. There is also a danger that no energy remains.
For this reason, as in Example 2, it is preferable to measure the pre-emission time and stop the emission from the CPU 8 in a predetermined time.

  As described above, according to the imaging apparatus of the present embodiment, it is possible to perform dimming from a short distance to a long distance by one method of the automatic dimming method. Dimming corresponding to the reflectance is also possible.

  Further, according to the imaging apparatus of the present embodiment, it is possible to prevent wasteful consumption of energy at a long distance or the like for the preliminary illumination.

  Further, according to the imaging apparatus of the present embodiment, it is possible to prevent wasteful consumption of energy even when the reflectance of the subject is extremely low or the size of the subject is too small for the preliminary illumination.

  As mentioned above, although the Example of this invention was described, it is not limited to the said Example, A various deformation | transformation is possible in the range which does not deviate from the summary.

  The present invention can be applied to an electronic imaging apparatus such as a digital still camera.

1 is a block diagram illustrating a hardware configuration of an imaging apparatus that is an embodiment of the present invention. It is a block diagram which shows the program structure of the imaging device which is one Example of this invention. 6 is a flowchart illustrating a main processing operation of the imaging apparatus according to the embodiment of the present invention. (A) is a flowchart which shows an example of the pre light emission process operation of the imaging device which is one Example of this invention, (b) is an example of light emission amount comparison operation of the imaging device which is one Example of this invention. It is a flowchart which shows. (A) is a flowchart which shows an example of the pre light emission process operation of the imaging device which is one Example of this invention, (b) is an example of light emission amount comparison operation of the imaging device which is one Example of this invention. It is a flowchart which shows. (A) is a flowchart which shows an example of the pre light emission process operation of the imaging device which is one Example of this invention, (b) is an example of light emission amount comparison operation of the imaging device which is one Example of this invention. It is a flowchart which shows. 6 is a timing chart illustrating timings of processing operations of the imaging apparatus according to the embodiment of the present invention. It is explanatory drawing which shows general triangulation.

Explanation of symbols

1 Lens (optical means)
2 Mechanical shutter 3 CCD (Imaging means)
4 CDS-A / D section 5 DSP section 6 Mechanical drive section 7 CCD drive circuit section 8 CPU (control means)
9 Memory 11 Memory card 12 Display unit 13 SW unit 14 AF unit (Distance detection means)
15 Strobe flash unit (lighting means)
16 Main capacitor 17 Strobe light receiving part (light receiving means)

Claims (4)

Optical means for forming an optical image of a subject;
An image pickup means for electrically picking up an optical image formed by the optical means;
Distance detection means for acquiring distance information indicating a distance to the subject;
Illumination means for illuminating the subject;
A light receiving means for receiving reflected light from a subject illuminated by the illumination means;
Automatic illumination stop means for stopping illumination by the illumination means in response to a light reception signal from the light reception means,
An image pickup apparatus for performing preliminary illumination for illuminating the subject prior to actual photographing and obtaining image data of the subject;
Further, based on the distance information acquired by the distance detection unit, a planned illumination amount determination unit that determines a planned illumination amount in advance,
Illumination amount comparison means for comparing the actual illumination amount from the start of illumination to the stop of illumination at the time of preliminary illumination and the planned illumination amount determined in advance by the scheduled illumination amount determination unit,
Based on the comparison result by the illumination amount comparison means, the reflectance of the subject is estimated,
When it is determined that the estimated reflectance of the subject is high, an automatic dimming stop amount set in the automatic illumination stop means at the time of the main photographing is set higher than a set value at the time of preliminary illumination,
When it is determined that the estimated reflectance of the subject is low, an automatic dimming stop amount set in the automatic illumination stop unit during the main photographing is set lower than a set value during preliminary illumination. An imaging device. It said predetermined amount of illumination and the actual amount of illumination, the imaging apparatus according to claim 1, characterized in that the time information relating to the illumination of the illumination means. Based on the distance information obtained by the distance detection means, the imaging apparatus according to claim 1 or 2, characterized in that to reduce the preliminary illumination amount. The imaging apparatus according to any one of claims 1 to 3, characterized by having a limiter to the preliminary illumination amount.

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