JP2009104090A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the focusing performance of an electronic camera. <P>SOLUTION: An imaging section 18 periodically outputs a raw image signal expressing an optical image of a field after passing through a focus lens 12. The raw image signal outputted from the imaging section 18 is amplified in an AGC section constituting a CDS/AGC/AD circuit 20. A focus evaluation circuit 20 detects the high frequency component of the amplified raw image signal as a focus evaluation value. A CPU 46 discriminates whether or not the S/N ratio of the raw image signal outputted from the imaging section 18 is excellent. When the discrimination result is positive, the CPU 46 shortens an imaging period and increases the amplification factor of the AGC section. When the discrimination result is negative, the CPU 46 prolongs the imaging period and decreases the amplification factor of the AGC section. After that, the CPU 46 executes focusing based on the focus evaluation value detected by a focus evaluation circuit 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electronic camera that adjusts a distance from an optical lens to an imaging surface based on an object scene image captured on the imaging surface.

An example of this type of camera is disclosed in Patent Document 1. According to this background art, if the brightness of the object scene is insufficient, the frame rate of the CCD imager at the time of focus adjustment is changed from 30 fps to 15 fps. As a result, noise superimposed on the camera signal is reduced. Focus adjustment is accurately performed based on such a high-frequency component of the camera signal.
JP 2001-257931 A [H04N 5/232, 7/36, 7/28, G03B 13/36, H04N 5/225]

  However, in the background art, although the frame rate of the CCD imager is adjusted according to the brightness of the object scene, the amplification factor of the amplifier is not adjusted. For this reason, in the background art, the focusing performance is limited.

  Therefore, a main object of the present invention is to provide an electronic camera that can improve focusing performance.

  An electronic camera according to the present invention (10: reference numeral corresponding to the embodiment; the same applies hereinafter) has an imaging surface on which an optical image of an object scene that has passed through an optical lens (12) is irradiated. Imaging means (18) for periodically outputting an image signal representing an optical image, amplification means (20) for amplifying the image signal output from the imaging means, and detection for detecting a high frequency component of the image signal amplified by the amplification means Means (30), discrimination means (S33) for discriminating whether or not the S / N ratio of the image signal output from the imaging means is good, and the image output of the imaging means when the discrimination result of the discrimination means is affirmative First control means (S35, S37) for shortening the cycle and increasing the amplification factor of the amplification means, when the discrimination result of the discrimination means is negative, the image output cycle of the imaging means is extended and the amplification factor of the amplification means is increased Second control means for reducing (S39), and first control means or second control means Adjustment means (S41) for adjusting the distance from the optical lens to the imaging surface based on the high-frequency component detected by the detection means after the control process.

  The imaging means has an imaging surface on which an optical image of the object scene that has passed through the optical lens is irradiated, and periodically outputs an image signal representing the optical image irradiated on the imaging surface. The image signal output from the imaging unit is amplified by the amplification unit. The detection means detects a high frequency component of the image signal amplified by the amplification means. Whether or not the S / N ratio of the image signal output from the imaging unit is good is determined by the determination unit. The first control unit shortens the image output cycle of the imaging unit and increases the amplification factor of the amplification unit when the determination result of the determination unit is affirmative. The second control means extends the image output cycle of the imaging means and decreases the amplification factor of the amplifying means when the determination result of the determining means is negative. The adjustment unit adjusts the distance from the optical lens to the imaging surface based on the high frequency component detected by the detection unit after the control process of the first control unit or the second control unit.

  Therefore, if the S / N ratio of the image signal is good, the image signal is output from the imaging means in a short cycle and amplified with a high amplification factor. As a result, the time required for focus adjustment can be shortened. On the other hand, if the S / N ratio of the image signal is inferior, the image signal is output from the imaging means with a long period and is amplified with a low amplification factor. This avoids a decrease in focusing accuracy. In this way, an improvement in focusing performance is realized.

  Preferably, the adjusting unit searches for a focal point by changing the distance stepwise in an image output cycle of the imaging unit. As a result, the focus adjustment can be performed quickly by shortening the image output cycle.

  Preferably, the determination unit performs the determination process based on the high frequency component detected by the detection unit.

  More preferably, the registration means (46r) for preliminarily registering the high-frequency component detected by the detection means with reference to the discrimination means in a state where the imaging surface is shielded and the amplification factor of the amplification means is set to a predetermined value, and discrimination Prior to the means discrimination processing, first setting means (S5) is further provided for setting the amplification factor of the amplification means to a predetermined value. This makes it possible to accurately determine whether or not the S / N ratio is good.

  More preferably, the second control means maintains the setting of the amplification means by the first setting means.

  In one aspect, the second setting for setting the distance from the optical lens to the imaging surface to a predetermined distance different from both the distance corresponding to the infinite end and the distance corresponding to the closest end when an activation operation for activating the imaging means is received. Means (S1) is further provided. By making the distance with a high possibility that the main subject is present as the default distance, the discrimination accuracy of the discrimination means is improved.

  Preferably, an activation means (S9) for activating the determination means in response to the focus adjustment operation is further provided.

  The focusing control program according to the present invention has an imaging surface on which an optical image of the object scene that has passed through the optical lens (12) is irradiated, and periodically outputs an image signal representing the optical image irradiated on the imaging surface. An electronic camera (10) comprising an imaging means (18), an amplification means (20) for amplifying an image signal output from the imaging means, and a detection means (30) for detecting a high frequency component of the image signal amplified by the amplification means A determination step (S33) for determining whether or not the S / N ratio of the image signal output from the imaging means is good, and when the determination result of the determination step is affirmative First control step (S35, S37) for shortening the image output cycle and increasing the amplification factor of the amplification means, and when the discrimination result of the discrimination step is negative, the image output cycle of the imaging means is extended and the amplification means is amplified A second control step (S39) to reduce the rate, and A focus control program for executing an adjustment step (S41) for adjusting the distance from the optical lens to the imaging surface based on the high-frequency component detected by the detection means after the first control step or the second control step. .

  The focus control method according to the present invention has an imaging surface that is irradiated with an optical image of the object scene that has passed through the optical lens (12), and periodically outputs an image signal representing the optical image irradiated on the imaging surface. An electronic camera (10) comprising an imaging means (18), an amplification means (20) for amplifying an image signal output from the imaging means, and a detection means (30) for detecting a high frequency component of the image signal amplified by the amplification means In this focusing control method, a discrimination step (S33) for discriminating whether or not the S / N ratio of the image signal output from the imaging means is good, and imaging when the discrimination result of the discrimination step is affirmative A first control step (S35, S37) for shortening the image output cycle of the means and increasing the amplification factor of the amplifying means; when the discrimination result of the discrimination step is negative, the image output cycle of the imaging means is extended and the amplifying means A second control step (S39) for reducing the amplification factor of And an adjusting step (S41) for adjusting the distance from the optical lens to the imaging surface based on the high-frequency component detected by the detecting means after the first control step or the second control step.

  According to the present invention, if the S / N ratio of the image signal is good, the image signal is output from the imaging means in a short cycle and amplified with a high amplification factor. As a result, the time required for focus adjustment can be shortened. On the other hand, if the S / N ratio of the image signal is inferior, the image signal is output from the imaging means with a long period and is amplified with a low amplification factor. This avoids a decrease in focusing accuracy. In this way, an improvement in focusing performance is realized.

  The above object, 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.

  Referring to FIG. 1, a digital camera 10 of this embodiment includes a focus lens 12 and an aperture unit 14. The optical image of the object scene that has passed through these members is irradiated on the front surface of the imaging unit 18 that constitutes the image sensor 16, that is, the imaging surface, and subjected to photoelectric conversion. As a result, a raw image signal composed of charges representing the object scene image is generated.

  When the power is turned on, the CPU 46 sets the focal length of the focus lens 12 to 2 m under the assumption that the main subject exists at a position 2 m away from the imaging surface. The lens position corresponding to this distance is different from the infinity side end and the close side end. Further, the CPU 46 sets an imaging cycle of “1/30 seconds” in the SG (Signal Generator) 24 and sets an amplification factor of “G_Low” in the AGC unit of the CDS / AGC / AD circuit 20.

  When such setting is completed, through image processing is executed. The CPU 46 instructs the driver 22 constituting the image sensor 16 to repeat the pre-exposure operation and the thinning-out reading operation in order to display the real-time moving image (through image) representing the scene on the LCD monitor 38.

  SG24 generates a vertical synchronization signal Vsync at the set imaging cycle. Each time the vertical synchronization signal Vsync is generated, the driver 22 performs pre-exposure on the imaging surface and thinning-out reading of the charges generated thereby. From the imaging unit 18, a low-resolution raw image signal based on a part of the charge generated on the imaging surface is periodically output in a raster scanning manner. The raw image signal of each frame output from the imaging unit 18 is subjected to a series of correlated double sampling, amplification according to the set amplification factor, and A / D conversion by the CDS / AGC / AD circuit 20 constituting the image sensor 16. Processed.

  In relation to the through image processing, the imaging cycle is set to “1/30 seconds”, and the amplification factor of the AGC unit is set to “G_low”. Therefore, the raw image signal of each frame is output from the imaging unit 18 every 1/30 seconds and is amplified with an amplification factor of “G_Low”.

  The amplification factor of the AGC unit is set to either “G_low” or “G_high”. Further, a relationship of G_low <G_high is established between the two amplification factors.

  The signal processing circuit 26 performs processing such as white balance adjustment, color separation, and YUV conversion on the raw image data output from the CDS / AGC / AD circuit 20 and writes the YUV format image data to the SDRAM 34 through the memory control circuit 32. . The LCD driver 36 repeatedly reads the image data written in the SDRAM 34 through the memory control circuit 32, and drives the LCD monitor 38 based on the read image data. As a result, a real-time moving image (through image) of the object scene is displayed on the monitor screen.

  Referring to FIG. 2, a photometric area EA and a focus area FA are allocated at the center of the imaging surface. The photometry area EA and the focus area FA have the same size and are arranged at the same position.

  The luminance evaluation circuit 28 integrates the Y data belonging to the photometry area EA among the Y data output from the signal processing circuit 26 every time the vertical synchronization signal Vsync is generated. The integral value, that is, the luminance evaluation value is output from the luminance evaluation circuit 28 in the generation cycle of the vertical synchronization signal Vsync. The CPU 46 repeatedly executes through image AE processing (simple AE processing) in parallel with the above-described through image processing in order to calculate an appropriate EV value based on the luminance evaluation value output from the luminance evaluation circuit 28. The aperture amount and the exposure time that define the calculated appropriate EV value are set in the aperture unit 14 and the TG 22, respectively. As a result, the brightness of the through image displayed on the LCD monitor 38 is appropriately adjusted.

  When the shutter button 48 s on the key input device 48 is half-pressed, the CPU 46 executes a strict recording AE process to calculate the optimum EV value based on the luminance evaluation value output from the luminance evaluation circuit 28. . The aperture amount and the exposure time that define the calculated optimum EV value are set in the aperture unit 14 and the TG 22, respectively, as described above.

  When the recording AE process is completed, the AF process based on the output of the focus evaluation circuit 30 is executed. The focus evaluation circuit 30 integrates the high-frequency component of Y data belonging to each evaluation area among the Y data output from the signal processing circuit 26 every time the vertical synchronization signal Vsync is generated. The integrated value, that is, the focus evaluation value, is output from the focus evaluation circuit 30 in the generation cycle of the vertical synchronization signal Vsync. The CPU 46 refers to the focus evaluation value output from the focus evaluation circuit 30 and searches for a focal point shown in FIG. 3 by so-called hill climbing processing. The focus lens 12 moves stepwise in the direction of the optical axis every time the vertical synchronization signal Vsync is generated, and is disposed at the detected focal point.

  When the AF process is completed, the recording process is executed in response to the shutter button 48s being fully pressed. The CPU 46 instructs the driver 22 to execute the main exposure operation and the all pixel reading once. The driver 22 performs main exposure on the imaging surface in response to the generation of the vertical synchronization signal Vsync, and reads out all charges generated thereby from the imaging unit 18 in a raster scanning manner. As a result, a high-resolution raw image signal representing the object scene is output from the imaging unit 18.

  The output raw image signal is processed in the same manner as described above. As a result, high-resolution image data conforming to the YUV format is secured in the SDRAM 34. The I / F 40 reads out the high-resolution image data thus stored in the SDRAM 34 through the memory control circuit 32 and records the read-out image data in the recording medium 42 in a file format. Note that the through image processing is resumed when high-resolution image data is stored in the SDRAM 34.

The AF process is executed as follows. First, it is determined whether or not the S / N ratio of the raw image signal currently output from the imaging unit 18 is good. The following condition 1 is used for this determination processing.
[Condition 1]
FE> NS + α
FE: focus evaluation value NS: noise component value α: margin

  According to the condition 1, the added value obtained by adding the margin α to the noise component value NS is compared with the focus evaluation value FE. Here, the focus evaluation value FE corresponds to the focus evaluation value output from the focus evaluation circuit 30 at the start of the AF process. The noise component value NS is a numerical value registered in advance in the register 46r. The focus evaluation circuit 30 is configured in a state where the imaging surface is shielded and an imaging cycle of “1/30 seconds” and an amplification factor of “G_Low” are set. This corresponds to the focus evaluation value output from.

  When the focus evaluation value FE has the level shown in FIG. 4A, Condition 1 is satisfied, and it is determined that the S / N ratio of the raw image signal currently output from the imaging unit 18 is good. On the other hand, when the focus evaluation value FE has the level shown in FIG. 4B, Condition 1 is not satisfied, and the S / N ratio of the raw image signal currently output from the imaging unit 18 is poor. It is determined that there is.

  As described above, the focal length of the focus lens 12 is set to 2 m in response to power-on. As a rule of thumb, the main subject is present at a distance of about 2 m from the imaging surface with a high probability, and the focus evaluation value obtained at this distance is high as shown in FIG. Further, once the focus lens 12 is placed at the focal point by the AF process, the focus lens 12 is continuously placed at the same position until the next AF process. Therefore, whether or not the S / N ratio of the raw image signal is good is accurately determined by referring to the focus evaluation value.

  If the condition 1 is satisfied, the imaging cycle set in the driver 22 is changed to “1/60 seconds”, and the amplification factor set in the AGC unit is changed to “G_high”. On the other hand, if the condition 1 is not satisfied, the imaging cycle set in the driver 22 is changed to “1/15 seconds”, and the amplification factor set in the AGC unit is kept “G_low”. That is, when the S / N ratio is good, the imaging cycle is shortened and the amplification factor is increased. On the other hand, when the S / N ratio is poor, the imaging cycle is extended and the amplification factor is reduced.

  When the setting of the imaging cycle and the amplification factor is completed, the mountain climbing process is executed. The focus lens 12 moves stepwise in the direction of the optical axis every time the vertical synchronization signal Vsync is generated, and is arranged at the focal point. When the mountain climbing process is completed, the imaging cycle and the amplification factor are returned to “1/30 seconds” and “G_low”.

  The CPU 46 executes a plurality of tasks including the imaging control task shown in FIGS. 5 to 6 in parallel. Note that control programs corresponding to these tasks are stored in the flash memory 44.

  First, in step S1 shown in FIG. 5, the focal length of the focus lens 12 is adjusted to 2 m. In step S3, the imaging cycle of “1/30 second” is set in the driver 22, and in step S5, the amplification factor of the AGC unit is set to “G_low”. When the setting of the focal length, imaging cycle, and amplification factor is completed, through image processing is executed in step S7. As a result, a through image representing the object scene is output from the LCD monitor 38.

  In step S9, it is determined whether or not the shutter button 48s has been half-pressed. If NO, the through-image AE process is repeated in step S11. If YES, the recording AE process is executed in step S13. The exposure amount on the imaging surface is roughly adjusted by the through-image AE process and strictly adjusted by the recording AE process. When the recording AE process is completed, the AF process is executed in step S15. The focus lens 12 is disposed at a focal point.

  In step S17, it is determined whether or not the shutter button 48s has been fully pressed. In step S19, it is determined whether or not the operation of the shutter button 48s has been released. If YES is determined in the step S17, the recording process is executed in a step S21, and thereafter, the process returns to the step S7. If YES is determined in the step S19, the process returns to the step S9 as it is. As a result of the recording process in step S21, the object scene image at the time when the shutter button 48s is fully pressed is recorded on the recording medium 42.

  The AF process in step S15 is executed according to a subroutine shown in FIG. First, in step S31, a focus evaluation value is fetched from the focus evaluation circuit 30. In step S33, whether or not the S / N ratio of the raw image signal output from the imaging unit 18 is good is determined based on the focus evaluation value captured in step S31. Specifically, it is determined whether or not the above condition 1 is satisfied.

  If condition 1 is satisfied, YES is determined in step S33, the imaging cycle is shortened to "1/60 seconds" in step S35, and the amplification factor is increased to "G_high" in step S37. If condition 1 is not satisfied, NO is determined in step S33, and the imaging cycle is extended to "1/15 seconds" in step S39. When the process of step S37 or S39 is completed, the hill-climbing process is executed in step S41 to place the focus lens 12 at the focal point. When the hill-climbing process is completed, the imaging cycle is returned to “1/30 second” in step S43, the amplification factor is returned to “G_low” in step S45, and then the routine returns to the upper layer routine.

  As can be understood from the above description, the imaging unit 18 has an imaging surface on which an optical image of the object scene that has passed through the focus lens 12 is irradiated, and periodically generates a raw image signal representing the optical image irradiated on the imaging surface. Output to. The raw image signal output from the imaging unit 18 is amplified by the AGC unit that constitutes the CDS / AGC / AD circuit 20. The focus evaluation circuit 20 detects a high frequency component of the amplified raw image signal as a focus evaluation value. The CPU 46 determines whether or not the S / N ratio of the raw image signal output from the imaging unit 18 is good (S33). When the determination result is affirmative, the CPU 46 shortens the image output cycle (imaging cycle) of the imaging unit and increases the amplification factor of the AGC unit (S35, S37). When the determination result is negative, the CPU 46 extends the imaging period and decreases the amplification factor of the AGC unit (S39). Further, the CPU 46 adjusts the distance from the focus lens 12 to the imaging surface based on the focus evaluation value detected by the focus evaluation circuit 30 after the setting of the imaging cycle and the amplification factor is completed (S41).

  Therefore, if the S / N ratio of the raw image signal is good, the raw image signal is output from the imaging unit 18 in a short cycle and amplified with a high amplification factor. As a result, the time required for focus adjustment can be shortened. On the other hand, if the S / N ratio of the raw image signal is poor, the raw image signal is output from the imaging unit 18 with a long period and is amplified with a low amplification factor. This avoids a decrease in focusing accuracy. In this way, an improvement in focusing performance is realized.

  In this embodiment, the focus lens 12 is moved in the optical axis direction for focus adjustment. However, the imaging unit 18 is moved in the optical axis direction instead of the focus lens 12 or together with the focus lens 12. You may do it.

It is a block diagram which shows the structure of one Example of this invention. It is an illustration figure which shows an example of the mapping state of the photometry area allocated to the imaging surface, and a focus area. It is a graph which shows an example of the relationship between the position of a focus lens, and a focus evaluation value. (A) is a graph showing the magnitude of the focus evaluation value when the S / N ratio is good, and (B) is a graph showing the magnitude of the focus evaluation value when the S / N ratio is bad. is there. It is a flowchart which shows a part of operation | movement of CPU applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU applied to the FIG. 1 Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 18 ... Imaging part 20 ... CDS / AGC / AD circuit 24 ... SG
30 ... Focus evaluation circuit 46 ... CPU

Claims (9)

An imaging unit having an imaging surface on which an optical image of the object scene passed through the optical lens is irradiated, and periodically outputting an image signal representing the optical image irradiated on the imaging surface;
Amplifying means for amplifying the image signal output from the imaging means;
Detecting means for detecting a high frequency component of the image signal amplified by the amplifying means;
Discriminating means for discriminating whether or not the S / N ratio of the image signal output from the imaging means is good;
A first control means for shortening an image output cycle of the imaging means and increasing an amplification factor of the amplification means when a determination result of the determination means is affirmative;
Second control means for extending the image output period of the imaging means and reducing the amplification factor of the amplification means when the discrimination result of the discrimination means is negative; and the first control means or the second control means An electronic camera comprising adjustment means for adjusting a distance from the optical lens to the imaging surface based on a high frequency component detected by the detection means after the control processing.   The electronic camera according to claim 1, wherein the adjustment unit searches for a focal point by changing the distance stepwise in an image output period of the imaging unit.   The electronic camera according to claim 1, wherein the determination unit executes a determination process based on a high frequency component detected by the detection unit. A registration unit that preliminarily registers the high-frequency component detected by the detection unit in a state where the imaging surface is shielded and the amplification factor of the amplification unit is set to a predetermined value for reference of the determination unit; and The electronic camera according to claim 3, further comprising first setting means for setting an amplification factor of the amplification means to the predetermined value prior to determination processing.   The electronic camera according to claim 4, wherein the second control unit maintains the setting of the amplification unit by the first setting unit.   Second setting means for setting a distance from the optical lens to the imaging surface to a predetermined distance different from both the distance corresponding to the infinite end and the distance corresponding to the closest end when an activation operation for starting the imaging means is received. The electronic camera according to claim 3, further comprising:   The electronic camera according to claim 1, further comprising an activation unit that activates the determination unit in response to a focus adjustment operation. An imaging unit having an imaging surface that is irradiated with an optical image of a subject field that has passed through an optical lens, and that periodically outputs an image signal representing the optical image irradiated on the imaging surface, and an image output from the imaging unit To a processor of an electronic camera comprising amplification means for amplifying a signal, and detection means for detecting a high-frequency component of an image signal amplified by the amplification means,
A determination step of determining whether or not the S / N ratio of the image signal output from the imaging means is good;
A first control step of shortening an image output period of the imaging unit and increasing an amplification factor of the amplifying unit when a determination result of the determining step is affirmative;
A second control step of extending an image output period of the imaging unit and decreasing an amplification factor of the amplifying unit when the determination result of the determining step is negative, and the first control step or the second control step A focusing control program for executing an adjustment step for adjusting a distance from the optical lens to the imaging surface based on a high frequency component detected later by the detection means. An imaging unit having an imaging surface that is irradiated with an optical image of a subject field that has passed through an optical lens, and that periodically outputs an image signal representing the optical image irradiated on the imaging surface, and an image output from the imaging unit An in-focus control method for an electronic camera comprising an amplifying means for amplifying a signal and a detecting means for detecting a high-frequency component of an image signal amplified by the amplifying means,
A determination step of determining whether or not the S / N ratio of the image signal output from the imaging means is good;
A first control step of shortening an image output period of the imaging unit and increasing an amplification factor of the amplifying unit when a determination result of the determining step is affirmative;
A second control step of extending an image output period of the imaging unit and decreasing an amplification factor of the amplifying unit when the determination result of the determining step is negative, and the first control step or the second control step An in-focus control method comprising an adjustment step of adjusting a distance from the optical lens to the imaging surface based on a high-frequency component detected later by the detection unit.

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