JP4726660B2 - Electronic camera - Google Patents

Description

  The present invention relates to an electronic camera, and more particularly to an electronic camera that removes fixed pattern noise (dark current noise) from an object scene image generated on an imaging surface, for example.

An example of this type of conventional circuit is disclosed in Patent Document 1. According to this prior art, the CCD imager is exposed with the mechanical shutter opened to obtain a main image representing the subject, and the CCD imager is exposed with the mechanical shutter closed to fix the CCD imager. A black image on which pattern noise is superimposed is obtained. The fixed pattern noise superimposed on the main image is removed by subtracting the black image from the main image.
JP 2004-23331 A [H04N 5/335]

  However, in the prior art, in order to reduce fixed pattern noise, it is necessary to store the main image and the black image in two memory areas. As a result, the memory capacity increases.

  Therefore, a main object of the present invention is to provide an electronic camera that reduces noise while reducing memory capacity.

An electronic camera (10) according to the invention of claim 1 includes an imaging means (18) having an imaging surface on which an optical image of a subject is irradiated, a reading means (20) for reading an image generated on the imaging surface, and shielding the imaging surface. First setting means (S53) for setting the state, second setting means (S59) for setting the imaging surface in the exposure state after the setting processing of the first setting means, and reading means in connection with the setting processing of the first setting means Detecting means (S61) for detecting noise information from the black image read out by means of (2), and detecting the noise contained in the subject image read out by the reading means in relation to the setting processing of the second setting means. A reduction means (S45) for reducing the noise based on the noise information.

The optical image of the subject is irradiated on the imaging surface of the imaging means. The image generated on the imaging surface is read by the reading unit. The imaging surface is set in a light shielding state by the first setting means. The imaging surface is also set to the exposure state by the second setting means after the setting process of the first setting means.

The detecting means detects noise information from the black image read by the reading means in connection with the setting process of the first setting means. The reducing means reduces noise included in the subject image read by the reading means in relation to the setting process of the second setting means based on the noise information detected by the detecting means.

In this way, the imaging surface is first set to a light shielding state and then set to an exposure state. The reading unit first reads a black image and then reads a subject image. Noise information is detected from a black image. Therefore, the memory capacity can be suppressed by overwriting the subject image on the portion of the black image where the detection of noise information has been completed. Further, by using the noise information detected from the black image, the noise included in the subject image can be accurately reduced.

Further , the image forming apparatus further includes writing means (42) for writing the black image and the subject image read by the reading means into a common memory area.

Then , the writing means overwrites the subject image on the black image. As a result, the memory capacity can be suppressed.

An electronic camera according to a second aspect of the present invention is dependent on the first aspect, and the noise information detected by the detecting means includes position information indicating a position where the noise appears. Thereby, noise included in the subject image is accurately reduced.

  According to the present invention, it is possible to accurately reduce the noise included in the object scene image while suppressing the memory capacity by overwriting the object scene image on the portion of the image where the detection of the noise information is completed. it can.

  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 (electronic camera) 10 of this embodiment includes an optical lens 12. The optical image of the object scene is irradiated on the imaging surface of the CCD imager 18 through the optical lens 12 and the mechanical shutter 14. On the imaging surface, a charge corresponding to the optical image of the object scene, that is, a raw image signal is generated by photoelectric conversion.

  When the power is turned on, a process for displaying a real-time moving image (through image) based on the optical image of the object scene on the LCD monitor 50 is executed. First, the CPU 30 sets an exposure time indicating an initial value in the timing generator (TG) / signal generator (SG) 20 and thins out the charges generated in the entire effective image area (not shown) formed on the imaging surface. A corresponding instruction is given to the TG / SG 20 to read in a manner.

  The CPU 30 also commands the driver 16 to open the mechanical shutter 14, connects the switches SW1 and SW2 to the terminals T1 and T3, respectively, and activates the video encoder 48. The CPU 30 further sets a write destination to the SDRAM 44 by the memory control circuit 42. Thereby, a through image area 44a described later is set as a writing destination.

  As shown in FIG. 2, the SDRAM 44 has a through image area 44a, a raw image area 44b, a noise data area 44c, and a compressed image area 44d. The through image area 44a is used after the power is turned on, the raw image area 44b is used after a full pressing operation by the shutter button 58, and the noise data area 44c is used during noise reduction processing (described later). The compressed image area 44d is used for JPEG compression processing (described later).

  Returning to FIG. 1, the TG / SG 20 generates a vertical synchronization signal Vsync every 1/30 seconds, and supplies a plurality of timing signals synchronized with the vertical synchronization signal Vsync to each of the CCD imager 18 and the CDS / AGC / AD circuit 22. The imaging surface of the CCD imager 18 is subjected to pre-exposure every time the vertical synchronization signal Vsync is generated, and the charge generated in the effective image area is subjected to thinning-out reading by raster scanning. The raw image signal with a low pixel number formed by the read charges has a frame rate of 30 fps.

  The CDS / AGC / AD circuit 22 performs a series of processes of correlated double sampling, automatic gain adjustment, and A / D conversion on the raw image signal output from the CCD imager 18, and outputs raw image data that is a digital signal. . The raw image data output from the CDS / AGC / AD circuit 22 is given to the signal processing circuit 24 via the switches SW1 and SW2.

  The signal processing circuit 24 performs processing such as white balance adjustment, color separation, and YUV conversion on the given raw image data. The YUV format image data thus generated is applied to the memory control circuit 42 via the buffer circuit 26 and the bus B1, and is written into the SDRAM 44 by the memory control circuit 42.

  The video encoder 48 reads the image data thus stored in the SDRAM 44 through the memory control circuit 42. The read image data is given to the video encoder 48 through the bus B1 and the buffer circuit 46, and is converted into an NTSC composite video signal. The converted composite video signal is applied to the LCD monitor 50. As a result, a through image representing the scene is reproduced on the LCD monitor 50.

  The luminance evaluation circuit 28 evaluates the luminance of the object scene every 1/30 seconds based on the image data generated by the signal processing circuit 24. The evaluation result, that is, the luminance evaluation value is used for the through image AE processing by the CPU 30. The CPU 30 calculates the optimum exposure time based on the luminance evaluation value, and instructs the TG / SG 20 to perform pre-exposure processing according to the calculated optimum exposure time. As a result, the brightness of the through image displayed on the LCD monitor 50 is appropriately adjusted.

  When the shutter button 58 is half-pressed, the recording AE process is executed. That is, the pre-exposure time of the CCD imager 18 is adjusted more strictly based on the above-described luminance evaluation value. Note that the optimum exposure time set in the TG / SG 20 by the recording AE process is not changed as long as the shutter button 58 is half-pressed.

  At this time, the CPU 30 determines whether or not the current setting satisfies an NR (Noise Reduction) imaging condition. This NR photographing condition includes an exposure amount condition that the optimum exposure time obtained by the recording AE process exceeds the threshold value “0.5 seconds”, and if the exposure amount condition is satisfied, the NR process is requested. Therefore, while the flag Fnr is set to “1”, if the exposure amount condition is not satisfied, the flag Fnr is set to “0” to request the normal photographing process.

  When shutter button 58 is fully pressed, CPU 30 connects switches SW1 and SW2 to terminals T2 and T4, respectively, and commands memory control circuit 42 to change the write setting. By changing the writing setting, the raw image area 44b (see FIG. 2) is set as the writing destination.

  Next, when the flag Fnr indicates “0”, a shooting process (described later) is quickly executed, and when the flag Fnr indicates “1”, the black image shooting process is executed prior to the shooting process.

  When executing the black image photographing process, the CPU 30 first instructs the video encoder 48 to display a black image. The video encoder 48 creates a composite video signal representing a black image and supplies the created composite video signal to the LCD monitor 50. As a result, the display of the through image is interrupted, and the black image is displayed on the entire surface of the LCD monitor 50.

  Subsequently, the CPU 30 gives a command for closing the mechanical shutter 14 to the driver 16. When the mechanical shutter 14 is closed, the CPU 30 next instructs the TG / SG 20 to read all the charges generated in the effective pixel area. The TG / SG 20 reads all the charges generated in the entire effective image area in a raster scanning manner after the optimum exposure time calculated by the recording AE process has elapsed.

  At this time, the imaging surface is scanned in an interlaced manner, and a raw image signal obtained in a light-shielded state, that is, with the mechanical shutter 14 closed, is output from the CCD imager 18. The output raw image signal is converted into raw image data by the CDS / AGC / AD circuit 22. As a result, raw image data (hereinafter referred to as black image data) captured in a light-shielded state is written in the raw image area 44b. Fixed image noise (dark current noise) is superimposed on the black image data.

  When the black image data is stored in the raw image area 44b, the CPU 30 instructs the driver 16 to open the mechanical shutter 14, and detects fixed pattern noise from the black image data. This detection result, that is, the noise information of the fixed pattern noise superimposed on the black image data is written in the noise data area 44c (see FIG. 2) of the SDRAM 44. This noise information includes information indicating the position and luminance level of fixed pattern noise.

  When the noise information is stored in the noise data area 44c, the CPU 30 changes the write destination of the memory control circuit 42 from the noise data area 44c to the raw image area 44b. Thus, processing according to the NR imaging condition is realized.

  Next, the CPU 30 gives an instruction corresponding to the driver 16 to close the mechanical shutter 14 in accordance with the optimum exposure time calculated by the recording AE process to execute the photographing process, and the charge generated in the effective pixel area. Are all instructed to TG / SG 20. The driver 16 closes the mechanical shutter 14 in response to this command, and the TG / SG 20 rasterizes all the charges generated by the CCD imager 18 after the optimum exposure time calculated by the recording AE process has elapsed. Read with. At this time, the imaging surface is scanned in an interlaced manner.

  The raw image signal having a large number of pixels output from the CCD imager 18 is subjected to the same processing as described above by the CDS / AGC / AD circuit 22 and converted into raw image data. The converted raw image data is given to the buffer circuit 32 via the switch SW1, and then written to the raw image area 44b via the bus B1 and the memory control circuit 42. As a result, raw image data corresponding to the object scene image (hereinafter referred to as object image data) is stored in the raw image area 44b. Fixed field noise is superimposed on the object scene image data.

  The position of the fixed pattern noise superimposed on the black image data substantially coincides with the position of the fixed pattern noise superimposed on the object scene image data. As a result, the position information of the fixed pattern noise superimposed on the black image data is used for the noise reduction process as the position information of the object scene image data.

  If the object scene image data is stored in the raw image area 44b and the flag Fnr is “1”, the fixed pattern noise superimposed on the object scene image is reduced based on the noise information detected from the black image. Is done. Specifically, the CPU 30 reads out the noise information stored in the noise data area 44c. By referring to the position information included in the read noise information, the position of the fixed pattern noise superimposed on the object scene image data is specified. Next, the CPU 30 subtracts the luminance level corresponding to the position information of the noise information from the luminance level of the fixed pattern noise thus identified. As a result, the fixed pattern noise superimposed on the object scene image data can be accurately reduced by using the noise information detected from the black image data.

  Raw image data for recording (hereinafter, image data for recording) in which fixed pattern noise is reduced is generated in the raw image region 44b. The scene image data and the recording image data are raw image data stored in the raw image area 44b.

  When the above processing is completed, the CPU 30 gives an instruction to the signal processing circuit 24, the JPEG encoder 38, and the I / F 52 to execute the recording processing. The signal processing circuit 24 reads the raw image data stored in the raw image area 44b through the memory control circuit 42 in a progressive scanning manner. The read raw image data is supplied to the signal processing circuit 24 via the bus B1, the buffer circuit 34, and the switch SW2, and is converted into image data in the YUV format. The converted image data is applied to the memory control circuit 42 via the buffer circuit 26 and the bus B1, and is written into the SDRAM 44 by the memory control circuit 42.

  When the switches SW1 and SW2 are connected to the terminals T1 and T3, respectively, the raw image data output from the CDS / AGC / AD circuit 22 is given to the signal processing circuit 24. On the other hand, when the switches SW1 and SW2 are connected to the terminals T2 and T4, the raw image data output from the CDS / AGC / AD circuit 22 is applied to the SDRAM 44 through the buffer circuit 32, the bus B1 and the memory control circuit 42. It is done.

  The JPEG encoder 38 reads the raw image data stored in the raw image area 44b through the memory control circuit 42. The read image data is given to the JPEG encoder 38 through the bus B1 and the buffer circuit 36, and subjected to JPEG compression. The compressed image data generated thereby is applied to the memory control circuit 42 via the buffer circuit 40 and the bus B1, and is thereby written in the compressed image area 44d (see FIG. 2) of the SDRAM 44. The I / F 52 reads the compressed image data stored in the compressed image area 44d through the memory control circuit 42, and records the read compressed image data on the recording medium 54 in a file format.

  That is, when the flag Fnr is “0”, the photographing process is promptly executed in response to the full pressing operation of the shutter button 58, and the recording process is performed after the object scene image data is stored in the raw image area 44b. Executed.

  On the other hand, when the flag Fnr is “1”, the shooting process is executed after the black image shooting process executed in response to the full-pressing operation of the shutter button 58, and the recording process is related to the noise reduction process. Executed.

  When the flag Fnr indicates “1”, the use area of the SDRAM 44 will be described with reference to FIGS. 3 (A) to (D) and FIGS. 4 (A) to (D). When the shutter button 58 is fully pressed at the timing shown in FIG. 3A, the black image photographing process is executed. At this time, the mechanical shutter 14 is closed (see FIG. 3 (B)), and the TG / SG 20 reads out charges from the CCD imager 18 after the optimum exposure time has elapsed (see FIG. 3 (C)) in a light-shielded state. The writing destination of the memory control circuit 42 is changed from the through image area 44a to the raw image area 44b as shown in FIG. As a result, as shown in FIG. 4A, the raw image area 44b is used to store black image data for one frame.

  When the black image data is stored in the raw image area 44b, the mechanical shutter 14 is opened (see FIG. 3B), and the write destination of the memory control circuit 42 is the raw image area 44b as shown in FIG. 3D. To the noise data area 44c. As a result, as shown in FIG. 4B, the raw image area 44b and the noise data area 44c are used for the detection process of the fixed pattern noise.

  When the detection process is completed, an imaging process (see FIG. 3A) is executed. At this time, the mechanical shutter 14 is closed (see FIG. 3B) according to the optimum exposure time (see FIG. 3C). The TG / SG 20 reads charges from the CCD imager 18 after the optimum exposure time has elapsed in the exposure state (see FIG. 3C). The write destination of the memory control circuit 42 is changed from the noise data area 44c to the raw image area 44b as shown in FIG. The memory control circuit 42 overwrites the object scene image data obtained by the photographing process on the black image data obtained by the black image photographing process. As a result, as shown in FIG. 4C, the raw image area 44b is used to store the object scene image data for one frame, and the memory capacity is suppressed.

  When the object scene image data is written in the raw image area 44b, the CPU 30 executes a noise reduction process (see FIG. 3A). As a result, as shown in FIG. 4D, recording image data in which the fixed pattern noise superimposed on the object scene image data is reduced is generated in the raw image area 44b.

  Thus, the optical image of the object scene is irradiated on the imaging surface of the CCD imager 18. The image generated on the imaging surface is read by the TG / SG 20. The imaging surface is set in a light shielding state by the CPU 30. The imaging surface is also set to an exposure state by the CPU 30 after being set to a light shielding state.

  The CPU 30 detects noise information from the black image data read by the TG / SG 20 in association with the process for setting the imaging surface in the light shielding state, and TG / SG 20 in association with the process for setting the imaging surface in the exposure state. The fixed pattern noise included in the object scene image data read out by the step S is reduced based on the noise information detected by the CPU 30.

  That is, the imaging surface is first set to a light shielding state and then set to an exposure state. The TG / SG 20 first reads black image data, and then reads object scene image data. Noise information is detected from black image data. Therefore, the memory capacity can be suppressed by overwriting the object scene image data after the detection of noise information in the black image data is completed. Further, by using the noise information detected from the black image data, it is possible to accurately reduce the fixed pattern noise superimposed on the object scene image data.

  Specifically, CPU30 performs the process according to the flowchart shown in FIGS. Note that the shooting control program corresponding to this flowchart is stored in the flash memory 56.

  According to FIG. 5, the exposure time indicating the initial value is set in TG / SG 20 in step S1. In step S3, the mechanical shutter 14 is opened through the driver 16, the switches SW1 and SW2 are connected to the terminals T1 and T3, respectively, in step S5, and the video encoder 48 is activated in step S7. In step S9, the TG / SG 20 is instructed to execute reading in the thinning mode, and in step S11, the write destination of the memory control circuit 42 is set in the through image area 44a. As a result, a through image representing the scene is displayed on the LCD monitor 50.

  In step S13, it is determined whether or not the shutter button 58 has been half-pressed. If the determination result is NO, through image AE processing is executed in step S15. The brightness of the reproduced through image is adjusted by the process in step S15. On the other hand, if the determination result is YES, it is determined that the shutter button 58 has been half-pressed, and the recording AE process is executed in a step S17. As a result, the optimum exposure time is calculated.

  In step S19, it is determined in step S25 whether or not the exposure time currently set in TG / SG 20 is "0.5 seconds" or more. If the determination result is YES, it is determined that the NR imaging condition is satisfied, and the flag Fnr is set to “1” in step S21. On the other hand, if the determination result is NO, it is determined that the NR imaging condition is not satisfied, and the flag Fnr is set to “0”.

  In step S25, it is determined whether or not the shutter button 58 has been fully pressed. In step S27, it is determined whether or not the operation of the shutter button 58 has been released. If NO in step S25, the process proceeds to step S27. If YES in step S27, the process returns to step S13.

  When the shutter button 58 is fully pressed, the switches SW1 and SW2 are respectively connected to the terminals T2 and T4 in step S29, and the write destination of the memory control circuit 42 is changed to the raw image area 44b in step S31.

  In step S33, the state of the flag Fnr is determined. If the flag Fnr is “0”, the photographing process is executed in step S39. At this time, the mechanical shutter 14 is closed according to the optimum exposure time. On the other hand, if the flag Fnr is “1”, a black image photographing process is executed in step S35, and a detection process is executed in step S37. When this process is completed, the step S photographing process is executed. That is, if the exposure time set in the TG / SG 20 is “0.5 seconds” or more, the NR process is executed prior to the imaging process.

  It waits until the object scene image data is stored in the raw image area 44b of the SDRAM 44 in step S41. When the object scene image data is stored in the raw image area 44b, the state of the flag Fnr is determined in step S43. If the flag Fnr is “1”, noise reduction processing is executed in step S45. Specifically, the noise information stored in the noise data area 44c is read, and the position of the fixed pattern noise superimposed on the object scene image data is specified according to the position information among the noise information. The luminance level of the fixed pattern noise superimposed on the black image data corresponding to this position information is subtracted from the luminance level of the fixed pattern noise thus specified. As a result, the fixed pattern noise superimposed on the object scene image data can be accurately reduced by using the noise information detected from the black image data.

  On the other hand, if the flag Fnr is “0”, the recording process is executed in step S47. As a result, compressed image data based on the raw image data stored in the raw image area 44b is recorded on the recording medium 54 in a file format. When the recording process is completed, the process returns to step S3.

  The black image photographing process in step S35 is executed according to a subroutine shown in FIG. First, in step S51, black image display processing is executed. As a result, a black image is displayed on the LCD monitor 50.

  In step S53, the mechanical shutter 14 is closed through the driver 16, and in step S55, a command corresponding to reading all pixels in the effective pixel area is given to the TG / SG 20. As a result, black image data is written in the raw image area 44b.

  In step S57, the process waits until the black image data is stored in the raw image area 44b of the SDRAM 44. When the black image data is stored in the raw image area 44b, the mechanical shutter 14 is opened through the driver 16 in step S59, and the process returns to the upper layer routine.

  The detection process in step S37 is executed according to a subroutine shown in FIG. In step S61, the write destination of the memory control circuit 42 is changed to the noise data area 44c. In step S63, fixed pattern noise is detected from the black image data. As a result, the detected noise information is stored in the noise data area 44c.

  When the detection of noise information is completed, the write destination of the memory control circuit 42 is changed to the raw image area 44b in step S67. As a result, the black image data stored in the raw image area 44b is overwritten with the object scene image data obtained by the photographing process. Thereby, the memory capacity can be suppressed. When this processing is completed, the routine returns to the upper-level routine.

  In this embodiment, it has been described that the photographing process is executed after the detection process of the fixed pattern noise superimposed on the black image data is completed. However, the present invention is not limited to this, and the detection of the fixed pattern noise superimposed on the black image data is performed. It is also possible to overwrite the object scene image data on the part where the above is completed.

  Since the digital camera 10 of the other embodiment is the same as the embodiment of FIGS. 1 to 8 except for the points described below, description of the same configuration is omitted.

  The CPU 30 executes steps S71 to S79 shown in FIGS. 9 and 10 instead of steps S19 to S23 shown in FIG.

  Referring to FIG. 9, in step S71, it is determined whether or not the NR mode has been set by an operation key (not shown) provided on digital camera 10. When the NR mode is set by the operation key, the flag Fnr is set to “1” in step S73. On the other hand, if the NR mode is not set, the flag Fnr is set to “0” in step S75. As a result, the NR shooting condition is changed according to the mode setting of the operation key. In other words, NR shooting conditions can be set prior to shooting the object scene image, which improves operability.

  In step S77, it is determined whether or not the exposure time is “0.5 seconds” or longer. If the exposure time is less than “0.5 seconds”, it is determined that there is no need to perform noise reduction processing on the object scene image data stored in the raw image area 44b, and the process proceeds to step S39. On the other hand, if the exposure time is “0.5 seconds” or longer, it is determined that it is necessary to perform noise reduction processing on the object scene image data stored in the raw image area 44b, and the process proceeds to step S35 to capture a black image. Processing (see FIG. 7) is executed. That is, even if the full-press operation is performed in the NR mode, if the exposure time is less than “0.5 seconds”, the photographing process is quickly executed.

  Note that, by excluding the determination process in step S77, the photographing process in the NR mode set in steps S71 to S75 is executed. This improves the operability.

  In step S79, it is determined whether or not the noise information of the black image data detected in step S37 is stored in the noise data area 44c. If the determination result is YES, noise reduction processing is executed in step S45, and the process proceeds to step S47. If the determination result is NO, a recording process is executed in step S47.

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 memory mapping of SDRAM44 applied to FIG. 1 Example. (A) is a timing chart showing an example of the operation of the CPU 30 applied to the embodiment of the present invention, and (B) is a timing chart showing an example of the operation of the mechanical shutter 14 applied to the embodiment of the present invention. (C) is a timing diagram showing an example of the optimum exposure time formed by the operation of the TG / SG 20 applied to the embodiment of the present invention, and (D) is applied to the embodiment of the present invention. FIG. 6 is a timing chart showing an example of the operation of the memory control circuit 42. It is an illustration figure which shows another example of the memory mapping of SDRAM44 applied to the FIG. 1 Example. It is a flowchart which shows a part of operation | movement of CPU30 applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU30 applied to the FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of CPU30 applied to the FIG. 1 Example. FIG. 10 is a flowchart showing yet another portion of behavior of the CPU 30 applied to the embodiment in FIG. 1. It is a flowchart which shows a part of operation | movement of CPU30 applied to the other Example of this invention. It is a flowchart which shows a part of other operation | movement of CPU30 applied to the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 14 ... Mechanical shutter 18 ... CCD imager 30 ... CPU
44 ... SDRAM
50 ... LCD monitor 58 ... Shutter button

Claims (2)

An imaging means having an imaging surface on which an optical image of a subject is irradiated;
Reading means for reading out the image generated on the imaging surface,
First setting means for setting the imaging surface in a light shielding state;
Second setting means for setting the imaging surface in an exposure state after the setting process of the first setting means;
Detection means for detecting noise information from the black image read by the reading means in relation to the setting process of the first setting means, and reading by the reading means in relation to the setting process of the second setting means Reduction means for reducing noise included in the subject image that has been detected based on the noise information detected by the detection means ,
A writing unit for writing the black image and the subject image read by the reading unit in a common memory area;
The writing means overwrites the subject image on the black image . The electronic camera according to claim 1, wherein the noise information detected by the detection unit includes position information indicating a position where noise appears .

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