JP2006222689A - Photographing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographing apparatus capable of carrying out shading correction with a comparatively simple configuration and suppressing the photographing time by reducing the time required for correction processing. <P>SOLUTION: A digital camera 10 includes: a CCD image sensor 37 for applying photoelectric conversion to an object light; a correction data generation circuit 42 for generating correction data; and an arithmetic processing circuit 43. The CCD image sensor 37 is provided with a light shield section for shielding some of a plurality of horizontal lines each arranged with a plurality of pixels along horizontal transfer paths. The correction data generation circuit 42 captures noise signals from each of regions resulting from dividing the light shield section in a way of segmenting the horizontal lines to calculate an average value, and applies linear interpolation to the average value to generate correction data corresponding to each pixel position. The arithmetic processing circuit 43 subtracts the correction data from an imaged signal by each horizontal line. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus including a solid-state imaging device that obtains an imaging signal by photoelectrically converting subject light.

  The subject light imaged by the taking lens is photoelectrically converted by a solid-state image sensor (image sensor), and image data is generated from the image signal output from the solid-state image sensor, and the obtained image data is stored in the memory. Digital cameras that record data are widely used. As this solid-state imaging device, a semiconductor device having a structure such as a charge coupled device (CCD) type or a complementary metal oxide semiconductor (CMOS) type is used.

  When shooting with such an imaging apparatus having a solid-state imaging device, horizontal and vertical directions of the solid-state imaging device are caused by dark noise caused by dark current and circuit noise due to variations in power supply voltage and element characteristics. As a result, there is a problem that fixed pattern noise called shading occurs in the image data, and the image quality deteriorates. The dark current is caused by generation of electron-hole pairs due to thermal excitation of the semiconductor, and the influence becomes larger as the exposure time (signal charge accumulation time) becomes longer. Therefore, since the influence of dark noise on image data cannot be ignored at the time of photographing in a dark place or during long exposure, various methods for correcting this shading are disclosed (for example, Patent Documents 1 to 3). 3).

Patent Documents 1 and 2 disclose a method in which noise data is generated by shielding a predetermined pixel (light receiving element) for each shooting, and correction is performed based on the noise data. Patent Document 3 discloses a method in which noise data for each pixel of a solid-state imaging device is stored in advance in a nonvolatile memory, and correction is performed based on the noise data.
JP-A 61-260771 JP-A-8-51571 Japanese Patent Laid-Open No. 9-18793

  However, in the case of the methods disclosed in Patent Documents 1 and 2, since the acquisition of noise data and the acquisition of image data are performed for each shooting, the shooting time is approximately doubled and the shooting time is long. It is. In addition, dark noise differs depending on the environment and shooting conditions, and circuit noise is affected by the same effect. Therefore, the method of Patent Document 3 cannot cope with various shot images and has a large capacity for storing noise data. This requires a non-volatile memory and is also a problem in terms of cost.

  The present invention has been made in view of the above circumstances, and provides a photographing apparatus capable of performing shading correction with a relatively simple configuration, reducing the time required for correction processing, and suppressing photographing time. The purpose is to do.

  The imaging apparatus according to the first aspect of the present invention includes a solid-state imaging device having a light-shielding portion that shields some of a plurality of horizontal lines in which a plurality of pixels are arranged along a horizontal transfer path, and the solid-state imaging device. When reading the imaging signal from the image, the noise signal is taken from each of the regions divided so that the light shielding part is divided into horizontal lines, an average value is calculated, and this is linearly interpolated to obtain a direction parallel to the horizontal line. Correction data generating means for generating correction data corresponding to each pixel position, and arithmetic processing means for subtracting the correction data from the imaging signal for each horizontal line.

  According to a second aspect of the present invention, there is provided a photographing apparatus including: a solid-state imaging device having a light-shielding portion that shields some of a plurality of vertical lines in which a plurality of pixels are arranged along a vertical transfer path; When reading the image signal from the above, the noise signal is taken from each region obtained by dividing the light-shielding portion into a plurality of parts so as to divide the vertical line, and an average value is calculated. Correction data generating means for generating correction data corresponding to each pixel position, and arithmetic processing means for subtracting the correction data for each vertical line from the imaging signal.

  In the photographing apparatus according to claim 1, the light shielding portion is divided so as to sandwich a photosensitive portion composed of a plurality of horizontal lines on which subject light is incident, and the correction data creating means is parallel to the horizontal lines. Correction data corresponding to each pixel position of the photosensitive portion is created by performing linear interpolation in a direction perpendicular to a horizontal line in addition to a specific direction, and the arithmetic processing means calculates the correction data from the imaging signal for each pixel. It is preferable to subtract.

  According to a third aspect of the present invention, in the case of performing multi-field reading of three or more fields when reading an imaging signal from the solid-state imaging device, the imaging device according to the invention described in claim 3 is one of the light shielding portions divided in the first field. It is preferable that the noise signal is captured from the second field, the noise signal is captured from the other divided light-shielding part in the second field, and the noise signal is not captured from any of the light-shielding parts after the third field. .

  In addition, the imaging apparatus includes a control unit that determines whether to operate the correction data generation unit and the arithmetic processing unit according to a signal charge accumulation time of the solid-state imaging device or a set value of sensitivity. It is preferable.

  Since the image capturing apparatus of the present invention requires a small amount of noise data to be captured, it does not require a large-capacity nonvolatile memory, can perform shading correction with a relatively simple configuration, and time required for correction processing. To shorten the shooting time. The photographing apparatus according to the first aspect of the invention can perform shading correction in the horizontal direction. In addition, the photographing apparatus according to the second aspect of the invention can perform shading correction in the vertical direction. Furthermore, the photographing apparatus according to the third aspect of the invention can perform shading correction in the horizontal direction and the vertical direction.

  A digital camera 10 shown in FIG. 1 is provided with a lens barrel 12 in which a photographing lens is incorporated on the front surface of a main body 11, and a power switch 13 and a shutter button 14 are provided on the upper surface of the main body 11. The shutter button 14 is a two-stage pressing switch, and when the shutter button 14 is lightly pressed and the first-stage switch is turned on (half-pressed), various shooting preparations such as focus adjustment and exposure adjustment of the shooting lens are performed. Processing is performed. Next, when the shutter button 14 is further pushed in and the second-stage switch is turned on (full depression), a photographing process is performed in which image data obtained based on the imaging signal obtained from the CCD image sensor is recorded on the memory card. .

  A finder eyepiece window 15, a mode switch 16, a general-purpose key 17, an LCD panel 18, and the like are provided on the back of the main body 11. The mode switch 16 switches between a shooting mode for performing an imaging process and a playback mode for playing back and displaying a recorded image on a memory card on an LCD (Liquid Crystal Display) panel 18. The LCD panel 18 functions as an electronic viewfinder that displays a playback image in the playback mode and displays a through image for subject confirmation in the shooting mode. The LCD panel 18 displays a setting screen for performing various settings.

  FIG. 2 shows an outline of the electrical configuration of the digital camera 10. Each unit of the digital camera 10 is controlled by a CPU (Central Processing Unit) 30. A ROM (Read Only Memory) 31 stores a control program and various setting data. The CPU 30 controls each unit according to the steps described in the control program based on the operation signal input from the operation unit (power switch 13, shutter button 14, mode switch 16, general key 17) 20. A RAM (Random Access Memory) 32 is a working memory for the CPU 30 to execute a control program.

  In the lens barrel 12, a photographing lens 33 that forms an image of subject light and a diaphragm mechanism 34 that limits the amount of light of the subject light are incorporated. The photographic lens 33 is moved along the optical axis direction by a lens motor 35 provided with a driver circuit to perform focus adjustment. The aperture mechanism 34 is driven by an actuator 36 having a driver circuit, and the aperture value is switched.

  Behind the diaphragm mechanism 34, a CCD image sensor 37 is disposed as a solid-state imaging device that photoelectrically converts subject light that has passed through the photographing lens 33 and the diaphragm mechanism 34 and formed an image. As shown in FIG. 3, the CCD image sensor 37 includes a pixel 50 composed of photodiodes (light receiving elements) arranged in a two-dimensional matrix, and a signal charge accumulated in the pixel 50 in the vertical direction for each horizontal line 51. The vertical transfer path (vertical register) 52 for transferring, the horizontal transfer path (horizontal register) 53 for transferring the signal charge for one horizontal line transferred by the vertical transfer path 52 in the horizontal direction, and the horizontal transfer path 53 And an output unit 54 for converting the signal charges into voltage signals and outputting them serially to the outside. The horizontal line 51 includes a plurality of pixels 50 arranged along the horizontal transfer path 53. The output unit 54 includes an amplifier that amplifies the voltage signal, and the amplification factor (sensitivity) can be changed.

  A pixel region in which a plurality of pixels 50 are two-dimensionally arranged includes a photosensitive portion 55 including a plurality of horizontal lines 51 on which subject light is incident, and a plurality of horizontal lines 51 covered and shielded by an aluminum film or the like. A light shielding portion (optical black portion) 56 is provided. Needless to say, the vertical transfer path 52 and the horizontal transfer path 53 are shielded from light.

  A color filter that transmits only light of a specific color (any of red (R), green (G), and blue (B)) is provided for each pixel 50 on the front side of the photosensitive portion 55. In the figure, a pixel 50 labeled R receives red light, a pixel 50 labeled G receives green light, and a pixel 50 labeled B receives blue light. Such an arrangement of colors is called a Bayer arrangement.

  Returning to FIG. 2, the CCD image sensor 37 is driven by a CCD driver 38. The signal charge accumulation time (exposure time) and sensitivity of the CCD image sensor 37 are changed by the CCD driver 38 based on an instruction from the CPU 30. The CCD image sensor 37 outputs an imaging signal (CCD-RAW data) in synchronization with the vertical transfer clock and horizontal transfer clock supplied from the CCD driver 38.

  The imaging signal output from the CCD image sensor 37 is input to an A / D (Analog to Digital) converter 39. The A / D converter 39 converts an analog imaging signal into a digital signal to generate image data, and inputs this to the buffer memory 40. The buffer memory 40 temporarily stores input image data. On the LCD panel 18, the image data stored in the buffer memory 40 is displayed as a through image via the LCD driver 41.

  The correction data creation circuit 42 takes in a noise signal (a signal mainly caused by dark current) from the pixels 50 included in the light shielding portion 56 of the CCD image sensor 37 and corrects the image data stored in the buffer memory 40. Correction data is calculated. This noise signal is output from the CCD image sensor 37 together with the imaging signal.

  Specifically, the correction data creation circuit 42 first takes in a noise signal from each block 57 obtained by dividing the light shielding portion 56 into a plurality of parts so as to divide the horizontal line 51 as shown in FIG. The average value is calculated by integrating each time. Then, this average value is used as the data of the pixel 50 located in the center in the horizontal direction of each block 57 as shown in FIG. Further, as shown in FIG. 5B, the correction data creation circuit 42 performs linear interpolation to create correction data corresponding to each pixel position in the direction parallel to the horizontal line 51. At this time, the data for the pixel position outside the average value is calculated by linear extrapolation (adjacent slope is extended). The created correction data is stored in the RAM 32.

  Returning to FIG. 2, the arithmetic processing circuit 43 corrects the shading in the horizontal direction by subtracting the correction data obtained by the correction data generating circuit 42 from the image data stored in the buffer memory 40 for each horizontal line. The corrected image data is stored in the buffer memory 40.

  The corrected image data is sent to the compression / decompression circuit 44. The compression / decompression circuit 44 performs compression processing on the input image data, and inputs this to the read / write circuit 45. The read / write circuit 45 writes the compressed image data to the memory card 46.

  The CPU 30 operates each part when the shutter button 14 is half-pressed to perform focus adjustment and exposure adjustment, and operates each part when the shutter button 14 is fully pressed to execute a photographing process. Further, the CPU 30 determines whether or not to operate the correction data generation circuit 42 and the arithmetic processing circuit 43 according to the signal charge accumulation time or sensitivity setting value of the CCD image sensor 37. Specifically, when the signal charge accumulation time is set longer than a predetermined value (or the sensitivity is higher than a predetermined value), the correction data generating circuit 42 and the arithmetic processing circuit 43 are operated to perform correction processing, and the signal charge is accumulated. When the accumulation time is set shorter than the predetermined value (or the sensitivity is lower than the predetermined value), the correction data generation circuit 42 and the arithmetic processing circuit 43 are not operated and the correction process is not performed.

  A photographing process procedure of the digital camera 10 configured as described above will be described with reference to a flowchart of FIG. In a state where the digital camera 10 is set to the shooting mode, when a shutter release operation is performed by pressing the shutter button 14 halfway and then fully, first, the captured image data is stored in the buffer memory 40. Is done. Thereafter, the CPU 30 determines whether or not to perform the correction process. If the CPU 30 determines not to perform the correction process, the image data in the buffer memory 40 is compressed and recorded in the memory card 46, and the photographing process ends.

  On the other hand, if the CPU 30 determines that the correction process is to be performed, as described above, the average value of the noise signal is calculated for each block 57 in which the light shielding unit 56 is divided by the correction data generation circuit 42, Correction data such as 5 (B) is created. Then, the correction data is subtracted from the image data for each horizontal line by the arithmetic processing circuit 43, and the shading correction in the horizontal direction is performed as shown in FIG. Thereafter, the image data subjected to the shading correction is compressed and recorded in the memory card 46, and the photographing process is completed.

  In the above embodiment, the light shielding portion 56 is provided so as to shield the plurality of horizontal lines 51. However, the present invention is not limited to this, and the pixels 50 are arranged along the vertical transfer path 52 as shown in FIG. The light shielding part 56 may be provided so as to shield the plurality of vertical lines formed. In this case, the light shielding unit 56 is divided into a plurality of blocks 57 so as to divide the vertical line by the correction data generation circuit 42, and the average value of the noise signal is calculated for each block 57 in the same manner as described above, and linearly Correction data corresponding to each pixel position in a direction parallel to the vertical line is calculated by interpolation. Then, the arithmetic processing circuit 43 subtracts the correction data from the image data for each vertical line to perform vertical shading correction.

  Further, as shown in FIG. 9, the light shielding portion 56 may be divided into a plurality of regions. This figure shows an example in which the light shielding portion 56 is divided and arranged above and below the photosensitive portion 55. The imaging process procedure in this case will be described based on the flowchart of FIG. After the shutter release operation, the captured image data is stored in the buffer memory 40. When the CPU 30 determines that the correction process is to be performed, first, the correction data generation circuit 42 blocks the light shield disposed above the photosensitive portion 55. An average value of noise signals is calculated for each block 57 of the unit 56, and correction data is calculated by linear interpolation. Similarly, the second correction data is calculated from the light shielding unit 56 disposed below the photosensitive unit 55.

  Based on the calculated first and second correction data, the correction data generation circuit 42 further calculates correction data related to each vertical pixel position of the photosensitive portion 55 by linear interpolation, and sets the correction data at each pixel position of the photosensitive portion 55. Corresponding correction data is created. Then, the shading correction in the horizontal direction and the vertical direction is performed by subtracting correction data corresponding to each pixel position from the image data by the arithmetic processing circuit 43. The image data subjected to the shading correction is compressed and recorded in the memory card 46, and the photographing process is completed.

  Next, FIG. 11 shows a method of reading a noise signal from the light-shielding unit 56, which is suitable when performing multi-field reading of three or more fields in the CCD image sensor 37 having the configuration of FIG. For example, in the case of three field readout, the first field readout for reading out the first horizontal line, the fourth horizontal line, the seventh horizontal line,..., The second horizontal line, the fifth horizontal line, the eighth horizontal line, ... And a third field for reading the third horizontal line, the sixth horizontal line, the ninth horizontal line,.

  As shown in FIG. 11, in the first field, the noise signal is captured only from the light shielding part 56 below the photosensitive part 55, and the noise signal is not captured from the light shielding part 56 above the photosensitive part 55. In the second field, the noise signal is taken in only from the light shielding part 56 on the upper side of the photosensitive part 55, and the noise signal is not taken in from the light shielding part 56 on the lower side of the photosensitive part 55. After the third field, no noise signal is captured from either the lower light shielding portion 56 or the upper light shielding portion 56. Thereby, it is not necessary to take in an extra noise signal when taking in image data, and it is possible to speed up reading. Also, with this method, correction data can be created by the correction data creation circuit 42 when image data is read up to the second field.

  In the above embodiment, the present invention has been described by taking a CCD image sensor as an example of a solid-state imaging device. However, the present invention can also be applied when a CMOS image sensor is used instead of a CCD image sensor. It is.

It is an external appearance perspective view of a digital camera. It is a block diagram which shows the electric constitution of a digital camera. It is a block diagram which shows the structure of a CCD image sensor. It is a figure which shows the example in which the light-shielding part was provided in the horizontal direction. (A) is a graph which shows the average value of the noise signal calculated for every block of a light-shielding part, (B) is a figure which shows the correction data calculated by linear interpolation. It is a flowchart which shows the imaging | photography process procedure of a digital camera. It is a graph which shows the luminance value before and after the shading correction | amendment in one horizontal line. It is a figure which shows the example in which the light-shielding part was provided in the perpendicular direction. It is a figure which shows the example in which the light-shielding part was provided in the upper and lower sides of the photosensitive part. 10 is a flowchart showing a photographing processing procedure of the digital camera having the configuration of FIG. 9. 10 is a flowchart showing a noise signal readout method suitable for the configuration of FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Digital camera 14 Shutter button 37 Image sensor 40 Buffer memory 42 Correction data creation circuit 43 Arithmetic processing circuit 46 Memory card 50 Pixel 51 Horizontal line 52 Vertical transfer path 53 Horizontal transfer path 54 Output part 55 Photosensitive part 56 Light-shielding part 57 Block

Claims (5)

A solid-state imaging device having a light-shielding part that shields some of a plurality of horizontal lines in which a plurality of pixels are arranged along a horizontal transfer path;
At the time of reading the imaging signal from the solid-state imaging device, the noise signal is taken from each region divided so as to divide the light shielding portion into horizontal lines, an average value is calculated, and this is linearly interpolated. Correction data creating means for creating correction data corresponding to each pixel position in the direction parallel to
An imaging apparatus comprising: arithmetic processing means for subtracting the correction data from the imaging signal for each horizontal line. A solid-state imaging device having a light-shielding portion that shields some of the plurality of vertical lines in which a plurality of pixels are arranged along a vertical transfer path;
When reading out the imaging signal from the solid-state imaging device, a vertical line is obtained by calculating an average value by taking a noise signal from each region obtained by dividing the light shielding unit into a plurality of parts so as to divide the vertical line, and linearly interpolating the noise value. Correction data creating means for creating correction data corresponding to each pixel position in the direction parallel to
An imaging apparatus comprising: arithmetic processing means for subtracting the correction data from the imaging signal for each vertical line. The light shielding part is divided so as to sandwich a photosensitive part composed of a plurality of horizontal lines on which subject light is incident,
The correction data creating means creates correction data corresponding to each pixel position of the photosensitive unit by performing linear interpolation in a direction perpendicular to the horizontal line in addition to a direction parallel to the horizontal line,
The photographing apparatus according to claim 1, wherein the arithmetic processing unit subtracts the correction data for each pixel from the imaging signal. In the case of performing multi-field readout of three or more fields at the time of readout of the imaging signal from the solid-state imaging device,
In the first field, a noise signal is taken in from one of the divided light shielding parts, in the second field, a noise signal is taken in from the other divided light shielding part, and in the third field and thereafter, any of the light shielding parts 4. The photographing apparatus according to claim 3, wherein a noise signal is not captured from the camera. The control unit for determining whether or not to operate the correction data generation unit and the arithmetic processing unit according to a signal charge accumulation time of the solid-state imaging device or a set value of sensitivity. The photographing apparatus according to any one of 1 to 4.

Images