JP2007195114A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which shortens processing time for shading correction to reduce storage capacity of correction data used for correction processing. <P>SOLUTION: In the imaging apparatus having a light receiving means for photoelectric conversion, an input means for inputting an electric signal and a correction means for the shading correction, the correction means axisymmetrically performs the shading correction to Y data of Y(xr, y0) based on an xc line. Namely, the correction processing is performed by multiplying the Y data of Y(xl, y0) symmetrically positioned to Y(xr, y0) by a correction coefficient of adj(xl, y0) corresponding to the Y data Y(xl, y0). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that performs shading correction processing of an image signal.

  In general, in an image acquired by an imaging device such as a digital camera, a phenomenon of a decrease in peripheral light amount called shading occurs. This shading is due to the optical characteristics of the lens unit. As shown in FIG. 3, when the center of the lens unit is used as a reference, the amount of light decreases as the distance from the center decreases. This is particularly noticeable with wide-angle lenses, and when the image is viewed, the periphery appears darker than near the center.

  Further, as a factor that darkens the periphery, there is one caused by the image sensor. The image pickup device has a large number of PD cells arranged. In order to increase the sensitivity, a microlens is arranged on each PD cell to improve the light condensing property. In the vicinity of the center of the image sensor, the position of the microlens is substantially coincident with the position of the PD cell. However, since the incident angle is large in the PD cell in the peripheral portion of the image sensor, as shown in FIG. The center position of the microlens is shifted, and the aperture amount becomes relatively small. For this reason, even when illumination with uniform luminance is used, the amount of peripheral light is reduced.

  Furthermore, since the microlens is pasted after manufacturing the PD cell, an error in the pasting position inevitably occurs. Since the sensitivity of the PD cell is improved by the microlens, the displacement of the microlens leads to a decrease in the sensitivity of the PD cell. In the peripheral part of FIG. 4, as shown in the figure, the center positions of the PD cell and the microlens are shifted in advance. However, if the light amount decrease due to the misalignment of the microlens is superimposed on this, the light amount decrease near the center. Although it is relatively small, it can be easily imagined that there is a large decrease in the amount of light due to the misalignment of the microlenses in the horizontal direction, especially in the peripheral part.

  As can be seen from FIG. 4, in the square pixel imager used in the digital camera, the pixel pitch is the same in both horizontal and vertical directions, but the transfer path and metal wiring are arranged in the vertical direction. Is elongated in the vertical direction, and the shape of the PD cell is vertically long. For this reason, the influence of the misalignment of the microlenses is greater in the horizontal direction than in the vertical direction.

  In order to improve the shading characteristics as described above, shading correction is performed. The shading correction method is a method for correcting the luminance value of each pixel using a correction formula, or having a reference table to store a correction coefficient corresponding to each pixel, and corresponding to each pixel by referring to the reference table. Some of them multiply by a correction coefficient. In recent years, the image size has become larger due to the increase in the number of pixels of the imaging device. Therefore, when shading correction is performed, the coefficient for generating a correction formula is read and multiplication is repeated for each pixel. It tends to be enormous and the correction processing time tends to be long. Further, when the correction coefficient corresponding to each pixel is stored in the reference table, as shown in FIG. 6, a storage capacity proportional to the number of pixels of the image is required, which causes an increase in cost.

On the other hand, in Patent Document 1, for example, it is possible to simplify the correction system and reduce correction data by switching whether or not to perform shading correction according to the shooting setting conditions, and to perform continuous shooting by increasing the calculation time. An imaging apparatus that can prevent a decrease in the number of shots due to an increase in interval and an increase in power consumption is disclosed.
JP 2006-13887 A

  The invention disclosed in Patent Document 1 has means for switching the implementation of shading correction based on shooting setting conditions such as zoom position, aperture, and focus position, and correction data corresponding to the shooting setting conditions is stored in a storage circuit. Therefore, it cannot be said that the correction data can be reduced. In addition, it is unlikely that the correction processing time can be shortened.

  Further, as described above, in shading, the difference in the amount of incident light between the central region and the peripheral region and the difference in the influence of the misalignment position of the microlens in the vertical direction and the horizontal direction appear from the characteristics of the lens unit. Making good use of the characteristics is desirable to realize a simpler and lower cost configuration.

  Therefore, an object of the present invention is to provide an imaging apparatus that shortens the processing time for shading correction and reduces the storage capacity of correction data used for correction processing.

  In order to achieve this object, the invention according to claim 1 is a light receiving means for converting an optical signal of a subject image into an electric signal, an input means for inputting the electric signal converted by the light receiving means as an image signal, An image pickup apparatus comprising: a correction unit that performs a shading correction process on the image signal input by the input unit, wherein the correction unit is axisymmetric in the horizontal direction with respect to the image signal input by the input unit. A shading correction process is performed.

  The present invention includes a light receiving unit, an input unit, and a correction unit, and the correction unit performs shading correction on the input image signal in line symmetry in the horizontal direction. For example, when shading correction is performed on a certain image signal, the correction processing is performed on the image signal at the address located on the line object on the left and right with respect to the address of the image signal and the center line. For this reason, it is not necessary to hold different correction data in the left and right areas, the storage capacity for storing the correction data can be reduced, and the shading correction processing time can be shortened.

  According to a second aspect of the present invention, in the imaging apparatus according to the first aspect, the correction unit performs a shading correction process for only one half region in the horizontal direction, and a region opposite to the one half portion. A shading correction process is performed with respect to the image signal located at a line symmetry in the horizontal direction.

  According to a third aspect of the present invention, in the imaging apparatus according to the first or second aspect, the correction unit does not perform a shading correction process on a central region of the image signal input by the input unit. Features.

  According to a fourth aspect of the present invention, in the imaging apparatus according to any one of the first to third aspects, the shading correction process is performed with the same correction amount in the vertical direction of the image signal input by the input unit. It is characterized by that.

  The invention according to claim 5 is the imaging apparatus according to any one of claims 1 to 4, further comprising storage means for storing a reference table of correction coefficients used for shading correction processing, wherein the correction means The shading correction processing is performed by referring to the reference table and multiplying by a correction coefficient corresponding to the image signal input by the input means.

  According to a sixth aspect of the present invention, in the imaging apparatus according to the fifth aspect, the storage unit stores a reference table of correction coefficients corresponding to image signals located in a half area in the horizontal direction, and When the correction means performs a shading correction process on the image signal in the region opposite to the one half region, the one half located in symmetry with the image signal in the opposite region with respect to the center line. The correction coefficient corresponding to the image signal of the area is used.

  According to the present invention, it is possible to realize an imaging apparatus that shortens the processing time for shading correction and reduces the storage capacity of correction data used for correction processing.

  First, the configuration of an imaging apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an imaging apparatus according to the present embodiment. The imaging apparatus according to the present embodiment includes an imaging device 1, an S / H circuit 2, an A / D circuit 3, an image data controller 4, a memory 5, a display device 6, a compression / decompression circuit 7, an image recording medium 8, and a timing generation circuit 9. , A system controller 10, an EEPROM 11, an operation switch 12, a shutter drive circuit 13, a shutter mechanism 14, and a lens unit 15.

  The light incident on the lens unit 15 from the subject forms an image on the image sensor 1. In the image sensor 1, charges corresponding to the amount of incident light are transferred and output by a photoelectric conversion action, and an optical signal is converted into an electrical signal.

  The shutter mechanism 14 controls the light amount and timing of the optical signal incident on the image sensor 1. Specifically, an open / close signal is output to the shutter drive circuit 13 in accordance with the operation state from the operation switch 12, and exposure and light shielding states are set in accordance with the open / close signal. The open / close signal is generated by the system controller 10 connected to the image data controller 4.

  The electrical signal photoelectrically converted by the image sensor 1 is input to the S / H circuit 2 and sampled and held to obtain an analog signal corresponding to each pixel. The S / H circuit 2 is a sample-and-hold circuit, and analogly outputs the transferred charges as image data. The analog signal output from the S / H circuit 2 is input to the A / D circuit 3 and converted into a digital signal. The A / D circuit 3 is an analog / digital conversion circuit.

  The digital signal converted by the A / D circuit 3 is subjected to image data correction processing by the image data controller 4, encoded by the compression / decompression circuit 7, output to the image recording medium 8, and stored as image data. The A memory 5 such as a semiconductor memory is used as a temporary storage location necessary for this work.

  The image data controller 4 has a function of performing correction processing of image data acquired by the image sensor 1, that is, interpolation processing, color processing, gradation control, edge enhancement, and the like, and performs shading correction as described later. Do. The image data controller 4 is connected to the A / D circuit 3 on the input side and the display device 6 on the output side. The memory 5, the compression / decompression circuit 7, the timing generation circuit 9 and the system controller 10 are connected so as to allow input / output. Has been.

  The system controller 10 controls the operation and the like of the entire image pickup apparatus, and data such as setting values and control items necessary for optimal operation of the system is stored in the EEPROM 11. These stored data are read from the EEPROM 11 by the system controller 10 as necessary, and used for the setting and calculation of each module. Also included are reference data necessary for shading correction, coefficients for calculation, and the like.

  The operation switch 12 is used by a user of the imaging apparatus to operate the imaging apparatus, and includes a release switch, a power switch, switching of recording and reproducing operations, and the like.

  The image sensor 1, the S / H circuit 2, the A / D circuit 3, and the image data controller 4 need to operate in synchronization with each other, and a signal for synchronizing them is generated by the timing pulse generation circuit 9, Supplied to each.

  In addition, the image being captured or the image that has been captured and saved is sent to the interface for the display device, converted into a signal format for display on the display device 6, and displayed.

  Next, shading correction processing in the imaging apparatus of the present embodiment will be described with reference to the drawings.

  FIG. 2 is a diagram illustrating a series of signal processing performed by the imaging apparatus of the present embodiment. Shading correction is performed in a series of signal processing in the image data controller 4.

  First, digital data (RAW data) after conversion by the A / D circuit 3 is subjected to interpolation processing and converted into RGB digital signals (RBG conversion 21). Next, gamma conversion is performed (γ conversion 22), the luminance signal and the color difference signal are separated (YCbCr conversion 23), and only the luminance signal is subjected to shading correction (shading correction 25). The luminance signal subjected to the shading correction is compressed together with the color difference signal corresponding to the pixel (compression process 24) and recorded on the image recording medium (recording medium 26).

  FIG. 3 shows the characteristics of shading. In general, an image sensor used in a digital camera or the like has an aspect ratio of 4: 3. Therefore, when the longitudinal direction is a horizontal direction, the vertical direction is the distance from the center to the edge of the image. In addition, as described with reference to FIG. 4, since the influence of the bonding deviation between the microlens and the PD cell in the image sensor is smaller in the vertical direction, the shading amount in the vertical direction is relatively small. Therefore, it is only necessary to perform shading correction only in the horizontal direction without performing shading correction in the vertical direction.

  FIG. 5 shows captured image data. As described above, after the captured image is converted into a digital signal, it is separated into a luminance signal and a color difference signal by YCbCr conversion, and this luminance signal is subjected to shading correction. There are approximately the same number of luminance signals as the number of pixels of the image, and x (m + 1) * y (n + 1) in the example of FIG. In order to perform shading correction of this number of pixels, at least the same number of calculations as the number of pixels is required.

  As described above, the shading characteristic of the lens unit is such that the amount of light decreases radially from the center toward the periphery, so that the degree of decrease in the amount of light is proportional to the distance from the center. Further, the incident angle of the image sensor increases with the distance from the center. Thus, it can be seen that both have shading characteristics that are symmetrical in the horizontal direction with respect to the center of the image, and that it is sufficient to perform shading correction depending on the distance from the center of the image.

  In the imaging apparatus according to the present embodiment, the image data controller 4 serving as a correction unit performs a shading correction process that is symmetrical with respect to the center in the horizontal direction by using the above-described property. Thereby, it is possible to greatly reduce the amount of calculation required for correction.

  FIG. 6 shows luminance signal data (Y data) and correction coefficients corresponding thereto. Assuming that the xc line is a center line orthogonal to the horizontal direction, for example, for Y data located at Y (xr, y0), Y data of Y (xl, y0) located symmetrically may be subjected to shading correction. It is sufficient to use the correction coefficient of adj (xl, y0) located at the left and right objects of adj (xr, y0), and the correction coefficient of the area from adj (x0, y0) to adj (xc, yn) is held as data. That's fine. That is, although the correction coefficient is stored in the reference table, as described above, since the shading correction processing is performed symmetrically in the horizontal direction, the correction coefficient used only needs to be a half on one side. Similarly, the memory capacity required for this is halved, which is a significant reduction.

  FIG. 8 is a flowchart showing the flow of shading correction processing in the imaging apparatus of the present embodiment. Here, as shown in the reference table of FIG. 6, it is assumed that x0 to xc have x (c + 1) correction coefficients in the horizontal direction.

  When the address of x is smaller than the center xc (step S801 / YES), the correction coefficient corresponding to the address is set as the correction coefficient of the Y data (step S802). On the contrary, when the address of x is larger than the center address xc (step S801 / NO), the correction coefficient at the address (xm-x) opposite to the center at the same distance from the center to the address is set as the Y data. Used as a correction coefficient (step S803). The correction coefficient obtained in this manner is multiplied by the Y data to obtain a shading correction result (step S804). Thereafter, 1 is added to the x address to change it, and shading correction of all addresses is performed (step S805).

  When shading correction processing is performed according to the above flow, the number of correction coefficients required for the reference table is half of the number of pixels of the image, and the number of computations is halved compared to when shading correction is performed for all pixels in the horizontal direction. I understand that

  It is also possible to reduce the time required for the shading correction process by reducing the number of computations by performing shading correction only on the peripheral part where the light amount drop is small without performing shading correction on the part where the light amount drop near the center is small. . As described above, as can be seen from the diagram on the left side of FIG. 3, the amount of light fall is small near the center of the image, and the degree of light fall accelerates as the distance from the center increases. The correction process is performed as described above using the characteristics.

  FIG. 9 is a flowchart showing the flow of the above operation in the imaging apparatus of the present embodiment. Here, as shown in the reference table of FIG. 6, Y data between the addresses xl to xr whose addresses in the x direction are near the center, that is, (xr−xl) Y data in total is not subjected to shading correction.

  If the x address is smaller than xl (step S901 / YES), the correction coefficient corresponding to the address is used as the correction coefficient for the Y data (step S902). On the other hand, if the x address is larger than xl (step S901 / NO) and larger than xr (step S903 / YES), the correction coefficient at the address (xm-x) located symmetrically with respect to the center is used to calculate the Y It is set as a data correction coefficient (step S904). If the x address is larger than xl (step S901 / NO) and smaller than xr (step S903 / NO), it is determined that the Y data is located in the area near the center, and the x address is not subjected to shading correction. Addition is performed (S906). Next, the Y data is multiplied by the obtained correction coefficient to obtain a luminance value after shading correction (step S905). Thereafter, the x address is added and changed to perform shading correction for all addresses (step S906).

  When shading correction processing is performed according to the above flow, the number of correction coefficients required for the reference table can be further less than half of the number of pixels of the image, and the number of calculations is similarly reduced. It can be seen that the time is further shortened and the storage capacity of the correction data can be further reduced.

  Further, by performing only the horizontal direction without performing the shading correction in the vertical direction, the storage capacity of the correction data can be further reduced. As described above, as shown in FIG. 4, since the shape of the PD cell is vertically long, the influence of the misalignment of the micro lens is larger in the horizontal direction. Thus, the correction process is performed as described above.

  FIG. 7 shows the correction coefficient when the shading correction is performed only in the horizontal direction as described above. The upper figure shows the case where shading correction is performed for all pixels in the horizontal direction as in the conventional case, the middle figure shows the case where shading correction is performed symmetrically with respect to the center line, and the lower figure shows the periphery where light loss is large. This is a case where shading correction is performed symmetrically only on the part. In this way, the number of correction coefficients used in the shading correction can be smaller than the number of pixels of the image, and the memory capacity required for the reference table can be greatly reduced.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

  According to the above embodiment, since the shading correction is performed symmetrically with respect to the horizontal center line, the number of calculations for correction can be reduced to almost half, and the time required for processing can be shortened.

  Further, according to the above-described embodiment, since the shading correction of the area near the center is not performed, the number of calculations for correction can be greatly reduced, and the time required for processing can be greatly shortened.

  Further, according to the above-described embodiment, by making the shading correction in the vertical direction the same correction value, it is possible to reduce the number of computations required for the correction and to shorten the time required for processing.

  Further, according to the above-described embodiment, by storing the correction coefficient in the reference table, the number of calculations for correction can be reduced, and the time required for processing can be shortened.

  Further, according to the above-described embodiment, the memory capacity necessary for storage can be reduced by reducing the correction coefficient stored in the reference table.

1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows a series of signal processing in the imaging device which concerns on embodiment of this invention. It is explanatory drawing which shows the characteristic of shading. It is explanatory drawing which shows the structure of an image pick-up element. It is a conceptual diagram which shows the imaged image data. It is a conceptual diagram which shows the image data and correction data in the imaging device which concerns on embodiment of this invention. It is a conceptual diagram which shows the correction data in the imaging device which concerns on embodiment of this invention. It is a flowchart which shows the flow of the shading correction | amendment in the imaging device which concerns on embodiment of this invention. It is a flowchart which shows the flow of the shading correction | amendment in the imaging device which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up element 2 S / H circuit 3 A / D circuit 4 Image data controller 5 Memory 6 Display apparatus 7 Compression / decompression circuit 8 Image recording media 9 Timing generation circuit 10 System controller 11 EEPROM
12 Operation switch 13 Shutter drive circuit 14 Shutter mechanism 15 Lens unit

Claims (6)

A light receiving means for converting an optical signal of a subject image into an electrical signal;
Input means for inputting the electric signal converted by the light receiving means as an image signal;
An image pickup apparatus comprising: a correction unit that performs a shading correction process on the image signal input by the input unit;
The image pickup apparatus according to claim 1, wherein the correction unit performs a shading correction process on the image signal input by the input unit in a line symmetrical manner in the horizontal direction.   The correction means performs a shading correction process only for a half area on one side in the horizontal direction, and performs a shading correction process in line symmetry with respect to the image signal located in the area on the opposite side to the one half area. The imaging device according to claim 1, wherein the imaging device is performed.   The imaging apparatus according to claim 1, wherein the correction unit does not perform a shading correction process on a central region of the image signal input by the input unit.   The imaging apparatus according to claim 1, wherein the correction unit performs shading correction processing with the same correction amount in the vertical direction of the image signal input by the input unit. Storage means for storing a reference table of correction coefficients used for shading correction processing;
5. The shading correction process according to claim 1, wherein the correction unit refers to the reference table and performs a shading correction process by multiplying a correction coefficient corresponding to the image signal input by the input unit. The imaging device described. The storage means stores a reference table of correction coefficients corresponding to the image signal located in the one half region in the horizontal direction,
When the correction means performs a shading correction process on an image signal in a region opposite to the one half region, the one side positioned symmetrically with the image signal in the opposite region with respect to the center line 6. The imaging apparatus according to claim 5, wherein a correction coefficient corresponding to an image signal of a half area is used.

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