JP2005277618A - Photography taking apparatus and device and method for correcting shading - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photography taking apparatus capable of correcting shading in an image at a high speed, and to provide a shading correcting device and a shading correcting method. <P>SOLUTION: Shading in an image photographed by an imaging device is corrected in the step of Bayer data. For each pixel P, horizontal and vertical distances H and V to the correction center O of a Bayer image 100 are acquired for being fit to a quadratic function, thus calculating a shading coefficient corresponding to a distance L to the correction center O in each pixel P. The shading can be corrected by simple processing at a high speed and in real time. The shading coefficient of each pixel P is acquired according to the same reference, thus obtaining a naturally corrected result. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus, an image shading correction apparatus, and a shading correction method.

  Conventionally, in imaging by an imaging device having an imaging device such as a CCD or a CMOS sensor, shading correction is necessary to eliminate this because shading occurs in the center of the captured image that is brighter in the center and darker in the periphery. Yes. Shading is a reduction in the peripheral light amount of the optical image in the optical characteristics of the imaging lens that forms an optical image on a photosensitive surface such as a CCD (decrease due to the ratio of the cosine fourth law). The constituent photodiode is embedded in the lower part of the microlens, the light incident angle becomes larger at the peripheral part, and it occurs due to uneven sensitivity because the light collection effect is lower than the central part. The degree becomes particularly large when a wide-angle lens is used.

As a shading correction method, for example, the following method is described in Patent Document 1 below. In other words, white reference data is acquired in advance at sampling points on the horizontal and vertical center axes of the effective imaging plane, a mesh area is set on the effective imaging plane, and a correction coefficient for the horizontal coordinate and a correction coefficient for the vertical coordinate. Is used to calculate a shading coefficient on an arbitrary coordinate in the effective imaging plane for each mesh area, and correct the brightness for each pixel based on the shading coefficient for each mesh area.
JP 2003-169255 A

  However, since the conventional shading correction described above is an interpolation method using sampling data in orthogonal coordinates, calculation of shading coefficients is complicated, and a camera system using a CCD performs high-speed processing such as moving image shooting. There was a problem that the processing speed was not in time when needed.

  The present invention has been made in view of such conventional problems, and an object thereof is to provide an imaging apparatus, a shading correction apparatus, and a shading correction method capable of performing shading correction of an image at high speed.

  In order to solve the above-mentioned problem, the invention of claim 1 is a shading correction apparatus for correcting shading of an image captured by an image sensor, wherein each pixel has a correction center of an image corresponding to the optical axis. The calculation means for calculating the shading coefficient of each pixel based on the distance and the adjustment means for adjusting the brightness of each pixel according to the shading coefficient for each pixel calculated by the calculation means are provided.

  In such a configuration, shading correction is performed by adjusting the brightness of each pixel according to a shading coefficient based on the distance from the correction center of the image. That is, the brightness of each pixel is adjusted by a shading coefficient that is easy to acquire. In addition, since the shading coefficient is based on the same standard such as the distance from the correction center of the image, the brightness adjustment amount of each pixel changes smoothly.

  Further, in the invention of claim 2, the calculation means calculates a shading coefficient for each pixel using a quadratic function whose variables are horizontal and vertical distances from the correction center in each pixel. did.

  According to a third aspect of the present invention, the pixel for which the calculation means calculates the shading coefficient is a pixel having different color information depending on the position in the image formed thereby.

  In such a configuration, shading correction is performed by processing for pixels having a single color information constituting a Bayer image or the like.

  According to a fourth aspect of the present invention, the calculation means calculates a shading coefficient of each pixel based on the distance from the correction center of the image corresponding to the optical axis and the color information of each pixel for each pixel. To do.

  In such a configuration, the brightness of each pixel is adjusted by a more accurate shading coefficient corresponding to the color information of each pixel.

  According to a fifth aspect of the present invention, the calculation means includes, for each pixel, a distance from the correction center of the image corresponding to the optical axis, and pixel thinning performed at the time of acquiring an image composed of each pixel. The shading coefficient of each pixel based on the content of processing is calculated.

  In such a configuration, a shading coefficient can be obtained according to the contents of the pixel thinning process.

  The invention according to claim 6 is a shading correction method for correcting shading of an image picked up by an image pickup device, wherein each pixel corresponds to the distance from the correction center of the image corresponding to the optical axis. The method includes a step of obtaining a shading coefficient and a step of adjusting the brightness of each pixel in accordance with the obtained shading coefficient for each pixel.

  According to this method, the brightness of each pixel is adjusted by a shading coefficient that is easy to acquire. In addition, since the shading coefficient is based on the same standard such as the distance from the correction center of the image, the brightness adjustment amount of each pixel changes smoothly.

  According to a seventh aspect of the invention, there is provided a shading correction device for correcting shading of an image picked up by an image pickup device, wherein each pixel having different color information depending on a position in an image formed thereby. An acquisition unit that acquires a shading coefficient and an adjustment unit that adjusts the brightness of each pixel having different color information depending on the position in the image according to the shading coefficient acquired by the acquisition unit. .

  In such a configuration, shading correction is performed by adjusting the brightness of each pixel having color information corresponding to the position in the image formed thereby according to the shading coefficient acquired for each pixel. . In other words, the shading correction is performed by a process for a pixel having single color information constituting a Bayer image or the like.

  According to an eighth aspect of the invention, there is provided storage means for storing the shading coefficient in association with the position in the image at each pixel, and the acquisition means is based on the position in the image at each pixel. The shading coefficient for each pixel is read from the storage means.

  In such a configuration, the process for obtaining the shading coefficient of each pixel is simplified.

  The invention according to claim 9 is a shading correction method for correcting shading of an image picked up by an image pickup device, wherein each pixel has different color information depending on the position in the image formed thereby. The method includes a step of acquiring a shading coefficient for each pixel and adjusting a brightness for each pixel having different color information depending on the position in the image according to the acquired shading coefficient.

  According to this method, the shading correction is performed by the process for the pixels having single color information constituting the Bayer image or the like.

  According to a tenth aspect of the present invention, there is provided a shading correction apparatus for correcting shading of an image captured by an image sensor, wherein pixel thinning performed when acquiring an image composed of each pixel for each pixel. It is provided with a determining unit that determines a shading coefficient according to the processing content and an adjusting unit that adjusts the brightness of each pixel according to the shading coefficient for each pixel determined by the determining unit.

  In such a configuration, since the brightness of each pixel is adjusted according to the shading coefficient corresponding to the content of the pixel thinning process performed at the time of image acquisition, shading correction corresponding to the pixel thinning is performed. The present invention can also cope with the case where the image sensor is driven by a driving method that performs pixel thinning.

  In addition, in the invention of claim 11, the determination means is acquired by the acquisition means for acquiring a shading coefficient for each pixel based on the distance from the correction center of the image corresponding to the optical axis. Correction means for correcting the shading coefficient for each pixel in accordance with the content of the pixel thinning process performed when acquiring an image composed of each pixel.

  The invention according to claim 12 further comprises storage means for storing a shading coefficient for each of the pixels in association with a plurality of types of pixel thinning processing having different processing contents. The shading coefficient stored in the storage unit corresponding to the type of pixel thinning process performed when acquiring the configured image is determined as the shading coefficient for each pixel.

  In such a configuration, the process for obtaining the shading coefficient of each pixel is simplified.

  The invention according to claim 13 is a shading correction method for correcting shading of an image picked up by an image pickup device, wherein pixel thinning performed when acquiring an image constituted by each pixel for each pixel. The method includes a step of determining a shading coefficient according to the content of processing and a step of adjusting the brightness of each pixel according to the determined shading coefficient.

  In such a method, since the brightness of each pixel is adjusted according to the shading coefficient corresponding to the content of the pixel thinning process performed at the time of image acquisition, shading correction corresponding to pixel thinning is performed. The present invention can also cope with the case where the image sensor is driven by a driving method that performs pixel thinning.

  According to a fourteenth aspect of the present invention, there is provided an image pickup apparatus including an image pickup device that picks up an optical image of a subject, and an image corresponding to an optical axis is obtained for each pixel of an image picked up by the image pickup device. A calculation unit that calculates a shading coefficient based on the distance from the correction center and an adjustment unit that adjusts the brightness of each pixel in accordance with the shading coefficient for each pixel calculated by the calculation unit are provided.

  In such a configuration, the shading correction is performed by adjusting the brightness of each pixel in the image captured by the image sensor in accordance with the shading coefficient based on the distance from the correction center of the image. That is, the brightness of each pixel is adjusted by a shading coefficient that is easy to acquire. In addition, since the shading coefficient is based on the same standard such as the distance from the correction center of the image, the brightness adjustment amount of each pixel changes smoothly.

  According to a fifteenth aspect of the present invention, there is provided an image pickup apparatus including an image pickup device for picking up an optical image of a subject, and an image picked up by the image pickup device is formed and differs depending on a position in the image. Acquisition means for acquiring a shading coefficient for each pixel having color information, and adjustment means for adjusting the brightness of each pixel having different color information depending on the position in the image according to the shading coefficient acquired by the acquisition means And provided with.

  In such a configuration, the brightness of each pixel that is imaged by the image sensor and has color information corresponding to the position in the image configured thereby is adjusted according to the shading coefficient acquired for each pixel. Thus, shading correction is performed. In other words, the shading correction is performed by a process for a pixel having single color information constituting a Bayer image or the like.

  According to a sixteenth aspect of the present invention, there is provided an image pickup apparatus including an image pickup device for picking up an optical image of a subject, and for each pixel constituting the image picked up by the image pickup device, the image pickup is performed A determining means for determining a shading coefficient according to the content of the implemented pixel thinning process, and an adjusting means for adjusting the brightness of each pixel according to the shading coefficient for each pixel determined by the determining means It was.

  In such a configuration, for each pixel, a determination unit that determines a shading coefficient corresponding to the content of the pixel thinning process performed when acquiring an image composed of each pixel, and the shading for each pixel determined by the determination unit An adjustment unit that adjusts the brightness of each pixel according to the coefficient is provided.

  In such a configuration, the brightness of each pixel constituting the image captured by the image sensor is adjusted according to the shading coefficient corresponding to the content of the pixel decimation process performed at the time of imaging, thereby reducing the pixel decimation. Since the corresponding shading correction is performed, it is possible to cope with the case where the image sensor is driven by a driving method that performs pixel thinning.

  The invention according to claim 17 further includes display means for displaying an image in which the brightness of each pixel is adjusted by the adjusting means.

  In such a configuration, the captured image can be displayed after being subjected to shading correction.

  The invention according to claim 18 further comprises recording means for recording an image in which the brightness of each pixel is adjusted by the adjusting means.

  In such a configuration, the captured image can be recorded with shading correction.

  As described above, in the inventions according to claims 1 to 6 and 14, the brightness of each pixel is adjusted by a shading coefficient that is easy to acquire. Therefore, it is possible to perform shading correction at high speed. In addition, since the brightness adjustment amount of each pixel changes smoothly, a high-quality correction result can be obtained.

  In addition to this, in the invention of claim 3, the shading correction is performed by the process for the pixel having the single color information constituting the Bayer image or the like. Therefore, it is possible to perform shading correction at an extremely high speed.

  According to the invention of claim 4, since the brightness of each pixel is adjusted by a more accurate shading coefficient corresponding to the color information of each pixel, it is possible to obtain a higher quality correction result. Become.

  In the invention of claim 5, since the shading coefficient corresponding to the content of the pixel thinning process can be obtained, the shading correction corresponding to the pixel thinning can be performed.

  According to the seventh to ninth and fifteenth aspects of the present invention, the shading correction is performed by a process for pixels having a single color information constituting a Bayer image or the like. Therefore, since the processing for each pixel can be simplified, shading correction can be performed at high speed.

  In addition, according to the eighth aspect of the invention, since the process for obtaining the shading coefficient of each pixel becomes simple, the shading correction can be performed at a higher speed.

  In the inventions according to claims 10 to 13 and 16, it is possible to cope with the case where the image pickup element is driven by a driving method for thinning out pixels. Therefore, it is convenient when high-speed shading correction for a Bayer image or the like composed of pixels having a single color information is simply performed.

  In addition, according to the twelfth aspect of the present invention, since the process for obtaining the shading coefficient of each pixel is simplified, the shading correction can be performed at a higher speed.

  According to the invention of claim 17, in the imaging apparatus, it is possible to display the captured image after performing shading correction.

  In the invention of claim 18, in the imaging device, it is possible to record the captured image after performing shading correction.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a digital camera (imaging apparatus) including a shading correction apparatus according to the present invention.

  The digital camera includes an optical system 1 composed of a plurality of lenses, and a CCD 2 that is an image pickup device arranged on the optical axis of the optical system. The CCD 2 is provided with a primary color filter having a Bayer arrangement as shown in FIG. 2 in a photosensitive portion where an optical image of a subject is formed by the optical system 1, and a predetermined frequency generated by a TG (Timing Generator) 3. Is driven by the timing signal, and an imaging signal corresponding to the brightness of the subject image (light image) is output.

  The CCD 2 is driven by a progressive (all pixel readout) method, and in a shooting standby state in which a through image is displayed as described later, driving by a vertical thinning readout method in which signals are read out. It is possible. Note that the switching of the readout method of the imaging signal is performed by, for example, assigning a readout channel in advance to each row (horizontal line) where the pixels of the CCD 2 are arranged, enabling charge transfer on / off control for each readout channel, and setting the readout channel. This is performed by controlling the readout line of the imaging signal by a combination of (selection) and a vertical transfer pulse and a horizontal transfer pulse supplied as timing signals from the TG 3.

  The imaging signal output from the CCD 2 is amplified by the gain adjusting amplifier 4 and output to the CDS / ADC block 5. The CDS / ADC block 5 includes a CDS (Correlated Double Sampling) circuit that holds the image signal after gain adjustment by correlated double sampling and an A / D converter (ADC), and removes noise in the image signal. Convert to digital signal.

  The imaging signal converted into the digital signal, that is, Bayer data composed of pixel data having any one of R, G, and B color information corresponding to the color arrangement of the filter, is a multiplication circuit 6 that is the adjusting means of the present invention. Thus, the gain is increased (shading correction) for each pixel at a magnification according to the shading coefficient K sent from the shading coefficient generation circuit 7 to be described later, and then sent once to the DRAM 9, where R corresponding to the color arrangement of the filter. , G, B color images (hereinafter referred to as Bayer images) are sequentially stored as pixel data. In the photographing standby state in the photographing mode, horizontal pixel thinning is performed in accordance with the vertical pixel thinning rate in the image pickup signal.

  Data stored in the DRAM 9 is sequentially read and sent to the digital signal processing circuit 8. The digital signal processing circuit 8 generates a pixel interpolation process for generating R, G, B color component data for each pixel based on the input image signal, and a luminance signal for each pixel from the generated R, G, B color component data. Luminance / color difference signal conversion processing for generating YUV data composed of (Y) and color difference signals (U, V) is performed. The digital signal processing circuit 8 also performs processing for improving image quality such as auto white balance and contour enhancement. The YUV data converted by the digital signal processing circuit 8 is sequentially stored in the DRAM 9, and YUV data for one frame is stored in the DRAM 9.

  In the shooting standby state, YUV data for one frame stored in the DRAM 9, that is, YUV data based on the imaging signal read out from the CCD 2 in a progressive manner is read out by the CPU 12 and sent to the image display unit 10. The image display unit 10 is a display means according to the present invention, and includes a video signal generation circuit, a color LCD, and a drive circuit thereof. The image display unit 10 converts YUV data for one frame sent from the CPU 12 into a video signal, which is converted into a color LCD. Display as a through image. In the playback mode, a recorded image or the like is displayed.

  The JPEG circuit 11 compresses the YUV data developed in the DRAM 9, that is, the YUV data based on the imaging signal read out by the progressive method, by the JPEG method at the time of image recording in which the shutter key is pressed in the photographing mode, and reproduces the reproduction mode. At the time of the operation, the compressed image data is expanded to YUV data. Image data encoded by the JPEG circuit 11 at the time of image recording is sent to the CPU 12 and finally recorded as an image file in the image recording unit 13. The image recording unit 13 is a recording unit according to the present invention, and is a variety of nonvolatile memories that are built in or detachable from the camera body. The image data recorded in the image recording unit 13 is read to the CPU 12 as necessary in the reproduction mode, decompressed by the JPEG circuit 11, and then reproduced in the image display unit 10.

  The key input unit 14 includes a switch key used for switching the operation between the shooting mode and the playback mode, and various operation keys such as a shutter key, and sends an operation signal corresponding to the key operation to the CPU 12. The flash memory 15 stores a program necessary for controlling the digital camera by the CPU 12 and various data used in executing the program. The CPU 12 operates in accordance with the operation signal from the key input unit 14 and the program to control the entire apparatus. When the shooting mode is set as will be described later, the CPU 12 is a signal indicating an operation state at that time, and is a through signal. A mode signal indicating the distinction between the shooting standby mode for displaying an image and the recording mode in response to pressing of the shutter key is output to the shading coefficient generation circuit 7.

  FIG. 3 is a block diagram showing the configuration of the shading coefficient generation circuit 7 described above. As shown in FIG. 4, the shading coefficient generation circuit 7 has color information of any one of R, G, and B corresponding to each pixel P, that is, a Bayer array, based on the imaging signals sequentially output from the CDS / ADC block 5. According to the distance L between the pixel position (coordinate position X, Y) where each pixel should be arranged as the Bayer image 100 and the center (correction center) O of the Bayer image 100 corresponding to the optical axis center of the optical system 1. The shading coefficient K is calculated using a quadratic function and is output to the multiplication circuit 6 and has the following configuration.

That is, the shading coefficient generation circuit 7 includes a horizontal position counter 41 and a vertical position counter 42 that operate based on the timing signal sent from the TG 3, thereby acquiring the horizontal position X and the vertical position Y of each pixel P, respectively. To the subtracters 43 and 44. The subtractors 43 and 44 subtract the horizontal / vertical position (Xo, Yo) of the center O previously registered in the register from the horizontal / vertical position (X, Y), respectively, to obtain absolute value circuits 45 and 46. Obtains the distance (H, V) in the horizontal / vertical direction by converting the value after subtraction into an absolute value. The squarers 47 and 48 square both distances (H and V), and the first multiplier 49 has a predetermined flatness corresponding to the mode signal sent from the CPU 12 only to the square value (V ² ) in the vertical direction. Multiply by factor (a).

  The flatness coefficient (a) is “1” when the mode signal indicates the recording mode, and when the mode signal indicates the shooting standby mode, the horizontal line is set by the above-described vertical thinning readout. During the photographing standby mode, pixels having the same distance from the pixel center corresponding to the optical axis center of the optical system 1 in the CCD 2 are arranged as the Bayer image 100 during the photographing standby mode. When this is done, it is an ellipse as shown in FIG. 4, and is a vertical coefficient for correcting it. By applying the flat coefficient (a), the shading coefficient that is finally output from the shading coefficient generation circuit 7 in the imaging standby mode is corrected according to the content of the readout process of the imaging signal by the vertical thinning readout method. It will be.

The adder 50 has the horizontal value (H ² ) squared by the squarer 47 and the vertical value (aV ² ) after being multiplied by the flatness (a) by the first multiplier 49. Is added. The second multiplier 51 multiplies the added value (H ² + aV ² ) by the adjustment coefficient (x1) for adjusting the shading coefficient (for adjusting the degree of opening of the quadratic curve) to obtain the shading coefficient (K). calculate. That means
K = x1 (H ² + aV ² )
Calculate

  The adjustment coefficient (x1) used in the above calculation is an adjustment coefficient for each color of R, G, and B registered in the coefficient register 53, and is switched by a switching operation according to the timing signal from TG3 in the coefficient switch 52. , One corresponding to the color of each pixel P is selectively used. As a result, as shown in FIG. 5, the shading coefficient (K) changes according to the distance L (FIG. 4) from the correction center O in the Bayer image, and the degree of opening for each color of each pixel P. Values for drawing different quadratic curves are calculated. Then, the shading coefficient generation circuit 7 sequentially outputs the shading coefficient (K) calculated by the second multiplier 51 to the multiplication circuit 6 at the timing indicated by the timing signal. That is, in the present embodiment, the shading coefficient generation circuit 7 functions as the calculation means and acquisition means of the present invention. FIG. 5 shows the change in shading coefficient for each color for convenience.

  FIG. 6 is a flowchart showing the contents of processing executed by the CPU 12 in the shooting mode in the digital camera having the above-described configuration.

  The CPU 12 starts processing in response to a switching operation of a mode switch from another mode to a shooting mode in a power-on state or a power-on operation in a state where the mode switch is at a shooting mode position. The method is set to the vertical thinning readout method (step S1), the mode signal indicating the photographing standby mode is output to the shading coefficient generation circuit 7 (step S2), and the imaging processing is started by setting the vertical thinning readout method (step S2). Step S3). Accordingly, the camera enters a shooting standby state, displays a through image on the color LCD of the image display unit 10, and continues the shooting standby state until a shooting operation is performed with the shutter button (NO in step S4). Update. Meanwhile, the shading coefficient generation circuit 7 sends the shading coefficient K for each pixel calculated in accordance with the above driving method to the multiplication circuit 6, and the Bayer data converted into a digital signal by the CDS / ADC 5 The shading correction based on the shading coefficient K is performed for each pixel, thereby preventing the occurrence of shading in the through image.

  Thereafter, when there is a photographing operation by the shutter button (YES in step S4), a mode signal indicating the recording mode is output to the shading coefficient generation circuit 7 (step S5), and the driving method of the CCD 2 is switched to the progressive method to record images. The imaging process is performed (step S6). In such an imaging process, shading correction based on the shading coefficient (K) for each pixel calculated corresponding to the progressive method is performed on the Bayer data converted into a digital signal by the CDS / ADC 5, thereby recording the data. Generation of shading in the image is prevented. Thereafter, the CPU 12 records the image data of the recorded image compressed by the JPEG circuit 11 in accordance with the image capturing process in the image recording unit 13 (step S7), and returns to step S1. The above-described processing is repeated until the mode is changed or the power is turned off.

  As described above, in the present embodiment, the shading coefficient K acquired for each pixel for shading correction is determined according to the distance L from the center O of the Bayer image 100 in each pixel P. As described above, the shading coefficient generation circuit 7 can easily calculate the shading coefficient K by applying the horizontal / vertical distance (H, V) to the quadratic function. Therefore, processing related to shading correction can be performed at high speed. Therefore, the flowchart of FIG. 6 shows the operation procedure when shooting a still image. However, even when a moving image is continuously captured at a predetermined frame rate at the time of moving image shooting, it can be dealt with.

  In addition, by calculating the shading coefficient K for each pixel from the same standard such as the horizontal (vertical) distance (H, V), the brightness adjustment amount of each pixel can be smoothly changed. A high quality correction result can always be obtained. That is, for example, as described above as the background art, in the shading correction method based on the shading coefficient in units of mesh regions, the brightness of the entire screen is uniform when the number of sampling points for obtaining the white reference is insufficient. When a simple image is taken (for example, when the sky is taken), the boundary of the mesh region may be seen, but in this embodiment, a natural image that never happens can be obtained.

  Further, since the shading correction is performed on the imaging signal at the Bayer data stage, that is, the brightness adjustment is performed on the pixel having the single color information, for example, when it is performed at the YUV data stage as described later. Compared to the above, it is easier to calculate the shading coefficient K for each pixel, and it can be performed at high speed. This also makes it possible to perform processing relating to shading correction at high speed.

  In addition, since the shading coefficient generation circuit 7 calculates the shading coefficient K multiplied by the adjustment coefficient corresponding to the color for each pixel, a more accurate shading coefficient K corresponding to the color of the pixel can be obtained. It is possible to obtain a higher quality correction result. Even when the shading correction is performed using the shading coefficient K not multiplied by the color-specific adjustment coefficient as it is, a natural image can always be obtained as described above.

  Further, when a through image is displayed in the shooting standby mode, an accurate shading coefficient K corresponding to the driving method of the CCD 2 can be calculated, and a shading correction similar to the recorded image can be performed on the through image. . Moreover, coupled with the fact that it is performed on the image pickup signal at the Bayer data stage, even if the driving method of the CCD 2 is the vertical thinning readout method, the shading correction of the through image can be performed at high speed.

  Here, in the present embodiment described above, the shading coefficient for each pixel is calculated by the shading coefficient generation circuit 7. However, the shading coefficient for each pixel is not necessarily obtained by calculation. For example, the shading coefficient for each pixel is calculated by the Bayer image 100. It is recorded in a memory (storage means of the present invention) in association with a position (horizontal / vertical direction position) in the image, and a shading coefficient corresponding to the position of each pixel is read from the memory and used. Good. In that case, the processing and circuit configuration for obtaining the shading coefficient can be simplified. However, in that case, for example, it is necessary to separately prepare a shading coefficient used in the above-described recording mode and a shading coefficient used in the shooting standby mode. In this case, the shading coefficient acquisition process may be performed by data processing of the CPU 12 without using hardware. The same applies to the case where the shading coefficient is calculated as in the present embodiment.

  In the present embodiment, the shading correction is performed on the Bayer data. However, the shading correction of the present invention is not limited to the Bayer data, and may be performed on, for example, YUV data after color separation. . In that case, the shading coefficient corresponds to the distance between each pixel having luminance information and color difference information and the correction center of the image formed thereby and each pixel. Even in such a case, the processing related to the shading correction can be performed at a higher speed and a higher quality correction result can be obtained as compared with the conventional case. In this case, in order to obtain a higher quality correction result, it is necessary to acquire a shading coefficient for each pixel corresponding to the content of color interpolation processing or the like when converting from Bayer data to YUV data.

  In this regard, when shading correction is performed on Bayer data as in the present embodiment, the CCD 2 is driven by a driving method other than the above-described progressive method or vertical thinning readout, such as multi-field readout, horizontal / vertical addition readout, Can be applied even when driven by various drive systems combining them. In this case, however, the horizontal position counter 41 and the vertical position counter 42 in the above-described shading coefficient generation circuit 7 are developed in the DRAM 9 and the state machine that performs the operation indicating the horizontal / vertical position of the Bayer array to be arranged is arranged. It is necessary to make such a circuit.

  Further, for example, in the case of performing shading correction on YUV data, the YUV data to be processed does not have to be data at the time of acquisition, for example, an image already recorded in the image recording unit 13 (shading You may perform with respect to the YUV data produced | generated when reproducing | regenerating (image which was not corrected). That is, the shading correction method of the present invention is effective not only when it is performed in real time during an imaging operation, but also when correcting an already recorded image.

  In the present embodiment, the CCD 2 is provided with a Bayer array primary color filter, and each pixel whose brightness is adjusted by shading correction has color information of any one of R, G, and B. Although the present invention has been described, the present invention is effective even in a configuration in which the CCD 2 has a complementary color filter. In this case, however, it is necessary to register the adjustment coefficient for each color corresponding to the coefficient register 53 of the shading coefficient generation circuit 7.

In this embodiment, even if the driving method of the CCD 2 is the vertical thinning-out reading method, the corresponding shading correction can be performed. However, other than this, for example, pixels in both horizontal / vertical directions from the CCD 2 are obtained. When an imaging signal is read out by the thinning driving method, a predetermined flatness coefficient is applied to the horizontal square value (H ² ) in the shading coefficient generation circuit 7 described above in parallel with the first multiplier 49. If other multipliers for multiplication are provided, this can be accommodated. Further, when the image pickup signal is read out by a driving method that thins out pixels only in the horizontal direction, a multiplier that multiplies a horizontal square value (H ² ) by a predetermined flattening coefficient instead of the first multiplier 49. May be provided.

  In the present embodiment, the case where the present invention is applied to a digital camera including a CCD has been described. However, the present invention is not limited to this, and the present invention is not limited to a digital camera including a CMOS sensor, a CCD, a CMOS sensor, or the like. The present invention can also be employed in other imaging devices including an imaging device, for example, various electronic camera devices such as a digital video camera, a mobile phone with a camera, a PDA with a camera, a personal computer with a camera. Even in that case, the above-described effects can be obtained.

It is a block diagram of a digital camera showing an embodiment of the present invention. It is a figure which shows the color filter arrangement | sequence of CCD. It is a block diagram which shows the structure of a shading coefficient production | generation circuit. It is explanatory drawing which shows the value used for calculation of a Bayer image and a shading coefficient. It is explanatory drawing which shows the change of the shading coefficient for every color produced | generated by the shading coefficient production | generation circuit. It is a flowchart which shows the processing content of CPU in imaging | photography mode.

Explanation of symbols

1 Optical system 2 CCD
3 TG
5 CDS / ADC
6 Multiplication circuit 7 Shading coefficient generation circuit 8 Digital signal processing circuit 12 CPU
41 horizontal position counter 42 vertical position counter 43, 44 subtracter 45, 46 absolute value circuit 47, 48 squarer 49 first multiplier 50 adder 51 second multiplier 52 coefficient switch 53 coefficient register 100 Bayer image L distance O Center of Bayer image P pixel

Claims (18)

A shading correction device that corrects shading of an image captured by an image sensor,
Calculating means for calculating a shading coefficient of each pixel based on a distance from the correction center of the image corresponding to the optical axis for each pixel;
An adjustment unit that adjusts the brightness of each pixel according to the shading coefficient for each pixel calculated by the calculation unit.   The shading correction apparatus according to claim 1, wherein the calculating unit calculates a shading coefficient for each pixel using a quadratic function having horizontal and vertical distances from the correction center in each pixel as variables.   The shading correction apparatus according to claim 1, wherein the pixel that is a calculation target of the shading coefficient in the calculation unit is a pixel having different color information depending on a position in an image formed thereby.   4. The shading according to claim 3, wherein the calculation unit calculates a shading coefficient of each pixel based on a distance from the correction center of the image corresponding to the optical axis and color information of each pixel for each pixel. Correction device.   The calculation means calculates, for each pixel, a shading coefficient of each pixel based on the distance from the correction center of the image corresponding to the optical axis and the content of the pixel thinning process performed when acquiring an image composed of each pixel. The shading correction apparatus according to claim 1, wherein the shading correction apparatus comprises: A shading correction method for correcting shading of an image captured by an image sensor,
Obtaining a shading coefficient corresponding to the distance from the correction center of the image corresponding to the optical axis for each pixel;
Adjusting the brightness of each pixel in accordance with the acquired shading coefficient for each pixel. A shading correction device that corrects shading of an image captured by an image sensor,
An acquisition means for acquiring a shading coefficient for each pixel having different color information depending on a position in an image formed thereby;
A shading correction apparatus comprising: adjustment means for adjusting the brightness of each pixel having different color information depending on the position in the image in accordance with the shading coefficient acquired by the acquisition means.   The storage unit stores the shading coefficient in association with the position of each pixel in the image, and the acquisition unit reads out the shading coefficient for each pixel from the storage unit based on the position of each pixel in the image. The shading correction apparatus according to claim 7. A shading correction method for correcting shading of an image captured by an image sensor,
Obtaining a shading coefficient for each pixel at a stage where each pixel has different color information depending on the position in the image constituted by the pixel; and
Adjusting the brightness for each pixel having different color information depending on the position in the image in accordance with the acquired shading coefficient. A shading correction device that corrects shading of an image captured by an image sensor,
Determining means for determining, for each pixel, a shading coefficient corresponding to the content of the pixel thinning process performed when acquiring an image constituted by each pixel;
An adjustment unit that adjusts the brightness of each pixel in accordance with the shading coefficient for each pixel determined by the determination unit.   The determination unit includes, for each pixel, an acquisition unit that acquires a shading coefficient based on a distance from the correction center of the image corresponding to the optical axis, and a shading coefficient for each pixel acquired by the acquisition unit. The shading correction apparatus according to claim 10, further comprising: a correction unit that performs correction according to the content of the pixel thinning process performed when acquiring the image to be processed.   Storage means for storing a shading coefficient for each pixel in association with a plurality of types of pixel thinning processing whose processing contents are different from each other, and the determination means includes pixel thinning performed when acquiring an image constituted by each pixel. The shading correction apparatus according to claim 10, wherein a shading coefficient stored in the storage unit corresponding to a type of processing is determined as a shading coefficient for each pixel. A shading correction method for correcting shading of an image captured by an image sensor,
For each pixel, determining a shading coefficient according to the content of the pixel thinning process performed when acquiring an image composed of each pixel;
Adjusting the brightness of each pixel according to the determined shading coefficient. An imaging device including an imaging device that captures an optical image of a subject,
Calculating means for calculating a shading coefficient based on a distance from a correction center of an image corresponding to an optical axis for each pixel of an image captured by the image sensor;
An image pickup apparatus comprising: an adjusting unit that adjusts the brightness of each pixel according to the shading coefficient for each pixel calculated by the calculating unit. An imaging device including an imaging device that captures an optical image of a subject,
An acquisition unit that configures an image captured by the image sensor and acquires a shading coefficient for each pixel having different color information depending on a position in the image;
An image pickup apparatus comprising: adjusting means for adjusting the brightness of each pixel having different color information depending on the position in the image according to the shading coefficient acquired by the acquiring means. An imaging device including an imaging device that captures an optical image of a subject,
Determining means for determining, for each pixel constituting the image captured by the image sensor, a shading coefficient according to the content of the pixel thinning process performed at the time of capturing the image;
An image pickup apparatus comprising: adjusting means for adjusting the brightness of each pixel in accordance with the shading coefficient for each pixel determined by the determining means.   The imaging apparatus according to claim 14, further comprising display means for displaying an image in which the brightness of each pixel is adjusted by the adjustment means. 18. The imaging apparatus according to claim 14, further comprising a recording unit that records an image in which the brightness of each pixel is adjusted by the adjustment unit.

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