Image processing apparatus, image processing method, program, and storage medium for correcting chromatic aberration

• US 8,305,458 B2
• Filed: 08/02/2010
• Issued: 11/06/2012
• Est. Priority Date: 07/21/2009
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Hara, Takayuki
• Primary Examiner(s): Whipkey, Jason
• Assistant Examiner(s): CAMARGO, MARLY S.B.
• Application Number:
  US12/848,882
• Publication Number:
  US 20110043657A1
• Time in Patent Office: 827 Days
• Field of Search: 348/223.1, 348/222.1, 348/242, 348/256, 348/246, 348/234, 348/653, 348/654, 348/655, 382/162, 382/164, 382/167, 382/165, 382/218, 382/272, 358/515, 358/518, 345/600, 345/604
• US Class Current: 348/222.1
• CPC Class Codes: H04N 2209/046 Colour interpolation to calculate the missing colour values
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements
• CPC Class Codes: H04N 25/611 Correction of chromatic aberration

Abstract

There is a problem in that when magnification chromatic aberration correction is carried out, the difference in reproducibility of high-frequency components, depending on the spatial position, between a color for which position shift correction is not performed and a color for which position shift correction is performed may influence the image quality of an output image. In order to perform magnification chromatic aberration correction, high-frequency components, which are lost due to the position shift correction of a color for which position shift correction is carried out, are extracted from a color for which position shift correction is not carried out, and are added to the color for which position shift correction is carried out. Therefore, the high-frequency components are restored in a pseudo manner.

Claims

1. An image processing apparatus comprising:

an image obtaining unit adapted to obtain an image having a plurality of colors, the image being generated using an image pickup element including a plurality of pixels;

a shift amount obtaining unit adapted to obtain an amount of shift of light flux of a second color with respect to light flux of a first color, the amount of shift being caused by optical characteristics of a lens through which light flux that arrives at the image pickup element is transmitted;

a shift correcting unit adapted to interpolate a signal level of the second color at aberration coordinates from signal levels of pixels having the second color around the aberration coordinates, the aberration coordinates representing a position that is shifted from a position of a pixel of interest by the amount of shift;

a high-frequency extracting unit adapted to extract a high-frequency signal level of the first color of the pixel of interest in accordance with a degree of reduction in a high-frequency signal level in the signal level of the second color at the aberration coordinates, the reduction being caused by interpolation performed by the shift correcting unit; and

an output unit adapted to output, as a signal level of a pixel of the second color in the pixel of interest, a signal level obtained by adding the signal level extracted by the high-frequency extracting unit to a signal level of a pixel of the second color calculated by the shift correcting unit.

2. The image processing apparatus according to claim 1, wherein the shift correcting unit interpolates the signal level of the second color at the aberration coordinates from the signal levels of the pixels having the second color around the aberration coordinates, using weights corresponding to distances between the aberration coordinates and centers of gravity of the pixels having the second color around the aberration coordinates.

3. The image processing apparatus according to claim 2, wherein the shift correcting unit interpolates the signal level of the second color at the aberration coordinates, by summing the signal levels of the pixels having the second color around the aberration coordinates using the weights.

4. The image processing apparatus according to claim 2, wherein the high-frequency extracting unit includes:

a high-frequency suppressing unit adapted to generate a signal in which the high-frequency signal level of the first color of the pixel of interest is suppressed in accordance with the weights, and

a subtracting unit adapted to subtract the signal generated by the high-frequency suppressing unit from a signal level of the first color of the pixel of interest,

wherein the output unit outputs, as a signal level of a pixel of the second color in the pixel of interest, a signal level determined by adding a signal level obtained by subtraction performed by the subtracting unit to the signal level of the pixel of the second color calculated by the shift correcting unit.

5. The image processing apparatus according to claim 4, wherein the high-frequency suppressing unit generates a signal in which the high-frequency signal level of the first color of the pixel of interest is suppressed, using a signal level obtained by weighting signal levels of pixels having the first color around the pixel of interest with the weights used by the shift correcting unit and summing the weighted signal levels.

6. The image processing apparatus according to claim 5, wherein the high-frequency suppressing unit generates a signal in which the high-frequency signal level of the first color of the pixel of interest is suppressed, by determining a signal level at a center of gravity of the pixel of interest using a plurality of signal levels obtained by weighting the signal levels of the pixels having the first color around the pixel of interest with the weights used by the shift correcting unit and summing the weighted signal levels.

7. The image processing apparatus according to claim 1, further comprising:

a second shift amount obtaining unit adapted to obtain an amount of shift of light flux of a third color with respect to the light flux of the first color, the amount of shift being caused by optical characteristics of a lens through which light flux that arrives at the image pickup element is transmitted;

a second shift correcting unit adapted to interpolate a signal level of the third color at aberration coordinates from signal levels of pixels having the third color around the aberration coordinates, the aberration coordinates representing a position that is shifted from a position of a pixel of interest by the amount of shift obtained by the second shift amount obtaining unit; and

a second high-frequency extracting unit adapted to extract a high-frequency signal level of the first color of the pixel of interest in accordance with a degree of reduction in a high-frequency signal level in the signal level of the third color at the aberration coordinates, the reduction being caused by interpolation performed by the second shift correcting unit,

wherein the output unit outputs, as a signal level of a pixel of the third color in the pixel of interest, a signal level determined by adding the signal level extracted by the second high-frequency extracting unit to a signal level of a pixel of the third color calculated by the second shift correcting unit.

8. The image processing apparatus according to claim 1, wherein the first color is green, and the second color is red or blue.

9. An image processing method comprising:

an image obtaining step of obtaining an image having a plurality of colors, the image being generated using an image pickup element including a plurality of pixels;

a shift amount obtaining step of obtaining an amount of shift of light flux of a second color with respect to light flux of a first color, the amount of shift being caused by optical characteristics of a lens through which light flux that arrives at the image pickup element is transmitted;

a shift correcting step of interpolating a signal level of the second color at aberration coordinates from signal levels of pixels having the second color around the aberration coordinates, the aberration coordinates representing a position that is shifted from a position of a pixel of interest by the amount of shift;

a high-frequency extracting step of extracting a high-frequency signal level of the first color of the pixel of interest in accordance with a degree of reduction in a high-frequency signal level in the signal level of the second color at the aberration coordinates, the reduction being caused by interpolation performed in the shift correcting step; and

an output step of outputting, as a signal level of a pixel of the second color in the pixel of interest, a signal level obtained by adding the signal level extracted in the high-frequency extracting step to a signal level of a pixel of the second color calculated in the shift correcting step.

10. A non-transitory computer-readable storage medium storing a program for causing a computer to execute the image processing method comprising:

an image obtaining step of obtaining an image having a plurality of colors, the image being generated using an image pickup element including a plurality of pixels;

a shift amount obtaining step of obtaining an amount of shift of light flux of a second color with respect to light flux of a first color, the amount of shift being caused by optical characteristics of a lens through which light flux that arrives at the image pickup element is transmitted;

a shift correcting step of interpolating a signal level of the second color at aberration coordinates from signal levels of pixels having the second color around the aberration coordinates, the aberration coordinates representing a position that is shifted from a position of a pixel of interest by the amount of shift;

a high-frequency extracting step of extracting a high-frequency signal level of the first color of the pixel of interest in accordance with a degree of reduction in a high-frequency signal level in the signal level of the second color at the aberration coordinates, the reduction being caused by interpolation performed in the shift correcting step; and

an output step of outputting, as a signal level of a pixel of the second color in the pixel of interest, a signal level obtained by adding the signal level extracted in the high-frequency extracting step to a signal level of a pixel of the second color calculated in the shift correcting step.