Enhanced Image Capture Sharpening

• US 20120013775A1
• Filed: 07/15/2010
• Published: 01/19/2012
• Est. Priority Date: 07/15/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Tsai, Richard
• Granted Patent: US 8,736,722 B2
• Time in Patent Office: Days
• US Class Current: 348/252
• CPC Class Codes: H04N 25/615 involving a transfer function modelling the optical system, e.g. optical transfer function [OTF], phase transfer function [PhTF] or modulation transfer function [MTF]
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction

Abstract

An image capture sharpening subsystem for a digital camera includes a capture sharpening processor and a memory that stores values for a capture sharpening amount. The values for the capture sharpening amount are a function of position on an image sensor of the digital camera. The capture sharpening processor receives a first value for a pixel in an image captured by the image sensor and a position value for the pixel on the image sensor. The capture sharpening processor determines a pixel sharpening amount from the values for the capture sharpening amount stored in the first memory according to the position value. The capture sharpening processor applies a capture sharpening process to the pixel to provide a second value for the pixel according to the pixel sharpening amount and stores the second value in a second memory that provides a sharpened version of the image captured by the image sensor.

Claims

1. An image capture sharpening subsystem comprising:

a first memory that stores values for a capture sharpening amount, the values for the capture sharpening amount being a function of position on an image sensor that captures an image;

a capture sharpening processor that

receives a first value for a pixel in the image captured by the image sensor, the first value being associated with a position value for the pixel on the image sensor,

determines a pixel sharpening amount from the values for the capture sharpening amount stored in the first memory according to the position value,

applies a capture sharpening process to the pixel to provide a second value for the pixel according to the pixel sharpening amount, and

stores the second value in a second memory that provides a sharpened version of the image captured by the image sensor.

2. The image capture sharpening subsystem of claim 1 wherein the values for the capture sharpening amount are further a function of a focal distance of a lens that forms the image on the image sensor and the capture sharpening processor further receives a focal distance value for the lens and further determines the pixel sharpening amount according to the focal distance value.

3. The image capture sharpening subsystem of claim 1 wherein the values for the capture sharpening amount are further a function of an aperture size of a lens that forms the image on the image sensor and the capture sharpening processor further receives an aperture size value for the lens and further determines the pixel sharpening amount according to the aperture size value.

4. The image capture sharpening subsystem of claim 1 wherein the values for the capture sharpening amount are further a function of a focal length of a variable focal length lens that forms the image on the image sensor and the capture sharpening processor further receives a focal length value for the lens and further determines the pixel sharpening amount according to the focal length value.

5. The image capture sharpening subsystem of claim 1 wherein the first memory stores values for the capture sharpening amount for selected positions on the image sensor and the capture sharpening processor further determines the pixel sharpening amount by interpolating between the stored values for the capture sharpening amount.

6. A method for sharpening a captured image by a capture sharpening processor, the method comprising:

storing values for a capture sharpening amount, the values for the capture sharpening amount being a function of position on an image sensor that captures the image;

receiving a first value for a pixel in the image captured by the image sensor with the capture sharpening processor and an associated position value for the pixel on the image sensor;

determining a pixel sharpening amount from the values for the capture sharpening amount according to the position value with the capture sharpening processor; and

applying a capture sharpening process to the pixel with the capture sharpening processor to provide a second value for the pixel according to the pixel sharpening amount to provide a sharpened version of the image captured by the image sensor.

7. The method of claim 6 wherein the values for the capture sharpening amount are further a function of a focal distance of a lens that forms the image on the image sensor, and the method further comprises receiving a focal distance value for the lens and determining the pixel sharpening amount according to the focal distance value with the capture sharpening processor.

8. The method of claim 6 wherein the values for the capture sharpening amount are further a function of an aperture size of a lens that forms the image on the image sensor, and the method further comprises receiving an aperture size value for the lens and determining the pixel sharpening amount according to the aperture size value with the capture sharpening processor.

9. The method of claim 6 wherein the values for the capture sharpening amount are further a function of a focal length of a variable focal length lens that forms the image on the image sensor, and the method further comprises receiving a focal length value for the lens and determining the pixel sharpening amount according to the focal length value with the capture sharpening processor.

10. The method of claim 6 wherein the stored values for the capture sharpening amount are for selected positions on the image sensor, and the method further comprises determining the pixel sharpening amount by interpolating between the stored values for the capture sharpening amount with the capture sharpening processor.

11. A system for sharpening image data captured by an image sensor, the system comprising:

a distance operation unit for obtaining distance values indicating the distance from an optical-axis position to a pixel in the image data;

a sharpening amount operation unit for obtaining a capture sharpening amount value for the pixel by reference to an approximation function that indicates a relation between capture sharpening amount values and distance values obtained by the distance operation unit; and

a capture sharpening unit for correcting a pixel value of the pixel based on the capture sharpening amount value obtained by the sharpening amount operation unit.

12. The system of claim 11 wherein the sharpening amount operation unit obtains the capture sharpening amount value for the pixel by further reference to a focal distance of a lens that forms an image on the image sensor.

13. The system of claim 11 wherein the sharpening amount operation unit obtains the capture sharpening amount value for the pixel by further reference to an aperture size value for a lens that forms an image on the image sensor.

14. The system of claim 11 wherein the sharpening amount operation unit obtains the capture sharpening amount value for the pixel by further reference to a focal length value for a lens that forms an image on the image sensor.

15. The system of claim 11 wherein the approximation function is divided into a plurality of segments, and represented by quadratic functions in the respective segments, the quadratic functions each being defined by a predetermined number of sample points, the sharpening amount operation unit further for obtaining data regarding the sample points for one of the segments to which the distance value belongs, and obtaining the capture sharpening amount value in accordance with one of the quadratic functions that is defined by those sample points.