Enhanced image capture sharpening

• US 8,736,722 B2
• Filed: 07/15/2010
• Issued: 05/27/2014
• Est. Priority Date: 07/15/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Tsai, Richard
• Primary Examiner(s): Tran, Nhan T
• Application Number:
  US12/837,196
• Publication Number:
  US 20120013775A1
• Time in Patent Office: 1,412 Days
• Field of Search: 348/251, 348/252, 348/222.1, 348/335, 348/187, 348/188, 382/266, 382/274, 382/275
• 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 of a digital camera, the image capture sharpening subsystem comprising:

a first memory that stores values for a capture sharpening amount, the values for the capture sharpening amount based on calibration of an optical subsystem of the digital camera during a manufacturing process and being a function of position on a surface of an image sensor of the digital camera that captures an image;

a capture sharpening processor

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

applies a capture sharpening process to the first value for the pixel to provide a second value for the pixel according to the pixel sharpening amount, the capture sharpening process enhancing contrast of transitions in brightness, 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 surface of 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 surface of 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 surface of 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 surface of 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 an image captured by a digital camera using a capture sharpening processor included in the digital camera, the method comprising:

calibrating an optical subsystem of the digital camera during a manufacturing process to obtain values for a capture sharpening amount as a function of position on a surface of an image sensor of the digital camera;

storing the values for the capture sharpening amount;

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 that indicates position for the pixel on the surface of the image sensor;

determining a pixel sharpening amount from the values for the capture sharpening amount according to the position value for the pixel on the surface of the image sensor with the capture sharpening processor; and

applying a capture sharpening process to the first value for 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, the capture sharpening process enhancing contrast of transitions in brightness.

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 surface of 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 surface of 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 surface of 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 surface of 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 of a digital camera, the system comprising:

a memory that is written during a manufacturing process of the digital camera to store capture sharpening amount values based on calibration of an optical subsystem of the digital camera during the manufacturing process;

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

a sharpening amount operation unit for obtaining a pixel sharpening amount value for the pixel by reference to an approximation function that indicates a relation between the 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 pixel sharpening amount value obtained by the sharpening amount operation unit to enhance contrast of transitions in brightness.

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

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

14. The system of claim 11 wherein the sharpening amount operation unit obtains the pixel sharpening amount value for the pixel by further reference to a focal length value for a lens that forms an image on the surface of 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 on the surface of the image sensor, 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 pixel sharpening amount value in accordance with one of the quadratic functions that is defined by those sample points.