AUTOMATIC TONE MAPPING FOR CAMERAS

• US 20100309346A1
• Filed: 06/05/2009
• Published: 12/09/2010
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: COTE, GUY, BRUNNER, RALPH, ZIMMER, MARK
• Granted Patent: US 8,358,351 B2
• Time in Patent Office: Days
• US Class Current: 348/254
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

A device, method, computer useable medium, and processor programmed to automatically generate tone mapping curves in a digital camera based on image metadata are described. By examining image metadata from a digital camera'"'"'s sensor, such as the light-product, one can detect sun-lit, high-light, and low-light scenes. Once the light-product value has been calculated for a given image, a tone mapping curve can automatically be generated within the sensor and adjusted appropriately for the scene based on predetermined parameters. Further, it has been determined that independently varying the slopes of the tone mapping curve at the low end (S₀) and high end (S₁) of the curve results in more visually appealing images. By dynamically and independently selecting S₀ and S₁ values based on image metadata, more visually pleasing images can be generated.

Claims

1. A computer processor programmed to perform an image processing method, the method comprising:

obtaining an image representative of a physical scene and comprising metadata;

calculating a first image processing parameter based at least in part on the metadata of the image;

determining first and second slope values of a tone mapping curve, wherein the first and second slope values are based at least in part on the generated first image processing parameter, and wherein the first and second slope values are representative of the slope of the tone mapping curve at a first and second endpoint, respectively; and

transforming the image according to the tone mapping curve having the first and second slope values.

2. The processor of claim 1, wherein the act of determining the first and second slope values that the processor is programmed to perform further comprises generating a table of values representative of the tone mapping curve between the first and second endpoints.

3. The processor of claim 1, wherein the processor is further programmed to perform the act of encoding the transformed data representative of the image into the YCbCr color space.

4. The processor of claim 1, wherein the first image processing parameter comprises a light-product.

5. The processor of claim 1, wherein the act of determining the first and second slope values that the processor is programmed to perform further comprises linearly interpolating between a first stored pair of first and second slope values representative of low-light conditions and a second stored pair of first and second slope values representative of high-light conditions.

6. The processor of claim 2, wherein the processor is further programmed to perform the act of combining the generated table of values representative of the tone mapping curve with a second table of values indicative of gamma correction, wherein the act of combining occurs before the act of transforming.

7. The processor of claim 1, wherein the act of obtaining an image representative of a physical scene comprises receiving an image from at least one of the following:

a digital camera, digital video camera, mobile phone, personal data assistant, portable music player, and computer.

8. The processor of claim 1, wherein the tone mapping curve comprises a cubic polynomial.

20. A computer usable medium having a computer readable program code embodied therein, wherein the computer readable program code is adapted to be executed to implement the method performed by the programmed computer processor of claim 1.

9. A consumer electronic device with an embedded camera, comprising:

a camera sensor unit;

memory operatively coupled to the camera sensor unit for receiving a image representative of a physical scene and comprising metadata from the camera sensor unit;

a processor unit operatively coupled to the memory, the memory comprising instructions for causing the processor unit to;

calculate a first image processing parameter based at least in part on the metadata of the image;

determine first and second slope values of a tone mapping curve, wherein the first and second slope values are based at least in part on the generated first image processing parameter, and wherein the first and second slope values are representative of the slope of the tone mapping curve at a first and second endpoint, respectively; and

transform the image according to the tone mapping curve having the first and second slope values.

10. The consumer electronic device of claim 9, wherein the act of determining the first and second slope values that the processor is programmed to perform further comprises generating a table of values representative of the tone mapping curve between the first and second endpoints.

11. The consumer electronic device of claim 9, wherein the first image processing parameter comprises a light-product.

12. The consumer electronic device of claim 9, wherein the act of determining the first and second slope values that the processor is programmed to perform further comprises linearly interpolating between a first stored pair of first and second slope values representative of low-light conditions and a second stored pair of first and second slope values representative of high-light conditions.

13. The consumer electronic device of claim 10, wherein the processor unit is further programmed to combine the generated table of values representative of the tone mapping curve with a second table of values indicative of gamma correction, wherein the act of combining occurs before the act of transforming.

14. The consumer electronic device of claim 9, wherein the tone mapping curve comprises a cubic polynomial.

15. The consumer electronic device of claim 9, wherein the consumer electronic device comprises at least one of the following:

a digital camera, digital video camera, mobile phone, personal data assistant, portable music player, and computer.

16. An image processing method comprising:

generating an image processing parameter for an image representative of a physical scene, the image processing parameter based at least in part on metadata of the image;

determining a tone mapping curve, wherein the tone mapping curve has a first slope value at a first endpoint and a second slope value at a second endpoint, and wherein the first and second slope values are independently determined at least in part by the image processing parameter; and

transforming the image according to the tone mapping curve having the first and second slope values.

17. The method of claim 16, wherein the act of determining further comprises generating a table of values representative of the tone mapping curve between the first and second endpoints.

18. The method of claim 16, wherein the act of determining further comprises linearly interpolating between a first stored pair of first and second slope values representative of low-light conditions and a second stored pair of first and second slope values representative of high-light conditions.

19. The method of claim 17, wherein the method further comprises the act of combining the generated table of values representative of the tone mapping curve with a second table of values indicative of gamma correction, wherein the act of combining occurs before the act of transforming.

21. A computer processor programmed to perform an image processing method, the method comprising:

obtaining an image representative of a physical scene and comprising metadata;

calculating a first image processing parameter based at least in part on the metadata of the image;

determining a non-symmetric tone mapping curve based at least in part on the first image processing parameter, wherein the non-symmetric tone mapping curve has first and second endpoints;

specifying a value for the first and second endpoints; and

transforming the image according to the non-symmetric tone mapping curve having the first and second endpoints.

22. The processor of claim 21, wherein the act of determining the non-symmetric tone mapping curve that the processor is programmed to perform further comprises generating a table of values representative of the tone mapping curve between the first and second endpoints.

23. The processor of claim 21, wherein the first image processing parameter comprises a light-product.

24. The processor of claim 21, wherein the act of determining the non-symmetric tone mapping curve that the processor is programmed to perform further comprises linearly interpolating between a first stored pair of first and second slope values representative of low-light conditions and a second stored pair of first and second slope values representative of high-light conditions.

25. The processor of claim 22, wherein the processor is further programmed to perform the act of combining the generated table of values representative of the tone mapping curve with a second table of values indicative of gamma correction, wherein the act of combining occurs before the act of transforming.