Imaging systems and methods for generating auto-exposed high-dynamic-range images

1. A method of using an image sensor and processing circuitry in an electronic device to generate an auto-exposed high-dynamic-range image, the method comprising:

with the image sensor, capturing a first image;

with the processing circuitry, generating a first exposure time and a second exposure time based on the captured first image, wherein generating the first exposure time and the second exposure time comprises generating statistics associated with the captured first image and determining an exposure level of the captured first image based on the generated statistics, and wherein determining the exposure level of the captured first image comprises identifying a target exposure level and a clipping exposure level of the captured first image and computing the exposure level as a linear combination of the target exposure level and the clipping exposure level;

with the image sensor, capturing a second image having long-exposure image pixel values and short-exposure image pixel values, wherein the long-exposure image pixel values are captured using the first exposure time and wherein the short-exposure image pixel values are captured using the second exposure time;

with the processing circuitry, generating a long-exposure image and a short-exposure image from the captured second image; and

with the processing circuitry, generating the auto-exposed high-dynamic-range image using the long-exposure image and the short-exposure image.

2. The method defined in claim 1 , wherein generating the statistics associated with the captured first image comprises generating a luma mean value and a luma low point value of the first captured image.

3. The method defined in claim 1 , wherein generating the first exposure time and the second exposure time further comprises:

generating an adjusted exposure level based on the determined exposure level; and

generating the first exposure time based on the adjusted exposure level.

4. The method defined in claim 3 , wherein generating the first exposure time and the second exposure time further comprises:

determining an exposure ratio based on the generated statistics; and

generating the second exposure time based on the determined exposure ratio and the first exposure time.

5. The method defined in claim 3 , further comprising:

with the processing circuitry, generating image sensor gain settings based on the adjusted exposure level.

6. The method defined in claim 5 , wherein capturing the second image comprises capturing the second image using the generated image sensor gain settings.

7. The method defined in claim 1 , wherein the captured first image includes initial long-exposure image pixel values and initial short-exposure image pixel values and wherein capturing the first image comprises:

capturing the initial long-exposure image pixel values using an initial long-exposure time that is different from the first exposure time.

8. The method defined in claim 7 , wherein capturing the first image further comprises:

capturing the initial short-exposure image pixel values using an initial short-exposure time that is different from the second exposure time.

9. The method defined in claim 1 , wherein generating the long-exposure image and the short-exposure image comprises:

interpolating the long-exposure image pixel values and the short-exposure image pixel values.

10. A method of using an image sensor and processing circuitry in an electronic device to generate an auto-exposed high-dynamic-range image of a scene, the method comprising:

with the image sensor, capturing image data from the scene by capturing initial short-exposure image pixel values;

with the processing circuitry, determining an auto-exposed short integration time and an auto-exposed long integration time based on the image data, wherein determining the auto-exposed short integration time and the auto-exposed long integration time comprises identifying first and second clipping percentages associated with the initial short-exposure image values, wherein the first clipping percentage represents the short-exposure image pixel values that exceed a first threshold value, and wherein the second clipping percentage represents the short-exposure pixel values that exceed a second threshold value that is different than the first threshold value;

with the image sensor, capturing a first image having long-exposure image pixel values and a second image having short-exposure image pixel values, wherein the short-exposure image pixel values are captured using the auto-exposed short integration time, and wherein the long-exposure image pixel values are captured using the auto-exposed long integration time; and

with the processing circuitry, generating the auto-exposed high-dynamic-range image using the first and second images.

11. The method defined in claim 10 , wherein capturing the image data from the scene comprises:

capturing initial long-exposure image pixel values using a first integration time that is different from the auto-exposed long integration time; and

capturing the initial short-exposure image pixel values using a second integration time that is different from the auto-exposed short integration time.

12. The method defined in claim 11 , wherein determining the auto-exposed short integration time and the auto-exposed long integration time comprises:

generating image statistics from the initial long-exposure image pixel values and the initial short-exposure image pixel values.

13. The method defined in claim 12 , wherein determining the auto-exposed short integration time and the auto-exposed long integration time further comprises:

determining an exposure level of the captured first image based on the generated statistics;

generating an exposure adjustment level based on the determined exposure level; and

generating the auto-exposed long integration time based on the generated exposure adjustment level.

14. The method defined in claim 10 , wherein the first threshold value is approximately half of the second threshold value.