Entropy maximization based auto-exposure

1. An image capture apparatus comprising:

an image sensor;

a motion sensor; and

an auto-exposure unit configured to:

obtain, from the image sensor, an input image signal representing an input image captured during an exposure interval;

obtain, from the motion sensor, motion data indicating motion of the image capture apparatus during the exposure interval;

obtain image information-amount data for the input image, wherein the image information-amount data is a sum of pixel information-amount data, wherein, for each pixel, the pixel information-amount data is obtained by:

in response to a determination that an input value for the pixel is a maximum pixel value, using zero as an information-amount value for the pixel; and

in response to a determination that the input value for the pixel is within the maximum pixel value:

obtaining a signal level information-amount for the pixel as the base two logarithm of a signal-to-noise ratio for the pixel, wherein the signal-to-noise ratio is a ratio of the input value to a noise value for the pixel, and wherein the noise value for the pixel is modeled as a square root of a sum of a first defined value and a product of a second defined value and the input value of the pixel; and

using a motion blur adjusted value for the pixel as the information- amount value for the pixel, wherein the motion blur adjusted value for the pixel is obtained based on the signal level information-amount for the pixel and the motion data;

obtain derivative information-amount data based on the information-amount data and a candidate exposure adjustment; and

obtain an information-amount maximizing exposure interval based on the information-amount data and the derivative information-amount data, wherein the image capture apparatus is configured to control the image sensor to obtain a subsequent input image signal representing a subsequent input image captured during the information- amount maximizing exposure interval, and output or store information representing the subsequent input image.

2. An image capture apparatus comprising:

an image sensor configured to capture an input image in accordance with an exposure interval;

a motion sensor configured to capture temporally corresponding motion data indicating motion of the image capture apparatus in accordance with the exposure interval; and

an auto-exposure unit configured to:

obtain, from the image sensor, an input image signal representing the input image;

obtain, from the motion sensor, the temporally corresponding motion data;

obtain image information-amount data for the input image based on the temporally corresponding motion data;

obtain derivative information-amount data based on the information-amount data and a candidate exposure adjustment; and

obtain an information-amount maximizing exposure interval based on the information-amount data and the derivative information-amount data.

3. The image capture apparatus of claim 2 , wherein:

the input image includes pixels; and

the auto-exposure unit is configured to:

obtain pixel information-amount data for the pixels; and

obtain a sum of the pixel information-amount data as the image information- amount data.

4. The image capture apparatus of claim 3 , wherein the auto-exposure unit is configured to obtain the pixel information-amount data by:

for each pixel from the pixels:

determining a pixel information-amount value for the pixel based on a signal-to-noise ratio for the pixel, pixel saturation, and motion blur.

5. The image capture apparatus of claim 4 , wherein the auto-exposure unit is configured to determine the respective pixel information-amount value by:

in response to a determination that an input value for the pixel is a maximum pixel value, using a defined value as the pixel information-amount value for the pixel; and

in response to a determination that the input value for the pixel is less than the maximum pixel value:

obtaining a signal level information-amount for the pixel as the base two logarithm of a signal-to-noise ratio for the pixel, wherein the signal-to-noise ratio is a ratio of the input value to a noise value for the pixel, and wherein the noise value for the pixel is modeled as a square root of a sum of a first defined value and a product of a second defined value and the input value of the pixel; and

using a motion blur adjusted value for the pixel as the pixel information-amount value for the pixel.

6. The image capture apparatus of claim 5 , wherein the defined value is zero.

7. The image capture apparatus of claim 6 , wherein the auto-exposure unit is configured to obtain the motion blur adjusted value for the pixel by:

determining an amount of motion blur based on the temporally corresponding motion data, the exposure interval, and a size of the pixel; and

using, as the motion blur adjusted value, a result of dividing the signal level information- amount by a sum of the size of the pixel and the amount of motion blur.

8. The image capture apparatus of claim 3 , wherein the auto-exposure unit is configured to obtain the pixel information-amount data by:

for each pixel from the pixels:

determining a pixel information-amount value for the pixel based on a histogram of the input image.

9. The image capture apparatus of claim 8 , wherein the auto-exposure unit is configured to obtain the pixel information-amount data by:

obtaining a saliency map indicating a relative importance of respective pixels within the input image; and

for each pixel from the pixels:

determining a saliency adjusted information-amount by multiplying a saliency value from the saliency map for the pixel by the pixel information-amount value; and

using the saliency adjusted information-amount as the pixel information-amount value.

10. The image capture apparatus of claim 9 , wherein the auto-exposure unit is configured to obtain the pixel information-amount data by:

in response to a determination that a pixel is a saturated pixel along a stitch line for image merging, weighting the pixel to minimize saturated pixels along the stitch line.

11. The image capture apparatus of claim 10 , wherein the image sensor is configured to capture a second input image in accordance with the information-amount maximizing exposure interval.

12. A method comprising:

performing, by an auto-exposure unit of an image capture apparatus, information-amount maximization based auto-exposure, wherein information-amount maximization based auto-exposure includes:

obtaining, from an image sensor of the image capture apparatus, an input image signal representing an input image captured in accordance with an exposure interval;

obtaining, from a motion sensor of the image capture apparatus, temporally corresponding motion data indicating motion of the image capture apparatus in accordance with the exposure interval;

obtaining image information-amount data for the input image based on the temporally corresponding motion data;

obtaining derivative information-amount data based on the information-amount data and a candidate exposure adjustment; and

obtaining an information-amount maximizing exposure interval based on the information-amount data and the derivative information-amount data.

13. The method of claim 12 , wherein the input image includes pixels, and wherein information-amount maximization based auto-exposure includes:

obtaining pixel information-amount data for the pixels; and

obtaining a sum of the pixel information-amount data as the image information-amount data.

14. The method of claim 13 , wherein obtaining the pixel information-amount data includes:

for each pixel from the pixels:

determining a respective pixel information-amount value for the pixel based on a signal-to-noise ratio for the pixel, pixel saturation, and motion blur.

15. The method of claim 14 , wherein determining the respective pixel information-amount value includes:

in response to a determination that an input value for the pixel is a maximum pixel value, using a defined value as the pixel information-amount value for the pixel; and

in response to a determination that the input value for the pixel is less than the maximum pixel value:

obtaining a signal level information-amount for the pixel as the base two logarithm of a signal-to-noise ratio for the pixel, wherein the signal-to-noise ratio is a ratio of the input value to a noise value for the pixel, and wherein the noise value for the pixel is modeled as a square root of a sum of a first defined value and a product of a second defined value and the input value of the pixel; and

using a motion blur adjusted value for the pixel as the pixel information-amount value for the pixel.

16. The method of claim 15 , wherein obtaining the motion blur adjusted value for the pixel includes:

determining an amount of motion blur based on the temporally corresponding motion data, the exposure interval, and a size of the pixel; and

using, as the motion blur adjusted value, a result of dividing the signal level information-amount by a sum of the size of the pixel and the amount of motion blur.

17. The method of claim 13 , wherein obtaining the pixel information-amount data includes:

for each pixel from the pixels:

determining a pixel information-amount value for the pixel based on a histogram of the input image.

18. The method of claim 17 , wherein obtaining the pixel information-amount data includes:

obtaining a saliency map indicating a relative importance of respective pixels within the input image; and

for each pixel from the pixels:

determining a saliency adjusted information-amount by multiplying a saliency value from the saliency map for the pixel by the pixel information-amount value; and

using the saliency adjusted information-amount as the pixel information-amount value.

19. The method of claim 18 , wherein obtaining the pixel information-amount data includes:

in response to a determination that a pixel is a saturated pixel along a stitch line for image merging, weighting the pixel to minimize saturated pixels along the stitch line.

20. The method of claim 19 , wherein information-amount maximization based auto-exposure includes obtaining, by the image sensor, a second input image signal representing a second input image in accordance with the information-amount maximizing exposure interval.