Method for producing high dynamic range images
A method for producing a high-dynamic-range image, comprising: receiving a low-resolution image of a scene having a first resolution and captured at a first exposure level; receiving a first high-resolution image of the scene having a second resolution and captured at a second exposure level different from the first exposure level, the second resolution being greater than the first resolution; forming a residual image corresponding to high spatial frequency content in the first high-resolution image; forming a second high-resolution image having the second resolution and the first exposure level by combining the low-resolution image and the residual image; producing the high-dynamic-range image by combining the first high-resolution image and the second high-resolution image; and storing the high-dynamic-range image in a processor accessible memory.
1. A method for producing a high-dynamic-range image, comprising:
a) receiving a low-resolution image of a scene having a first resolution and captured at a first exposure level;
b) receiving a first high-resolution image of the scene having a second resolution and captured at a second exposure level different from the first exposure level, the second resolution being greater than the first resolution;
c) using a data processor to form a residual image corresponding to high spatial frequency content in the first high-resolution image;
d) using a data processor to form a second high-resolution image having the second resolution and the first exposure level by combining the low-resolution image and the residual image;
e) using a data processor to produce the high-dynamic-range image by combining the first high-resolution image and the second high-resolution image; and
f) storing the high-dynamic-range image in a processor accessible memory.
2. The method of claim 1 wherein the low-resolution image and the first high-resolution image are captured using a digital camera.
3. The method of claim 2 wherein the digital camera has a preview mode providing a live view image stream, and wherein the low-resolution image is a live view image captured from the live view image stream.
4. The method of claim 1 wherein the first exposure level is less than the second exposure level.
5. The method of claim 1 wherein the first exposure level is greater than the second exposure level.
6. The method of claim 1 wherein step c) includes:
i) determining a representative low-resolution image from the first high-resolution image, wherein the representative low-resolution image has substantially the same resolution as the low-resolution image;
ii) resizing the representative low-resolution image to produce a resized representative low-resolution image having the same resolution as the first high-resolution image, and
iii) determining the residual image responsive to a difference between the first high-resolution image and the resized representative low-resolution image.
7. The method of claim 1 wherein step c) includes:
i) determining a low-pass image by applying a low-pass convolution filter to the first high-resolution image; and
ii) determining the residual image responsive to a difference between the first high-resolution image and the low-pass image.
8. The method of claim 1 wherein step c) includes applying a high-pass convolution filter to the first high-resolution image, the high-pass convolution filter being designed to provide an estimate of frequency content from the first high-resolution image that is not included in the low-pass image.
9. The method of claim 1 wherein step d) includes adding the low-resolution image and the residual image.
10. The method of claim 1 wherein step d) includes the step of modifying the residual image in pixel neighborhoods surrounding pixels where either the first high-resolution image or the low-resolution image is clipped.
11. The method of claim 10 wherein the residual image is modified by multiplying the residual image by a correction factor, and wherein the correction factor is a function of the maximum amount of clipping in the pixel neighborhood.
12. The method of claim 1 wherein pixel values for the high-dynamic-range image are determined by forming a weighted combination of corresponding pixel values from the first high-resolution image and the second high-resolution image.
13. The method of claim 12 wherein weights for the weighted combination vary as a function of pixel value in the first high-resolution image or the second high-resolution image.
14. The method of claim 12 wherein any clipped pixels are excluded from the weighted combination.
15. The method of claim 1 further including using an alignment step to correct for alignment differences between the low-resolution image and the first high-resolution image.
16. The method of claim 1 wherein pixel values of the low-resolution image and the first high-resolution image are linear with scene exposure.
17. The method of claim 1 wherein the low-resolution image and the first high-resolution image are color filter array images captured with an image sensor having an array of color filters disposed over photo-sensitive pixels, the array of color filters including at least three different types of color filters corresponding to at least three different color channels, and wherein the steps c)-e) are applied independently to image pixels corresponding to each of the color channels such that the high-dynamic-range image is a color filter array high-dynamic-range image.
18. The method of claim 17 further including applying a color filter array interpolation algorithm to determine a full color high-dynamic-range image responsive to color filter array high-dynamic-range image.
19. The method of claim 1 further including receiving a second low-resolution image of the scene having the first resolution and captured at a third exposure level, the third exposure level being different from the first and second exposure levels, and wherein the high-dynamic-range image is produced responsive to a third high-resolution image having the second resolution and the third exposure level, the third high-resolution image being formed by combining the second low-resolution image and the residual image.
20. The method of claim 19 wherein the first exposure level is less than the second exposure level and the third exposure level is greater than the second exposure level.
21. A digital camera system for producing high-dynamic-range images, comprising:
an image sensor for capturing digital images;
an optical system for forming an image of a scene onto the image sensor;
a data processing system;
a storage memory for storing captured images; and
a program memory communicatively connected to the data processing system and storing instructions configured to cause the data processing system to implement a method for producing high-dynamic-range images, wherein the instructions include:
a) capturing a low-resolution image of a scene having a first resolution and a first exposure level;
b) capturing a first high-resolution image of the scene having a second resolution and a second exposure level, the second exposure level being different from the first exposure level and the second resolution being greater than the first resolution;
c) determining a residual image corresponding to high spatial frequency content in the first high-resolution image;
d) determining a second high-resolution image having the second resolution and the first exposure level by combining the low-resolution image and the residual image;
e) producing the high-dynamic-range image by combining the first high-resolution image and the second high-resolution image; and
f) storing the high-dynamic-range image in the storage memory.