SYSTEM AND METHOD FOR AUTOMATIC EXPOSURE AND DYNAMIC RANGE COMPRESSION
A method of capturing a digital image with a digital camera includes determining a first exposure level for capturing an image based on a first luminance level of the image, determining a second exposure level for capturing the image based on a threshold exposure level of the image, configuring an exposure level of a sensor of the digital camera based on the second exposure level, capturing the image as a digital image, and adding a non-linear digital gain to the digital image based on a difference between the first exposure level and the second exposure level.
1 . A method of capturing a digital image with a digital camera comprising:
determining a first exposure level for capturing an image based on a first luminance level of the image;
determining a second exposure level for capturing the image based on a threshold exposure level of the image;
configuring an exposure level of a sensor of the digital camera based on the second exposure level;
capturing the image as a digital image; and
adding a non-linear digital gain to the digital image based on a difference between the first exposure level and the second exposure level.
2 . The method of claim 1 , wherein determining the second exposure level comprises determining an exposure level at which a threshold percentage of pixels of the digital image have a luminance value below a threshold luminance value.
3 . The method of claim 1 , wherein determining the first exposure level comprises determining an exposure level based also at least on a histogram of the image.
4 . The method of claim 1 , wherein adding the non-linear gain comprises adding a first gain to a first portion of the pixels and a second gain to a second portion of the pixels.
5 . The method of claim 4 , wherein the first portion of the pixels comprises a portion of pixels below a threshold luminance value.
6 . The method of claim 4 , wherein the first gain comprises a gain such that adding the first gain results in a second luminance level of each of the pixels of the first portion based on the first exposure level.
7 . The method of claim 4 , wherein the second gain comprises a gain such that adding the second gain results in a maximum luminance level based on the first exposure level.
8 . The method of claim 1 , wherein adding the non-linear gain comprises adding a first gain to a first portion of the pixels and no gain to a second portion of the pixels.
9 . The method of claim 1 , wherein adding the non-linear gain comprises adjusting a gamma correction factor.
10 . The method of claim 1 , wherein adding the non-linear gain comprises adjusting a dynamic range compression factor.
11 . The method of claim 1 , wherein the first and second exposure levels are determined concurrently based on a first and second subset of the pixels, respectively.
12 . The method of claim 1 , wherein the threshold exposure level is determined for each color channel separately.
13 . The method of claim 12 , wherein the second exposure level is determined based on the lowest of the threshold exposure levels of each color channel.
14 . The method of claim 12 , wherein the second exposure level is determined based on a weighted average of the threshold exposure levels of each color channel.
15 . The method of claim 1 , wherein determining the second exposure level further comprises:
comparing a difference between the first exposure and the second exposure level to a predetermined maximum difference; and
based on the comparison, setting the second exposure level to a level based on the first exposure level and the predetermined maximum difference.
16 . A digital camera system for image processing comprising a processor configured for:
determining a first exposure level for capturing an image based on a first luminance level of the image;
determining a second exposure level for capturing the image based on a threshold exposure level of the image;
configuring an exposure level of a sensor of the digital camera based on the second exposure level;
capturing the image as a digital image; and
adding a non-linear digital gain to the digital image based on a difference between the first exposure level and the second exposure level.
17 . The system of claim 16 , wherein the processor is configured for determining the second exposure level by at least determining an exposure level at which a threshold percentage of pixels of the digital image have a luminance value below a threshold luminance value.
18 . The system of claim 16 , wherein the processor is configured for determining the first exposure level by at least determining an exposure level based also at least on a histogram of the image.
19 . The system of claim 16 , wherein the processor is configured for adding the non-linear gain by at least adding a first gain to a first portion of the pixels and a second gain to a second portion of the pixels.
20 . The system of claim 19 , wherein the first portion of the pixels comprises a portion of pixels below a threshold luminance value.
21 . The system of claim 19 , wherein the first gain comprises a gain such that adding the first gain results in a second luminance level of each of the pixels of the first portion based on the first exposure level.
22 . The system of claim 19 , wherein the second gain comprises a gain such that adding the second gain results in a maximum luminance level based on the first exposure level.
23 . The system of claim 16 , wherein the processor is configured for adding the non-linear gain by at least adding a first gain to a first portion of the pixels and no gain to a second portion of the pixels.
24 . The system of claim 16 , wherein the processor is configured for adding the non-linear gain by at least adjusting a gamma correction factor.
25 . The system of claim 16 , wherein the processor is configured for adding the non-linear gain by at least adjusting a dynamic range compression factor.
26 . The system of claim 16 , wherein the first and second exposure levels are determined concurrently based on a first and second subset of the pixels, respectively.
27 . The system of claim 16 , wherein the threshold exposure level is determined for each color channel separately.
28 . The system of claim 27 , wherein the second exposure level is determined based on the lowest of the threshold exposure levels of each color channel.
29 . The system of claim 27 , wherein the second exposure level is determined based on a weighted average of the threshold exposure levels of each color channel.
30 . The system of claim 16 , wherein the second exposure level is determined based on:
comparing a difference between the first exposure and the second exposure level to a predetermined maximum difference; and
based on the comparison, setting the second exposure level to a level based on the first exposure level and the predetermined maximum difference.