Image acquisition method and apparatus
An image acquisition method operates in a hand held image acquisition device with a camera. A first image of a scene is obtained with the camera at a nominal exposure level. A number of relatively bright pixels and a number of relatively dark pixels within the first image are determined. Based on the number of relatively bright pixels, a negative exposure adjustment is determined and based on the number of relatively dark pixels, a positive exposure adjustment is determined. Respective images are acquired at the nominal exposure level; with the negative exposure adjustment; and with the positive exposure adjustment as component images for high dynamic range (HDR) image of the scene.
1. A system comprising:
one or more processors;
an image sensor;
memory comprising computer executable instructions that, when executed by the one or more processors, cause the system to perform operations comprising:
obtaining a first image via the image sensor based at least in part on a first exposure level;
identifying a first set of pixels of the first image based at least in part on a light thresholding curve and first intensities associated with the first set of pixels;
identifying a second set of pixels of the first image based at least in part on a dark threshold curve and second intensities associated with the second set of pixels;
determining an underexposure adjustment level based at least in part on the first set of pixels;
determining an overexposure adjustment level based at least in part on the second set of pixels;
obtaining, via the image sensor, a second image based at least in part on the underexposure adjustment level; and
obtaining, via the image sensor, a third image based at least in part on the overexposure adjustment level.
2. The system of claim 1 , wherein obtaining the first image comprises:
obtaining an image via the image sensor; and
sub-sampling the image to obtain the first image.
3. The system of claim 1 , wherein determining the underexposure adjustment level comprises:
obtaining a fourth image via the image sensor based at least in part on the first exposure level and the underexposure adjustment level;
sub-sampling the fourth image; and
modifying, based at least in part on the first set of pixels, the underexposure adjustment level.
4. The system of claim 1 , wherein determining the overexposure adjustment level comprises:
obtaining a fourth image via the image sensor based at least in part on the first exposure level and the overexposure adjustment level;
sub-sampling the fourth image; and
modifying, based at least in part on the second set of pixels, the overexposure adjustment level.
5. The system of claim 1 , wherein:
determining the underexposure adjustment level comprises:
filtering a histogram associated with the first image based at least in part on the light thresholding curve to obtain a first filtered histogram,
and integrating the first filtered histogram;
determining the overexposure adjustment level comprises:
filtering the histogram associated with the first image based at least in part on the dark thresholding curve to obtain a second filtered histogram, and
integrating the second filtered histogram; and
the histogram comprises luminance values associated with pixels of the first image.
6. The system of claim 1 , wherein the operations further comprise generating a high dynamic range (HDR) image based at least in part on the second image and the third image.
7. The system of claim 1 , wherein the light thresholding curve is based at least in part on a high pass filter and the dark thresholding curve comprises is based at least in part on a low pass filter.
8. The system of claim 7 , wherein:
a first corner frequency of the low pass filter is less than twenty percent of a maximum intensity indicatable by an intensity value associated with a pixel; and
a second corner frequency of the high pass filter is more than seventy-eight percent of the maximum intensity.
9. A method comprising:
obtaining a first image via an image sensor based at least in part on a first exposure level;
identifying a first set of pixels of the first image based at least in part on a high pass filter and first intensities associated with the first set of pixels;
identifying a second set of pixels of the first image based at least in part on a low pass filter and second intensities associated with the second set of pixels;
determining an underexposure adjustment level based at least in part on the first set of pixels;
determining an overexposure adjustment level based at least in part on the second set of pixels;
obtaining, via the image sensor, a second image based at least in part on the underexposure adjustment level; and
obtaining, via the image sensor, a third image based at least in part on the overexposure adjustment level.
10. The method of claim 9 , wherein determining the underexposure adjustment level comprises:
obtaining a fourth image via the image sensor based at least in part on the first exposure level and the underexposure adjustment level;
sub-sampling the fourth image; and
modifying, based at least in part on the first set of pixels, the underexposure adjustment level.
11. The method of claim 9 , wherein determining the overexposure adjustment level comprises:
obtaining a fourth image via the image sensor based at least in part on the first exposure level and the overexposure adjustment level;
sub-sampling the fourth image; and
modifying, based at least in part on the second set of pixels, the overexposure adjustment level.
12. The method of claim 9 , wherein:
determining the underexposure adjustment level comprises:
filtering a histogram associated with the first image based at least in part on the light thresholding curve to obtain a first filtered histogram, and
integrating the first filtered histogram;
determining the overexposure adjustment level comprises:
filtering the histogram associated with the first image based at least in part on the dark thresholding curve to obtain a second filtered histogram, and
integrating the second filtered histogram; and
the histogram comprises luminance values associated with pixels of the first image.
13. The method of claim 9 , further comprising generating a high dynamic range (HDR) image based at least in part on the second image and the third image.
14. The method of claim 9 , wherein:
a first corner frequency of the low pass filter is less than twenty percent of a maximum intensity indicatable by an intensity value associated with a pixel; and
a second corner frequency of the high pass filter is more than seventy-eight percent of the maximum intensity.
15. A non-transitory computer-readable medium comprising processor-executable instructions that, when executed by one or more processors, cause the one or more processors to perform operations comprising:
obtaining a first image via an image sensor based at least in part on a first exposure level;
identifying a first set of pixels of the first image based at least in part on a high pass filter and first intensities associated with the first set of pixels;
identifying a second set of pixels of the first image based at least in part on a low pass filter and second intensities associated with the second set of pixels;
determining an underexposure adjustment level based at least in part on the first set of pixels;
determining an overexposure adjustment level based at least in part on the second set of pixels;
obtaining, via the image sensor, a second image based at least in part on the underexposure adjustment level; and
obtaining, via the image sensor, a third image based at least in part on the overexposure adjustment level.
16. The non-transitory computer-readable medium of claim 15 , wherein determining the underexposure adjustment level comprises:
obtaining a fourth image via the image sensor based at least in part on the first exposure level and the underexposure adjustment level;
sub-sampling the fourth image; and
modifying, based at least in part on the first set of pixels, the underexposure adjustment level.
17. The non-transitory computer-readable medium of claim 15 , wherein determining the overexposure adjustment level comprises:
obtaining a fourth image via the image sensor based at least in part on the first exposure level and the overexposure adjustment level;
sub-sampling the fourth image; and
modifying, based at least in part on the second set of pixels, the overexposure adjustment level.
18. The non-transitory computer-readable medium of claim 15 , wherein:
determining the underexposure adjustment level comprises:
filtering a histogram associated with the first image based at least in part on the light thresholding curve to obtain a first filtered histogram, and
integrating the first filtered histogram;
determining the overexposure adjustment level comprises:
filtering the histogram associated with the first image based at least in part on the dark thresholding curve to obtain a second filtered histogram, and
integrating the second filtered histogram; and
the histogram comprises luminance values associated with pixels of the first image.
19. The non-transitory computer-readable medium of claim 15 , further comprising generating a high dynamic range (HDR) image based at least in part on the second image and the third image.
20. The non-transitory computer-readable medium of claim 15 , wherein:
a first corner frequency of the low pass filter is less than twenty percent of a maximum intensity indicatable by an intensity value associated with a pixel; and
a second corner frequency of the high pass filter is more than seventy-eight percent of the maximum intensity.