Systems and methods for high dynamic range imaging using crossed polarizers
According to one embodiment of the present disclosure, an imaging system includes: an image sensor including a plurality of subpixels grouped into a plurality of pixels; a polarization system including: a rotatable linear polarizer; and a polarizer mask including a plurality of polarizer filters, the polarizer filters being aligned with corresponding ones of the subpixels, the subpixels of a pixel of the plurality of pixels being located behind polarizer filters at different angles of linear polarization; and imaging optics configured to focus light from a scene onto the image sensor.
1. An imaging system comprising:
an image sensor comprising a plurality of subpixels grouped into a plurality of pixels;
a polarization system comprising:
a rotatable linear polarizer; and
a polarizer mask comprising a plurality of polarizer filters, the polarizer filters being aligned with corresponding ones of the subpixels, the subpixels of a pixel of the plurality of pixels being located behind polarizer filters at different angles of linear polarization;
imaging optics configured to focus light from a scene onto the image sensor; and
a processing circuit configured to perform operations to generate a high-dynamic range image by iteratively determining a polarization angle and exposure settings for a scene being imaged, the operations comprising:
iteratively modifying a polarizer angle of the rotatable linear polarizer based on a number of overexposed or underexposed subpixels in image sensor data until there are no overexposed or underexposed subpixels in the image sensor data;
iteratively modifying exposure settings of the image sensor until a dynamic range of the image sensor data matches a dynamic range of a radiance of the scene being imaged; and
generating the high-dynamic range image from final values for the polarizer angle and the exposure settings.
2. The imaging system of claim 1 , wherein the processing circuit is configured to:
control the image sensor to capture an image of the scene;
determine that the image includes underexposed pixels and overexposed pixels; and
adjust a dynamic range of the imaging system by controlling an angle of the rotatable linear polarizer.
3. The imaging system of claim 1 , wherein the processing circuit is further configured to iteratively adjust the dynamic range of the imaging system until the dynamic range of the imaging system is equal to or larger than a dynamic range of the scene.
4. The imaging system of claim 1 , wherein the processing circuit is further configured to control a plurality of exposure settings in accordance with the dynamic range of the imaging system and the dynamic range of the scene.
5. The imaging system of claim 1 , wherein the processing circuit is further configured to compute a high dynamic range image from a plurality of polarization channels of captured image.
6. The imaging system of claim 1 , wherein the rotatable linear polarizer comprises an electronically controlled mechanically rotatable linear polarizer.
7. The imaging system of claim 1 , wherein the rotatable linear polarizer comprises a liquid crystal polarization rotator.
8. The imaging system of claim 1 , wherein the rotatable linear polarizer is in front of the imaging optics.
9. The imaging system of claim 1 , wherein the rotatable linear polarizer is behind the imaging optics.
10. The imaging system of claim 1 , further comprising a color filter.
11. The imaging system of claim 1 , wherein the polarizer mask comprises a repeating mosaic of the polarizer filters at the different angles of linear polarization, the different angles of linear polarization comprising a first angle 0°, a second angle of 45°, a third angle of 90°, and a fourth angle 135°, and
wherein a pixel of the pixels comprises:
a first subpixel behind a first polarizer filter of the polarizer mask at the first angle of 0°;
a second subpixel behind a second polarizer filter of the polarizer mask at the second angle of 45°;
a third subpixel behind a third polarizer filter of the polarizer mask at the third angle of 90°; and
a fourth subpixel behind a fourth polarizer filter of the polarizer mask at the fourth angle of 135°.
12. The imaging system of claim 11 , wherein the processing circuit is configured to control the rotatable linear polarizer to rotate in a range from 0° to 22.5°.
13. The imaging system of claim 1 , wherein generating the high-dynamic range image comprises generating the high-dynamic range image from a single capture of the image sensor.
14. The imaging system of claim 1 , wherein iteratively modifying the exposure settings comprises:
determining that the dynamic range of the image sensor data does not match the dynamic range of the radiance of the scene being imaged; and
in response, adjusting the polarizer angle of the rotatable linear polarizer to decrease the dynamic range of the image sensor data.
15. The imaging system of claim 1 , wherein iteratively modifying a polarizer angle of the rotatable linear polarizer comprises:
determining that the image sensor data includes at least a threshold number of overexposed subpixels, underexposed subpixels, or both; and
in response, adjusting the polarizer angle of the rotatable linear polarizer to increase the dynamic range of the image sensor data.
16. A method for capturing images comprising:
controlling, by a processing circuit, an image sensor of an imaging system to capture an image,
the image sensor comprising a plurality of subpixels grouped into a plurality of pixels,
the imaging system further comprising:
a polarization system comprising:
a rotatable linear polarizer; and
a polarizer mask comprising a plurality of polarizer filters, the polarizer filters being aligned with corresponding ones of the subpixels, the subpixels of a pixel of the plurality of pixels being located behind polarizer filters at different angles of linear polarization; and
imaging optics configured to focus light from a scene onto the image sensor;
performing, by the processing circuit, operations to generate a high-dynamic range image by iteratively determining a polarization angle and exposure settings for a scene being imaged, the operations comprising:
iteratively modifying a polarizer angle of the rotatable linear polarizer based on a number of overexposed or underexposed subpixels in image sensor data until there are no overexposed or underexposed subpixels in the image sensor data;
iteratively modifying exposure settings of the image sensor until a dynamic range of the image sensor data matches a dynamic range of a radiance of the scene being imaged; and
generating the high-dynamic range image from final values for the polarizer angle and the exposure settings.
17. The method of claim 16 , further comprising iteratively adjusting the dynamic range of the imaging system until the dynamic range of the imaging system is equal to or larger than a dynamic range of the scene.
18. The method of claim 16 , further comprising controlling a plurality of exposure settings in accordance with the dynamic range of the imaging system and the dynamic range of the scene.
19. The method of claim 16 , further comprising computing a high dynamic range image from a plurality of polarization channels of captured image.
20. The method claim 16 , wherein the rotatable linear polarizer comprises an electronically controlled mechanically rotatable linear polarizer.
21. The method of claim 16 , wherein the rotatable linear polarizer comprises a liquid crystal polarization rotator.
22. The method of claim 16 , wherein the rotatable linear polarizer is in front of the imaging optics.
23. The method of claim 16 , wherein the rotatable linear polarizer is behind the imaging optics.
24. The method of claim 16 , wherein the imaging system further comprises a color filter.
25. The method of claim 16 , wherein the polarizer mask comprises a repeating mosaic of the polarizer filters at the different angles of linear polarization, the different angles of linear polarization comprising a first angle 0°, a second angle of 45°, a third angle of 90°, and a fourth angle 135°, and
wherein a pixel of the pixels comprises:
a first subpixel behind a first polarizer filter of the polarizer mask at the first angle of 0°;
a second subpixel behind a second polarizer filter of the polarizer mask at the second angle of 45°;
a third subpixel behind a third polarizer filter of the polarizer mask at the third angle of 90°; and
a fourth subpixel behind a fourth polarizer filter of the polarizer mask at the fourth angle of 135°.
26. The method of claim 25 , further comprising controlling the rotatable linear polarizer to rotate in a range from 0° to 22.5°.
27. The method of claim 16 , wherein generating the high-dynamic range image comprises generating the high-dynamic range image from a single capture of the image sensor.
28. The method of claim 16 , wherein iteratively modifying the exposure settings comprises:
determining that the dynamic range of the image sensor data does not match the dynamic range of the radiance of the scene being imaged; and
in response, adjusting the polarizer angle of the rotatable linear polarizer to decrease the dynamic range of the image sensor data.
29. The method of claim 16 , wherein iteratively modifying a polarizer angle of the rotatable linear polarizer comprises:
determining that the image sensor data includes at least a threshold number of overexposed subpixels, underexposed subpixels, or both; and
in response, adjusting the polarizer angle of the rotatable linear polarizer to increase the dynamic range of the image sensor data.