When imaging bright objects, a conventional detector array can saturate, making it difficult to produce an image with a dynamic range that equals the scene's dynamic range. Conversely, a digital focal plane array (DFPA) with one or more m-bit counters can produce an image whose dynamic range is greater than the native dynamic range. In one example, the DFPA acquires a first image over a relatively brief integration period at a relatively low gain setting. The DFPA then acquires a second image over longer integration period and/or a higher gain setting. During this second integration period, counters may roll over, possibly several times, to capture a residue modulus m of the number of counts (as opposed to the actual number of counts). A processor in or coupled to the DFPA generates a high-dynamic range image based on the first image and the residues modulus m.
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1. A method of generating a digital representation of a scene with a detector element operably coupled to an m-bit counter, the method comprising: (A) generating, in the m-bit counter, a first count of less than or equal to 2 m −1, the first count representative of detections by the detector element during a first integration period; (B) generating, in the m-bit counter, a residue modulo m of a second count of greater than 2 m −1, the second count representative of detections by the detector element during a second integration period; and (C) generating the digital representation of the scene based at least in part on the first count and the residue modulo m of the second count, wherein step (C) comprises generating the digital representation of the scene with a bit depth of greater than m, and m is a positive integer.
2. The method of claim 1 , wherein step (B) further comprises selecting the second integration period to be longer than the first integration period.
3. The method of claim 1 , wherein step (B) further comprises setting a gain of the detector to be greater during the second integration period than during the first integration period.
4. The method of claim 1 , wherein step (C) further comprises: (C1) estimating a flux incident on the detector element during the first integration period based at least in part on the first count; and (C2) estimating the second count based at least in part on the flux estimated in (C1), the second integration period, and the residue modulo m of the second count.
5. The method of claim 1 , wherein step (C) further comprises generating the digital representation of the scene by concatenating k bits of the first count with l bits of the second count, wherein k≦m, l≦m, and l+k≧m+2, and k and l are positive integers.
6. The method of claim 1 , wherein step (C) comprises generating the digital representation of the scene in real time.
7. The method of claim 1 , further comprising: (D) estimating a noise level associated with the digital representation of the scene based on a comparison of a most significant bit of the first count to a corresponding bit in the residue modulo m of the second count.
8. The method of claim 1 , further comprising: (E) generating a third count of less than or equal to 2 m −1, the third count representative of detections by the detector element during a third integration period.
9. The method of claim 8 , further comprising: (F) performing a comparison of the first count generated in step (A) to the third count generated in step (E); (G) identifying motion in the scene based on the comparison performed in step (F); and (H) adjusting the digital representation of the scene to compensate for the motion identified in step (G).
10. The method of claim 9 , wherein step (C) further comprises: (C4) estimating a first flux incident on the detector element during the first integration period based at least in part on the first count generated in step (A); (C5) estimating a third flux incident on the detector element during the third integration period based at least in part on the third count generated in step (E); and (C6) generating the digital representation of the scene based at least in part on the first flux estimated in step (C4) and the third flux estimated in step (C5).
11. A system for generating a digital representation of a scene, the system comprising: a detector element to detect incident photons during a first integration period and during a second integration period; an m-bit counter, operably coupled to the detector element, to generate: (i) a first count of less than or equal to 2 m −1, the first count representative of photons detected by the detector element during the first integration period; and (ii) a residue modulo m of a second count of greater than 2 m −1, the second count representative of photons detected by the detector element during the second integration period; and a processor, operably coupled to the m-bit counter, to generate the digital representation of the scene based at least in part on the first count and the residue modulo m of the second count, wherein the processor is configured to generate the digital representation of the scene with a bit depth of greater than m, and m is a positive integer.
12. The system of claim 11 , wherein the second integration period is longer than the first integration period.
13. The system of claim 11 , wherein the detector is configured to detect the incident photons at a first gain during the first integration period and at a second gain greater than the first gain during the second integration period.
14. The system of claim 11 , wherein the processor is configured to generate the digital representation of the scene by: (i) estimating a photon flux incident on the detector element during the first integration period based at least in part on the first count; and (ii) estimating the second count based at least in part on the photon flux estimated in (i), the second integration period, and the residue modulo m of the second count.
15. The system of claim 11 , wherein the processor is configured to generate the digital representation of the scene by concatenating k bits of the first count with l bits of the second count, wherein k≦m, l≦m, and l+k≧m+2, and k and l are positive integers.
16. The system of claim 11 , wherein the processor is configured to generate the digital representation of the scene in real time.
17. The system of claim 11 , wherein the processor is configured to estimate a noise level associated with the digital representation of the scene based on a comparison of a most significant bit of the first count to a corresponding bit in the second count.
18. The system of claim 11 , wherein: the detector element is configured to detect photons during a third integration period shorter than the second integration period, the m-bit counter is configured to generate a third count of less than or equal to 2 m −1, the third count representative of photons detected by the detector element during the third integration period, and the processor is configured to identify and/or compensate for motion in the scene based on a comparison of the first count to the third count.
19. The system of claim 11 , wherein: the detector element is configured to detect photons during a third integration period shorter than the second integration period, the m-bit counter is configured to generate a third count of less than or equal to 2 m −1, the third count representative of photons detected by the detector element during the third integration period, and the processor is configured to generate the digital representation of the scene based at least in part on the third count.
20. A method of generating a digital representation of a scene with a plurality of detector elements, each detector element in the plurality of detector elements operably coupled to a corresponding m-bit counter in a plurality of m-bit counters, where m is a positive integer, the method comprising: (A) generating, in a first m-bit counter in the plurality of m-bit counters, a first count of less than or equal to 2 m −1, the first count representative of photons detected by a corresponding first detector element in the plurality of detector elements during a first integration period; (B) generating, in the first m-bit counter, a residue modulo m of a second count of greater than 2 m −1, the second count representative of photons detected by the corresponding first detector element during a second integration period longer than the first integration period; (C) generating, in the first m-bit counter, a third count of less than or equal to 2 m −1, the first count representative of photons detected by the corresponding first detector element during a third integration period shorter than the second integration period; (D) performing a comparison of the first count to the third count to determine if motion was present in the scene during the second integration period; and (E) generating the digital representation of the scene based at least in part on the first count, the residue modulo m of the second count, the third count, and/or the comparison of the first count to the third count.
21. The method of claim 1 , wherein step (B) is performed after step (A).
22. The method of claim 1 , wherein step (B) comprises: estimating, based on the first count, a photon flux incident on the detector element during the first integration period; and selecting the second integration period based at least in part on the photon flux.
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April 25, 2014
February 23, 2016
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