Dynamic range compression for thermal video
Various embodiments of the present disclosure may include an imaging system that allows for absolute radiometry of low dynamic range (LDR) radiometric images down-sampled from high dynamic range (HDR) radiometric thermal images. The imaging system may capture HDR images. The HDR images may be converted to LDR images by a transfer function. In certain embodiments, a video and/or a stream of HDR images may be captured. A sequence of frames may be defined for at least a plurality of the HDR images. Each of the HDR images of the sequence of frames may be converted to LDR images using the same transfer function.
1. A method comprising:
receiving a plurality of successively captured high dynamic range (HDR) images, wherein each HDR image comprises a plurality of pixels and each pixel is associated with a HDR image value;
defining a plurality of successive sequences of the HDR images, each sequence comprising a plurality of successively captured HDR images;
determining a transfer function for each sequence, wherein the transfer function associates each HDR image value of at least a portion of the HDR image values with a corresponding low dynamic range (LDR) image value;
for each sequence, converting, with the associated transfer function, each HDR image of the sequence to a corresponding LDR image.
2. The method of claim 1 , wherein for each sequence, the transfer function is defined by the HDR images of the sequence; and
each HDR image is an infrared image.
3. The method of claim 1 , further comprising detecting an environmental condition;
wherein at least one transfer function is determined responsive to the environmental condition.
4. The method of claim 1 , wherein at least one transfer function is determined responsive to a time of day.
5. The method of claim 1 , wherein each sequence of HDR images comprises HDR images captured during a corresponding event in a sequence of events.
6. The method of claim 5 , wherein each image is obtained using a camera, and each event is a dwell point at which the camera images a part of a scene before moving to image another part of the scene.
7. The method of claim 1 , wherein for at least one sequence, the transfer function is determined responsive to detecting an object in the images.
8. The method of claim 1 , further comprising:
determining, for at least one transfer function, that at least one of the HDR images comprises an unassociated HDR image value not associated with a LDR image value within the transfer function; and
updating the transfer function to associate the unassociated HDR image value to a LDR image value.
9. The method of claim 1 , further comprising analyzing the LDR images obtained from each sequence of the HDR images to detect an object and its position in multiple LDR images obtained from the sequence.
10. A system for performing the method claim 1 , the system comprising:
a logic device;
a memory configured to store instructions comprising the method of claim 1 for communication to and execution by the logic device; and
a camera configured to capture and output the image data comprising the HDR images defined in each sequence of the HDR images to the logic device.
11. A system comprising a logic device associated with a camera, the logic device configured to:
receive a plurality of successively captured high dynamic range (HDR) images, wherein each HDR image comprises a plurality of pixels and each pixel is associated with a HDR image value;
define a plurality of successive sequences of the HDR images, each sequence comprising a plurality of successively captured HDR images;
determine a transfer function for each sequence, wherein the transfer function associates each HDR image value of at least a portion of the HDR image values with a corresponding LDR image value;
for each sequence, convert, with the associated transfer function, each HDR image of the sequence to a corresponding low dynamic range (LDR) image.
12. The system of claim 11 , wherein the transfer function is defined by the HDR images of the sequence; and
each HDR image is an infrared image.
13. The system of claim 11 , further comprising:
determining, for at least one transfer function, that at least one of the HDR images comprises an unassociated HDR image value not associated with a LDR image value within the transfer function; and
updating the transfer function to associate the unassociated HDR image value to a LDR image value.
14. The system of claim 11 , wherein at least one transfer function is determined responsive to a time of day.
15. The system of claim 11 , wherein each sequence of HDR images comprises HDR images captured during a corresponding event in a sequence of events.
16. The system of claim 15 , wherein each image is obtained using a camera, and each event is a dwell point at which the camera images a part of a scene before moving to image another part of the scene.
17. The system of claim 11 , wherein for at least one sequence, the transfer function is determined responsive to detecting an object in the images.
18. The system of claim 17 , wherein determining the transfer function for each sequence comprises selecting one of a plurality of pre-determined transfer functions for each sequence.
19. The system of claim 11 , further comprising a sensor for detecting an environmental condition, wherein the logic device is further configured to detect at least one transfer function responsively to the environmental condition.
20. The system of claim 11 , wherein the logic device is further configured to analyze the LDR images obtained from each sequence of the HDR images to detect an object and its position in multiple LDR images obtained from the sequence.