Apparatus and method
An apparatus comprising a spectral filter ( 26 ) with a variable spectral filter transmission (FT(λ)); an event-based imaging sensor ( 27 ) configured to produce measurement events (y 1 , y 2 , . . . , y n ) which correspond to a change in a filter response (Y(t)) that is generated by an observed spectrum (X(λ)), and a processor ( 28 ) configured to control the filter transmission (FT(λ)) of the spectral filter ( 26 ) so that it sweeps over wavelength (λ) with time (t), and to generate an estimation (X*(λ)) of the observed spectrum (X(λ)) based on the measurement events (y 1 , y 2 , . . . , y n ) that correspond to the filter response (Y(t)) and based on the filter transmission (FT(λ)).
1. An apparatus comprising
a spectral filter with a variable spectral filter transmission;
an event-based imaging sensor configured to produce measurement events which correspond to a change in a filter response that is generated by an observed spectrum, and
a processor configured to
control the filter transmission of the spectral filter so that it sweeps over wavelength with time, and to
generate an estimation of the observed spectrum based on the measurement events that correspond to the filter response and based on the filter transmission.
2. The apparatus of claim 1 , in which the processor is configured to control the spectral filter transmission of the spectral filter so that it sweeps linearly or non-linearly over wavelength with time.
3. The apparatus of claim 1 , wherein the event-based imaging sensor is configured to create the filter response by recording any intensity changes that result from changes in the spectral filter transmission.
4. The apparatus of claim 1 , wherein the event-based imaging sensor is configured to register pixel intensity changes in an asynchronous way.
5. The apparatus of claim 1 , wherein the event-based imaging sensor is configured to create, from incidents on the imaging sensor, events that indicate an intensity increase or decrease.
6. The apparatus of claim 5 , wherein the events indicate an intensity increase or decrease of a pre-defined threshold which is fixed or adaptively changed by the processor.
7. The apparatus of claim 5 , wherein the processor is configured to create the filter response from the detected events.
8. The apparatus of claim 7 , wherein the processor is configured to reconstruct the observed spectrum from the measured filter responses by a numerical reconstruction method.
9. The apparatus of claim 8 , wherein the numerical reconstruction method is a Tikhonov regularization.
10. The apparatus of claim 9 , wherein the numerical reconstruction method is based on a matrix containing the known filter responses of the spectral filter.
11. The apparatus of claim 8 , wherein in the numerical reconstruction method, a single event or a sum of events related to a measurement between a time interval is formulated as a linear or higher order combination.
12. The apparatus of claim 11 , wherein the linear or higher order combination is y m =[FS(t 1 )−FS(t 0 )]·x·(t 1 −t 0 ), where FS is the filter transmission of the spectral filter, x is the observed spectrum and (t 1 −t 0 ) is the time interval.
13. The apparatus of claim 8 , wherein the numerical reconstruction method is based on compressive sensing principles.
14. The apparatus of claim 1 , further comprising a lens system and a band-limiting filter.
15. A method, comprising
producing measurement events which correspond to a change in a filter response of a spectral filter that is generated by an observed spectrum;
controlling the filter transmission of the spectral filter so that it sweeps over wavelength with time; and
generating an estimation of the observed spectrum based on the measurement events that correspond to the filter response and based on the filter transmission.