A method comprising: receiving a first image captured on an image sensor, the image sensor comprising an array of pixels; obtaining a scene estimate for the first image, wherein the scene estimate comprises an array of values, each value comprising an estimate of the background signal for a region of space being imaged onto a respective one of the pixels of the image sensor; storing the scene estimate in memory; receiving a plurality of successive images, wherein for each one of the successive images, the field of view is shifted with respect to the preceding image and overlaps partially with that of the preceding image, for each one of the successive images: retrieving the scene estimate from memory; subtracting the scene estimate from the image to obtain a background-subtracted image for output; updating the scene estimate based on the signal detected at the location on the image sensor to which the region of space is being imaged, characterized in that the updating the scene estimate comprises: determining a value of the background-subtracted image for the location on the image sensor to which the region of space is being imaged; if a magnitude of the value of the background-subtracted image is below a pre-defined threshold value, updating the scene estimate based on the value of the background-subtracted image; and if the magnitude of the value of the background-subtracted image is equal to or above the pre-defined threshold value, updating the scene estimate based on the threshold value; wherein the pre-defined threshold value varies depending on the location on the image sensor to which the region of space is being imaged; and replacing the scene estimate stored in memory with the updated scene estimate. receiving a first image captured on an image sensor, the image sensor comprising an array of pixels; obtaining a scene estimate for the first image, wherein the scene estimate comprises an array of values, each value comprising an estimate of the background signal for a region of space being imaged onto a respective one of the pixels of the image sensor; storing the scene estimate in memory; receiving a plurality of successive images, wherein for each one of the successive images, the field of view is shifted with respect to the preceding image and overlaps partially with that of the preceding image, for each one of the successive images: retrieving the scene estimate from memory; subtracting the scene estimate from the image to obtain a background-subtracted image for output; updating the scene estimate based on the signal detected at the location on the image sensor to which the region of space is being imaged, characterized in that the updating the scene estimate comprises: determining a value of the background-subtracted image for the location on the image sensor to which the region of space is being imaged; if a magnitude of the value of the background-subtracted image is below a pre-defined threshold value, updating the scene estimate based on the value of the background-subtracted image; and if the magnitude of the value of the background-subtracted image is equal to or above the pre-defined threshold value, updating the scene estimate based on the threshold value; wherein the pre-defined threshold value varies depending on the location on the image sensor to which the region of space is being imaged; and replacing the scene estimate stored in memory with the updated scene estimate. retrieving the scene estimate from memory; subtracting the scene estimate from the image to obtain a background-subtracted image for output; updating the scene estimate based on the signal detected at the location on the image sensor to which the region of space is being imaged, characterized in that the updating the scene estimate comprises: determining a value of the background-subtracted image for the location on the image sensor to which the region of space is being imaged; if a magnitude of the value of the background-subtracted image is below a pre-defined threshold value, updating the scene estimate based on the value of the background-subtracted image; and if the magnitude of the value of the background-subtracted image is equal to or above the pre-defined threshold value, updating the scene estimate based on the threshold value; wherein the pre-defined threshold value varies depending on the location on the image sensor to which the region of space is being imaged; and determining a value of the background-subtracted image for the location on the image sensor to which the region of space is being imaged; if a magnitude of the value of the background-subtracted image is below a pre-defined threshold value, updating the scene estimate based on the value of the background-subtracted image; and if the magnitude of the value of the background-subtracted image is equal to or above the pre-defined threshold value, updating the scene estimate based on the threshold value; wherein the pre-defined threshold value varies depending on the location on the image sensor to which the region of space is being imaged; and replacing the scene estimate stored in memory with the updated scene estimate.