A computer-implemented method comprising: receiving pixel intensity values corresponding to at least part of a first, second and third image frame, acquired by an imaging system comprising at least two imaging devices for acquiring the first, second and third image frames, of a subject illuminated by temporally modulated illumination, wherein a time delay between an acquisition start time of the first and second image frames is such that there is an overlap in time during acquisition of the first and second image frames, and wherein a time delay between an acquisition start time of the second and third image frames is such that there is an overlap in time during acquisition of the second and third image frames, wherein: the time delay between the acquisition start times of the first and second image frames, and the time delay between the acquisition start times of the second and third image frames, is based on a modulation time period of the temporally modulated illumination; and the time delay corresponds to the modulation time period divided by the number of image frames that are partly acquired at a time within an overlapping acquisition time such that a timing relationship between an imaging time period over which the imaging system acquires each image frame and the modulation time period of the temporally modulated illumination is such that a different spatial intensity modulation pattern is registered in each of the first, second and third image frames; and determining modified pixel intensity values for constructing a modified image of the subject based on: a difference between the received pixel intensity values of each different pair combination of the first, second and third image frames to determine pixel intensity values for each different pair combination, wherein the difference reduces an effect of ambient lighting present when each of the first, second and third image frames were acquired; and a combination of the determined pixel intensity values for each different pair combination to cancel out the spatial intensity modulation pattern apparent in each of the first, second and third image frames. the time delay between the acquisition start times of the first and second image frames, and the time delay between the acquisition start times of the second and third image frames, is based on a modulation time period of the temporally modulated illumination; and the time delay corresponds to the modulation time period divided by the number of image frames that are partly acquired at a time within an overlapping acquisition time such that a timing relationship between an imaging time period over which the imaging system acquires each image frame and the modulation time period of the temporally modulated illumination is such that a different spatial intensity modulation pattern is registered in each of the first, second and third image frames; and determining modified pixel intensity values for constructing a modified image of the subject based on: a difference between the received pixel intensity values of each different pair combination of the first, second and third image frames to determine pixel intensity values for each different pair combination, wherein the difference reduces an effect of ambient lighting present when each of the first, second and third image frames were acquired; and a combination of the determined pixel intensity values for each different pair combination to cancel out the spatial intensity modulation pattern apparent in each of the first, second and third image frames. a difference between the received pixel intensity values of each different pair combination of the first, second and third image frames to determine pixel intensity values for each different pair combination, wherein the difference reduces an effect of ambient lighting present when each of the first, second and third image frames were acquired; and a combination of the determined pixel intensity values for each different pair combination to cancel out the spatial intensity modulation pattern apparent in each of the first, second and third image frames.