Signal-to-noise ratio targeting

Apparatus comprising processing circuitry, the processing circuitry comprising:

• a receiving module configured to receive data corresponding to an ambient-corrected image of a subject illuminated by an illumination unit providing temporally modulated illumination with a modulation frequency that is higher than a frame acquisition rate used by an imaging device to obtain a set of images having a different spatial intensity modulation pattern in each image due to the temporally modulated illumination and the imaging device operating in a rolling shutter mode, wherein pixel intensity information from the obtained set of images is used to construct the ambient-corrected image by determining, from the pixel intensity information, pixel intensity registered due to ambient lighting and the pixel intensity registered due to the temporally modulated illumination and constructing the ambient-corrected image based on the pixel intensity registered due to the temporally modulated illumination in the obtained set of images;
• a determining module configured to determine a signal-to-noise ratio, SNR, of at least a portion of the ambient-corrected image;
• and
• an indicating module configured to cause, in response to determining that the SNR is below a target SNR, an indication of an illumination parameter to be sent to the illumination unit to increase an amplitude modulation depth of the temporally modulated illumination used to illuminate the subject while the imaging device acquires a subsequent set of images for constructing a subsequent ambient-corrected image with increased SNR for at least a portion of the subsequent ambient-corrected image.