Embodiments generally relate to a system for reading fluorescent-labelled diagnostic assays for in-vitro diagnostic applications. The system comprises a receiving member adapted to receive a fluorescent-labelled diagnostic assay cartridge carrying a fluorescent-labelled diagnostic assay; at least one excitation module configured to illuminate the diagnostic assay, when the diagnostic assay cartridge is placed in the receiving member; a camera module for capturing an image of the illuminated diagnostic assay placed in the receiving member; a processor for receiving the captured image from the camera module and determining whether or not a target analyte was present in the diagnostic assay captured by the camera module; and memory storing firmware, the firmware including a brightness compensation module configured to adjust the intensity of an image of a diagnostic cartridge captured by the camera module, in order to emulate a uniform field of illumination over the diagnostic cartridge. The brightness compensation module is configured to adjust the intensity of the captured image based on an illumination compensation look-up table.