A biometric imaging arrangement comprising: a photodetector pixel array including at least a first portion of pixels arranged to receive light transmitted from a spectral filter with a spectral transmission band and at least a second portion of pixels arranged to receive light not transmitted from the spectral filter, wherein the biometric imaging arrangement is configured to acquire an image of an object and perform user authentication at least partly based on, in the acquired image, a relationship between the intensity of light received by the first portion of pixels and the intensity of light received by the second portion of pixels.