A method of modifying a digital video signal obtained from a photo-sensor having a two-dimensional array of individual pixels with an optical field incident thereon wherein the video signal of the optical field is altered according to an additional intensity distribution pattern across the array, a sequence of outputs of the individual pixels resulting from said pixels being linearly scanned across the optical field forming the photo-sensor digital video signal, the modifying to correct for the additionally intensity distribution pattern, the method comprising: maintaining modification data (93, 95, 97, 113-123, 133, 135) of the intensity distribution pattern as a function of radial distances of the pixels from an optical center; calculating the radial distances, from the optical centre, of the individual pixels being scanned from their linear position within the two-dimension array, generating modifications (98, 99, 100, 120, 122, 124, 137-140) for the individual pixels being scanned from the image modification data (93, 95, 97, 113-123, 133, 135) being accessed by the calculated radial distances thereof, and combining the generated image modification data (93, 95, 97, 113-123, 133, 135) with the outputs (87-91, 101-111,125-131) of the corresponding individual pixels being scanned, thereby modifying the sequence of outputs (87-91, 101-111,125-131) of the individual pixels according to the image modification data (93, 95, 97, 113-123, 133, 135); CHARACTERISED IN THAT: the optical centre is an optical centre of the intensity distribution pattern defined to include at least one elliptical or hyperbolic intensity pattern across the sensor; wherein maintaining image modification data (93, 95,97, 113-123, 133, 135) includes storing points along at least a radius extending across the intensity distribution pattern from the optical center thereof and values of slopes between said points; wherein the values of said stored points have been calculated from measurements through the optical sensor by the device optical system (13, 33) viewing an image field having a uniform intensity there across, characterising intensity variations of the video signal output of the sensor by defining one or more sets of ellipses or hyperbolas, finding a single optical center of the intensity variation pattern and then calculating values of a set of points along the one radius as the modification data. maintaining modification data (93, 95, 97, 113-123, 133, 135) of the intensity distribution pattern as a function of radial distances of the pixels from an optical center; calculating the radial distances, from the optical centre, of the individual pixels being scanned from their linear position within the two-dimension array, generating modifications (98, 99, 100, 120, 122, 124, 137-140) for the individual pixels being scanned from the image modification data (93, 95, 97, 113-123, 133, 135) being accessed by the calculated radial distances thereof, and combining the generated image modification data (93, 95, 97, 113-123, 133, 135) with the outputs (87-91, 101-111,125-131) of the corresponding individual pixels being scanned, thereby modifying the sequence of outputs (87-91, 101-111,125-131) of the individual pixels according to the image modification data (93, 95, 97, 113-123, 133, 135); CHARACTERISED IN THAT: the optical centre is an optical centre of the intensity distribution pattern defined to include at least one elliptical or hyperbolic intensity pattern across the sensor; wherein maintaining image modification data (93, 95,97, 113-123, 133, 135) includes storing points along at least a radius extending across the intensity distribution pattern from the optical center thereof and values of slopes between said points; wherein the values of said stored points have been calculated from measurements through the optical sensor by the device optical system (13, 33) viewing an image field having a uniform intensity there across, characterising intensity variations of the video signal output of the sensor by defining one or more sets of ellipses or hyperbolas, finding a single optical center of the intensity variation pattern and then calculating values of a set of points along the one radius as the modification data. the optical centre is an optical centre of the intensity distribution pattern defined to include at least one elliptical or hyperbolic intensity pattern across the sensor; wherein maintaining image modification data (93, 95,97, 113-123, 133, 135) includes storing points along at least a radius extending across the intensity distribution pattern from the optical center thereof and values of slopes between said points; wherein the values of said stored points have been calculated from measurements through the optical sensor by the device optical system (13, 33) viewing an image field having a uniform intensity there across, characterising intensity variations of the video signal output of the sensor by defining one or more sets of ellipses or hyperbolas, finding a single optical center of the intensity variation pattern and then calculating values of a set of points along the one radius as the modification data.