A method for calibrating a specular reflectance measurement sensor for use in a device, the method comprising: providing a sensor module, the sensor module comprising: (i) an illuminator configured to emit a beam of light at a target, thereby producing specular reflectance at an angle; (ii) a linear array sensor configured to detect said specular reflectance; and (iii) a processor configured to process the specular reflectance detected by the linear array sensor; measuring a specular reflectance profile of a diffuse white reflecting surface using the sensor module and storing the measured diffuse white reflecting surface specular reflectance profile in a memory; determining a pixel-wise non-uniformity correction factor which quantifies reflectance non-uniformity differences between a target and the diffuse white reflecting surface; measuring a specular reflectance profile of a target using the sensor module; determining a calibrated specular reflectance profile of the target based upon the pixel-wise non-uniformity correction factor, and providing the calibrated specular reflectance profile of the target to the device, characterized by determining the calibrated specular reflectance profile of the target comprises: scaling the diffuse white reflecting surface specular reflectance profile with respect to a photoreceptor reflectance profile of a photoreceptor of the device; and scaling the pixel-wise non-uniformity correction factor based on a diffuse content of the reflected light; wherein scaled diffuse white reflecting surface specular reflectance profile (R W PR) is determined, as follows: R W PR i = WHITE i − DARK i / PR i − DARK i × PR ̅ WHITE ̅ where: WHITE is the pixel-wise reflectance profile for the diffuse white reflecting surface; DARK is the pixel-wise reflectance profile for the photoreceptor having no light thereupon it; PR is the pixel-wise reflectance profile for the bare photoreceptor; WHITE is the mean value for WHITE; and PR is the mean value for PR; and i is an index for the pixel of the linear array sensor. providing a sensor module, the sensor module comprising: (i) an illuminator configured to emit a beam of light at a target, thereby producing specular reflectance at an angle; (ii) a linear array sensor configured to detect said specular reflectance; and (iii) a processor configured to process the specular reflectance detected by the linear array sensor; (i) an illuminator configured to emit a beam of light at a target, thereby producing specular reflectance at an angle; (ii) a linear array sensor configured to detect said specular reflectance; and (iii) a processor configured to process the specular reflectance detected by the linear array sensor; measuring a specular reflectance profile of a diffuse white reflecting surface using the sensor module and storing the measured diffuse white reflecting surface specular reflectance profile in a memory; determining a pixel-wise non-uniformity correction factor which quantifies reflectance non-uniformity differences between a target and the diffuse white reflecting surface; measuring a specular reflectance profile of a target using the sensor module; determining a calibrated specular reflectance profile of the target based upon the pixel-wise non-uniformity correction factor, and providing the calibrated specular reflectance profile of the target to the device, characterized by determining the calibrated specular reflectance profile of the target comprises: scaling the diffuse white reflecting surface specular reflectance profile with respect to a photoreceptor reflectance profile of a photoreceptor of the device; and scaling the pixel-wise non-uniformity correction factor based on a diffuse content of the reflected light; wherein scaled diffuse white reflecting surface specular reflectance profile (R W PR) is determined, as follows: R W PR i = WHITE i − DARK i / PR i − DARK i × PR ̅ WHITE ̅ where: WHITE is the pixel-wise reflectance profile for the diffuse white reflecting surface; DARK is the pixel-wise reflectance profile for the photoreceptor having no light thereupon it; PR is the pixel-wise reflectance profile for the bare photoreceptor; WHITE is the mean value for WHITE; and PR is the mean value for PR; and i is an index for the pixel of the linear array sensor. scaling the diffuse white reflecting surface specular reflectance profile with respect to a photoreceptor reflectance profile of a photoreceptor of the device; and scaling the pixel-wise non-uniformity correction factor based on a diffuse content of the reflected light; wherein scaled diffuse white reflecting surface specular reflectance profile (R W PR) is determined, as follows: R W PR i = WHITE i − DARK i / PR i − DARK i × PR ̅ WHITE ̅ where: WHITE is the pixel-wise reflectance profile for the diffuse white reflecting surface; DARK is the pixel-wise reflectance profile for the photoreceptor having no light thereupon it; PR is the pixel-wise reflectance profile for the bare photoreceptor; WHITE is the mean value for WHITE; and PR is the mean value for PR; and i is an index for the pixel of the linear array sensor. WHITE is the pixel-wise reflectance profile for the diffuse white reflecting surface; DARK is the pixel-wise reflectance profile for the photoreceptor having no light thereupon it; PR is the pixel-wise reflectance profile for the bare photoreceptor; WHITE is the mean value for WHITE; and PR is the mean value for PR; and i is an index for the pixel of the linear array sensor.