An image printing system includes a print engine and a sensing system. The print engine is configured to print a marking material image on a image bearing surface. The sensing system includes a plurality of illuminators, a modulator, a sensor, and a demodulator. Each illuminator is configured to simultaneously emit a light beam at the marking material image on the image bearing surface, thereby producing reflectance from the marking material image at least in a first direction. The modulator is configured to modulate an intensity characteristic of each of the light beams emitted by the illuminators such that each light beam has a different modulated waveform characteristic, where the waveform characteristic includes at least frequency. The sensor is configured to detect the reflectance from the plurality of light beams in the first direction and output a reflectance signal. The demodulator is configured to demodulate the reflectance signal to isolate a response of the marking material image to each of the individual illuminators.
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