The third generation of infrared (IR) focal plane arrays (FPA) will have to detect simultaneously at least two different spectral bands. Small pixel pitches (less than 25-30 mm) will also be needed to achieve the resolution required for such devices without degrading performances, introducing difficult technological challenges. Among those is optical filling: the third generation will have to retain the high filling factor obtained with a planar single-color FPA. It thus appears necessary to estimate the sensible areas of small pitched dual-band pixels. Scanning a controlled IR spot on the FPA surface allows the observation of the spatial response of a pixel. Such spotscan measurements have been carried out on Hg 1ÿ x Cd x Te dual-band arrays. Different device structures have been tested: planar structures and NPN mesa structures, produced at LETI LIR. The spotscan bench test is first presented, in order to clarify characterization conditions and understanding. Measurement results are then discussed and compared with modeling, in order to identify the main physical parameters determining the optical area of such dual-band IR detectors. Emphasis on modulation transfer function (MTF) estimation and X talk is finally carried out.