Figure 2

Double-Scan procedure. In (1) the transfer function of the photo detectors used in the scanners is depicted. At high intensities the relationship between the incident light level and the output current begins to deviate from the ideal intensity in an effect called saturation that is typically drawn in an arrow shape (see 2a). On the other hand, quantization occurs when digitizing. All the unlimited physical values have to be encoded by a reduced set of discrete values, producing the same rate for a range of different values [21]. This effect can be observed in (2b) as a set of parallel lines. 2-Scan strategy [16] is based on the rather simple idea of producing two images with different calibrations, from which a mathematical model produces a coherent but extended range of values.