## 1 Introduction
The unique advantage of FTP is its one-shot capability of 3-D surface imaging. However, for exacting 3-D profile reconstruction, one of the key issues in FTP is to extract accurately the first-order spectrum from the spectral domain. The extraction would require an adequate band-pass filter to obtain accurate spectral information from the first-order spectrum and separate it from the background spectrum (zero-order spectrum). Conditions for separating these spectrum regions have been investigated by considering the minimum distance between spectrum regions [5; 6; 7]. The single elliptic band-pass filter [8] and double orthogonal elliptic band-pass filter [9; 10] have been developed to extract accurately the first-order spectrum from the spectral domain. Nevertheless, FTP still lacks a robust algorithm for detecting the first-order spectrum to reconstruct accurately 3-D profiles. Apart from these methods, scanning white light interferometry (SWLI) is powerful for its phase unambiguity and nano-scale depth resolution [11]. It has been widely applied for precise sub-micro-scale and nano-scale surface profilometry, especially in semiconductor microstructure metrology. The method is mainly used for review or off-line metrology since its scanning efficiency is limited by vertical scanning required. A major challenge for 3-D scanning techniques using FPP is the presence of specular reflectance on the tested object surface. Specular highlights occur on object surfaces when the specular element of reflection is dominant. Specular highlight can easily saturate the detected image and seriously deteriorate image quality. In the literature, several techniques have been proposed for resolving the problem when measuring specular targets. All these techniques can effectively reduce specular effects to different extents but cannot resolve the problem completely. One of the proposed techniques was to separate specular components from diffuse components and remove the specular components using polarizers [12; 13; 14; 15]. [PERSON] and [PERSON] relied on image color properties when transferring image color to the hue domain [16]. This technique effectively eliminated image-saturated regions mainly because the saturation value of every pixel was made constant for achieving maximum chromaticity while keeping their hue. Other techniques, such as using multi-exposure time [17] or projecting special structured light with strip edges [18] have been experimented for handling non-uniform light reflection. Phase measuring deflectometry (PMD) is a specular surface measuring technique using a Thin-Film-Transistor Liquid-Crystal Display (TFT LCD) screen as the pattern-projecting light source [19; 20]. The maximum detectable surface curvature is currently limited by the LCD light dispersion angle. More recently, single-shot deflectometry using a single composite pattern was developed for one-shot measurement of three-dimensional imaging using Fourier transform (FT) and spatial carrier-frequency phase-shifting (SCPS) techniques [21]. However, generally for PMD, due to demanding computation in slope integration, the absolute shape measurement may not be accurately achieved. Thus, apart from visible moire fringe projection, [PERSON] et al. used high-power infrared laser pattern to project on the measured object surface, in which the projected laser power was partly transferred into dispersive heat [22]. Since heat dispersion can be generated from a highly specular surface, extremely dark or transparent materials can be observed clearly by a proper heat sensor [23]. Phase shifting technique can be employed to measure 3-D profile according to distortion of the heat pattern on the object surface. The current limitation of the method is its low measuring accuracy, which still requires further improvement.