Very high resolution 3D surface scanning using multi-frequency phase measuring profilometry

Abstract

Structured light projection is one of the most accurate non-contact methods for scanning surface topologies. The field of view of such a scan may range from millimeters to several meters. One of the most precise and robust methods of structured light is Phase Measuring Profilometry. This method utilizes a sinusoidal pattern that is laterally shifted across a surface. An image is captured at uniform intervals and the "phase" is recovered for each pixel position by correlating across the shifted patterns. In general, the more pattern shifts and the higher the spatial frequency, the more accurate the depth measurement becomes, at each pixel location. However, with a high frequency, ambiguity errors can occur, so a dual frequency approach is commonly used where a low frequency pattern is used for non-ambiguous depth, followed by high frequency pattern. The low frequency result is used to unwrap the high frequency to yield a nonambiguous and precise phase. If the high frequency is too high, then ambiguity errors will occur. The solution is a multi-frequency method. We present experimental results for several variations of the multi-frequency approach yielding accuracies of 0.127mm standard deviation in depth with 0.92 mm pixel spacing. With consumer camera mega pixel technology this equates to a 0.127mm deviation over a field of view of 2 to 3 meters. To achieve this level of accuracy also requires calibration for radial and perspective distortions. Applications for this technology include noncontact surface measurement and robotic and computer vision.

Single-shot three-dimensional reconstruction based on structured light line pattern

“…For the traditional phase shift profilometry [10] , at least three images are required to obtain the closed form solution for the phase map. As a result, the traditional phase shift profilometry is not suitable for on-line 3D measurement or deformable object reconstruction.…”

“…Based on the surface characteristics of the object, the non-contact three-dimensional surface imaging techniques could be divided into two categories: techniques to measure the specular surfaces [1][2][3][4][5] and techniques to measure the diffuse surfaces [6][7][8][9][10][11][12][13][14][15][16][17][18] . No matter for the specular surfaces or the diffuse surfaces, the robust measurement with one-shot is very challenging, however, it is highly desired especially when the measured surfaces are dynamic and deformable.…”

3D minutiae extraction in 3D fingerprint scans.

“…In an attempt to build such a system, Flashscan3D LLC and the University of Kentucky [23] have been developing a non-contact, 3D finger scanning system. A prototype scanner is shown in Figure 1.…”

“…A prototype scanner is shown in Figure 1. This system uses multiple, highresolution, commodity, digital cameras and utilizes Structured Light Illumination (SLI) through phase measuring profilometry (PMP) [23][24][25] as a means of acquir-ing 3D scans of the fingers with sufficient high resolution so as to record 3D ridgedepth information. SLI is a popular sensing technique that calculates the 3D geometry of a target by illuminating the target with structured projection patterns and capturing and decoding the reflected image to obtain the projector co-ordinates corresponding to the image pixel.…”

“…It also requires no point-matching or image enhancement to obtain the fringe distortion, making it suitable for a pipelined or parallel processing implementation. In PMP, the light pattern projected is a sine-wave pattern shifted several times with the captured light pattern [23]. Figure 2 demonstrates 3D fingerprint acquisition using the PMP technique.…”