KEYWORDS: 3D metrology, Fringe analysis, 3D image processing, Fourier transforms, Projection systems, 3D image reconstruction, Cameras, Phase measurement, RGB color model, Digital imaging
In three dimensional (3D) shape measurement based on fringe projection, a serial of well designed color strips is used to
encode each period of the projected sinusoidal fringe. It is considered one of the most reliable techniques for recovering
3D shape of a tested objects, even with spatially isolated surface. The sinusoidal fringe intensity is used to extract the
phase information of the tested object, and the color strips with known order is assisted to recover its corresponding
natural phase distribution. Principles of this technique and three color encoding methods with difference color
codification are described in this paper. Some experimental results are also presented. In each method, each fringe order
only depends on its own corresponding color information, has nothing to do with the neighborhood fringes in space,
thus, unwrapping error is limited in a small area and won't expand to other pixels. It takes great convenience for 3D
measurement of an object with spatially isolated surface. With only one image, 3D shape of the tested object can be
exactly reconstructed, thus the speed is limited only by the frame rate of camera, so these methods can also be used in 3D
shape measurement for dynamic object.
A new coding method is proposed for measuring the three-dimensional (3D) shape of spatially isolated objects .
Based on Gray Code and sinusoidal stripe, this coded fringe pattern whose RGB components comprise the
multiplications of three different frames in Gray Code and sinusoidal stripes, appears to be digital color coded sinusoidal
fringes. The digital color coded sinusoidal fringe pattern is created by software on a computer and then projected to the
tested object's surface by a projector, and the image of the object is captured by a camera positioned at an angle different
from that of the projector, then the image is processed, color Gray Codes are used to obtain the phase order and
sinusoidal stripes are used to get the wrapped phase, then the wrapped phase can be unwrapped and the 3D surface
information can be retrieved. With only one image, 3D shape of the isolated objects can be exactly reconstructed, thus
the speed is limited only by the frame rate of camera. The principle of this technique is described and an actual
measurement is presented, the result of the reconstructed shapes proves the correctness and feasibility of this new coding
method.
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