1 © 2015 IOP Publishing Ltd Printed in the UK
1. Introduction
The 3D measurement method that uses structured light and the
triangulation principle typically yields high-speed measure-
ments that have a high accuracy. This method has been applied
in many elds, such as aerospace, machining, reverse engi-
neering, and the protection of cultural relics [1–3]. Although
color-coding methods can improve the measurement ef-
ciency of a structured light system, they typically cause certain
problems to occur. The reliability of color-coding is typically
lower than that of monochromatic coding. Additionally, the
measurement accuracy is generally decreased due to color
crosstalk and chromatic aberration. Many studies have been
performed to improve the efciency of coding and the reli-
ability of decoding [4–7]; however, little attention has been
devoted to the lower measurement accuracy caused by color
crosstalk and chromatic aberration.
To solve the problems caused by color crosstalk, Caspi [8]
proposed a color model for a structured light system. Based
on the model, color crosstalk can be calculated and then elimi-
nated. There are several parameters in the model that must be
calibrated before the rst measurement is made. Additionally,
the reectivity and background must be calibrated for each
measurement; this process of calibrating the model decreases
the measurement efciency. Da [9] simplied the calibration
process, but reectivity is still required for each measure-
ment. Zhang [10] used a color model similar to Dalit Caspi’s
to compensate for the color cross talk, which also included
a pre-calibration. Skydan [11] proposed a multi-projector
scheme with color fringes projection which can obtain the
data in the shadow areas. In the scheme, the color cross talk is
reduced by using only two color channels and increasing the
intensity of the fringes. However the increase of the intensity
decreased the contrast of the patterns. Pan and Huang [12]
introduced a set of narrow band lters into a structured light
system to eliminate the inuence of color crosstalk, but their
experimental device was complex and expensive. Zou [13]
proposed a method based on the empirical mode decompo-
sition to lter out the color cross talk component. Since the
peaks in the image have to be searched, the method is sensitive
to noise. Da [14] presented a color decoupling method based
on a neural network. The method is fast, easy to carry out
Measurement Science and Technology
A two-level space-time color-coding method
for 3D measurements using structured light
QiXue, ZhaoWang, JunhuiHuang, JianminGao and ZhaoshuaiQi
State Key Laboratory for Manufacturing System Engineering, School of Mechanical Engineering,
Xi’an Jiaotong University, Xi’an, Shaanxi, People’s Republic of China
E-mail: xueqi82@gmail.com
Received 10 June 2015, revised 11 September 2015
Accepted for publication 21 September 2015
Published 16 October 2015
Abstract
Color-coding methods have signicantly improved the measurement efciency of structured
light systems. However, some problems, such as color crosstalk and chromatic aberration,
decrease the measurement accuracy of the system. A two-level space-time color-coding
method is thus proposed in this paper. The method, which includes a space-code level and a
time-code level, is shown to be reliable and efcient. The inuence of chromatic aberration
is completely mitigated when using this method. Additionally, a self-adaptive windowed
Fourier transform is used to eliminate all color crosstalk components. Theoretical analyses
and experiments have shown that the proposed coding method solves the problems of color
crosstalk and chromatic aberration effectively. Additionally, the method guarantees high
measurement accuracy which is very close to the measurement accuracy using monochromatic
coded patterns.
Keywords: structured light, 3D measurement, color-coding method, chromatic aberration,
color crosstalk, self-adaptive windowed Fourier transform
(Some guresmay appear in colour only in the online journal)
Q Xue et al
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115204
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© 2015 IOP Publishing Ltd
2015
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Meas. Sci. Technol.
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Measurement Science and Technology
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doi:10.1088/0957-0233/26/11/115204
Meas. Sci. Technol. 26 (2015) 115204 (12pp)