两级时空颜色编码：3D测量的结构化光新方法

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"这篇研究论文探讨了一种两级时空颜色编码方法，用于利用结构化光进行3D测量。文章提到了几种相关的3D光学测量技术，包括高精度的多频消像差模式、带有变焦镜头的新型3D光学扫描仪以及基于优化脉宽调制二进制条纹投影的实时显微3D形状测量。此外，还讨论了色散对彩色编码结构光3D测量系统的影响分析与补偿策略。" 在3D测量领域，结构化光技术结合三角测量原理是一种高效且精度高的方法。本文提出的两级时空颜色编码技术旨在进一步提高测量的精度和效率。这种技术可能涉及到将不同编码的光栅图案在空间和时间上分层次投射到被测物体表面，通过捕捉返回的编码光栅图像，然后解码这些图像来计算物体的三维几何信息。论文中提到的"Defocusing rectified multi-frequency patterns for high-precision 3D measurement"研究，是关于使用多频消像差模式进行高精度3D测量的技术。这种技术通过调整图案的频率和焦点状态，可以减少测量过程中的像差，从而提高测量精度。 "Design and experimental validation of novel 3D optical scanner with zoom lens unit"探讨了一种配备变焦镜头的新型3D光学扫描仪的设计与实验验证。这种扫描仪能够适应不同的测量距离和范围，增加系统的灵活性和实用性。 "Real-time microscopic 3D shape measurement based on optimized pulse-width-modulation binary fringe projection"则关注实时显微3D形状测量，它采用优化的脉宽调制二进制条纹投影，实现了快速的微观物体3D形状获取，对于生物医学和微制造等领域具有重要意义。同时，"Analysis and Compensation for Lateral Chromatic Aberration in a Color Coding Structured Light 3D Measurement System"研究了色散问题对彩色编码结构光3D测量系统的影响，并提出了补偿策略。由于不同波长的光在传播过程中速度不同，会导致色散现象，影响测量的精确性。这项工作为改善3D测量系统的整体性能提供了理论依据和技术支持。这篇论文及相关的研究工作展示了3D测量技术的最新进展，特别是在提高测量速度、精度和实时性方面的创新。这些技术的应用涵盖了从宏观物体到微观结构的广泛范围，对于工业检测、机器人导航、虚拟现实和生物医学等多个领域具有重要价值。

Q Xue et al

and needs no extra hardware. However it is not suitable for

colorful objects and is potentially inuenced by ambient light.

To solve the problem of chromatic aberration, Zhang [15]

described a method that used a chessboard calibration object

to calibrate the chromatic component; however, the chro-

matic component of the projector was neglected. Pagès [16]

projected three patterns that included red, green, and blue

stripes onto a plate board. The average distances between

the different color stripes in each place were then calculated.

Then, the average distance was considered to be the compen-

sation of the error caused by the chromatic aberration. This

method compensates for the error with a constant; however,

the error varies with location. Zhang and Towers [17] pro-

posed a method that a linear error model could compensate

for phase errors caused by chromatic aberration. Although

this method yields accurate results, the phase errors are not

equally spaced.

The primary purpose of this study is to obtain a high meas-

urement accuracy in the presence of color crosstalk and chro-

matic aberration. A two-level space-time color-coding method

is thus proposed. The rst-level code is the space-code, which

is composed of periodic color stripes at different frequencies;

the stripes are encoded by the color sequence of the stripes.

The second-level code included is the time-code, which

distinguishes different periods of the space-code with gray

code. The red (R) channel, green (G) channel and blue (B)

channel of the rst level of the coded pattern are composed

of periodic stripes with three different frequencies, respec-

tively. The highest frequency is the integral multiple of the

others. Because only the centers of the stripes in the highest

frequency channel are required to be extracted, the inuence

of chromatic aberration can be avoided. Due to the integral

multiple relationship between the three frequencies, we use

a self-adaptive windowed Fourier transform to remove the

inuence of color crosstalk. The experimental results verify

that the proposed coding method improves the measurement

accuracy and guarantees the measurement efciency and reli-

ability of the coding.

The organization of this paper can be described as follows.

Section 2 introduces the two-level space-time color-coding

method. The data processing methods used are described

in section 3. The system and results of the experiments are

shown in section4, and section5 presents the conclusions of

the study.

2. Two-level space-time color-coding method

Color-coding methods have improved the measurement ef-

ciency of 3D measurement systems that use structured light;

however, the reliability of color-coding is lower than that of

monochromatic coding. Additionally, the measurement accu-

racy decreases due to color crosstalk and chromatic aberration.

In this section, a two-level space-time color-coding method is

introduced. This method avoids chromatic aberration, yields

good efciency, guarantees coding reliability, and solves the

problems of color crosstalk using multiple frequencies.

2.1. First-level code

The rst-level coding pattern is a space-coded pattern that

consists of periodic color stripes. Three channels (R, G and

B) of the pattern are composed of periodic stripes at three dif-

ferent frequencies respectively. The channel with the highest

frequency stripes is dened as the channel used for stripe

center extraction (CSCE), while the other two channels are

dened as coding channels. The channel that has a reectivity

that varies most slowly is chosen to be the CSCE. The con-

crete method for choosing CSCE is shown in gure1. Then,

three frequencies must be calculated.

First, the smallest distance between the stripes in the CSCE

is calculated using equation(1):

⩽∆ =

×∆

(1)

As shown in gure2, S is the eld size, N

is the resolution

of projected image along the direction perpendicular to the

stripes. ΔS is the desired spatial resolution for measurement

object. f

is the frequency of stripes in the CSCE. The other

frequencies are denoted by f

and f

, which are dened by

equation(2);

⎧

⎨

⎪

⎩

⎪

(2)

where k

and k

are different integers that are larger than 1.

Three gray patterns are combined into one color stripe pattern;

these combined color stripes are periodic, the period of which

is dened by equation(3):

Figure 1. The ow chart of the method for choosing CSCE.

Meas. Sci. Technol. 26 (2015) 1152 04

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两级时空颜色编码：3D测量的结构化光新方法

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