Sein, Myint Myint/ Hama, Hiromitsu

Yuan, Liyi

Osaka City University Repository

Mem. Fac. Eng., Osaka City Univ., Vol. 38, pp.165-169 (1997)
Multicolor-Pattern Light Projection
for 3D Image Matching
Liyi YUAN*, Myint Myint SEIN** and Hiromitsu HAMA***
(Received September 30,1997)
Synopsis
In this paper, a new kind of pattern called Multicolor-pattern for image matching is
proposed. The Multicolor-pattern possesses the advantage over conventional pattern
in high-precision of 3D image matching abuse its wide matching extent and has great
potential in the application areas of image processing. In this paper, we will describe
the principle of Multicolor-pattern light projection and describe how to design the
Multicolor-pattern and its application of image processing.
keywords: multicolor-pattern, structured light, light projection, opening width, point correspondence
1 Introduction
In recent years, image matching in the field of 3D image processing such as image
recognition , recovery of the 3D image have attracted more and more interest. Up to
now, various methods have been proposed in image matching, it can be generally
divided into two categories, that is Contact-Matching and Non-contact Matching .
Both of them consider about color, shape or scheme to resolve the problem of image
matching. The Non-contact Matching is an initiative stereo method which take
advantage of the principle of structured light. For this reason, the system for Non-
contact Matching can be called light projection system. During the past years, various
patterns such as Width Changed Pattern, Density Changed Pattern and Color
Changed Pattern have been proposed. The Multicolor-pattern which proposed in this
paper appears to be more effective in dealing with 3D image matching, owing to its
advantage of wide matching extend and strong mapping capability. In Section 2, we
will briefly review the light projection system. In Section 3, we will show how to
design the Multicolor-pattern. The advantage of Multicolor-pattern is its wide
matching extent.
* Master-Course Student, Dept. of Information and Communication Engineering
** Doctor-Course Student, Dept. of Information and Communication Engineering
*** Professor, Dept. of Information and Communication Engineering
165
166
2 Light Projection
Various methods have been proposed in light projection such as Spot Light
Projection, Slit Light Projection and Step Light Projection. But the method of Spot, Slit
or Step all used simple light pattern to scan object space. To catch a 3D image, it
requires to input image every a minute change of light pattern and detect a position
of Spot, Slit or Step in every image. Therefore, to catch a high analysis and high-
precision 3D image, a great deal of input are required. To resolve this problem, a
method which called Encoded Pattern Light Projection in Space is suggested, fewer
inputting images are required because of the encoded object space.
The Changed Opening Width Encoded Pattern is one of this kind of patterns as
shown in Fig.l,
M
P - internal; W - opening width; M - pattern width
Fig.l Changed Opening Width Encoded Pattern
As Fig.l shows, the Changed Opening Width Encoded Pattern has a characteristic of
fixed slit internals and changed opening width. The more the changed opening width,
the higher efficiency in encoded space is obtained, but on the other hands, the
judgment becomes difficult and the possibility of misjudgment increases. To overcome
this limit, a new pattern which called Multicolor-pattern is proposed here, it changes
color not only changing opening width. Multicolor-Pattern provides more high-
precision and wider pattern width than any other patterns.
3 Designing Multicolor-Pattern
In order to describe how to design the Multicolor-Pattern, some symbols and terms
are defined as follows:
167 .
P ------- internal
W ------ opening width
D ------- pattern width
M ------ block (a part of pattern)
N ------ the number of colors
S ------ the register memory for storing the fundamental Multicolor-Pattern
Making the Multicolor-Pattern is based on Changed Opening-Width Encoded
Pattern. The case of two colors(Black and Gray), which are used to make the pattern,
is shown in Fi .2,
D
M - length of block(a part of pattern); D - pattern width
Fig.2 a kind of Multicolor-Pattern
It can be easily seen that the pattern width can be expanded by 2 times. But is it
possible to expand the pattern width more than 2 times in order to obtain wider
pattern width? The answer is in affirmative, arranging the pattern like the way as
shown in Fig.2, The pattern width have been expanded by 7 times, but whether or not
the judgment is accurate enough to match image by such a wide pattern? For example,
how can we make a distinction between parttern-linel and pattern-line2 shown in
Fig.3.
I = 1111111
I = 1111111
behind-line
of pattern-line1
III II
+
+
I"".IIIIAI...: ~~ f· ..... [ ~:~:>:
partten-line1 partten-line2
1111111
front-line
of pattern-linel
Fig.3 Multicolor-pattern using two colors
168
The processing is actually as follows: at first, the color of the front-line which is the
length M in the front of the pattern-line! is black can be judged, and secondly, the
behind-line which is the length M behind of the pattern-linel is gray also can be
judged. Do as the same, the front-line of pattern-line2 is gray and the behind-line of
pattern-line2 is black can be judged. Since the front-line and behind-line of every
pattern line in different block are different, the correct judgment can be obtained.
To implement this method of judgment with the help of computer programming, the
following steps are required. At first, storing the fundamental pattern in register
memory 8,
S = { ( s[O] [O],s[O] [1], s[O] [6]),
( s[l] [O],s[l] [1], s[l] [6]),
( s[6] [0],s[6] [1], s[6] [6])}
and assume the matched pattern-line is X then judge the matched line through the
method proposed above, the program shown as follows,
Judge_patternO
{
VALUEI =get_front_behind(~X); to get the color of front-line and
behind-line of matched line
B =judge_block(VALUE 1); to judge the matched line is in
which block according to VALUE 1
L = judge_Iine(X); to judge the position of matched line
in a block
the result is the matched line Xis corresponding the line to
B-th block of L-th line.
}
The more colors are used, the wider pattern width can be obtained. Through a host
of experiments, the formula for the relation between the number of colors and the
pattern width is obtained as follows,
D = 7 ·P ·N ! (3-1)
where N is the kinds of color, D is the pattern width and P is the internal. According
to this formula, the corresponding table of the pattern width and the number of colors
169
is shown in Table. I,
Table.!
N D
1 7P
2 49P
3 98P
It is easily proved that the number of colors become larger, the pattern width has
expanded times by times accordingly. But the much more memory size is required, the
quantity of judgment will be increased and the ability of colors' judgment becomes
difficult. In practical use, considering the weakness of Multicolor-pattern , using two or
three colors to design the multicolor-pattern is suggested and the chosen rule of colors
is that the difference of colors' brightness is large enough to judge, it means that the
colors which are easy to be confused is not suggested.
4 Conclusion
The Multicolor-pattern has wider pattern width than any other patterns. The design
rule of it can be used to make fundamental patterns for various light projection
system such as Spot, Slit, Step light projection and so on. The future study lies in
improving the ability of judgment. Maybe adding shapes such as round, square and
triangle to make pattern is a good idea.
References
[1] Sanz J.L.C.: "Advances in Machine Vision", Springer-Verlag (1989)
[2] Oshima ,M. and Shirai,Y.: "Object recognition using three-dimensional information",
IEEE Trans., vol.PAMI-5, no.4,pp.353-361 (1993)


Multicolor-Pattern Light Projection for 3D Image Matching

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Multicolor-Pattern Light Projection for 3D Image Matching

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