Practical issues for binary code pattern unwrapping in fringe projection method - Emerging Trends in Image Processing, Computer Vision, and Pattern Recognition - page 480

The code value will be a number between 0 and 63 which actually is the 2π coefficients in
phase ambiguity and can be used to unwrap the phase. It is mandatory to create one black
and one white binary patern in order to convert the gray-level pictures to binary. Hence, a
threshold value should be defined based on the gray value norm and for each code if norm
value is greater than the threshold, then it is going to change to one, otherwise it is going to
change to zero. Therefore, the number of binary code paterns will be raised to eight as can be
seen in Figure 7 .
FIGURE 7 Binary fringe patterns: black pattern, code patterns 001-006, white pattern.
5 Practical issues for projected fringe pattern
photography
Three crucial points should be considered regarding the optical arrangement and calibration
in the projected fringe patern photography:
• The position of the projector and camera should not be moved at all during the process of
taking pictures. The camera should not be touched at all, and the pictures should be taken
using a remote controller. These modest facts are significantly crucial in view of a very
simple optical fact that if the camera lens moves one-hundredth of a millimeter, the picture
pixels will move in scale of 10 or 20 (pixels) according to the distance between the camera
and the reference plane.
• The projector and the camera should be focused on the object. Regarding the camera, it
comes with beter practical results if the camera seting be set on auto focus. Additionally,
the projector should warp enough by choosing a precise focusing value that the pixels of
the projected paterns on the objects should not be distinguishable from a near distance.
• The projector brightness level has to be chosen very precisely to avoid any distribution of
the white lights fraction on the black part of the projected paterns on the object. The level
of brightness can be set using the projector setings or by choosing smaller values (150 or
even 100 instead of 255 as the gray values) for paterns on the brighter areas. These vari-
ables are mostly difering from one to other practical atempts. They are highly related to
the level of brightness of the sculpture, how much light it will reflect, and how much dark
or bright is the room or the wall behind the object.
Three fringe paterns and eight code paterns were created and projected on the object and
reference plane separately. Figures 8 and 9 present the binary code paterns and projected
fringe paterns on the object and reference plane, respectively.