User manual

Small Vision System User Manual 19
2.1.11 Vergence
When in subwindow mode, the two cameras in a stereo rig generally will have the same X and Y
offsets, so that they keep the parallel line-of-sight characteristic of the stereo rig. However, for viewing
close objects, it is advantageous to toe-in, or verge, the two stereo cameras. In this way, the images of the
near object will both contain the object in the center.
Human eyes verge mechanically when viewing close objects. Mechanical vergence for stereo cameras
is difficult, however, since it involves complicated motor control, and more importantly, disturbs the
calibration that is critical for stereo analysis. Instead, with the subwindow capability of the MEGA-D, it is
possible to verge the stereo images electronically, by choosing appropriate horizontal offsets for each
image.
Figure 2-6 shows the effects of using electronic vergence. The top stereo pair, of a close object, puts
the object into the center of the left frame. In the right frame, the object has a large disparity and is visible
in the left side of the frame.
The bottom stereo pair is created by adding vergence to the subwindow process, offsetting the right
subwindow horizontally by 120 pixels, relative to the left subwindow. Both frames now have the near
object centered.
Vergence of the subwindows is set using the vergence control in the Subimage box of the
Subwindow dialog. It is a real time control, just like the X and Y subwindow offsets.
Figure 2-6 Parallel image subwindows (top) and verged image subwindows (bottom), showing a
close object.