User manual

Small Vision System User Manual 12
2.1 Inputting Live Stereo Video
The SVS libraries provide support for live video as stereo input. To input video, you must do the
following steps.
1. Decide on a stereo head and framegrabber.
2. Install the framegrabber, following instructions that come with the framegrabber or the stereo head
(STH-V3 or MEGA-D).
3. Copy the appropriate framegrabber DLL to bin\svsgrab.dll (MS Windows), or
bin/libcap.so (Unix); see Section 2.1.2).
4. Set the appropriate video format using the Video Format menu.
5. Set the video frame size.
6. Set the input mode to video.
This section gives details necessary for performing these steps.
2.1.1 Stereo heads
Stereo requires two images from different viewpoints. The most common way to get these images is to
use two identical cameras separated by a horizontal baseline. It is important the cameras have lenses with
the same focal length, and that the pixel elements have the same size.
The baseline is typically from 3 to 8 inches wide, and the cameras are aligned parallel to each other,
although other configurations are possible. Figure 2-2 shows a typical stereo camera setup. Two cameras
are pointed in the same direction, and they are connected by a cable that genlocks the cameras, that is,
synchronizes them so that they capture images at the same time. Genlocking is important if there is any
motion in the scene. If the cameras are not genlocked, they can capture the image at slightly different
times, and any moving objects will be at a slightly different position in one camera relative to the other,
than if it they had taken the image at the same time. If the scene is static, then genlocking is not necessary.
Not every camera can be genlocked; check that the ones you have can be.
Genlock
signal
Video
signal 2
Video
signal 1
Parallel
line of sight
baseline
Figure 2-2 Stereo camera setup. Cameras are positioned with parallel
lines of sight. Their video signals are synchronized using cross-fed
signals.
A word about monochrome vs. color cameras. If your application does not need color, it is preferable
to use monochrome cameras, because stereo relies only on the luminance component of the video signal.
Monochrome cameras have much better spatial resolution and dynamic range than color cameras of the
same quality, since they do not have to deal with three color channels. Having said this, the MEGA-D
megapixel cameras have such high resolution that using color imagers is generally not a problem, since
most applications can use 640x480 or 320x240 image sizes, and the color imagers produce excellent
quality by binning (averaging) a set of pixels.
The cameras produce two video outputs, which must be input to the PC running the SVS system.
There are three ways to get these video signals into the PC.
1. Use two framegrabbers, and input one signal on each.