User manual

Small Vision System User Manual 15
Single
video
stream
Left camera
field
Right
camera field
Interlaced
field
Figure 2-3 Line-interlaced stereo cameras (STH-V3 stereo head). Alternate lines
from each camera are interlaced into a single video stream.
Analog camera input goes through an analog framegrabber , where it is converted into digital form and
sent to the host computer memory. The smallv interface will input video from the cameras through
either one or two framegrabbers, depending on the type of setup. There are three choices:
1. Line interlace [default]. This is the mode for the STH-V3 line interlace stereo head. Any
framegrabber can be used in this mode.
2. Dual framegrabbers. This mode uses two framegrabbers, with one framegrabber per camera.
Check Table 2-1 for supported framegrabbers.
3. RG components. This mode uses the Matrox Meteor RGB or Meteor II, and inputs one
camera video stream on the R channel, and one on the G channel.
It is important for stereo processing to have the left camera image appear as the left image in the
smallv program. Once the video input is displayed, you can check this by pointing the cameras along
your line of sight. The right camera appears on your right side, and the right image on the smallv display
should show this image. You can cover one camera with your hand, and observe which displayed image
goes dark. With dual framegrabbers or RG input, the solution to having the wrong camera inputs is to
simply switch the inputs, or to use the swap button in smallv, which interchanges the images in
memory.
Under line interlace mode (Figure 2-3), the first horizontal line of a video field is from the left camera,
the second from the right, the third from the left, and so on, making a single video stream. The SVS
software de-interlaces the video stream, reconstructing the left and right images in memory, at half the
original vertical resolution. Because of the variation in how framegrabbers determine which is the first line
of a field, the SVS software will sometimes switch the left and right fields during de-interlacing. The
swap button switches the left and right fields during deinterlacing.
The smallv application interfaces only to one analog stereo head, using the first one or two
framegrabbers that it finds. It is possible to specify other framegrabbers from a use application, using the
SVS API.
2.1.5 Frame Size
The SVS libraries as delivered can work with frame sizes up to 1288 by 1032. In fact, the SVS
algorithms can work with arbitrarily sized frames.
A subset of frame sizes are supported for video input in the smallv application; the following table
summarizes them. Most framegrabbers support hardware interpolation and scaling, so that bus traffic is
minimized by working with smaller frames. The exception is the Meteor RGB, which passes a full field to
memory, where it is decimated by the SVS software.