User manual

Small Vision System User Manual 14
Combination sampling modes are available, e.g., “x4 bin+dec” samples the image down to ¼ size in
horizontal and vertical directions, by decimating by 2 and then binning by 2.
2.1.7 Image Source
The source for stereo images can be either a memory buffer or a live video stream. The Source
drop list lets you choose between these, or to stop any input. Buffer input is discussed in Section 2.1.9.
2.1.8 Streaming Mode
Images from video cameras or the buffer can be processed in three acquisition modes. Only one
acquisition mode is active at a given time.
• Continuous mode. In this mode, stereo pairs are continuously input, processed, and
displayed. The maximum frame rate is 30 Hz for live analog image data, and up to 80 Hz for
the MEGA-D digital system. See Section 3.6 for performance information. The rate is
indicated next to the text information area.
• Single frame mode. In this mode, a single stereo pair is input, processed, and displayed each
time the Single button is pressed.
• Freeze mode. In this mode, a single stereo pair is input, then the same frame is continuously
processed and displayed. This mode is useful in checking the effect of different stereo
parameters on the same image.
2.1.9 Adjusting Video Parameters
Most framegrabbers support some kind of video image adjustments, such as contrast or brightness.
The video parameter dialog is invoked using the Video… menu item (Figure 2-4).
Most analog cameras have automatic adjustment of exposure and gain, which change according to
lighting conditions. The user can set brightness and contrast, which are framegrabber parameters that
change the processing of the analog signal.
The MEGA-D digital stereo head has manually controlled exposure and gain. Exposure is the time
that any given pixel is exposed to light before being read out. Gain is a amplification of the signal that
comes out of the pixel. In general, it is best to increase the exposure first, and if necessary, to increase
gain once exposure reaches a maximum. The reason for this is that gain will increase the video noise,
while exposure increases the pixel’s response to light. In some cases, though, short exposure times are
Figure 2-4 Video Parameter dialog box.