Chapter 3
Hardware Overview
3-6
ni.com
Clamping
The NTSC camera file sets the default values of Clamp Start and Clamp
Stop to 106 and 116, respectively. These settings place the clamp pulse,
which restores the DC level of the video signal, between the color burst
signal and the beginning of active video. Because some cameras deviate
from the exact timing required by the NTSC standard, the clamping pulse
may intersect either the color burst or the active video portions of the
signal. If this occurs, an acquired image may appear to have dark and light
bands, as in the following image.
To prevent this problem, open Measurement & Automation Explorer
(MAX) and navigate to the Advanced tab of the camera file property page.
Use the following guidelines to adjust the Clamp Start and Clamp Stop
values until the image is corrected:
•
Minimum Clamp Start is 100
•
Maximum Clamp Stop is 120
•
Difference between Clamp Start and Clamp Stop is at least 10
