Chapter 3
Hardware Overview
3-6
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Pixel aspect ratio—The pixel aspect ratio is the ratio between the
physical horizontal size and the vertical size of the region covered
by the pixel. An acquired pixel should optimally be square, thus the
optimal value is 1.0, but typically it falls between 0.95 and 1.05,
depending on camera quality.
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Field—For an interlaced video signal, a field is half the number of
horizontal lines needed to represent a frame, as shown in Figure 3-3.
The first field of a frame contains all the odd-numbered lines. The
second field contains all of the even-numbered lines.
Figure 3-3.
Video Field
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Frame—A frame is a complete image. In interlaced formats, a frame is
composed of two fields.
Programming Video Parameters
You can program all of these video parameters on the PCI/PXI-1407:
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Programmable pixel and line count—The PCI/PXI-1407 uses an
advanced genlock circuit to generate an internal PCLK. This circuit
generates a PCLK frequency from 11.7 to 15.8 MHz, depending on
the total number of pixels per line. The standard sampling rate for
RS-170 video signals is 12.27 MHz, and the standard sampling rate
for CCIR is 14.75 MHz.
The PCI/PXI-1407 also includes a programmable line count, which
you use to switch between RS-170 (525 lines) and CCIR (625 lines).
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Acquisition window—After setting the pixel and line count, you must
program the active pixel region and active line region. The active pixel
region selects the starting pixel and number of pixels to be acquired
relative to the HSYNC signal. The active line region selects the starting
line and number of lines to be acquired relative to the VSYNC signal.
Vertical Sync
Line Region
Horizontal
Sync
Video
Line
