Chapter 3
Hardware Overview
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National Instruments Corporation
3-5
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Frame/field selection—With an interlaced camera and the
PCI/PXI-1407 in frame mode, you can program the PCI/PXI-1407
to start acquisition on any odd field or any even field.
Acquisition Window Control
You can configure numerous parameters on the PCI/PXI-1407 to control
the video acquisition window. A brief description of each parameter
follows:
•
Active pixel region—The active pixel region is the region of pixels
actively being stored. The active pixel region is defined by a pixel start
(relative to HSYNC) and a pixel count.
•
Horizontal count—The horizontal count is the total number of pixels
between two HSYNC signals. The horizontal count determines the
frequency of the pixel clock.
•
Active line region—The active line region is the region of lines
actively being stored. The active line region is defined by a line start
(relative to VSYNC) and a line count.
•
Line count—The line count is the total number of horizontal lines in
the picture.
•
Video line—A video line consists of an HSYNC, back porch, active
pixel region, and a front porch. The 1407 device requires a positive
video signal, as shown in Figure 3-2.
Figure 3-2.
Positive Video Line
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Picture aspect ratio—The picture aspect ratio is the ratio of the active
pixel region to the active line region. For standard video signals like
RS-170 or CCIR, the full-size picture aspect ratio normally is
4/3 (1.33).
•
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
Horizontal Sync
Pixel Region
Back Porch
Front Porch
