National Instruments Corporation IMAQ PCI-1408 Getting Started
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Chapter 3 Hardware Overview©National Instruments Corporation3-7PCI/PXI-1408 and NI-IMAQ for Win95/NT• Active pixel region—The active pixel region is the region of pixelsactively being stored. The active pixel region is defined by a pixelstart (relative to HSYNC) and a pixel count.• Horizontal count—The horizontal count is the total number ofpixels between two HSYNC signals. The horizontal countdetermines the frequency of the pixel clock.• Active line region—The active line region is the region of linesactively being stored. The active line region is defined by a linestart (relative to VSYNC) and a line count.• Line count—The line count is the total number of horizontal linesin the picture.• Video line—A video line consists of an HSYNC, back porch, activepixel region, and a front porch, as shown in Figure 3-2.Figure 3-2. Video Line• Picture aspect ratio—The picture aspect ratio is the ratio of theactive pixel region to the active line region. For standard videosignals like RS-170 or CCIR, the full-size picture aspect rationormally is 4/3 (1.33).• Pixel aspect ratio—The pixel aspect ratio is the ratio between thephysical horizontal size and the vertical size of the region coveredby the pixel. An acquired pixel should optimally be square, thus theoptimal value is 1.0, but typically it falls between 0.95 and 1.05,depending on camera quality.Horizontal Sync Pixel RegionBack Porch Front Porch |
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