6.1.1. Video Input Mux
The multiplexer selects the video source for the Automatic and Fixed Gain from the S-Video input connector (mux 0), from the
BNC1 connector (mux 1), or from the BNC2 connector (mux 2). The multiplexer is designed to be switched during vertical
blanking.
6.1.2. Automatic and Fixed Gain
The PIXCI® SV4 is configured for Fixed Gain by providing a fixed reference voltage for the A-D converters. Optionally, it can
be modified to provide automatic gain for the A-D converters. Automatic gain automatically compensates for reduced amplitude
in the analog signal input by adjusting the reference voltage for the A-D converters. Automatic gain, hue, brightness, saturation,
and contrast adjustments can be programmed from 0% to more than 200%. The automatic gain control adjusts the video
reference level for the A-D converters until the back porch of the Y video input is equal to a programmable value, nominally
0x38. Three other values may be selected for non-standard sync height to video, they are: 0x30, 0x34, and 0x3C.
6.1.3. Luminance A/D
Provides analog to digital conversion of NTSC, RS-170, CCIR, PAL, and the luminance (Y) component of S-Video sources. A
programmable prefilter is used for horizontal luminance scaling to reduce aliasing artifacts. The luminance gain can be selected
from values of 0% to 236.57%. The luminance and chrominance A-D converters run at 28.636363 MHz for NTSC video formats
and 35.46895 MHz for PAL video formats. Digitizing the video signals at twice the typical sampling rate provides low noise
digitization. The video inputs only need to be band limited to 14 MHz instead of the 7 MHz limit that would be required at the
typical sampling rate. The chrominance and luminance inputs from the S-Video connector and each BNC input connector have
low pass filters in the video input. The inputs to the A/D converters are AC coupled.
6.1.4. Chrominance A/D
Provides analog to digital conversion of the color (C) component of S-Video. A chroma comb filter may be enabled or disabled by
software. The chrominance U component gain can be selected from values of 0% to 201.18%. The chrominance V component
gain can be selected from values of 0% to 283.89%. The hue can be selected from values of -89.3 degrees to +90 degrees.
6.1.5. Decoder
The decoder separates the Y/C components and generates the U/V color difference signals. The PIXCI® SV4 imaging board
converts analog video inputs from standard video sources such as S-Video, NTSC, RS-170, PAL, and CCIR to YCrCb in a 4:2:2
format.
6.1.6. Digital Genlock
The digital genlock circuit is used for precise digitization. It interpolates lines with lengths less than or greater than the
programmed number of pixels. It generates the pixel clock for transferring image data to the PCI bus interface. The digital
genlock circuit automatically recognizes unstable signals (for example, from a VCR) and adapts its locking mechanism to
accommodate the source.
6.1.7. Scaling, Cropping
Interpolation is used to scale images down to 1/14 of their original size. Independent horizontal and vertical down scaling of the
video input can be selected from ratios of 1:1 to 1:14. For horizontal scaling, 32 phase interpolation is used to accurately
determine the value of a pixel. For vertical scaling, an 8 phase interpolation filter is used with a 768 pixel line store.
The window of video to be captured may be cropped in single pixel increments, then scaled in ratios from 1:1 to 1:14, down to as
few as 4 pixels by 1 line of image data. Horizontal and vertical scaling is performed in real-time by interpolation, providing an
accurate representation of the original image. Either frames or fields of video can be selected.
Some of the possible video formats are:
640 by 480 for NTSC square pixels,
720 by 480 for NTSC CCIR 601,
720 by 576 for PAL CCIR 601, and
768 by 576 for PAL square pixels.
6.1.8. Temporal Scaling
PIXCI® SV4 User's Manual
http://www.epixinc.com/manuals/pixci_sv4/index.htm
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