VCG is an integrated VGA Graphics and Video Capture card combining
a 1024 x 768 pixel VGA and an image capture at up to 768 x 576 pixels.
The VCG provides full featured live video in a window, and a frame
buffer which is available to the host processor, but with no PCI bus
bandwidth overhead.
By integrating the graphics and video capture on one board, all the
timing difficulties associated with two boards interconnected at the
Feature Connector are avoided. The graphics controller used supports
a baseline implementation VESA Advanced Feature Connector (VAFC) with
pixel frequency extended to 80MHz for a 16 bit wide pixel bus. This
means that video input on the VAFC can be colour keyed on single
width pixels at resolutions up to 1024x768 non-interlace at 75 Hz
vertical refresh rate. The video input may be 32K (5:5:5) or 64K
(5:6:5) colour mode but the graphics standard can be 256 colour
(single byte comparison), 32 or 64K (double byte comparison) or True
Colour (3 byte comparison). A display X-Y rectangle may also be
defined with a complete set of keying modes formed from boolean
combinations of the rectangle and key colour comparison.
Video sources are input to the SAA7110 Digitizer/Decoder. Up to
four CVBS inputs or two YC inputs are supported. Video encoding may
be PAL, NTSC or SECAM. The video input selected is converted to YUV
4:2:2 digital values with square pixel resolution conforming to CCIR
601 definition. This digital data is passed as a 16 bit bus to the
SAA7140A advanced scaler. A high degree of control is available over
the scaler which can perform pre-filtering and sophisticated
averaging both horizontally and vertically so that image features are
not lost and are positioned proportionally as scaling factors
increase. The scaler also includes a selectable anti-gamma look-up
table and a YUV to RGB converter.
