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VGA Graphics
to Video
Overlay Encoders
Since 1984, video professionals have relied on Magni for innovative,
yet practical products for producing top-quality video pictures. These
products include overlay encoders and scan converters. Their technology
advances have earned EMMY and trade media awards.
Why are scan converters necessary? On the surface it would
seem simple to convert computer display output to a broadcast quality
video signal, but the two signal formats are quite different.
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1. |
Computer display signals
are progressively scanned, with each line refreshed 60 times
per second and higher. In comparison, video signals are interlace
scanned, with every other line refreshed at a rate of 30 frames
per second. Scan converters must translate these refresh rates
using proper filtering and flicker stabilization to ensure that
the video signal closely resembles the video display. |
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2. |
Computer displays operate
at a variety of resolutions; e.g. 640x480, 800x600, 1024x768,
1280x1024, whereas analog video supports 525 lines (NTSC) or
625 lines (PAL). Scan converters must translate the often-higher
computer resolution to video resolution with minimal content
loss. |
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3. |
Computers generally encode colors
on three primary color signals; red, green and blue. Video signals
are encoded differently. Scan converters must transcode the
signals while maintaining signal timing and color balance. |
What is meant by broadcast quality? An objective measure
of broadcast quality is whether or not the scan converter meets
all of the RS-170A standards (Electronics Industries Association).
RS-170A defines NTSC signal characteristics to make sure the signal
is correct in terms of sync width, burst, amplitude, etc. A similar
standard for PAL (CCIR Rec. 624) exists. Broadcast quality is also
determined by a subjective measure of picture quality. Filtering,
which reduces flicker and/or sharpness, is an important determinant
of picture quality. Nearly all scan converters claim to have filtering;
however, high quality models use sophisticated filtering technology
which results in a high quality picture. Tip: To evaluate output
quality, look at the output and see if there are artifacts on the
picture or keyed transitions. Are colors correct in hue and saturation?
How sharp is the flicker-stabilized image? Does the graphics lock
to the incoming video and overlay onto the video without jitter?
MagniCoder Premier
Overlay Encoder
DVI/VGA-to-Video Scan
Converter with Overlay and Mixed Effects
High quality conversion of DVI and VGA graphic displays to SDI
601 and Composite NTSC/PAL, or Component analog video.The Magni
MCP-601
provides the highest quality and the most cost effective means of
scan conversion of PC graphics to broadcast video. It provides a
method of overlaying computer graphics with video for applications
such as titling, logo insertions, and adding computer generated
data to video.
The MCP-601’s
novel Video/Graphics Split function provides a way to add graphic-based
information from the computer display—such as commercial messages—to
the output, while preserving the full television picture in reduced
size.
The MCP-601 has SDI 601, composite NTSC/PAL, and component analog
inputs and outputs.
The unique SDI 601 key output provides downstream keying
capability for digital switchers. Key colors are palette register
selectable from a VGA display or from a video signal, and are used
to overlay selected VGA areas onto the video or overlay video onto
the scan converted VGA in the video output. The Transparent Key
mode provides a convenient method of adding transparent logos
to video. The Alpha Key mode provides a method of full field spatial
keying defined by luminance key levels.
NOTE: (1) Full
scan mode: blanking width and active video meet broadcast standard
(2)Underscan
mode: Full screen VGA output fits inside of the Active Video area;
bounded between the Safe Action (5%) and the Safe Title (10%) region.
July
27 , 2004
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