Why Saddle Yourself with Standard Video Formats When You Could Think Outside the Box?
For those of you engaged in day-to-day production of media, you no
doubt are aware that there’s more than one way to skin a cat when it
comes to your acquisition format. There are 704 x 480p/24, 1280 x
720p/30, and now (courtesy of Sony) 1920 x 1080i with 24p, 30p and 60i
output formats, thanks to on-the-fly signal format reprocessing.
That’s fine for traditional distribution of video. But what if you have
a special project that doesn’t require support for any standard video
format, such as a museum exhibit or rental and staging project?
The answer is to go your own way by using some products you may not be
aware of. These products give you the ability to convert SD and HD
video to virtually any progressive-scan format you choose to match the
native resolution of a projector, or allow the use of multiple
projectors in a seamless panoramic image.
The technique of seamless blending is not new, although pulling it off
electronically is. Way back in the late 1980s, when I contributed my
first article to this magazine (then known as AV Video), I was quite involved in the design, production, programming and staging of multi-projector 35mm slide shows.
To achieve larger aspect ratios than the standard 2 x 3 offered by a
single slide, I used a technique of overlapping two or more projected
images by a set percentage. The most common implementation was two
full-screen images edge-to-edge (a two-screen "butt" configuration)
with a third image overlaid across the center.
This "two-screen overlap" format was a nightmare to design for until an
enterprising Canadian company, DSC Laboratories, started producing the
required soft-edge masks to bi-pack with 35mm slide graphics in special
pin-registered mounts. Once the projectors were all aligned, the
resulting panoramas were quite spectacular.
Of course, back then the only options for displaying video were
480-line interlaced images, projected by stacks of CRT projectors.
Special masks were developed to let video be projected into those
panoramic slide images. (If all this sounds a bit complicated, it was!)
Fast forward to the present, where video projectors weigh about as much
as a gallon of milk and can show images with resolutions of 1024 x 768
pixels, 1280 x 1024 pixels, or higher. Slides have pretty much gone by
the boards for business graphics. And gadgets known as seamless
switchers can now provide those blended, widescreen images using as
little as two projectors.
Here’s How It Works
A pair of XGA (1024 x 768) projectors is set up with a 25 percent
overlap to create a widescreen image with 1792 x 768 pixels and a
2.33:1 aspect ratio. (That’s pretty close to the Cinemascope standard
Graphics can either be created with that same aspect ratio and enlarged
to fill the two screens, or built in halves with full vertical (768
pixel) screen resolution and seamlessly spliced together, using a
256-pixel overlap (redundant pixels on both halves). Catching on yet?
Here’s a cool way to create "pseudo" 1920 x 1080 graphics and mix them
with video. Start with two SXGA (1365 x 1024) projectors. The total
available horizontal pixels are 3200 across both screens. A 25 percent
overlap brings that number down to 1920, and the remaining vertical
resolution remains 1024 pixels for an aspect ratio of 1.875:1.
Incoming HD video clips that you need blended with graphics and photos
are simply overscanned by 5 percent or adjusted so their geometry is
also 1.875:1. Any image distortion is slight in this mode and
Seamless switchers come in many shapes and forms, but two companies – Analog Way (www.analogway.com) of France and Barco Folsom (www.folsom.com)
of California-are credited with developing the market for these
products. A seamless switcher can take a variety of incoming video and
graphics sources and converts them all to one user-specified output
resolution, enabling broadcast-quality transitions such as dissolves,
wipes, luminance leys, picture-in-picture and fades.
Most of these products can accept signal sources with resolutions as
high as 2046 x 1536 pixels (RGB color space) and 1920 x 1080 pixels
(YPbPr color space), converting them to standard formats like 1024 x
768 (XGA), 1280 x 1024 and 1365 x 1024 (SXGA), 1400 x 1050 (SXGA+),
1280 x 720 (720p HD) and 1920 x 1080i (1080 HD).
A second processor, which provides precise horizontal and vertical
sizing of the converted image and lets you create a gradation of
varying intensity for greater or lesser overlaps, handles the blending
part of the equation. Individually, the segments of the panoramic image
appear to fade out toward the edges.
When superimposed correctly, the fadeout on one image coincides with
the fade-in on the next image, and no change in luminous intensity is
perceived (assuming the projectors are calibrated correctly).
More potent image processing to handle tiling of individual static or
motion images over dissolving high-resolution images-signal processing
that would have exhausted our efforts 20 years ago and probably would
have caused me to have a nervous breakdown-is also now possible.
Folsom’s Encore and Vista’s Montage (www.vistasystems.com)
systems both offer multiple channels of independently sized video and
graphics elements running over HD backgrounds, static or otherwise.
That’s a lot of CPUs! But it shows that you can basically achieve any
widescreen effect (or other geometric shapes) that you want, at any
resolution, with or without seamless-edge blending.
So what are you waiting for? How about a triangle screen with diagonal
edge blending, picture-in-picture, at 1024 x 1600 resolution with
anamorphic image compression?
Piece of cake.
Write Pete at firstname.lastname@example.org