Precision Software Appli…tions Silver Collection 1/Precision Software Applications Silver Collection Volume One (PSM) (1993).iso/tutor/fp1tvn10.arj/FP-TVN10.TXT

Text File | 1992-11-30 | 29KB | 506 lines

The following is a basic discussion about computer graphics as it
relates to video and specifically as an introduction to the
capabilities and requirements for Truevision products.

What is the difference between my computer monitor and my
television?

There is a somewhat complex distinction between what appear to be
similar technologies. In fact, about the only thing in common
between a television and a computer monitor is the use of an
electron beam used to excite the phosphors on the inside surface
of a cathode ray tube. For the sake of simplicity, I have broken
down this question into several related areas.

VIDEO:

A history of video begins with the advent of television. In the
United States, the National Television System Committee (NTSC)
set the standard for video transmission in the black and white
past and we are still using the same narrow signal bandwidth to
carry all video information. When color television was developed
in the fifties, the industry wanted to maintain backwards
compatibility so that the older black and white sets would still
be able to read the signal. This resulted in an additional color
channel modulated over the black and white original. Other
countries have other standards, such as PAL and SECAM, but
essentially all broadcast video in the world today consists of a
medium resolution black and white image combined with minimal
color information. It is our perceptions that fill in the missing
information as to how things are supposed to look. A video signal
contains color, brightness and timing information which is
interpreted by the receiver to create an image. This strict
standard is needed to ensure compatibility between the
broadcasting source and the television receiver. A television
signal is analog, meaning that it consists of a continuous,
varying voltage to produce a theoretically infinite number of
shades. Actually, due to the low resolution nature of video
signals and technology, you never get to see any subtle hues or
shading. The television industry has become very sophisticated in
using the medium to look as good as possible. The composition,
lighting and color choices are made with the limitations of video
in mind and only when someone shows up on the Tonight Show
wearing a herringbone jacket, which appears to vibrate, do the
weaknesses of video become glaringly apparent. This is due to a
trait shared among all video standards that describes how the
electron beam "paints" the image on the screen called
interlacing. That means that the beam scans down the screen
hitting only every other line and then returns back to the top of
the screen and fills in the missing lines. Thin horizontal lines
will appear to jump as the beam hits and misses them as it scans
the image. Each scan down the image is called a field, with the
combined two fields making up one frame of video. When you hit
the pause button on a 2-head VCR and the image is jumping around,
it's because the play head of the VCR is stuck between fields.
Video, like film, is actually made out of still frames passing by
so fast that our eyes are fooled into thinking the motion is
continuous. NTSC video displays 60 fields, or 30 frames, every
second. An important consideration in the video market is the
relative low cost required to build an interlaced monitor like
your home television set.

What is the difference between analog RGB and composite video?

Consumer grade video cameras have a single tube or chip that
receives and must separate all the colors presented to it.
Industrial and professional cameras have separate elements for
each shade of red, green and blue. This results in more
information available for each color component and therefore a
higher quality signal. Computer displays also have separate red,
green, blue and sync wires contained in their cables. While RGB
is the preferred method of creating and viewing images, because
the separate components remain distinct resulting in a cleaner
look, most video equipment works only with composite. Composite
video, called RS170A by the NTSC, is a combined signal that holds
luminance (brightness), chrominance (color) and timing
(synchronization or sync) all in one signal. When all these
components are combined, through a process called encoding, into
a single signal, it is composite video. Remember, if you are
working with computer video, the work you are creating that looks
so good on your RGB display may look completely different once
the signals have been encoded into composite. Another difference
between most computer displays and NTSC video is the subject of
aspect ratios that will be discussed later. One improvement in
video standards is the relatively new standard S-VHS. It provides
separate signals for color and brightness, and so provides a
better quality than RS170A composite, which rolls everything into
one.

COMPUTER DISPLAYS:

Since computer displays are not tied to any 50 year old
specification as to how fast and frequently they refresh the
screen, they can exceed the video standard of 60 fields per
second (60Hz) and 525 lines for the sharp presentation of text
and graphics. The only standards in the PC industry are those
that have been traditionally passed down from IBM and Apple. Most
importantly, computer displays are non-interlaced, meaning that
each pass down the cathode ray tube in the monitor, they hit
every line and start the process again from the top. The faster
the scanning, the more stable the image appears, and the more
lines to be scanned, the sharper the image. Non-interlaced
displays are more expensive to produce but have a much sharper
appearance. The increased screen resolution of new standards
means different screen descriptions and pushed monitor technology
to accept higher and higher frequencies. The state of evolving
computer display technology makes buying a multiscanning monitor
a necessity to keep up with the latest video cards.

When the IBM PC was first introduced, it was a monochrome system,
and a low resolution one at that. It was a digital display,
meaning that each picture element, or pixel, was either on or
off. Strictly speaking, monochrome systems are only capable of
displaying text. The display card manufacturer Hercules was the
first to introduce a black and white graphics adapter. In 1984,
IBM introduced their first color display called CGA (Color
Graphics Adapter). Like the monochrome display it was digital and
non-interlaced, but it was capable of 320 vertical lines by 200
horizontal resolution with 4 colors. When on, the pixels could be
several different colors meaning that the video card's memory had
to be large enough to "remember" and display the additional
information. As we will see later, more colors and higher
resolutions means that much more data the card's memory must
contain and process. EGA (Extended Graphics Adapter), their next
color standard ran at 640 x 350 with 16 possible colors. The next
step up, VGA (Video Graphics Array), originally meant 16 colors
at 640 x 480, although now with SuperVGA cards from a variety of
manufacturers and IBM's own 8514/A, VGA now usually means at
least 256 colors. The VGA resolution of 640 x 480 has also been
pushed to 1024 x 768 and beyond, territory in the past that was
reserved for high resolution CAD work stations. As the amount of
on-screen information increases the display board must run at a
faster speed to paint all the rows quickly enough to maintain
stability. Many of the fastest boards available have an
accelerator or graphics co-processing chip on board to keep this
refresh level up and free the computer's CPU (Central Processing
Unit) from performing such a mundane task.

TRUEVISION:

Truevision, formerly known as EPIC (Electronic Photography and
Imaging Center), started producing graphics adapters for the
young PC market in 1984. They began as an entrepreneurial subsidy
of AT&T and, although they became a privately owned company in
1987, they still have access to AT&T technological resources.
Their first two products were the ICB (Image Capture Board) and
the VDA (Video Display Adapter), introduced when CGA and EGA were
the only available color boards for the PC. The VDA was capable
of displaying 256 colors at a resolution of 256 x 240. The ICB
went further because, as it's name implies, it could do a real
time capture of a video signal at the same low resolution, but
with a palette of more than 30,000 colors. Here was an exciting
product that allowed an interlaced signal to pass though the
computer for capture or overlay of computer images. Since they
were not compatible with any of the digital standards such as CGA
or EGA, or existing software, Truevision stations took on their
now familiar two monitor configuration. One display is the
standard DOS system monitor, whether monochrome or color, and the
other monitor was usually a NTSC frequency RGB (Red, Green, Blue)
display cabled to the Truevision board. As you might imagine,
although there wasn't even any specific software available yet
for these products, the sight of thousands of colors on a PC
display when 16 was the maximum was pretty impressive. The real
problem was one of resolution and that would be addressed by
their future products that will be discussed shortly.


So even now we have a fixed, interlaced standard for video and an
ever changing game of one upmanship among the manufacturers of
displays cards that involve higher and higher non-interlaced
frequencies to accommodate better resolution and image quality.
The worldwide video community is still trying to decide upon a
high definition video standard, but this will require a larger
bandwidth to pass the additional information and specialized
televisions to receive the new signal. Each country and company
has what it thinks should be the new standard, while still
providing backwards compatibility with the millions of existing
television sets. Chances are that the adopted high definition
standard will require some form of image compression to move the
images.

VGA/NTSC SIDEBAR:

The term "multimedia" is defined in a thousand different ways. In
my opinion, Apple's advertising people created a future market
for something that didn't even exist at the time. On the PC side
we have seen two converging technologies: VGA to NTSC devices and
"high color" VGA cards. Ever since the dawn of computer displays,
people wanted the ability to take what they saw on their monitor
and dump it somehow to video. The proliferation of many animation
programs available for the PC, such as Paul Mace's GRASP and
Autodesk's Animator, has made this seemingly simple process even
more attractive. In a simple sense, this technology has been with
us for some time and the only device required was called a scan
converter. This is the type of technology required to convert a
European PAL video, which has more lines (625) and a slower
refresh (50Hz) than NTSC. The drawback to scan converters is
their price. A typical professional unit, capable of producing
broadcast quality video, costs well in excess of $ 10,000, more
than the price of most entire PC systems. Several hardware
developers, such as Willow, USVideo and Jovian, produced VGA
boards, add-in boards or external devices that would take the
non-interlaced computer signal, slow it down and turn it into a
RS170A compatible signal. Now, there are literally dozens of
products like this on the market, providing different features
and capabilities. Some offer a genlock ability, meaning that it
can sync to an external video source for a more stable image and
perhaps even combining some form of live video pass through or
overlay features. Some can even do frame grabbing and digitizing
although, unlike the Targa technology, they must do their
capturing in a VGA compatible format, meaning a variable
resolution, usually 320 x 200, with a maximum of 256 colors per
"grab". I have seen several of these devices in action and have
been underwhelmed. They may have some limited appeal, but the
quality of the affordable units will not give most people the
quality they expect. One thing to consider when attempting to
convert computer graphics to video are the different aspect
ratios of the different formats that I touched on before.
Computer displays work in an underscan mode, meaning that they
will show all the available information on your monitor.
Television standard video works in overscan, in that it is
designed to "bleed" off the edges of the television set, filling
the entire screen edge to edge. More exciting for the VGA artist,
in my opinion, is the new generation of "high color" VGA display
boards. These sophisticated VGA cards have special circuitry,
called RAMDAC, that greatly expands the number of displayable
color from 256 to more than 60,000. This allows the computer to
display nearly photorealistic images on a standard VGA monitor.
Since VGA is an analog signal, like video, the monitor can
display an infinite spectrum of colors, it is the card that
determines the number of shades displayed. Since they do not yet
effectively allow the images created to be sent out directly to
video, I will return to the development of Truevision's product
line:

TRUEVISION TODAY:

In 1985, only one year after introducing the ICB and VDA,
Truevision came out with their Targa series of video graphics
adapters. With four times the displayable resolution and up to
512 more available colors than the earlier boards, the Targa
boards were the state of the art in color boards for the PC. The
first Targa boards came in both underscan (512 x 400 displayable
resolution) and overscan (512 x 482) versions. Since then, all
new Truevision boards come with built in overscan capabilities.
Two years later they followed with their ATVista series for true
broadcast quality video. The company still aggressively develops
new products that add more features, at lower prices, for all
levels of PC computer artists. They have set the standard for
others to follow with their NuVista Plus boards for the Apple
Macintosh and the new family of Targa, the Plus series, which can
operate at different resolutions and offers VGA pass through for
a potential one monitor solution. They also have recently
introduced their own VGA to NTSC board, the VideoVGA, and the
1024/32 color board for high end 32-bit desktop graphics. The
Targa Plus and NuVista Plus boards produce RGB, composite and
S-VHS signals internally. The ATVista series only outputs RGB and
so requires an encoder.

A quick course on color depth: I will be referring to color by
describing the amount of color information that the particular
Truevision frame buffer can contain and process. The terminology
is to describe a file as either 16 or 32 bits deep. Actually,
some of the bits are used for video imaging purposes only, so let
me start by describing 15 and 24 bit color before addressing 16
and 32. A 15-bit image contains 5 bits of information for red,
green and blue. A bit is either on or off, meaning that there are
2 to the fifth power of information possible for each color
component. In other words, you can define 32 shades of red, green
and blue for each individual pixel in your 15-bit image. More
math will tell us that means a total of 32,768 possible
combinations (32 x 32 x 32) or shades available, from a value of
0 red, 0 blue and 0 green, which is displayed as pure white, to
32 red, 32 green and 32 blue, which is completely black.
Interestingly, 15-bit color can describe only 32 shades of gray.
Since gray is composed of equal amounts of red, green and blue,
there are only 32 available combinations with that ratio. 32,000
colors sounds like more than enough, but it's not: The human eye
is capable of distinguishing more than 40,000 shades and so a
15-bit image appears slightly blotchy upon close inspection. When
you have subtle shading, the colors tend to band or dither from
one to the next. For low resolution video output this may be
acceptable, usually it is not. This brings me to 24-bit color:
With this expanded file type, we can now have 8 bits of
information, or 256 possible shades, each for red, green and
blue. That means each pixel could be any one of 16,777,216
distinct colors (256 x 256 x 256). Now we have a file that can be
called "truecolor", meaning photographic quality. What about
those additional bits that make a file 16 or 32-bits? Those are
called alpha channel information and are only used with video.
The alpha channel tells each pixel if it is on or off, meaning
can live video pass through the frame buffer transparently or
opaquely. The 16-bit image has 15 color bits and a 1-bit alpha
channel, meaning that either that bit is on or off, live or not.
The 8-bit alpha channel of the 32-bit image has 256 "shades" of
on and off, giving the live video pass through many potential
levels of transparency.

Resolution: All the Truevision video boards can work in different
resolutions, both interlaced and non-interlaced, but all are
limited by the amount of VRAM they have on board. As a general
rule, with a fixed video memory, it becomes a trade off between
the amount of color information and physical resolution that the
board can support. Obviously a 32-bit image carries more
information per pixel than does a 16-bit image. Similarly, an
entire image at high resolution contains more video information
than a low resolution image. Time for more math: The equation for
figuring out the file size at a specific resolution is the
following: (Hs x Vs x Bp)/8 = file size, where Hs is horizontal
size, Vs is vertical size and Bp is bits per pixel. We divide by
eight to turn bits into bytes. Using that formula, we can see
that a Targa 16 image at 512 x 486 NTSC resolution is ((512 x 486
x 16)/8) 497,664 bytes, or almost a half megabyte, in size. This
fits neatly in the half meg of video memory on the Targa Plus 16.
At the high end of the spectrum, a Vista board will go as high as
1024 x 768 x 32-bits for an image size of greater than three meg.
The only board capable of displaying a file that large would be
the 4Mb Vista. Of course a scanner can create a Targa file much
larger than 3Mb, but the entire image wouldn't be viewable
without specialized software.

Before investing in a Truevision system, you should have a good
idea of both your input and final output options. For the most
part, inputing images into the Targa environment ranges in
quality from scanning to video grabbing. With high resolution
color scanners dropping in price, you could create images many
megabytes in size, much larger than the frame buffer size of most
Truevision boards. When grabbing from a video source, you are at
the mercy of both the input quality from either tape or live
camera and the capture resolution of your Truevision board. There
are professional quality video cameras that will output a
relatively high quality RGB signal for the frame buffer. This
results in a better source input than sending in a composite
signal that must be decoded (the opposite of encoding, decoding
turns RS170A composite video back into RGB and sync information)
for the frame buffer to accept. When outputing your images you
can either create high resolution slides, variable resolution
color or black and white prints or relatively low resolution
video. Since we are used to the poor quality of television (most
of the better TV sets are only capable of displaying 350 to 400
lines of resolution), people are not bothered by the low quality
of video so long as it moves and looks good. Obviously a 512 or
756 line video image can't compete in quality with a 4,000 or
8,000 line 35mm slide for still images.

Once you have decided upon your output requirements you can look
at the software available for the Truevision file format. Since
Truevision pioneered it in the early eighties, the Truevision
.TGA Targa file format has become an industry standard, supported
by hundreds of software titles for a variety of purposes, and
compatible with almost any possible output device. The most
common program would be "Paint" software, that would allow you to
touch up acquired images or create your own artwork. These
packages range in price and power from less than $ 500.00 to more
than $ 2,000.00.

TRUEVISION BOARDS:

Targa Plus series: All share some features such as VGA pass
through, RGB and composite output and input. Note that, while the
16/32 and 64 boards can display higher resolutions, they have an
upper NTSC limit of 512 x 486 at 32-bits. They must be ordered as
NTSC or PAL and offer a MCA (Microchannel) bus model.

Targa Plus 16: has a .5Mb frame buffer of high speed video
memory, or VRAM. Capable of grabbing and displaying a 16-bit
image up to 512 x 486 NTSC resolution. This is a fairly limited
board that replaces the original Targa 16 at a lower price.

Targa Plus 16/32: With 1Mb VRAM, it can go up to 32-bits at 512 x
486.

Targa Plus 64: 2Mb VRAM, capable again of 512 x 486 at 32-bits
for video display. The 64 board allows for dual buffering,
meaning that you can fade from two images that are in the board's
memory at one time for some excellent video effects. This would
be the premium Targa Plus board if you are planning to work
extensively in video production.

ATVista series also differ in the amount of on board video
memory, either 1, 2 or 4Mb versions are available. The ATVista
series differ from their Targa counterparts in that they do not
have composite input or output. They also do not offer VGA pass
through and are available only in ISA or Mac bus versions. They
do not share the 512 line limit of the Targa series, meaning
that, if their memory allows, they can go as high as 756 x 486
broadcast video resolution or even to 1024 x 768 if you aren't
going out to video. The Vista is a programmable board with an on
board video processor. Vista software tends to be higher priced
than their Targa based counterparts and Vista systems are
typically more hardware intensive as well.

The NuVista Plus boards share the same programmability as their
AT bus  counterparts, except they have built-in encoding and
decoding, like the  Targas, so that they can directly accept
composite video in and out.

The VidI/O box is Truevision's standalone encoder/decoder box. It
provides for RGB input, output, looping, composite and S-VHS in
and out. Decoding, the reverse of encoding, turns a composite
video source into separate RGB and Sync components to run into an
ATVista for image grabbing.

VideoVGA: A VGA to NTSC board that allows for overlaying VGA
images or animations over a live video pass through. It can
simultaneously output non-interlaced VGA and interlaced composite
NTSC signals.

1024/32 board is an advanced, co-processed board for Windows and
CAD applications. It works at 32-bits at resolutions up to 1024 x
768 at up to 76Hz for a stable, high resolution display. It also
has on-board VGA and can run in standard NTSC and PAL modes.

If you are looking to do true broadcast quality, the Vista is the
board for you. Keep in mind that what separates true broadcast
quality isn't always apparent to the untrained eye; sometimes the
signals must be analyzed by an engineer through a scope to
determine their true quality. Naturally, an encoder built into
the Targa board can't hope to match the stringent specifications
as to what constitutes broadcast quality like an external $ 5,000
professional encoder can do. The Targa, however, is well suited
to all forms of industrial video applications.

Generic Truevision configuration (s), excluding board and
software:

Computer:        Minimum                    Recommended

                 386SX 20MHz                386/33 or better
                 4Mb RAM                    8Mb RAM
                 80Mb fast hard drive       200Mb drive
                 monochrome card            VGA card
                 monochrome monitor         VGA monitor (**)
                 mouse                      digitizing tablet
                 13" Long Persistence        19" Long Persistence
                 Phosphor monitor (*)       Phosphor monitor (**)

Due to the potentially large image files, especially if you have
access to a scanner, some form of removable mass storage is
highly recommended.

* The Targa Plus sends out both RGB and, due to the on board
encoder, composite video signals. Therefore it would be possible
to hook the Targa directly to a VCR or NTSC monitor that accepts
composite. While this would provide you with a good idea of how
your images will look if they are going out to video as your
primary output medium, it will not give you a high quality
interface to work from. Also, if you don't use a multiscan
monitor, you will be limited to working at a fixed NTSC
resolution. A quality display will greatly reduce eye fatigue and
make you more happy and productive in the long run.

** The Targa Plus series can run what is called VGA pass through,
meaning that you could have a one monitor solution if you already
have a VGA card. Some software, however, requires a two monitor
configuration and the only cost savings is that of the additional
VGA display. To run the Targa Plus in an interlaced (video) mode,
the Long Persistence monitor is required to reduce the amount of
flicker. Also, be warned if you want to try running a single
monitor with the VGA pass through: Truevision obviously can't
test compatibility between the Targa and every VGA card to hit
the market. There are some VGA adapters that will not function
properly in this configuration. We have noted this problem with
the higher end cards, especially those using the Tseng chip set.

Some application notes:

Video pass through: This technique of combining video with
computer graphics can be accomplished in two ways: Overlay and
Chroma Key. Overlay takes advantage of the alpha channel and
allows live video to literally pass through the frame buffer.
Chromakeying is the process that puts the television weatherman
in front of the map. It involves a screen behind the subject that
is a consistent color, usually blue or green so it won't
interfere with flesh tones. When the image passes through the
frame buffer, the key color is stripped out electronically and is
replaced by the computer generated graphic. Sometimes you may
have noticed, if he is wearing a blue tie, you can see the map
through the weatherman.

A word about 3-D animation. Some people are convinced that 3-D is
the ultimate combination of computer imaging and video. While
this may be true, they may not have a full understanding of how
complex it is to lay down rendered images to tape so that they
appear in continuous motion. As we have calculated, a broadcast
quality Vista frame at 756 x 486 x 32-bits can yield a file
1.469664Mb in size. Obviously, unless you have an enormous RAM
drive, your hard drive won't be capable of displaying files that
large at 30 images per second for video output. Additionally,
depending on your choice of 3-D animation software and the
complexity of the scene, each image may take many minutes to
fully render, especially if the PC calculates shadows, texture
maps, reflections and the like. Therefore you will need an
animation controller that will interface between the PC and your
frame by frame editing VCR. Essentially, the controller holds the
video tape at a specific frame until the PC is done rendering an
image, it then tells the deck to record that image and then wait
for the next one. This can be a time consuming process, as well
as an expensive one: an animation controller costs a few thousand
and a broadcast quality deck many times more. Additionally, you
may require one or more of the following pieces of video
equipment: A Time Base Corrector, a Sync Generator and encoder.
Some of the more expensive pieces may be rented until they can be
cost justified.

Kevin Freeman