Silicon Valley Computer SHUGART 706 User Manual download pdf (Page 37)

032

THERE

ARE MANY

INSTANCES IN

VIDEO

work

when

is desirable

or necessary to

modify a

video signal

in one

way or

an-

other. In the

home, modifying

video

signal usually

means a

simple color cor-

rection attained

by adjusting

the

TV's tint

and color

controls. But

for professional

artistic

video -signal control,

a much

wider range of

signal

modification

must

available.

For example,

there

must be a

way

to correct

contrast

when the the

color

but

the signal's

luminance compo-

nent is

weak. Another modification

might

include deliberate

distortions

of the signal

many applications,

and is also

great fun

can be

more fun

than a

video game.

Some

of its

serious applications

are:

Video

Recording

Tint correction

b. Chroma

boost/cut

c. Luminance

/synch boost and

cut

d. Additions

of special

effects

to re-

cordings

Posterization

and solarization

for

effects

and titling

2. Photographic Uses

Viewing

color negatives

positives

separate camera

required)

(0-4 MHz)

75 -ohm

source

impedance

NTSC

video signal

having a

nominal

am-

plitude of

volt

peak

-to -peak

with

nega-

tive

sync is applied

the

system

via the

VIDEO IN jack.

A BYPASS

SWITCH iS

provided

to bypass

the

system, and

a VID-

EO LOOP

-THROUGH

connection

is also

provided

for loop- through

setups. Switch-

es enable

or DC coupling,

and

75 ohm

or Hi

-Z (high

impedance)

input,

which

useful

in loop-

through

applications

where another

75 ohm device

is already

terminating

the

input

line.

video amp

boosts the

input up

to 3

VIDEO

EFFECTS

1AA BURST

FFFDECOTS

O.....

OUT

VIDEO

LETTEN

INVERT

POST

STEPS

SOL

FOLDOVER

SOL

GAIN

LEVEL INPUT

OUTPUT

OFF

POWER

GENERATOR

Color

correction,

deliberate

distortion,

artistic picture

control.

Our

video palette

puts

all

at your fingertips.

for the purpose

of creating

special effects:

such as color and/or

luminance

reversal

(positive-

negative); posterization,

which

the

video

signal

altered

such

that

there are

only a few discrete

values of

luminance

(usually

2, 3, or4);

or solariza-

tion.

in which the gray

scale (luminance)

"folded" on

itself, producing

an eerie,

surrealistic -looking

picture that

contains

both positive

and

negative tones.

course,

several effects

may be performed

simultaneously.

Devices that provide

a high

degree of

color

control

are used in

virtually all

ma-

jor TV

production facilities.

Regardless

what the

brand name

might be,

techni-

cians

often refer to

such a device

video

palette;

hence.

will

also call

our device

video

palette.

Our

video palette is designed

work

On any

standard

NTSC

video signal. It

has

RUDOLF F.

GRAF

and WILLIAM

SHEETS

Advance predictions

of the

finished

appearance

of pho-

tographic

special

effects

c. Negative

inspection and

analysis

Video Production

Simulation

b. Special

effects

c. Artistic

effects

Some

of the

video palette's effects are

shown in Figs. 1 -a, l -b,

1 -c, and 1 -d, and

they

are

just

a tiny sampling

what

possible.

will

be evident

after an hour or

of experimentation,

using

video

source (VCR,

TV tuner, etc.)

and a

video

monitor to observe the

results, that a

wide

range of effects

are possible

by manip-

ulating

the front -panel controls.

How it works

A block diagram of the

video

palette is

shown

Fig. 2. A standard

baseband

volts

p -p, and at the

same time

inverts it so

that the

sync tips are positive.

The

video

signal,

which is now still unaltered

but

greater

in amplitude and

inverted, is then

fed to a

sync separator and

a SPDT

CMOS

video switch.

The

video switch splits

the

video signal

into two

components:

Synch,

blanking,

and burst pulses

only;

Video

and chroma

information

without

sync,

burst, or blanking.

The reason

for the splitting up

of the

signal is to allow

separate processing

and

treatment

of the four

signal components:

sync, burst,

luminance (black

-and -white

component).

and chroma

(color -dif-

ference). (Figure 3

shows the

four compo-

nents parts of

a standard NTSC

color

signal.)

There are other

reasons

why

it's

neces-

sary to extract the discrete

signal compo-

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