Large-screen analog (vector) color display: convergence?

[Nicholas Bodley]

Some time back, an arcade game had a large-screen *vector* color display;
it might have been Arkanoids. I had a close look, and even played a few
games. Convergence of the three primaries was superb. Pretty early for
digitally-controlled convergence, and am essentially positive that it was
analog; no hint of a raster. So, my question is, how was the convergence
done? Maybe not that hard to do? Little doubt that it must have been a
collection of analog circuitry.

===

Another one; hope these long-standing queries don't annoy too much. At
least they are closer to the intent of this n/g than some discussions,
not that I mind OT stuff. (I find it almost too easy.)

TIA, and regards
--
Nicabod =+= Waltham, Mass.
who loved Pac-Man, naturally

 

[Arfa Daily]

"Nicholas Bodley" <n_bod_ley@speakeasy.net> wrote in message
newsan.2009.07.21.15.54.03@speakeasy.net...

Some time back, an arcade game had a large-screen *vector* color display;
it might have been Arkanoids. I had a close look, and even played a few
games. Convergence of the three primaries was superb. Pretty early for
digitally-controlled convergence, and am essentially positive that it was
analog; no hint of a raster. So, my question is, how was the convergence
done? Maybe not that hard to do? Little doubt that it must have been a
collection of analog circuitry.

===

Another one; hope these long-standing queries don't annoy too much. At
least they are closer to the intent of this n/g than some discussions,
not that I mind OT stuff. (I find it almost too easy.)

TIA, and regards
--
Nicabod =+= Waltham, Mass.
who loved Pac-Man, naturally

The arcade game "Tank Battle" used a monochrome stroke writer, so no
convergence issues with that. Around 27 years ago, I worked with some very
high end graphics systems from a U.S. company called Vector General. They
used a colour stroke writer (vector display) from a company whose name I
can't remember now, but they were in San Jose. There was not any convergence
issues, because they employed a special CRT type known as a Beam Penetration
Display. It worked by having different colour phosphors layed on top of each
other at the faceplate. Individual colours were 'selected' by modulating the
high voltage supply to the final anode, which in turn modulated the
'intensity' of the electron beam, and determined how far into the layers of
phosphor it penetrated, and hence which ones it excited. Obviously, its
pallette was very limited - just the basic primaries and a couple of
complimentaries as I recall, but still quite impressive.

The exact details might not be quite right, but good enough to give you the
idea. It's been a long time since I did the factory course on it, and they
were never very popular with our customers this side of the pond. I'm sure
there must be references on the 'net that you could look at.

Arfa

 

[D Yuniskis]

Nicholas Bodley wrote:

Some time back, an arcade game had a large-screen *vector* color display;
it might have been Arkanoids. I had a close look, and even played a few
games. Convergence of the three primaries was superb. Pretty early for
digitally-controlled convergence, and am essentially positive that it was
analog; no hint of a raster. So, my question is, how was the convergence
done? Maybe not that hard to do? Little doubt that it must have been a
collection of analog circuitry.

Atari was big on "vector scan" monitors in the late 70's/ early 80's
for their (arcade) video games. IIRC, Asteroids was one of the first
of these. It, however, was monochrome. IIRC, Tempest, Space Duel,
et al. used *color*.

At the time, the biggest annoyance in using vector displays was
their inability to draw "curves". I.e., you have to resort to
a piecewise linear approximation of those curves. This is fine
if the opbject stays in a particular Z plane. But, since vector
displays made it *so* easy to scale things (e.g., to zoom into
or out of the screen), a linearization that looked good at one
scale factor would look really bad at a larger factor. Conversely,
drawing a good approximation at a large scale factor used up lots
of unnecessary display bandwidth at low scale factors. (see below)

Someone (?) also had a vector graphic engine that only drew *arcs*.
This was an interesting twist as it made curves a real possibility.
However, it *only* drew arcs. So, it would have to "approximate"
straight line segments (e.g., as used in *text*!) with arcs of
suitably large radii. :>

I think one reason color seems so "pure" in most of these applications
is that the number of colors actually used is usually very limited.
And, since you aren't doing large area fills, you don't see artifacts
in color gradations that would otherwise be visible, for example, on
a raster scan monitor.

IIRC, the color monitors were essentially the same as raster scan
monitors but the deflection amplifiers were controlled externally
(via "X" and "Y"). The scan rate of most of these vector monitors
was considerably less than that of a raster scan monitor of that
period -- like one fourth of that! (N.B. Electrohome had a vector
scan monitor that could actually *emulate* a raster scan monitor
with its deflection amplifiers. I think they are/were located
somewhere in Canada?).

A problem with vector scan displays is that you either adopt a
"constant drawing speed" in the design of your graphics engine
(i.e., slew the deflection amps at a constant rate) *or* you
try to optimize the drawing *time* by maximizing the drawing
speed (takes more smarts in the graphic engine). The flip side of
this is variations in drawing speed -- stroke to stroke -- cause
variations in the intensity of the displayed stroke. (think about
it) Since the bandwidth of the vector display's amplifiers is
so constrained, one would like to draw things in the minimum
time necessary to allow you to get more on the screen at a given
time.

Of course, nowadays, processing power makes the advantages of
vector scan displays largely meaningless -- drive a raster scan
display at an insanely high resolution and just *draw* the lines
that you want to draw!

 

[Nicholas Bodley]

On Tue, 21 Jul 2009 18:51:47 +0100, Arfa Daily wrote:

The arcade game "Tank Battle" used a monochrome stroke writer, so no
convergence issues with that. Around 27 years ago, I worked with some
very high end graphics systems from a U.S. company called Vector
General. They used a colour stroke writer (vector display) from a
company whose name I can't remember now, but they were in San Jose.
There was not any convergence issues, because they employed a special
CRT type known as a Beam Penetration Display. It worked by having
different colour phosphors layed on top of each other at the faceplate.
Individual colours were 'selected' by modulating the high voltage supply
to the final anode, which in turn modulated the 'intensity' of the
electron beam, and determined how far into the layers of phosphor it
penetrated, and hence which ones it excited. Obviously, its pallette was
very limited - just the basic primaries and a couple of complimentaries
as I recall, but still quite impressive.

The exact details might not be quite right, but good enough to give you
the idea. It's been a long time since I did the factory course on it,
and they were never very popular with our customers this side of the
pond. I'm sure there must be references on the 'net that you could look
at.

Interesting! I'm just about positive that Tektronix made 'scopes using
peam-penetration CRTs for a limited color palette. Those CRTs can't
change color quickly without a heck of a lot of fuss, because the
accelerating voltage has to change by several kV, and that take a little
while, maybe milliseconds. Afaik, the 'scope changed color to display a
different category of data, perhaps alphanumerics, possibly a ground ref.
line, multiplexed with the waveform display.

Furthermore, the CRT's sensitivity changes a lot, just about sure, so the
gain of the deflection amps needs to change when color changes.

Thanks much, and best regards!

--
Nicabod =+= Waltham, Mass.
who once owned a Western Electric
224-B gas focused CRT (burned out).

 

[Nicholas Bodley]

{Good grief; I must learn to check back for replies! Been away from
USENET for quite a while. --nb}

On Wed, 22 Jul 2009 11:56:42 -0700, D Yuniskis wrote a very interesting
reply; considering elapsed time, I'm quoting in full.

Nicholas Bodley wrote:
Some time back, an arcade game had a large-screen *vector* color
display; it might have been Arkanoids. I had a close look, and even
played a few games. Convergence of the three primaries was superb.
Pretty early for digitally-controlled convergence, and am essentially
positive that it was analog; no hint of a raster. So, my question is,
how was the convergence done? Maybe not that hard to do? Little doubt
that it must have been a collection of analog circuitry.

Atari was big on "vector scan" monitors in the late 70's/ early 80's for
their (arcade) video games. IIRC, Asteroids was one of the first of
these. It, however, was monochrome. IIRC, Tempest, Space Duel, et al.
used *color*.

Now that pou mention it, it might have been Tempest that I saw (and
played, a bit). I remember something like a hint of a tunnel into which
you were looking, and a spiky creature that attached itself spider-like.

At the time, the biggest annoyance in using vector displays was their
inability to draw "curves". I.e., you have to resort to a piecewise
linear approximation of those curves. This is fine if the object stays
in a particular Z plane. But, since vector displays made it *so* easy
to scale things (e.g., to zoom into or out of the screen), a
linearization that looked good at one scale factor would look really bad
at a larger factor. Conversely, drawing a good approximation at a large
scale factor used up lots of unnecessary display bandwidth at low scale
factors. (see below)

Most interesting.

Someone (?) also had a vector graphic engine that only drew *arcs*. This
was an interesting twist as it made curves a real possibility. However,
it *only* drew arcs. So, it would have to "approximate" straight line
segments (e.g., as used in *text*!) with arcs of suitably large radii.
:

Seems really silly not to be able to also draw straight lines. Reminds me
of a US Navy sonar analog fire-control computer (ca. 1956) that could
solve for a target moving with a constant turning radius. Unfortunately,
the extra components were disabled, because the computer itself was
unreliable. (I saw it at a Navy school, not on a ship.)

I think one reason color seems so "pure" in most of these applications
is that the number of colors actually used is usually very limited. And,
since you aren't doing large area fills, you don't see artifacts in
color gradations that would otherwise be visible, for example, on a
raster scan monitor.

Indeed, in the game i saw, the palette was very limited. Convergence was
amazingly good, though.

IIRC, the color monitors were essentially the same as raster scan
monitors but the deflection amplifiers were controlled externally (via
"X" and "Y"). The scan rate of most of these vector monitors was
considerably less than that of a raster scan monitor of that period --
like one fourth of that! (N.B. Electrohome had a vector scan monitor
that could actually *emulate* a raster scan monitor with its deflection
amplifiers. I think they are/were located somewhere in Canada?).

Good glory! Reminds me of a little low-cost consumer vector display game
(Vectrex?); had mag. X-Y defl., and was probably monochrome. Could
display little rasters. Also, the remarkable H-P wide-deflection-angle
electrostatic CRT X-Y display. Its deflection amps were limited to small
swings for fast writing.

A problem with vector scan displays is that you either adopt a "constant
drawing speed" in the design of your graphics engine (i.e., slew the
deflection amps at a constant rate) *or* you try to optimize the drawing
*time* by maximizing the drawing speed (takes more smarts in the graphic
engine). The flip side of this is variations in drawing speed -- stroke
to stroke -- cause variations in the intensity of the displayed stroke.
(think about it) Since the bandwidth of the vector display's amplifiers
is so constrained, one would like to draw things in the minimum time
necessary to allow you to get more on the screen at a given time.

Once again, much appreciated.

Of course, nowadays, processing power makes the advantages of vector
scan displays largely meaningless -- drive a raster scan display at an
insanely high resolution and just *draw* the lines that you want to
draw!

At a trade show, I once saw a monochrome large-screen (21 inch, maybe
bigger) raster-scan monitor that did 4096 (just about sure) x 3480
(probably). IIrc, dot clock was around 1.2 GHz. One of their demo
displays included one black pixel in a while field. You required a
magnifier to see it.

They showed a three-view line illustration of a small boat, an
engineering drawing minus most callout detail. What with the curves of a
boat hull, the image was extremely susceptible to jaggies, and they
weren't using anti-aliasing. Try as one might, without a magnifier, one
could not see any jaggies at all.

Iirc, the resolution mas 300 dpi. Extremely impressive.

They were proud of their low-power horizontal deflection design.
The deflection yoke was more like a "stator" yoke, used for X-Y displays,
but dramatically different in that its individual coils extended out from
the core like huge flower petals; I don't know why.

Unfortunately I've forgotten the trade name, but I think it was Megascan.

At the same trade show, Sony showed a square large-screen Trinitron, 4096
px square. Back then, they didn't have any images larger than 2K, so they
tiled four different ones. A plastic housing was optional, and cost
$7,000.

As to the original query, I guess I'll assume that convergence was done
by some very well-designed analog circuitry. Maybe I should ask Analog
Devices!

The displays were once available affordably as surplus, but I already had
too much Stuff and a slim budget.

Best regards.

--
Nicabod =+= Waltham, Mass.

 

[Bob Larter]

Nicholas Bodley wrote:

Good glory! Reminds me of a little low-cost consumer vector display game
(Vectrex?); had mag. X-Y defl., and was probably monochrome.

Yep, that's the Vectrex. Back in the '80s, a friend & I picked up two
remaindered units for a song. Lots of fun.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

 

[William Sommerwerck]

Good glory! Reminds me of a little low-cost consumer vector display
game (Vectrex?); had mag. X-Y defl., and was probably monochrome.

One of the great videogame systems. I had one, and all the carts and
accessories, but sold them when I was in bad financial straits.

It originally sold for $200, then dropped to $100. The games were generally
very good.

The display was, of course, monochrome. However, there was an accessory pair
of goggles with a rotating filter wheel (provided with the game) for
color -- and 3D. (I don't remember if you could have color and 3D at the
same time.)