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interlace mode [message #282293] Fri, 17 January 1986 23:37 Go to next message
daveb is currently offline  daveb
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Article-I.D.: amiga.570
Posted: Fri Jan 17 23:37:52 1986
Date-Received: Sun, 19-Jan-86 07:43:59 EST
Organization: Commodore-Amiga Inc, Los Gatos, CA
Lines: 15
Keywords: AMIGA INTERLACE



	There has been a lot of talk (and flak) about the apparent
'unusable' interlace mode of the AMIGA. I have seen a 640 x 400
screen that didn't seem to flicker at all and looked dynamite!
BUT the programmer did use a trick to accomplish this feat.

	The trick is to plot a pixel ON and ABOVE the line where the
pixel is to be placed. This still results in an effective resolution
of 400 lines BUT reduces the flicker to almost zilch. I saw this
implemented on a terminal program and a graphics display and they
both looked great on a 1080 monitor. Give it a try, the results
may surprize you!

	Regards, David Berezowski (CBM/AMIGA East Coast)
Re: interlace mode [message #282308 is a reply to message #282293] Sat, 18 January 1986 13:05 Go to previous messageGo to next message
breuel is currently offline  breuel
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Article-I.D.: h-sc1.877
Posted: Sat Jan 18 13:05:46 1986
Date-Received: Mon, 20-Jan-86 05:48:50 EST
References: <570@amiga.amiga.UUCP>
Organization: Harvard Univ. Science Center
Lines: 37

|	There has been a lot of talk (and flak) about the apparent
|'unusable' interlace mode of the AMIGA. I have seen a 640 x 400
|screen that didn't seem to flicker at all and looked dynamite!
|BUT the programmer did use a trick to accomplish this feat.
|
|	The trick is to plot a pixel ON and ABOVE the line where the
|pixel is to be placed. This still results in an effective resolution
|of 400 lines BUT reduces the flicker to almost zilch. I saw this
|implemented on a terminal program and a graphics display and they
|both looked great on a 1080 monitor. Give it a try, the results
|may surprize you!
|
|	Regards, David Berezowski (CBM/AMIGA East Coast)

Sure, if you use 640x400 as a 640x200 mode, then you won't see
any flicker, you won't have any higher resolution either, though,
and you'll waste a lot of memory.

The only thing I don't like about the AMIGA (apart from its
price) is the fact that it doesn't manage to produce 640x400
graphics. I have seen several demos in high-resolution mode,
and the flicker is really unbearable for any real work.

WHAT I WOULD LIKE TO KNOW IS: is Commodore/AMIGA planning on
releasing a version of the AMIGA in which this problem has
been fixed (e.g. in which the monitor can be run at either
60Hz or 70Hz)? Is there a hardware patch that can be applied
to current machines to solve the problem?

I find that for serious use as a desktop workstation,
a resolution of 640x200 pixels is just not enough.
The Mac is just barely usable (slightly lower horizontal
resolution and larger vertical resolution), and the LISA is
probably the only low-end work-station on which you can afford to
have two reasonably sized windows open at the same time.

						Thomas.
Re: interlace mode [message #282317 is a reply to message #282293] Sun, 19 January 1986 22:37 Go to previous messageGo to next message
breuel is currently offline  breuel
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Article-I.D.: h-sc1.878
Posted: Sun Jan 19 22:37:55 1986
Date-Received: Tue, 21-Jan-86 07:24:45 EST
References: <570@amiga.amiga.UUCP> <877@h-sc1.UUCP> <511@well.UUCP>
Organization: Harvard Univ. Science Center
Lines: 45

|||	The trick is to plot a pixel ON and ABOVE the line where the
|||pixel is to be placed. This still results in an effective resolution
|||of 400 lines BUT reduces the flicker to almost zilch. I saw this
||
||Sure, if you use 640x400 as a 640x200 mode, then you won't see
||any flicker, you won't have any higher resolution either, though,
||and you'll waste a lot of memory.
|
|    This isnt 640X200 mode.  You still have 400 (399, actually) vertical
|pixel locations, it's just that each pixel is now 2 lines high instead of
|one.  It's the same sort of thing that a lot of machines (specifically
|Atari 800 and Apple II) did to avoid horizontal color aliasing when using
|a standard NTSC type composite monitor.

This may do the trick for certain kinds of graphics. For a high-resolution
text display, it may make your characters look nicer, but it does not
allow you to display significantly more characters on the screen.

|  The necessary fix would be fairly expensive. The biggest reason for the
|640 X 200 limitation on each field is to reduce the bandwidth requirements
|of the coprocessor and the memory, and to allow the CPU more cycles. 
|Maintaining the current hardware capabilities and adding the extra capability
|you describe isn't an easy job. (Before I hear anything about the Atari ST
|and its 640X400, 70Hz screen, let me remind you that that is a one-bit-per-
|pixel monochrome screen.  It's ONLY color option is 320X200.  If you are
|willing to accept THAT limitation, then the problem isn't too hard.  If you
|want a color screen such as the Amiga's, at a reasonable cost, compromises
|have to be made.)

Yes, that is precisely the point. For word processing and program development
I vastly prefer high monochrome resolution to low colour resolution. That
is not a bad limitation, it is a reasonable compromise (between cost
and performance). What counts for those applications is whether you can
display one, two, or four usable windows on the screen at the same time,
not whether your menu bar is green and your pop-up menus are pink.

I guess we just have different applications in mind. For my purposes,
a machine with true 640x400 monochrome resolution is just superior to
one with 640x200 colour resolution because I can display more text
on the screen at the same time. Since I otherwise like the AMIGA,
I really regret that it doesn't have this capability. It is unfortunate
to hear that Commodore/AMIGA seems to have no intention of adding
a high-resolution monochrome mode.

							Thomas.
Re: interlace mode [message #282320 is a reply to message #282293] Sun, 19 January 1986 14:13 Go to previous messageGo to next message
farren is currently offline  farren
Messages: 36
Registered: November 1985
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Article-I.D.: well.511
Posted: Sun Jan 19 14:13:35 1986
Date-Received: Tue, 21-Jan-86 08:14:02 EST
References: <570@amiga.amiga.UUCP> <877@h-sc1.UUCP>
Organization: Whole Earth Lectronic Link, Sausalito, CA
Lines: 36

In article <877@h-sc1.UUCP>, breuel@h-sc1.UUCP (thomas breuel) writes:
 >  |	The trick is to plot a pixel ON and ABOVE the line where the
 >  |pixel is to be placed. This still results in an effective resolution
 >  |of 400 lines BUT reduces the flicker to almost zilch. I saw this
 >  
 >  Sure, if you use 640x400 as a 640x200 mode, then you won't see
 >  any flicker, you won't have any higher resolution either, though,
 >  and you'll waste a lot of memory.

    This isnt 640X200 mode.  You still have 400 (399, actually) vertical
pixel locations, it's just that each pixel is now 2 lines high instead of
one.  It's the same sort of thing that a lot of machines (specifically
Atari 800 and Apple II) did to avoid horizontal color aliasing when using
a standard NTSC type composite monitor.
 
 >  WHAT I WOULD LIKE TO KNOW IS: is Commodore/AMIGA planning on
 >  releasing a version of the AMIGA in which this problem has
 >  been fixed (e.g. in which the monitor can be run at either
 >  60Hz or 70Hz)? Is there a hardware patch that can be applied
 >  to current machines to solve the problem?

  The necessary fix would be fairly expensive. The biggest reason for the
640 X 200 limitation on each field is to reduce the bandwidth requirements
of the coprocessor and the memory, and to allow the CPU more cycles. 
Maintaining the current hardware capabilities and adding the extra capability
you describe isn't an easy job. (Before I hear anything about the Atari ST
and its 640X400, 70Hz screen, let me remind you that that is a one-bit-per-
pixel monochrome screen.  It's ONLY color option is 320X200.  If you are
willing to accept THAT limitation, then the problem isn't too hard.  If you
want a color screen such as the Amiga's, at a reasonable cost, compromises
have to be made.)

-- 
           Mike Farren
           uucp: {your favorite backbone site}!hplabs!well!farren
           Fido: Sci-Fido, Fidonode 125/84, (415)655-0667
Re: interlace mode [message #282326 is a reply to message #282293] Tue, 21 January 1986 10:04 Go to previous messageGo to next message
long is currently offline  long
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Registered: January 1986
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Article-I.D.: sask.322
Posted: Tue Jan 21 10:04:03 1986
Date-Received: Tue, 21-Jan-86 23:18:53 EST
References: <570@amiga.amiga.UUCP>
Organization: University of Saskatchewan, CANADA
Lines: 23

 >  
 >  
 >  	There has been a lot of talk (and flak) about the apparent
 >  'unusable' interlace mode of the AMIGA. I have seen a 640 x 400
 >  screen that didn't seem to flicker at all and looked dynamite!
 >  BUT the programmer did use a trick to accomplish this feat.
 >  
 >  	The trick is to plot a pixel ON and ABOVE the line where the
 >  pixel is to be placed. This still results in an effective resolution
 >  of 400 lines BUT reduces the flicker to almost zilch. I saw this
 >  implemented on a terminal program and a graphics display and they
 >  both looked great on a 1080 monitor. Give it a try, the results
 >  may surprize you!
 >  
 >  	Regards, David Berezowski (CBM/AMIGA East Coast)


Doesn't this little trick drop the resolution down to 200 lines????
(at least for all intents and purposes.)

				 Warren Long
				 University of Saskatchewan
				 Canada
Re: interlace mode [message #282333 is a reply to message #282293] Tue, 21 January 1986 19:36 Go to previous messageGo to next message
tynor is currently offline  tynor
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Article-I.D.: gitpyr.1271
Posted: Tue Jan 21 19:36:49 1986
Date-Received: Wed, 22-Jan-86 05:48:24 EST
References: <570@amiga.amiga.UUCP> <877@h-sc1.UUCP> <511@well.UUCP>
Reply-To: tynor@gitpyr.UUCP (Steve Tynor)
Organization: Georgia Institute of Technology
Lines: 8

 > you describe isn't an easy job. (Before I hear anything about the Atari ST
 > and its 640X400, 70Hz screen, let me remind you that that is a one-bit-per-
 > pixel monochrome screen.  It's ONLY color option is 320X200.  If you are
 > willing to accept THAT limitation, then the problem isn't too hard.  If you
 > want a color screen such as the Amiga's, at a reasonable cost, compromises
 > have to be made.)

Medium res (high res color) on the atari st is 640x200.
Re: interlace mode [message #282343 is a reply to message #282293] Wed, 22 January 1986 10:06 Go to previous messageGo to next message
tainter is currently offline  tainter
Messages: 3
Registered: January 1986
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Article-I.D.: ihlpg.1569
Posted: Wed Jan 22 10:06:58 1986
Date-Received: Thu, 23-Jan-86 20:40:09 EST
References: <570@amiga.amiga.UUCP> <877@h-sc1.UUCP> <511@well.UUCP>
Organization: AT&T Bell Laboratories
Lines: 7

 >  you describe isn't an easy job. (Before I hear anything about the Atari ST
 >  and its 640X400, 70Hz screen, let me remind you that that is a one-bit-per-
 >  pixel monochrome screen.  It's ONLY color option is 320X200.  If you are
 >             Mike Farren

WRONG!  The ST also has 640x200 color, albeit with fewer color choices.
--johnathan a. tainter
Re: interlace mode [message #282347 is a reply to message #282293] Tue, 21 January 1986 15:41 Go to previous messageGo to next message
mjg is currently offline  mjg
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Article-I.D.: ecsvax.1108
Posted: Tue Jan 21 15:41:53 1986
Date-Received: Thu, 23-Jan-86 21:05:15 EST
References: <570@amiga.amiga.UUCP>
Organization: North Carolina Educational Computing Service
Lines: 17

 >  
 >  
 >  	The trick is to plot a pixel ON and ABOVE the line where the
 >  pixel is to be placed. This still results in an effective resolution
 >  of 400 lines BUT reduces the flicker to almost zilch. I saw this
 >  implemented on a terminal program and a graphics display and they
 >  both looked great on a 1080 monitor. Give it a try, the results
 >  may surprize you!
 >  
 >  	Regards, David Berezowski (CBM/AMIGA East Coast)


Doesn't this mean that the vertical positioning resolution is 400
lines but that objects can only be described to the nearest 1/200th
of the screen height.

Mike Gingell     ..decvax!mcnc!ecsvax!mjg
Re: interlace mode [message #282349 is a reply to message #282293] Tue, 21 January 1986 13:04 Go to previous messageGo to next message
mykes is currently offline  mykes
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Article-I.D.: 3comvax.365
Posted: Tue Jan 21 13:04:11 1986
Date-Received: Thu, 23-Jan-86 21:28:14 EST
References: <570@amiga.amiga.UUCP> <877@h-sc1.UUCP> <511@well.UUCP>
Reply-To: mykes@3comvax.UUCP (Mike Schwartz)
Organization: 3Com Corp; Mountain View, CA
Lines: 10


There is little doubt in my mind that the Amiga could have had much better
resolution than it already does, but the tradeoff would have been non-NTSC
standard.  This means that not only could the Amiga not be plugged into
a TV and features like GENLOCK would be much more expensive.  A distinct
advantage of being NTSC standard is that not only can input from a video
camera be mixed in, but the output can be recorded on standard video tape.

Blame for the flicker in interlace mode should be placed on the NTSC standard,
not the Amiga.  NTSC is not exactly the best quality video standard anyway.
Re: interlace mode [message #282371 is a reply to message #282293] Thu, 23 January 1986 05:46 Go to previous message
farren is currently offline  farren
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Article-I.D.: well.538
Posted: Thu Jan 23 05:46:01 1986
Date-Received: Fri, 24-Jan-86 22:16:22 EST
References: <570@amiga.amiga.UUCP> <877@h-sc1.UUCP> <511@well.UUCP> <1271@gitpyr.UUCP>
Organization: Whole Earth Lectronic Link, Sausalito, CA
Lines: 31

I wrote:
 >> you describe isn't an easy job. (Before I hear anything about the Atari ST
 >> and its 640X400, 70Hz screen, let me remind you that that is a one-bit-per-
 >> pixel monochrome screen.  It's ONLY color option is 320X200.  If you are
 >> willing to accept THAT limitation, then the problem isn't too hard.  If you
 >> want a color screen such as the Amiga's, at a reasonable cost, compromises
 >> have to be made.)
And Steve Tynor replied:
 >  Medium res (high res color) on the atari st is 640x200.

   Thanks for the information.  I hadn't realized there was a med-res mode.
It still doesn't change things, though.  The limitation is the number of
bytes you're shoving through the graphics hardware every frame, and I
would believe that med-res mode on the Atari cuts the number of colors
displayable in half?  Twice the resolution = half the colors = same number
of bytes/line.

   It might be possible, by limiting the bit-planes to one (or possibly 2),
to get the bandwidth you'd need to put out a 640X400 non-interlaced screen,
as someone else suggested.  The secondary problem that that brings up is
simple:  you need a different monitor.  A monitor that will handle 640X400
is forced to operate with a MUCH higher horizontal frequency, and would    
either be much more expensive (if color), or incompatible with the lower
resolution modes (rendering a lot of software incompatible), or both.
I'm pretty sure this is the reason the STs have two non-intermixable
monitors.

-- 
           Mike Farren
           uucp: {your favorite backbone site}!hplabs!well!farren
           Fido: Sci-Fido, Fidonode 125/84, (415)655-0667
Re: interlace mode [message #282372 is a reply to message #282293] Thu, 23 January 1986 01:40 Go to previous message
mykes is currently offline  mykes
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Article-I.D.: 3comvax.377
Posted: Thu Jan 23 01:40:38 1986
Date-Received: Fri, 24-Jan-86 22:17:00 EST
References: <570@amiga.amiga.UUCP> <322@sask.UUCP>
Reply-To: mykes@3comvax.UUCP (Mike Schwartz)
Organization: 3Com Corp; Mountain View, CA
Lines: 5


The double height pixel trick for interlace mode yields 399 vertical 
positions that the top pixel (of the two) can be.  However, the OS does 
not take advantage of this trick, but a Mac-write style word processor
could.
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