Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!mentor.cc.purdue.edu!ahg
From: ahg@mentor.cc.purdue.edu (Allen Braunsdorf)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: (Non) Square Pixels?
Summary: In general, I don't need (or want) square pixels.
Message-ID: <7378@mentor.cc.purdue.edu>
Date: 12 Feb 90 19:06:05 GMT
References: <4687@lmrc.uucp>
Reply-To: ahg@mentor.cc.purdue.edu (Allen Braunsdorf)
Organization: 3-D Computer Graphics From Hell
Lines: 82

In article <4687@lmrc.uucp> hassinger@lmrc.uucp writes:
>A posting today reminded of an issue that I have not seen discussed very much.
>The issue of the lack of "square pixels" on the Amiga.  I think it was
>suggested that just getting the right monitor would solve the problem for the
>case in point.  I don't know that that is a real answer.

It depends on what The Problem is.  I don't think there is one.

>Perhaps you can buy a monitor with a suitable aspect ratio and certainly you
>can adjust the aspect ratio of many monitors so the pixels appear square.  So,
>how do you even decide if the Amiga pixels *are* square or not?  You have to
>refer back to some standard display format.  In the Amiga case it seems obvious
>that the reference should be a standard NTSC television format.
>
>I think I am correct that the pixels are not square on a normal 1084 or on a
>normal television monitor.  Does anyone other than me care about this?

The early Amiga manuals claimed that the pixel aspect ratio (the relative
dimensions of a pixel) should be 10:11 for "normal" pixels (LORES NOLACE
or HIRES LACE) and therefore 5:11 (HIRES NOLACE) and 20:11 (LORES LACE).
I measured my monitor and these didn't sound quite right, so I consulted a
higher power.

The printer device!  The printer software uses 6:7 (3:7, 12:7), and this
looks great on my monitor.  It's also the value that most of the ANIMs
I've come across use.  So let's say it's right (because if it's not, we're
in trouble (ie: the printer software is wrong)).

Why would anyone want non-square pixels?  Simple, more pixels make for a
better image.  If we want to stay NTSC, the Amiga's vertical resolution
can't be changed, so our only hope for squeezing out more pixels is to
increase the horizontal res, and make the pixels non-square.  If the
pixels on an Amiga were square, a 320 x 200 screen would be 274 x 200.
The image quality would take a hit.  If you filly with your monitor, this
is what you'll get.  (Yeah, you'll get as many pixels (until you fill your
monitor), but I'll get more in the same space- same difference (since I
use full overscan).)

>The case I have noticed is to take a brush in DPaintIII and use it to create a
>rotating animation - a simple spinning title for example.  Displayed on my 1084
>or recorded to tape and played back on a standard television monitor it seems
>to distort as it rotates.  I think because of the non-square Amiga pixels.
>
>Can others confirm this observation?  Am I missing something to avoid this
>problem?  If I am right, would it be something appropriate to ask be addressed
>in a new generation Amiga design?  Say in a post-3000 design that was going to
>have a new generation of custom chips and other significant extensions of the
>present hardware and software designs?

It's very easy to fix in software.  In fact, the raytracers and other
renderers on the Amiga do address the problem.  It's just a matter of
changing a number in a matrix, (or the step, depending on the
implementation) so it's trivial for programs of that type.

In paint programs, it's just as easy for rotates, but harder for general
brush control.  Some paint programs have an option that corrects for
aspect ratio in primitives such as circle draws and brush ops.  Consult
your manual, and if you don't find something similar, call up the
manufacturer and ask them.

In general, I don't see non-square pixels as a problem, because I use my
Amiga as a display for images that were made (or made to fit) its aspect
ratio.  If the pixels were square, my pictures wouldn't look as good.
(Nor would NewTek's or Sculpt Animate's or Videoscape's.) While it is a
problem in some paint programs, it is a shortcoming in the program and not
a >fault< of the hardware.  (Though it is certainly caused by the
hardware.)

I would not tweak my monitor to make the pixels square, as it would make
the machine different from the norm and it would lower the image quality
(by reducing the number of pixels/inch).  I would take steps in any
software I write to take the aspect ratio of the display (or the image in
an IFF reader) into account.  Most IFF readers and paint program will
butcher an image that isn't "the right" aspect ratio.  Again, it's the
author's fault, not the image's, or the hardware's.

Mail me if you've any questions, as I don't follow the Amiga groups
regularly.

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Allen Braunsdorf			Purdue University Computing Center
cc.purdue.edu!ahg			UNIX Group Part Time