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Re: Square pixels?

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Thomas Harte wrote:
> I am the author of an Apple II emulator; I recently received a bug report
> that its pixels aspect ratio is off — e.g. in text mode, pixels are not
> square.
> 
> I checked the arithmetic on that and the emulator's workings seems to be
> correct that vanilla NTSC would produce pixels around 93% as wide as tall.
> 
> But then I also took a look at photographic evidence of Apple IIs paired
> with appropriate monitors and indeed the few of those that are
> appropriately framed to be able to take measurements from appear to show
> square pixels*.
> 
> Can anyone give me a sense of the probability distribution here? How
> common
> was it to calibrate an Apple II's display to try to make the pixels
> square?
> Am I even right to think they wouldn't be square on a television?
> 
> * E.g. this one of Mouse Desk:
> https://www.oldcomputr.com/wp-content/uploads/2015/12/apple_iie.jpg from
> which I measured the aspect ratio of the desktop and compared to the
> aspect
> ratio when output at around the 93% number as shown above; the photograph
> was roughly 8% wider.
>

Thomas Harte wrote:
> I am the author of an Apple II emulator; I recently received a bug report
> that its pixels aspect ratio is off — e.g. in text mode, pixels are not
> square.
> 
> I checked the arithmetic on that and the emulator's workings seems to be
> correct that vanilla NTSC would produce pixels around 93% as wide as tall.
> 
> But then I also took a look at photographic evidence of Apple IIs paired
> with appropriate monitors and indeed the few of those that are
> appropriately framed to be able to take measurements from appear to show
> square pixels*.
> 
> Can anyone give me a sense of the probability distribution here? How
> common
> was it to calibrate an Apple II's display to try to make the pixels
> square?
> Am I even right to think they wouldn't be square on a television?
> 
> * E.g. this one of Mouse Desk:
> https://www.oldcomputr.com/wp-content/uploads/2015/12/apple_iie.jpg from
> which I measured the aspect ratio of the desktop and compared to the
> aspect
> ratio when output at around the 93% number as shown above; the photograph
> was roughly 8% wider.
>

I really doubt that you can get a definitive answer on this. I enjoy
converting graphics to Apple II formats and I have tried to figure out some
rule about this, but they all have some caveats.

You would assume that someone with a 4:3 Monitor would like to use the whole
screen real state to display full-screen graphics, so they would adjust the
visible area to leave symmetric borders for both axis. In that case the
aspect ratio in HiRes would be about 91,4%. 

The Apple IIe Card for the Mac LC uses this aspect ratio as well. For
example, when installed on a Color Classic, the monitor would switch its
native resolution of 512x384 to 560x384 to make room for the full resolution
in 80 cols and DHGR. By doing so, it would stretch the pixels to exactly
32:35. 

But this does not seem to be the common assumption. For example the Analog
Clock from AE assumes an aspect ratio of 83%, see
https://macgui.com/spyglass/r/0ed4df212b04180a/ANALOG.CLOCK?f=DmNtZWlpYAZqZmRvZg&fk=af3627ab31
This looks vertically squashed on every system I tried, so I wonder if
anyone ever adjusted their screen to see this as a circle.

My PAL Apple //c using the color adapter and connected to a relatively
modern PAL TV without position controls fixes the aspect ratio to ~1,114 and
leaves an uncentered image with unsymmetrical borders.

I don't think that the MouseDesk Screenshot is a good example. First, it is
a modern mock-up. Second, Mouse Desk uses the Monochrome DHGR resolution of
560x192 which produces tall pixels, not square pixels. 

Anyway, I think that it might be a good idea if the emulator could allow to
select the 1:1 pixel ratio as a non-default option.

Just a side question... how do I swap disks on your emulator? I have not
been able to use multi disk programs with it. Am I missing something?

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Square pixels? Thomas Harte <thomas.harte@gmail.com> - 2021-06-07 08:20 -0700
  Re: Square pixels? kegs@provalid.com (Kent Dickey) - 2021-06-07 16:44 -0500
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    Re: Square pixels? Michael J. Mahon <mjmahon@aol.com> - 2021-07-05 11:08 -0500
  Re: Square pixels? "Michael 'AppleWin Debugger Dev'" <michael.pohoreski@gmail.com> - 2021-07-07 09:10 -0700

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