Correct Amiga Aspect Ratio

This article is about what to expect from a correctly configured display, and what aspect ratios to consider when drawing graphics for PAL and NTSC.
This question asked on the English Amiga Board interested me, because answering both those questions requires a lot of small pieces of information:
How did most people back in the day view their games?
The answer I suggest is simple, but there's also some details that could help you run your favorite game as it should look, and... have you adjusted your monitor yet? ;)
Direct answer: They were viewed on the family's TV or used with a 14" monitor (CRT, of course). All other cases were very rare. There were no widescreen displays then, of course.
Now to the details, what we use today, and the difference between display aspect ratio and pixel aspect ratio.

CRT monitors and TVs

Standard 15 kHz CRT monitors are 4:3 display aspect ratio and adjustable, so it was and is no problem getting a 1:1 pixel aspect ratio. TVs were 4:3 and not adjustable. On NTSC they were stretched tall, and on PAL they were slightly squashed.
On all displays, you would almost fill the bezel, but typically leave a fingernail border (margin) all around - to fit the square picture within the curved corners of the bezel.
This was relied upon by overscan games, so that they would let graphics go fully out to behind the bezel to avoid graphics "plopping on-screen". (Or, stated more aptly: the reason that the Amiga had hardware overscan, and games used it, was because of this border. All platforms had it, since it was a good default for displaying text. But Amiga had built-in support for transgressions.)
Note for gamers: this means that an overscan shoot'em-up would show oncoming enemies earlier for gamers on CRTs than if you have one of the monitors below that do not show this border.
  • PAL - Monitor: Pixels squashed by just a few % to almost fill the frame, but can be adjusted to square pixels, see below. TV: almost exactly the same, but non-adjustable.

  • NTSC - Monitor: Pixels stretched by 20%, again to almost fill the frame, border was the same but because of the 4:3 aspect, the top and bottom margin was larger. TV: almost exactly the same, but pre-stretched and non-adjustable.

Squashed and stretched graphics in some games

Game graphics drawn in the USA (such as Zany Golf, Outlands) look very squashed (compressed vertically) on a PAL display because they were drawn on these pre-stretched NTSC displays.
Similarly, PAL games that run on NTSC have graphics that look tall (stretched vertically).
There was just no way they could spend the money to draw two sets of graphics, not to mention fit them on disk.

Correct aspect ratio on a CRT monitor

If you have a CRT monitor, it's easy to make the pixels perfectly square:
  • Open Preferences with no overscan (or maximize a Shell/CLI window) and adjust the picture until you have a 5mm margin in the corners.
  • Open a paint program and draw a big square. Use a grid or measure Coords to make sure it's as many pixels high as it is wide!
  • Measure the width of the square with a ruler, and use the vertical adjustment of the monitor until the height of the square equals the width physically.

PAL vs NTSC

If a PAL user does the above, graphics will still look correct because you already had your CRT set to - not PAL pixel aspect, but something in between PAL pixel aspect and 1:1 (in fact, if you have a flatscreen monitor, this matches it perfectly). If you switch it to NTSC mode, early NTSC game graphics now look correct.
The same is true for an NTSC user doing the same, starting out in PAL mode.
In this way, all Amiga users get the same results and for artists, there's a common pixel aspect ratio to make new graphics for, that is also compatible with modern flatscreen monitors. (In fact, if they used an emulator or PC pixeling software, they already drew their graphics for 1:1 pixel aspect.)

A Commodore 1084S CRT monitor, correctly set up for 1:1 pixel ratio. Note the resulting wide left and right borders. The photo quality is not representative of the display quality.

Modern flatscreen TVs and monitors


There are too many variants that do things differently, so that there isn't a single answer. All of this is assuming you got a display working reasonably (without major issues like cropping or widescreen-stretching).

PAL:


  • Non-widescreen monitors used are typically 5:4 and uses square pixels without exception, and no border, matching the 320x256 resolution in PAL snugly.
  • Non-widescreen PAL TVs are typically 4:3, and they can crop the picture to 320x240 like 4:3 monitors do, or resize the picture, which will give 16 scanline skips. No borders.
  • In flatscreen TVs, it's completely up to the PAL/NTSC chip inside how the picture is resized. Flatscreen LCD TVs made after 2011 all have the new chip, and give a correct PAL display, with horizontal borders only. On widescreen, very wide borders. :) Vertical border is slim to none.

NTSC:

  • Here, the best match is a 4:3 TV, which may display the border, or a 4:3 monitor, which will not.
  • The widescreen flat LCD TVs made after 2011 mentioned above will also display NTSC correctly, again with very wide borders.
  • If you want to create new graphics, you could draw two sets, or draw them in NTSC and not care how they look on PAL. But I think that, since most Amiga users are on PAL, it's best to not draw them in slightly squashed PAL or stretched NTSC, but draw them on a square pixel display.

Users with correctly setup displays will then see them exactly as intended, and, as mentioned, ECS/AGA/OCS+ACA500Plus NTSC Amigas support PAL and their CRT monitor or CRT/Flatscreen TV also does, so that they will be able to see them as intended, if you use square pixels.
Side note: Those who like to play 3D vector games and watch 3D vector demos may have noticed the slight "PAL-squash" (it would be much less noticeable for pixeled 2D graphics). It comes from the programmer not having adjusted the perspective transformation to squashed displays, but to square pixels. This is expected for the most part, and all it takes is a square pixel display to make the vectors look perfect!

Summary

NTSC-stretched graphics look squashed in PAL mode, and PAL-squashed graphics look stretched in NTSC mode, but almost all Amigas can display both.
The most-used displays are modern Widescreen Flatscreen LCD TVs, and 4:3 CRT monitors and TVs. All flatscreen monitors have square pixels.
It's best to make sure that you set up your display correctly before drawing graphics (calibration is a separate topic). For square pixels, the difference to "PAL-squash" is small. And if you want to draw specifically for "NTSC-stretch" like the early Amiga games, that's fine too, however I think the recommendation to simply draw for square pixels is sound:
NTSC and PAL users can adjust their displays for square pixels following this guide, the only exception being NTSC TVs. I think that most users will already have their displays correctly or almost correctly set up in a way that makes graphics not look stretched.
In this way, square pixels becomes not a compromise between two aspect ratios, but a platform that users can support, fully and consistently, across display types on both NTSC and PAL - and that artists can draw for.
If they drew the graphics on PC, they already did.