Pixel art and retro resolution scaling
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The biggest whole multiple that still fits on the screen
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| How big the image ends up at that multiple | — |
| Screen left over around it | — |
| The multiple that would fill the height exactly | — |
| Rows of the original, by how tall each one comes out | — |
Screen heights that divide this image evenly
| Screen height | Multiple of the original size | Width it would need |
|---|
This is why a game that ran at three hundred and twenty by two hundred and forty looks right on a fourteen forty screen and slightly wrong on a full high definition one. Two hundred and forty goes into fourteen forty six times, and into ten eighty four and a half times.
Consoles that drew two hundred and twenty four rows have it worse: that number divides none of the usual screen heights, so there is no multiple that fills the screen cleanly at all. The way out is the same one arcade cabinets use, which is to accept the black border and keep the whole multiple.
Why does an old game look slightly wrong on a modern screen?
Because the number of rows almost never divides evenly. A game drawn at two hundred and forty rows stretched to a full high definition screen is four and a half times, and half a row does not exist.
What the screen does instead is give some rows four pixels and others five. Exactly half and half in that case, which means every second horizontal line of the picture is a quarter thicker than the one above it.
What is the fix?
Keep to a whole multiple and accept the black border. Four times two hundred and forty is nine hundred and sixty, which leaves sixty rows of screen unused at the top and bottom, and every pixel of the original comes out the same size.
This is what arcade cabinets and careful emulator setups do. The border is not a defect, it is the price of every pixel being the same shape.
Which screens divide evenly?
It depends entirely on the number of rows the original had. Two hundred and forty divides seven hundred and twenty, twelve hundred, fourteen forty and twenty one sixty. One hundred and forty four, the Game Boy, divides seven hundred and twenty, fourteen forty and twenty one sixty.
Two hundred and twenty four, which is what the consoles of that generation drew, divides none of the usual screen heights at all. There is no multiple that fills the screen, so the border is the only honest option.
Does it matter for the width as well?
It matters, but far less in practice, because screens are wider than the images and there is room to spare sideways. The multiple that fits is limited by whichever side runs out first, and that is almost always the height.
The page shows both, and the table on the right prints the width each whole multiple would need, so you can see whether it still fits across.
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