Screen and image sizes

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A screen or an image is a width and a height, written the way they are sold and saved: 1920x1080, 4000x3000. Two questions come up about a pair like that. What shape is it, and what does it become at a different size.

The shape of a pair

The aspect ratio is the shape of a rectangle with the size taken out of it: a 1920 by 1080 screen and a 3840 by 2160 screen are both 16:9, which is why a film fills either one the same way. as ratio reduces a pair to that shape.

1920x1080 as ratio // 16:9
3840x2160 as ratio // 16:9
1024x768 as ratio // 4:3

The spaces are yours to keep or drop, and in reads the same as as.

1920 x 1080 as ratio // 16:9
1920x1080 in ratio // 16:9

This is the same reduction ratio does, in the spelling a screen is written in. ratio(1920, 1080) gives the same answer, and takes more than two parts.

The other side of a resize

Scaling a picture down usually means fixing one side and letting the other follow, so the shape survives. State the side you know and resize works out the other.

resize 4000x3000 to 1200 wide // 1200 x 900
resize 4000x3000 to 900 tall // 1200 x 900

Both lines are the same resize written from either end. width and across read as wide, and height and high read as tall, so the sentence can sit whichever way it comes out.

resize 4000x3000 to 1200 width // 1200 x 900
resize 4000x3000 to 900 high // 1200 x 900

The side that follows is rounded to a whole pixel, because that is what an image file holds. A pair whose shape does not divide evenly lands on the nearest one rather than a fraction of a pixel that nothing can store.

resize 1000x333 to 500 wide // 500 x 167

When it cannot answer

A resize says which side the size is, and the number alone does not say it. A half-written resize 4000x3000 to 1200 is reported as a line that still needs "wide" or "tall" rather than guessed at, and a resize 4000x3000 with no size at all says it expects to and then a size. Both are reported where the missing part should be, so a line being typed says what it is still waiting for.

Why the pair needs the rest of the line

1920x1080 on its own is still 1920 times a variable called x1080, which is what it has always been, and a note that says 3x4 still means what it did. The pair is only read as a width and a height when the line goes on to ask something of it: after resize, or before as ratio. A rule that claimed every <number>x<number> would quietly change what other people’s lines mean, and this deliberately does not.