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Most displays get advertised with either 16:9 or 4:3 display ratio. However, if you compare the resolution with the display ratio, it's most often neither of both.

For example, the resolution of my notebook display is 1366x768.
But 1366/768 = 683/384 != 688/387 = 16/9
Another common resolution is 1920/1200 = 8/5

But for some resolutions it's correct:
1024/768 = 4/3
800/600 = 4/3

Is there a technical reason / user experience reason for this? Why do displays have other ratios than what they get advertised?

(I assume that every pixel is a perfect squre. Is this assumption wrong?)

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<irony>In love and in advertising lying is not only allowed, but expected...</irony>; – lexu Jan 6 at 10:41
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I would say 1366 x 768 is close enough 16:9. To be 16:9 exactly, it would have to be 1365 1/3 x 768 or 1366 x 768 3/8. – Bavi_H Jan 6 at 20:39
or simply 1360 x 765 which would be exactly 16:9 – moose Jan 7 at 9:45
@moose Which is a horrible choice because the height is not an even number. This breaks a lot of applications, in particular graphics rendering, where many techniques, both software and hardware, implicitly require height in pixels to be a multiple of two. – Thomas Jan 10 at 4:04
@Thomas I didn't know that. This is the kind of answer I've expected to get with this question. Can you tell me an example for such a technique? – moose Jan 10 at 8:50

2 Answers

up vote 7 down vote accepted

Not every display resolution has to be 16:9 or 4:3.

My laptop and my TV have the well known 16:9 ratio.
My regular display has 16:10, at least they are marketed as 16:10, however the image below has them as 8:5. The broken screen that still sits on top of the locker behind me has a resolution of 5:4.

The image below shows most of the standard resolutions that are available.

source

I actually like 16:10 more than 16:9 and would pay a fair amount more money to get one of these instead. This however is personal opinion but should exemplary show you why there are not only two but a lot more standards to choose from.
Why do I like it so much? Not all movies are 16:9, there are a lot of 4:3 shows out.
When playing games I like it more to have a bit more vertical space to place menus, HUDs etc.
This of course comes down to personal preference. Personal preference between individuals is different and so are displays.

Why are displays marketed as 16:9 if they are not?
If this is done knowingly, I'd call that a scam.

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Great & comprehensive answer. Re: your comment "marketed as 16:10, however the image below has them as 8:5", those are, obviously, the same ratio. I reckon calling it 16:10 is market-speak to make it sound similar to (and comparable to) the common 16:9 aspect ratio. – yosh m Jan 6 at 17:11
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-1: Using the picture of CRT phosphor dots to say "pixels aren't squares" is misleading. Pixels refers to the rectangular grid of picture elements in the computer video memory. This doesn't always line up with the color dots on the screen. A CRT monitor doesn't line up pixels to phosphor dots in any particular way, so on a CRT, a pixel is usually not the same as a trio of phosphor dots. An LCD screen is able to line up a pixel with a trio of color elements exactly (when you use the LCD's native resolution). Subpixel methods only work well on LCD screens because of this. ... – Bavi_H Jan 7 at 0:07
... I drew some white pixels on a black background in Paint, then photographed them on a CRT at its best resolution, then an LCD at its best resolution: image. I don't know how to take macro pictures well, so the LCD color elements are blured together, but you should be able to get the idea. ... – Bavi_H Jan 7 at 0:08
... I believe Moose was asking if pixels are always square or if they are sometimes non-square rectangles. My understanding is that in modern computer resolutions, pixels are square. In very old computer resolutions (like CGA 320 x 200), the image fills a 4:3 monitor, so the pixels are sometimes non-square rectangles. I think some TV formats use non-square rectangular pixels (for example, see the footnotes in the resolution diagram). – Bavi_H Jan 7 at 0:08
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I rolled back the revision that suggested the picture of the phosphor dots and LCD segments illustrated non-square pixels, and removed my downvote. – Bavi_H Jan 10 at 3:05
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Yeah, it's to do with manufacturing.

We already made loads of 1024x768 panels, so why not just make them wider so they are 1366x768.

I'm not sure about the other one, I haven't come across panels with that resolution.

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