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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 '13 at 10:41
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 '13 at 20:39
or simply 1360 x 765 which would be exactly 16:9 – Martin Thoma Jan 7 '13 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 '13 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? – Martin Thoma Jan 10 '13 at 8:50
up vote 16 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.


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 '13 at 17:11
-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 '13 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 '13 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 '13 at 0:08
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 '13 at 3:05

Resolutions tend to be a power of 2 (or a multiple of a power of 2 that is as large as possible), possibly because 3D graphics renderers often use a technique called mipmapping, and many image formats as well as video codecs also process the image in block sizes that are powers of 2 like 8x8, 16x16...

Obviously 1360:765 is precisely 16:9, but 765 isn't divisible by any power of 2, while 768 can be divisible by 256 (28), so 768 for the height is a better choice.

768/(16/9) = 1365.333..., so if you round it up, you'll get a common resolution that is 1366x768, which is very close to 16:9. But again, 1366 is only divisible by 2 so some screen manufacturers use 1360x768 instead since 1360 is divisible by 16 which is much better. 1360/768 = 1.7708333... which approximates 16/9 to about 2 decimal places, and that's enough.

Many 12MP cameras have effective resolution of 4000x3000, and when shooting in 16:9, instead of using the resolution 4000x2250 which is exactly 16:9, they use 4000x2248 because 2248 is divisible by 8 (which is the common block size in many video codecs), and 2500 is divisible by 4.

Some Kodak cameras use 4000x2256 too, since 2256 is divisible by 16, and 4000/2256 still approximates 16/9 to about 2 decimal places. If shooting in 3:2 they'll use 4000x2664, not 4000x2667 which is closer to 3:2, for the same reason.

And this is true for other resolutions too. You won't find any image resolutions that are odd. Most will be at least divisible by 4 - or better, 8. The full HD resolution, 1920x1080, has a height not divisible by 16, so many codecs will use 1920x1088 instead, then crop it down when displaying or after processing. But sometimes it's not cropped so you can see there are many 1920x1088 videos on the net. Some files are reported as 1080 but actually 1088 inside.

You may also find the option to crop 1088 to 1080 in various video decoder's settings.

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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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You're asking a lot of different questions here.

Pixels are not square. Pixels have their own aspect ratio which is separate from the display's aspect ratio.

Display resolutions have to be whole, even numbers. 1366x768 is as close as you can get to 16:9 in that ballpark.

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For all intents and purposes, pixels are square. This goes for virtually all consumer electronics. I’m too lazy to try now, but I’m pretty sure the last paragraph is wrong. Multiples of 2, 4, 8 or whatever are just convenient, that’s all. – Daniel B Aug 10 '14 at 0:45
@DanielB Pixels can be square, but are not always. Here's some examples. I said "whole, even numbers", not multiples of other numbers. As an example, if you didn't have even numbers, you wouldn't be able to display interlaced video. – Jason Aug 11 '14 at 5:57
@DanielB no, it's not. You can see the DVD resolutions 720x576 (PAL) and 720x480 (NTSC) both uses rectangular pixels and result in 4:3 or 16:9 image exactly. Even some Full HD cameras support the 1440x1080 resolution where pixel aspect ratio is 4:3 and also result in exact 16:9 image like 1920x1080. If you import a 1440x1080 (exact 4:3) image into some video editting softwares like Sony Vegas it'll be recognized as non-square pixel images automatically and you'll need to resize the image – Lưu Vĩnh Phúc Aug 11 '14 at 9:23

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