X:Y ratios vary?

I just noticed that all of the common monitor resolutions have an x:y
ratio of 1.33:1 except for 1280 x 1024, which is 1.25:1.

Does anyone know why this one is different?

Does this mean that images are slightly distorted at 1280x1024 as
compared to the other resolutions?

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 > Does this mean that images are slightly distorted at 1280x1024 as
 > compared to the other resolutions?

There are two factors that contribute to this.. aspect ratio of the display
device "viewable area", and aspect ratio of pixelsize. Pixels are square in
320x240, 512x384, 640x480, 800x600, 1024x768 and so forth when the display
device viewable area is 4:3 (such as "typical" CRT monitor).

1280x1024 TFT monitors have square pixels, so the display viewable area is
5:4, not 4:3.. the difference is very small.. 1280x960 would have square
pixels on 4:3 display .. the 2D display software such as picture viewers,
web browsers, anything could measure these things and take them into
consideration when "painting" the image. However, this would require
correction in either vertical or horizontal dimension and this would either
cost image quality or performance. It is efficient to assume that pixels are
square in 2D software which are not "mission critical" for such issues.

For 3D graphics the aspect ratio correction is "free", because it can be
embedded into the graphics pipeline when doing perspective or
map-to-viewport transformation. Perspective transformation is very commonly
used place where this correction is implemented in.

When doing the aspect ratio correction THREE factors step into effect:

1. display device viewable area (4:3, 16:9, 5:4, ...) aspect ratio
2. pixel size aspect ratio (1.0 is VERY common)
3. window or viewport aspect ratio (varies radically)

Regarding 1280x1024 vs. 1280x960 the ratio change is small, only ~6%, unless
this is taken into consideration, yes, there will be distortion. But this
case would assume pixels don't map 1:1 from source to destination when
blitting, displaying, whatever.. if the image is copied 1:1, then pixels
will still be square and ergo, no distortion. However, if 4:3 image is
*stretched* to fill 5:4 area completely, then, yes, there will be 6%
distortion.

So it's completely up to the software if there is "distortion" or not,
atleast the pixels are square on a 1280x1024 5:4 display. I'm not 100%
certain if I answered the right question, so be more specific if I avoided
the issue somehow. <!-- ~MESSAGE_AFTER~ -->