So let's get print products out of the way first. Lets take an image of 500px X 375px. If you set it to 3dpi and print it, the print will have 3 X 3 dots spaced across each inch. The physical size of the print will be a whopping 168 X 125 inches, but you'll need to stand around 100 yards away to recognise it.
If we set the resolution of the exact same image to 300dpi the physical size of the image (kb) remains exactly the same, but when printed it will have 300 dots spread across an inch. The print size will be 1.67 X 1.25 inches – little better than a thumbnail.
A comparison of 3dpi and 30 dpi in print
To Scale, but not actual size
Depending, of course, on your screen resolution (ppi)
Now let's take a look at video screens. Video screens only display pixels and are set to a screen resolution in ppi (Pixels Per Inch) a common setting today is, for instance 1920px X 1080px.
Any dpi information contained within an image is disregarded. An image with a pixel size of 500px X 375px will always display at 500px X 375px – on your monitor, on my monitor, or on Joe Blogs' monitor regardless of the dpi settings. It will never change either its pixel size, or its appearance. The physically displayed size will depend on your monitor's ppi settings.
Here's Proof That Video Systems don't use dpi
Don't believe me? Then take a closer look at the two images below. The first is set to 3dpi, the second is set to 300dpi. Both are 500px X 375px.
Do you see any difference? I don't. And yes, I have my glasses on.
Image set to 3dpi
Image set to 300dpi
Still don't believe me? Then drag the images to your desktop (or right-click and save.)
Don't use the clipboard function. The copy function won't copy any dpi information and Windows image editors will automatically set the resolution to 96dpi, whilst Mac editors will set the resolution to 72dpi.
Now open both images in your favourite editor and check the size and resolution for yourself.
Believe me now?
In the end, it's all just pixels.
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Mae Na Toeng Nai, Pai
Mae Hong Son
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