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When I see the details of an image in windows, there are two data namely “Horizontal Resolution” and “Vertical Resolution” which are in DPI unit.

I know that DPI and PPI values are applicable in printing and monitor resolution, and they only use the image's pixel dimensions to print or display it using their own DPI values. In that case, what are the actual use of those DPI units that are embedded in an image?

For example, if I create two images, both having same pixel dimensions of 1200×600 pixels but with different DPI values of 200 DPI and 300 DPI embedded in them, at which place these values will play a role?

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  • Possible duplicate: graphicdesign.stackexchange.com/questions/77371/… DPI, if used properly and not mistakenly used to mean PPI, is only relevant when printing.
    – Scott
    Jun 11, 2022 at 19:03
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    This question is also related: graphicdesign.stackexchange.com/q/130476. In short: An image's resolution is just a setting to show applications which dimensions the image is intended to have. It has no influence on image quality or file size.
    – Wolff
    Jun 11, 2022 at 20:10
  • Also relevant is The Myth of DPI - an old but still very relevant article.
    – Billy Kerr
    Jun 11, 2022 at 23:55
  • Some software will respect the DPI value stored in your image files when you insert the images. In that case, it'd place your 1200 pixel wide image at 6 and 4 inches, respectively (1200dots/200dots per inch = 6 inches and so on). That doesn't mean that either is necessarily the best size for the image, just that it's doing what the metadata in the image tells it to do.
    – Steve Rindsberg
    Jun 14, 2022 at 19:56

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DPI is an entirely semantic piece of information. What you do with that info is entirely up to you.

This is arguably the hard part. The thing is DPI and PPI values only play a role if you have defined a role. If you really do not know what to do with this info ignore it.

For me it only plays a role if I service print for somebody else. There used to be a time when nearly every image was destined for this kind of treatment. But that kind of thinking has not been current for over 25 years. There are uses but its okay if you dont have one.

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    I agree but you almost make it sound like it's an outdated concept. For example when scanning originals it's important to have the resolution set correctly so the physical size is stored within the image. In general people are very sloppy with this though, so I never really trust the resolution setting of images I haven't scanned myself.
    – Wolff
    Jun 12, 2022 at 7:46
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    @Wolff well its not an outdated concept its just that its itrelevant for most usecases. A lot of people will work with pictures and never need this for anything. It used to be 100% of the usecases now its like 2%. So it has a over elevated position in software, in modern use author or copyright metadata should be more important. But your usecase is valid, but because you define meaning for the values. And you dont really trust other peoples values...
    – joojaa
    Jun 12, 2022 at 8:15

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