Picture resolution/Photoshop question

Started Apr 28, 2017 | Discussions thread
richardplondon Forum Pro • Posts: 10,797
Re: DPI is meaningless in digital photography

Jestertheclown wrote:

Kaj E wrote:

Jim Hess wrote:

And in reality it doesn't even affect the quality of printing. You're looking at pixels per inch, and regardless of what that setting is it isn't going to change the quality of the image. If you don't have enough pixels and you try to display the image too big on screen or too large of a print it isn't going to look very good.

Dpi indeed affects the quality of a print. For a Canon printer anything below 300 dpi reduces quality and anything below 360dpi (or 720dpi if you examine through a loupe) reduces quality of a Epson printer.

Saving or exporting an image at the pixel dimensions, or ppi; "pixels per inch", a longitudinal measurement, that will suffice, is all that you need to do.

It's the pixel dimensions that need to be set, and ppi alone cannot do this. Various different ppi / dpi settings can be used, or changed, and these may or may not make a difference to the pixel dimensions depending how this is done. Otherwise different inch sizes may be set, and your ppi will then need to give way in order to achieve the desired pixel dimensions.

There's no option in Photoshop, to my knowledge, to set the dpi; which actually stands for "droplets per square inch", a unit of area,

The D actually stands for "dots", not "droplets". This figure is largely notional for inkjet printers - where it likely refers to the internal addressable resolution of an intermediate virtual image, as considered in the carriage direction only, before that is rendered into a multi-coloured scattering of variable size and variable overlap droplets.

And certainly not per square inch! (720 droplets, or dots, to the square inch would be only 27 per inch, while 1440 would be only 38 per inch).

Many people do misunderstand this issue, but that's not because of using the 'wrong' abbreviation; it's because they don't grasp the concepts of resolution clearly.

So. Before correcting other people in a technical discussion, as to a usage convention which YOU think is somehow definitive - though many others clearly disagree, or think it simply does not matter - (just a suggestion) it might be as well to make very sure of your own technical ground first. You know; so as not to embarrass yourself.

at which an image will be printed.

DPI also refers to input resolution, as with scanners. And to display resolution, as with screens etc. Many people extend this concept across to digital images too; since these may derive from a scanner or else may be prepared for a particular output situation. And I'm not going to be the one to say they are wrong to do so. Not if they have deployed the underlying concepts properly; frankly, who then cares... this sense of DPI is too widespread an alternative usage, especially in publishing, to get remotely bent out of shape about.

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