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please look at these pictures. i couldn't figure out, why this happens? enter image description here

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    ppi means pixel per inch. If your document is 1*1inch at 27ppi that means it is 27x27 pixels. If your document is 1*1 inch at 72 it means your document is 72x72px. – mnxd May 5 '16 at 15:18
  • okay but why in same view size (100%) i see one bigger than another? – kokabi May 5 '16 at 15:25
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    because one IS bigger than the other! – Cai May 5 '16 at 15:33
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    I’m not a native speaker, so please excuse if my explanation does sound clumsy, but I’ll do my best :) — Photoshop only displays the actual pixels of an image. That means that one pixel (at 100%) has exactly the same size as one pixel of your screen. So naturally the image with more pixels in it will be displayed larger. BUT: If you were to safe these files and load them for example in an InDesign-document, they will have the same dimensions (at different resolutions), because InDesign in contrast to Photoshop actually makes use of the ppi information in the file. I hope I could help. – mnxd May 5 '16 at 15:45
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    @mnxd your explanation was a lot clearer than a lot of native speakers'! – Cai May 5 '16 at 16:32
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As a general rule, when your working on a screen, forget about physical dimensions and resolution (PPI). All that affects the size you see something on screen is its pixel dimensions. Your screen doesn't know what an inch is, all it knows is pixels.

In your examples:

  • 1×1 inch image at 72PPI is 72×72 pixels.
  • 1×1 inch image at 27PPI is 27×27 pixels.

Your screen shows those images at their pixel size, ignoring any physical dimensions or resolution settings.

If you were to print those images they would both print at 1 inch square. The only time the resolution really comes in to play is when you print.

If you were to import your images in to say InDesign, they would both show at 1x1 inch because InDesign is resolution aware. This is because InDesign is made for (or at least was traditionally) print design—where resolution really matters.

  • and on a paper? – kokabi May 5 '16 at 15:49
  • On paper, both will print at 1 inch. I'll update my answer when I'm back at my computer. – Cai May 5 '16 at 16:02
  • thanks, okay screen just see pixels but why printer just didn't see dots instead inch or cm and so on? – kokabi May 5 '16 at 16:15
  • Pretty much. Some programs are resolution aware, but that tends to just be stuff geared towards print design, which is when you should worrying about this stuff... If you're working for screen, forget about it. Just think about pixels. – Cai May 5 '16 at 16:21
  • @programmer1 Different technology base. making a image by controlling output directly is much harder so printers have abstracted away the rasterisation prococess. The pixels on a screen are much more straightforward. Also your operating system does not know how big your screen is. – joojaa May 5 '16 at 16:35
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Your screen's resolution (as are most screen resolutions) 72 ppi. If you change the resolution to be higher, it will appear larger on your screen to achieve the same visual "density" if you will. Likewise, when the resolution is lower, it will appear smaller.

Allow me a metaphor.

Imagine you cover 1 sq. inch with 72 cheerios and you are looking at it from 3 feet away. Now imagine you remove cheerios till you are left with 27 cheerios, but those cheerios have taken on milk and are much larger to fill the space. In order for those cheerios to appear the same size as the 72 did before, you have to look at it from further away. Thus, the smaller square.

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    Most screens are not 72 ppi. 72 PPI is just the magick number that makes a postscript point equal to a pixel. User mnxd and the answe of CAI is correct. – joojaa May 5 '16 at 18:08
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    Screens havn't actually been 72PPI in about 30 years. It was only a standard for Macs and it didn't last very long.. Also changing the resolution of an image makes no difference to how you see it on screen. – Cai May 5 '16 at 18:17
  • Talking exclusively about photoshop, which is the only one of the creative suite that uses pixels as its primary framework. And as the question noted, it actually appears smaller and provides less pixels to use within an artboard. So yes, there is a difference in Photoshop. And it's also why the standard resolution for exporting any assets to the web is 72ppi, and @2x simulates retina. – Peacockerie May 5 '16 at 18:32
  • No. Not at all. Images at a different resolution and the same physical dimension will look different but that is because the pixel size is changing. They look different in Photoshop because they are different sizes. One is 72 pixels the other is 27 pixels. – Cai May 5 '16 at 19:37
  • Make a 100x100px image and save it at 72ppi... Make anther 100x100px image and save t at 300ppi... They look exactly the same on screen. No difference at all. The only thing that matters is pixels. – Cai May 5 '16 at 19:37

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