Save for Web and Devices

[Peter S]

As I understand, from reading and my own experiments in making audio visuals, it makes absolutely no difference to a video screen what the ppi is set at.  A crop 1024 x 768 at 10 ppi looks identical with one at 100 ppi.  Why is therefore that Save for web and devices in Photoshop always produces an image that has its document size reolution shown as 72 ppi which is the figure that used to be erroneously quoted as being best for images to be displayed on monitors?  Does this help to perpetuate the wrong message?

Many thanks
Peter

[Mark D Segal]

The message isn't necessarily "wrong". It's right for all those displays which have a resolution of 72 PPI. It's just that these days most displays resolve in the range of the mid to high 90s. But it's not a train smash in terms of this algorithm. Simply means the image dimensions on the display will not be the same as envisioned in <Save for Web and Devices>. What matters more is the total pixel dimensions of the image. A maximum linear dimension in the range of 800 to 1000 pixels for web display should be good.

[Peter S]

The message isn't necessarily "wrong". It's right for all those displays which have a resolution of 72 PPI. It's just that these days most displays resolve in the range of the mid to high 90s. But it's not a train smash in terms of this algorithm. Simply means the image dimensions on the display will not be the same as envisioned in <Save for Web and Devices>. What matters more is the total pixel dimensions of the image. A maximum linear dimension in the range of 800 to 1000 pixels for web display should be good.

But displays do NOT have a resolution in ppi do they?  They are simply x pixels wide and y pixels high.

Peter

[DarkPenguin]

But displays do NOT have a resolution in ppi do they?  They are simply x pixels wide and y pixels high.

Peter

Yes they do.  Divide it out.  How many pixels per inch?

[Mark D Segal]

But displays do NOT have a resolution in ppi do they?  They are simply x pixels wide and y pixels high.

Peter

By derivation. So for example if your display were 17 inches wide and it displayed 1700 pixels along that width, by derivation its resolution would be 100 PPPI. But essentially, you are correct, it's pixels high by pixels wide.

[Peter S]

Yes they do.  Divide it out.  How many pixels per inch?

Well my iMac 24" works out at 93.6 but that is rather meaningless.  If I save an image at 1 ppi it will still show full screen.  The 72 is only relevant for a printed document.  This link http://www.scantips.com/no72dpi.html  is mainly about scanning and is the thing that got me thinking about the rationale for the 72 in save for web and devices.  I am still no further forward in understanding why the people at Adobe chose this number rather than say 100 or any other number.  Maybe it just doesn't matter.

Peter

[Mike Boden]

Maybe it just doesn't matter.

Peter,

You're right...it doesn't matter. So it's time to move on, because there's no need to spend any more energy on this. But if you're still curious, check out the following link for a little history: 72dpi