canvas/image size wrong??

[Mobos]

Hi forum!

A funny (NOT ) thing happened .... my image size in photoshop doesn't match reality! It's difficult explaining, but if you take a look at the screenshot you'll see what I mean ....

I have a new computer and compared all photoshop settings with the one on my 'old' computer and they are all the same.

[D Fosse · Accepted solution]

Mobos  wrote

I have a new computer

...with a retina display! Read a little about how screen resolution affects physical size on screen.

Photoshop is in fact right. It always displays 100% as one image pixel represented by one screen pixel. That's the correct way to do it; the very definition of 100% in a raster image editor. But you can set it to View > 200%, and you get the same size if that's what you want.

It is the native Mac OS apps that compensate for the retina display by scaling images up. One image pixel is now represented by no less than four screen pixels. They can do that - they have no obligation to display accurately.

They do this so that images will display at roughly the size people are used to from traditional displays - in order to avoid complaints like yours here.

Photoshop is a professional-grade image editor and has to do it right.

[Mobos]

Thanks D Fosse for your answer!!

[Norman Sanders]

An alternate work around passed along to me by gener7​

1. Quit the app if it's open.
2. In the Finder, choose Applications folder
3. In the Applications folder that opens, choose the Adobe Photoshop CC 2018 folder and inside that folder click the Adobe Photoshop CC 2018.app icon so it's highlighted. 
   
4. Choose Get Info from the File menu.
5. Place a checkmark next to "Open in Low Resolution"
   

[Mobos]

Hi Norman,

Great tip, thanks!!

But ..... I now thinking .... as probably more and more people are going to watch on screens with a higher dpi, it's better to design on 150/200 dpi?? What is your opinion about that?

[Norman Sanders]

Sorry, Mobos, but am not qualified to offer an informed opinion on that.

[D Fosse]

A pixel is still a pixel, nothing has changed there. You can forget about ppi - that is still as irrelevant on screen as it has ever been. Ppi is a print parameter.

What has changed is how those pixels are displayed on high resolution displays: much smaller. When you have more screen pixels, they get smaller to fit more of them in. So the image gets smaller.

You have to understand that this is a display property - it has nothing to do with the file!

This is what the Mac OS viewers and web browsers compensate for, by scaling up so that four screen pixels are used to represent each image pixel. Thus the image is displayed at the size people are used to. This is a workaround, a hack, nothing more. What it does, is to turn your high resolution display into a perfectly ordinary low resolution one.

When the day comes that we all have high resolution displays, this workaround is no longer needed. Then, only then, can you start designing with more pixels.

[Mobos]

Thanks D Fosse for your explanation! So I stay working with 72 dpi ...

[D Fosse]

If you're working for screen / web, you don't work with any ppi. It doesn't matter, it's moot and irrelevant. You only work with pixels - so many pixels wide by so many pixels high.

This image is 650 pixels wide. The top one is 72 ppi, the second one is 300 ppi, and the third one Is no less than 2500 ppi. They're all the same on screen:

The on-screen scaling that Safari does when it detects a high-resolution display is something else. It doesn't scale the image as such - it lowers the resolution of your display. It lowers the screen pixel count by a linear factor of 2. The image stays exactly the same.

Pixels per inch (ppi) matters only for print. On screen, the image pixels align to the screen pixel grid, whatever that is. On paper there is no such pixel grid, so one has to be invented. That's what ppi is.

And BTW, it is pixels per inch (ppi), not dots per inch (dpi). Correct terminology aids understanding.

[Mobos]

Thanks D Fosse!!