General question about pixels vs dimensions

[80sTherapy]

Could someone explain to me how two identical icons with the same resolution - say 256x256 pixels, can have different sizes on screen? I am not understanding how some app icons on macOS appear larger than other when the resolutions are identical.

Thanks in advance.

[v_kyr]

Usually they shouldn't, do you have any examples which do prove and demonstrate this to share here?

[thomaso]

33 minutes ago, 80sTherapy said:

same resolution - say 256x256 pixels

Actually the size/dimensions is not resolution. While 256x256 pixels are absolute values, the resolution concerns the displayed size of 1 pixel which also depends possibly (not necessarily) on a setting within the image but definitely on the monitor hardware and its GPU setting. A monitor with higher resolution has a higher pixel density and its pixels are smaller. (compare: LED billboard, TV, laptop, smart watch or phone would show 256 pixels in quite different physical dimension, ranging from e.g. one metre to just a few millimetres). (see also https://www.howtogeek.com/743152/what-is-a-retina-display/)

Thus the number of pixels is unambiguous while a DPI setting ('the resolution') in a saved image is rather irrelevant because lossless flexible … while a document's resolution matters when working within the document (e.g. when rasterizing).

[80sTherapy]

15 minutes ago, v_kyr said:

Usually they shouldn't, do you have any examples which do prove and demonstrate this to share here?

Sure, here is how the icon for the app DisplayBuddy looks on my MacBook Pro. Yet, it is 256x256 just like the icon for DiskDrill. 

 

 

[80sTherapy]

19 minutes ago, thomaso said:

Actually the size/dimensions is not resolution. While 256x256 pixels are absolute values, the resolution concerns the displayed size of 1 pixel which also depends possibly (not necessarily) on a setting within the image but definitely on the monitor hardware and its GPU setting. A monitor with higher resolution has a higher pixel density and its pixels are smaller. (compare: LED billboard, TV, laptop, smart watch or phone would show 256 pixels in quite different physical dimension, ranging from e.g. one metre to just a few millimetres). (see also https://www.howtogeek.com/743152/what-is-a-retina-display/)

Thus the number of pixels is unambiguous while a DPI setting ('the resolution') in a saved image is rather irrelevant because lossless flexible … while a document's resolution matters when working within the document (e.g. when rasterizing).

I knew that pixel density affected size, and it makes sense that things don't look the same on different displays, but I'm talking about the same display (my MacBook Pro's). Probably something about the image files themselves?  

[markw]

Could it be as simple as the DisplayBuddy icon is filling all the available space of the 256px square right up to the edges, while DiscDrill is only using the central portion of the square with it’s graphics?
What do the icons look like opened in Preview?

[thomaso]

18 minutes ago, 80sTherapy said:

Probably something about the image files themselves?  

Apart from the mentioned DPI setting that can be saved with an image file, the Apple .icns file format is special and can confuse with various sizes contained in 1 file. If you open such a file in Apple's Preview.app it will show more of its contents than possibly Affinity does.

https://docs.fileformat.com/system/icns/

https://developer.apple.com/design/human-interface-guidelines/app-icons#App-icon-sizes

https://developer.apple.com/documentation/Xcode/configuring-your-app-icon

Attached an icon copied from a Finder Info window -> opened in Preview via File > 'new from clipboard'. Use Preview's sidebar to scroll through its various sizes. apub.icns.zip

[v_kyr]

Well an ICNS file is a macOS icon resource file (mostly generated/used via XCode) which usually holds several icon sizes: 16x16, 32x32, 48x48, 128x128, 256x256, 512x512, and 1024x1024 pixels. - See also for example ...

• https://www.lifewire.com/icns-file-2621787
• How to create an .icns macOS app icon

... or the links thomaso showed above. - Further what markw suggested above might be valid here, some third-party macOS software icons do not fully make use of a full drawn/filled 256x256 px area, meaning the rest might be just filled with surrounding transparency here. - Thus you have to check them individually by opening and inspecting them in APh, GraphicsConverter, Preview.app ... etc.

 

[80sTherapy]

27 minutes ago, markw said:

Could it be as simple as the DisplayBuddy icon is filling all the available space of the 256px square right up to the edges, while DiscDrill is only using the central portion of the square with it’s graphics?
What do the icons look like opened in Preview?

Oh, yeah. The relative sizes are the same in Preview, but in Designer in a 256x256 square, the DisplayBuddy actual icon definitely looks larger. I think that is it.  

[80sTherapy]

20 minutes ago, v_kyr said:

Well an ICNS file is a macOS icon resource file (mostly generated/used via XCode) which usually holds several icon sizes: 16x16, 32x32, 48x48, 128x128, 256x256, 512x512, and 1024x1024 pixels. - See also for example ...

• https://www.lifewire.com/icns-file-2621787
• How to create an .icns macOS app icon

... or the links thomaso showed above. - Further what markw suggested above might be valid here, some third-party macOS software icons do not fully make use of a full drawn/filled 256x256 px area, meaning the rest might be just filled with surrounding transparency here. - Thus you have to check them individually by opening and inspecting them in APh, GraphicsConverter, Preview.app ... etc.

 

Yep, I think that was it. Same overall size, but the actual icon is bigger.