is the defaul display for a 27" iMac meant to be 5120×2880?

[milomak]

so it seems even in default I see 3840 x 2160

what could be causing this?

 

[pigoo3]

But what's the point of the "5120-by-2880" resolution screen if you can't use it at that resolution?

Retina displays are supposed to be clearer & sharper than older non-retina displays. How this is done is more densely packed pixels. Retina displays have 2 pixels where normally there is 1 pixel in non-retina displays (length & height). This is called "pixel doubling".

- With a non-retina 27" display…native resolution = 2560 x 1440.
- With a retina 27" display…native resolution = 5120 x 2880.

Notice how the pixels values are exactly double in the retina 27" display.

There are actually 4x the number of pixels on a retina display (when you take into account width & height of the display):

- 2560 x 1440 = 3,686,400 pixels
- 5120 x 2880 = 14,745,600 pixels (4x pixels of non-retina 27" display)

With a 27" retina display or a non-retina 27" display...you still have the same exact "screen real estate" (can see the same amount of stuff on the display). But with the retina display…it is clearer & sharper.

You can run a 27" retina iMac at an actual 5120 x 2880 resolution. At this resolution it will not have the clearer & sharper qualities when running at the native retina resolution…and at a 5120 x 2880 non-retina resolution…everything will be very small.

Here's a example what what the full non-retina 5120 x 2880 resolution looks like on a 27" retina iMac. Notice how small the icons are in the dock…and notice how small the menu bar headings & icons are:

- Nick

 

[usagora]

Thanks, Nick. That was a very clear explanation. I actually have a late 2012 iMac. I ain't got no double pixels

 

[lclev]

I just went back and looked through all the post and checked out all the links. I think I might have missed what the OP is trying to ask. Correct me if I am wrong.

The OP - milomak - has a 5K iMac that is only able to provide a resolution of 3840 x 2160 if the iMac is to work correctly. If the resolutions is changed by selecting scaled and picking a difference resolution (should I assume the 5120 x 2880 or is that even an option?) then moving a window on the screen causes weird horizontal lines to appear in the moving window rendering it's contents unreadable. This is not normal if what I am understanding is happening.

The OP should be able to select 5120 x 2880 and while it will make everything really tiny, moving a window around should not produce horizontal lines of colors in that window making it unreadable.

Am I understanding this correctly?

Lisa

 

[Ember1205]

Retina displays are supposed to be clearer & sharper than older non-retina displays. How this is done is more densely packed pixels. Retina displays have 2 pixels where normally there is 1 pixel in non-retina displays (length & height). This is called "pixel doubling".

- With a non-retina 27" display…native resolution = 2560 x 1440.
- With a retina 27" display…native resolution = 5120 x 2880.

Notice how the pixels values are exactly double in the retina 27" display.

There are actually 4x the number of pixels on a retina display (when you take into account width & height of the display):

- 2560 x 1440 = 3,686,400 pixels
- 5120 x 2880 = 14,745,600 pixels (4x pixels of non-retina 27" display)

With a 27" retina display or a non-retina 27" display...you still have the same exact "screen real estate" (can see the same amount of stuff on the display). But with the retina display…it is clearer & sharper.

You can run a 27" retina iMac at an actual 5120 x 2880 resolution. At this resolution it will not have the clearer & sharper qualities when running at the native retina resolution…and at a 5120 x 2880 non-retina resolution…everything will be very small.

Here's a example what what the full non-retina 5120 x 2880 resolution looks like on a 27" retina iMac. Notice how small the icons are in the dock…and notice how small the menu bar headings & icons are:

- Nick

Retina is a "marketing term" that Apple came up with that roughly means "at least" 300 pixels per inch and has absolutely NOTHING to do with resolution number - it is purely related to the pixel size itself (being small enough to allow you to cram 300 of them side-by-side in an inch or less of space). You can't have 5120x2880 resolution on a 27" monitor WITHOUT having Retina resolution.

Your screen cap is what my system looks like because I'm running that resolution - that is what it looks like to run the monitor at native resolution and take advantage of the "Retina" aspect.

 

[milomak]

I just went back and looked through all the post and checked out all the links. I think I might have missed what the OP is trying to ask. Correct me if I am wrong.

The OP - milomak - has a 5K iMac that is only able to provide a resolution of 3840 x 2160 if the iMac is to work correctly. If the resolutions is changed by selecting scaled and picking a difference resolution (should I assume the 5120 x 2880 or is that even an option?) then moving a window on the screen causes weird horizontal lines to appear in the moving window rendering it's contents unreadable. This is not normal if what I am understanding is happening.

The OP should be able to select 5120 x 2880 and while it will make everything really tiny, moving a window around should not produce horizontal lines of colors in that window making it unreadable.

Am I understanding this correctly?

Lisa

you've nailed it

 

[chscag]

@milomak:

If that's what is happening, make an appointment with your local Apple Store genius bar and have them look at it. It could be a graphics chipset problem or something else. Is your iMac still covered by the Apple warranty?

 

[lclev]

Yes unfortunately, it needs to go back to Apple. Make a really good backup with either Carbon Copy Cloner or SuperDuper and call Apple. That is a graphics card issue and you have proof of a problem as you can reproduce it - and you have a video!

Lisa

 

[craigvolpe]

What exactly are you trying to do? There is no way you're going to be able to view your iMac at 5120×2880 as the characters on the screen would be too small. (unless you have super eyesight)

What resolution are you trying to scale up to? You should be viewing your iMac at 2560 x 1440 which is the correct resolution for that 27" screen. And, did you read the Apple article about retina screens?

What is your source for this? My understanding is that a 5K iMac display works by always maintaining 5120x2880 resolution, but uses display scaling (not actually resolution scaling) to change the appearance of things on screen to simulate the scale of different resolutions. Despite Apple using the misleading term "resolution scaling" when discussing retina displays, I can't find any sources saying anything about pixel doubling or displaying at 2560x1440 (display scaling can be used to scale things to the same relative size as a 27" 2560x1440 screen for example, but it's not actually displaying at 2560x1440). The display setting even prefaces different scaling settings with "looks like", suggesting it's changing relative sizes and not actually changing the screen resolution. Besides not being able to find any sources stating retina screens are actually displaying at different resolutions, it's easy to test it yourself if you have a retina display.

To test how scaling works on Retina displays, all you need is an image that has the same dimensions as the native screen resolution of the Retina display (in my case 5120x2880). Set the image as your background wallpaper. Now go into display settings and try all the scaling options. While windows and text change how much space they take up on the screen, the wallpaper in the background stays the exact same with extremely fine details. If it was actually scaling the resolution, that background image would look much less detailed when setting display scaling to the largest text option. It's just unfortunate that Apple chose to use the term "resolution scaling" in the setting menu rather than a more accurate term like "display scaling".

I suppose it's possible I'm wrong about this, but it sure doesn't seem like it. Please provide sources or rationale against my arguments if you think I am.

 

[craigvolpe]

Kind of reinforces my thinking...

The display's resolution is "x" always and forever. You can scale that to make it seem better or worse, but the monitor / display has a specific resolution it's capable of. The scaling affects the size of a pixel, but at "default resolution", the pixel size is what it is and everything else is related to how MANY pixels get used to draw something that determine actual size on the screen and how easily it's viewed at any particular distance.

That's how Apple seems to handle displays these days - always displayed at native resolution but scaling display elements to simulate relative sizes of other resolutions. With external displays, you can actually change the resolution, but it looks horrible on an LCD display because it's using interpolation to display that many pixels. Only the old CRT displays are any good at actual resolution scaling. Wikipedia does a good job explaining it here: https://en.wikipedia.org/wiki/Native_resolution

 

[Ember1205]

This is how I've thought of it as well. With a Windows machine, you ACTUALLY change display resolution and that typically mucks with the refresh frequency. In order to change the settings, the display has to be blanked and then re-enabled. And, with the change in refresh, the image is never positioned in exactly the same place and often times the image will have "jitter" to it. This sort of stuff never happens on the iMac Retina that I have.

 

[milomak]

Sent it in and looks most likely it will be replaced as it had a SMC error and the fan was running higher than it should

 

[lclev]

Excellent! There was obviously a problem with the video. As for the fan - nice that they caught that. So do you have extended apple care???

Lisa

 

[craigvolpe]

I hope they're able to fix your computer, milomak!

 

[milomak]

Back and working as it should

 

[milomak]

actually just seen today that this is a refind issue

as soon as i reinstalled refind the same issue returned. solved simply by changing the startup device to the osx drive

 

[lclev]

Really?? What is Refind and what does it do? Just curious.

Lisa

 

[chscag]

Really?? What is Refind and what does it do? Just curious.

Lisa

It's a boot menu to setup dual booting between OS X and Linux or Windows. Not recommended as it can cause problems not only with normal operation but as the OP found out, it sometimes can change the display resolution. However, when it's working OK, it shows a nice boot menu and easy switching between operating systems.

This is another case where the OP wasn't telling us the complete story about his problem....

 

[pm-r]

This is another case where the OP wasn't telling us the complete story about his problem....

Hmmm…??? And I wonder if Apple caught on to that…???

 

[lclev]

Okay thanks chscag. I learned something new. And yes, it is always nice to have a full picture when trying to figure out a problem. But given they ran diagnostics on the iMac and it showed SMC and fan control issues sounds like there were problems anyway.

And now we know this Refind app can create unusual problems. I am wondering how it caused the video issues that were shown in the video the OP posted. Very weird.

Lisa