I don't understand the iMac resolution

jonatious

macrumors member
Original poster
Sep 29, 2016
86
33
So this is my first iMac and yes it is 5k. But Apple mentions that It looks best at half the resolution, lets say 2.5k, downscaling it by 2. So I don't get how 4 pixels forced to display the same color of a dot is better than 4 pixel being able to display 4 variants of the same color for the dot? Isn't that the whole point of high res displays?

The second question is what happens to my media at native 2.5k resolution? My desk background image? The videos I watch and the images/photos I edit? Are they all downscaled by 2?

I am pretty sure there is a valid reason for this. But I am just not getting it. Any insight is appreciated :)

For people who don't get it, the iMac ships and runs with 2560x1440 resolution by default and not the 5k resolution of the display
 

SkiHound2

macrumors regular
Jul 15, 2018
231
163
5k is basically 2 x the 2560 x 1440 resolution in both dimensions. But think about how small text would be if displayed at that resolution on a 27" monitor. I'm writing this on a 2560 x 1440 monitor and the fonts and icons are about the right size for me. The 27" iMac monitor displays text and icons at the same size, but with with 4 pixels for every 1 displayed by my monitor. Just looks nicer and sharper. Because it's doubled it scales easily. The 4k 21.5" has pretty much the same screen quality, but 2560 x 1440 would make things too small for most of us on a 27" screen. 4k is essentially a doubling of 1080p in both dimensions (4 x the pixels). Scaling at resolutions that aren't native to the monitor (e.g, 4 k on a 5k monitor) can really tax the gpu and often doesn't look very good.
 

Zandros

macrumors regular
Sep 1, 2010
114
62
No, the 27" iMac ships with a Hi-DPI mode setting that makes things look the same size as a traditional 2560x1440 monitor. Applications that are not aware of this will indeed be rendered by using four pixels of the same colour on the display for each pixel the app thinks it's using which looks kind of bad (but makes the app an usable size at least), but nowadays almost everything is aware and will use the full resolution available to them.

How videos and photos are rendered by default is up to the app (I think Preview will pixel-double everything when you tell it to zoom to native resolution, which is kind of weird), but be assured you are viewing all the data available.

With some trickery you can set the display to a 5160x2880 non-Hi-DPI mode, but everything will look really small.
 

scottrichardson

macrumors 6502
Jul 10, 2007
498
5
Ulladulla, NSW Australia
The whole hi-DPI thing can be confusing at first.

Allow me to help.

Think of there being two actual resolutions at play now. One is the pixel resolution, and one is the logical or perceived resolution measures in “points”.

So your iMac has a pixel resolution of 5120 x 2880 pixels.

And a logical point resolution is 2560 x 1440.

It renders elements on screen the same physical size as a non retina 2560 x 1440 monitor but with four times the density of pixels.

So the user interface elements and text will be twice as sharp, as there’s now four pixels available in the space where there would normally be one pixel.

Images or photos viewed at 100% will now occupy a quarter of the desktop space they used to.

So interface designers like myself now need to create artwork assets and images that are double the pixel count in both dimensions to ensure they take up the right amount of space when viewed at 100% on retina displays. So an icon that I want to “look like” a 100 x 100 pixel icon needs to be created at 200 x 200 pixels in photoshop. That 200 x 200 icon will take up the “space” of a 100 x 100 point icon.
 

macduke

macrumors G4
Jun 27, 2007
11,080
14,906
Central U.S.
All that is happening is that it makes everything look sharper at the same UI scale. Just like the iPhone and iPad. It’s basically a retina display.

Otherwise if you run at 1:1 5K scale your windows and text will be very small for only a 27” display.
 

TheyCallMeBT

macrumors regular
Jan 9, 2013
115
14
I'll be going from a non retina 27" iMac to the 2019 27". When using Photoshop and setting up a canvas-- how does it appear? Like say I want to make an icon for a website at 250 x 250 px, 72 dpi. Is it going to appear like the 2560 x 1440 "logical" resolution, or is it going to be the actual pixel count at 5K?
 

Zdigital2015

macrumors 68030
Jul 14, 2015
2,643
3,172
East Coast, United States
So what is the best display setting to see the best images on a 5k retina iMac?

"Best for Display" or 2560X1440, which will be the most crisp resolution as it is @2x of 5120x2880, meaning divisible by two (2).
[doublepost=1556494733][/doublepost]
I'll be going from a non retina 27" iMac to the 2019 27". When using Photoshop and setting up a canvas-- how does it appear? Like say I want to make an icon for a website at 250 x 250 px, 72 dpi. Is it going to appear like the 2560 x 1440 "logical" resolution, or is it going to be the actual pixel count at 5K?
You have to choose between Points or Pixels, each pixel is two points when running @2x Retina resolution.
 

Fishrrman

macrumors Core
Feb 20, 2009
20,186
7,119
Zdigital wrote:
"You have to choose between Points or Pixels, each pixel is two points when running @2x Retina resolution."

Is not "retina" actually 2x2 ?
Double the pixels vertically, AND double horizontally?

Seems to me that "looks like" 2560x1440 would use 4 pixels for each "virtual pixel"...
 

Zdigital2015

macrumors 68030
Jul 14, 2015
2,643
3,172
East Coast, United States

Zdigital wrote:
"You have to choose between Points or Pixels, each pixel is two points when running @2x Retina resolution."

Is not "retina" actually 2x2 ?
Double the pixels vertically, AND double horizontally?

Seems to me that "looks like" 2560x1440 would use 4 pixels for each "virtual pixel"...

Yes, I had a complete brain fart on that one...I was watching TV and answered in haste.

1 point = 2pixels, so a 1 point x1 point square on a Retina = 2 pixels x 2pixels. You are both correct, my apologies.

Here is a post that describes things in more detail for those that wish to explore the subject further - https://medium.com/@pnowelldesign/pixel-density-demystified-a4db63ba2922
 
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