Apples retina scaled vs native - which is sharper?

[VirtualRain]

I suspect many people in this forum probably have little experience but I'm curious if anyone has any knowledge of this...

Retina displays obviously look ideal at "Best for Retina" which is where everything is rendered at double resolution. In my experience, if you choose a scaled resolution on a retina display it's just as sharp. I wonder if scaled retina resolutions are sharper than native or vice-versa?

For example, if you run a 24" 4K display at "best for retina" it will offer a desktop resolution equivalent to 1920x1080 but it's incredibly sharp. If you scale it to something like 3000x1600 (somewhere between "best" and native) it will still look reasonably sharp on a retina display as Apple scaling algorithim will first render the display at 6000x3200 and then downsample it to 3840x2160 resulting in very sharp output. So in effect, you're using 3840x2160 pixels to render a 3000x1600 image.

Now my question is... is such a display that uses 3840x2160 pixels to render a 3000x1600 (first doubled to 6000x3200 and then down sampled to 3840x2160) image sharper than a 3000x1600 native display would be... or worse?

EDIT: at the risk of answering my own question, I'm guessing the answer is that retina scaled is better than native. More pixels (with the benefit of Apple's scaling algorithm) are always better than less. My sense is that my 13" rMBP at a scaled resolution of 1680x1440 looks much better than a native 13" 1680x1440 display.

 

[VirtualRain]

In case anyone else cares about this, here's another thread that dives into This topic... https://forums.macrumors.com/showthread.php/showthread.php?t=1668105

The last post seems to concur with what I believe that in terms of sharpness you have...
"Best for Retina" > Apple's Scaling Algorithm on Retina > Native Resolution

If you're wondering why I care, it's because I've been grappling with what size of 4K display(s) to go with. Since I seem to prefer my UI and text at 150 PPI, I could go for a 30" 4K2K display (4096x2160) and run it at native resolution. Or, I could get a pair of 24" 4K displays (each 3840x2160) and run them at a HiDPI scaled resolution of around 3000x1600 (effective) for the same PPI.

It seems the wiser choice is the pair of 24" 4K displays displays rather than the larger 4K2K option...
- Running in HiDPI they should be sharper than the native res display
- They will offer more desktop real-estate (6000x1600 effective vs 4096x2160)
- A pair of displays is nice from a usability perspective
- A pair of 24" 4K displays may be cheaper than a 30" single panel

Is there anything I'm overlooking?

 

[goMac]

For example, if you run a 24" 4K display at "best for retina" it will offer a desktop resolution equivalent to 1920x1080 but it's incredibly sharp. If you scale it to something like 3000x1600 (somewhere between "best" and native) it will still look reasonably sharp on a retina display as Apple scaling algorithim will first render the display at 6000x3200 and then downsample it to 3840x2160 resulting in very sharp output. So in effect, you're using 3840x2160 pixels to render a 3000x1600 image.

Have you verified this? I don't know of any Apple device that renders like that. The iPhone 6 Plus is the only I know of that will over render and then downsample, but it doesn't quite work like that.

As far as I know, if you pick 3000x1600, it will render at 3840x2160, using some geometric scaling algorithms to do the interpolation. You're just altering the scale of things on screen, not introducing an intermediate frame buffer.

The 6 Plus is a little different because it's pretending it has a 3x screen even though it only has a 2.5x-ish screen. So it's rendering at 3x because that's what it claims to the user and the developer of the app is it's resolution, and then downsampling. A Mac app running at 3000x1600 knows it's running at 3000x1600, so I don't think the same algorithm is used.

 

[VirtualRain]

Have you verified this? I don't know of any Apple device that renders like that. The iPhone 6 Plus is the only I know of that will over render and then downsample, but it doesn't quite work like that.

As far as I know, if you pick 3000x1600, it will render at 3840x2160, using some geometric scaling algorithms to do the interpolation. You're just altering the scale of things on screen, not introducing an intermediate frame buffer.

The 6 Plus is a little different because it's pretending it has a 3x screen even though it only has a 2.5x-ish screen. So it's rendering at 3x because that's what it claims to the user and the developer of the app is it's resolution, and then downsampling. A Mac app running at 3000x1600 knows it's running at 3000x1600, so I don't think the same algorithm is used.

AnandTech has discussed this topic a few times, here's a good and relevant article... http://www.anandtech.com/show/7847/improving-the-state-of-4k-display-support-under-os-x

I've verified it myself with my rMBP... If I do a screen cap of the desktop with my rMBP set at a scaled resolution of 1680x1050 (effective) on it's 2560x1600 screen, I get a file that is 3360x2100.

This is why Apple and retina screens are so kick-ass... you don't need to run them at 1/2 native res to get the benefits of the added sharpness. MY rMBP look sharper than any other notebook out there even at a scaled resolution.

 

[goMac]

AnandTech has discussed this topic a few times, here's a good and relevant article... http://www.anandtech.com/show/7847/improving-the-state-of-4k-display-support-under-os-x

I've verified it myself with my rMBP... If I do a screen cap of the desktop with my rMBP set at a scaled resolution of 1680x1050 (effective) on it's 2560x1600 screen, I get a file that is 3360x2100.

This is why Apple and retina screens are so kick-ass... you don't need to run them at 1/2 native res to get the benefits of the added sharpness. MY rMBP look sharper than any other notebook out there even at a scaled resolution.

Interesting. No wonder the graphics card starts to chug at those resolutions.

To answer your question, I've been told Apple's scaling algorithms are very good, but they still aren't going to look as nice as that output at native. There is going to be slight blurriness as it does the point to pixel conversion.

If I had time I'd draw a bunch of Photoshop stuff to explain, but maybe I can do some text.

If you have this:
1 1 1
0 0 0
0 0 0

And you need to scale it to a 4x4 grid, how do you do that? Neither:
1 1 1 1
0 0 0 0
0 0 0 0
0 0 0 0

or

1 1 1 1
1 1 1 1
0 0 0 0
0 0 0 0

are quite right.

Basically, if your rendering resolution and your actual display resolution aren't multiples of each other, your output will degrade. In your example, even the up-scaled 6000x3200 buffer is not a multiple of 3840x2160, so your output will degrade when it actually goes to draw that on the physical screen.

I'm assuming this factored into Apple's decision to go 5k. 5120x2880 is a multiple of 2560x1440, so they can reproduce the previous screen area with no artifacting.

 

[fisha]

Could you not have:

1111
1010
0000
0000

but you are right, you can't do it perfectly ... there will always be a trade-off.

 

[VirtualRain]

To answer your question, I've been told Apple's scaling algorithms are very good, but they still aren't going to look as nice as that output at native. There is going to be slight blurriness as it does the point to pixel conversion.

Do you have any links to any analysis? Everything I've seen/read says that Apples scaling is as sharp or sharper than native.

BTW, your exercise neglected the two times upscaling before mapping to native resolution and pixels are not 0 or 1... adjacent pixels can help smooth edges with dithering and font smoothing technology which looks much better on higher density displays.

Look at the difference in the "a" in these two images. Even if you offered pixel density half way between the two, you'd get a better looking "a" than the native one.

 

[goMac]

Could you not have:

1111
1010
0000
0000

but you are right, you can't do it perfectly ... there will always be a trade-off.

Yes, you could, but that's still a quality decrease. It's workable though.

Do you have any links to any analysis? Everything I've seen/read says that Apples scaling is as sharp or sharper than native.

BTW, your exercise neglected the two times upscaling before mapping to native resolution and pixels are not 0 or 1... adjacent pixels can help smooth edges with dithering and font smoothing technology which looks much better on higher density displays.

Look at the difference in the "a" in these two images. Even if you offered pixel density half way between the two, you'd get a better looking "a" than the native one.

Image

It can't be sharper than native. You simply can't pretend to have output pixels you don't have.

Even if I follow this double exercise where i want to display a 3x3 pattern on a 2x2 display...

1 1 1
0 0 0
0 0 0

To:

1 1 1 1 1 1
1 1 1 1 1 1
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0

Now downsample that back to 4x4 without any quality loss and maintaining the same sharpness as a native 4x4 output.

Can't be done unless the resolutions are multiples of each other.

 

[VirtualRain]

Yes, you could, but that's still a quality decrease. It's workable though.







It can't be sharper than native. You simply can't pretend to have output pixels you don't have.



Even if I follow this double exercise where i want to display a 3x3 pattern on a 2x2 display...



1 1 1

0 0 0

0 0 0



To:



1 1 1 1 1 1

1 1 1 1 1 1

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0



Now downsample that back to 4x4 without any quality loss and maintaining the same sharpness as a native 4x4 output.



Can't be done unless the resolutions are multiples of each other.

I'm no expert, but I think you may be over simplifying to such an extent that you can only prove your outcome.

As I said earlier, rendering even black text on a white background is not limited to all white pixels (0) or all black pixels (1)... font smoothing, blending, anti-aliasing and other interpolation technologies will make things look a lot smoother by introducing shades of grey in adjacent pixels. And no modern font maps directly to pixels... All systems use font smoothing techniques... And I believe the more pixels you have the better the outcome.

We need some real screen shot comparisons.