How does resolution work.

[ger19]

I'm trying to understand resolution with regard to text size. According to the specs I've read, the monitor on the iMac 24" is 4480 x 2520. When I go into display settings and there is an option to decrease resolution to increase the text size. When I did that, I found that 1600 x 900 results in a nice text size. When I do that, does that mean my entire screen is now a much lower resolution - e.g. for pictures or the background?

I also noticed that the highest resolution in the display settings for text size is 2560 x 1440. That makes me wonder where's the published resolution of 4480 x 2520? Again, is this only for text scaling?

 

[Bigwaff]

Resolution is 4480x2520. Scaling in macOS is 2x. The UI “looks like” 2240x1620 but uses all pixels. Each scaled “virtual” pixel uses 4 real pixels. That is why text looks wicked sharp on retina displays using scaled resolutions.

 

[joevt]

Yes, 1600x900 is a lower resolution but it is not 1600x900. 1600x900 is a Retina mode which means the frame buffer has 3200x1800 pixels which the GPU scales to fill the native resolution of 4480 x 2520.

Retina mode draws text at 200% with respect to each dimension (twice as many pixels in the horizontal and vertical direction) or 400% with respect to area (four times as many pixels total) compared to a display that only has 1600x900 pixels.

In Windows, you would choose a resolution of 4480 x 2520 and use a text scale of 280% (or 784% if it refers to area) to achieve the same text size but with more pixels.

In the past, macOS had an experimental option for arbitrary rendering scaling up to 300% but now Apple only allows 100% (lores, not retina) and 200% (Hi DPI or Retina).

The 2240x1620 retina mode uses all 4480 x 2520 pixels.

2560x1440 might be a retina mode that uses a frame buffer that has 5120 x 2880 pixels. The GPU scales that down to 4480 x 2520.

You might be able to select a non-retina 4480 x 2520 mode which makes everything smaller but doesn't give any more pixels. In Sonoma System Settings -> Displays -> Advanced... -> Show resolutions as list -> Show all resolutions. You'll see new modes that are "(low resolution)" which are non-retina. You'll also see the native resolution of the display 4480 x 2520 which is also non-retina but doesn't have the "(low resolution)" description because it's the max resolution and it would be weird to call that low resolution.

 

[picpicmac]

there is an option to decrease resolution

Sadly, Apple misleads many a newbie by refusing to use a word that today's users are more likely to understand: zoom.

Instead, Apple uses the phrase "looks like", which many people seem to not register.

I found that 1600 x 900 results in a nice text size

In this case, you've 2250/900 = 2.5x, or put another way, you're zooming the user (visual) interface by 250%.


Those of us with poor eyesight will often use 200% ("looks like 2240 x 1260") or 250% ("looks like 1600 x 900") zoom.

 

[picpicmac]

The 2240x1620 retina mode uses all 4480 x 2520 pixels.

The iMac display will always use all physical 4480x2520 picture elements (pixels) on the LCD.

The only difference between the different "looks like" settings is how macOS works internally is adjusting the user interface elements.

 

[curnalpanic]

This question seems to be coming back every so often. Time to make a sticky thread?

 

[kagharaht]

Although I've been a Mac person since 1984 since not working in the industry for years and retired I'm not very verse with this Retina thing and M chips. I'm learning thanks to these threads. As far as performance is concerned, no matter what resolution you choose there is no hit on GPU processing speed right? It doesn't matter anymore?

 

[joevt]

The iMac display will always use all physical 4480x2520 picture elements (pixels) on the LCD.

The only difference between the different "looks like" settings is how macOS works internally is adjusting the user interface elements.

True most modes will be scaled to fill the entire LCD. Modes that don't have the same aspect ratio may have black bars on the top or bottom or the mode may be stretched depending on whether the GPU or the display is doing the scaling and what settings the display has for changing the zoom preference. Mac displays have no settings but third party displays usually do.

There is a difference between the number of pixels used for each mode. Some modes have more or less pixels than other modes.

The iMac uses the frame buffer pixels which can be up to 16K x 16K or more depending on the drivers and hardware. The GPU can scale that up or down to an output resolution which is limited by the connection bandwidth. The display can scale that output resolution up or down to a display resolution limited by the display's resolution and scaler capabilities (if it has a scaler).

For example, there's multiple ways to do 2560x1440 to a 4480x2520 display.
1) 2560x1440 framebuffer and output resolution scaled up to 4480x2520 by the display. An old computer that only supports DisplayPort 1.1 would use this.
2) 2560x1440 framebuffer, scaled up by the GPU to 4480x2520 output resolution, no scaling by the display. This is a low resolution mode.
3) looks like 2560x1440 retina mode 5120x2880 framebuffer scaled down to 4480x2520 by the GPU and output to the display which does no scaling. This is the normal macOS method.
4) looks like 2560x1440 retina mode 5120x2880 framebuffer output as 5120x2880 and scaled down to 4480x2520 by the display. This requires an EDID override to make macOS think the display can use 5120x2880. Many displays don't have a scaler that can scale down like this. My 4K display can take 8K30 input and scale it down to 4K.

 

[ger19]

All interesting but as a practical issue, I look at pictures for my desktop at a site called wallpapers wide and while they can be close, I can never find one that is the max of the iMac or some natural scaled resolution from the max. Simply put, what is the best resolution to pick? Just take the maximum resolution of any picture and let the computer handle it? Is there a certain ratio that would work best?

 

[picpicmac]

Simply put, what is the best resolution to pick?

Are you referring to:
1) the scaling (aka zoom) setting of macOS, or
2) the dimensions of the wallpaper image (jpeg, png?)

 

[ger19]

Are you referring to:
1) the scaling (aka zoom) setting of macOS, or
2) the dimensions of the wallpaper image (jpeg, png?)

2). I understand the text scaling now but am trying to understand the resolution of the wallpaper image.

 

[picpicmac]

the resolution of the wallpaper image.

Use Get Info on whatever image is of interest, to get the dimensions.

 

[ger19]

Use Get Info on whatever image is of interest, to get the dimensions.

I get that, I’m wondering when there’s a choice, like there is on Wallpapers Wide, what resolution should I pick. On my Win machine, with an HD monitor, I selected the one that exactly matched my monitor - 1920 x 1080. I can’t do that with the iMac so I’m wondering if it matters. Should I just select any one that’s high resolution and let the monitor display it as best it can? Does it not really matter? That’s what I’m wondering.

 

[picpicmac]

Should I just select any one that’s high resolution and let the monitor display it as best it can?

I'd just get the highest resolution image that is available. Then in the System Preferences you can tell macOS how you want the image used as the backdrop.