100% zoom is not actual size on external display

[retepnamenot]

Hi,

I've recently switched from a 27" 5K iMac to a 15" MacBook Pro with an external LG 4K display, which I'm using as my primary monitor.

However I have noticed that when the zoom setting is at 100%, pages are not actual size on my 4K display like they were on my old iMac.

If I move the InDesign window to my MacBook display, 100% is actual size, but on the external display it is not (a 210mm (w) page becomes ~180mm), ie. around 85.7% of actual size.

I assume this is due to the difference in DPI between my built-in display and the external display, but can I resolve this issue?

macOS 11.5.2 (20G95)

InDesign 16.3.2

[rob day · Accepted solution]

The 100% view in InDesign is the actual print output size (it’s not the same as Photoshop’s 1:1 100% view)—when you show rulers as Inch units 1 inch should meaure as 1 inch with a physical ruler.

However, that would only work on the main monitor, the MacBook Pro 15" display in your case. InDesign uses the main monitor resolution info coming from the OS to calculate the actual print view.

If you want the external monitor to display 100% as the print size, it could be set via scripting. If you know the LG display’s  pixel per inch resolution, replace the number in the first line with the display’s resolution:

//monitor resolution as pixels per inch
var mppi = 167

app.generalPreferences.customMonitorPpi = mppi;
app.generalPreferences.useCustomMonitorResolution = true;

This resets to the default:

//reset to ID default
app.generalPreferences.useCustomMonitorResolution = false;
app.activeWindow.zoomPercentage = 100;

[retepnamenot]

It's a shame that InDesign doesn't do this automatically depending on the screen it's being used on, but thanks Rob, this works perfectly.

I run the external display at 150% scaling so the effective PPI is 108.79, and everything is now 1:1.

[rob day]

You could file a feature request.

Photoshop has the Actual Size and Print Size views—Actual Size uses the OS reported main monitor resolution, and Print View uses the Units & Rulers Screen Resolution Preference. I set the Screen Resolution Preference to my 2nd monitor resolution, so on the main monitor I can use Actual Size to show the print size and on the 2nd monitor I can use Print Size. Niether view is normally 100% because the image resolution has to also be taken into account, and Photoshop’s 100% magnification is an image to monitor 1:1 ratio.