100% vs Print Size vs Actual size : something stays unclear

[mbrch]

Dear all, 

When the year starts, I used to teach my students how to properly preview a photoshop document :

- that will be used on screen (View > 100%)

- that will be printed (View > Print size)

I also teach them how to properly set Preferences > Units and Rulers > Screen resolution, to their screen ppi, in order to get accurate display size of their printed document on their own screen.

But then I see that function I never noticed before View > Actual size.

My question is simple : What is it for ?

To that day, Help webpages, Forums, and online experts chat ("not trained for this")  were not able to answer that question.

My question is not just out of curiosity. Because on some of my students Macs, the View>Print size setting does not give accurate display after proper ppi setting in preferences, but View>Actual size does.

Why ?

All the best,

M

[rob day · Accepted solution]

Actual Size considers your main monitor’s resolution and displays actual dimensions—if you show rulers and take a physical measurement 1" will equal 1".

Print Size uses your Preferences>Units & Rulers>Screen Resolution setting. If that setting is the same as your main monitor’s resolution, Actual Size and Print Size should be the same.

[rachaelk11682490]

Sorry to bump an old thread and thanks for the info. Where does "acutal" size get the monitor resolution and physical size information? I set my Screen Resolution based on dividing my display's horizontal pixels by the measured width and now it is spot on when I use Print Size. Actual Size is a couple percent too small though. Kind of an esoteric question, I guess, since Print Size works perfectly well, but I am curious where PS gets the pixels/inch number from and why it's wrong. Thanks!

[TheDigitalDog]

From the preferences of which you must enter the correct display resolution. 

Measure the width of your display and divide that by the number of pixels its displaying.

For example, on my NEC 3090, the width is 25.25 inches. Its resolution is 2560x1690. 2560/25.25=101.4 PPI.
On my NEC PA271Q, the width is 23.5 inches. Its resolution is 2560x1440. 2560/23.5=109PPI.

Then enter the value into the preferences. Of course, you need to use the Print Size option in the View menu.

[rachaelk11682490]

Yes, that is how I got my setting for screen resolution, as I said. I measured, did the math, and entered the numbers. The print size zoom is now correct. My question was why isn't the "actual size" function also correct? The two should be the same when screen resolution is correctly set, no?

[TheDigitalDog]

It's correct for me. Make a document that is 3x3 inches. Set print size option in view menu.Ruler shows it is exactly 3 inches. 

[rachaelk11682490]

It's not for me. I've got two different 8x10 images open on my screen. When I set zoom to print size, it goes to 36.33% and exactly matches a ruler held up to the screen. But when I use the actual size zoom, it goes to 36% and is noticeably smaller than the ruler. I'm on a Windows system, which I'm sure is somehow at the root of the problem, but nevertheless, "Actual Size" isn't actually actual size. "Print Size" is correct, after I set the screen resolution based on measuring the actual screen.

[TheDigitalDog]

---

@rachaelk11682490 wrote:

It's not for me. I've got two different 8x10 images open on my screen. When I set zoom to print size, it goes to 36.33% and exactly matches a ruler held up to the screen. But when I use the actual size zoom, it goes to 36% and is noticeably smaller than the ruler. 

---

It doesn't matter what zoom ratio it goes to. You need to use Print Size. And as you see, the size is correct. 

[gener7]

In Photoshop Preferences > Units & Rulers

This sets it up for New Documents in Photoshop, but if you open a document from the web, it may well be 72 ppi (Old 1984 Mac screen resolution) in the Print Resolution field and not the typical offset press 300 ppi.

Now the  114 screen resolution will make sure the onscreen inches on my laptop match physical inches as in a ruler. It has no effect on the document print ppi setting. Actual Size and Print Size should be the same zoom level. You may have to switch between the two to get them to match up.

[rachaelk11682490]

They're just not the same for me. My "Actual Size" zoom is noticeably smaller than reality. When I hold a ruler up to the ruler in PS, after zooming to "Actual Size" the on-screen ruler is off by a percent or so. When I zoom to "Print Size", after correctly setting my screen resolution, the on-screen ruler exactly matches a physical ruler held up to it. No amount of switching zoom levels changes that.

[TheDigitalDog]

The two options produce identical size/results for me. IF you want the size on-screen to match the document, and you've provided the correct screen resolution as outlined, that's what you get with Print Size (and for me, Actual Size). It works for you too if you use Print Size so, use that. 

[rachaelk11682490]

I will totally use Print Size and be happy with it. I was just curious where PS got its information from for the Actual Size calculation. I'm guessing there is something the operating system (Windows 10) is relaying to PS about the monitor that is incorrect.  While I can absoutely use Print Size and be happy with it, my unquenchable desire to understand and fix things drives me to want to know how Actual Size works, that's all.

[TheDigitalDog]

I'm on a Mac so I can not comment on Windows. Gener7 reported what I see. 

[gener7]

That is odd. On my Mac, a file zooms to 32.57% in both Print and Actual Size, but the same file is 32.57% zoom in Print Size and 28.57% zoom in Actual Size in Windows 10 Photoshop.

At this time I don't have an answer because I use Photoshop on the Mac, so I don't know where Photoshop in Windows in getting that reference.

I'll report back if I find out.

[gener7]

It's almost like Actual Size assumes a screen resolution of 100 ppi, because setting that in Units and Rulers gives me the same 28.57%  in Print and Actual. Don't know how it acts on your rig.

In short, Actual Size is hard wired to 100 ppi on my W10 rig, while Print Size will pick off the screen resolution I entered.

I suspect it is a bug on the Windows version, but can't call it yet.

Gene

[rob day]

Kind of an esoteric question, I guess, since Print Size works perfectly well, but I am curious where PS gets the pixels/inch number from and why it's wrong. Thanks!

InDesign’s 100% view is the print output size, and its scripting API lets you get the main monitor’s resolution used to calculate the 100% view. So rather than measuring you could run this script from InDesign to get what ID and I assume PS use as the main monitor resolution for displaying Actual Size.

#target indesign
alert(app.generalPreferences.mainMonitorPpi)

A 21" iMac—if I use this number as the Screen Resolution Preference Actual and Print Size match (but only on the display I set as the main monitor in my OS System preferences):

Actual vs Print size could be useful when there are two monitors. I set the Screen Resolution Preference to my 2nd monitor’s resolution (99ppi)—so Actual Size displays the image’s rulers at their actual dimensions on both displays.

[gener7]

Update: reported as a possible bug in

https://feedback.photoshop.com/conversations/photoshop/view-actual-size-reflects-the-screen-resoluti...

Go there if you want to add to it.

[rachaelk11682490]

Mine behaves pretty much the same as your Windows machine, except mine seems to be using 108ppi in Actual Size, when the correct value, and what I entered in settings, of 109ppi. So it doesn't appear to be a fixed 100ppi, but rather a variable number that is just off. I added my report to your thread. Not holding my breath for it to be addressed though.

[rob day]

I think your manual measurements might be off, or don’t match the OS’s reported main monitor ppi.

Can you run the script I posted above in InDesign?

Here it is saved as a .jsx file. If you put it in your InDesign Scripts folder you can run it from the Scripts panel in ID:

https://shared-assets.adobe.com/link/17ecd250-0e9c-48fe-6944-8cbccb877f6d

https://shared-assets.adobe.com/link/17ecd250-0e9c-48fe-6944-8cbccb877f6d

https://shared-assets.adobe.com/link/17ecd250-0e9c-48fe-6944-8cbccb877f6d

[rachaelk11682490]

My manual measurement must be correct, since when I enter my calculated value in the Units & Rulers settings page, my "Print Size" zoom level produces exact results, whether by measuring the image or comparing the displayed ruler to a physical ruler.  My calculated correct value, that I used in Units & Rulers, is 109ppi. 

Your script returns a value of 120. That is not even close to accurate - if I was to enter that value into Units & Rulers, the images would be very oversize when viewed at Print Size zoom level.  The "Actual Size" zoom level in PS produces an image that is too small by about a percent, which I can reproduce by setting the ppi in Units & Rulers to 108, so I believe that is what Windows is somehow feeding PS, not the 120 reported by your script.  120ppi does happen to be 96ppi x 125% though, and given that my Windows scaling is set to 125%, that probably isn't a coincidence.

System is Win10, Nvidia graphics card, monitors are both 2560x1440 and running at native resolution, and scaling is set at 125% in Windows settings.

[rob day]

Your script returns a value of 120.

Does your InDesign’s Actual Size (100%) view display ruler units at print size?

[rachaelk11682490]

No, actually. I'm not a regular ID user, so I had to go check it, but opening a blank document and zooming to Actual Size yields an on-screen ruler that is off by around 10%.  9.2" on the on-screen ruler equals about 10" on a real tape measure.

[rachaelk11682490]

InDesign, in the settings for UI Scaling specifically says that ID doesn't support the 125% OS scaling level though, and will round up or down, according to the user's selection, to 100% or 150%, so I think that error is to be expected, since I do use a 125% OS scaling level.

[rob day]

Have you tried setting your OS Scaling to 100% to see if the Actual and Print Views match?

[rachaelk11682490]

I haven't, no. It's too small to use on my monitors, so it never crossed my mind to try it. The experiment might yield some data, I suppose, but I can't keep it that way. I'll try it if I can find some spare time.