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

[davescm · Accepted solution]

A bit of clarity

100% is simple - it is 1 screen pixel mapped to 1 image pixel.

Print Size - is calculated from the document resolution and the monitor resolution as manually entered in Preferences.

Actual Size - is calculated from the document resolution and the monitor resolution as reported by the operating system which in turn gets it from the monitor itself using Extended Display Identification Data (EDID). Whilst this needs no manual entering of values by the user, it only works correctly if the correct value is returned from the monitor and OS. Hence print size is also in the menu for cases where an incorrect value is returned.

Dave

[rob day]

Hence print size is also in the menu for cases where an incorrect value is returned.

Hi Dave, If you have a second monitor with a different res you can get an accurate output view (1" = 1") on both displays by using the res of the monitor that is not the main monitor for the Screen Resolution preference, and using Actual Size to view the image on either display.

[davescm]

Good idea Rob.

Unfortunately here the wrong value is used for my pair of Eizo monitors so only Print Size is accurate.

Dave

[Conrad_C]

davescm got the fundamentals right. Some important additional notes:

Actual Size works for print only, where the unit of measure is inches. Actual Size does not work and must not be used for previewing the real world viewing size for documents where pixels are the unit of measure (mobile, web, or video). I think the command should have been named more precisely since print is probably not a majority delivery method for images these days.

Actual Size requires that the document ppi value (in Image > Image Size) matches the ppi at which the document will be printed. If you have two documents with the same pixel dimensions (such was 900 𝗑 600 px), with one set to 300 ppi and the other set to 240 ppi, and you set both to Actual Size magnification, the rulers will display exactly the same correct real world size in both documents, but the 240 ppi document will appear larger. The one that is the correct size is the one matching the final print resolution.

And now the big one…

Where the new Actual Size magnification makes the most difference over Print Size is on displays set to Retina/HiDPI (2x scale factor) resolutions. Actual Size usually gets it right (one inch on screen ruler matches real world ruler) regardless of the display scale factor, but the Print Size method will fail unless you account for both the UI resolution (the Scaled setting in Displays) and the Retina scale factor. For example, my MacBook Pro display hardware resolution is 227 ppi, but if you enter that for Print Size ppi, it will be wrong for 3 of the 4 Scaled options in the Displays system preference. What you need to enter in Print Size is the UI (not hardware) resolution times the Retina scale factor. For example, when the selected Scaled setting is Default (“Looks Like 1440 𝗑 900”), the correct ppi value for Print Size is 256, because that is 2x (Retina scale factor) the UI resolution (128 ppi). It turns out that the InDesign script in this thread is a nice quick way to get the correct 1x-equivalent ppi resolution for the Print Size method, because it gives you the UI resolution, the one that changes depending on the Scaled setting in Displays. (We didn’t have to think about this on 1x displays because the UI ppi almost always matched the hardware ppi.)

*The reason the basic Print Size method still works for one of Scaled options is because that one (“Looks like 1280 𝗑 800”) is exactly half the 2560 𝗑 1600 hardware resolution, so 2x that equals 2560 𝗑 1600, same result as doing Print Size for a 2560 𝗑 1600 non-Retina display.

Knowing the calculation for Retina (Mac) and HiDPI (Windows) displays is important because they are becoming so much more common. All Mac displays are now Retina.

[davescm]

Some good additions Conrad.

There is an issue though with either some monitors, Windows or the PS implementation in Windows. My monitors are 109ppi , both measured and specified by the manufacturer - Eizo. When set in preferences and using Print Size, on screen rulers and docs match the real world exactly. However, using Actual Size the rulers and docs are displayed a fraction smaller which seems also to be the experience of others that I seen reporting the same issue. 

I don't use any UI scaling or Windows scaling - I chose those monitors carefully to ensure I could see and judge image quality at 100% zoom.

I haven't dug further into it to try and find the cause, as I just use Print Size which works perfectly.

Dave

[rachaelk11682490]

I think it's actually a truncation problem (dropping the digits after the decimal point) in the Windows implementation of PS.  The exact PPI of my monitor is 108.968. The setting under Units & Rulers allows for three decimal places - in fact, when you use the arrows, it increments by 0.001 with each click. Yet 108.9 produces the exact same zoom level at Print Size (36% in this case) as 108.0 does and it is slightly wrong (too small). When I round up to 109.0 in the setting, Print Size results in 36.33% zoom level, which is correct.  So if the OS/monitor are reporting 108.9 and Actual Size behaves mathmatically the same as Print Size, that would explain why Actual Size is a bit off, since Actual Size is also producing a zoom level of 36% on this example piece.

[davescm]

Highly likely Rachel. If it bothers you, you could raise it at the link below which is monitored by Adobe developers.

https://feedback.photoshop.com/photoshop_family

Dave

[rachaelk11682490]

We did in fact start a thread over there. It's at https://feedback.photoshop.com/conversations/photoshop/view-actual-size-reflects-the-screen-resoluti....  I'll add this extra information to it though, just in case a developer is interested in fixing it.