Display wall portraits at actual size?

For your 55-inch display, this is easier to do in Photoshop, not Lightroom Classic. The reason is that Lightroom Classic displays images as pure pixels, and does not map them to any real-world unit of measure like inches until print or export. But if you are showing the images inside Lightroom Classic, they’re not being printed or exported, therefore they are not shown at a real world size.

You can’t do this using 100% magnification in Lightroom Classic, because 100% is not a real world size, it’s one image pixel to one display pixel, so the displayed size changes depending on the display ppi.

In Photoshop, you would get this done with these steps:

1. Choose Image > Image Size, confirm that the Width and Height in inches are correct, and confirm that the Resolution in ppi is correct. Then click OK.

2. Choose View > Actual Size. (Not 100%, and not Print Size unless set up properly)

That’s it. Photoshop should display the image so that one inch on screen equals one inch in the real world. This works as long as Photoshop can get the actual ppi resolution of the display from the operating system, which should be no problem with newer hardware and OSs.

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@Studio Galvan wrote:

or with my video projector

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For your video projector, nothing above will work. Because no application can know the exact size of your projected image by the time it hits the wall…that size will change if you move the projector a couple inches forward or back. So, for your projector, what you must do is manually adjust the projected size on the wall until it matches real world size.

The convenient thing about the display size being so variable from a projector is that now you might as well use Lightroom Classic. Show an image (maybe in Full Screen mode if you want), then adjust the projector until the projected size matches the real world size.