The current zoom behaviour is a bit confusing

[phaolo]

1- some zoom functions aren't too clear.
Does "Real size" mean the physical size? So, the images on screen would appear big like the printed IRL?
Is 1:1 a fixed zoom of 100%, equal to "No fit"?

Maybe you should add "Real Size" to the "Fit" menu and rename it to "Physical Size".
And 1:1 should just be 100%.

2- it's not clear what should work only for the current image and what for all images in the current session.
Maybe you should just make all the functions apply only to the current image and make "Lock Zoom" remember also the current "Fit" level and Real Size.

[jon_joy_1999]

It's not possible to determine the physical size of an image because there is no way to determine the physical size of your display device.

Real Size scales the image to your current DPI scaling setting, so a higher DPI scaling will result in a visually larger image on your display, it is only equivalent to 1:1 at 100% DPI scaling, it should not affect your print size.

"No fit" means XnView will keep whatever zoom setting is applied and will not attempt to scale images to the window boundaries.

Lock Zoom only affects scrolling through different images with one of the "Fit Image to X" settings enabled, essentially a toggleable "No fit" setting. Normally changing images also changes the zoom level to fit the window, Lock Zoom "temporarily" disables this behavior.

[phaolo]

Real Size [..] is only equivalent to 1:1 at 100% DPI scaling.

Ah, then I don't need it. 100% DPI scaling is a very common setting.
Btw, I noticed that various images get scaled to a zoom % different than 100%..

"No fit" means XnView will keep whatever zoom setting is applied and will not attempt to scale images to the window boundaries.

So, if I understood correcty, the only combos are these:
- No fit - Zoom 100% (fixed zoom, full size)
- No fit - Zoom X% (fixed zoom)
- No fit - Real Size (dynamic zoom, DPI scaling)
- Fit to window.. (dynamic zoom)

Maybe the "Fit" menu should be called "Dynamic Zoom" and include "Real Size" (Scale to DPI) ?

Lock Zoom only affects scrolling through different images with one of the "Fit Image to X" settings enabled, essentially a toggleable "No fit" setting. Normally changing images also changes the zoom level to fit the window, Lock Zoom "temporarily" disables this behavior.

It wasn't like that in older versions, I think (or was it ACDsee?).
"Lock Zoom" only affected.. "Zoom X%". Makes sense, no?
Or call it.. "Lock Scaling"?

"Zoom X%" was useful to temporarly check an image's detail, but "Lock Zoom" was useful to check small differences in similar pictures.

[XnTriq]

'Real size' is not 100%, it's depend on the dpi of the picture and the screen

To summarize, for example in my case, for a dpi image = 72x72 dpi, and, a screen setting at = 87x87dpi , then I have the ~1:1 scale on the screen (it's useful) ... So a custom dpi size screen is needed into XnViewMP to adjust and meet the scale ~1:1.