100% image display on iMac 24 inch

I have tried to find the answer to this without success. It has bugged me for years.

I have an A4 size image file and want to open it on the screen so that it's proportions are exactly 100% - ie A4 size on the display.

When I choose zoom to 100% it never shows anything like 100% on the screen, regardless of what application I use to open it.

Please, does anyone know how I can do this?

I think in order to do that, the software would have to compare the size of the image with the physical dimensions of the display, and most applications aren't written to do that. They are designed to display based on a specified display resolution. So for example, a picture could be shown at actual pixel size, but the physical size of the image would vary based on the PPI of the display.

But I could certainly be wrong.

Thanks for the reply, EvenStranger.
Sounds right to me. Too many variables I guess.
Pity. Never mind.
Depending on the application, I suppose setting the view 'to fit the window', then resizing the window would do it. I know it can be done that way in Acrobat.