hello
my kde is 4.8.5, last update version.
but i dont find how to block scala 1:1 in mode full screen...?
thank you

You can't. On image change, Gwenview will scale bigger images to fit screen size.

This change was introduced in 2.8 (KDE SC 4.8) (see Bug #291759). In 2.9 (KDE SC 4.9) there is hidden button that allows you to switch zoom-lock on and off (see blog post about Gwenview 2.9).

You have to either upgrade to 4.9 or use another image viewer in the meantime. I have found that these image browsers can zoom-lock: gThumb, qiv, pqiv, Viewnior, Comix, geeqie (which I personally like best, but still less than Gwenview).

Thanks Minio for linking to the solution.