When trying to open an png image of about 700 megapixel (36k x 18k), gwenview only shows a red box saying the loading failed. I can display images up to about 31k x 16k from the same source without problem though with good performance.
*** Bug 338916 has been marked as a duplicate of this bug. ***
I can't reproduce this with Gwenview 17.11.70 and a humongous 48k x 12k 340 Mb image from http://www.noao.edu/image_gallery/images/d8/M31LGS_UBVIha.jpg. Loads fast and works properly.