My latest foray into the American West has resulted in some very large (>100Mb) panoramas. XnView Classic and MP both have difficulty making thumbs and displaying these images.
See below (click proxy for full size image):
Notice that both versions of XnView make thumbnails of even the largest files, but fail to render them correctly. If you look closely at the thumbs of the largest files, you will see apparently accurate but faint representations of the original images.
In MP's case, it appears to me as if the faulty thumb images may have been correctly calculated for luminance, but then overlaid semi-transparently with a color that may correspond to the color of the 1,1 position pixel present in the original image. This might explain why some of the thumbs are "light" and some "dark".
In the Classic version, all of the failed thumbs are "dark".
Using MP to display any of the "incorrectly thumbed" images results in an immediate Exit: no error message, MP simply unloads without warning.
XnView Classic exhibits no issues loading one of the largest (274,272kb) of these files into a view tab, but the browser preview remains blank. Some of the other large images fail with the "Not enough memory" alert. This must not be related to actual file size, but rather: image dimensions. Some of the files that will not load are physically smaller than the one that does load correctly but have more pixels.
Sometimes with Classic, once one of these files has successfully opened in a view tab and then been closed, subsequent attempts to reopen it fail with the "Not enough memory" alert. Restarting Classic allows the file to be opened again.
(FWIW, Zoner 64 creates correct thumbnails of these images and can both view and edit them regardless of original file size.)
Here a couple of the images in question. Feel free to experiment with them.
282MB
268MB
