Don’t bother trying to open large images with Preview 8.1, which is part of the current 10.11.5 release of macOS El Capitan. They are likely to scramble and become unusable, although this does not seem to lead to file corruption.
I have today tried opening two large JPEG images – each 53671 x 47584 pixels in size, one of 110 MB, the other 272 MB – and found that Preview cannot handle them. Both opened correctly scaled into a window, but trying to do anything with the window, such as zooming in, resulted in breakup of the contents of the window and substitution by junk image fragments.
Both images open fine in other apps such as GraphicConverter 10. Although that suggests that it is a bug specific to Preview, as it appears to be a problem in managing the image buffer for the window, it is possible that it is an indicator of an underlying graphics driver issue (as some of us suspect might be the cause of sporadic freezing). No warning or error messages were written into the logs, although QuickView was a bit reluctant to create a preview of such large images.
I am running an iMac17,1, 8 GB of RAM, with an AMD Radeon R9 M395 graphics card with 2 GB of VRAM. Your mileage on other systems may vary.
I will add this to the list of known bugs in macOS 10.11.5.