The release notes say: “New sub-sampling option: You can now choose to deactivate sub-sampled image previews, which are displayed in the main viewer, when setting your parameters. This will let you view the image at a high resolution while applying corrections.”
I can’t find anything in the Mac version of DPL5 that corresponds to this option, unless it’s the option for ‘high-quality’ previews in the Preferences dialog. But is that new? I’m pretty sure it was in PL4.
Introduced with PL version 5, sub-sampling helps to get a better preview while applying corrections – when your system is fast enough. Otherwise you have the option to switch to the old behaviour.
screenshot taken in Windows
It is indeed this high quality preview option. If you have it in PL4 there’s a wormhole hidden in your Mac 
Hi Lucas,
Thank you. I deleted PL4 when I upgraded so was relying on memory… The wormhole is in my head, it seems. 
Peter
Hi Wolfgang: yes, same in Mac version. See below. My mistake. P
no problem – try out what works for you