Re the above, since switching for my main computer from a PC to a Mac about 3 years ago, I had to find a replacement for my beloved image browser program on the PC called Faststone. I tried a number of alternatives on the Mac and settled on a small program called Lyn. Now Lyn has been working just fine, but I recently updated my new 2018 MacBook pro to OS Mojave. Since then despite my mac being having a quite fast built in Radeon discreet 4gb graphics card and a 6 core I7 processor, when I'm zoomed into an image in Lyn and try and drag the image around (to move about the image), it's really laggy. I'm not sure if this is because the developers of Lyn haven't yet optimised it for Mojave (or High Sierra before that), of if it's defaulting to the Intel graphics and not the Radeon card ? So is there a way to force a program to use the Radeon card graphics processor on a Mac please to see if that improves matters ?