Even when alt+tabbing between the two I can hardly tell the difference. Yes, it is discernible, but only when I know what to pay attention to.
to me it is so very clear that i'm often getting pissed seeing how poor actual maps look compared to what the mapmaker creates.
and it's not just about my maps.
here's king's court 2. a beautiful piece of art ruined by jpeg compression
original ............. compressed
notice how everything is blurred on the compressed image and how various artefacts and graphical aberrations appear.
in fact when we make maps we go through extensive work and sometimes do unreasonable amounts of work just to lessen the effect of lack's compression.
for example we have to make sure each line is in pristine shape, that it is sharp and crisp with no blurriness. because any blurriness in our image would be increased ten fold after lack compresses it.
so an image that looks decent when we make it is not enough because it will look like crap after the compression. hence we have to make it great so it looks at least decent in the end.