On: I took 50k images of the night sky to make an 81 M...

[systemcluster]

Yes, since neither GPU drivers nor most displays currently support integer scaling. See http://tanalin.com/en/articles/lossless-scaling/ for more a more in-depth explanation.

[Waterluvian → systemcluster]

Fascinating. I assumed that an even multiple is all you need to ensure crispness.

[andy_ppp → systemcluster]

I mean would the display need to know - just GPU drivers should be able to send a 4k signal that has 4px squares each of one colour? Interesting though.

[tpolzer → andy_ppp]

It doesn't need to, but it would suffice in case your GPU doesn't manage.