It looks like tumblr now automatically converts png files to jpg – if you have a fairly “clean”/simple digital art style that gets wrecked by jpg artifacts, you’ll want to put transparency somewhere in the image – tumblr will leave pngs with transparency alone (a single pixel border of transparency around the image works and is pretty non-intrusive).
Incidentally twitter has done this for a while, the same method of fixing it works there.
******HEY YOU READING THE NOTES, UPDATE FROM OP:******
Just an important ammendum since a lot of people have been commenting
saying it isn’t happening for them.After a bit of experimentation
with the original artwork I used to find this out (mainly steadily
increasing a big white square in the middle of it to reduce the filesize
bit by bit and reuploading it after each edit to see if it got
converted to jpg), it seems this only affects images that are over 370kb.In
addition, if you are using png (and using the suggested method to keep
it png), tumblr doesn’t particularly play nice with PNG images unless
they are very particular sizes, causing a slight blurriness when viewed
at dashboard view. Accepting the jpeg conversion will result in a
crisper image for those who don’t click to view your artwork at full
size.Finally, just a reminder that this only is particularly
noticable with cel-shaded/ solid colour art styles. If you’re a
traditional artist who photographs/scans in their work, or you use any
kind of painterly/soft colouring techniques, the jpg conversion probably
won’t be noticable at all, especially to the average audience who are
only going to look at your art for a few seconds before scrolling on
(even if they like it, them’s the breaks folks). A lot of people are
being all “TUMBLR WHY” but this isn’t TOO much to get hung up about.
Honestly, the blurry png at dashboard view thing is kind of much worse
and that’s been around for ages now.My revised advice would be
that if you’re concerned about this, just upload your art as a draft
first to test out how it looks both in dashboard view and full size when
clicked, both with and without a transparent bit, then simply publish
the one that you feel looks best on a case by case basis.To be
honest I’m not even mad at tumblr, I haven’t paid a dime for my usage of
this site so who am I to judge when they want to save bandwidth costs
with jpg conversions.Also why the heck did like a million porn bots latch onto this post and replace it with malicious links. Watch out for those, note-surfers.
Just another WordPress site