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The main issue would be the low resolution that IG posts that I can see ?

Now that you mention it, I noticed how bad the IG version looks like compared to the one on my computer. I put the resolution at 1080 wide, to match the one on IG, but the quality is a lot worse than what I have.

I might check to see how steepshot compresses it. Maybe it's better than IG.

You should also check out APPICS.

Is it out already? I thought it's still in development and not yet out there.

The beta is out. If you can get though their waiting list ;-)

I'm already subscribed since a few months ago, but haven't yet received any email letting me know about the beta.