How do I avoid Keynote reducing image quality? I want to create an animation in Keynote for a proof of concept. So I create a custom 16:9 document with 1440 x 810 pixel size. Then I add an image with a 1440 x 6395 pixel size. When I first add the image it's downsized so that it doesn't stretch beyond the slide height, but I click the Original size to have it fill the width (and stretch beyond the height). 

The problem now is that even though I've clicked Original size, I'm quite sure the image isn't actually its original size, at least not in resolution. 

When I set the presentation in full screen this is part of what I see:


When I look at the same area of the image in Finder Preview this is what I see:


So you see, the image in Keynote is undoubtedly reduced in quality.

Does anyone know how I avoid this?
After some research I found that this is a problem that has appeared since Keynote 6, and is probably due to iOS compatibility (limiting PNG original quality to stick up to 4096px height).

A tip however was to import your image as PDF instead, then Keynote won't downsample it. 

Here's the result: