How to use Scale Action to scale up an image in Keynote without loosing quality?
I found two workarounds for this, but both are a pain.


The first is to replace the scaled up image after the scale action completes. This works pretty well, but during the scale process you can see the loss of quality until the regular image replaces it.
The second is more complicated, but produces better results:


Start with small scaled version of the image (image A) where you want it. Apply any Build In animations on it.
Have a full size image (image B) with the opacity set to 0%.
Have a Scale Action on the image B setting it to the size of Image A.
Add a Opacity Action on image B to 100%.
Use a Disappear Build Out on image A.
Then use the Scale Up Action on Image B to the new size you want it to be.



This produces perfect results, but as you can see is very complicated. I created a little video to show the steps and the results.