I just registered and wrote a lengthy explanation of my problem just to find the answer myself (after trying for hours without success). I still post for people who might be as slow as I am (I searched the manual and the forum for answers and could not find anything).
I was trying to get a big table that takes a whole A4 page in print from Microsoft Word as a picture into SAB. My problem was that, no matter what resolution I used, the text got unreadable as soon as you tapped the picture to “zoom in” (the thumbnail is obviously way too small). What surprised me was that there was no difference between a 3179 x 3488 and a 1034 x 1022 png picture.
The solution is way too obvious: in SAB > Images > Illustrations untick the box that says “Resize the image files to reduce the app size” and your pictures won’t get reduced anymore.
Having said that - happy Easter everybody!