He glosses over the 6's resolution of 750x1334 vs the 5's 640x1136. Will 2x image assets be slightly blown up for the bigger screen? And what about the very slightly thinner aspect ratio?
As for "downsampling" of new 3x assets, the main image processing artifact to look out for is moire which happens to images with small repeated details. There are techniques to mitigate these artifacts but it will have to be a very smart algorithm to avoid artifacts in all cases.
OTOH, Android seems to have no problem handling small resizings of images within their size buckets system.
Wouldn't the apps simply have the 1x, 2x, and 3x bundled in. This means the size of apps is going to grow, yet again. Yey...... As for iPhone 5 vs 6. I think legacy apps, games mostly, would be blown up. Anything that uses standard UI widgets would be starched to fill the screen. So in a list view you see more lines, in a text box more characters, etc. I hope that's the solution, at least.
As for "downsampling" of new 3x assets, the main image processing artifact to look out for is moire which happens to images with small repeated details. There are techniques to mitigate these artifacts but it will have to be a very smart algorithm to avoid artifacts in all cases.
OTOH, Android seems to have no problem handling small resizings of images within their size buckets system.