So I am currently having some images designed for my app (social stickers Facebook style/ Line) I'm not really sure what resolution the images should be. iPhone 5s is 320*568 pts so a perfect square panning the width of the screen would be 320*320 points and because 5s is retina that would be 640*640 pixels. Is that correct? For a pixel perfect image spanning the width it would be 640*640 pixels?
I saw that iPhone 6 plus is 414*736 pts which scales up by *3 so it's 1242*2208, so would a pixel perfect square spanning the width for the iPhone 6 plus be 1242*1242 pixels?
If I was to get my graphic artist to draw on a 1242*1242 canvas would I lose much quality scaling it down for the iPhone 6 and the iPhone 6 plus?
Not really sure how to go about this. Just want to make sure my square canvas rescales without loss of quality between the 6+,6 and 5. Any help would be greatly appreciated. Thanks!
When you rescale from higher pixels to lower pixels it never lose any quality, so in your case yes you must ask for iPhone 6+ size of images to your designer and you can rescale as per your need, you won't lose any quality for sure.
width for the iPhone 6 plus be 1242*1242 pixels?
Yes you are right, you will need 1242 x 1242 for iPhone 6+.