I apologise if this is obvious, but I'm not too experienced with graphics.
I'm looking at making a game of solitaire for iOS. I understand that the resolution of the iPhone 6s Plus (biggest iPhone) is 414x736, but this is scaled up by x3.
I'm wondering if I should design my images for the 414x736 resolution and have scale them up for the bigger iPhones, or design them for 1242x2208 and scale them down for smaller resolutions?
The latter. A scaled down image looks pretty good. A scaled up image looks blocky, and on a higher resolution screen, this will be obvious.
Moreover, if automatic scaling down doesn't look good enough, you can hand-tweak and provide both a 3x and a 2x image and the right one will be used automatically depending on the screen resolution of the current device.