How to handle image scale on all the available iPhone resolutions?
What sizes would be the best to use for images: background.png, [email protected] and [email protected] if we want to use this image for example to cover the full width and half height of the screen on all resolutions for iPhone portrait app?
This is what we have now:
Device Points Pixels Scale Physical Pixels PPI Ratio Size
iPhone XS Max 896x414 2688x1242 3x 2688x1242 458 19.5:9 6.5"
iPhone XR 896x414 1792x828 2x 1792x828 326 19.5:9 6.1"
iPhone X 812x375 2436x1125 3x 2436x1125 458 19.5:9 5.8"
iPhone 6 Plus 736x414 2208x1242 3x 1920x1080 401 16:9 5.5"
iPhone 6 667x375 1334x750 2x 1334x750 326 16:9 4.7"
iPhone 5 568x320 1136x640 2x 1136x640 326 16:9 4.0"
iPhone 4 480x320 960x640 2x 960x640 326 3:2 3.5"
iPhone 3GS 480x320 480x320 1x 480x320 163 3:2 3.5"
Some people say that for edge to edge image (like a banner on the bottom from left to right edge of the screen) for iPhone 6 Plus they would prepare [email protected] with width 1242 and for iPhone 6 [email protected] with width 750 to match the iPhone 6 screen size however I do not think that this is a good idea because 1242 / 3 = 414 and 750 / 2 = 375 so naming them as @2x and @3x does not have sense. And then what width should have back.png - 375 or 414?
Graphics names are using @2x and @3x suffixes so if for example [email protected] has 30x30 resolution then logically thinking [email protected] should have 20x20 resolution and image.png should be 10x10. This means that if we want to have sharp full width image for each screen then we probably should create [email protected] with width 4143=1242px, [email protected] with width 4142=828px and back.png with width 414px. This however means that on every iPhone except for iPhone 6 Plus you will need to setup your uiimages to use for example aspect fit content mode and they will be scalled down so this again is not a perferct solution and probably would really slow down the application if we use a lot of scalling on older devices.
So what do you think would be the best solution to solve this problem?
Answer
You don't have to have each image in all scales if it won't be used. Make only the sizes you need and name them according to their width. For portrait full-device-width images, you need 320px wide at 1x and 2x, 375px wide at 2x and 414px wide at 3x.
4" devices used "-568h" suffix for naming their launch images, so I'd recommend a similar naming scheme:
- ImageName-320w (@1x & @2x)
- ImageName-375w (@2x)
- ImageName-414w (@3x)
Then figure out what image you need at runtime:
NSNumber *screenWidth = @([UIScreen mainScreen].bounds.size.width);
NSString *imageName = [NSString stringWithFormat:@"name-%@w", screenWidth];
UIImage *image = [UIImage imageNamed:imageName];
This might break if other widths are added in future, but so far Apple has always required rebuilding the app to support new displays so I guess it's somewhat safe to assume they will continue doing that.