How to handle image scale on all the available iPhone resolutions?

Question

What sizes would be the best to use for images: background.png, background@2x.png and background@3x.png if we want to use this image for example to cover the full width and

Answer 1

I've created category for this:

+ (UIImage *)sizedImageWithName:(NSString *)name {
    UIImage *image;
    if (IS_IPHONE_5) {
        image = [UIImage imageNamed:[NSString stringWithFormat:@"%@-568h",name]];
        if (!image) {
            image = [UIImage imageNamed:name];
        }
    }
    else if (IS_IPHONE_6) {
        image = [UIImage imageNamed:[NSString stringWithFormat:@"%@-750w",name]];
    }
    else {
        image = [UIImage imageNamed:name];
    }
    return image;
}

you can take full code here: https://gist.github.com/YGeorge/e0a7fbb479f572b64ba5

Answer 2

the @2 and @3 is not the real image scaling, but only represent how much real pixel represent one virtual pixel on screen, some sort of hdpi/xhdpi/xxhdpi/blabla from android universe. it only show to system what image should be used for some device screen.

so if you need to use whole screen image - prepare it dependently of real screen size.