iOS pictures 1x 2x 3x convert?

Question

I coded an App, its done now but if I go to Images.xcassets, it looks like I need 1x 2x and 3x pictures. I tested the App on my iPhone 6 and everything runs fine. My pictures are all in the 1x Boxes.

( its an universal App ).

I guess if I test it on iPhone 4 now, the images will be too big or the other way, on an iPad the images will be too small. I think thats why I need those 1x 2x 3x, am I right?

Could somebody tell me, how I get my 1x pictures now converted to 2x and 3x?

Thanks for any help

Answer 1

Those images are for different screen DPI. Eg Retina in iPhone 4 will use 2x images and Retina in iPhone 6 Plus will use 3x images, while 1x images will be used on old non-retina devices like iPad 2.

If you want to use different sized image on iPhone 5S and on iPhone 6 you need to provide it as different asset and set it in the code.