First, I'm a UI/UX Designer so be patient with me please :)
I designed a new app. The app will only be viewed in portrait mode. My image area at the top of the page is fixed at 280px tall, but the image will always fill the width of the screen.
What I'm trying to avoid is scaling the image for each size. I want to crop the image instead.
I imagine it working like this: There's an image bounding box that is fixed at 280px tall but set to 100% width. This box has a background image that is set to always be fixed centered and to the top (like you can do with CSS). So on smaller screens, the image is cropped on the left/right. On larger screens, the image shows more detail to the left and right. So the image never scales. Only MORE of the image is shown on larger screens.
My question: what size do I need to create my master image (that will be scaled and reused for all devices) if my image bounding box is fixed @ 280px tall? For iOS and Android.
You can see by the example how the image should look on each screen below.
Example shows iPhone SE, iPhone 7, iPhone 7+ and default Android.