iOS理想的图像分辨率

Question

I'm having a real hard time understanding this, but let's say I have an iOS app for both iPad and iPhone and I want to download an image from a server and display it in full screen.

I have read that the iPad pro has a resolution of 2732x2048 and if we want to display an image in fullscreen we would need to download the image with this size right? However, I also read that the image should never be over 300KB. I was not able to bring an image with this size under 2MB (I used JPEGmini for example to reduce size).

And I don't think that iPhone user would need to download such a huge image, so my question is: what resolution should my images be on the server and how can I manage to keep them in a rational file size. Also should I upload multiple images for different devices? If so, how many and at what resolutions?

Answer 1

Isn't the problem merely that you are holding incompatible beliefs? This is the belief that is giving you trouble:

I also read that the image should never be over 300KB.

Let go of it.

Clearly it is right to say that the image should be no larger than needed for display. But an image to be shown as a 3x scale image on the iPad pro needs to be 2732x2048. So that's that.

(You could, alternatively, use an image 2/3 of that size and show it as a 2x scale image. It wouldn't look quite as good as the 3x scale image, but it might be acceptable.)

On a smaller device, yes, you should scale down the image in code, so that you are not holding in memory an image larger than needed for display. But in this case, you need the large image for display.