The simplest answer to an iOS native app is to always use PNG, unless you have very good reasons not to.
When an iOS app is built, Xcode optimizes. png files in a way that does not optimize other file formats . It's pretty well-tuned.
There are the following differences between them:
1. A picture of the same resolution, save as PNG larger than JPG;
The 2.png image has an alpha channel, so it supports picture transparency, which is especially important in iOS development, and JPG does not support transparency
3.xcode special optimizations are made to PNG format, while other images are not processed
A summary of the following points:
1. If your picture is Xcode local, then use PNG, if the picture is downloaded from the network, considering the traffic and speed, you can consider JPG because it has a high compression rate
2. Local PNG optimizations are done for you by Xcode; Other formats need to be optimized when the program is running, more performance-consuming
3. If your picture requires high color saturation and image quality, use jpg
IOS Development Picture Resource Select PNG format or JPG format