Optimizing Iphone Storage & Media Quality

Using the Optimize Storage option will save a smaller size version of the photos on your device. If you zoom, edit, print, or share your photo, it will automatically download a higher resolution to fit your needs. Everything is done automatically depending on how much storage space is available and works seamlessly as long as you have an internet connection. The quality of the photo is not impacted as the screen resolution is much smaller than the resolution of the actual photo and for photos that are not viewed much, only the icon size is stored on your device for viewing when scrolling the library until you tap on the photo.

You can shut the feature off to always save the high resolution photos back to your device. There may be an instance where you do not have enough space to store the high resolution photos when shutting off, but they will be stored in iCloud with high resolution as long as you continue using iCloud Photos. I think the only way you may get into trouble is if you turned off Optimized Storage, and the device had no storage space, and at the same time shut off iCloud Photos. There would simply be no place to store the additional data.

I do not have those apps to check, but I would guess that since those apps are mainstream and have frequent updates, they would both be using the high resolution version of the photos.

From a Developer's point of view, Apple changed the way the photos were requested from the device about 5 years ago when writing a program. It used to be that you would request a photo from the Camera Roll on the device and you would get the size of the image the way it was stored and this still works if the app developer uses this old way of requesting a photo. Nowadays, the better way for apps to request a photo, involves specifying the ID number of the photo (usually obtained from a Picker View) along with the size you want the photo to be. The phone will do its best to return the size requested including the full size even if it needs to download it from iCloud. The app will get messages from the device on whether it was able to accomplish the task or any errors it received such as the internet being down, but it is up to the app to pass those messages to the user or just accept the size of the image that it was able to get.

Sorry for the deep dive. Apps are able to get the high resolution photo with Optimized Storage turned on and any decent photo app will be using the high resolution version.