From the javadoc of FileEncodedImageAsync I didn't understand two things:
Does the placeholder have an impact on RAM or is it immediately destroyed completely as soon as the image is displayed?
Can the placeholder have any size or must it have the exact same size as the image saved on file, i.e. the one to be displayed?
Placeholder should be global and should be an image that's efficient otherwise it will thrash ram. Since it's global it doesn't matter that it takes RAM.
It must have the exact same size since it needs to occupy the same space. That's why most apps of infinite scroll type standardize the size of the image view area.