Don’t want to do necroposting here but I think it should be possible to configure the “strength” of the compression algorithm.
Pasting a screenshot from a 2K screen into DeltaChat with the “balanced” compression option set results in something like this:
As people are used to have a more fine-grained control over the quality of images DeltaChat should do the same. Otherwise people might say: DeltaChat suxx because the image quality of my last vacation picture is garbage.
So I think there should be a setting like “high” or “original” or something like that.
Option in Signal Desktop:
Option in Telegram Desktop:
For the sake of completeness:
Sending a screenshot of the same size with DeltaChat compression set to “Bad quality, small files” results in this:
The “bad quality” really looks like being sent over a dialup connection from the 90s 
I’m sure nobody will seriously use this in production 